FACADE RESEARCH

NICHOLAS SOCRATESFacade Research Document

Lloyds of London, Richard Rogers & Partners, 1986

adaptive functions of facades adaptive functions of facadesThermal comfortAcoustic comfort

Visual comfort

Comfort

Thermal comfort:convectionradiation

Comfort

ComfortThermal comfort:convectionradiation

Comfort

Thermal comfort:convectionradiation

Comfort

Comfort depending to requirementsPercentage Predicted Dissatisfied (PPD): 5-10%

Visual comfortLightnessGlareAtmosphere

Acoustic comfort

adaptive functions of facades

Ventilation

adaptive functions of facades

HeatingcoolingVentilationLightSun protection

Natural ventilation:Gap ventilationWindowChimney

Ventilation

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AR3B430 Facade Technology

Adaptive Facades

Understanding of the Facade as a skin/ organ of the building

Mick Davies / Polyvalente Wall, 1984

Lloyds of London, Richard Rogers & Partners, 1986

Heating

ventilationNatural ventilation:Gap ventilationWindow

Natural ventilation:Gap ventilationWindowChimneymechanical ventilation

ventilationNatural ventilation: Gap ventilation Window, Chimney Mechanical ventilation

ventilationNatural ventilation: Gap ventilation Window, Chimney Mechanical ventilation

Radiator RadiatorConvector heating

RadiatorConvector heatingUnder floor convector heating

RadiatorConvector heatingUnder floor convector heating, Façade heating

CoolingNight time cooling Night time cooling

Chilled ceiling (concrete floor activation)

Night time coolingChilled ceilingCooling ceiling

Night time coolingChilled ceilingCooling ceilingCooling wings

SunscreenShading

SunscreenBrises soleil

SunscreenBrises soleilFixed lovers

SunscreenBrises soleilFixed loversGreen

SunscreenBrises soleilFixed lovers

GreenRoller blinds

SunscreenBrises soleilFixed lovers, GreenRoller blindsVenetian blinds

SunscreenBrises soleilFixed loversGreenRoller blinds Venetian blindsHorizontal sliding blind

Alte

rnat

ing

Faca

de

Twin Face Façade Development

Seco

nd S

kin

Faca

de

Dou

ble

Faca

de

Boxe

d W

indo

w F

acad

e

Twin face facade: extra glass layer for wind and noiseprotection and integration of installation

Corr

idor

Fac

ade

Chim

ney

Boxe

d W

indo

w F

acad

e

Com

pone

nt F

acad

e

Short Cuts for Air:Box-window

Closing the opening for Special climate reasons:Boxed window„intelligent“ use: depending of the period of the year theinner / outer Window has to be removed / opened

Closing the opening for Special climate reasons:Boxed window„intelligent“ use: depending of the period of the year theinner / outer Window has to be removed

Box-window:Frankfurt Westhafen

Controls unclear Second Skin Facade

Second Skin Facade: XX Hamburg

Second Skin Facade: Tore Agbar - Barcelona

Problem sound transportCorridor façade

Corridor façade: Stadttor Düsseldorf

Corridor façade: Stadttor Düsseldorf

Corridor façade: Stadttor Düsseldorf

Corridor façade: University of Frankfurt

height leads to more energyChimney-box-window

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Chimney-box-window:ARAG Düsseldorf

Chimney-box-window:ARAG Düsseldorf

Alternating Facade Alternating Facade:Debitel Stuttgart

Alternating Facade:Debitel Stuttgart

Alternating Facade:Debitel Stuttgart

Alternating Facade:Surface partly glazed, Window elements in the effectiv

areas of the façade: Concept Schüco

Alternating Facade:Debitel Stuttgart

Alternating Facade:Concept Schüco

Twin Face FacadesMain problems with twin face facades:

Acoustics

Acoustics, Heat Twin face facade in Madrid: temperature in thefacade at sunny day in winter

Acoustics, Heat, Condensation

Copyright: W. Heussler / Schüco Copyright: W. Heussler / Schüco

Acoustics, Heat, Condensation

So twin face facades are mainly used at skyscrapers,windy areas and noisy places.and the user has to live with the building.P+C Kaufhaus / KölnRenzo Piano Building Workshop

Twin Face Facades:„Component Facade“: Integration of Mechanical ComponentsDecentralized mechanical services:

HeatingVentilationAirLight

Component Facade

Component Facade:Posttower Bonn, Decentralized Mechanical Services in the Floor Slab

Component Facade

“Component façade”Facade mock-up / DetmoldPartly twin face facade and decentralised mechanicalservices

Component Facade

Component Facade, Capricon Düsseldorf:TE-Motion Facade from

WiconaDecentralized

mechanical services in the facade panels

Decentralized mechanical services in the facade panelsComponent Facade

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Component Facade

Integrated design

Mick Davies / Polyvalente Wall for Lloyds of London

Smartbox / CEPEZED, Leven, ECN, TNO, v d Vlugt etc.

TE-Motion Facade from WiconaDecentralized mechanical services in the facade panels

Mick Davies / Polyvalente Wall for Lloyds of LondonUnderstanding of the Facade as skin / organ of the

building

E² facade by Schüco / Uni Stuttgart (Prof. Behling) Component Facade

Active Facade

Daniel Westenberger / Technische Universität München

Sunscrean Daylight controle Open view Electric light Daylight controle Active Facade

logical, maybe even mandatory. Particularly if one considers the in-depth planning require-ments and high level of prefabrication needed for facades and building services elements, as well as the dramatic increase in complexity. The projects Posttower Bonn / Helmuth Jahn with Transsolar and Capricon in Düsseldorf / Gaterman + Schossig are examples of the developmen-tal steps described – both integrating building services modules into the facade. At the same time, several suppliers have worked on incorporating these technical possibilities into their products – such as t-motion by Wicona, smart box by CEPEZET as well as E² by schüco – however, these products have not yet been implemented on a large scale (1/6/7/8).

previously seen (3/4).Today’s developments are – besides various design trends – primarily driven by material-related or technological innovations. This is evident in fully glazed constructions, a trend that started at the end of the last century, whereby the technological finesse is part of the esthetic fascination. Examples are the works by Peter Rice and Ian Ritchie, Mick Eekhout and Rob Nijsse (4/5). The conception of glazed double facades must be considered as part of this development.In addition to a continuing dissolution of the envelope, this concept also tried to fulfill the de-mand to optimize the building climatically, since the many winter gardens proved as climati-cally and energetically problematic and a longer usable period was required. A generation of double facades evolved that, with its four main variants second-skin façade, corridor façade, box window facade and shaft-box façade, was no longer merely a building envelope, but rather an integral part of the building’s climate design by integrating climatic concepts (3/4/6/7).Based on this fact, the next step – the integration of building services into the facade – seems

The façade technology of the 20th century can be characterized by the dissolution of the mas-sive wall into a separation of structure and façade. With regards to esthetics and construction, the development of façade technology today, after 60 years of curtain wall systems, 30 years of element façade systems, 15 years of double skin façades and 10 years of experience with the integration of environmental services, it seems that the peak of optimization of the existing façade systems has been reached. By continuing the path of adding extra layers for each addi-tional technical function will limit further developments to small technological steps.

1. Background

From a historic point of view, facades have evolved from two structural directions: light con-structions based on the requirements of nomadic people, that allow for simple and quick assem-bly, as well as massive constructions derived from the permanent need for protection at a given location and the locally available materials (1). Following the fulfillment of these fundamental re-quirements, the facade’s esthetic design developed with the goal to emphasize certain building parts, functions or entire buildings. One example in this context is the step from Romanesque to Gothic. The conception of light in the interior space served as a motor for the development of ever bolder constructions with maximum window dimensions and minimal gravity-loaded vault structures. In contrast, driven by the necessity of functional buildings to be efficiently constructed, industrialization brought about the separation of the master-builder into the dis-ciplines architecture and engineering – with the result of an alienation of these disciplines and the creation of individual esthetic forms of expression (2). One step in the direction of esthetic qualities still favored today is the dissolution of the wall, associated with modernity, into load-bearing components – the building skeleton – as well as enveloping components – the facade. The goal to seemingly dissolve the structure into individual parts created an esthetic form not

Figure 1 – Facade Principles : second-skin façade, box window façade, corridor façade and shaft-box façade (1)

Figure 2 – Facade principles with building services integration: ventilation, humidification, light (1).

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is more efficient to combine the outer leaf with the inner leaf and insulation in the factory to one prefabricated element. Due to their layered structure, these elements are called sandwich ele-ments, but there is no mechanical cooperation between the inner and outer leaf. The inner and outer leaf are quite thick, so a tight connection between these two will create internal forces due to differences in temperature. A strong connection, to activate the mechanical sandwich action, is not necessary either, because the inner leaf can easily resist the wind forces.These sandwich elements could serve, like single interior leafs, as a load bearing element. How-ever, this is not frequently done. The risk of damage to the exterior during the earlier rough building phase is considered a disadvantage. Also the dimensional tolerances in this phase are quite large. These tolerances would become visible in the irregularity of the width of the joints in the rain screen.From a distance and with a rough texture, these variations could be made less obvious.In recent projects, however, load bearing prefabricated sandwich elements are used, especially in high rise projects (fig. 1.3.5.). The logistic advantages of a single hoist will make more strict dimensional tolerances economical.However, the sandwich elements are generally non load bearing as a parapet element or as a full storey high element.The cross section of the sandwich elements is largely determined by considerations related to their heavy weight and the fixing procedure.Parapet element (fig. 1.3.2.)The centre of gravity lies between the inner and outer leaf, so a crane may lower the element vertically and directly onto the floor. There is no need to pull the element inwards.Please note: With just a separate inner leaf of concrete, a façade element supported by consoles on the columns is a more attractive solution. These consoles, however, penetrate the inner leaf. This is no disadvantage because these openings can be closed from the outside. For a sandwich element this is not a good solution because closing the airtight joints around the console is only possible from the inside.If the inner leaf is put on top of the floor, it is not logical to make the inner leaf underneath the floor also of concrete. This would complicate the element and make positioning more difficult. As a consequence, in that position light panels will be used. The wind load from the bottom on the windows will be resisted by the concrete parapet panels. At the top of the windows the wind load must be distributed to the underside of the floor. Then it is logical to consider the inner leaf above the windows as an extension of the window frame. The inner and the outer leaf may be produced separately and connected in a later production stage. Then both the outer surface of the outer leaf and the interior side of the inner leaf may be put at the bottom side of the formwork (the procedure is explained later on). Then on both sides fine detailing is possible. With this production method it is also possible to form an open, ventilated cavity.

Storey high element (fig. 1.3.3.)

Also with these elements, the centre of gravity makes it easy to lower the element onto the floor. The el-ement must be pulled horizontally between the floors. Then a wide gap is needed to accommodate dimensional tolerances between the floor levels.The connection to the floor is made with angled pro-files or steel strips.

A simpler fixing is found in adding a continuous ridge on the inside of the top. The element may now be hung instead of stand, making it at once stable after positioning. The horizontal joint between the elements is easily accessible at floor level. If the ridge is unacceptable in the interior, a lowered floor edge is used. This is simple in a prefabricated structure with separate beams and floor elements (fig. 1.3.4.).

In the building of Civil Engineering the collected water is guid-ed to the outside and downwards over a recessed surface cov-ered with strips of black tiles. The tiles don’t absorb the water and the different colour doesn’t show the staining.Some surface treatments, like sandblasting, make the surface more sensitive to staining.

1.3. Types of façade elements

An exterior leaf of concrete, like other materials, could be hung on an already positioned inner leaf. Because of the heavy weight, however, a crane must be used. Also the fixing and adjustment is more elaborate than with lighter panels. Strong and expensive anchors are needed (fig. 1.3.1.). Until 1980, con-crete outer leafs were fixed directly to the floors with consoles extending from the concrete elements. Requirements for thermal insulation and the prevention of cold bridges did not play a role. As an inner leaf, light panels or brickwork was used. This type of fixing is no longer accepted.To avoid additional adjustment and double use of the crane it

Dust will be collected on horizontal surfaces and this material will be washed away by periodical rain. In an early stage of a period with little rain, the limited amount of water will remove some dust, but lower on the façade this water will be absorbed by the porous concrete. This leaves the dust on the façade in specific areas.On the other hand, during heavy rain a lot of dust is washed away, but this water flows rapidly downwards. If all the dust is removed, the rest of the water will partially clean the façade.With this mechanism an uneven staining appears, very soon giving the façade a rundown appearance. Because the eastern façades in The Netherlands are exposed to irregular rainfall, these façades generally show more stain-ing than the others. Especially south and west façades receive much more water due to the prevailing winds.By adequate detailing, the staining can be slowed down and also be made more even. In the literature on concrete façades, a lot of attention is paid to this aspect.Some of the measures are:− drip rails to stop the water, hanging on underside surfaces, from flowing backwards.− external rims keeping the water from the surface as much as possible.− horizontal surfaces, sloping inwards and collecting the water sideways to concentrated spots.− hidden gutters below the windows and draining these gutters to a pipe system.In fig 1.2.4 several solutions are given.

Dust will be collected on horizontal surfaces and this material will be washed away by periodical rain. In an early stage of a period with little rain, the limited amount of water will remove some dust, but lower on the façade this water will be absorbed by the porous concrete. This leaves the dust on the façade in specific areas.On the other hand, during heavy rain a lot of dust is washed away, but this water flows rapidly downwards. If all the dust is removed, the rest of the water will partially clean the façade.With this mechanism an uneven staining appears, very soon giving the façade a rundown appearance. Because the eastern façades in The Netherlands are exposed to irregular rainfall, these façades generally show more stain-ing than the others. Especially south and west façades receive much more water due to the prevailing winds.By adequate detailing, the staining can be slowed down and also be made more even. In the literature on concrete façades, a lot of attention is paid to this aspect.Some of the measures are:− drip rails to stop the water, hanging on underside surfaces, from flowing backwards.− external rims keeping the water from the surface as much as possible.− horizontal surfaces, sloping inwards and collecting the water sideways to concentrated spots.− hidden gutters below the windows and draining these gutters to a pipe system.In fig 1.2.4 several solutions are given.

An important aspect of concrete façades is staining (fig. 1.2.3.)

Fig. 1.2.2 Some examples of surface treatment

Fig. 1.2.3 Uneven stainingFig. 1.2.4 Precautions to prevent water from running over the façade surface.

Fig. 1.3.1 Adjustable anchors for façade panels Fig. 1.3.2. Parapet element

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medium rise buildings.A better rain proofing may be wanted in sandwich panels without a cavity. These are normally insulated by polystyrene foam, a material with a hard surface. In the joints, the sides of the in-sulating layer do not catch water, and this may easily flow along to the interior leaf and airtight joint. To improve the effectiveness of the rain proofing, one or more slotted grooves may be added in the vertical joints of the rain screen and also an overlapping form in the horizontal joint.To improve the rain proofing even further, a flexible strip may be put into the vertical joint (fig. 1.5.3.). The openings in the rain screen are enough to equalize the pressure between the exterior and the cavity. In this way a very effective and reliable joint is achieved, fit for high rise buildings.

The formwork, however, is complicated by these refinements and during transportation the fin-er detailed edges are vulnerable. A straight edge, closed with a mastic joint is an alternative, but this solution has some disadvantages. The life of the material itself is limited and the adhesion to the concrete depends to a great extent on the condition of the surfaces. The mastic material may also spread some of its components over the surface of the concrete near the joint. This staining is not visible in itself, but dirt sticks to it and causes dark stripes beside the joint.Sooner or later the mastic joint between the exterior panels will show some defects. This does not have serious consequences if enough outside air can flow behind this joint to equalize pres-sure differences over these joints.Trying to completely close the vertical and horizontal rain proof joints with mastic may easily lead to leaks into the interior. The airtight joints on the interior side will have some small air leaks and these reduce the pressure in the cavity if the rainproof joints are closed to a high degree. This air leakage to the interior increases the pressure difference over the rain screen, creating a large influx of water. This will finally find its way to a small opening on the interior side, were it will be pushed to the inside. The origin of the water is then impossible to detect. A mastic joint may function well, but then the pressure equalisation to the outside must be guaranteed by adequate local openings.Sometimes the vertical rain proof joint is closed with elastic strips (fig. 1.5.4.). These profiles have a limited range of compression in which they have sufficient contact pressure to the sides of the opening. If this pressure is too low, the strips may fall out of the joint. This can happen in cold periods when the concrete panels shrink and the elasticity of the material is low. Repeated ther-mal movements can also gradually push the profile to the outside. The strip cannot be used in a position accessible for vandalism.

1.6. Fixing

An exterior leaf of concrete may show a considerable variation in temperature. However, the maximum temperature, caused by the sun, will not be as high as that reached by thin light weight panels. The thermal mass is much higher, absorbing about 500 Wh for every 10 oC rise in temperature. By the slower rise in temperature the sun will have lost it maximum strength before a stationary balance is achieved.The orientation is also less influential. For light weight panels the SW-façade is generally heated up the most, caused by the high air temperature in the afternoon and the more perpendicular angle of the sunrays to the surface. For a massive concrete panel, the loss of the intensity of the sun soon restricts the warming up.With a variation of the temperature from -20 oC to 55 oC, the change in length of a 7.2 m1 wide façade panel is:ΔL=ΔT*α*L=75*12*10-6*7200=6.5 mmThe interior leaf has a fixed temperature and does not follow these movements. Then, a rigid connection between exterior and interior leaf is unacceptable, for this would cause high internal stresses. A concrete connection would also form a serious cold bridge.To prevent this, an exterior leaf of a sandwich element is fixed with stainless steel anchors. These must be strong enough to resist the gravity load and the wind load, but they must be flexible enough to limit the tresses caused by the forced movement.By positioning the fixed and rigid supports in the middle of the panel, the movements at the joint are limited. Around the perimeter flexible, hinged or sliding connections resist the wind load only. In fig. 1.6.1 an example is given of the positioning of the anchors and their purpose. In the middle, two anchors resist wind forces and the vertical loads and one anchor resists wind loads and fixes the panel in a horizontal position.To restrict the movements of the exterior panel with relation to the interior leaf, a solution may be to combine for example two outer leafs of 3.6 m1 wide with an interior leaf of 7.2 m1 wide.A smaller panel also has the advantage of less deformation caused by warping or bending in the curing stage. During warming by the sun, some bending will occur, because the warming

1.4. Manufacturing

For sandwich elements two production methods are used.− The element is produced in one cycle of operation. These elements have an exterior surface, shaped by the bottom of the formwork and the interior surface of the interior leaf is flat and just levelled.− The element is produced in two phases. First, the interior leaf, with the interior side at the bot-tom of the formwork, is cast. On the topside (cavity side) anchors are cast in. After hardening, the insulation material is applied around these anchors and fixed to the inner leaf. Next, the outer leaf is cast, with the outer surface at the bottom of the formwork. The inner leaf is lowered with the anchors in the not yet hardened concrete. By keeping a distance between the outer leaf and the insulation, a cavity may be formed.The second way of manufacturing is of course more expensive, but the freedom of form and the high quality on the inside may be a good ground to do so. However, a ventilated cavity is seldom required for a concrete exterior leaf. Concrete is permeable to vapour, it can absorb a lot of water and it is resistant to frost. For very dense exterior surface materials, however, like enamelled tiles, the ventilated cavity may provide extra safety.The choice of treatment of the exterior surface, besides the aesthetic demands, is also influ-enced by the shape of the element.To wash away the cement, to show the pebbles better, the curing of the cement is delayed by a chemical put on the surface of the formwork. For vertical planes in the formwork, for example around the windows, this chemical may flow downwards and spread over the bottom. This may cause irregular effects in appearance. Also, a curved surface may become irregular. For these forms, methods like blasting with grit may be a better choice.Sometimes a surface with a rough appearance must be given flat edges to accentuate the joints. In this way the attention is drawn to these stripes and the real joint with its varying width is less obvious. These strips must be covered with grit blasting, but the cover must be very strong to withstand the blasting. Then washing the surface may be favoured.Concrete exterior leafs are produced in a factory, because there controlled working conditions exist. To compact the concrete, vibrating tables are used, and these can only be placed in a fac-tory.Also for quality control, a factory is a better location than the building site. It can guarantee an even surface quality and colour. This is important because the slightest difference will be visible and it will ruin the image of a whole façade.Recently, however, the production process was changed.The development of high strength concrete resulted in thin self compacting mixtures. This is also very favourable for the production of façades. In the factory, the noise of the vibrating ta-bles is avoided and the formwork is much less stressed. Occasionally, concrete façades are cast in situ. On the building site a high quality is easier to achieve, without air bubbles, uneven mixed pebbles and discolouration.

1.5. Joint constructions

The joints between concrete exterior panels must be quite wide, for the dimensional tolerances are large in comparison to products made of other materials. On average, the joints are 2 cm wide.Concrete will shrink during hardening and sometimes the elements show some warping. Then the width of the joints will be variable and also in the depth differences appear between the adjacent panels. The positioning of the elements is also less precise, caused by their large weight and more difficult handling.Due to their width, the joints have a major influence on the appearance of the façade. Therefore it is important to use visual tricks to make them as even as possible. The detailing should be aimed at hiding the differences.One possibility is to chamfer the edges of the panels or to make details, suggesting a wider joint (fig. 1.5.1.). In this way the variations in width are relatively less important. With chamfered edges also the risk of damage at hoisting the element from the formwork or during handling is reduced.At the corners of a building, dimensional tolerance in two directions must be dealt with. Here a grave risk exists of an unequal and tapered joint width. By designing overlapping joints the tolerances may be masked.The location of the joint must be chosen in such a way that fragile edges are avoided (fig. 1.5.2.). Due to the thickness of the exterior panel, the joint is quite deep. Then, an open joint is a good solution, for the edges will efficiently catch the drops of water. These open joints level out the air pressure difference between the exterior and the cavity. This joint will function well up to

Fig. 1.3.4. Hanging, strorey high façade elelemnt

Fig. 1.3.5 Storey high, load bearing sandwich facade elelement

Fig. 1.5.1 Joints, designed to hide dimensional tolerances

Fig. 1.5.2 Solutions for corners

Fig. 1.5.3. Additional strips for improved waterproofing

Fig.1.5.4. Elastic strip for rainproofing of a vertical joint

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The inner and the outer leaf may be produced separately and connected in a later production stage. Then both the outer surface of the outer leaf and the interior side of the inner leaf may be put at the bottom side of the formwork (the procedure is explained later on). Then on both sides fine detailing is possible. With this production method it is also possible to form an open, ventilated cavity.Storey high element (fig. 1.3.3.)Also with these elements, the centre of gravity makes it easy to lower the element onto the floor. The element must be pulled horizontally between the floors. Then a wide gap is needed to ac-commodate dimensional tolerances between the floor levels.The connection to the floor is made with angled profiles or steel strips.

is not equal in the depth of the concrete. The inside surface temperature follows the outside temperature with some delay.The anchors resisting the wind load must be resistant to buckling. This requires a minimum out-side dimension of the cross section. This must be balanced with the want for sideway flexibility.Façade panels of concrete are heavy and therefore dangerous if they fall down.Therefore the anchors must be resistant to the continuous attack by the exterior climate and protected from fire.The anchors inside the building are protected from fire by the concrete inner leaf.However, the fire may enter the element from below and attack the anchors. If an open ven-tilated cavity is present, the chimney effect may draw the flames into the element. To protect the anchors and to prevent the fire from reaching the next storey, an insulation of mineral wool or foam glass must be selected. These are not combustible and will maintain their insulating capacity.An insulation of plastic foam will burn or melt. This does not create a problem if the cavity is completely filled. Because the supply of oxygen is restricted, the flames will stop after about one meter.Manufacturing sandwich elements without an open cavity may be done layer after layer, in one formwork. Finally, the concrete of the inner leaf is poured on the insulating layer. Choosing an impermeable insulation material, like foam, is then favourable.As a result, the logical combinations are: foam insulation with no open cavity and mineral wool with an open cavity.

Literature:“Architectural Precast Concrete”Prestressed Concrete Institute, Chicago, 1989Kind-Barkauskas e.a.“Beton-Atlas”Verlag Bau und Technik, Dűsseldorf, 2001Themanummer Detail 4, 2003Publicaties van BeltonThemanummer “Schoon beton”Cement 1999, nr 3Bundels “Beton in beeld”

2. Exterior leaf of bricks

2.1 Introduction

A brick façade used to have a load bearing function besides separating the interior from the exterior climate. The thickness was 22 to 33 cm.With the introduction of the cavity wall, the brick wall was split into two layers, connected by small steel connectors. The vertical loads from the floor rested on the interior leaf. Generally, these were about 10.5 cm thick, but for concentrated loads they were made thicker.Originally, the cavity had just the function to keep the moisture away from inside of the façade. The cavity was about 6 cm deep. The exterior leaf was connected to the interior leaf with thin bars to increase the stability of the 10 cm thick leafs and to distribute the wind loads.From 1975 on, the cavity was filled with thermal insulation to reduce the energy losses. Over the years, the thickness of the insulation increased to about 15 cm.Nowadays the exterior leaf does not take any part in resisting loads from the building. It only serves the architecture and the rain proofing. It is a cladding material like others, but with some typical aspects, such as stiffness without strength and the way it is made.A façade of masonry has the advantage of consisting of small elements, giving it a homogenous surface. The surface is not split into panels with obvious joints. It can easily accommodate an irregular façade with windows of different sizes and positioning. With special formed bricks, dif-ferent surface textures and colours are possible and with a different style of laying the bricks all kinds of images may be created. Also the surface treatment of the joints and their width offers ways of achieving the desired effect (fig. 2.1.1).Brickwork is relatively insensitive to staining because the surface in itself is already irregular. No maintenance is required, as opposed to plate materials.Only lightly coloured stones should be treated with care. To prevent irregular wet areas, the wa-ter flow over the surface must be controlled. Especially areas below windows and at the exposed top of a wall are sensitive.An exterior leaf of masonry has a low tensile strength, making it sensitive to restricted move-

ment and forced displacement. In this it does not differ from other façade materials.A brick wall will deform with a change in temperature. To enable an unrestricted movement, the exterior leaf should be connected to the load bearing structure as loosely as possible. It should also be kept free from other rigid elements, such as window frames and roofs.The brickwork, however, must be supported by the load bearing structure to resist the wind and gravity loads. This load bearing structure will also show deformations, caused by other loads. These movements of the structure may not be forced back upon the brick wall.As a result, dilatations in the brickwork are necessary. Based on the idea that no cracks are allowed in the brickwork, guidelines were developed for the position of dilatations. These guidelines were so strict that the façade was covered with a lot of joints that were clearly visible, especially with lightly coloured bricks. The homogenous surface was disrupted by dark lines. This effect eliminated one of the attractions of bricks as a façade material.In more recent recommendations, the general idea is to accept cracks while controlling their width. As long as they are not visually annoying and don’t create a safety risk, they are accept-able. In certain areas, a steel reinforcement in the horizontal joint may be a solution to spread the extension over a large number of smaller cracks (fig. 2.1.2.).Note:. Also in concrete technology one of the design criteria is the restriction of the width of cracks by an evenly distributed reinforcement.

2.2. Restricted movements

The brickwork follows the average air temperature and it is additionally heated by sun radiation. The range of the temperature is comparable with that of a concrete exterior leaf, so -20 oC to 55 oC.To estimate the degree of unrestricted expansion, the temperature at the time of construction is important. Starting at 5 oC, a section of 12 m1 long will expand:

Thermal coefficient of expansion (α): 6*10-6 /oCRise in temperature (ΔT): 50 oCLength (L): 12 mthen:

ΔL = ΔT * α* L = 60*6*10-6 * 12 = 0.0036 in = 3.6mm

An open expansion joint of 5 mm is then adequate.

The sliding of brickwork over a foundation is limited to a practical maximum. The wire anchors, necessary for the distribution of the wind forces will also be bent sideways.With this approach, a vertical dilatation is advised for every 12 m of length of the façade. The vertical dilatations are noticeable because they form a straight line instead of the staggered lines of the normal joints. For a low façade, the vertical compression is less, making it advisable to restrict the length between dilatations to 5 times the height.The thermal coefficient of expansion of brickwork, in vertical direction, has a higher value. For a high façade, therefore, about every 10 m a support is needed. This equals three storeys. Below this support a horizontal expansion joint must be designed. This joint is closed with a mastic material against rain penetration. The compression and expansion of mastic materials is limited to about 20%, making 15 mm the minimum width of this joint. This is more than the normal thickness of a horizontal mortar joint, which makes these dilatations visible.At corners, the sideway movement of one façade is pushing the other façade outwards. How-ever, the wire anchors connecting the inner and outer leaf cannot stretch several millimetres. To prevent damage, a dilatation is needed just around the corner. If this is unacceptable, the anchors should be installed at a generous distance from the corner. For an exterior continuous leaf around the corner, dilatations 1.5 m respectively 4 m from the corner may prevent cracks.Window frames are fixed to the interior leaf to restrict, as much as possible, the movement of the airtight joint connecting them.Wooden frames do not expand or shrink that much, and consequently they are fixed rigidly. To the exterior leaf they act as a rigid element. To allow for movement of the masonry, a joint around the window frame of about 5 mm should be kept open.Through an open joint of that size, water can penetrate the cavity. To protect the wood, flexible slabs just behind the bricks are used. This solution is only possible when the exterior leaf is con-structed after putting the window frame in position.Window frames of aluminium or plastic show large thermal movement, caused by the high ex-pansion coefficient and their small thermal mass. A larger joint is then needed.

These window frames are always installed after the exterior bricks. For wooden frames this phase is also favourable, because it reduces the risk of damage during the building phase. With a wider joint around the window frame, additional rain proofing strips may be used.

2.3 Forced deformation

The weight of the exterior leaf must be distributed to the foundation, but this may be done by different routes.Normally the masonry is carried directly by the foundation. However, above windows, at balco-nies and around cantilevered façades the brickwork will stop at a higher level.One way to support the brickwork is to use lintels, distributing the load sideways to the adjacent masonry. With larger openings these lintels may be connected backwards to the interior leaf or beams or columns of the load bearing structure (fig. 2.3.1.).

Fig. 1.6.1 Separate anchors for gravity load, windforces and horizontal forces in the pane of

the element

Fig. 2.1.1. Brickwork with a rough texture

Fig. 2.1.2. Reinforcement of brickwork

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Fig. 2.3.1. Supports for brickwork. Gravity weight transferred to the

inner leaf.

Fig.2.3.2. Support of the exterior leaf above and below the window by the inner leaf. Besides the window the brickwork is supported by the foundation.

In many cases one part is supported by floors or consoles, and the parts beside are supported by the foundation. This always creates a different vertical deformation (fig. 2.3.2.).

Floors are generally designed for a maximum deflection of 0.002 to 0.003 times the length of the span. Reduction of the deflection is difficult to achieve, because a floor beam may take away too much natural light. A beam may also hinder the building process and with a tunnel form work this is even impossible. Prefabricated floor elements are generally unsupported at the side façade.An exterior brick leaf supported by these floors must follow the deflection of the floor.The deflection of the floor increases from the supports to the centre of the span. The differences in vertical movement must be possible without overstressing the brickwork. This is possible with vertical joints.Prefabricated lintels made of steel or concrete have a larger thermal expansion than brickwork (12 and 6*10-6 /oC ). Thus, lintels for large openings must be able to slide at their supports to some extent. At the end of the lintel a vertical joint is necessary (fig. 2.3.3.). The main structure of the building will bend sideways under wind load. This causes floors to slide in relation to the floors above and below.The load bearing structure also may have dilatations due to the building process or the assem-bly of prefabricated elements. Between high and low building volumes generally a dilatation is designed to accommodate a different settlement of the foundation.Dilatations in the load bearing structure generally must be repeated in the façade.

Literature:“Ontwerpen met dilataties”Koninklijk Verbond van Nederlandse Baksteenfabrikanten, 2003“Beheersing van scheurvorming in steenconstructies”CUR-aanbeveling nr. 82

Fig. 2.3.3 Joint near the end of a lintel, supported by the adjacent brickwork.

3. Multi layer glass windows and façades

3.1. Climate windows and double-skin façades

Basically every façade in a moderate climate has three layers: an airtight inner layer, a thermal insulation layer and a rainproof/aesthetical layer. Considerations originating from the construc-tion process or building physics sometimes lead to an open cavity behind the rain screen.In double glass façades this air space is made wider to accommodate an adaptable sunscreen (louvers, curtain etc.).The air space may be equipped with controllable openings to the outside and/or the interior. An air flow with air from the outside or interior can reduce the temperature of the sunscreen and the cavity. This enhances the comfort by reducing the surface temperature of the inner glass pane. It is also possible to use exterior air, guided through the cavity, for ventilation of the room. A wide cavity can also be useful to improve the sound insulation. A lot of combinations have been investigated and used with a wide range of technical complexity.The most commonly used types are known as “climate façade” and the “double-skin façade” (fig. 3.1.1.)

The principle of the “climate façade” is generally used for windows. The air, evacuated from the room, is guided through the cavity back to the installation. The outer window is a standard double glass unit and on the inside a single, inward openable glass panel is added. The airflow is controlled by the installation.In the climate façade, the airflow is derived from the ventilation requirements for the occupants, ranging from 30 to 60 m3/hm1 façade length.The cavity is 10 to 15 cm deep. Since the installation ducts are generally placed above a ceiling, the air flow is upwards.Below the window, over the full width, a slot is left open. Above the window a plenum is needed to create an even flow from the wide window to the duct of Ø 10 cm. Sufficient space must be reserved for this plenum between the window and the bottom of the floor.An open able inner glass window facilitates cleaning of the cavity and maintenance to the sun-screen. Influx of interior air to the cavity through the joints around this window must be re-stricted. These leaks would disturb an even air flow.This system is possible with some relatively simple additions to the normal façade.For the “double-skin façade” a wide variety is used, ranging from a simple extra glass panel in front of a window, protecting the sunscreen, up to quite elaborate assemblies.In the more complex variety, an all glass façade is achieved.A storey high exterior glass panel is supported by a slender structure, hung from outriggers at-tached to the floor. Generally the interior façade also contains a large glass surface. To be able to clean the glass surfaces of the cavity without disturbing the occupants by opening large glass doors, a wide cavity is chosen. This cavity must be 80 cm deep, at least.Generally the cavity will be ventilated by outside air to cool the sunscreen. The air flow depends on the chimney effect. Due to the large glass surface, a lot of sun energy enters the cavity and this requires large openings. These will be closed in cold periods.In spring and autumn, the temperature in the cavity may be used for natural ventilation of the room, by opening the inner façade. In summer the temperature in the cavity will be too high and an additional climate installation is used.In high rise buildings the cavity is closed on every floor level, for fire safety reasons. This is limit-ing the effective chimney height.

Fig. 3.1.1. Climate façade and second skin facade

For lower buildings, the chimney can continue over 4 floors as a maximum. The limiting factor is the increasing temperature of the air at the upper floors.There are many options for the various design decisions:− Air flow by natural convection or by ventilators− Number of storeys along the height of the cavity− Openings fixed or controllable− Using double glazing for the interior side and/or the outside− Cooling the sunscreen by interior or outside air, or making combinations possible.− Pre-heating of outside ventilation air for the room, in the cavity− Transporting of absorbed heat in the sunscreen to colder parts of the building.− Expanding the cavity of a second skin façade to create a small atrium− In a climate façade, the sunscreen can be made of a continuous porous cloth. Then the air can be sucked through the sunscreen to the cavity between the sunscreen and the outer glass panel. This airflow is cooling the sunscreen directly, avoiding the single glass panel on the inside.

3.2 Choice of a system

Just cooling the sunscreen will not provide enough justification for choosing a system with a ventilated façade. Other considerations will be taken into account.− Saving of energy by cooling the rooms at night, by natural ventilation, without the risk of burglary− Energy saving by the higher thermal resistance of triple glazing− Control of cold bridges− A wider choice of materials possible, for the inner window frame (like lower grade wood prod-ucts).− In refurbishing of old buildings, improving thermal performance and appearance.

However, the main reason for choosing a second skin façade is architectural. Goals are creating a wide view to the outside for prestige and the display of the interior activity to the outside world. This leads to large glass areas.Large glass areas have many disadvantages for the comfort (unstable temperatures, sound transmission) and the use of energy for cooling. These disadvantages can be partly compen-sated by the second skin concept.Therefore, these expensive façades are only applicable if the client wants a prestigious building.

In many cases the original idea for a transparent façade (fig. 3.2.1.) is frustrated by the necessary technology. In fig 3.2.2 the finished building is shown.

Fig. 3.2.1. Visualisation of the intention of the architect.

Fig. 3.2.2. The building of fig. 3.2.1. as build.

The transparency to the interior is not achieved because the level of light in the interior is too low, caused by the deep cavity, ventilation boxes and interior partitions. In addition, the three glass surfaces will reflect a high percentage of the, much lighter, sky. Only at night the illumi-nated interior will be visible.A transparent appearance can be more easily achieved at corners, where light is transmitted

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through the building. Another possibility is designing atriums, several storeys high, allowing light deep into the building.A double-skin façade is costly in building and maintenance. If the building volume is restricted by urban planning, the loss of rentable floor area also is a major disadvantage. With some com-promise, cheaper technical solutions may be considered.− Natural ventilation can be achieved with separate ventilation openings, equipped with sound-proofing. These can be used during a longer period, since the ventilation is independent of the temperature in the cavity.− The heating of the interior glass pane by the sunscreen can be reduced by a heat reflecting coating on the glass surface. This will also reduce the heat losses in winter.− A sunscreen may have a highly reflective surface. Without an air flow in the cavity the reflective capacity is not spoiled by dust.− An exterior sunscreen is cooled more effectively than a sunscreen in a ventilated cavity. The extra cost for the strong structure may be less than the costs for extra glass and controllable openings.As a conclusion it may be stated that multi layer glass façades can give a good solution for build-ings where a lot of requirements must be met (south façade with large glass area, individual con-trol of sunlight and ventilation, architectural expression) and where ample budget is available.

3.3. Geometry of the cavity

The depth of the cavity has a direct relation with the size of the glass area.With small dimensions it is possible to use inward opening windows on the inside for cleaning. This will be necessary 2-3 times a year. This will not cause great disturbance for the use of the room. The depth of the cavity follows from the dimension of the sunscreen and the free flow of the air. A greater depth is unfavourable because this will be more apt to an uneven airflow.If the glass area covers almost the entire façade, a simple openable window is not enough. Large swing doors of glass need a lot of floor space, so all furniture must be moved 1 meter from the façade. A sliding door is better, also for structural reasons. The cavity side of the sliding doors can only be cleaned by a person, standing in the cavity. This enhances the depth to more than 80 cm. The cleaning can be done from an open grid of balcony at every floor level, or from a hoist able cage.The deep cavity of the double-skin façade has consequences for the structure of the floor.The exterior glass panels must be connected by narrow joints to maintain a clear view to the outside. Narrow joints are possible only when the relative movement between the glass panels is limited. Since the glass panels are about 1.5 m wide, there must be outriggers at this distance.These outriggers need a connection to the floor, which will not rotate. Floor beams at right an-gles to the façade could provide enough rigidity, but their distance is generally over 3.6 m. This means that the floor edge must be very stiff to rotation between the columns or beams. This increases the height and depth of the floor edge.For medium high buildings, it therefore becomes attractive to hang the complete exterior glass façade on outriggers from the roof. There, ample space is available to make a stiff outrigger. The mechanical connection from the exterior façade to the normal floors then only has to resist the wind load.Opening windows, in the interior façade of a double-skin façade, can cause hinder from sounds. The noise will be reflected between the glass surfaces and can enter the building elsewhere. Also smoke can be guided through the cavity.To prevent this, the balconies in the façade can be closed, but this causes a considerable reduc-tion of natural light in the rooms. The chimney height is also less, requiring larger ventilation openings to get the needed air flow for cooling the sunscreen.To prevent noise problems between rooms on the same floor, vertical separations may be need-ed. This can also be useful to reduce wind forces on the outer façade, at the corners of the build-ing. Overpressure in the cavity, on the windward side, should not be guided around the corner, where negative outside pressure exists. This horizontal flow of air also prevents efficient cooling of the sunscreen.

3.4. Air flow and cooling capacity

In a climate window the air flow is determined by the required refreshment of the interior air. Starting with this volume per hour, and the horizontal percentage of glass of the façade, a vol-ume for every m1 of window can be derived. In a high climate window this air will stay in the cavity longer and consequently get a higher temperature. Air has a low specific thermal capacity and this will limit the desired effect of cooling of the sunscreen.A second restriction is caused by the low velocity of the air in the cavity. For the given speed, the

convective transfer of heat from the sunscreen to the air is limited.As an indication, the next example is given:

Thermal coefficient of expansion (α): 6*10-6 /oCRise in temperature (ΔT): 50 oCLength (L): 12 mthen:

ΔL = ΔT * α* L = 60*6*10-6 * 12 = 0.0036 in = 3.6mm

Height of the window (h): 2 m1Surface of sunscreen (A): 2 m2/ m2 windowConvective heat transfer coefficient (αc |): 3 W/m2KAir flow through the cavity (V): 40 m3/hIncreasing of temperature in the cavity (ΔT): 10 oCTemperature interior(T): 20 oCSpecific heat air (ρ): 1000 J/kgKSpecific weight air (c): 1,2 kg/m3

For the transfer of this energy the sunscreen must be warmer than the average temperature of the air. The tem-perature difference must be:

If the rise in temperature over the height of the window is supposed to be linear, then the average temperature in the cavity is:

Now the temperature of the sunscreen must be:

25 + 11.1 = 36.1 oC

With this temperature, still a large portion of the energy will pass through the interior glass panel by radiation and convection. With a difference of 16.1 oC , this will amount to 56 W/m2.For 2 m2 of window, 112 W will enter the room, compared with 133 W, removed by the air flow.It is often suggested that a climate window removes the whole heat load from the sunscreen. In fact it reduces the amount. A climate window is more effective than an interior sunscreen, but is less effective than an exterior screen.The air is generally transported to the climate installation. If this air is reused, no reduction in cooling load is accomplished.In winter, without sun load, the exhaust air is transported along the outside, double glazing. Then the loss of heat energy is comparable with normal double glazing, without the advantage of the extra cavity.With a second skin façade, usually the option is used to get direct natural ventilation by opening the interior window or door. However, when the sun gives a high thermal load on the sunscreen in the cavity, generally at the same time the outside temperature is also quite high. Then the rising of the air temperature in the cavity must be significantly restricted, if this air must be used for the ventilation of the room.For a modest rise in temperature a large air flow is needed. The air flow, however, is generated

by the chimney effect. The driving force is the pressure difference between inlet and outlet, be-ing linear with the temperature difference. For the necessary large air flow then large openings are needed.Compared with a climate window, also more sun radiation reaches the sunscreen. This is caused by the outside single glass pane which reflects and absorbs less light than a double glass unit.As a result of these effects, it is not possible in summer to use natural ventilation through the cavity. Depending on the size of the openings (0.1 to 0.3 m2/m1 façade) natural ventilation is possible up to about 15 oC outside temperature. For the warmer periods normal air condition units must be used. These must be designed in relation to the façade design.Large openings must be equipped with shutters for the colder periods. These openings are vis-ible from the outside, while making the façade less transparent. The costs of building and main-tenance will also increase.

3.5. Balance between requirements and complexity for second skin façades

Due to the amount of design variables there is a wide choice, ranging from simple additions to a standard façade to very elaborate and costly assemblies. The project and the location decide which combination of qualities and cost is useful.In figure 3.5.1 a simple solution is shown for a three storey building, with a continuous cavity. A grating serves as a platform for cleaning of the glass and partial sunscreen. The vertical sun-screen is put directly in front of the relatively small windows.The exterior glass panels are supported by mullions hung from the roof. The panels are me-chanically fixed with bolts between the panels.

In the example in fig. 3.5.2, the air in the cavity is exchanged separately for every window. The depth of the cavity is limited, making cleaning of the cavity possible by opening the turn and tilt window. The cavity is per-manently open.

Fig. 3.5.1. Simple second skin façade with ventilation

over three storeys

Fig. 3.5.2. Second skin façade with ventilation over the height

of the window

1. Double glass unit3. 6 mm prestressed glass4. 8 mm prestressed glass (not transparent)5. Sun shading7. Anchor for fixing

In fig. 3.5.3, the interior façade is alternating transparent and closed for about every 1.8 m. The ventilation open-ings in the façade have a modest dimension. The cavity has an additional thermal mass by the concrete balconies reducing the rise of the temperature for several hours. The sliding rigid wooden sunscreens can cover the glass doors.

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Fig. 3.5.3. Second skin façade in front of a concrete interior leaf

In fig. 3.5.4., an example is given for a façade with a large glass area and enormous ventilation equipment. These openings are the consequence of choosing a long period in which natural ventilation must be usable, increasing cost and architectural impact. This is the façade of the building in fig. 3.2.2.

Fig. 3.5.4. Second skin façade with large ventilation openings.

1. Sliding doors6. 12 mm prestressed glass7. Aluminium lamellas8. Adjustable valve9. Engine10. Grid as a walkway12. Sun shading

4. Large transparent façade and roof surfaces

4.1. Introduction

For buildings, sometimes large glass surfaces in façades or roofs are required, generally at the entrance or for atria.In this way the building is opened from the inside to the outside. Also it is possible go get a view to the activity inside the building to create a lively image.On some locations, a large number of educational, cultural or commercial functions must be accommodated. These can be put in one complex to make a more efficient use of general facili-ties. The separate building elements may be connected by a semi public glass covered street or a central square.For large mono functional buildings this approach can also be used. An early example is the AMC (university hospital) in Amsterdam. This one building volume in fact consists of separate build-ings connected by streets and a central covered square.Structured by their repetitive character, office buildings and hotels have a floor plan of a central corridor with rooms on both sides. This leads to slender buildings with a monotonic façade. With a generous entrance and reception area of glass, the desired prestige can be acquired. Structur-ally the simplest solution is to position this volume beside the more closed part of the building.With a sectional building, the space between the outstretched wings of the floor plan may be closed by a glass covered space. Then the outer surface area of the building is significantly re-duced. This is favourable for energy conservation and for reduction of noise, especially in city centres. The extra cost of the atrium façade can partly be compensated by the inner façade which does not have to be waterproof and needs less maintenance.By landscaping the space with trees, gardens and benches the illusion of an exterior space, with a moderated climate, can be created. This is necessary to prevent the offices, with only a view into the atrium, from being too claustrophobic.The created atrium may also be used for recreation in the lunch hour, receptions etc.Large glass areas can also be used just to acquire prestige.An early example of this are the façades of Hardwick Hall in England, built in 1597 (fig. 4.1.1.). The desire to present an image and to show wealth, largely overruled the disadvantages of the cold in winter (just open fires) and the heat in summer (no sunscreens). Glass was very expensive at that time.In this building, the transparency is only achieved from the inside to the outside. From the out-side it is a closed building with symmetry as a main goal. The façades have false windows in several places and all chimneys are put at internal walls.The exhibition buildings of Crystal Palace (London, 1851) and Paris (1889) are also early exam-ples. Very transparent examples are the shopping arcade of Milan (1867, fig. 4.2.1.2.) and the Koornbeurs in Groningen (1865).In some cases these structures would not be acceptable today, as a result of increased safety standards.

Literature:Compagno

“Intelligente Glasfassaden”Birkhäuser, Bazel-Boston-Berlijn 1996

Oesterle e.a.“Doppelschalige Fassaden”Callwey, München, 1999

Danner e.a. “Die Klima-aktive Fassade”Alexander Koch, Leinfelden-Echterdingen, 1999

Schittich e.a.“Glass construction manual”Birkhäuser, Bazel-Boston-Berlijn 1999

Vakgroep Bouwtechnologie“Façade & Klimaat”Fac. Bouwkunde, TU Delft, 1996

v.d. Voorden en de Bruijn-Hordijk“Geventileerde gevels”Dictaat TU Delft, Fac. Bouwkunde, 2000

Themanummer GevelsBouwwereld, 2001, nr. 9

Fig. 4.1.1 Hardwick Hall

Developments since 1975 are:

− Use of double glass− Toughened glass with point like mechanical fixing− Support structures with prestressed cables to distribute wind load and dead load− Glass panels hanging from cables or hanging from each other− Glass beams as a support

In this chapter an overview is given of the principles and technical detail solutions that can be used. These can be combined to a large number of forms. Details of realised buildings are widely published.

4.2. Functional aspects

4.2.1. Transparency from the inside to the outside

This means that the view, looking outward through the façade, is obstructed as little as pos-sible by the support structure. Then of course an important factor is the percentage of the area, taken up by structural elements. However, the form and regularity of the structure is almost as important.The roof in fig. 4.2.1.1 has a structure that is a homogenous grid, creating the image of a net or wire mesh. The thin elements are stabilised in their form by prestessed wires. If it would consist of elements in only one direction, having double dimensions, the impression of enclosure would be stronger.

Fig. 4.2.1.1 Museum in Hamburg

It is often thought that large glass panels create transparency. This is notecessableFig. 4.2.1.1 Museum in Hamburgnrily so. Large panels must be thicker and the support structure must be stronger and stiffer. This is because the impression of safety de-pends on the visideformations. These depend on the absolute de-flections and the angles between theedges of the glass panels at the supports.

Large glass panels are not necessary; a fine meshed structure with small panel can be very transparent (fig. 4.2.1.2.).

If the support structure is different in the two directions, the orienta-tion is important. In the example in fig. 4.2.1.3 the vertical supports create a column like effect for a person walking along the façade.

Fig. 4.2.1.2 Galleria Vittoria Emanuele, Milaan

Fig. 4.2.1.3 La Bibliothèque De La France, Paris

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By opening vertical or horizontal supports with holes or creating trusses the transparency is increased (fig. 4.2.1.4.). In trusses, the out-side dimension of the bars is important. Heavy, massive thin bars give a more open and lighter image than bars made of tube section with wider outside dimensions. Material economy is then secondary to the visual impression.

With vertical supports minimised and at great distances from each other, and long horizontal beams for the wind load, the horizontal view is much more open (fig. 4.2.1.5.). It is possible to remove the support structure from the actual glass area. It may be separately positioned in the interior or more outward-ly. The effect is that the supporjust look like objects without a direct relation to the façade (fig. 4.2.1.5.). The wind load is distributed to these supports by horizontal bars.

The transparency is often reduced by additional elements like gangways for the accessibility for cleaning, movable scaffolding, sun shading or ducts for warm air to control the climate.

4.2.2. Transparency from the outside to the inside

Without adequate measures it is very difficult to look through a glass panel to the inside of a building. This is caused by the low level of light in the interior, compared with the reflections from the very bright sky. Even reflec-tions from buildings around are lighter than the interior.If transparency to the inside is insufficient, the impression from the outside will be a reflective enclosure of an inac-cessible building volume.

A view to the interior is only possible with a high level of light in the interior and a reduced reflection of the exterior and especially the sky.The first can be improved by a large glass area in the roof.Reflection from the sky can be reduced by putting a hori-zontal canopy or sunscreen above the façade. This is often

used by shops and showrooms for cars.The reflection can also be reduced by tilting the façade outwardly (fig. 4.2.2.1.). Then the ground level is reflected in the glass and this area is much darker than the sky. These visual effects can be seen at the Central Library of the TU Delft:− Around the corners one can look through the building and the activities are well lit and visible.− At the eastern side the façade is tilted outwardly, and the roof is extended, making the interior visible for the first few metres.− The northern façade is tilted backwards, making the in-terior invisible.Please note: In the night the effect of reflection is opposite. Then a view into the lighted building is easy. From the in-side only the reflection from the interior is visible, unless the exterior is well lighted by streetlamps or other lighted

buildings.The windows of towers for traffic control at airports, bridges etc are generally tilted outwards. At night the view outside is not hindered by reflections from the interior if the ceiling is kept dark and the interior lamps are kept at the level of the desks.Double glazing and coating to reduce heat radiation will enhance the reflection of light in rela-tion to normal single glass. Infrared selective coatings are normally not visible, but some part of the visible light spectrum is affected.During the day there will always be some reflection. Therefore it is important for the glass panels to be flat. A small curvature is clearly visible, especially if the panel is hollow to the outside. A deflection of 0.005 times the length of the span creates a distance to the focus of 40 – 60 metres. Seen from that position the reflection is highly distorted.A curvature is often caused by the process of heat strengthening of the glass.The supporting structure does not affect transparency from the outside to the interior to a great extent. The observer is not enclosed by the structural elements, but is looking at the building from a distance. The glass façade and the interior are seen as a whole picture.

4.2.3. Thermal climate

4.2.3.1. Preventing low temperatures

The level of thermal insulation is determined by the intended function of the atrium. It is also important to establish to what extent compromises are acceptable for periods when a function cannot be fulfilled.Inside a single glass enclosure, especially during spring and autumn, an acceptable climate can be achieved for recreational activities at lunchtime, receptions, exhibitions etc.An improvement of the external climate, by eliminating wind and rain and catching the received warmth of the sun, is enough. If a compromise is acceptable for the coldest and hottest days of the year, with an atrium much value may be created for the building, at restricted costs.In the entrance zone of the building, low temperatures are no problem.To argue in favour of an atrium, in the design stage, there is a tendency to increase its usability for more activities and functions. However this goes along with higher standards for the climate.For a longer stay in a restaurant or reception area in winter, heating will become necessary. Then for economy the thermal insulation must be improved by double glazing, even with infrared coating, reducing transparency.The double glass panels accept less bending than single glass, because bending leads to shear-ing forces at the edge connections. These forces are acceptable to a certain extent and over-loading may cause leaks, with condensation in the cavity as a result. The consequence is a stiffer support structure, again reducing the transparency.In summer the extra thermal insulation leads to higher temperatures. These must be tackled by sunscreens, extra ventilation or even a cooling system.If the atrium is additionally heated, the surface temperature of the glass on the inside is still colder than the air temperature in the atrium. The inside air is cooled close to the glass and flows downward. The speed of this flow increases with the height of the surface. This cold draft is very uncomfortable and precautions may be needed. By adding heat to the glass façade this draft can be avoided. The simplest way is warm air blown to the glass. The low heat capacity of air makes large volumes necessary, resulting in wide ducts to distribute the heat evenly over the large glass area. By using a transport system with water, with a much higher heat capacity, smaller dimensions are possible. Locally, a much smaller air flow can transport this heat to the neighbouring glass surface.The conclusion is that it is possible to make the climate in an atrium controllable in winter, to facilitate a wide range of functions. This, however, requires a lot of costly additional elements, hampering the transparency.

4.2.3.2. Preventing high temperatures

Through the large glass area, much light comes in and is partially absorbed by the floor, the walls and interior objects. This light is transformed into heat. Heat radiation is long wave, and this radiation cannot pass through the glass, backwards to the outside. This leads to increased temperatures of the air and all material in the atrium.To reduce the rise in temperature, a light coloured floor helps by reflecting most of the light. The light is a short wave radiation, and this energy may escape to the outside.The part of the energy, absorbed by the floor, should be transported from the surface to deeper layers. If this transport is fast, the temperature of the surface stays cool.

A floor material with a low heat resistance and a high thermal capacity in a thick layer is favour-able. The heat is quickly transported inside the material and a high capacity can take several hours of this heat without rising too much in temperature. An example is white natural stone tiles on a concrete floor. The absorbed energy can be drawn out of the floor during the night, by natural ventilation.Water has a large thermal capacity. This capacity is equal to that of steel and double this value for concrete (for a given volume). A small basin can stabilise the temperature and an additional fountain can absorb much heat by evaporation.Additional measures cannot be avoided if the temperature must be restricted to about 25 oC on the hottest day, with the maximum sun load.Light reflecting coatings on glass are unacceptable because they would make the atrium a mir-ror like block, generally offensive to the environment. A reflective roof is also to be avoided because, seen from the inside, it would differ very much from the façade.Fixed or adjustable louvers on top of the roof or in front of the façade are an effective solution, but these have much influence on the architecture.For the façade only removable sunscreens are possible because otherwise the whole idea of transparency is lost.An alternative are dots or stripes printed on the glass. If they are white on the outside, the ab-sorption is restricted. From the inside, fine black dots are not visible separately.Sometimes electrical sun cells are used to reduce the heat load.An internal sunscreen must have a light colour. The variant of the climate window, where the exhaust air from the atrium is sucked through the mesh like sunscreen, taking away part of the heat, may also be used.Like in winter, to make the climate fully controllable, a great many additional elements will ham-per the transparency.

4.2.3.3. Ventilation

For incidental activities in a large atrium, the need for fresh air will be limited. Per hour, only a small portion of the atrium volume must be exchanged.Generally the volume of ventilation is determined by the need to control the temperature in summer. Sometimes used air from the building is led through the atrium, or ventilation air for the building is drawn from the atrium.An exhaust opening in the roof or high up the façade must be combined with openings that are situated as low as possible. However, the openings should stay several meters above ground level, to avoid draft over the floor, incoming dust and intrusion.The chimney effect is the driving force. On the hottest days, however, the cooling capacity must be at maximum, while the available margin between interior and outside air temperature is minimal. Therefore the ventilation openings must be quite large (about 5% of the floor area) for this extreme situation. In normal situations they must be smaller and consequently they must be adjustable. In some cases the whole atrium roof can be lifted to create an opening along the perimeter.The idea to cool the atrium at night is attractive. Then for safety, grids must be placed in the lower openings.In case of fire, ventilation smoke must escape through the ventilation openings. An automatic opening mechanism is needed. The smoke must be kept high enough above floor level to keep this free from the poisonous gasses. Generally the atrium is also the entrance of the building, and a natural escape route.

4.2.4. Maintenance

A glass façade and roof is expected to be transparent. This is only true with regular cleaning.For cleaning, easy and safe access is conditional, meaning hanging scaffolds, catwalks or lift-ing platforms. All of these are hindered by structural elements, expanding from the inside or outside.A hanging scaffold needs rails and a stiff support along the roof, creating a strong accent.If the façade is supported by wide horizontal trusses, these can serve as a catwalk if an open grating is added.In most cases, however, a lifting platform is used. For this equipment, about 3 m1 from the in & outside of the façade must be kept free of landscaping. A flat and hard surface is needed for the stability of this equipment.In some projects the glass is so poorly accessible that, due to staining, the intended prestige is lost.

Fig. 4.2.1.4 Exposition hall in the Castle Garden in Arcen

Fig. 4.2.1.5 Atrium of the CentraalBeheer building in Apeldoorn

Fig. 4.2.2.1. Western Morning News,

Derriford (GB)

12

Replacing mastic joints is part of the maintenance.Mastic joints are often used to create a flat exterior of the glass area, without cover strips at the joints. The service lifespan of this material is limited to about 20 years, due to hardening and loss of adhesion. The quality of these joints depends on the working conditions in the building stage. Dirt or damp edges of the glass, for example, may prevent a good adhesion. An earlier replacement is necessary sometimes.In a glass façade or roof, a leaking mastic joint seldom leads to extended damage, because the leak is easily detected and the materials around the joint are not affected by moisture.

4.2.5. Safety

Glass is a brittle material; it breaks suddenly without plastic deformation. It breaks at spots where micro cracks or scratches appear on the surface. The material also contains internal re-sidual stresses from the solidifying during the manufacturing (see also chapter 7). The material has a high stiffness (about 1/3 of steel), meaning modest deformation before breaking.Without plastic deformation, a redistribution of forces after local overstressing is not possible. Therefore, stresses must be predictable and not be influenced by tolerances and movements of building parts. A statically determined fixing is the simplest way to create a reliable solution.This applies not just to the connection of anchors to the structure, but even more so to the con-nection between anchors and the glass. A rigid connection of an anchor to the glass could easily lead to unintended, secondary bending moments or sliding forces. Especially around holes in the glass for a bolt connection, bending moments create a risk.In early examples, designers often chose for complex ball joints in the centre of the thickness of the glass. This safeguards free rotation at the support if the panel is bent. The glass panels were always supported at the corners.Later, after more experience was gained and better modelling of the behaviour was possible, more rigid connections were used. The position of the support also was chosen more freely, away from the perimeter. By accepting bending moments at the fixing points, deflection is re-duced, or wider spans are possible with the same glass thickness.Glass has mechanical qualities that makeI it not very suitable for distributing mechanical loads. However, with the right precautions it can handle these loads.Modelling glass structures is not possible in the same way as modelling structures of steel or concrete. There, redistribution of stresses is incorporated before the ultimate limit state arises.Also, glass does not have a fixed material strength. The “strength” of glass is determined by the number and nature of faults in the surface. Small pieces of glass have less cracks from the shrink-ing during solidifying than large pieces and consequently the material seems stronger.For large assemblies of glass it can prove to be advantageous to incorporate plastic behaviour in the connection points to reduce forces due to local collapse. It is also possible to construct con-nections that are stiff in normal conditions but are much more flexible in an overload situation (see also 4.6.4.).If normal glass breaks, the large sharp peaces form a grave risk to passers-by. This risk can be reduced by hardening the glass, where high internal stresses are generated. In the event of lo-cal breakage, the equilibrium of the internal stresses will be disturbed. The glass panel will then break in a large number of small pieces that are less dangerous. This can be a good solution for vertical windows at low level. For horizontal glass panels over a circulation zone, hardened glass is still a major risk.Another way to reduce the risk following breakage is laminating two or more layers of glass, with a plastic foil in between. Then the broken pieces are kept together. A precondition is that the broken, more or less flexible panels, stay in their position. This can be achieved by clamping the glass panel strongly to the supports. Gluing the glass is also possible.A wire mesh encapsulated in the glass also keeps the glass together.The biggest threat to large glass areas is equipment of people working on a glass roof. Also un-predicted movement of the structure and temperature effects cause breakage.Vandalism also forms a risk, but experience shows that large glass panels are less inviting.Large glass panels are relatively safe. Large panels will generally be made of hardened glass to obtain a higher breaking strength for the same thickness. The stiffness, however, is not affected. Then the deflection before breakage is quite large. The bending radius for hardened glass at the breaking stress is about 870 times the thickness of the panel. For a panel of 2 m1 span and 6 mm thick this means a deflection of about 10 cm. Such a deflection will be very noticeable.

4.2.6. Sound

Reducing the heating of the air in the atrium with a large heat capacity leads to floors covered with tiles. In combination with the glass walls and roof, there is hardly any sound absorbing sur-face in the atrium. The volume of the space is also quite large. The reverberation time depends on the relation between volume and absorption surface. To reduce the noise nuisance, addition-al absorption panels can be used. Hanging objects and landscaping with trees may also be used.

4.3 Fixing of glass panels to the structure

The glass is held in position by a supporting structure, to which it is connected in different ways.The following ways of fixing may be chosen:− External cover strips on four sides This technique has the visual disadvantage that the glass area is divided into small sections. On angled roofs also water is trapped above the horizontal cover strips. After evaporation dirt stays behind. This way of fixing, however, is simple and reli-able. − External cover strips on the vertical sides and a glued connection on the backside on the hori-zontal side. This is attractive for roofs. The horizontal joints, formed by mastic joints and flush with the surface, will prevent the problem of staining.− Glued connection on four sides. From the outside, the glass façade appears as one unbroken surface. The glue technique is quite reliable, although some municipalities demand additional mechanical connections that become active in case of failure.− Visible point like connections around the edges. These connections are hardly visible, but locally high tensions appear at the edges. The closing of the joints near the connections is dif-ficult. This fixing method is frequently used with atria where single glass and open joints are acceptable.− Bolt connections through the glass. The bolts are hardly visible if they are kept flush with the surface. In double glass units the bolt can also just penetrate the inner glass panel. To restrict the secondary bending moments in the glass around the holes, hinges or flexible connections can be put close to the surface. A large number of systems is available.− Point like glued connection on the backside. Here the glass has no drilled holes, which reduces some of the problems with tolerances, compression forces in the glass, etc. The risk, however, is increased. The stress on the glued connection is very high. A rotating connection can only be placed at a distance from the surface. Therefore bending moments will always appear in the glue. Not one of the four connections may fail, because this creates a large increase of the forces on the other points. Also the small area of glue, compared with a linear gluing along the perim-eter, reduces the margin for error. Because the thermal behaviour of the anchor is different from that of the glass (absorption of sunlight, thermal mass), the glue must have some flexibility. At the moment of this writing just one example is known, the atrium in the Prinsenhof in Delft (fig. 4.3.1.). For the vertical panels additional mechanical support is used to prevent the continuous gravity load on the glue.

At the bottom of this list, the visibility of the fixing is reduced. The susceptibility to errors in de-sign and realisation, however, increases. This makes strict quality control essential.

A point like connection is only useful in combination with a very transparent support structure. The only continuous lines are formed by the joints of about 20 mm wide and thin cables or bars. If the support is more massive, with wider members, then a continuous glued connection is more logical. This is simpler, less sensitive and a thinner glass panel is possible.Glued fixings are not always allowed. For example in Germany and Rotterdam additional me-chanical fixing is compulsory above a certain level.

4.4. Wind load

4.4.1. Introduction

The size of the glass panels is limited by the accepted deflection and the steep increase of the price of glass with thickness (fig. 7.4.1.1.). Also the equipment in the industrial process of harden-ing or laminating limits the size.Generally, the wind load is dominant, leading to a maximum of about 2 m1 for the shortest side of a panel.For horizontal panels, smaller dimensions are favoured. In laminated glass, necessary for safety, the glass layers do not act together for a permanent gravity load. This means extra thickness.

To combine the small glass panels to a large glass façade, a support structure must be used. For the purpose of transparency, this must be as unobtrusive as possible. To reach this goal, several techniques are available. These may be combined for the primary and secondary structural ele-ments.For a systematic approach they are presented separately. In projects, however, all kinds of com-binations may be seen.In fig. 4.4.1.1 a part of an atrium roof is shown as an example.

For downward loads the primary structure is a truss with thin diagonals, fit only for tension. For the upward loads the diagonals are ineffective, and the truss acts as a frame truss. The slen-der trusses are stabilized by prestessed diagonal cables. As secondary beam, a laminated glass beam is used. The glass panels are fixed to these beams with point like mechanical connectors.

N.B. There is no mechanical cooperation between glass panel and beam to form a T-shape. This has been experimented in the laboratory, but is not yet a reliable technique.

Fig. 4.3.1. Roof over the interior square of the Prinsenhof, Delft

13

To minimize the structural elements, these are designed to distribute the maximum load on the material, meaning large deformations. Especially in the building stage, different loads will appear if not all panels are fit. The increased deformations make the building process more dif-ficult. In a partially closed façade uneven wind loads may appear.Because hardly any unnecessary material is used that could cope with the various situations, this building stage must be taken into account in the design.Transparency from the inside of the façade is greatly influenced by the structural elements. The transparency from outside is mainly influenced by the level of light in the atrium and the reflec-tion from the sky. In the following paragraph the structure is always considered from the inside.4.4.2. Making the structural elements less visible

The following measures may be taken to make elements less obtrusive:− By giving the interior side of the element a light colour, there is less contrast with the clear outside.− To enhance this effect, the sides of the member may be angled. These sides are still lighted by the sky, but they reduce the width of the darker interior side. By a curved side the reduction of light is gradual. The sides can even come together, avoiding an unlit backside (fig 4.4.2.1. and 4.4.2.2.).− The beam in the façade can be made of glass, avoiding even further a dark backside.− Already mentioned was the orientation: horizontally a wide span with deep members to facilitate an unobstruct-

Fig. 4.4.1.1 Main Office Proctor & Gamble, Weybridge (GB)

Fig. 4.4.2.1 Mullion and transom with tapered interior side

Fig. 4.4.2.2 Visual effect

ed view in the horizontal direction instead of deep vertical members.− A truss without diagonals has fewer elements and gives a more open view than a truss with diagonals (fig. 4.4.2.3.). The need for more material can be neutralised by more massive sec-tions with small exterior dimensions. The goal is visual transparency; material efficiency comes second.− Round or oval tubes are visually thinner than rectangular or square tubes. H-type sections are worst.

4.4.3. Reduction of visual surface of the members.

For transparency it is essential to reduce the exterior dimensions of the members in the plane of the façade. Here, the parts resisting compression forces, are the most important. To resist buck-ling, they must have a minimal bending stiffness. Therefore it is useful to try to avoid compres-sion forces in beams and trusses. This can be achieved by prestressing where the compression forces are overruled by an external tension force. The principle is explained here.− A post or beam must resist wind pressure and wind suction. With wind pressure, compression forces appear on the outside and with suction, the inside takes the compression. This means that on both sides of a truss, a wide outside dimension is needed. This is illustrated in fig.4.4.3.1. Shown are the forces in unloaded and loaded situation. For clarity, the connecting bars and diagonals are not shown.− By prestressing the system of fig. 4.4.3.2, both tension bars are under tension and the central compression bar under compression (figs. 4.4.3.3. and 4.4.3.4.). With a bending moment, one

as a central compression bar. To prevent buckling for larger glass panels, glass ribs can be added. This solution has been applied on some small projects. The central compression bar may be eliminated if the pre-stress cables are put into an external frame of support structure (fig. 4.4.3.6.). The total amount of forces and bending moments increases drastically, but the accompanying material is kept out of the area where it matters. This solution is very attractive if the frame around the façade is already pres-ent, for example trusses for a roof or other parts of the building. The structure will show deformations and also the cables of the façade structure will shrink and expand by thermal movement. The thermal mass is small and the cables receive a lot of sun en-ergy. For this reason the cables are sometimes put in series with a flexible spring (fig. 4.4.3.7.). This spring has shown a large de-formation to obtain the required pretension. Due to the small stiffness, a small displacement will not change the pretension to a great extent. − If the tension cables are put in two directions, the ends of the cables may be spread around the frame. Numerous configura-tions are possible (fig. 4.4.3.8.). Double curved nets are also used for façades.− If large deflections are acceptable (0.01 to 0.02 times the length of the span) with the maximum load, a completely flat net or cable system is possible. The pretension must be very high,

since the reactive bending moment is equal to the product of the pre-stress and the displace-ment. Displacements may go up to 50 cm, and the joints must be able to accept angled defor-mations, especially along the perimeter of the façade.The given principles may be used for primary, secondary structural elements or both.

4.4.4. Reducing the number of elements in a sup-port structure

The support structure can become more trans-parent by omitting certain supports or by mak-ing linear members non continuous.By supporting glass panels only on two sides, only horizontal or vertical lines remain (4.2.1.5.). In the other direction only a narrow weather

tension bar gets double tension and the other one almost zero tension. The amount of compres-sion is unaffected. The bending stiffness is formed by the area of the tension bars and the full height. Because of the height and the double surface, the stiffness is doubled in comparison with 4.4.3.1.

− To gain a flat exterior tension bar, lying in the face of the façade, the geometry may be bent

Fig. 4.4.2.3 John Moores University (GB)

Fig.4.4.3.2 Forces in the tension bars and the central compression member (non prestressed

system), without and with wind load0 = no force

++ = tension--= compression

Fig.4.4.3.3 Forces in the tension bars and the central compression member (prestressed

system), without and with wind load0 = no force

++ = tension--= compression

Fig. 4.4.3.5. − To reduce the number of compression bars, 4 or more tension cables can use the same compression member. A spatial truss is then formed. Again, the outside dimension of the compression member can stay the same, only the area of the cross section increases. It is also possible to use the glass panels of the façade

Fig. 4.4.3.4 Horizontal truss system with pre stressed cables and a central compression bar.The vertical cables only support the truss and

not the glass panels.Park André-Citroën, Parijs

Fig. 4.4.3.5 Truss system like fig. 4.4.3.3. but with a curved compression bar.

Fig. 4.4.3.6 Atrium Parc de la Vilette, Paris

Fig. 4.4.3.7. Spring structure at the bottom of a cable truss to absorb movement and maintain

the pre stress.

Fig. 4.4.3.8 Cable structure in two directions.

14

seal, for example a mastic joint, remains. The glass is now bending along one axis, making the deflection much larger than with a support along the four edges. Therefore, even with thick glass panels (> 10 mm) only a limited span is possible. From an economic perspective, a span of 1.4 m1 is about the maximum (see also Ch 7).The secondary structure may be divided into smaller sections, acting as outriggers from the primary structure. They can even be kept separate from the plane of the glass, reducing the support even further to a support on four corners (fig. 4.4.4.1.). By shifting the supports from the corners to a position at a distance from the edges, a reduction of the glass thickness can be achieved. Bending moments in the glass at the supports makes modelling of the behaviour more complicated, especially around the hole for a mechanical fixing. It is also possible to decide to have six supports in stead of four.

4.5. Gravity load in vertical façades

4.5.1. Introduction

The gravity load from the glass panels may be guided to the foundation by means of several

In figs. 4.5.4.2 and 4.5.4.3 a practical technical design is shown. This was used in the atria in the Parc de la Vilette in Paris.

4.6. Joints between the glass panels

The joint construction follows from the requirements for the intended function of the atrium (exclusion of rain and wind, temperature stability and sound level). Aesthetic considerations control the width and how much the joint can extend from the surface. There is also a relation with the way of fixing of the panels.Starting with the least visible one, the following types of joint may be chosen: − For an atrium without heating or cooling, open joints, with a width of 10 – 15 mm, are a simple solution. This may be adequate for a protected exterior climate, fit for an entrance area, covering stairs and balconies. For an internal garden these joints may also be used, simplifying ventila-tion. Because the glass panels are thin, and some air will flow through the joint, some rainwater

will enter the joints. This can cause staining of the glass from the dust, which is collected in the horizontal joints. A solution is an overlapping horizontal joint, protecting the horizontal surface from the rain.− Mastic joints, with a width of 15 – 20 mm, are an efficient solution. The risk of insufficient ad-hesion and limited life span of this material create no serious problem. Failure is directly visible and the glass is not sensitive to water. It being accessible from both sides makes inspection and repair easy. The colour is black, preventing entering sun radiation through to the material. Trans-parent materials have a very limited life span in exterior applications. With single glass, the joint is just 10 – 14 mm deep. To prevent pushing the material through the joint and to create enough sideway force for adhesion, a backing is needed. To prevent adhesion of the mastic to this back-ing, PVC strips are used. PVC is completely unaffected and leaves a very smooth surface. When double glass units are used, a foam backing rod in the centre is used. In fact, two joints are cre-ated then. To avoid absorption of water penetrated through the outer joint, a closed cell material must be used. A more open backing profile with local drainage openings is also a good solution. For roofs, a horizontal mastic joint will not trap the water, because it is flush with the surface.− If the glass panels are supported in linearly along the perimeter by a glued connection, this is generally done to an intermediate aluminium profile. Then an overlapping airtight joint is formed by rubber profiles between the support structure and this profile. On the outside, a rain proof joint is formed by a mastic material or an elastic profile pushed between the edges off the glass.− Rubber gaskets, clamping over the edges of the glass panels, are a simple solution for single glass façades. At the crossing of two joints the rubber material must be glued together and this is not reliable on site. The profiles should be assembled as a net in a factory. This, however, makes strict dimensional tolerances necessary.− The most reliable joints are formed by an overlapping rain proof joint on the outside with a cover strip and an overlapping wind proof joint on the inside, using the support structure. This solution divides the glass area into many small rectangular panels, separated by clearly visible lines. These lines can be made less obtrusive by choosing a flat profile with soft edges, reducing the additional black shadow lines. The depth of the profile cannot be taken too thin, because otherwise the cover strip will show wavy deformation between the bolts. It is also possible to use omega shaped cover strips, sunken between the glass edges. The narrow cylinder head bolts can be covered by an additional aesthetic strip.

− The secondary bending moments in the lower panels, due to the weight of the panels above, is a disadvantage. This also increases the curvature, creating a distortion of the reflected images.− Stacking up the panels seems much easier than hanging. However, panels of hardened glass are generally slightly curved, due to the prestressing. Also the outward dimensions show varia-tions. These tolerances at the supporting points lead to more sophisticated connectors. The connectors must be able to adjust for height.4.5.4. Safety of glass panels hanging from each other:Considering this solution, it is necessary to look at the consequence of the destruction of one panel.To get a safe construction, an alternative route for the forces must be available in order to pre-vent progressive collapse of a larger part of the façade.Since the glass panels are generally connected with mastic joints, these elastic joints can trans-port the forces over the façade area. The panels nearby must suddenly take additional load because the panels themselves are very rigid in their plane.To prevent a shock, some flexibility is needed in the fixing points. However, this flexibility is not wanted during normal use.A solution may be found in a fixing element that is stiff up to a normal load, but flexible at a higher load. The principle is represented in fig. 4.5.4.1.By putting pre-stress in the flexible spring, it is pressed against the fixed support. As long as the external load is smaller than the pre-stress, the central bolt stays in its position. The external force is taken by a reduction of the contact pressure between bolt and support.As the external force increases above the pre-stress, the bolt is loosened from the support. Then the stiffness is equal to the stiffness of the spring. The behaviour of the connector can be de-signed to need.

(fig. 4.5.1.2.).

− With an even more increased column distance, a high truss above the façade may be used. If the distance to the building is limited, this truss can be eliminated and replaced by outriggers from the roof of the building (fig. 4.5.1.3.).

routes. Here also many laborious ways are used to avoid too many compression members in de plane of the façade. The weight of the façade can even be distributed backwards to the roof of the build-ing.− The simplest way is taking the weight directly from the glass panel to vertical columns. Their distance is the maximum size of a glass panel, so 2 – 3.5 m1 (fig. 4.4.2.3.).− By adding horizontal beams that can also resist the gravity load, the column distance is increased. However, these beams must also resist the wind loads, meaning the size of their cross section must be large in two directions. This reduces the transparency, intended by a larger column distance.− The height of the horizontal beams can be reduced by support-ing them on two positions. This is done by tension bars with a small diameter that distribute the weight upwards. On top of the façade the weight is guided sideways via diagonals in the façade to the columns (fig. 4.5.1.1.). − These hanging bars can also be used without a horizontal beam if the wind load is distributed backward via compression bars

− A step further is avoiding the vertical tension bars. The glass panels themselves can resist the tension load, meaning the top panel carries the weight of all panels below (fig. 4.4.3.4.). − If the façade has a modest height, it is possible to put the glass panels on top of each other, bringing the weight directly to the foundation. By the weight, a fact that the panels are not completely flat. A small deformation is very visible due to reflecting images. At deflection from wind load, also second-ary bending moments will occur. However, danger of collapse through buckling will only appear in very high façades. This way of taking the weight of the façade is of use if at the top structural elements are to be avoided. It can also be attractive if the roof of the atrium will show large vertical displacements.The methods mentioned here have different degrees of trans-parency and technical complexity. For the choice, important factors are the form of the building and atrium and acceptabil-ity of complications in design and erection. Some additional aspects are:4.5.2. Hanging glass panels:

− If the panels are hung from vertical cables it is possible to prestress the cables, to a value comparable with to the stress in the finished façade. This makes it possible to reduce defor-mations during erection, because the forces of the weight re-place the external prestressing force. This makes positioning

Fig: 4.4.4.1Printer Building

Financial Times, London

Fig. 4.5.1.1. Thin tension bars, supporting the transoms. Forces are led sideways to columns.

Fig. 4.5.1.2 Gravity load directly led to the tension bars.Wind load resisted by compression bars.

of the panels easier.− The replacement of a broken glass panel in a system with ca-bles is much easier than with panels, hung from each other.− Proof of safety is simpler with a vertical cable system, because established standards are available.− In a hanging façade the movement from mechanical load or thermal effects must be accepted by a flexible joint at the bot-tom of the façade. With a high façade these movements may be substantial, for the cables have a small thermal mass, meaning rapid increase of temperature under sun radiation. A flexible joint below is more vulnerable to water and mechanical attack and it is more directly visible than a joint at the top of the façade. Therefore this joint is generally hidden below floor level. A hid-den gutter below street level on the outside can drain away rain-water. If the glass panels are hung from each other, their connec-tion elements must be freely rotating in the centre of the glass panels (fig. 4.5.2.1.).

Otherwise large additional bending moment will be caused by the eccentric tension forces. With panels hung separately to the structure, the eccentric tension is much smaller, making more simple connectors acceptable.

4.5.3. Standing glass panels

− The edge of the floor has a foundation beam, which is strong and stiff enough to support the façade. This support requires no extra cost, in strong contrast with the support of a hanging façade. A truss for such a system must be very stiff, to restrict deformation of the joints in the façade.− The risk of destruction of a glass panel at street level is much larger than for glass panels at the top of the façade.

Fig. 4.5.1.3. Tension bars for the gravity load hung from an

outrigger at the top.

Fig.4.5.2.1. Free rotating fixing point at the centre of the glass panel.

Fig. 4.5.4.1 Fixing with a pre-stressed spring.

Fig. 4.5.4.2. Gravity anchor of the atrium in the Parc de la Vilette, Paris

Fig. 4.5.4.3. Interior structure

15

− These hanging bars can also be used without a horizontal beam if the wind load is distributed backward via compression bars (fig. 4.5.1.2.).− With an even more increased column distance, a high truss above the façade may be used. If the distance to the building is limited, this truss can be eliminated and replaced by outriggers from the roof of the building (fig. 4.5.1.3.).− A step further is avoiding the vertical tension bars. The glass panels themselves can resist the tension load, meaning the top panel carries the weight of all panels below (fig. 4.4.3.4.). − If the façade has a modest height, it is possible to put the glass panels on top of each other, bringing the weight directly to the foundation. By the weight, a fact that the panels are not completely flat. A small deformation is very visible due to reflecting images. At deflection from wind load, also secondary bending moments will occur. However, danger of collapse through buckling will only.

4.7. Sloped glass areas

Sloping glass areas are only different from façades in having bending moments and deflection due to the gravity load and needing more elaborate detailing for draining the joints.

4.7.1. Gravity load and vertical live load

Depending on the angle, the downward wind loads may be as large as the wind load on the façade. Added to this is the permanent gravity load. This makes the supporting structure more massive. It will also become asymmetric because the upward wind forces are smaller than the combined downward forces.A cable supported beam can be used where the cable only functions for the downward force. The same is possible for a truss with rigid connections, where slender diagonals are only effec-tive for downward forces.In fig. 4.8.1.1 a structure is shown with only cables as diagonals. The system works in two direc-tions and external pre-tensioning the system is applied. In one direction the downward forces are resisted and in the other direction the upward forces.Special is here that the glass panels are put directly onto the support structure. Practical con-siderations, however, like making different suppliers commonly responsible for the detailing, often prevent such a combined solution. Generally, a load bearing structure does not have the tight dimensional tolerances, and an extra grid for the glass is added. This reduces the open view. Glass panels must be thicker in horizontal orientation, especially with laminated glass. The plastic connection between the glass layers cannot resist the permanent sliding forces and the layers will deform without combined resistance. The bending stiffness is just the sum of the

Fig. 4.6.1.1 Roof structure without compression members

separate stiffnesses of the two layers.The reason is that the connecting layers in laminated glass are developed for safety in cars and security in buildings. Here the aim is absorption of mechanical energy, making a plastic behaviour a desired quality.A frequently used combination in double glazed units is a laminated pane on the inside for safety after breakage and a heat strengthened pane on the outside for strength and stiffness.Wire reinforced glass can also be used for safety. However, the strength is less than that of normal glass, due to the irregular internal stresses. After overloading and breakage the glass keeps its deflected form. The wire will be forced to a large elongation, overstressing and yield at the cracks in the glass, since the adhesion of steel to glass is very strong.N.B. This differs from the behaviour of steel bars in con-crete.In concrete, the coupling between the steel and the con-

crete is less strong. Around the crack the steel is loosened and the stretching caused by the crack is divided over a greater length. This makes elastic deformations possible.In double glass units, wired glass may be used as an inner glass panel. However, this creates the risk of thermal breakage. The inner panel absorbs more heat from the sun and the additional thermal load from the interior enhances the difference.Glass roofs are susceptible to falling objects and equipment. The glass panels must be able to withstand these events up to a certain degree. In formulating the resistance it may be taken into

account that the roof is obviously vulnerable and precautions will be taken. For normal mainte-nance, like cleaning, movable bridges must be included in the design. The safety of personnel is regulated in compulsory standards.4.7.2. Waterproofing and condensationFor an angled or even horizontal area, where the gravity load is constantly trying to push the water inwards, a separate water and airtightness is an absolute necessity.In a vertical joint the water, penetrating through the rain proofing, will flow downwards in a hol-low section of the cross section. Because there is almost no air flow through the joint, the water will not be driven to potential leaks in the airtight joint. Several centimetres is enough distance between the airtight joint and the rainproof joint.If the glass area is tilted backwards, the water behind the rain proofing will always flow to the inside on its way down. To prevent this water from causing a leak to the interior, a small gutter must be incorporated in the cross section, to catch the water before it reaches the airtight joint.In the horizontal sections this hidden gutter must be able to drain to a gutter in the angled sec-tions (fig. 4.7.2.1.). Finally, the water must be drained outside.This solution with the hidden gutter and the protected airtight joint was already known in the earlier years of the 20 century. In fig. 4.7.2.2 an example is shown of a wooden support, covered with zinc plate covers.

Only on the horizontal sections this condensation gutter is needed. On angled support bars, condensation will flow downwards and will not form large enough drops.In fig. 4.7.2.1 this gutter is visible. It is put on both sides of the horizontal profile for practical reasons.Also the use of condensation gutter was an issue in earlier examples. Especially with single glass panels, much condensation is formed. In fig. 4.7.2.3 an old example within a massive steel sec-tion is shown. 5. Choice of a façade system

In the following article, two façade systems are compared. The systems differ in their structure, although the buildings have the same function, the same dimensions and a similar appearance. The architect and the client were the same and the buildings were constructed only several years after one another.

On angled surfaces, horizontal glazing bars are a barrier to water flowing downwards. The trapped water has ample time to penetrate the waterproof joint, especially at crossings with the other joints. The water left on the surface will evaporate and leave dust and staining on the glass surface.To prevent this as much as possible, for horizontal glazing bars, generally massive and thin bars are used.Another possibility is the use of mastic joints, flush with the surface, for the horizontal joints. The durability may be limited, but this is acceptable since failure causes no secondary damage.A good solution is the use of overlapping joints. These are frequently used for greenhouses.A glass roof has a small thermal mass and heat radiation to the sky at night will quickly cool a glass roof. A roof can even have a temperature far below the outside air temperature.If a lot of people are present below the roof, for example during a reception, moist air will cause condensation on the inside of the roof.By gravity this water will flow downwards and will be stopped at the horizontal supports of the glass roof. If this water concentrates at the lowest part of the cross section, the droplets formed will fall on the people below.To prevent this, a small gutter on the inside can catch the water and hold it for a period of time. The volume of water is quite small, so a narrow gutter is sufficient. The water will evaporate after a while, so no drainage is necessary.

Fig. 4.7.2.1 Hidden gutter in a glass roof. Horizontal cover strips not shown.

Fig. 4.7.2.2 Wooden glass support with zinc cover and a hidden gutter.

Fig. 4.6.2.3 Steel glass support with condensation channel.

Differences were the local experience and the location (New York and London), and the col-umn distance and the stiffness requirements.The building in New York has 9 meter wide spandrel elements as an interior leaf. The ele-ment is covered with natural stone. The gravity load is transported sideways to the columns. The deformation of the floor does not influence the façade.The spandrel element is fabricated with a steel support structure and steel panels. This type of

element is used in the Netherlands with a concrete structure.The building in London is closed with storey high, integrated curtain wall elements, about 1 m1 wide. The elements are hung from the floor. The column distance is about 3 m1.The façade columns and the façade beams take care of the horizontal stiffness of the building (tube structure). Because of the high façade beams the deflection of the floor is negligible.

6. Maintenance facilities for facades

Facades must be cleaned on a regular basis. For windows generally twice a year andfor aluminium parts 1- 3 times a year. This depends on the air pollution, orientationand the form of the profiles. Parts like adjustable sunscreens and soundproofventilation units have a limited life span due toe their movable parts and engines.In The Netherlands the window cleaners are entitled to normal safe workingconditions, meaning for example a balcony without parapet and only a safety harnessis not allowed anymore.Facades between cantilevered façade sections require a special hanging scaffold or amovable lifting platform (fig. 6.1.)In fig. 6.2 a façade is shown where a permanent hanging platform is chosen to provideaccess to the façade between the fixed lamellas for the sun shading.

Fig. 6.1 Hanging scaffold with balancing weights for recessed windows.

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As a consequence of the strict regulations, the facilities for the cleaning of facades have an im-portant impact on the appearance and detailing of the façade. They are not a small addition to be given attention in a late design stage.In 1995 a standard was published, giving the minimal level for safe working conditions.Only existing buildings are allowed to use a lower level on a temporary basis. In fig. 6.3 the guarded access to a hanging ladder is shown. A scaffold may also be hung from a movable verti-

by external forces to a value resulting in local breakage. By this the internal equilibrium is disturbed, resulting in a complete fracturing of the panel. The glass shatters in small par-ticles instead of larger more dangerous parts. This quality is used for safety glass, for exam-ple in side windows for motorcars.

The assumed strength of glass is in fact a mea-sure for the surface quality. Because the cracks grow with aging of the glass, the strength will also reduce over the years. In several tens of years the strength is reduced to 10 – 20 %. Old glass is therefore hardly removable and reus-able. Cutting this glass to a new dimension is not possible.

forcement. Only in the final stage, after a large deformation, the concrete will crumble.Wood has a low stiffness. This means that a large deformation will be visible before collapse.Glass, on the other hand, is a stiff and brittle material that breaks suddenly without warning. The strength of a glass object is determined by the quality of the surface.This surface will always show small cracks, caused by shrinking during cooling in the manufac-turing process. A local area with larger cracks in combination with a high local load will lead to breakage. This loss of load bearing capacity will create an increasing load in the rest of the glass, especially at the end of the crack. This causes a fast extension of the cracks and a consequent destruction of the glass object. Even a small local overloading, for example at a local inflexible support or a forced assembly, will cause the destruction of the complete structure.The research on the load bearing capacity of glass is not based on existing modelling for normal structures. There are two reasons for this:− The standards are based on the used materials with a high capacity for plastic deformation.− The standards are aimed primarily to the ultimate state of collapse.The modeling of structures with a large capacity for deformation is relatively easy, because in the ultimate state, by yielding the most efficient redistribution of the forces is reached. The prog-ress of the preceding deformation is of less concern.For load bearing structures of buildings the main consideration is generally safety from collapse. This originates from governmental requirements. The government, however, is only interested in the specific aspects of buildings, like safety, health and environmental effects, including en-ergy consumption. The deformation of the structures is of no concern to the government. Con-sequently it got less attention.Too large deformation leads to damage of the building and a lesser comfort. If a building fails in this respect, the owner may try to get compensation of the builders. This is handled by civil law. For glass, this approach of the ultimate state is not possible. In several stages of the non linear deformation, local breakage may appear. This local breakage may stop, but mostly it will prog-ress to a complete failure.

7.3 Strength of glass

The strength of the material itself is not a usable concept for glass. A larger object will shrink more during the production process and as a result more and larger cracks will appear on the surface. These cracks will cause peak stresses at the point where they stop. Deeper cracks will cause higher stress concentrations. As a result, small glass objects, like glass wires, are relatively much stronger than large objects like glass panels.Translated to a fictitious “material strength” this means that glass in fibres has strength of 10000 N/mm2 and glass in normal window panels about 50 N/mm2 (without safety factors).Instead of “material strength of glass” it is better to use the notion of “resistance to tension forces in the surface area”.The acceptable risk of local stress over the “material strength” is also related to the bsize of the object. Breakage of several glass fibres in an object of glass fibre reinforced polyester will not create a problem. Local overstressing in a window pane will destroy the whole panel and a larger panel will create a more dangerous situation.In standards, to evaluate the safety of glass panels in a way familiar to building engineers, these dimensional influences are translated into a fictitious material strength.Acceptable stresses, as given in a standard, therefore are only usable withinthe context of that standard.In prestressed glass panels, normal glass is treated in such a way that compression forces appear on the surfaces and tension forces in the interior. Generally this is done by extra cooling of the surface during solidification. The surface is hardened before the core has completely shrunk. The surface will not completely follow the shrinking and develops a resisting compression force. The core will stay under tension, which is not harmful, because there are no cracks. The result is a more or less parabolic curve forthe stresses in the cross section, with a maximum compression of about 100 – 200 N/mm2 (fig. 7.3.1 top picture). The prestressing may be done in different ways and the curve of the prestress-ing can be manipulated for the desired effect.In fact compression forces, additional to the loads in service, are put onto the surface.During bending, compression and tension forces will be added, resulting in an asymmetric stress curve. The bending tension stress, from external loads, is reduced by the original compression force to about 25 N/mm2.In fact the material does not change by prestressing, only the loads on the material.For convenience’s sake however, it is assumed in simple calculations that the strength of the prestressed material has increased. The existing tension forces in the interior may be increased

Fig. 6.3. Hanging ladder with a guarded access.

Fig. 6.4. Fixed hanging platform.

cal guiding rail (fig. 6.4.). Bosun chairs are mentioned in the standard, but they are only allowed for existing buildings if no other options are available.

7. Designing of the thickness of glass panels

7.1 Introduction

For small sized window panes there is no need to calculate the minimum thickness for wind loads or deflection. Practical considerations lead to 3 to 4 mm. Only in historic periods of short-age sometimes 2 mm was used.The current standards in The Netherlands (NEN 2608 and NPR 3599) originate from 1991. These are aimed at use for normal glass areas. They are based on simple calculation models. Due to this, they don’t use the strength of the glass to the full and the margins for safety are not constant.Based on these standards a window breaking from wind loads never happens. Windows break as a result of impact or from poorly locked casement window.From the architectural discipline, after 1975, the demand came for large glass panes with mini-mum support structure. Also glass façades were in demand without visible handrails for safety.If these structures were to be designed with the available standards, very thick glass panes would be necessary.Thick glass, above the common 4-6 mm, however, is disproportionately expensive. In fig. (7.1.1.) a trend is presented for float glass and heat strengthened glass for orders over 200 m2. For large glass areas generally heat strengthened or laminated glass is used. This Increases the cost even more. These circumstances generated a demand for more sophisticated mechanical modeling.Research in recent years has led to proposals for CEN standards, containing more precise meth-ods for designing glass areas. In Germany “Technische Regeln” have been established including these developments.

7.2 Glass as a structural material

Glass is not a logical choice for distributing forces, compared with steel, concrete or wood. Steel breaks after a long elongation, possible by the high yield. During this elongation it keeps its strength and allows other parts of the material or structure to contribute in the resisting of the forces. In this way, a redistribution of the forces is possible when local overloading occurs.Concrete structures are designed in such a way that they deform by yielding of the steel rein-

Fig. 7.3.1 Stresses from exterior loads added to internal stresses

7.4. Deformation of glass panels

Glass, although fracturing in a brittle fashion, is a strong and stiff material. Therefore a thin panel may be used for a large span. In normal situations the accepted deformation depends on main-taining a safe feeling to the occupants of the building. Also structural considerations may limit the deflection, like overloading the edge connections of double glazed unit or preventing un-desired clamping of the edges.

For glass panels over 1 m2 the deflection under maximum load is more than the thickness of the panel. The linear plate theory then is no longer valid. That theory is valid for deflections up to about half the thickness.

With these large defections the panel starts to act as a membrane. In a membrane, loads per-pendicular to the surface are resisted just by tension forces, guided to the edges. In a glass panel this happens if inside the panel a compression ring can develop, resisting radial tension forces from the centre (fig. 7.4.1.). In a square panel this effect is the strongest. As an illustration, in the annex of this chapter, an example is given to show the effectiveness of the “cable action” in relation to pure bending. Pure cable action may take morethan ten times the load of the bending action with the same maximum tension stress.

For a very long glass panel, this membrane action cannot develop. In the centre ection just bending is effective and just in one direction because in the other direction the span is much larger and can not contribute. This is a very unfavourable situation requiring a large thickness of panel for a small span. In fact the required thickness of the glass is determined by the smallest span if the ratio length/width is over 3.

Between 1 and 2 the major influence on the thickness is the total surface area. In fig. 7.4.2 an example is given of a graph to determine the relation between length, width and usable glass thickness. A square panel with the same thickness may have a dimension of 2100*2100 mm2 ! In the graph it is shown with a dotted line that for other relations of length and width even more capacity is available. This extra capacity is neglected for the sake of simplicity.

7.5. Double glazing

7.5.1. Distribution of external load

In a double glass unit the glass panels are only connected at the edges. The enclosedvolume of air will not be compressed easily and therefore the two panels will show thesame deflection. The external load will be dis-tributed evenly with the stiffness of thepanels. The bending stiffness is proportional

Fig. 7.4.1 Membrane action in a panel with large deflection. Deformation is exaggerated for clearness.

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Fig. 7.4.2 Allowed dimensions for several thicknesses. From: R. Hess 1986

develop more membrane action. More external load can be resisted.In fig. 7.5.1.1 a table is shown, originating from the Dutch standard (NPR). Here it isalso apparent that a panel of 5+5 always may get a larger surface than a panel of6+4.

7.5.2. Air pressure in the cavity

TThe cavity between the glass panes is closed airtight in the production stage. Therefore the internal pressure will only change with a deflection of the glass panes, reducing or expanding the volume.The variation of atmospheric pressure in The Netherlands goes from about 970 to 1040 hPa (millibar). If a unit is produced (in the autumn) with a low pressure, then in summer with a high pressure the glass unit will be compressed. In this example, the external load on a closed double glazed unit in summer in a not deformed state, would be 70 hPa =7000 N/m2 .The glass panes are not stiff and strong enough to resist this external load and must accept a forced displacement. If the distance between the glass panes is 14 mm, then the cavity must be compressed with an average of 1 mm. Because the edges are fixed in the middle, (centre?) a larger deflection is re-quired. Depending on the ratio between length and width this extra factor is 1.5 to 2. Both glass panes must then deflect inwardly about 1 mm.This deflection is equal for small and large glass unit.This means that with a small span the bending will be stronger. This results in high bending stresses.The conclusion is that glass panels with a deep cavity, especially those with a short span, are very sensitive to overloading caused by a change in atmospheric pressure.The same effect arises when a glass unit is produced at a low altitude and is transported to a high elevation. A rise of 500 m equals a reduction of the atmospheric pressure of 500*12 =6000 N/m2.These effects may also appear in combination (fig. 7.5.2.1.).The forced deflection by different air pressure, altitude and temperature also has an influence on the distribution of wind loads over the two glass panes. The pane with a curvature towards the wind load will first be flattened and only thereafter accepts some of the load. The other pane will distribute a larger part of the wind load. This means that the loads from each cause must be added for each pane.In small panes, the stresses by different air pressures are high, but the stresses caused by wind are relatively low.In tests it appeared that of double glazed units, the glass pane directed away from the load, usually was the first to break. An explanation could be that the quality of the surface of the glass in the cavity was better than that of the surface influenced by the outside air. Favourable in the cavity are the dryness of the air and sometimes a filling with gas.

7.6. Laminated glass

Laminated glass consists of two or more layers of glass, glued together wit a plastic foil. The purpose of the foil may be the prevention of large glass splinters (safety), the resistance to con-centrated loads (bullet proof) or to provide a certain rest capacity in the event of breakage.For the automotive industry and protection the first are developed. For buildings where glass is

used for light openings in roofs, for balusters and floors the behaviour after breakage is important. The choice of the foil is guided by this.For resistance to a fast concentrated load (security, fly-ing object from a hurricane) the panel must be able tot absorb much energy and therefore show large displace-ments. If the glass breaks in numerous particles, energy is used at all the cracks. The foil must be strong and show a plastic behaviour.For prevention of loose glass particles and a reserve load capacity, a large distance between the cracks is an ad-vantage. The cracks in the two panes will have a different position, so due to the coupling by the foil, a damaged,

the third power of the thickness. Acombination of 5+5 mm is more flexible than a combination of 6+4 mm. The symmetrical com-bination, however, is stronger because with the same deflectionthe bending stress is less. The maximum bending stress in a combination of 5+5 mm isthen 0.94 times smaller (by the lesser stiffness but the smaller thickness) than thestresses in a combination of 6+4 mm. With the same bending stress a symmetrical panel may deflect more and in this way

but still relatively stiff panel will remain. For horizontal load bearing panels a restriction of creep and insensitivity to high temperatures is also favourable.Under impact load, the panes act together for a short period of time, but in case of permanent load creep will prevent this.Under permanent load, the stiffness of the glass panes may be added. In the thin panes the membrane action will develop earlier than in a thick panel, where the panes are tightly con-nected. Therefore a package of loose panes may be as strong as a rigid panel of the same total thickness. The stiffness, however, is much less.

7.7. Resistance to fire

In buildings it is essential to limit the spread of fire, in order to maintain short escape routes. These fire compartments are separated by structures resisting fire starting from 60 min and more.A floor structure usually remains intact for at least 2 hours, but in the façade and at staircases fire may go from one storey to the next.Glass surfaces, sometimes storey high, may be desired in those positions, for openness in the architecture. In case of fire the glass is heated, but equally over the whole surface and thickness. After about one minute the difference may be over 40 oC and normal glass will break due to internal stresses. Heat strengthened glass may allow higher temperature differences, up to 300 oC. Then break-age occurs after 20 minutes.By applying reinforcement with a steel wire net, the effect of breakage is reduced. After break-age of the glass, the pieces are kept together. At a higher temperature the glass will become plastic. At 500 oC it will be weakened so much, that it will be able to flow. For a panel smaller than 0.9 m2 a separation of 60 minutes is possible. For a larger glass panel of 1.7 m2 ,the tensile stresses in the plastic phase are higher, so the time lapse is restricted to 30 minutes.Another method is hardening the glass in combination with a heat reflecting coating. This coat-ing reduces the amount of absorbed energy. This reflecting layer must face the fire, so the pro-tection only works in one direction. Larger areas are possible than with wire reinforcement.For increased fire resistance, laminated glass may be glued with a foil which expands at a high temperature, forming a thermal insulating layer. In this way the glass pane on the cold side is heated more slowly. Various combinations are possible.With very strict requirements, two laminated glass panels may be put at a distance from each other, each in their own frame. An example is the façade of the Bibliothèque Nationale in Paris (fig.3.2.5.2 in the chapter Curtain walls).For all fire separations with glass, the fixing of the glass in its frame and the frame itself are im-portant. The joints between glass and frame must remain closed even with deformation of the frame. To achieve this, tapes are used that expand at high temperatures.The fixing with cover strips should also remain intact during a deformation and keep the panel in position, even when the glass is weakened and becomes slightly plastic. The panel must not fall out of the frame.Wood and steel are used for the frames because they keep their strength up to a high tempera-ture. Aluminium is not fit for a fire separation.

Annex

In this example a glass panel has a span of 1200 mm and a deflection of 12mm. A comparison is made of the load needed for this displacement.The first assumption is resistance by bending stiffness. In a second assumption the bending stiff-ness is zero, but the panel is rigidly fixed at the supports. The load is resisted by tensile stresses.The calculation is based on a width of 1 mm and a thickness of 6 mm.This is much more than when only bending stiffness is available.For a glass plate, the membrane action goes along with contraction of the edges to the centre. The tensile action is therefore less than with completely rigid support. However, it may be clear that a considerable contribution is possible if large deflections occur.

Structural silicone glazing

The application of glue to fix exterior panels was introduced in glass facades. The purpose was to create a smooth surface without interruption from glazing bars. Only a narrow (15-20 mm) joint of mastic separated the glass panels.Later this technique was also used for other materials like thin composite panels and natural. Fig. 7.5.1.1 Glass areas allowed by NPR 3599

Fig. 7.5.2.1 Influence of air pressure and temperature on the loads on double glass units.

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Key factor of this approach is the belief that even coincidental predictions can enable focused and resilient developments. The group uses the heuristic method with the following working levels: engagement, immersion, incubation, explication and creative synthesis (15). Workshop participants come from different target groups – students, architects, engineers, climate design-ers as well as façade planners. Depending on the situation they provide either quick innovative ideas or conduct multi-day seminars to generate topic oriented or completely free develop-ments. The working method of choice is brainstorming which, with the parameters “collect as many ideas as possible, all ideas are welcome, no discussion, do not criticize, documentation of all ideas, set time limit” has proven to be successful and versatile (16). However, this free brain-storming phase is followed by an evaluation of the individual solutions presented as well as technical and esthetic post processing to organize the ideas systematically and prepare them for documentation in digital and printed form.

In the course of investigating the parameters influencing the planning and building processes, the following top-ics were identified as technical corner points of an area of tension that encompasses the new developments and conception of facades in addition to esthetic trends: en-ergy, efficiency and individuality. Energy as the motor for all actions, paired with the actuality of the energy market and the climate change. Efficiency in the sense of perfor-mance expected from the facade as a technically sophis-ticated building component. Individuality as part of the architecture that reflects the particular urban, spatial and

In parallel with the above described development, a trend toward further research and development of new materi-als can be observed. The research mainly focuses on mate-rials for the building envelope, with the goal to create for-mative innovation by material innovation. This, of course, again creates a multiplicity that becomes part of the over-all concept. On the downside trends are being set by using terms such as ‘smart’ or ‘nano’; in many cases abusing the potential by merely using these terms for branding pur-poses (9/10/11). 2 Today’s drive

Figure 10 – Future façade principles – Category Materials (17)Figure 11 – Future façade principles – Category Adaptables (17)

Figure 3 – Façade Posttower Bonn

Figure 4 – Façade Capricon Bonn

Figure 8 – Facade Research Group of the Faculty of

Architecture / Delft University of Technology

esthetic form of the building (12/13).It quickly becomes apparent that the above mentioned parameters require a high degree of technical competence with regard to development, planning and realization of facades; espe-cially the integration of functions poses a difficult problem, since these functions might contra-dict or even exclude each other. Thus, expenditures for further development become increas-ingly complex, which in turn poses the question of the relationship between expenditure and benefit.We can summarize citing Michiel Cohen (CEPEZED), remarking in closing his lecture at the first “The Future Envelope” conference in 2007 in Delft: “The future has to be simpler” (12).

Future facade principles

Against the background of the above described situation, the Facade Research Group was formed at the Delft University of Technology in 2005. This group is currently engaged in various topics related to facade technology: problem solving oriented research with the goal to provide solutions to short-term problems – e. g. issues with facade refurbishment or the manufacturing process of free-form facades – as well as to develop working methods and tools to standardize planning procedures and technology transfer. For these research areas the group employs tradi-tional scientific methods by establishing statistical data, evaluating constructional and technical solutions, developing new technologies for specific issues as well as developing planning tools and methods (12).

point for new designs. Here for, the group uses conventional tools for new developments to en-sure that the development process is controllable as well as traceable, even if the results can not be predicted. The group follows the train of thought of De Jong – to travel from “technological research” to “design research” to “study by design” without necessarily following straight-lined developmental steps (14).

Figure 8.1 – Future façade principles – Category Concept (17)Figure 8.2 – Future façade principles – Category Concept (17)

ment in order to faster identify future developments and their potential and risks. Thus, in ad-dition to gaining knowledge about individual technological options, we learn to quickly assess and evaluate them. The analysis does not only consider purely technical parameters (construc-tion and energy) as deciding factors for whether or not a certain technology is worth pursuing but also social and economic criteria.An example: The reason why building services integrated facades, one of the above mentioned topics, have been hard to realize is not only due to their technical complexity – but rather the dif-ficulties of the economic process: areas of responsibility and issues with the concrete realization of the product are difficult to define and solve (12).But this example also shows how different the reflections of the possibilities can be, for example for the executing companies: system suppliers are more interested in all-in-one solutions that do not facilitate an exchange of components whereas manufacturers of customized solutions want to streamline the engineering process. Interestingly enough both processes have one thing in common: motivation for innovation originates in the design – either from a special for-mative idea and/or a specific technical solution. Thus, the Posttower Bonn as well as the Capri-con project in Düsseldorf (18) as interconnected solutions were only made possible because the integration of building services components into the façade followed a clear formative as well as a technical approach.This leads us back to the starting point of the developments of technical ideas for the Future Facade Principles: developing possible scenarios to motivate the designers to strive for new for-mative and technical solutions. It is the reversal of the traditional planning principle, which was to solve the technical issues created by the design through targeted development of technical visions and depiction of the resulting design possibilities. It is obvious that with this method not only the best but also ideas of lesser quality are being pursued and realized, because factors other than the technical and formative parameters come into play. However, it is exciting to see which trends develop through the core of the formative, technical and economic possibilities, and sometimes being able to influence these trends through new developments.

The ideas are organized in different categories such as concepts (results, which are expected to be realizable in the future), systems (ideas related to principle construction and not specific technical solutions), deflateables (results based on vacuum stabilized construction), materials (constructions based on the use or development of material related solutions) and adaptables (principles using ideas from different disciplines or technologies). The interest of the Façade Re-search Group is to enhance the possibilities for everyone rather than keeping them hidden away, because if something is not used or applied it is not relevant. The results of the Future Façade Principles are a growing amount of ideas for facades or skin structures, principles or even meth-ods of thinking (17/18).

5 Conclusion

Building on existing knowledge and employing classic scientific research methods – problem outline, compilation of material and knowledge, evaluation and interpretation, structuring and lastly the development of subsequent steps – the group employs the idea of heuristic develop-

Figure 9.1 – Future façade principles – Category System (17)Figure 9.2 – Future façade principles – Category Deflateables (18)

References

(1) Knaack, Klein, Bilow, Auer: Principles of Construction – Facades; Birkhäuser – Basel, Boston, Berlin 2007(2) Kohlmaier, G; von Santory, B: Das Glashaus – ein Bautypus des 19. Jahrhunderts; München 1981(3) Thomas Herzog, et al, Facade Construction Manual; Basel/Boston/Berlin 2005(4) Knaack, 1998: Konstruktiver Glasbau: Müller Verlag Köln(5) Wurm, Glass Structures, Basel/Boston/Berlin 2007(6) Oesterle, Lieb, Lutz, Heusler; Doppelschalige Fassaden; 1999 München(7) Pottgiesser; Fassadenschichtungen – Glas; Berlin 2004(8) Compagno; Intelligente Glassfassaden / Intelligent Glass Facades; Basel/Boston/Berlin 1995/2002(9) Brownell; Transmaterial 2; New York 2008(10) van Uffelen; pure Plastic – new materials for today´s Architecture; Berlin 2008(11) Ritter; smart materials – in Architektur, Innenarchitektur und Design; Basel/Boston/Berlin 2007(12) Knaack, Klein: The Future Envelope – a multidisciplinary approach, Delft 2007(13) Knaack, Hasselbach: New Strategies for Systems, Delft 2006(14) De Jong, van der Voordt, 2002: Ways to research and study urban, architectural and technology design; DUP Delft(15) Kim Etherington: “Heuristic research as a vehicle for personal and professional development” Magazine Counselling and psychotherapy research, 2004 – vol 4, no2(16) Kleining, Gerhard, Witt, Harald: The Qualitative Heuristic Approach, Forum Qualitative Social Research, No1, Art 13(17) Knaack, Bilow, Klein, 2007: Imagine 01 – Future Facade Principles, 010 Rotterdam(18) Knaack, Bilow, Klein, 2007: Imagine 02 – Deflateables, 010 Rotterdam

4 The method - Imagine Series

Another focal point is the development of visions for the future development of facades. The goal is to generate potential development methods with the associated discussion and evalu-ation of technical possibilities identifying design, manufacturing and structure related options for the designer. The aim is not to solve concrete technical problems, but rather to change the traditional working method to a new approach that offers possibilities and options as a starting

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With these materials a saving in the panel thickness was possible.The reliability of a glued connection depends on the selected materials (mastic type, primers, coatings on glass etc.), the compatibility of these materials and the modelling of the mechanical behaviour.In the modelling the large deformations of the glue must be taken into account. Glass panels also show large deflections and these affect the distribution of the wind forces over the perim-eter. The next article presents an overview over the different aspects.“Exterior Wall Systems: Glass and Concrete Technology, Design and Construction”STP 1034B. DonaldsonASTM, Philadelphia, 1991

12. Deformation of load bearing structures

12.1. Introduction

Damage in a façade construction is often caused by a deformation of the structure that forces movements on the façade. An example is a floor, unintentionally resting on a façade mullion. The mullion is not capable of following this displacement and not able to resist the force.On the other hand, parts of the façade may show a displacement or an expansion, resisted by the load bearing structure. An example of a resisted movement is an exterior leaf of bricks trying to expand, by heating caused by radiation of the sun, while being too rigidly connected to the structure.The task of the load bearing structure is to support interior and exterior walls, floors and roofs including the loads acting upon them. These forces must be distributed to the foundation. Re-acting forces can only be generated by deformation of the structure. A part of this deformation is of interest for the façade.It is possible to design a façade in such a way that very large deformation can be accepted. Therefore the joints and fixings must have enough flexibility to limit the forces on the generally weak façades. With a larger movement, however, in an increasing degree elastic materials, slid-ing connections and wider joints must be used. The disadvantages for the façade are:− Complex structure (man hours, many parts and connections)− Expensive materials− Reduced durability (elastic materials, movement)− Sensitive to damage− Less attractive appearance (wide joints of variable widths)To avoid this, it is useful to restrict the deformation of the load bearing structure on certain positions. In an early design stage it is possible to incorporate these requirements without large additional costs.If these requirements are not disputed, the designer of the structure will use the large displace-ments allowed by the standards. In that way the costs of the load bearing structure are mini-mized without taking into account the possible savings at the other building elements.

12.2. Deformation in the plane of the façade

sate some part of the shortening of the distance, but this is negligible. An acceptable additional bending may be 10 mm. For a glass façade, differences in curves are clearly visible by the distorted reflection.In this example, the horizontal joint requires an extremely stiff floor. It may be better to consider a more flexible or sliding joint.The deformation of a beam at the edge of a floor is influenced in the following sequence by:− Distance between the columns (effect in the 4th order)

− Mechanical static scheme of the sup-ports (effect is factor 1….5)− Height and form of the beam (effect in the 2th to 3th order)− Amount and type of the material (lin-ear effect)In this example a wide column distance is combined with an all glass façade. The result is a high beam, reducing the

12.2.1. Introduction

For the façade rigid panels and elements are used. These are fabricated for example of glass, metals, concrete and all kinds of composite plate materials. Brickwork is also split up into parts rigid in their plane. These stiff, but not strong panels don’t accept a forced deformation.The joints between façade panels must absorb the movements of the building as a whole. Large panels go along with less total length of the joints. The same movement must be absorbed by less joint length, meaning more movement in the individual joint. If the façade design incorpo-rates large elements and narrow joints, these will require a relatively stiff load bearing structure.The position of the connections between façade panel and structure also influences the move-ment in the joints. Fixing an element on several points with a different deformation is unfavour-able. An example is a façade supported on one side at a column and on the other side at the middle of a floor span. This will cause tilting of the element.A prefabricated element is rigid in its plane. To control the forces to the gravity supports, and their reaction to the panel, only two gravity supports must be used. If three or more supports are used, the distribution of the forces depends on the flexibility of the supports. Then it is uncertain if the gravity is distributed by one, two or all the supports.The gravity may be distributed at the top of the element by a hanging connection or below or halfway by a support. The choice depends on the weight of the element and the ability of the façade to distribute tensile forces.Depending on the size of the panel two or more additional fixing points are used to distribute the wind loads.

12.2.2. Deflection of the floor

Heavy and large façade elements are best supported near or by the columns. In that way the stiffness of the floor does not influence a deformation of the façade (fig. 12.2.2.1.). This figure also shows the relation between a stiff element and a flexible floor; only the supports at the sides distribute the gravity load. In façades with smaller panels, hung on individual mullions fixed to the floor, a different situa-tion arises (fig. 12.2.2.2.). The deformation in the façade is largest at ¼ and ¾ of the span. The deformation comes from the rotation of the span. The small panels must be able to rotate or slide between mullions and transoms. It may be clear that a non continuous façade beam, with a hinged connection to the columns, will show the largest rotation near the column. Brickwork is stiff in its plane, but is needs a continuous support. With a flexible edge of the floor, vertical dilatations are needed in the brickwork to allow sections to slide along each other.An example of a façade, sensitive to deformation of the structure, requiring a stiff edge of the floor:− Glass panels from floor to ceiling, 1185 mm wide− Mastic joints (elastic compression and elastic sliding)− Joints 15 mm wide− Beams at the façade, with hinged joints to the column− Column distances 7.2 mThe façade is constructed when the finishing floor, interior partitions and installations are not in position yet.The 7.2 mm is related to these loads in combination with the service load. With a concrete beam, the creep of the material must also be taken into account.Floors in a building don’t have the same load. If two floors above each other show a different deflection, their distance may become smaller or bigger. A horizontal mastic joint will be com-pressed. This causes a compression force on the glass panels, causing buckling. Example: A mastic joint may be compressed up to 3 mm (20%). With an average deepness of 10

mm and elasticity E= 1 N/m2 a compres-sion of 20% causes a force of 2 N/mm1 . This forces an extra curvature in the pan-els. The panels must be rigid enough to create this reacting force at a limited bending.N.B. This extra bending will also compen-

Resisting loads by bending stresses

Fig. 12.2.2.1 Rigid facade element resting on a flexible floor

visibility to the outside and the level of natural light. Only from the outside the all glass appear-ance is maintained, but from the inside a sense of enclosure is enhanced.12.2.3. Deflection of a cantilevered floorFor a cantilevered floor a vertical displacement is combined with a large rotation at the end. If two cantilevered floors meet at a corner, the deformation will soon be noticeable.In a second skin façade, an all glass façade is hung on the outside of a balcony, in front of a nor-mal façade. To facilitate cleaning, the distance between the two façades is generally between 0.6 and 1 m. The balcony and the second façade are hung from cantilevers, connected to the floor edge.The glass panels in the second skin are 1.2 -1.5 m wide, so for this distance a support is needed along the façade. Some of these will be connected to the floor in between the columns. The displacement of the glass façade is a superposition of deflection and torsion of the edge of the floor and deflection of the console. To get a straight horizontal line in the glass façade, all vertical displacements should be equal.To avoid a large structural height on every floor for the console and the need to increase the rotational stiffness of the floor edge, often the second skin is hung from one large cantilever from the roof. At floor level only wind forces are resisted. 12.2.4. Horizontal deformation of the main structureThe horizontal wind forces are resisted by the stability elements, generally a core or walls of con-crete. These elements restrict the deformation. The bending of these stability elements causes floors to slide horizontally over a certain distance. This distance will be different for floors above each other.With a core or stability wall, the difference in horizontal displacement of the floors is at its maxi-mum at the top.At a horizontal displacement of 0.002*height, the rotation angle at the top is about 0.0027 radial. With a storey height of 3 m, this means a difference in horizontal displacement of 8 mm. The horizontal joint between large, storey high façade elements, like in fig. 12.2.4.1, must then be able to accommodate a sliding of 8 mm.If the horizontal forces are resisted by a framework instead of a core, the maximum difference in horizontal displacement is found in the lowest storey. If these large façade elements are sup-ported by the columns, the deflection of the edge of the floor has no influence on the joints between the façade elements. Only the joint between the façade and the floor will be affected because the floor slides vertically behind the façade. This joint must be closed in a flexible way, to resist fire and sound.Wide parapet elements, with window strips in between, are generally hung on the columns. These are also unaffected by the deflection of the floor (fig. 12.2.4.2.).The sliding movement between the floors now must be absorbed by the joint between the top of the window and the bottom of the parapet element.If this connection is rigid, the mullions of the window strip will be rotated (fig. 12.2.4.3). This rotation is quite large. With a difference in horizontal displacement of 8 mm and a height of the windows of 1600 mm, the rotation is +/- 0.005 rad.If the window elements are narrow and rigid, they will be angled as a whole. At the vertical joint

Fig. 12.2.2.2. Flexible façade follow the deflection of the floor

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between them, they will slide vertically along each other.With windows constructed of separate mullions and sills, the frames will become rhomboidal. The glass panels will slide and rotate inside the frames.Beside sideway displacement, the building may also show torsion along a vertical axis. With a rotation, also horizontal displacements and a rhomboidal deformation in the façade appear.

12.3. Deformation perpendicular to the façade

Small deformations perpendicular to the façade are clearly visible. If a panel is tilting backwards, it receives light from a greater, and lighter, part of the sky. The average angle of incidence is also better. If the backwards angle of the panel is 0.01 radial, it receives about 0.8 % more light in case of an overcast sky. A difference in light of 1 % is noticeable for some persons and at 1.5 % this goes for most people.In fig 12.3.1 the rotation of a beam along the façade is shown. This façade beam is supporting a secondary beam. The façade beam has limited torsion stiffness. Halfway the span of the façade, the beam will just follow the rotation of the end of the secondary beam. The lower flange of the façade beam

will then move outwards 700*0.013=9 mm in rela-tion to the upper flange. A façade panel fixed to the lower flange will tilt and receives a different amount of light.Closer to the column the façade beam will not ro-tate. Here the façade will not show a distortion. The result is a façade with visible horizontal and vertical

Fig. 12.2.4.1. Storey high facade elements, supported by consoles on the columns.

differences in illumination. This will ruin the intended image of a well made flat façade.With direct sunlight, much smaller deviations of flatness will become visible. If the light is sweep-ing along the façade, even the smallest deviations are visible, although this happens only during a short period of time. How long this is visible is determined by the differences in angle. If two panels have an opposite angle of 0.002 radial at the joints, the difference will be visible during half an hour. With an angle of 0.004, which is still quite small, this period is about one hour.Curved façades are very sensitive to sweeping sunlight. During several hours a borderline be-tween sun and shadow will expose all irregularities.Façades with a reflecting surface act like a mirror. By different angles at the joints, the lines of a reflected image are jagged. Then even the smallest distortion of the façade becomes visible.

It is therefore important that the position of the fix-ing points for the façade are chosen with regard to perpendicular deformation of the structure, even on a small scale. Generally the connection should be at the level of the floor where horizontal displace-ments are minimal. The least vertical displacements can be found on or near the columns.

12.4. Allowable deformations

Most literature about structures is concerned with safety. However, for the façade the deforma-tion is more important.The prediction of this deformation is difficult because the load (wind, live load) will deviate from the schematic assumptions. Also the behaviour of the structure differs from the modelling. This modelling does not take favourable effects into account, like separation walls improving the stiffness and damping. For safety also an unfavourable combination of loads is assumed that probably will never happen.The value of the deformation, from which damage or unwanted visual effects appears, depends on the materials and the texture of the façade.A not very flat concrete or brick façade is not very sensitive to visual effects. Of these two, the brick façade, however, will show cracks, with just small deformation of the supports. A concrete façade will only show movements displacements at the wide joints. These are hardly visible.Important is also how permanent the effects on the façade are. Some deformation will directly

Fig. 12.2.4.2. Spandrel panels supported by the columns

Fig. 12.2.4.3 Rotation of window frames between spandrel panels

result in a permanent and clearly visible damage, while other deformations just have a temporary effect. The government does not care for displacements as long as the integrity of the building remains intact and nothing falls off the building.

Fig. 12.3.1 Rotation of a floor beam between the columns

The values for maximum displacement, as mentioned in standards, are quite high. They are based on publications like the one mentioned under “Literature”.The following values for allowable deformations must be considered just as an indication.Here, as an acceptable deformation a value is understood which may be accommodated with reasonable effort and use of material. The deformations will be hardly visible in average situa-tions.The values may be useful as a start for discussion.Deflection of the edge of the floor < 6 to 8 mm

< 0.0015 to 0.002 from the spanRotation of beams near the support < 0.002 radVertical rotation of columns < 0.002 radThese values are relevant for the deformation after positioning of the façade. The loads involved are: the weight of finishing floors, interior separations, installations and the live loads.

Future Facades Principles

Driving force „Energy“

North and south facade Academia Brasileira de Letras,Rio de Janeiro, Le Corbusier and Oscar Niemeyer, 1943North and south facade of the former ministry ofeducation with varying sun protection systems to preventthermal energy from incident sunlight from entering thebuilding on the north side.

Exterior leaf of prefabricated concrete

INTRODUCTIONConcrete, carefully manufactured, is resistant to the exterior climate and consequently fit as an exterior leaf. Creat-ing a robust surface, it can also resist strong mechanical forces. Because a formwork is used, a three-dimensional form, complicated edges and a rough texture are possible. The material itself is relatively cheap.Up to the 1980’s, façades of concrete were used frequently, but later on these façades became less popular. For a short period of time, flat, shiny up to reflective façades became fashionable. After that, coloured surfaces and natural stone panels were introduced.In recent architecture, more complex façades appeared, also with ornamentation. The materials fit for these three dimensional forms are brickwork and also concrete.

CHOICE OF FORMS AND SURFACESExterior leaves of concrete are produced in a factory in moulds. As a result of this production technique, deep ele-ments are possible, with the outer surface flowing inwards or outwards around windows.

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Daylight is directed into the building via heliostats on theglass roof.

Many new materials are available on the market. Their usein the façade industry is being investigated.

Genzyme Center, Cambridge, Massachusetts, BehnischArchitekten, 2003

Collection of materials

Allianz Arena, Munich, Herzog & de Meuron, 2005

Sandwich panels could be applied in architecture as large load-bearing panels.

Manufacturing of sandwich panels for the automotive industry

Smart MaterialsNano Technology

Nano technologyThis fluid contains metal particles and can therefore be pulled by magnet force.

PCM - Phase-change materials

Model of a PCM ceiling moduleThis ceiling module (not yet filled with PCM) canclimatise the room. The tempera-ture will also be buffered through the PCM. EMPA (Material testing and research institute of Switzerland) and Transsolar, 2005

The sculpture’s extensively polished stainless steel surface creates a unique appearance.

Cloud Gate, Millenium Park, Chicago, Anish Kapoor, 2006

Rapid Manufacturing

Generative manufacturing methodsBased on 3D computer data, generative methods make it possible to build up three dimensional mod-els or components layer by layer.

Jay Pritzker Pavilion, Millenium Park, Chicago, Frank O.Gehry, 2004Free-formed surface supported by a sub-structure andsmall surface elements.

Phaeno Science Center, Wolfsburg, Zaha Hadid, 2005The complex geometry of this building could only beaccomplished through the use of CAD design technology.

Free Form Design and Computer Technologies

Structure of the facade / single lay-ered facade

Driving Force “Architectural vision”

Skin Tower / Sobek Ingenieure / StuttgartAdaptive textile Building facade

Concept for a facade for High-rise completely fromtextiles. Within the textile facade their are PCM‘swoven, which actively regulate the climate of thebuilding

Carbon tower, LA Architects

Driving force „Functionalities“

Lloyds of London

Mike Davies / Polyvalente WallUnderstanding of the Facade as skin / organ of the building

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16-06-2006Invented by Ulrich Knaack Marcel BilowPictures by Torben InderheesKeywords: mono material, freeform, load bearing, transpar-ency, solid, facade, roof, structure, 10-20 years, glassMore Info:

Materials

16-06-2006 Invented by Torben InderheesSupported by Ulrich Knaack Marcel BilowKeywords: mono material, freeform, load bearing, transparency, solid, facade, roof, structure, 10-20 years, glassMore Info:

In-situ Glass / OrtglasIn the future site glass could be possible.Moulding glass in situ like concrete is a idea to create freeform or rectangular shapes out of monolithic glass. The mould had to be resist the high temperature of the liquid glass. The reinforcement of the “site glass” is pos-sible with glass fibres knitted or woven textiles, creating glass textiles that becomes highly transparent when the liquid glass is inserted into the mould. In fact of that, every surface of the glass is possible using different moulding surfaces.

Welded GlassIn the future welding glass could be possible.If it possible one is able to create free formed high trans-parent load bearing structures shaped like the trade roof in Milan, but without steel. Pieces of molded curved glass trimmed in exact shapes are welded together on site.Only a supporting structure that holds the panes in position during the welding is necessary.After welding glass diamante grinding tools smoothes the welding seams to a high transparent monolithic glass enve-lope

Fiber glass info cement Glass element

16-06-2006Invented by Ulrich Knaack Marcel BilowPictures by Torben InderheesKeywords: mono material, freeform, load bear-ing, transparency, solid, facade,roof, structure, 10-20 years, glassMore Info:

EDGED GLASSESIn the future glass could be shaped into shapes like steel or other metals.Creating a tool that heats up a line in a glass pane edged glass constructionare possible. Using these folded glass elements a transparent constructionis useable.

16-04-2006Invented by Ulrich Knaack Marcel BilowPictures: Michael SchmitzKeywords: mono material, prefabricated, load bearing, transparency,structure, glass, 10-20 yearsMore Info:

Glass BridgeIn the future glass becomes more stiffer just like steel constructions.When the development of these glass is finished, load bearing structuresare possible. So just like these sample a prefabricated bridge molded out ofglass sections uses the possibility of prefabricated molded glass.The aim of these technique is to create high transparent load bearingstructures. As seen on the pictures steel traction relieves supported theexternal tension forces.

15-06-2006Invented by Ulrich Knaack Marcel BilowPictures by Michael SchmitzKeywords: layered construction, transparency, roof, lighting, building physics, glass, 10-20 yearsMore Info:

Glass SandwichIn the future glass welding or gluing is also possible as molding it into every shape wanted. The idea is to create glass panes out of two panes glued or welded highly transparent together with glass spacers to cre-ate a load bearing sandwich used for roofs or facades. Supporting the inner forces the spacers are arranged into closer gabs on the corners of the elements. Using this elements as high transparent roof sections a natural light using museum is possible without any necessary windows or facades. So new spaces and sites in the city will be possible to use cause of getting the light from the top.

22-05-2006Imagined by Linda HildebrandSupported by Ulrich Knaack & Marcel BilowKeywords: filter, microstructureMore information: www.goretex.de/published/gfe_navnode/de.prod.mem.breath.html

breathable und waterproofThe membrane’s pores are so refined that only small water vapour mol-ecules can come through but not the water drops. Therefore it is possible that inside the jacket a micro climate accrues whose moisture content and temperature is comfortable.

02-07-2006Imagined by Uli KnaackKeywords: layered-construction, structure, load bearing, wood

3-D MultiplexWood has it´s load bearing capacity in on e direction. The combination of sever-al layers in Multiplex of Kerto are giving the chance to use wood as a monolithic material in two directions.The Idea of this 3-D-Multiplex is to create a wood material, which can be used in all three dimensions for load bearing structures. The combination of wood elements in all three directions comes also to the result of reducing the dead load by 1/4.

10-05-2006Invented by Ulrich Knaack Daan RietbergenKeywords: layered constructions, composite, load bearing, lightness, facade, roof, composite,More Info:

Many Material SandwichesSandwiches are a combination of supplementary materials. For claddings many combinations are imaginable. To create lighter, cheaper or stronger panels, and probably a combination.This concept is to produce a system of panels with all the required functions (such as in water-tightness and insulation) one common panel, and finished with an exclusive material such as natural stone, wood, thin-sliced bricks or gravel (e.g. drained in epoxy). Any material is possible on both sides of the panel.

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Functionalities Structural principles

invented by Ulrich Knaack Marcel BilowKeywords: prefabricated, decentralized, modular, system, moving, adapting, façade, interior, installations

Furniture elements for façades-Just like modular facades elements furniture is designed to fit into the façade grid. These elements can include tables, cupboards, beds, or showers.-Prefabricated just like the shown airplane door its easy to handle with different styles and designs. Different materials are possible.-For easy assemble and a bigger range it would be nice if a regulated grid is possible, just like the I Pod standard connection, today there are over1000 components available to handle with the I Pod.-The modules also can be take with the user as a personal equipment andpart of a living unit.

Imagined by WiglinghoffSupported by Ulrich KnaackKeywords: pneumatic, prefabricated, freeform, moving, lightness, transport, textile, foil, mem-brane www.studioorta.free.fr

Imagined by Wouter Blondeel,Supported by Till Klein, Marcel Bilow, Thiemo EbbertKeywords: freeform, pneumatic, system, load bearing, lightness, structure, enve-lope, 0-10 years, foil, membraneMore Info:

Imagined by Jürgen Heinzel, supported by Marcel BilowKeywords: modular, system, ventilation, pneumatic, transparency, organic, facade, installations, foil, membranes, air,More Info:

Imagined by Ulrich KnaackKeywords: layered construction, pneumatic, ventilation, lightness, envelope, façade, textile, glass, metal

Take your home with you-A rope is a tent is your home ….-Using combinations of textiles and structural pneumatic beams, you are able to handle a small room or tent for travel-ling around.-Everything you need is in the coat, it can also named as “coat-ing” in a different way of seeing….

Invented by Ulrich Knaack, Marcel BilowKeywords: decentralized, heating cooling, transparency, instal-lations, facade, concrete

Integrated module facade Add new functions into a façade module is the aim of this pro-totype project.A decentral climate unit is added into the façade frame, also a cable duct to support the data and electric power to the office is added to the system.

Invented by Stephanie Erben, supported by Marcel BilowKeywords: prefabricated, modular, system, facade, international facades,

4 gewinnt facade-Modular frames that combines a set of frames to install like a element facade-Moulded out of fibre reinforced plastic-Every element can save a single problem-A wide range of design available-The model shows an abstract detail of assembling, normally it is designedto fix the elements an the ceiling line

Deflatable Freeform StructuresThe inherent force of air-pressure can be used as an integrated element in the structural system of facades.The goal is to design structural elements that allow free form constructions that are finally stiffened by vacuum. The elements are put in form first and than inter-lock through the pressure force so that the shape of the construction gets fixes“Peanut“ Bridge There are different possibilities to build a deflated bridge. One possibility is the

Peanut solution. A Material is packed into a pre-shaped bag. In hanging position the ideal “arch-form” can be practically discovered. After evacuation of the air the construction is stiff and can be turned into the upright position.The “Peanut” represents all positive characteristics this Material must have: Good packing possibilities because of shape, friction because of rough surface, lightweight.

Vacuum Wave Facade panelUsing the vacuum wave principle a closed and transparent façade panelcould be possible using sandwich structures hold together with vacuum.For the solid areas a metal sheet covers a powdered silica core - the same used in vacuum isolation panels. This is a good iso-lation and also a self supporting benefit. The transparent area could be possible like the developed vacuum panesusing glass marbles as a spacer to create space for the vacuum.

transparent areaGlass / vacuum marbles

closed areaMetal / vacuum silica

Honeycomb EnvelopeA real good illustrated Idea with a new fresh look.The solutions: Modular frames that combines a set of frames to in-stall like a element facadeVentilation through a Gore-Tex Membrane breathy but watertightMoulded out of fibre reinforced plastic Good solution to fit the ceiling lining by adding mechanical servicecomponents like ventilation, cooling and also cable conduitsInnovative Idea for shading: In the chambers of the pneus a can with apneumatic balloon is filled into the pneuchamber to regulate the shading

14-08-2006Invented by Jürgen HeinzelSupported by Ulrich Knaack Marcel BilowKeywords:freeform, pneumatic, moving, adapting, facade, structure, adjustable mould, foil, air

Air-B-WallUsing airfilled ballon I a flexible airtight bag a adjust-able wall could be created.A few ideas are possible.1. Fill all the ballons and have a recangular wall after deflating2. Fill lines of ballons to create a mowing wall3. Fill each ballon separately to have the most indi-vidual shape4. The pipes can also be attached to a computer con-trolled valve system,to let the wall moving under different situations

Imagined by Ulrich Knaack, Marcel Bilow.Keywords: composite, energy generating, load bearing, freeform, organic, textile, 3D fabrics, concreteMore Info: www.durapact.de / fibre rein-forced concrete www.bioclina.de / heating systems

3D concrete structureThe idea is to use the possibilities of 3 di-mensional woven structures to bestabilised by concrete in the surface. Here also components for insulation, energycollection (water pipes etc) and transpar-ency can be integrated.

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Invented by Marcel BilowKeywords: pneumatic, moving, load bearing, adapting, struc-ture, foil, composite

Production and Assembly

Invented by Marcel BilowKeywords: layered construction, freeform, other functions, organic, envelope,textile

Wrap it textile facadeAn envelope looking like a curtain wall wrapped around a building is possible for cladding elemenents using a glue or matrix soaked textile that will held the ma-trix. A good idea is to use a 3D fabric.1. You are able to wrap the dry textiles around a building as you wand just like Cristo did it with the Reichstag in berlin. When the shape is perfect you can fill in the liquid matrix. and let it dry. A supporting loadbearing grid is necessesary only for the moment of drying. After the form should hold itself.

2. A second idea is to spray resin or concrete on the wrapped skin toharden it.3. A third but dirty solution is to wrap the soaked textiles around the buildingjust like doing a gypsum bandage

Imagined by Till KleinKeywords: freeform, commercial, adapting, tool, 0-10 years, unknown Material

Extrusion MouldThe aim is to create a tool that continuously produces freeform elements that can be assembled to a bigger structure. The extrusion mold can be adjusted in two dimensions. The third dimension is introduce by the flow of the material itself. Temperature, pressure, speed of the process are im-portant factors. Flexible core-materials can be introduced. Reinforcement of the outer material can done with fibers. The cooled material is to be cut into certain sizes. With complex cutting machines different edge types can be produced.If a load bearing construction is necessary, the parts of it will only need to be formed in two dimension as result of the rectangular projection of the elements..

Self erecting constructionInserting pre-cut elements into a airtight bag creates a self erect-ing construction. In fact of this phenomenon a biform construc-tion is possible. For easy han-dling and transportation the ele-ments need less space than in its deflated erected position. So ev-ery construction has two shapes one in his starting and a second after deflating. It is also a kinetic principle cause of “growing” or moving into its final shape.

Invented by Herbert Funke Marcel BilowKeywords: layered construction, composite, load bearing low cost, structure, compositesMore Info:

Folding a sandwich boatA glass-fibre reinforced plastic (GRP) boat has been developed in the framework of a plastic seminar. This hull has been construct-ed as a blank and has been built as a plain layer as opposed to usual constructions of boat hulls. The boat has been folded to the final shape only after laminating a planar level with rigid foam. After testing the construction it has been secured that a delami-nation would only take place in the direct area of the bend. On the basis of this small sample that could have been coped in the seminar this type of construction has been verify ed. It has been shown that the use of accurate edges for architectural purposes is possible. Those edges can be manufactured economically.This project was supported by the companies Gebr. Becker GmbH & Co KG /Wuppertal (vacuum pump), Hyco-Vakuumtechnik GmbH / Kraill-ing, R&G GmbH Faserverbundstoffe / Waldenbuch (GRP), epurex films / Walsrode ( foil for vaccuumpressing)

Invented by Ulrich Knaack Daan Rietber-genKeywords: layered constructions, freeform, composite, load bearing, lightness, facade, roof, composite

Freely Curved Metal PU-PanelsThis concept is to produce freely-curved sandwich panels with a PU-core and an aluminum surface.The method is described in the following pictures.The panels can be of varying thickness, giving extra stiffness to certain parts of the panel. Extra stiffness is also possible by using several densities of the polyure-thane.

1. Two sheets (e.g. aluminum)are positioned between two

adjustable moulds

2, The moulds take their position,the sheets are pushed more or

less in place

3, By injecting the polyurethane,the sheets are pushed in their

final position

Next step would be thedetailing of the panel.

Integral Envelope

Invented by Ulrich KnaackKeywords: pneumatic, controlling, liquid, facade, foil, water

Liquid FaçadeThe liquid façade tries to deal with: load bearing thermal mass for energystoring different possibilities of thermal insulation By using water in the middle pneumatic element, the thermal mass can be used for storing energy. By using different positions of insu-lation pneumatics at the outer surface the insulation against cold and sun can be controlled.

Imagined by Marcel BilowKeywords: decentralized, heatin/cooling, lightness, installations, concrete

Facade Heating / Cooling PanelTo avoid the classical heating units in front of the glass surfaces these un-glazed units should be used as heating / cooling surfaces. The developed facade panels are formed of fiber reinforced concrete which is imbedded with textile.They are used as load bearing construction of the panels and can be in-serted into the facade framework. The surface oriented towards the room is inlaid with meadows of capillary tubes which heat in summer and cool in winter. The use of fiber reinforced concrete provides a good heat con-duction as well as stability.

Imagined by Marcel BilowKeywords: layered construction, composite, modular, en-ergy generating, load bearing, strength, facade, envelope, textile, concrete, 3D fabrics, composite

facade heating / cooling panelThe Idea is to create collectors of areas that are usually used for traditional solutions. Walls or roofs can used as solar energy plants with inserted capillary tube systems, so the functions load bearing, insulations and weather protection can be added with the function of solar energy input. The material is fibre reinforced concrete Main ideas are industrial roofs or facades, also a prefab Roof for housing To store the energy a geothermic storage space would be possible.

roofs Industial facades

Ground storage

Also possible to the sunpower in the summer

and heat the rooms in the winter

Sandwich panel

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Invented by Ulrich KnaackKeywords: layered construction, composite, energy generating, solid, facade, composite

Sandwich façadeThe idea of this façade is to create a sandwich structure which uses different pos-sibilities of sandwiches to solve different needs of facades.The main structure is made out of acrylic and glass fibre surfaces and foam in the middle. This should solve insulation and structural issues.Windows are to be made out of acrylic. Reflection and light transport could be made by using “TWD” (Transparente Wärmedämmung) Finally the water tubes in the surface can collect sun energy for heating. The energy could be stored in geothermic stores.

Water tubs to collect sun energy

Foam

Acrylic glass

Transparent

Light reflection

TWD

Acrylic with Gypsum andGrass fibre

Bionic Principles

Wrapped TowerThe Tuaregs, who live in the Sahara, still cloak themselves with dark cotton or lambs wool shawls. They cover themselves with it to protect themselves against the extreme sun of the desert. They wrap the fabric loosely around their head and body several times. The spaces in between the layers of fabric are necessary for the air circulation. The wind in the desert assures a comfortable blood temperature under the dark cover. Darker material heats up more quickly than brighter material. While dark fabrics absorb infrared beams more than brighter ones do, black material is able to release the heat more quickly than a brighter material would. This effect requires the circulation of air. The principle is suitable for a high-rise building because in those heightsthere is enough air circulation for a good cooling effect.

Imagined by Linda Hildebrand Supported by Ulrich Knaack & Marcel BilowKeywords: absorption, circulationMore information: www.zeit.de/2005/36/Stimmt_s_36

Imagined by Till KleinKeywords: freeform, layered construction, ventilation, insulation, moving, organic, beauty, facade, envelope, building physics, technology transfer, 10- 20 years, unknown material

Feather EnvelopeHouses could be covered by feathers. They provide a water tide and insulating surface which in the same time can adjust to movement and is permeable for ventilation if needed.There are two types of feathers in nature: Contour-Feathers are building the outer layer. They are strong and are used for steering and protection. Down-feathers are more fine and responsible for insulation. The free part of the Federkiel outside of the skin is called shaft. It carries the Fahne which itself is divided into air filled Äste and Strahlen. The Strahlen can be melted together or have little hooks to provide more connection and strength.Water tidinesss is made to the dense.Blue colours a created by distribution of light. Green and violet are created by yellow or red layers on top. Changing colours come from interfering white light.

Imagined by Linda HildebrandSupported by Ulrich Knaack & Marcel BilowKeywords: temperature regulation by lightMore information: Behling/ Braun: Bionic Skins- Natürliche Hüllen und Häute, Stuttgart, 2003

ChameleonThe chameleon is able to adapt to the colour of its sur-rounding, so that an enemy can not see it or a potential partner can not overlook it. The lighting conditions and temperature determine this process. If the temperature of the animal’s skin low, it becomes darker so that the skin absorbs the light more rather than reflecting it. The principle can be transferred to a facade: the proportion between reflection and absorption affects the tempera-ture. The analogy would be a facade whose colour is de-termined by the temperature inside.

Imagined by Linda HildebrandSupported by Ulrich Knaack & Marcel BilowKeywords: guiding sunlight, directed energy effortMore information: www.daserste.de/wwiewissen/thema_dyn-id.y45wugb8qbl 374r4-cm. asp

ChameleonA polar bear’s hair functions similar to a fibre optic cable. Beams are con-ducted inside the hair or cable by refraction. The polar bear uses this ef-fect to produce heat from the irradiation. This principle can be transferred to regulate and guide the beams to use them. The light conductive fibres will be structured, take up the irradiation and lead them to a layer which serves energy generation. Beams are turned into electrical energy in this layer. Depending on the position of the sun the angle of the fibres can be changed by a pulling tool. In contrast to polar bear hairs coat fibres are aerated and straight therefore less heat develops just before the skin. Overheat could be avoided and the energy could be used selectively, which makes this principal prettyattractive for the desert.

beam is guided to become electricity, heataccumulation avoided by flowing air

Concrete Façades

ir. Roel SchipperFaculty of Civil Engineering& GeosciencesBuilding Engineering

A. recognize possibilities with the material concreteB. be able to survey architectural and structuralconsequences of choicesC. be able to draw basic detailsD. learn about possible future developments

1. functional (dis)advantages why (not) choose concrete?

some reasons to choose for concrete in the façade:quick assembly & closing of building skinintegration with load bearing structure (double function)building physics: thermal mass & sound insulationairtight – limited length of joints & seamsfire resistancereliable & robustless expensive than some other optionsextra helpful in case of limited building site

2. functional aspects

some reasons to choose for concrete in the façade:quick assembly & closing of building skinquick assembly & closing of building skin integration with load bearing structurebuilding physics: thermal mass & sound insulationairtight – limited length of joints & seams- production in factory

- simple details - less emphasis on building site - less chance of damage

costs

Some reasons not to choose for concretein the façade: weight:- transport (factor 5)- assembly (permanent crane use)- foundation (extra piles)calculation necessaryfor objective comparisonsustainability (C2C, CO2)- separation into reusable components- fossil energy involved in manufacturing cement- energy use for transport

GreenCalc-analysisnecessary

limited adaptability- integral part of structure- window openings- thermal insulation

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Architectural Aspects

necessary

other material

aggregate)

thinner structure

Architectural Aspectsfaçade as integral part of structure structural connection façade - floor contribution to stability forces require reasonable

minimum sizes Red Apple Rotterdam

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Research & Development project: Der Neue Zollhofplaats: Düsseldorf, 1999architect: Frank O. Gehry Associatesmateriaal:prefab beton

prefabricated freeform concrete façade elements

project: Hungerbrugbahnplaats: Innsbruck, 2007architect: Zaha Hadidmateriaal:glas op carbon fibre

project: Dio Padre Misericordiosoplaats: Rome, 2003architect: Richard Meiermateriaal:zelfreinigend prefab beton

why prefabricated concrete?1. very much suitable as material2. Netherlands are in advance3. promising niche-market4. many unsolved technological questions

unsolved issues:

Transparent façades and roofsGreenhouses, atria, second skins

Transparency inwards high daylight factor in the building minimum sky reflection (appearance) contact with the building

Transparency outwards light color, transparent orientation of structureframe dimensions distance between glass and structure cable systems

Design aspectsFunctionTransparencyStructural systemsTemperature / energyAcousticsFire / smoke

present situation

new situation: glass covered space

function:indoor spaceUniversity ofCambridge - UKFaculty of Law

function: “Raincoat” Banque Parisbas, London, UK

transparency:light color

Transparency:Frame

Transparency:Details

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Transparency:Orientation Vertical

Example:Parc de la VilletteParis - France

Maintenance

Facility for possibledeflection

Orientation Horizontal Vierendeel ColumnsDistance BetweenGlass and Structure Secondary Beam Interrupted

Frame With Diagonals

Two possibly pressedelements(depending on winddirection) buckling thick profiles

central pressed element

Central pressed elementwith pretensioning

Limit Elements Under Pressure Example of cable system

Museum Prinsenhof Delft

How to bear glass weight

Visually minimize size of elementstransport forces sidewaystransport forces backwardshang glass panels

Transport forces sidewaysto some heavy columns

With big framework

Forces to cantileversin the roof

No cable

No horizontal beam:wind to structure backwards via bar

How to deal with deflectionsRoofs (2nd rain barrier andcondensation)

Facade functionsDevelopment of the metal-glass facade

Key factors:

- Society/ architecture- Management/ collaboration- Technological possibilities- Norms and regulations- Markett- New functionalities- a.s.o

Arrangement of facade

Functions PlaneLayeredConstruction is the 3- dimensional arrangement ofmaterials and elements according to the best possibleperformance for the system.

Ready-made productE2 Facade, Schueco, Stefan Behling, 2007 Component Facade Leonie van Ginkel Matrix Grid -

Nathan Volkers

Sinosteel International Plaza, MAD Architects

Commercial Complex Omotensando, Japan, UN Studio

Spanish Pavillion Expo 2005, Foreign Office Architects

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residential building;problem:

through AC-outlet

Learning ObjectivesFaçade technology – what can go wrong?

Objectives of today’s lecture:become aware of the risk of making faults and of their possible consequenceslearn how to prevent faults3. learn to know most import damagecauses4. get some skill in recognizing and solvingmistakes in time5. learn how to diagnose errors afterwards

anonymous parking garagewrong detail for drainage

Rain Rain

Slope >100

drippinggroove

Collectedilth flowsover façade

Hilton Rotterdamjoints between facade panels filled with cement mortarunaware of stacking effect

Handboek Bouwgebreken

(SDU)

source: Bouwdetails Online (SDU)

Residential building in Het Funen, Amsterdam

source: archive RS

source: archive RS

source: Bouwdetails Online (SDU)

Residential building in Het Funen, Amsterdam

Rresidence in Woudrichem

source: archive RS

Dwelling in Woudrichem

Primary school de Balans Leidschenveen

source: archive RS

source: Handboek Bouwgebreken (SDU)

(e.g. leakage, internal condensation, construction moisture,raising from foundation)

(e.g. displacement of load bearing structure, foundation)

(e.g. temperature shrink or extension, moisture shrink or extension)

(finishing structure unintentially becomes load-bearing)

(acid / alkaline, nickel-sulfide, solution / deposition of salts)

(insufficient thinking of spatial situation)

important causes of damage?(only related to façade or roof)

Brainstorm What -do you think- are important causes of damage?(only related to façade or roof)

Causes most found in practice

Moisture damage

source: Handboek Bouwgebreken (SDU)

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Moisture damage

Handboek Bouwgebreken (SDU)

NPS/ Vara building Hilversumt

source: Handboek Bouwgebreken (SDU)

Strips are made of untreated Western Red Cedar soft kind of wood untreated very sensitive to moisture differences unevenly drying causes algae and an uneven surface

Other typical problem with WRC is caused by a misunderstanding inchange of colourWe think WRC changes colour due to UV radiation. But this is caused bya ‘colourfungus’ which is very sensitive to humidity and the changes inmoist. This causes uneven changes of colour ranging from grey to black.

NPS/ Vara building Hilversumt

What can go wrong...Façade technology – what can go wrong?

Diagnose / prevention

‘Zilvervloot’ Pien Heinkade AmsterdamLyceum Ypenburg

Lyceum YpenburgUnforeseen loads

NAI Rotterdam

Concrete beam above terrace

thermal bridges (cold bridges) molding

severe pollution

Concrete beam above terrace

thermal bridges (cold bridges) molding

severe pollution

Chemical reaction

Vaktechnisch lyceum Utrecht

Vaktechnisch lyceum Utrecht

Rockwool behind glass facadeDeteriorated by moisture and wind, which loosened the surface. This

happens irregularly, partly through the openings between the glass plates.The detached fibers attach themselves to the glass of the windows in

the inner leaf. These pollute quickly because they are not sprinkled.Cleaning from the outside would be possible if you could at least reach them.Wooden facade

Irregular discoloration of the impregnated wooden facade. Normallynot a problem but in this case waterproofing vapor-permeable membraneis severely affected by UV because of the big joints between the boards

Vaktechnisch lyceum Utrecht

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Vaktechnisch lyceum Utrecht

Facades of internal spaces in which the auditorium is, are made of 8mmclear glass only.There is an outdoor environment, although not completely the case dueto the lack of air circulation. This causes condensation at low outdoortemperatures.

Rockwool behind glass facade

The users were seriously concerned about the dust. The windows were shuttight while it was the only possibility for necessary ventilation. There was anunbearable indoor climat.Solution:

Entire facade dismantledThe facade with rockwool was cladded with made wooden slats on which

plastic roofing material and fixed with plastic clip dishes. (Chesterfield effect)A new danger occurs:

condensation behind the film which can lead to rotten span slats.

2D – 3D – thinking

The curve is covered with 50mm shotconcrete on a layer of flexiblematerial (elastomeerlaag) to make thermal movements possible.

This causes extra high differences in temperature in the shotconcreteCauses cracking from glassfacade upwardsThese cracks show tracks of chalk/ salt

The building is partly built in ‘clean concrete’, including the roof On the inside the building is made dampproof, on teh outside the roof is covered with 80mm of ‘pearl concrete’ with a black pigmentation. On the inside there foam glass insulation. The difference in temperature can riseto 80 ºC.

Causes crackingConcrete ‘crumbles’ at the corner connectionsDue to the severe movements in the roof the covering of the roof cracks and leaks. This is temporarily solved by covering with plastic foil and bags with sand.

The bay windows are made of painted plywood and finished in transparent lacquer, the minimum protection you can offer some wood.

Inwatering occurs almost immediatelylocal cracking and deterioration of the wood as an result

The lower bay windows are in direct contact with the ground, allowing the bottom to a permanent supply of moisture. Even exterior plywood is will not survive this.

Window wallIs affected by cement

water every time it rains This causes etching ofthe glass and this is irreparable.

Educatorium Uithof Utrecht

www.bouwfouten.com www.bouwfouten.com www.bouwfouten.comwww.bouwfouten.com

Building:A matter of the right order?

What can go wrong…

Police department Vaals

Case

ImplementationImplementation considerationsFreedom in placing order:

Logical placing order:

Police department VaalsPrimary school de Balans Leidschenveen

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Housing Ypenburg

Roof and facade are the same. “What one can put on a roof, can be put on a facade”That would mean that the requirements for a roof are the same as those for a facade.The homes are distinguished from each other by the different finishings: wooden shingles, tiles, seamed aluminum roof panels, corrugated board and fiber cement board coated with polyurethane.

Roofing materials are very vulnerable, especially to 2 meters above ground levelDamaged tiles and wooden shingles

RVU building Hilversum

What can go wrong...The roof is designed as a continuation of the surrounding parkland. The roof

is covered with loose single layed roofingmaterial. In case of lekage your in big trouble because the spot can hardly be found.

The only suitable finishing is a glued two layered roofing system.

Until the 19th century on either side of the Zijlpoort there was an earthen city wall. In the new extension, walls are the same shape as the original city wall. The slope of the wall/roof is 55° which is a problem when you cover it vegetation.

In normal dikes groundwater follows the form. In artificial dikes a substrate is used in plastic elements or ‘bags’ to hold water.Because of the steepness rainwater does not stay long enough on the upper part. Vegetation roofs can only survive 6 weeks max., in this case even 3 weeks.

1. become aware of the risk of making faults and of their possible consequences2. learn how to prevent faults3. learn to know most import damage causes4. get some skill in recognizing and solving mistakes in time5. learn how to diagnose errors afterwards

RVU building Hilversum

Zeilpoort Leiden

Learning Objectives

Each building has several connections regarding the facade, f.i.

In de facade different building components are joined.These are grouped as follows:

Decisions made for one part of thefacade will be of influence on all theseconnections

Building component groups

Integration in the building skinBearing structure:

The use of certain caracteristics of the bearing structure can result in adistinctive spacial forms

Relationship between

Skin/ Bearing structure:

Integration of bearing and seperating:

Relationship between

Skin/ Bearing structure:

Separation of bearing and separating :

Integration in the building skinThe Skin:

Part of the building where all important seperating functions like protectionfrom wind, water and heat are placed.

Position of the skin:

In front of the constructionAn important aspect is the position of the skin i.r.t. the bearing structure.

In front of the construction

In front of the constructionBetween beams and columns

In front of the constructionBetween beams and columnsBetween Floors

Integration in the building skinPosition of the skin:Between floors: Thermal bridge and drainage

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