theory of structures_floor systems

8/10/2019 Theory of Structures_Floor Systems

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Theory of Structures_ ARCH 310

Lecture Topic: Structural Floor Systems

Name: Lawrence Ogunsanya

Email : [email protected]

Struct

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Introduction Floor systems are the horizontal planes that must support both

live loads and dead loads.

A group of components fastened together make up this

horizontal frame and it require support at two sides opposite

each other.

Floor systems must transfer their loads horizontally across

space to either beams and columns or to load bearing walls Floor systems may be composed of a series of linear beams

and joists overlaid with a plane of sheathing or decking or

consist of a homogenous slab of reinforced concrete.

The depth of the floor system is directly related to the size and

proportion of the grid network it must span and the strength ofthe materials used.

Floor systems can be in 3 main forms: Concrete, Steelor

Timber.Struct

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Introduction

Concrete:

Concrete floor slabs are

supported by columns, beamsand loadbearing walls

Steel:

Steel beams support steeldecking or precast concrete

planks or slabs These beams may be

supported by girders, columnsor load bearing walls

Beam framing is typically anintegral part a steel frame

system.

Timber/wood:

Wood beams are alsosupported by girders, columnsor load bearing walls


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Struct

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What drives the choice of a

floor system?

Speed of construction

Services

Adaptability of space

Day lighting Aesthetics

Acoustics

Fire Resistance

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floor system? Speed of construction For some projects the need to reduce to a minimum the

construction time (on site) may play a determining role. Indeed,

time is often one of the key drivers for choosing a structural steel

framework solution.

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The Ark Hotel, ChinaBuilding with steel frame
http://www.google.co.za/url?sa=i&source=images&cd=&cad=rja&docid=jmg_nxeRPpGZ9M&tbnid=9FChwgl8tu3rAM:&ved=0CAgQjRwwAA&url=http%3A%2F%2Fwww.dailymail.co.uk%2Fnews%2Farticle-2083883%2FArk-Hotel-construction-Chinese-built-30-storey-hotel-scratch-15-days.html&ei=TYNcUu_GAsKBhAeIuIG4DQ&psig=AFQjCNEt6c48COPMF34vbcU0G1CAtnPnnQ&ust=1381881037088541


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floor system? Services When a lot of service ducts are to be accommodated it may be

beneficial to adopt a floor solution that provides a flat soffit in order

to maximise the flexibility in routing these ducts beneath the

structural floor.

It will also be easy to remove and/or replace these ducts to meetfuture needs.

Solutions that provide a flat soffit don't also allow long spans. So an

alternative in a building that is both highly serviced and requires

long-span floors is to integrate the services within the beam depth,

so that the total depth of structural floor plus service zone isminimised

Another option is to use webbed or castellated beamsStruct

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Services intergraded into the floor

system


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Need for adaptable space This is dependent on the spanning ability of the floor material

This spanning ability allows the number of internal load bearing

walls and columns to be minimised.

Open floor spaces can be created, or non load-bearing

partitions (that are easily moved) used to form (temporary)individual areas.


floor system?

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Estimate span ranges for different floor slab systems

Floor slab spans

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Floor slab spans

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Day lighting requirements 'Deep' floor plans (floor plan widths that are more than15 metres)

may mean that, occupants of a building are not exposed to

natural lighting.

Long span solutions may not then be the most appropriate

solution for certain situations, rather a short span design (for

example using shallow floors ) with an internal atrium may

provide a more appropriate internal environment.

The shallowness of the floors is achieved by placing the slabs

and beams within the same zone. An added benefit is that a flatsoffit is achieved.


floor system?

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Shallow floors
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floor system?

Aesthetics If false ceilings are used then the aesthetics of the soffit of a

given structural floor system are clearly irrelevant.

However, a number of clients have recently been looking for

exposed soffits, exposed primarily so that the thermal mass of

the floor is exposed.

The soffit must also then be visually appealing.

Struct

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floor system?

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Acoustics In terms of resisting airborne sound a massive floor is beneficial,

and when considering impact sound avoiding stiff structural

connections between components is helpful.

Good detailing and installation of sound proof membranes are

needed.
http://www.steelconstruction.info/File:Fig_2_Junction_of_a_twin_light_steel_frame_separating_wall_with_a_shallow_composite_separating_floor.png


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Acoustic floors

Under screed isolation materials

Floated wood and composite

floor systems


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Fire resistance The most common solution adopted to provide fire

resistance is to protect the steel members so that they

remain at a sufficiently low temperature).

Use a lot of concrete on the building.

Intumescent coatings, which are applied off-site and expand

with temperature to provide an insulation layer, are often

used.

If the steel elements are embedded in concrete this can

provide the necessary insulation against fire. Other options include board protection and the use of a

cementitious spray.


floor system?

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Fire protection

Application of thin film intumescentcoatings offsite

Board protection systems
http://www.steelconstruction.info/File:Off_site_application_2.png


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Struct

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Concrete floor slab systems

Flat slab Flat plate

Beam and slab

Ribbed (waffle slab) Hollow core slab (precast)

Solid slab (precast)


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FLAT SLAB

A flat slab is a one-way or two-way system with thickenings

in the slab at the columns and loadbearing walls called 'drop

panels.

Drop panels acts as T-beams over the supports. They

increase the shear capacity and the stiffness of the floor

system under vertical loads, thus increasing the economicalspan range.

Struct

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FLAT SLAB

Advantages

Simple formwork

No beamssimplifying under-floor services outside the

drops

Minimum structural depth

Usually does not require shear reinforcement at the columns.

Disadvantages:

Medium spans

Generally not suitable for supporting brittle (masonry)

partitions

Drop panels may interfere with larger mechanical ducting

Vertical penetrations need to avoid area around columns

For reinforced flat slabs, deflection at the middle strip may be

critical.

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FLAT PLATE

Advantages: Simple formwork and suitable for direct fix or sprayed ceiling

No beamssimplifying under-floor services

Minimum structural depth and reduced floor-to floor height.

Disadvantages: Medium spans

Limited lateral load capacity as part of a moment frame

May need shear heads or shear reinforcement at the

columns or larger columns for shear Long-term deflection may be controlling factor

May not be suitable for supporting brittle (masonry) partitions

May not be suitable for heavy loads.


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BEAM AND SLAB

This system consists of beams framing into columns and

supporting slabs spanning between the beams. It is a very traditional system. The relatively deep beams

provide a stiff floor capable of long spans, and able to resist

lateral loads.

However, the complications of beam formwork, co-ordination

of services, and overall depth of floor have led to a decrease

in the popularity of this type of floor.


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BEAM AND SLAB

Advantages:

Traditional effective solution

Long spans.

Disadvantages:

Penetrations through beams for large ducts

difficult to handle

Depth of floor

Greater floor-to-floor height


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RIBBED [WAFFLE] SLAB

The basic construction method begins by digging a trenchdown to undisturbed mineral subsoil.

Ribbed floors consisting of equally spaced ribs are usually

supported directly by columns

They are either one-way spanning systems known as ribbed

slab or a two-way ribbed system known as a waffle slab.

This form of construction is not very common because of the

formwork costs and the low fire rating.

Ribbed slabs are suitable for medium to heavy loads, can

span reasonable distances, are very stiff and particularlysuitable where the soffit is exposed.

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Concrete floor slab systemsRIBBED [WAFFLE] SLAB

Advantages:

Savings on weight and materials Long spans

Attractive soffit appearance ifexposed

Economical when reusableformwork pans used

Vertical penetrations betweenribs are easy.

Disadvantages:

Depth of slab between the ribsmay control the fire rating

Requires special or proprietaryformwork

Large vertical penetrations are

more difficult to handle.

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HOLLOWCORE

Hollow core floor planks are precast, pre-stressed units

produced on long-line casting beds using slide forming orextrusion methods

During manufacture, cores are formed throughout the unit,

reducing its self-weight.

Planks are usually 1200-mm-wide, though somemanufacturers can produce 2400-mm-wide units.

These wider units may require increased crane capacity but

offer greater speed of placement, less joints, grouting and

sealing.

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SOLID SLABS

Solid precast pre-stressed floor slabs are typically wet-cast on

long-line beds in unit moulds or by hollowcore equipmentusing slip form or extrusion methods.

Thickness is usually 150, 200 and 250 mm.

Solid slabs are chosen where the loading results in high

shear or there are heavy point loads;

the environment is aggressive, for example in splash zones or

where condensation may occur over water, dry arid areas.

High cover or special concrete is required;

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PRECAST CONCRETE SLABS

Advantages

Durability and low maintenance.

Corrosion and impact resistance,

Fire resistance

Able to control the quality of materials and workmanship

better than onsite

Manufactured to various sizes and thickness

Disadvantages:

Handling and transporting

Stresses induced during handling and erecting units may

cause significant structural design concerns

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