space frames

SPACE FRAMESBy

J.C.WASON

DIFFERENCE BETWEEN A PLANE FRAME AND A SPACE FRAME

Plane Frames & Space Frames :• A PLANE FRAME :

A 2D structure whose all elements lie in the same plane.

Examples :

• A Portal Frame• An ordinary Roof Truss

PLANE TRUSS ( All members and All loads lie in the same Plane )

PLANE FRAMES : PORTAL FRAMES( All loads and All members in the same Plane )

PLANE FRAMES :A Plane Frame can resist loads applied only in its

own plane.

A Plane Frame is not stable to forces perpendicular to its plane.

SPACE FRAMES :

• A Space Frame is a Three dimensional assembly.

• A Dome is a Typical example of a Space Frame.

• A Space structure can resist loads applied at any point, at any inclination to surface of structure and in any direction.

SPACE FRAMES :

• Thus, for a Space Frame: ( i ). Members of the Space Frame are located

in Three dimensions in space.

( ii ). Loads may be applied on the structure acting in Any direction in space.

Py

Pz

Px

A MULTISTOREYED FRAMED BUILDING IS A SPACE STRUCTURE WITH MEMBERS LOCATED IN SPACE, AND SUBJECTED TO FORCE IN X, Y & Z PLANES

BEAM

Pz

Px

A MULTISTOREYED FRAMED BUILDING IS A SPACE STRUCTURE WITH MEMBERS LOCATED IN SPACE, AND SUBJECTED TO FORCES IN X, Y & Z PLANES

BEAM

Py

Py

COLUMN

Z X

Y

FORCES ACTING IN A TYPICAL FLOOR IN A MULTISTOREYED BLDG.

Advantages of Space Frames :

• A Space Frame can :(i). Gives greater freedom of design.(ii). Span larger col. free areas.(iii). Give pleasing appearance.(iv). May lead to lower cost.

However, Analysis of Space Structures is more complex and generally needs computer analysis.

SPACE STRUCTURES :Steel Space Frames RCC Space Frames

(i). Single layered Space Structures :(Derive strength due to curvature)Example : Retreading Factory, Jabbalpur.

(ii). Double Layered Space Frames : (Double layered space structures)Example : Hall of 14, Pragati Maidan, New Delhi.

Example : Hall of Nations

HALL OF NATIONS, PRAGATI MAIDAN, NEW DELHI – AN EXAMPLE OF CONCRETE SPACE STRUCTURE

HALL OF NATIONS, PRAGATI MAIDAN, NEW DELHI – AN EXAMPLE OF CONCRETE SPACE FRAME

CONCRETE SPACE FRAME FOR HALL OF NATIONS, NEW DELHI (INDIA)

(b) HALF ELEVATION HALF SECTION

39014.431

035.

6987654321

LVL 0

4876

.8

4876.84876.8

73152

3448.4

LVL .5

LVL .4

(c) PART PLAN; LEVELS 4 & 5

(d) PYRAMID GEOMETRY

LC

54º 44’ 24”

HALL OF NATIONA, PRAGATI MAIDAN, NEW DELHI- TOP PLAN

3901

4

7315

2

SPACE STRUCTURES - TYPES

1. SINGLE LAYERED

2. DOUBLE/MULTILAYERED

STEEL SPACE FRAMES :

• Span Range : (i). Single layered = 20 – 30 m (ii). Double layered = 50 – 80 m

• Uses : (i). Industrial Bldgs. (ii). Exhibition Halls (iii). Sports pavallions (iv). Gymnasiums etc.

SINGLE LAYERED SPACE STRUCTURES – SALIENT POINTS :

(i). Single layer of Triangular network of members.

(ii). Curved, Shaped like shells to obtain space geometry.

(iii). Derive strength through space geometry (curved shape).

(iv). Joints hinged and members subjected to Axial Forces (Axial compression/axial tension).

(v). Similar to shell behavior.

SINGLE LAYERED SPACE STRUCTURES – Examples :

1. Hall of Technology at Pragati Maidan, New Delhi.

2. Roof of Talkatora Indoor Stadium, New Delhi.

STEEL DOME – AN EXAMPLE OF A SINGLE LAYERED SPACE STRUCTURE

STEEL DOME – AN EXAMPLE OF A SINGLE LAYERED SPACE STRUCTURE

ADD YOUR TEXT

ELEVATION

PLAN

TRUSSED TRIANGULATED SINGLE LAYERED ROOF

ELEVATION

PLAN

SIDE VIEW

A TAPEZDOIDAL TRIANGULATED SINGLE LAYERED ROOF

PLAN

A TRIANGULATED STEEL DOME ROOF- AN XAMPL OF A SINGLE LAYERED SPACE STRUCTURE

ELEVATION

196 m Dia ( 50000 seating Capacity) Steel Dome Roof for Haris County Sports Stadium, Texas, USA

DOUBLE LAYERED SPACE STRUCTURES SAILIENT FEATURES :

1. Visualised as a 2D surface layers, (Top + Bottom), connected by verticals and diagonals.

2. Derive Plate Behavior ( Two way slab actions).

3. Derive bending strength due to depth of system.

4. Unlike single layered systems, Double layered systems need not be curved in shape.

Example: HALL NO 14, PRAGATI MAIDAN, NEW DELHI

DOUBLE LAYERED SPACE STRUCTURES – SAILIENT FEATURES (CONTD.) :

5. The surface grids could be Square or Equilateral Triangles.

6. Web members are diagonals or a combination of verticals and diagonals.

Advantages of Two layered systems : 1. greater rigidity :

(i). Hence can have larger spans.

(ii). In Double layered grid systems, there is more flexibility in positioning of column supports. Supports may be widely spaced and may be ,if necessary, irregular.

(iii). High rigidity of double layered grids reduces the deflection of the structure.

2. Higher Indeterminancy :

• Due to high level of indeterminancy, overstressing or buckling of any individual member under any concentrated load may not lead to collapse of the structure.

• The load will get distributed to other adjoining members leading to even distribution of stress under concentrated loads in several directions.

3. Space for accomodating Electric and Service conduits :

• Services/AC ducts may conveniently be accomodated within the double layered grid.

4. Feasibility of using standard modules and mass production :

• Double layered grids are usually built from simple prefabricated standard units, which can be mass produced in a factory and can be easily and rapidly assembled at site.

SKELTEL SPACE STRUCTURE :

• Most common form of Space structures are the Skeltel Space Structures consisting of a . network of interconnected members.

• Such structures are appreciated due to their visual beauty and impressive simplicity.

• Accordingly, there is a trend to leave structural grid members exposed as part of the Architectural expression.

Advantages of Skeltel Space Frames : 1. Less self weight ( Light weight system)

( i ) Feasibility of Large Spans. ( ii ). Reduction in Cost. ( iii ). Reduced loading on Supporting Columns and

Foundations. ( iv ). Less Earth quake forces.

2. . Visual beauty and ex pressive simplicity.

3 . Structural efficiency.

4. Efficient for loads acting in Any plane.

1. Less self weight ( Light weight system) :

• Skeltel Space Frames have : light sheeting roofing which normally does

not require any terracing for drainage of rain water.

Self wt of such systems is about 1 to 2 KN/m2 against self wt of 10 to 12 KN/m2 for tradition RCC roofs with Beam and slab systems.

Table : Approx. weights of Space Structures

Type of Structure

Span Range(m)

Weight Range (Kgs/m2 )

1. Conventional Trusses

20 - 30 20 - 26

2. Domes 60 - 80 ‘32 - 45

3. Double layeredGrids

20 - 30 15 - 20

( i ) Feasility of Large Spans :

• Space frames of about 80m X 80 m and Steel Domes over 100 m Dia have been planned using the concepts of Skeltel Space Structures.

( ii ). Reduction in Cost :

• Cost of roofing with such systems is less than cost of traditional RCC systems.

( iii ). Reduced loading on Supporting Columns and Foundations :

• Due to less self weight, loads on the supporting columns and foundations is reduced leading to Economy in design of these structural elements.

( iv ). Less E Q forces :

• E Q force acting on a structure is a function of mass of the structure. As Mass of such systems is comparatively small, E Q force on such structure is also small.

• Due to smaller overall wt. E Q forces normally are NOT critical for their design. Such strctures are more critical for wind loads and not for E Q loads.

2. Visual beauty and expressive simplicity:

• Due its form, such structures are visually beautiful and have bold e x pression, which is generally integrated into Architectural aesthetics and, as such, structural members are normally left e x posed for bold Architectural e x pression.

( 3 ). Structural efficiency :

• Due to its interconnected members in space, any load applied at any point gets distributed to other distant members leading to a leading to reduction of stresses in members directly under the load and a fairly even distribution of the stresses throught the structure. This results in more efficient and economical Structural design.

(4). Efficient for loads acting in Any plane :

• Space structures are efficient to resist loads acting in any plane.

STRUCTURAL PROPORTIONING OF DOUBLE LAYERED GRID SPACE SYSTEMS :

• EMPIRICAL RULES FOR FIXING UP THE DOUBLE LAYERED GRID SPACE STRUCTURES ARE DISCUSSED.

DOUBLE LAYERED SPACE STRUCTURES OVERALL STRUCTURAL PROPORTIONING :

1. Typical (Span/Depth) ratios :

(i). Simply supported spans : d/L = 1/18 to 1/25 (ii). Cantilevered spans : d/L = 1/9 where : d = Depth of system L = span 2. Optimum bay dimensions : a = 1.2d to 2.5d

DOUBLE LAYERED SPACE STRUCTURES - OVERALL PROPORTIONG (CONTD.) :

• Bay dimensions : are restricted to about 3 to 4m due to Buckling of compression members.

• Individual members: Hollow circular Tube sections are preferred due to uniform structural strength/Buckling Strength along all axis.

DOUBLE LAYERED GRIDS – ROOF COVERINGS :

• Roof claddings suitable for Space grid roofs are :

• ( i ). AC Sheets

• ( ii ). Aluminium corrugated sheets

• ( iii ). Precast ferrocement slabs

DOUBLE LAYERED GRIDS- METHOD OF ANALYSIS :

Computer based Analysis adopted. Stiffness

Matrix method of Analysis is used as basis for most of the computer programmes available for analysis of Space Structures.

DOUBLE LAYERED GRID - PLAN OF GRID

ELEVATION OF GRID

0.866a

a

a

DOUBLE LAYERED GRID : PERSPECTIVE VIEW

SQUARE OVER SQUARE - PLAN OF GRID

ELEVATION OF GRID

a

a

(a) TWO-WAY LATTICE GRID

BASIC UNIT

PLAN

ELEVATION

(c) TWO-WAY SPACE GRID WITH SQUARE PYRAMIDS (SQUARE ON SQUARE OFFSET)

a a√2/2

(e) TWO-WAY SPACE GRID WITH SQUARE PYRAMIDS

TOP GRID

BOTTOM GRID

BRACING

ADD YOUR TEXT

ADD YOUR TEXT

(b) GRID EDGE PROFILES

a b c

d

CORNICE VERTICAL MANSARD

(a) METHODS OF SUPPORTING THE GRID

METHODS OF SUPPORTING DOUBLE-LAYERED GRIDS

(C) LOCATION OF SUPPORTS

(C) METHODS OF SUPPORTING DOUBLE-LAYER GRIDS

(C) LOCATION OF SUPPORTS

METHODS OF SUPPORTING DOUBLE-LAYERED GRIDS

LOCATION OF SUPPORTS

(C) METHODS OF SUPPORTING DOUBLE-LAYER GRIDS

(C) LOCATION OF SUPPORTS

PLANAR TRUSSES ON LATTICE GRID

A) ONE WAY ACTION :

B) TWO WAY ACTION :

PLANAR TRUSSES ON LATTICE GRID

C) THREE WAY ACTION :

PLANAR TRUSSES ON LATTICE GRID

MULTILAYER SYSTEMS ( Double layer systems )

KEY PLAN

M.S. COLUMN CAPITAL

M.S. COLUMN 300 Ø

4000

500

11000

INCLINED MEMBER 50 Ø M.S. PIPE

BOTTOM CHORD50 Ø M.S. PIPE

TOP CHORD50 Ø M.S. PIPE

500 500 500 500 500 500

PART PLAN AT – A

50 Ø M.S. BOTTOM CHORD

4 MM THICKM.S. CONNECTINGPLATE

500X500 M.S.COLUMNCAPITAL

50 Ø M.S. TOP CHORD

300 Ø M.S.COLUMN

SECTION

M.S. COLUMN CAPITALDISTRIBUTERS POINTLOAD ACTING ON IT

FIBRE GLASS ROOFING M.S. ANGLE 50X50X6

TOP CHORD M.S. PIPE 50 Ø

CONNECTING PLATE M.S. 4 MM THICK

INCLINED MEM.30 Ø M.S. PIPE

M.S. COLUMN300 Ø

CONNECTING PLATEM.S. 4 MM THICK BOTTOM CHORD

50 Ø M.S. PIPE

Ajay/pentium 4/ D - Drive

CONNECTIONS IN DOUBLE LAYERED SPACE STRUCTURS :

• A No. of members meet at a joint in a Two layered Grid Space Structures. Accordingly, jointing of these members at a joint poses problems due to congestion of members. A no. of standard methods are adopted to provide jointing. Some of the methods adopted are illustrated in the sketches that follow.

Mero System - (developed in Germany in 1940) :

• This system consists of prefabricated tubular steel components screwed into forged spherical steel connectors known as Mero tubes and Mero balls respectively. The Mero joint enables upto18 members to be joined together without any eccentricity. The connectors do not requires any site welding and are capable of creating any shape of space structure merely by being screwed together.

KK – SYSTEM (MERO)

NODE

HOLE FOR INSERTION OF BOLT

WELDED SEAM

SLEEVE

DOWEL PIN

TUBEEND CONE

THREADED BOLT

MERO JOINTING SYSTEM – JOINTING DETAILS AT BOTTOM CHORD

THE TRIODETIC SYSTEM

TUBE

BOLT

CHORD MEMBER

SLOT JOINT

NUT

PLATE JOINT SYSTEM

VIEW B – B

WEB MEMBER

BOLT

TUBE

TUBE

RETAINING WASHER

CHORD MEMBER

TUBE

WEB MEMBER

RETAINING WASHER

SLOT JOINT

SECTION A –A

TYPICAL TRIODIC JOINT CONFIGURATIONS

(1) (2) (3)

(6)(5)(4)

STEEL SKELTEL DOUBLE GRID SPACE FRAMES – ALTERNAT JOINTING DETAILS