Tos syllabus

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PRE FABRICATED

MODULAR STRUCTURES

GUIDED BY:SOUMYA MISSASST PROFFESSOR,UKFCET, KOLLAM

PRESENTED BY:FAIZAL.A.M7TH SEMESTERCIVIL ENGINEERINGUKFCET, KOLLAM

Contents

Introduction

Features

Comparison

Design concept

Components

Types of precast system

Design consideration

Equipments

Assembling

scheduling

Advantages

Limitations

Conclusion

references

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Introduction

The concept of precast structures also known as prefabricated/modular structures.

The structural components are standardized and produced in plantsin a location away from the building site.

Then transported to the site for assembly.

The components are manufactured by industrial methods based onmass production in order to build a large number of buildings in ashort time at low cost.

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Features

The division and specialization of the human workforce.

The use of tools, machinery, and other equipment, usually automated, in the production of standard, interchangeable parts and products.

Compared to site-cast concrete, precast concrete erection is faster and less affected by adverse weather conditions.

Plant casting allows increased efficiency, high quality control and greater control on finishes.

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Comparison

Site-cast

no transportation

the size limitation is depending on the elevation capacity only

lower quality because directly affected by weather

proper, large free space required

Precast at plant

transportation and elevation capacity limits the size-

higher, industrialized quality – less affected by weather

no space requirement on the site for fabrication

unlimited opportunities of architectural appearance

option of standardized components

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Design concept for precast concrete buildings

The design concept of the precast buildings is based on

1.build ability.

2.economy 3.standardization of precast components.

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Precast concrete structural elements

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Precast slabs

Precast Beam & Girders

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Precast Columns

Precast Walls

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Precast stairs

Precast concrete StairsSteel plates supported on 2 steelbeams

Design considerations

final position and loads

transportation requirements – self load and position during transportation

storing requirements – self load and position during storing – (avoid or store in the same position as it transported / built in)

lifting loads – distribution of lifting points – optimal way of lifting (selection of lifting and rigging tools)

vulnerable points (e.g. edges) – reduction of risk (e.g. rounded edges)

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Types of pre cast system

1. Large-panel systems

2. Frame systems

3. Slab-column systems with walls

4. Mixed systems

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box-like structure.

both vertical and horizontal elements are load-bearing.

one-story high wall panels (cross-wall system / longitudinal wall system / two way system).

one-way or two way slabs.

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1. Large-panel systems

2. Frame systems

Components are usually linear elements.

The beams are seated on corbels of the pillars usually with hinged-joints (rigid connection is also an option).

Joints are filled with concrete at the site.

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3.Lift-slab systems

- partially precast in plant (pillars) / partially precast on-site (slabs).

- one or more storey high pillars (max 5).

- up to 30 storey high constructions.

- special designed joints and temporary joints.

-slabs are casted on the ground (one on top of the other) – then lifted with crane or special elevators.

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Lift-slab procedure

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1. pillars and the first package (e.g. 5 pieces) of slabs prepared at ground level2. lifting boxes are mounted on the pillars + a single slab lifted to the first floor level3-8. boxes are sequentially raised to higher positions to enable the slabs to be lifted to their requiredfinal position - slabs are held in a relative (temporary) positions by a pinning system

Planning traffic route

How long transporter vehicle is required?

What is the required load capacity of the transporter vehicle?

What is the maximum vertical extension of the shipment

Routs on the site

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• Is route permission required?

Equipmentscranes:

mobile crane

tower crane (above 3stories)

lifting tools:

spreader beams

wire rope slings

rigging tools:

eye bolt

shakles

hooks17

Assembling….

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Column to column connection

Beam to column connection

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Beam-slab joints

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Precast concrete structure consisting of solid wall panels and hollow core slabs.

Wall to slab connection

Advantages

Quick erection timesPossibility of conversion, disassembling

and moving to another sitePossibility of erection in areas where a traditional

construction practice is not possible or difficultLow labor intensivityReduce wastage of materialsEasier management of construction sitesBetter overall construction quality Ideal fit for simple and complex structures

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Limitations

size of the units.

location of window openings has a limited variety.

joint details are predefined.

site access and storage capacity.

require high quality control.

enable interaction between design phase and production planning.

difficult to handling & transporting.

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Scheduling

some approximate data for installation

emplacement of hollow core floor slabs - 300 m2/day

erection of pillars/columns - 8 pieces/day

emplacement of beams - 15 pieces/day

emplacement of double tee slabs - 25 pieces/day

emplacement of walls - 15 pieces/day

construction of stair and elevator shafts - 2 floors/day

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Examples….

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The hospital will feature multi-trade prefabricated racks in the corridors, anapproach that is still new in the U.S.

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Miami Valley Hospital Dayton,OH

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Conclusion

oThe use of prefabrication and preassembly is estimated to have almost doubled in the last 15 years, increasing by 86%.oThe use of precast concrete construction can significantly reduce the amount of construction waste generated on construction sites.o Reduce adverse environmental impact on sites.o Enhance quality control of concreting work.o Reduce the amount of site labour.o Increase worker safety .o Other impediments to prefabrication and preassembly

are increased transportation difficulties, greater inflexibility, and more advanced procurement requirements.

LARGE SPAN STRUCTURES

LARGE SPAN STRUCTURES

Large Span Systems

Large span systems are structural systems whose dimensions exceed thelimits of standardbeams and slabs and thus require changes totheir

geometry, configuration, or shape.

In general, long span systems tend towards a handfull of basic types, relying on principles of bending, compression,

tension to carry roof or floor loads over large distances.

Large-span structures createunobstructed, column-free spaces greater than 30 m (100 feet) for avariety of functions.

The most common types are :

or

simple beam

space frame

gable frame

folded platescable stayed

truss

pre-stressed beam

suspension

pneumatic

arch castellated beam

Large span structures are the structures that provide large column free spaces.

They are used in roofs for halls & other hall type structures.

They are composed of steel in the form of truss system.

They are quiet strong in nature

They are unique because of their aesthetic properties..

For example they are used in airport, railway station, stadium, assembly hall, godown & temple etc.

Materials suitable for various forms of long span and complex structure span and complex structure

1. All reinforced concrete including precast

2. All metal (e.g. mild-steel, structural steel, stainless steel or alloyed alumimum,

3. All timber

4. Laminated timber

5. Metal/RC combined

6. Plastic-coated Textile material

7. Fiber reinforced plastic

Common Structural Forms Common Structural Forms for Long Span Building Structures for Long Span Building Structures

1. Insitu RC, tensioned

2. Precast concrete, tensioned

3. Structural steel – erected on spot

4. Structural steel – prefabricated and installed on spot

5. Portal frame – insitu RC

6. Portal frame – precast

7. Portal frame – prefabricated steel

Large span structures can be constructed by-

Shell structures.

Folded plate.

Trusses

Steel space frame.

Coffered slab

SHELL STRUCTURES

A SHELL STRUCTURE IS A THIN CURVED MEMBRANE OR SLAB USUALLY OF REINFORCED CONCRETE THAT FUNCTIONS BOTH AS STRUCTURE AND COVERING.

THE TERM “SHELL” IS USED TO DESCRIBE THE STRUCTURES WHICH POSSESS STRENGHT AND RIGIDITY DUE TO ITS THIN, NATURAL AND CURVED FORM SUCH AS SHELL OF EGG, A NUT, HUMAN SKULL, AND SHELL OF TORTISE

It transmits load more than 2 directions to support.

It is highly efficient.

Shaped, proportioned & supported

It transmits load without bending or twisting.

Its thickness is small compared to its other dimension.

Deformation not large as compared to its thickness.

Consist of shearing stress which should be normal to the middle surface and should be negligible

Application: Used in fuselages of aero plane, boat hulls, roof structures.

• .. SHELLS OCCURING IN NATURE

Depending upon the geometry of middle surface the shells can be classified as :

1.Domes

2.Shell Barrel Arch / Vault

3.Translation shells

4.Ruled Surfaces shell

DOMES Are hemispherical in shape.

Used as roof structure.

Constructed of stone , concrete & brick.

Supported on circular / regular polygon shaped walls.

Have certain height & diameter ratio.

Have very small thickness.

Can b constructed with or without lanterns.

Are of 2 types:

i. Smooth shell domes & ii Ribbed shell domes RIBBED SHELL DOMES

SMOOTH SHELL DOMES

TYPES OF DOMES

SPHERICAL DOMES TRIANGULAR DOME

CYLINDERICAL DOME RECTANGULAR DOME

SHELL BARREL VAULT Is an Arched form.

Used to provide a space with ceiling or roof.

Elements of barrel shell:

*Curved membrane

*Tension zone

*Rise

*Span

*Width

*Edge beams

*End frame of diaphragm

TYPES OF SHELL VAULTS

MULTI BARREL VAULT CANTILEVER BARREL VAULT

SHORT SPAN BARREL VAULT NORTH LIGHT BARREL VAULT

TRANSLATION SHELL Is a type of shell structure.

Dome set on four arches

Different from spherical dome

Easier to form than spherical dome

Obtained by moving a vertical curve parallel to itself along another vertical curve usually in plane at right angles to the plane of sliding curve.

High tension forces in the corner.

Special cases are:

1.Cylindrical shell &

2. Hyperbolic paraboloid

HYPERBOLIC PARABOLOID

Is a special case of translation shell.

Obtained by sliding a vertical parabola with upward curvature on another parabola with downward curvature in a plane at right angles to the plane of first.

Carries load on 2 directions.

Diagonal element sags in tension

Other element is an arch which is in compression.

Consist of saddle surface.

STEEL SPACE FRAMES Are used in the form of grids of rectangular,

diagonal , triangular or hexagon pattern, arches domes &other large column free areas.

Highly efficient.

Obtained by connecting the parallel trusses, not by flexible elements but by transverse trusses as rigid as the main truss.

Deflection of the truss is transmitted to the adjoining trusses & the entire roof works act more or less monothically.

Such special systems of hinged bar are called SPACE FRAMES.

Offers an economical solution to roofing of large rectangular areas.

Are stiffer than system of parallel trusses.

Shallower in depth .

TYPES OF SPACE FRAMED SYSTEMS

BRACED BARREL VAULT STRUCTURE

The braced double layer barrel vault is composed of member elements arranged on a cylindrical surface. The basic curve is a circular segment; occasionally, a parabola, ellipse or funicular line may also be used.

Its structural behavior depends mainly on the type and location of supports, which can be expressed as L/R, where L is the distance between the supports in longitudinal direction and R is the radius of curvature of the transverse curve

RIBBED DOME STRUCTURE

Ribbed dome is the earliest type of braced dome that has been constructed . A ribbed dome consists of a number of identical meridional solid girders or trusses, interconnected at the crown by a compression ring. The ribs are also connected by concentric rings to form grids in trapezium shape. The ribbed dome is usually stiffened by a steel or reinforced concrete tension ring at its base.

GEODESIC DOMED STRUCTURE

The framework of these intersecting elements forms a three-way grid comprising virtually equilateral spherical triangles

HIPPED END STRUCTURE

is a type of roof where all sides slope

downwards to the walls, usually with a

fairly gentle slope. Thus it is a house with

no gables or other vertical sides to the roof.

A square hip roof is shaped like a pyramid.

Hip roofs on houses could have two

triangular sides and two trapezoidal

ones. A hip roof on a rectangular plan has

four faces. They are almost always at the

same pitch or slope, which makes them

symmetrical about the centerlines

https://en.wikipedia.org/wiki/Roof

https://en.wikipedia.org/wiki/House

https://en.wikipedia.org/wiki/Gable

https://en.wikipedia.org/wiki/Pyramid

POLYGONAL DOMED STRUCTURE

ADVANTAGES OF SPACE FRAMES One of the most important advantages of a

space structure is its lightweight. This is mainly due to the fact that the material is distributed spatially in such a way that the load transfer mechanism is primarily axial — tension or compression.

Space frames can be built from simple prefabricated units, which are often ofstandard size and shape. Such units can be

easily transported and rapidly assembled on site by semi-skilled labor. Consequently,

space frames can be built at a lower cost. A space frame is usually sufficiently stiff in spite

of its lightness. This is due to its three dimensional character and to the full participation of its constituent elements.

Space frames possess a versatility of shape and form and can utilize a standard module to generate various flat space grids, latticed shell, or even free-form shapes.

What is the difference between truss and frame?

1. Truss is essentially a frame and is fabricated using the structural steel.2. Truss is a flexural member and is normally used for supporting a roof.3.Truss is composed of many triangles connected together .4. Frames, on the other hand have right angles between different members ( such as a door fame , window frame, portal frame )

1- The joints in a truss are pinjointed whereas in case of frames rigid joints are provided by bolting or welding. In a truss, the joints are pin type joints and the members are free to rotate about the pin. As such, a truss cannot transfer moments and members are subjected to only axial forces (tensile and compression). On the other hand, members of frames are connected rigidly at joints by means of welding and bolting. Therefore the joints of frames can transfer moments in addition to the axial loads.

2- Truss memebers are designed for axial force(tensile or compression) only i.e. there is no bending moment in trusses while on the other hand frames are designed shear force and bending moment

Trusses are 2 dimensional. Space frame 3-d

In a practical setting, you may see trusses with no flexibility in joints, but it is still acceptable to analyze them as a perfect truss.

FOLDED PLATE STRUCTURES

Consist of series of thin planer elements.

Flat plates are connected to one another along their edges.

Used in long span especially for roofs.

Give mutual support to each other.

Plates may be continuous over their supports longitudinally.

Capable of transmitting both moment & shear or only shear.

These plates carry the load from slab longitudinally to the support.

The support must be capable of resisting both horizontal & vertical forces.

Beam theory may be applied to design if the span is long.

TYPES OF FOLDED PLATE

PRISMATIC: if they consist of rectangular plates.

PYRAMIDAL: when consists of non-rectangular plates.

PRISMOIDAL: triangular or trapezoidal.

FOLDED PLATE BEHAVIOR

Each plate is assumed to act as a beam in its plane ,this assumption is justified when the ratio ofThe span “length” of the plate to its height“width” is large enough . But when this ratio is small,the plate behaves as a deep

beam.

COFFERED SLAB STRUCTURES A coffer in architecture is a sunken panel in the shape of a

square, rectangle, or octagon in a ceiling, or vault.

A series of these sunken panels were used as decoration for a ceiling or a vault.

Also known as caissons ('boxes"), or lacunaria ("spaces, openings").

The strength of the structure is in the framework of the coffers.

The stone coffers which is cut in soft tufa-like stone reproduces a ceiling with beams and cross-beams lying on them, with flat panels fillings the lacunae.

Wooden coffers were first made by crossing the wooden beams of a ceiling.

Experimentation with the possible shapes of coffering, which solve problems of mathematical tiling, or tessellation, were a feature of Islamic as well as Renaissance architecture.

The more complicated problems of diminishing the scale of the individual coffers were presented by the requirements of curved surfaces of vaults and domes.

Example of Roman coffering, employed to lighten the weight of the dome, can be found in the ceiling of the rotunda dome.

TRUSSES A truss is a structural frame based on the geometric rigidity of the triangle.

Linear members are subjected only to axial tension and compression. They support load much like beams but for larger spans.

To prevent secondary shear and bending stresses from developing, the centroidalaxes of the truss members and the load at a joint should pass through a common point

Different types of Wooden and Steel Roof Trusses:

King Post Truss

Queen Post Truss

Howe Truss

Pratt Truss

Fan Truss

North Light Roof Truss/ SAWTOOTH TRUSS

Quadrangular Roof Truss

Tubular Steel Roof Truss

Tubular Monitor Steel Roof Truss

King Post Truss

•King Post Truss is a wooden truss.

•It can also be built of combination of wood

and steel.

•It can be used for spans upto 8m.

Queen Post Truss

•Queen Post Truss is also a wooden

truss.

•It can be used for spans upto 10m.

Howe Truss

•It is made of combination of wood and

steel.

•The vertical members or tension members

are made of steel.

•It can be used for spans from 6-30m.

Pratt Truss

•Pratt Truss is made of steel.

•These are less economical than the Fink

Trusses.

•Vertical members are tension and diagonal

members are compression.

•Fink Trusses are very economical form of roof

trusses.


Fan Truss

•It is made of steel.

•Fan trusses are form of Fink roof truss.

•In Fan Trusses, top chords are divided into

small lengths in order to provide supports for

purlins which would not come at joints in Fink

trusses.


North Light Roof Truss

•When the floor span exceeds 15m, it is generally more

economical to change from a simple truss arrangement to one

employing wide span lattice girders which support trusses at right

angles.

•In order to light up the space satisfactorily, roof lighting has to

replace or supplement, side lighting provision must also be made

for ventilation form the roof.

•One of the oldest and economical methods of covering large areas

is the North Light and Lattice girder.

•This roof consists of a series of trusses fixed to girders. The short

vertical side of the truss is glazed so that when the roof is used in

the Northern Hemisphere, the glazed portion faces North for the

best light.


•Used for industrial buildings, drawing rooms etc.

Quadrangular roof Trusses

• These trusses are used for large spans such as railway sheds and Auditoriums.

LARGE SPAN TRUSSESTUBULAR STEEL ROOF TRSSES are

used for large span constructions such as

factories, industry worksheds, shopping

malls, huge exhibition centres, multiplexes

etc. They are generally used for spans as

large as 25-30m.

Advantages of Tubular Steel Roof Trusses

• Structures designed for material handling equipments (e.g., a bridge and a tower crane) where weight savings may be very substantial economic consideration.

• 30% to 40% less surface area than that of an equivalent rolled steel shape. Therefore, the cost of maintenance, cost of painting or protective coatings reduce considerably.

• The moisture and dirt do not collect on the smooth external surface of the tubes. Therefore, the possibility of corrosion also reduces.

• The ends of tubes are sealed. As a result of this, the interior surface is not subjected to corrosion. The interior surface do not need any protective treatment.

• They have more torsional resistance than other section of the equal weight.

• They have a higher frequency vibrations under dynamic loading than the other sections including the solid round one.

•The Vierendeel truss/girder is characterized by having only vertical members between the top and bottom chords and is a statically indeterminate structure. Hence, bending, shear and axial capacity of these members contribute to the resistance to external loads. •The use of this girder enables the footbridge to span larger distances and present an attractive outlook. •However, it suffers from the drawback that the distribution of stresses is more complicated than normal truss structures.

VIERENDEEL TRUSS

•Elements in Vierendeel trusses are subjected to bending, axial force and shear , unlike conventional trusses with diagonal web members where the members are primarily designed for axial loads

DISADVANTAGES•Vierendeel trusses are usually more expensive than conventional trusses.•Their use limited to instances where diagonal web members are either obtrusive or undesirable•but the resulting joints are often very heavy in appearance.

LOAD DISTRIBUTIONVierendeel trusses are moment resisting. Vertical members near the supports are subject to the highest moments and therefore require larger sections to be used than those at mid-span. Considerable bending moments must therefore be transferred between the verticals and the chords, which can result in expensive stiffened details.

ADVANTAGES•The joints may be heavy, but the absence of diagonals makes this form suitable for storey-height construction.•Using standard computer programs, the analysis is not difficult, However the system does allow full storey-height construction without obstruction to openings.

Vierendeel bridge at Grammene, Belgium

TENSILE STRUCTURES

The term ‘tensile structures’ covers a broad category of structures:•Fabric membranes•Pre-stressed cable nets•Cable beams in form of trusses and girders

•Although compression, bending and shear maybe present in some of these structures, tension stress is more prominent.•Compared to bending and compression , tensile elements are more efficient as they use the material to its full capacity.•Bending elements use only half the material effectively, since bending stress varies from compression to tension with zero stress at neutral axis.•Compression elements are subjected to bucking of reduced capacity as slenderness increases. •However, the efficiency of tensile structures depends greatly on the type of support.

Tensile structures are characterized by the

prevalence of tension force in their structural

systems and by limitation of compression

Forces to a few support members. Thus

These lightweight structures do not require

The considerable amount of construction

Material to absorb the Buckling and bending

Moments in compression members.

Tension

Compression

Elements of a membrane structure:•Highly flexible fabric held under tension in order to generate stiffness in surface•One-dimensional flexible elements i.e. ties or cables to creates ridges, valleys and edge boundaries•Rigid support members sustaining compression/bendingNote: Cable structures are constructed using a combination of the first two elements.Cable structures can be tensioned by applying direct axial forces to the cables or by loading free suspended cables with heavy cladding/decking.

Three main categories:•Boundary tensioned membranes•Pneumatic structures•Pre-stressed cable nets and beams

Boundary Tensioned Membranes

•Lightweight (typically 0.7–1.4 kg/m2 ), highly flexible membranes with a level of pre-tension which generates stiffness in the surface.•The overall equilibrium of the structure is provided by rigid edges and supporting members generally subjected to compression and/or bending.•Under imposed load due to snow or wind, the fabric surface undergoes large displacements and a consequent increase in the material stress, which can increase up to ten fold. For this reason a safety factor higher than four is highly recommended.•Membrane structures are basically realised with coated fabrics, with growing interest towards open mesh coated fabrics and foils.•Coating layer can be of either PVC, PTFE (polytetrafluroethlyene) or PVDF (polyvinylidinedifluride)

Pneumatic Structures

•The term pneumatic structures includes all the lightweight structures in which the load bearing capacity is achieved by means of air under pressure. •They are mainly subdivided into two categories: the buildings characterised by a single layer, stabilised by a slight difference in pressure between the inside and the outside of the structures, and the building envelopes stabilised by air under pressure enclosed between two or more membrane layers.•Air-supported structures provide a cost effective alternative for seasonal wide span coverings, nevertheless, the reduced resistance under bad weather conditions combined with high costs due to great pressure losses, reduced insulation, maintenance and the seasonal mounting and dismounting costs can progressively reduce the initial convenience over the entire life span

Pre-stressed Cable Nets, Beams and Domes

•Cable structures are load bearing structures composed of linear flexible elements under tension, with the only exception being rigid members or supports such as rigid ring beams or masts. •They can be subdivided in cable nets, which describe three-dimensional surfaces, cable domes and their two-dimensional version represented by cable trusses.•Cable nets share the basic physical principles which regulate their equilibrium and shape with the boundary tensioned membranes described above. •Cable domes are based on a slightly different structural scheme which is generally circular in plan and based on radial trusses made of cables with the only exception of vertical compression struts. •Cable trusses mostly present a planar structure, with a top cable and a bottom cable with a considerable cross-sectional area due to their load bearing function.•The load bearing capacity of pre-stressed cable nets, domes and beams depends on the geometry chosen, the level of pre-stress and the allowable deformation and fatigue strength of each member, the higher the pre-tension the lower the deflection under external loads, but with a consequent increase in costs and material stress.

Cables can be of mild steel, high

strength steel , stainless steel or

polyester or aramid fibres.

Structural cables are made of a series

of small strands twisted or bound

together to form a much larger cable.

The tensioned members are termed as

cables are group of wires, strands or ropes.

A wire is a continuous length of steel that

has a circular cross section. Cables do not

loose strength in

case of failure of one wire. The wires in the

strand are zinc coated and stranded into

helix whichforms a regular cross section.

Cables

Cable Stayed Structures

•Usually used in bridges.•Adaptation of suspension bridge principle.•The deck structure is supported by tension stays sloping from one or more towers. •There may be either a single plane of stays down the centre of the bridge, or two planes; one on each side of the bridge.•The towers act in compression and can have a variety of forms (A-frame, H-frame or columns). The deck girders sustain compression forces as well as bending forces.•Economic spans range from 200m to over 850m, and as such cable-stayed bridges fill the gap between large arches / trusses and small suspension bridges.•Span/depth ratio is an important design factor-A shallow depth results in great tension and compression in stays and beams respectively, a steep slope has opposite effect.

Cable Suspended Structures

•Used for long-span roofs.•Suspended cables effectively resist gravity loads in tension burt are unstable under wind uplift and uneven loads.•Suspended Structures are those with horizontal planes i.e. floors are supported by cables (hangers) hung from the parabolic sag of large, high-strength steel cables. The strength of a suspended structure is derived from the parabolic form of the sagging high strength cable.To make this structure more efficient, the parabolic form is so designed that its shape closely follows the exact form of the moment diagrams.•The large curving cable may consist of many smaller cables which are tightly spun together. As the cables are being spun together, they are also stretched over the span and attached to the supports.

•Stadiums•Stages•Covered malls•Walkways•Play areas•Entrances•Atriums•Sports arenas•Airports•As fabric cladding panels

•Unique building medium.

•Lightweight and flexible, fabric interacts with and expresses natural forces.

•Fabric structures have higher strength/weight ratio than concrete or steel. Most fabrics can be A fabric structure can be designed for almost any condition, heavier fabrics and more 3 dimensional frecycled.

• forms will cope with extreme wind and snow loads.

•Translucency – In daylight, fabric membrane translucency offers soft diffused naturally lit spaces reducing the interior lighting costs while at night, artificial lighting creates an ambient exterior luminescence.

•Low Maintenance – Tensile membrane systems are somewhat unique in that they require minimal maintenance when compared to an equivalent-sized conventional building.

•Cost Benefits – Most tensile membrane structures have high sun reflectivity and low absorption of sunlight, thus resulting in less energy used within a building and ultimately reducing electrical energy costs.

•Fabric structures being mainly fabric and cables have little or no rigidity and therefore must rely on their form and internal pre-stress to perform the this function.

•As a rule of thumb spans greater than 15 metres should be avoided however, much greater spans can be achieved by reinforcing the fabric with webbing or cables.

•Loss of tension is dangerous for the stability of the structure and if not regularly maintained will lead to failure of the structure.

A space frame is a truss-like, lightweight rigid structure constructed from interlocking struts in a geometric pattern.

• A three-dimensional structures.

• The assembled linear elements are arranged to transfer the load.

• Take a form of a flat surface or curve surface.

• Designed with no intermediate columns to create large open area.

• Space frames usually utilize a multidirectional span, and are often used to accomplish long spans with few supports.

• They derive their strength from the inherent rigidity of the triangular frame; flexing loads (bending moments) are transmitted as tension and compression loads along the length of each strut.

MBS SCHOOL OF PLANNING AND ARCHITECTURE THEORY OF STRUCTURES - SPACEFRAMES IV AALANKRITA | DIVYA | GARIMA | KHUSHBOO |SHASHI | SHRISHTI

• Space frames are an increasingly common architectural technique especially for large roof spans in modernist commercial and industrial buildings

http://www.amiyaco.com/prod_space_frames.htm

http://www.amiyaco.com/prod_space_frames.htm


TYPES OF SPACE FRAMESAccording to curvature1- Flat coversThese structures are composed of planar substructures. Theplane are channeled through the horizontal bars and the shearforces are supported by the diagonals.

2- Barrel vaultsThis type of vault has a cross section of a simple arch. Usuallythis type of space frame does not need to use tetrahedralmodules or pyramids as a part of its backing.

3- Spherical domesThese domes usually require the use of tetrahedral modules orpyramids and additional support from a skin.

According to the number of grid layers1- Single-LayerAll elements are located on the surface to be approximated.

2- Double-LayerThe elements are organized in two parallel layers with eachother at a certain distance apart. The diagonal bars connectingthe nodes of both layers in different directions in space.

3- Triple-LayerElements are placed in three parallel layers, linked by thediagonals. They are almost always flat. This solution is todecrease the diagonal members length.


TYPES OF SPACE FRAME

1) Two and three-way grids

Characterized as two way or three way

2) Single, Double and Triple Layered

Single layer frame has to be singly or doubly curved.

Commonly used space frames are double layered and flat.

Triple layered is practically used for a large span building.

i. Skeleton (braced) frame work e.g. domes, barrel vaults, double and multiplier grids, braced plates. They are more popular. They are innumerable combinations and variation possible and follow regular geometric forms.

ii. Stressed skin systems e.g. Stressed skin folded plates, stressed skin domes and barrel vaults, pneumatic structures.

iii. Suspended (cable or membrane) structures e.g. Cable roofs


COMPONENTS OF SPACE FRAME

Consists of axial members : which are tubes and connectors

TUBES

1) CIRCULAR HOLLOW SECTIONS

2) RECTANGULAR HOLLOW SECTIONS

CONNECTORS

1) Tuball Node Connector

A hollow sphere made of spheroidal graphite

The end of the circular hollow section member to be connected is fitted at its ends by welding.

Connection from inside the cup is using bolt and nut.

2) Nodus Connector

• It can accept both rectangular and circular hollow sections and that the cladding can be fixed directly to the chords.

• Chord connectors have to be welded to the ends of the hollow members on site.


3) Triodetic Connector

• It consists of a hub, usually an aluminium extrusion, that has slots or key ways, which the ends of members are pressed or coined to match the slots.

4) Hemispherical Dome Connector

• Usually use for double layer domes.

• Has a span more than 40m.

• More economical for long span.

• The jointing is connect by slitting the end of the tube or rod with the joint fin.

• There are 2 types of joint, pentagonal joint and hexagonal joint.

Load Distribution

Some space frame applications include:• Hotel/Hospital/commercial building entrances

• Commercial building lobbies/atriums

• Parking canopies

Tension


METHOD OF SUPPORT

1. Support along perimeters—This is the most commonly used support location. The supports of double layer grids may directly rest on the columns or on ring beams connecting the columns or exterior walls. Care should be taken that the module size of grids matches the column spacing.

2. Multi-column supports—For single-span buildings, such as a sports hall, double layer grids can be supported on four intermediate columns . Figure 13.5a

For buildings such as workshops, usually multi-span columns in the form of grids . Figure 13.5b

Sometimes the column grids are used in combination with supports along perimeters . Figure 13.5c

Overhangs should be employed where possible in order to provide some amount of stress reversal to reduce the interior chord forces and deflections. Figure 13.6

3. Support along perimeters on three sides and free on the other side—For buildings of a rectangular shape, it is necessary to have one side open, such as in the case of an airplane hanger or for future extension.


Advantages of space frame systems over conventional systems:

• Random column placement

• Column-free spaces

• Minimal perimeter support

• Controlled load distribution

• Design freedom

• Supports all types of roofing• Light• Elegant & Economical• Carry load by 3D action.• High Inherent Stiffness• Easy to construct• Save Construction Time & Cost• Services (such as lighting and air conditioning) can be integrated with space

frames• Offer the architect unrestricted freedom in locating supports and planning the

subdivision of the covered space.


Advantages of Space Frames

1. LightweightThis is mainly due to the fact that material is

distributed spatially in such a way that the loadtransfer mechanism is primarily axial; tensionor compression. Consequently, all material inany given element is utilized to its full extent.Furthermore, most space frames are nowconstructed with aluminum, which decreasesconsiderably their self-weight.

2. Mass ProductivitySpace frames can be built from simpleprefabricated units, which are often of standardsize and shape. Such units can be easilytransported and rapidly assembled on site bysemi-skilled labor. Consequently, space framescan be built at a lower cost.

3. StiffnessA space frame is usually sufficiently stiff in

spite of its lightness. This is due to its three-dimensional character and to the full participation of its constituent elements.

4. VersatilitySpace frames possess a versatility of shape

and form and can utilize a standard module togenerate various flat space grids, latticed shell,or even free-form shapes. Architectsappreciate the visual beauty and theimpressive simplicity of lines in space frames.


Disadvantages of Space Frames

1. CostThe main criticism of space grids is their cost, which can

be high when compared with alternative structural systems. This is particularly true when space grids are used for short spans.

2. Visually busy structuresVisually, space grid structures are very 'busy'. They are

rarely seen in plan or in true elevation and at some viewing angles the lightweight structure can appear to be very dense. Grid size and depth as well as the grid configuration can have considerable influence on the perceived density of the structure.

3. Longer erection timesThe number and complexity of joints can lead to longer

erection times on site. This is obviously very dependent on the system being used and the grid module chosen.

4. Large surface areaWhen space grids are used to support floors some form

of fire protection may be required. This is difficult to achieve economically due to the high number and relatively large surface area of the space grid elements


SHASHI | SHRISHTI

SPACE FRAME METHODS OF ERECTION• The method chosen for erection of a space frame depends on its behavior of load

transmission and constructional details, so that it will meet the overall requirements of quality,

safety, speed of construction, and economy.

• The scale of the structure being built, the method of jointing the individual elements, and the strength and rigidity of

the space frame until its form is closed must all be considered.

1- SCAFFOLD METHODIndividual Elements are Assembled in Place at

Actual Elevations, members and joints or

prefabricated subassembly elements are

assembled directly on their final position. Full

scaffoldings are usually required for this type of

erection. Sometimes only partial scaffoldings

are used if cantilever erection of space frame

can be executed. The elements are fabricated at

the shop and transported to the construction

site, and no heavy lifting equipment is required.

2. BLOCK ASSEMBLY METHOD

The space frame is divided on its plan into individual strips or blocks. These

units are fabricated on the ground level, then hoisted up into its final

position and assembled on the temporary supports. With more work

being done on the ground, the amount of assembling work at high

elevation is reduced. This method is suitable for those double-layer grids

where

the stiffness and load-resisting behavior will not change considerably after

dividing into strips

or blocks, such as two-way orthogonal latticed grids, orthogonal square

pyramid space grids, and the those with openings. The size of each unit

will depend on the hoisting capacity available.


SHASHI | SHRISHTI

EXAMPLES OF POPULAR BUILDINGS WITH SPACEFRAMES

INDIAN HABITAT CENTRE , LODHI ROAD JEEVAN BHARTI BUILDING, CP

HALL OF NATIONS, PRAGTI MAIDAN STANSED AIRPORT, LONDON

RAILWAY STATIONS SUPPORTED BY BARREL VAULT STRUCTURE LOUVRE PYRAMID, LOUVRL PALACE, PARIS


SHASHI | SHRISHTI

JOINTING SYSTEMS AND TERMINOLOGYJOINTING SYSTEMS• The jointing system is an extremely important part of a space frame design. The joints for the space frame are more important than the

ordinary framing systems because more members are connected to a single joint

• Also, the members are located in a three dimensional space, and hence the force transfer mechanism is more complex

• The type of jointing depends primarily on the connecting technique, whether it is bolting, welding, or applying special mechanical

connectors. It is also affected by the shape of the members.

• This usually involves a different connecting technique depending on whether the members are circular or square hollow or rolled steel

sections.

• Requirements considered for designing the jointing systems :-The joints must be strong and stiff, simple structurally and mechanically, and

easy to fabricate without recourse to more advanced technology and joints of space frames must be designed to allow for easy and

effective maintenance

• All connectors can be divided into two main categories: the purpose-made joint and the proprietary joint used in the industrialized system

of construction

• Purpose-made joints-usually used for long span structures where the application of standard proprietary joints is limited.

Example -cruciform gusset plate for connecting rolled steel sections.

• All the connection techniques can be divided into three main groups: (1) with a node

(2) without a node, and (3) with prefabricated units.

TERMINOLOGIES• Aspect ratio: Ratio of longer span to shorter span of a rectangular space frame.

• Braced (barrel) vault: A space frame composed of member elements arranged on a

cylindrical surface.

• Braced dome: A space frame composed of member elements arranged on a spherical surface.

• Depth: Distance between the top and bottom layer of a double layer space frame.

• Double layer grids: A space frame consisting of two planar networks of members forming the top and bottom layers parallel to each other

and interconnected by vertical and inclined members.

• Geodesic dome: A braced dome in which the elements forming the network are lying on the great circle of a sphere.

• Lamella: A unit used to form diamond shaped grids, the size being twice the length of the side of the diamond.

• Latticed grids: Double layer grids consisting of intersecting vertical latticed trusses to form regular grids.

• Latticed shell: A space frame consisting of curved networks of members built either in single or double layers.

• Latticed structure: Astructuralsystemintheformofanetworkofelementswhoseload-carrying mechanism is three-dimensional in nature.

• Local buckling: A snap-through buckling that takes place at one point.

• Module: Distance between two joints in the layer of grid.

• Space frame: A structural system in the form of a flat or curved surface assembled of linear elements so arranged that forces are transferred

in a three-dimensional manner.

• Space grids: Double layer grids consisting of a combination of square or triangular pyramids to form offset or differential grids.

• Space truss: A three-dimensional structure assembled of linear elements and assumed as hinged joints in structural analysis.

Arunima G

Prabhnoor S

Raunak R

Saurabh K

Sudhanshu M

Tanvi G

Steel Trusses

Steel Trusses

Introduction

• Steel trusses were taken up as against wooden trusses because the scarcity of quality timber was increasingin manyareas.

• Steel is also a superior building construction material when compared to wood. Unlike timber, it is a

homogenous and isotropic material, i.e. it has same characteristics in all directions.

• Another major advantage steel provides in roof trusses is that it is much lighter and often more economical inlarge roof systems.

Tension

Steel Trusses

Roof truss design

The following are the conditions that influence the design of a roof truss:

1. Loads:

Roof trusses are especially adapted to such buildings where they support the roof and still afford a clear space without the use of

intermediate columns. They support loads of various kinds, such as the dead load, due to the weight of material used in constructing

and covering the roof, the wind load, the snow load, and frequently the weight of plastered ceilings, as well as loads from

attic floors and from suspended platforms and galleries. In laying out the stress diagrams, all these loads are considered, and

both members and details are then proportioned to withstand the various stresses produced. Purlins, that rest on and connect the

trusses at their panel points, or points at which the main rafter and the web members intersect. These purlins support the rafters of

the roof, on which the wood sheathing and roofing material are placed. In iron and steel construction I beams and Z bars are

generally employed. Great care should be taken to avoid, as far as possible, the accidental stresses to which trusses are so often

subjected during erection, and which can scarcely be calculated.

2. Slope of Roof:

The character of the roofing material must be considered in determining the direction of the upper chord.

For instance, when shingles are used, the pitch should not be less than 1 of rise to 2 of run, while with slates if the pitch is less

than 1 to 3, the wind is liable to blow the rain under the slate, thereby causing leaks. A slope of 1 to 2, however, is preferable for slate,

although, when occasion requires, the minimum pitch of 1 to 3 may be employed. Corrugated iron is liable to leak if laid with a

pitch of less than 1 to 3, while in a gravel and tar roof, if the slope is greater than 1 to 4, the heated tar is apt to run down

and collect at the lower portion of the roof, leaving the upper part exposed and unprotected, and rain falling on such a roof flows

off so quickly that the pebbles are washed out of the roofing.Flat clay tile set in asphalt may be used on flat roofs, but clay and metal tile simulating corrugated or Spanish tile are usually

laid with a pitch somewhatgreater than 1 to 2.

Steel Trusses

Roof truss design

3. Distance between Trusses:

The fact that the economy of the design is so largely dependent on the spacing of the trusses, makes it necessary that an

effort be made to ascertain the distance that may most economically exist between them. This is especially the case when the

building over which they are to be placed is of sucha character that the spacing of the trusses governs, or, at least, affects the

exterior design. Often, too, the engineer is restricted by the fact that the size of the lot must be considered when determining the size

of the building, and hence, the distance between the trusses is influenced to a certain degree, particularly when architectural effect is

desired.

4. Material used:

The general design of a truss is influenced by the material employed in its construction, and the choice of material is influenced by

its cost and availability, as well as by the span of the truss and the loadsthat come on it. When the span exceeds 80 feet, and the loads

are comparatively heavy, steel is usually the best material to use; but if steel is unavailable, timbermay be used for trusses having

spans as great as 150 feet. When timber trusses have as great a spanas this, they are usually arched, and built in pairs. While steel may

be used for the construction of trusses of all spans,great and small, the designer is frequently compelled to use timber because the

cost of the work is limited.

5. After the general dimensions of the roof truss have been determined, if economy is to be considered, the cost mustbe

investigated. Should the conditions admit a choice of several designs, it is often desirable to estimate the cost of each, and

adopt the one whose construction costs the least. In designing trusses it is generally cheaper to use stock sizes of timber or steel

shapes, for by so doing,even though the members are of a larger size than actually required, the work is usually facilitated to such

an extent that the time required in its performance is materially reduced, which is frequently a factorof the utmost importance.

Steel Trusses

System options

Steelsections are available in many different extrusion types and systems, the following may be used for steel roof trusses:

Angle and flat bar truss:

• Small angle bars may be welded directly onto each other forming very

light trusses up to about 12 m span.• The length of the compression members mustbe reduced as muchas

possible to avoid buckling. This results in trusses with a large numberof

diagonals and connections.

• Examples: Fink or Polonceau Truss.

Steel tube truss:

• Steel tubes are readily available throughout the world and at reasonable

prices, since they are also used for steel pipes and piping systems.

• The jointing of the round surfaces is difficult; butt and fillet welding of

properly cut and shaped tubes is possible but slow and expensive.

• When using tubes, the number of connections per truss should be

reduced as much as possible.

Steel Trusses

System options

Rolled sections truss:

• Rolled sections other than angle bars used in truss designs are the

channeland universal beams.

• Half-section universal beams are particularly useful in truss design but are

not readily available.

• Used in trusses of spans larger than 12 m.

Rectangularhollow section truss:

•

•

RHS providea particularly neat appearance of steel trusses.

Welded connections are common thanks to the regular shapes of the

RHS.

• RHS are particularly expensive and are not readily available in many

countries.

PINNED/BOLTED CONNECTIONS

TYPICALLY, THE JOINT CONNECTIONS ARE FORMED BY BOLTING OR WELDING THE END MEMBERS TOGETHER TO A COMMON PLATE, CALLED A GUSSET PLATE.

JOINING DETAILS

Generally in steelwork construction, bolted site splices are preferred to welded splices for economy and speed of erection.

•CHORDS The outer members of a truss that defi ne the envelope or shape.• TOP CHORD An inclined or horizontal member that establishes the upper edge of a truss. This member is subjected to compressive and bending stresses. •BOTTOM CHORD The horizontal (and inclined, ie. scissor trusses) member defining the lower edge of a truss, carrying ceiling loads where applicable. This member is subject to tensile and bending stresses. (On a simply supported, non-cantilevered truss).•CLEAR SPAN The horizontal distance between inside faces or supports.•HEEL The joint in a pitched truss where top and bottom chords meet.•HEEL HEIGHT - The "thickness" of a truss at the end of the Bottom Chord. Measured from the bottom of the Bottom Chord (or top of top plate) to the top of the Top Chord (underside of sheathing) at the end of the truss.•JOINT The point of intersection of a chord with the web or webs, or an attachment of pieces of lumber (eg. splice)•LATERAL BRACE A permanent member connected to a web or chord member at right angle to the truss to restrain the member against a buckling failure, or the truss against overturning.

•OVERHANG The extension of the top chord beyond the heel joint.•OVERALL HEIGHT - - A vertical measurement taken at the midpoint of a truss from the bottom of the Bottom Chord to the peak.•PANEL The chord segment between two adjacent joints. •PANEL POINT The point of intersection of a chord with the web or webs.•PANEL LENGTH - The horizontal distance between the centerlines of two consecutive panel points along the top or bottom chord.• PEAK Highest point on a truss where the sloped top chords meet.•SLOPE (PITCH) The units of horizontal run, in one unit of vertical rise for inclined members. (Usually expressed as 3:12, 5:12, etc.)•SPLICE POINT The location where the chord member is spliced to form one continuous member. It may occur at a panel point but is more often placed at 1/4 panel length away from the joint.•WEBS Members that join the top and bottom chords to form the triangular patterns that give truss action. The members are subject only to axial compression or tension forces (no bending)•WEDGE - THE TRIANGULAR PIECE OF LUMBER INSERTED BETWEEN THE TOP AND BOTTOM CHORDS, USUALLY TO ALLOW THE TRUSS TO CANTILEVER.

Metal Roof Truss – Advantages and Disadvantages of Metal Roof Truss Structures.

Metal roof trusses, just like wood trusses, have their advantages and disadvantages. Some builders prefer to the metal roof truss because the building of a structure is all about precision and metal has a more precise measurement than wood. Safety is also an issue when deciding to use a metal roof truss or a wood truss system, building codes and other procedures may require certain trusses.

Advantages of Metal Roof Truss Structures

•Even though they are considered to be more expensive, metal roof trusses can span further than wood.•Metal roof trusses can be manufactured to exact standards.•They are much more lightweight and this allows for larger shipments. This reduces the time it takes to get to the project site.•Metal roof trusses are fire resistant.•They are compatible with almost all types of roofing systems.•No insect infestations can occur.•Chemical treatments are not necessary to maintain the trusses.•Metal roof trusses are recyclable and therefore environmentally friendly.

Disadvantages of Metal Roof Truss Structures

•Skilled labor is required to install metal roof trusses.•They are not energy efficient since they allow more heat to escape from the structure.•Metal roof trusses allow sound to be more easily transmitted.•Temperature fluctuations allow them to move more.•When the metal is cut, drilled, scratched or welded, rust can become a problem.•The workers have a higher risk of electrocution when installing the metal roof trusses.•Wires that are on the trusses can rub over time creating a hazard to anyone who happens to touch the metal trusses.

Steel Trusses

Truss forms

7. King post truss:

It is the simplest form of roof truss, a triangular frame consisting

of two equal rafter members connected by a tie-beam.

The tie beam becomes necessary when the outward thrust of the rafters

is too great for the resistance of the walls.

In a king post truss the bending moment on the tension member, dues to

its own weight and load of the ceiling, increases as the span of the truss

increases. The section required to resist both the tensile and transverse

bending stresses would necessarily be large; hence, to reduce the size of

this member a suspension rod is introduced.

The king post is in tension, usually supporting the tie beam as a truss

but the crown post is supported by the tie beam and is in compression. The

crown post rises to a crown plate immediately below and supporting collar

beams, it does not rise to the apex like a king post.

It is limited to a spanof 24 feet.

Simple representation of aKing post truss

Representation of a King post truss showing jointing

Steel Trusses

Truss forms

Steel roof trusses are available in many different forms and systems, the following may be used for steel roof trusses:

1. Fink truss:

The Fink truss offers greater economy in terms ofsteel weight forshort-span high-pitched roofs as the members are

subdivided into shorter elements.

There are many ways of arranging and

subdividing the chords and internal members.

This type of truss is commonly used to construct

roofs in houses. when made of steel it is more

economical for long spans than either the howe or

the pratt.

Most types of roofing use a“W” pattern truss.

1/3 1/3 1/3

USING SIMILAR TRIANGLES, THE LENGTH (X) OF THE TOP CHORD IS DETERMINED. X/42 = 13.89/12 X = (42 X 13.89) 12 = 48.615” OR 4’ ⅝”. TRUSSES ARE BUILT ON A FLAT SURFACE AND THE PIECES ARE CUT TO SUIT THE LAYOUT MARKS.

USES : FINK TRUSSES ARE USES FOR SHORT SPAN STRUCTURES

MAXIMUM 9’. TRUSSES ARE USED FOR PITCHED ROOF IN HOMES.

DISADVANTAGE :

FINK TRUSSES ARE NOT USES FOR LONG SPAN (USE FOR ONLY SMALL SPAN)

Steel Trusses

Truss forms

2. Queen post truss (Fan Truss):Principal Rafter

It is useful as a rectangular space is desired in thecenterof the room ,

an attic or small hall.

If the span length is in between 8 to 12 meter then queen post trusses

are used.

Two vertical posts are provided in 2 sides at a distance which are

termed asqueen posts.

Straining beam and straining seal is used to keep the queen posts in exact

position.

Top endsof two main rafters are joined with thequeen postsheads. It

can be used in longer spans when it is cross-braced in the center.

Double FanThe fan truss has three or four members fanningout from a common

point at the bottom of the truss.

The double fan has twocommon points where members fan out.

Fan truss

3.

Double-Fan truss

4. Cambered Fink With Fink or Fan trusses having an inclination for the rafter not exceeding 30 degrees it is

more economical to employ a horizontal chord or tie since it obviates bending of the

laterals.

Raising the bottom chord, also materially increases the strains in the truss members,

hence it increases the cost.

A truss whose bottom chord has a rise of two or three feet, presents a better appearance,

however, than one with a horizontal chord, and for steep roofs, it will generally be fully as

economical toraise the bottomchordbecause of the shortening of the members.

Trusses with raised ties are designated as“Cambered."

Queen Post

Steel Trusses

Truss forms

6. Howe truss:

The method of increasingthe number of triangles, as shown ,may go on indefinitelyand the naturaloutcome is the howe truss. Thistruss maybe extended to very large spans by increasingthe number ofpanels, but it is not suitable for steep roofs, because as the spanincreases,the length of the struts towardthe centre becomes so great asto requiretimberof large size. For long trusses the usual rise is one-seventh of the span. With long spans, it is customaryto reduce the shearat the heel of the truss by placing the compression member nearest thewall more nearly vertical.The Howe Truss was and sometimeseven now is used in steel bridges.It's impressive strength over long spanscontributedto its overwhelmingpopularityas a railroadbridge.

The design of Howe truss is the oppositeto that of Pratt trussin whichthe diagonal members are slanted in the direction opposite to that of Pratt truss (i.e. slantingaway from the middleof bridge span) and as such compressive forces are generated in diagonalmembers. Hence, it is not economical to use steel members to handlecompressive force.

Simple representation of aHowe truss Representation of a Howe truss showing jointing

Steel Trusses

Truss forms

8. Pratt truss:

Pratt its similarity to the Howetruss, and the pointsof

difference readily noted. In the Pratt truss, the compression members of

the web of the frame, or the struts a, a are vertical, while the tension

rods b, b are oblique. In the Howe, a reversed condition exists, for the

struts are obliqueand the tension members vertical.

The Pratt offers rather a better appearance than the Howe from the fact

that the oblique members, whichusually extend at different angles, are

round bars that are hardly noticeable, but in the Howethey are made of

timbers, which are frequently unnecessarily heavy and far from pleasing

in appearance, while the vertical timber struts used in the Pratt arc

entirely unobjectionable.

The howe truss, however, has the advantage that the connections at

c, d, and e are more conveniently made. The design uses vertical

members for compression and horizontal members to respond to

tension.

Simple representation of aPratt truss

Lateral (wind) bracing

Struts

Sway bracing Portal strut

and bracing

Deck

StringersFloor beams

Representation of a Pratttruss showing jointing

Steel Trusses

Truss forms

9.

Flat Warren truss:

It is a typeof Parallel Chord truss.

Warren truss containsa series of isosceles triangles or equilateral

triangles. To increase the span lengthof the truss bridge, verticals

are added for Warren Truss.

The unique design of a Warren truss structure ensures that no strut,

beam or tie bends or withstands torsional straining forces but is only

subject to tension or compression. The loads on the diagonals alternate

between tensionand compression, whereas the elements near the

center are required to supportboth compression as well as tension in

response to live loads. The use of the Warren truss design is common

in prefabricated modular bridges wherein all the girders are of equal

length. Warren truss is a notchbetter than Neville truss, which has

isosceles triangles filling up the entire length of a bridgedesign.

Warren TrussAdvantages- There is less material required for the constructionof a Warren

truss bridge.

Simple representation of aFlat warren truss

- There is less blockage of view.

- The constituents of a Warren truss bridgecan be assembledpiece wise.

Representation of a Pratttruss showing jointing

WARREN TRUSS ADVANTAGES- THERE IS LESS MATERIAL REQUIRED FOR THE CONSTRUCTION OF A WARREN TRUSS BRIDGE.- THERE IS LESS BLOCKAGE OF VIEW.- THE CONSTITUENTS OF A WARREN TRUSS BRIDGE CAN BE ASSEMBLED PIECE WISE.

WARREN TRUSS BRIDGE DISADVANTAGES- THE MAINTENANCE OF THE JOINTS AND FITTINGS OF A WARREN TRUSS BRIDGE COULD BE EXPENSIVE.- THE CALCULATIONS TO DETERMINE THE LOAD-BEARING CAPACITY OF A WARREN TRUSS BRIDGE CAN BE HASSLING.- MANY WARREN TRUSS BRIDGES ARE NOT AESTHETICALLY APPEALING TO THE EYE.- THERE COULD BE TOO MUCH DEFLECTION FOR LONG SPANS.

NORTH LIGHT TRUSS North light trusses are traditionally used for

short spans in industrial workshop-type buildings. They allow maximum benefit to be gained from natural lighting by the use of glazing on the steeper pitch which generally faces north or north-east to reduce solar gain. On the steeper sloping portion of the truss, it is typical to have a truss running perpendicular to the plane of the North Light truss, to provide large column-free spaces.

The use of north lights to increase natural daylighting can reduce the operational carbon emissions of buildings although their impact should be explored using dynamic thermal modelling. Although north lights reduce the requirement for artificial lighting and can reduce the risk of overheating, by increasing the volume of the building they can also increase the demand for space heating. Further guidance is given in the Target Zero Warehouse buildings design guide .

http://www.steelconstruction.info/Operational_carbon

http://www.steelconstruction.info/Target_Zero

http://www.steelconstruction.info/Trusses

SAWTOOTH TRUSS

A truss made with one top chord steeper than the

other, usually to add windows.

A variation of the North light truss is the saw-

tooth truss which is used in multi-bay

buildings. Similar to the North light truss , it is

typical to include a truss of the vertical face

running perpendicular to the plane of the saw-

tooth truss.

SPAN: 5m to 8mMATERIAL : steel or timber

Saw-tooth roofs may be constructed of heavy timber or steel trusses .

This is generally used in factories where more light is required.

WIDELY USED TO SERVE TWO MAIN FUNCTIONS: To carry the roof load To provide horizontal stability.

Light fills the space from clerestory windows in the sawtooth-style roof

EXAMPLES

WINDOWS

green house with saw tooth roof truss

ADVANTAGES

The major advantage of installing a saw-tooth roof truss on a structure is the uniform diffusion of light throughout the space below it.

Saw-tooth roofs prevent the influx of direct sunlight while providing northern light.

In saw-tooth design, every bay has an angled skylight. Less glare and unwanted heat also offer better working conditions, increased production

The complex design and various building materials needed will make the sawtooth roof much more expensive than other roof types.

It’s also a high maintenance roof. Adding windows, valleys and varying slopes creates a higher chance for

water leaks. For this reason, sawtooth roofs aren’t advisable in heavy snowfall areas.

DISADVANTAGES

APPLICATIONS

o Loftso machine shopso Warehouseso factorieso Residences

SHELLS THEORY OF STRUCTURES

GROUP MEMBERS

ANJALI KOLIANOUSHKA SHARMAKANISHKA SHARMALIPIKA AGGARWALSHUBHAM GUPTATEJASVI KAUR

A shell is a type of structural element which is characterized by its geometry, being a three-dimensional solid whose thickness is very small when compared with other dimensions. A shell structure is a thin, curved membrane or slab, usually of reinforced concrete, that functions both as structure and covering, the structure deriving its strength and rigidity from the curved shell forms.

Essentially, a shell can be derived from a plate by two means : by initially forming the middle surface as a singly or doubly curved surface and by applying loads which are co planar to a plate’s plane which generate significant stresses. Shell structures predominantly resist loads on them by direct compression. That is without bending or flexure.

Since most materials are more effective in compression than in bending, shell structures result in lesser thickness than flat structures

TYPES: Single curvature shells, curved on one linear axis, are part of cylindrical or cone in the

form of barrel vaults and conoid shells.

Double curvature shells are either part of a sphere, as a dome, or a hyperboloid of revolution.

INTRODUCTION

THIN CONCRETE SHELLS

The thin concrete shell structures are a lightweight construction composed of a relatively thin shell made of reinforced concrete, usually without the use of internal supports giving an open unobstructed interior. The shells are most commonly domes and flat plates, but may also take the form of ellipsoids or cylindrical sections, or some combination thereof. Most concrete shell structures are commercial and sports buildings or storage facilities.

There are two important factors in the development of the thin concrete shell

structures:

The first factor is the shape which was developed along the history of these constructions. Some shapes were resistant and can be erected easily. However, the designer’s incessant desire for more ambitious structures did not stop and new shapes were designed.

The second factor to be considered in the thin concrete shell structures is the thickness, which is usually less than 10 centimeters. For example, the thickness of the Hayden planetarium was 7.6 centimeters.

• Shells belong to the family of arches, vaulted halls and domes. We can understand that a vault is a shell with one singly curved surface and a dome is a shell with doubly curved surfaces.

• A saddle shell has also doubly curved surfaces, but with a difference. If we cut a dome in two directions at right angles to one another, both cuts are convex curves. If we cut a saddle shell in the same way, one curve is convex and the other is concave.

• Examples ; • Hyperbolic paraboloids and hyperboloids

• Shells are generally made out of reinforced concrete : from 40m (130 ft) to 73 m in span. However, people have materialize the form of shells with space frames, lattices and membranes, allowing larger spans (up to 200 meters.)

The Roman Pantheon, as it stands today in the centre of the city of Rome, really is a remarkable and imposing structure. The Pantheon is a masterpiece of ancient shell construction and has withstood for almost two-thousand years. Today, the span of 43 m still impresses the engineering profession. The Pantheon, built in the early 2nd century A.C., approximately 125, is the largest unreinforced dome in the history.

HISTORY

• The membrane behaviour of shell structures refers to the general state of stress in a shell element that consists of in-plane normal and shear stress resultants which transfer loads to the supports. In thin shells, the component of stress normal to the shell surface is negligible in comparison to the other internal stress components and therefore neglected in the classical thin shell theories. The initial curvature of the shell surface enables the shell to carry even load perpendicular to the surface by in-plane stresses only.

• The carrying of load only by in-plane extensional stresses is closely related to the way in which membranes carry their load. Because the flexural rigidity is much smaller than the extensional rigidity, a membrane under external load mainly produces in-plane stresses. In case of shells, the external load also causes stretching or contraction of the shell as a membrane, without producing significant bending or local curvature changes. Hence, there is referred to the membrane behaviour of shells, described by the membrane theory.

• Carrying the load by in-plane membranes stresses is far more efficient than the mechanism of bending which is often seen by other structural elements such as beams. Consequently, it is possible to construct very thin shell structures. Thin shell structures are unable to resist significant bending moments and, therefore, their design must allow and aim for a predominant membrane state. Bending stresses eventually arise when the membrane stress field is insufficient to satisfy specific equilibrium or deformation requirements.

MEMBRANE BEHAVIOUR

Material Effects on Shell Behaviour

Reinforced concrete shells have complicated nonlinear material behaviour with strong influence on the structural behaviour. Significant tensile stresses in the shell will cause cracking and with that weakening of the shell cross-section.

Micro-cracking at the surface is caused by the evaporation of water. Due to the high amount of surface exposed the micro-cracking in the shell surface may exceed the allowable value.

Furthermore, creep of concrete will cause flattening of the shell surface, resulting in less curvature and possible bending stresses to occur. Additionally, shrinkage may lead to unwanted residual stresses.

CYLINDRICAL CONICAL SHELL

Cylindrical Shell Conical Shell

They may be of wood, steel, plastic or reinforced concrete. They may form the roof and containing walls for long span structures.

Cylindrical Shell is a shell that is a structure about an axis parallel to the sides of an imaginary straight sheet.It distributes wind load equally on the structure sides.

Conical Shell is a shell that is a structure about an axis non-parallel to the sides of an imaginary straight sheet.It is a stable structure for standing high pressure winds.

The elements of a barrel shell are:(1) The cylinder,(2) The frame or ties at the ends, including the columns, and(3) The side elements, which may be a cylindrical element, a folded plate element, columns, or all combined.For the shell shown in the sketch, the end frame is solid and the side element is a vertical beam.A barrel shell carries load longitudinally as a beam and transversally as an arch. The arch, however, is supported by internal shears, and so may be calculated.

They maybe used as:(1) Long-span structures(2) Short-span structures

BARREL VAULTS

Cylindrical shell used in the roof are also known as barrel shell or vault

These may be of multiple numbers joined together to increase strength

POSSIBLE METHODS OF JOINING CYLINDRICAL CONICAL SHELLS

SANGATH, AHMEDABAD

DELFT UNIVERSITY LIBRARY, NETHERLANDS

A dome is an architectural element that resembles the hollow upper half of a sphere. There are also a wide variety of forms and specialized terms to describe them. A dome can rest upon a rotunda or drum, and can be supported by columns or piers that transition to the dome through squinches or pendentives. A lantern may cover an oculus and may itself have another dome.

A dome is a rounded vault made of either curved segments or a shell of revolution, meaning an arch rotated around its central vertical axis.

Domes have a long architectural lineage that extends back into prehistory and they have been constructed from mud, stone, wood, brick, concrete, metal, glass, and plastic over the centuries. The symbolism associated with domes includes mortuary, celestial, and governmental traditions that have likewise developed over time.

The word "cupola" is another word for "dome", and is usually used for a small dome upon a roof or turret. "Cupola" has also been used to describe the inner side of a dome. Drums, also called tholobates, are cylindrical or polygonal walls with or without windows that support a dome. A tambour or lantern is the equivalent structure over a dome's oculus, supporting a cupola.

SPHERICAL DOMES

As with arches, the "springing" of a dome is the point from which the dome rises. The top of a dome is the "crown". The inner side of a dome is called the "intrados" and the outer side is called the "extrados". The "haunch" is the part of an arch that lies roughly halfway between the base and the top.

A masonry dome produces thrusts down and outward. They are thought of in terms of two kinds of forces at right angles from one another.

Meridional forces (like the meridians, or lines of longitude, on a globe) are compressive only, and increase towards the base, while hoop forces (like the lines of latitude on a globe) are in compression at the top and tension at the base, with the transition in a hemispherical dome occurring at an angle of 51.8 degrees from the top.

The thrusts generated by a dome are directly proportional to the weight of its materials. Grounded hemispherical domes generate significant horizontal thrusts at their haunches.

Concave from below, they can reflect sound and create echoes. A dome may have a "whispering gallery" at its base that at certain places transmits distinct sound to other distant places in the gallery. The half-domes over the apses of Byzantine churches helped to project the chants of the clergy.

BEHAVIOUR

When the base of the dome does not match the plan of the supporting walls beneath it (for example, a dome's circular base over a square bay), techniques are employed to transition between the two. The simplest technique used is diagonal lintels across the corners of the walls to create an octagonal base.

Another is to use arches to span the corners, which can support more weight. A variety of these techniques use what are called "squinches". A squinch can be a single arch or a set of multiple projecting nested arches placed diagonally over an internal corner.Squinches can take a variety of other forms, as well, including trumpet arches and niche heads, or half-domes.

The earliest domes were built with mud-brick and then with baked brick and stone. Domes of wood were allowed for wide spans due to the relatively light and flexible nature of the material and were the normal method for domed churches by the 7th century.

Wooden domes were protected from the weather by roofing, such as copper or lead sheeting. Domes of cut stone were more expensive and never as large, and timber was used for large spans where brick was unavailable. Brick dome was the favoured choice for large space monumental coverings until the Industrial Age, due to their convenience and dependability.

TECHNIQUES & MATERIALS

A grid shell is a structure which derives its strength from its double curvature but is constructed of a grid or lattice.

The grid can be made of any material, but is most often wood or steel.

Grid shells were pioneered in the 1896 by Russian engineer Vladimir Shukhov in constructions of exhibition pavilions of the All-Russia industrial and art exhibition 1896 in Nizhny Novgorod.

GRID SHELL DOME

Louisiana Superdome, New Orleans Architect: Curtis and Davis Engineer: Sverdrup and Parcel With a 680 ft diameter the Louisiana

Superdome is the largest dome in existence. Designed for 75,000 spectators, the

multipurpose arena serves many functions from various sports events to rock concerts and political conventions.

The patented lamella dome structure features a peripheral tension ring truss.

A Tension ringB Radial ribsC Diagonal struts, parallel to radial ribsD Hoop rings, combined with diagonal struts,form a diamond bracing gridE Roof joistsF Metal deckG Single-ply water proof membrane

EXAMPLE

Walter Bauersfeld built the first geodesic dome in 1922 for a planetarium in Jena, Germany. Buckminster Fuller developed his geodesic dome for low-cost housing 1942.

A basic geodesic sphere, referred to as single frequency, consists of 20 spherical triangles that form pentagons. Dividing single frequency into more units forms hexagons.

Frequencies: 1 2 3 4

GEODESIC DOME

1 Single frequency dome: 10 triangles forming pentagons2 Single frequency dome of 10 spherical triangles3 Two-frequency sphere4 Two-frequency hemisphere dome5 Four-frequency hemisphere dome6 Football of 10 hexagons, 12 pentagons

US pavilion Expo 67 Montreal Architect: Buckminster Fuller & Shoji Sadao The 250 feet diameter by 200 feet high dome

roughly presents a three-quarter sphere, while geodesic domes before 1967 were hemispherical. The dome consists of steel pipes and 1,900 acrylic panels. To keep the indoor temperature acceptable, the design included mobile triangular panels that would move over the inner surface following the sun. Although brilliant on paper, this feature was too advanced for its time and never worked. Instead valves in the centre of acrylic panels enabled ventilation.

EXAMPLE

Climatron, Missouri Botanical Gardens, St Louis (1959) Architect: Murphey & Mackey Engineer: Paul Londe The dome of 175 feet diameter and 70 feet height permits tall palm trees to tower

above tropical streams, waterfalls and 1,200 species of exotic trees and plants. Temperature ranges 64 to 74 degrees and average humidity is 85 percent.

EXAMPLE

• Spruce Goose dome, Long Beach, USA• Architect: R. Duell and Associates• Engineer/builder: Temcor• This aluminium dome for Hugh’s Spruce

Goose(at 415 ft diameter among the largest geodesic domes). The dome of 15 geodesic frequencies weighs < 3 psf.

• The design had to provide a temporary opening for the plane of 320 ft wing-span to pass through.

A Aluminium cover plate with silicone sealB Aluminium gusset plates, bolted to strutsC Aluminium batten secure silicone gasketsD Triangular aluminium panelsE Wide-flange aluminium strutsF Stainless steel bolts

EXAMPLE

HPR dome, Walla Walla, USAArchitect: Environmental Concern, Inc.Engineer/builder: TemcorAluminum dome of 206’ diameter and 42 ft depth(span/depth ratio 4.9), weighs less than 3 psf.

EXAMPLE

HYPERBOLIC PARABOLOID

Formed by sweeping a convex parabola along a concave parabola or by sweeping a straight line over a straight path at one end and another straight path not parallel to the first.

Structural behaviours

Depending on the shape of the shell relative to the curvature, theere will be different stresses.

Shell roofs, have compression stresses following the convex curvature and the tension stresses following concave curvate.

PROPERTIES

Hyperboloid structures are superior in stability towards outside forces compared to "straight" buildings, but have shapes often creating large amounts of unusable volume (low space efficiency) and therefore are more commonly used in purpose-driven structures, such as water towers (to support a large mass), cooling towers, and aesthetic features.

Water tank hyperbolical concrete shell structure

MIAMI MARINE STADIUM

Preserving the Miami Marine Stadium is a cast-in-place concrete 100-meter long building with an eight-section hyperbolic paraboloid roof

It is 33-meter wide with a cantilever of 20 meter over the stands; one third of the structure is built on piers into the water.

Used for motorboat racing and various types of concerts on a floating stage.

CONCRETE SHELL

The material most suited for construction of shell structure is CONCRETE because it is a highly plastic material when first mixed with water that can take up any shape on centering or inside formwork.

Small sections or reinforcement bars can readily be bent to follow the curvature or shells.

Once cement has set and the concrete has hardened the R.C.C membrane or slab acts

a strong, rigid shell which serves as both structure and covering to the building.

RCC & STEEL STRUCTURE

TYPES AND FORMS

Folded plates

Barrel shells

Domes

Translation shell

CENTERING OF SHELL

Centering is the term used to describe the necessary temporary support on which the curved R.C.C. Shell structure is cast.

The centering of a barrel vault which is a part of a cylinder with same curvature along its length , is less complex.

The centering of concoid, dome and hyperboloid of revolution is more complex due to additional labour and wasteful cutting of materials to form support for shapes that are not of uniform linear curvature.

CONCRETE SHELL CONSTRUCTION

Shells may be cast in place, or pre-cast off site and moved into place and assembled. The strongest form of shell is the monolithic shell, which is cast as a single unit.

Geodesic domes may be constructed from concrete sections, or may be constructed of a lightweight foam with a layer of concrete applied over the top. The advantage of this method is that each section of the dome is small and easily handled. The layer of concrete applied to the outside bonds the dome into a semi-monolithic structure.

Monolithic domes are cast in one piece out of reinforced concrete and date back to the 1960s. It is cost-effective and durable structures, especially suitable for areas prone to natural disasters. Monolithic domes can be built as homes, office buildings, or for other purposes.

Monolithic dome in Alaska

Completed in 1963, the University of Illinois Assembly Hall, located in Champaign, Illinois was and is the first ever concrete-domed arena. The design of the new building, by Max Abramovitz, called for the construction of one of the world’s largest edge-supported structures.

The Seattle Kingdome was the world's first (and only) concrete-domed multi-purpose stadium. It was completed in 1976 and demolished in 2000. The Kingdome was constructed of triangular segments of reinforced concrete that were cast in place. Thick ribs provide additional support.

• Concrete shells are naturally strong structures, allowing wide areas to be spanned without the use of internal supports, giving an open, unobstructed interior.

• The use of concrete as a building material reduces both materials cost and a construction cost, as concrete is relatively inexpensive and easily cast into compound curves.

• The resulting structure may be immensely strong and safe; modern monolithic dome houses, for example, have resisted hurricanes and fires, and are widely considered to be strong enough to withstand even F5 tornadoes.

• Very light form of construction, to span 30m shell thickness required is 60mm.

• Dead load can be reduced economizing foundation and supporting system.

• Aesthetically it looks good over other forms of construction.

ADVANTAGES

Since concrete is porous material, concrete domes often have issues with sealing. If not treated, rainwater can seep through the roof and leak into the interior of the building.

On the other hand, the seamless construction of concrete domes prevents air from escaping, and can lead to buildup of condensation on the inside of the shell. Shingling or sealants are common solutions to the problem of exterior moisture, and dehumidifiers or ventilation can address condensation.

Shuttering problem

Greater accuracy in formwork is required

Good labour and supervision is necessary

Rise of roof may be a disadvantage.

DISADVANTAGES

The Market Hall in Leipzig, Germany (1929) by Franz Dischinger

Petroleum Coke Bulk Storage - Pittsburg, California

OPAC Consulting Engineers

FOLDED PLATES

Nikhita Khurana

Pulkit Chawla

Tanvi Yadav

Dhruv Khurana

INTRODUCTION

• FOLDED PLATES is one of the simplest shell structure.

• They are more adaptable to smaller areasthan curved surfaces which require multiple use of forms for maximum economy.

• A folded plate may be formed for about the same cost as a horizontal slab and has much less steel and concrete for the same spans.

• Folded plates are not adapted to as wide bay spacings as barrel vaults.

SHELL STRUCTUREFOLDED PLATE STRUCTURE

BAY WIDTH OF

FOLDED PLATES

BAY

WIDTH OF

BARREL

VAULT

BEHAVIOUR Each plate is assumed to act as a beam in its own

plane, this assumption is justified when the ratio of the span "length“ of the plate to its height“ width“ is large enough. But when this ratio is small, the plate behaves as a deep beam.

• When the folded plate is that with simple joint , which mean that no more than 2 elements are connected to the joint.

• But when more than 2 elements are connected to the joint, it can be named as multiple joint. The width of any plate should not be larger than 0.25 its length to be considered to act as beam.

• Actions of Folded plate due to loads :

1) SLAB ACTION : loads are transmitted to ridges by the bending of plates normal to their planes.

2) BEAM ACTION : Loads are transmitted through plates in their planes to diaphragms.

RIDGE

COMPONENTS• The principle components in a folded plate structure are illustrated in the sketch below. They

consist of, 1) the inclined plates,

2) edge plates which must be used to stiffen the wide plates, 3) stiffeners to carry the loads to the supports and to hold the plates in line, and

4) columns to support the structure in the air.

• A strip across a folded plate is called a slab element because the plate is designed as a slab in that direction.

• The span of the structure is the greater distance between columns and the bay width is the distance

between similar structural units. • If several units were placed side by side, the edge plates should be omitted except for the first and last

plate. • If the edge plate is not omitted on inside edges, the form should be called a two segment folded plate

with a common edge plate. • The structure may have a simple span or multiple spans of varying length, or the folded plate may

cantilever from the supports without a stiffener at the end.

TAPERED FOLDED PLATES

Inclined plates

Edge plates

Stiffeners

Columns

Span

THE PRINCIPLE OF FOLDING

STRUCTURAL BEHAVIOUR OF FOLDING

• The inner load transfer of a folding structure happens through the twisted plane, either through the structural condition of the plate (load perpendicular to the centre plane) or through the structural

condition of the slab (load parallel to the plane).

• At first, the external forces are transferred due to the structural condition of the plate to the shorter edge of one folding element.

• There, the reaction as an axial force is divided between the adjacent elements which results in a strain of the structural condition of the slabs. This leads to the transmission of forces to the bearing.

FORMS OF FOLDED PLATE STRUCTURES• By using folded structures different spatial

forms can be made.

• The straight elements forming a foldedconstruction can be of various shapes:rectangular, trapezoidal or triangular.

• By combining these elements we getdifferent forms resulting in a variety of shapesand remarkable architectural expression.

• Folded structures in the plane are thestructures in which all the highest points ofthe elements and all the elements of thelowest points of the folded structure belongto two parallel planes.

• Frame folded structures representconstructional set in which the elements ofeach segment of the folds mutually occupya frame spatial form. This type of foldedstructure is spatial organization of two ormore folds in the plane.

• Spatial folded structures are the type of astructure in which a spatial constructive set isformed by combining mutually the elementsof a folded structure.

FORMS OF FOLDED PLATE STRUCTURES• The shape of folded structures affects the transmission of load and direction of relying of folded

structures. Based on these parameters, folded plate systems are further classified into :

1. linear folded plate structure2. radial folded plate structure3. spatial folded plate structure

LINEAR FOLDED

PLATE STRUCTURE

RADIAL FOLDED

PLATE STRUCTURE

SPATIAL FOLDED

PLATE STRUCTURE

• Combined folded constructions are carried out over the complex geometric basis, formed by thecombination of simple geometric figures, rectangles and semicircles on one side or both sides.

• This type of folded structure can be derived in the plane or as a frame (cylindrical) structure, andrepresents a combination of folded structure above the rectangular base and ½ of the radialconstruction.

EXAMPLE OF A COMBINED FOLDED STRUCTURE FORMED BY A CYLINDRICAL

FOLDED STRUCTURE AND HALF OF DOME STRUCTURE

TYPES OF FOLDED PLATE STRUCTURES

LONGITUDINAL/ PRISMATIC FOLDING

• Longitudinal folding is characterized through uninterrupted

and linked folding edges where parallel and skew up folds anddown folds alternate.

• Single-layered longitudinal folding corresponds in their loadbearing structure to a linear load bearing system whereas adouble-layered folding with different directions of their foldscan create the structural condition of the plate.

SPOT OR FACET FOLDING• Also called spot or facet folding, requires that several folds

intersect like a bunch in one single spot. This results in pyramidalfolds with crystalline or facet-like planes.

• Facet folding can either be based on a triangular shape or ona quadrangular shape.

• A single or double-layered facet folding resembles the loadbearing structure of a plate and can be compared to spaceframeworks

SKETCH PYRAMIDAL FOLDING

SKETCH LONGITUDINAL FOLDING

•Reinforced Cement Concrete•Steel Plate•Mixture of Concrete and lightweight terracotta tiles•Polymer mixture of concrete and fibreglass•Scored laminated timber sheets

•Prestressed concrete folded plates•Extremely light with concrete thickness of 200mm•An existing hangar at Santa Cruz Airport, Mumbai (Bombay), India, has been extended to accommodate additional aircraft and engineering facilities. •Contains 8 folds•62 m long cantilever of the new folded-plate roof• Measure152 x 60 m in plan, and is symmetrically divided by a longitudinal expansion joint•The 152 m length consists of two cantilevered roofs, each 62.3 m long, and a central roof 27.4 m long over the maintenance building.•Highest point of roof is 32.3m above ground•The transverse section of the folded plate consists of eight 7.6 m wide modules, each having a corrugated plate arrangement, with horizontal top and bottom plates inclined at 45° between the webs.

EXAMPLE: THE CHURCH OF NOTRE DAME, THE CITY OF ROYAN

•Walls can be designed and carried out as folded

structures, since by folding we get a solid

construction that can accept large vertical and

horizontal impacts, which enables exceptional

height of the wall fabric.

•This type of folded structures, due to their

geometry, provides an economical solution and

the rational use of material when compared to

the height of the building.

•Walls made as folded structures can be

materialized in reinforced concrete.

•Facility constructed with this structure is the

church of Notre Dame, the city of Royan, France,

1958, with the walls built in the form of folded in

"V" shape of reinforced concrete.

•Viable galleries, which have a constructive role

of the diaphragm, are built on them

• since they are of concrete, such roofs have inherent resistance to fire, deterioration and to atmospheric corrosion.

• They allow large spans to be achieved in structural concrete. This allows flexibility of planning and mobility beneath.

• Where ground conditions require expensive piled foundations the reduced number of supporting columns can be an economic advantage.

• The plates are required to be thicker than the shells, and there are more firms who will tackle constructing them without excessive prices, increasing competition and sometimes making the cost more competitive than for cylindrical shells.

DISADVANTAGES• Skilled labor is required in the construction of curved shuttering.• Since concrete is porous material, concrete domes often have issues with sealing. If not treated,

rainwater can seep through the roof and leak into the interior of the building• Labor skilled in curved shuttering are very expensive• Skilled labor for folded plates are hard to find

ADVANTAGES

•Storage buildings•Swimming pools•Gyms•Airports etc.

USES

APPLICATION• Folded structures have found the application in

architectural buildings and engineering structures.

• Based on the position in the architectural structure, this

type of construction can be divided into: roof, floor and

wall folded constructions.

• The largest number of examples of folded structures are

roof structures.

• The need for acquiring the larger range and more cost

effective structure led to the emergence of this type of

structure.

• The largest application of folded structures is in the

formation of trapezoidal sheet.

• This type of folded structure can absorb and receive the

load without introducing additional structure.

• Application of trapezoidal sheet, except as roofing, is in

making the thermal insulation of roof and wall sandwich

panels.

HIGH RISE BUILDINGS

PRESENTED BY :

•KARTIK KUMAR•PAYAL GUPTA•PRACHI ARORA•MEGHA KASHYAP•NEETU SHARMA•ARJUN•MOHIT GUPTA

INTRODUCTION AND DEFINITIONHigh rise is defined differently by different bodies.

Emporis standards-“A multi-story structure between 35-100 meters tall, or a building of unknown height from 12-39 floors is termed as high rise.

Building code of Hyderabad,India-

A high-rise building is one with four floors or more, or one 15 meters or more in height.

The International Conference on Fire Safety –"any structure where the height can have a serious impact on evacuation“

U.S., the National Fire Protection AssociationA high-rise as being higher than 75 feet (23 meters), or about 7 stories

PLANNING ASPECTS OF HIGH RISE BUILDINGS :

• Area Shall not be less than 1000 sq.m

• Setbacks of 12 m on either sides of High Rise Buildings shall be provided.

• Parking floor height shall not be more than 4.2 m.

• Minimum 2 Nos. of staircases shall be proposed for High Rise Buildings.

• The first refuge floor to be at 24 m and thereafter the refuge floor shall be provided at interval of 15 m.

• If building height is more than 70 m., break tank of 30,000 Liters (Thirty Thousand Liters) minimum capacity shall be provided.

• Projections beyond the building line in the form of flowerbed, niche, deck etc including the balcony, terrace shall not exceed 1.2 m.

PRINCIPLES & DESIGN STANDARDS RELATED TO USE CONSTRUCTION

SYSTEMS ARE AS :

The building must achieve all building laws related to internal spacing.The Building must apply modern technological systems.

It must constructed using suitable structure systems.Application of all civil defense requirements related to safety and fire fighting.

Provision of all services (car parking ,fire fighting water tanks ,water supply tanks, etc).Fire escape stairs should consist of 2 flights each flight must not be less than 90 cm wide.

Fire escape staircase must connect to outside of the building.Ease of access of all floors to civil defense units.

The building must be constructed out of fire resistant materials (or materials with a high rate of fire resistance).

The main stair case flight must not be less than 135 cm wide.The main staircase & elevators should be present in every main core of the building.

Provision of sufficient parking slots to the number of the building users.Basement floors with all the suitable systems to the required use.

ECO-FRIENDLY HIGH RISE BUILDINGS DESIGN STANDARDS:

Environmental standards must be applied when designing high rise

buildings. As most of the countries nowadays seek to achieve sustainable

buildings to maintain the efficiency of the building through applying the following:

Use of renewable energies.

Use of eco-friendly construction materials.

Water rationalization inside the high rise building.

Air Quality inside the high rise building.

Proper lighting inside of the building.

Color selection philosophy.

Acoustic design.

Building security issues and its design.

Environmentally compatible architectural style.

MATERIALS USED IN HIGH RISE BUILDINGS :

Reinforced Concrete

Light Weight Concrete Brickwork Glass being used as Walling in Kohinoor Square,Dadar

Steel used for reinforcement

Plastic used as pipe material for waste and rainwater

Mineral Wool used as Insulating Material

ANALYSIS & DESIGN OF HIGH RISE BUILDINGS :

High Rise Buildings generally have following type of structural loads & thus analysis of the same is an important aspect determining the designing parameters of the Buildings.

• Gravity loads– Dead loads– Live loads– Snow loads

• Lateral loads– Wind loads– Seismic loads

• Special load cases– Impact loads– Blast loads

Snow Load

Dead & Live Load

WindLoad

Earth Quake Load

Structural Loads

Wind LoadsSeismic Loads

• Gravity loads– Dead loads– Live loads– Snow loads

• Lateral loads– Wind loads– Seismic loads

• Special load cases– Impact loads– Blast loads

• A type of rigid frame construction.

• The shear wall is in steel or concrete to provide greater lateral

rigidity. It is a wall where the entire material of the wall is employed

in the resistance of both horizontal and vertical loads.

• Is composed of braced panels (or shear panels) to counter the

effects of lateral load acting on a structure. Wind & earthquake loads

are the most common among the loads.

• For skyscrapers, as the size of the structure increases, so

does the size of the supporting wall. Shear walls tend to be used only

in conjunction with other support systems.

Shear wall system

FRAMED-TUBE STRUCTURES]The lateral resistant of the framed-tube structures is provided by verystiff moment-resistant frames that form a “tube” around the perimeterof the building.

The basic inefficiency of the frame system for reinforced concretebuildings of more than 15 stories resulted in member proportionsof prohibitive size and structural material cost premium, and thussuch system were economically not viable.

The frames consist of 6-12 ft (2-4m) between centers, joined by deepspandrel girders.

Gravity loading is shared between the tube and interior column or walls.

When lateral loading acts, the perimeter frame aligned in the direction of loading acts as the “webs” of the massive tube of the cantilever, and those normal to the direction of the loading act as the “flanges”.The tube form was developed originally for building of rectangular plan, and probably it’s most efficient use in that shape.

Dewitt chestnut

THE TRUSSED TUBEThe trussed tube system represents a classic solution for a tube uniquely suited to the qualities and character of structural steel.

Interconnect all exterior columns to form a rigid box, which can resist lateral shears by axial in its members rather than through flexure.

Introducing a minimum number of diagonals on each façade and making the diagonal intersect at the same point at the corner column.

The system is tubular in that the fascia diagonals not only form a truss in the plane, but also interact with the trusses on the perpendicular faces to affect the tubular behavior. This creates the x form between corner columns on each façade.

Relatively broad column spacing can resulted large clear spaces for windows, a particular characteristic of steel buildings.

The façade diagonalization serves to equalize the gravity loads of the exterior columns that give a significant impact on the exterior architecture.

John Hancock Center introduced

trussed tube design.

Recently the use of perimeter diagonals – thusthe term “DIAGRID” - for structural effectivenessand lattice-like aesthetics has generated renewedinterest in architectural and structural designersof tall buildings.

Introducing a minimum number of diagonals on each façade andmaking the diagonal intersect at the same point at the corner column

The concept allows for wider column spacing in the tubular walls than would be possible with only the exterior frame tube form.

The spacing which make it possible to place interior frame lines without seriously compromising interior space planning.

The ability to modulate the cells vertically can create a powerful vocabulary for a variety of dynamic shapes therefore offers great latitude in architectural planning of at all building.

Burj Khalifa, Dubai.

Sears Tower, Chicago.

BUNDLED TUBE SYSTEM

TUBE-IN-TUBE SYSTEM

This variation of the framed tube consists of an outer frame tube, the “Hull,” togetherwith an internal elevator and service core.

The Hull and core act jointly in resisting both gravity and lateral loading.

The outer framed tube and the inner core interact horizontally as the shear and flexural components of a wall-frame structure, with the benefit of increased lateral stiffness.

The structural tube usually adopts a highly dominant role because of its much greater structural depth.

Lumbago Tatung Haji Building, Kuala Lumpur

Construction materials

Advantages are:

Plasticity

Easily availability

Easy in casting

Non corrosive

Can be cast in situ

Disadvantages are:

Cost of form

Dead weight

Difficulty in pouring

CONCRETE:- cellular concrete of clay-gypsum &

invention of light weight concrete.

FERRO CONCRETE:-it is layer of fine mesh

saturated with cement.

GUNITE:- it is also known as shot Crete.

compressed air to shoot concrete onto (or into) a frame or structure. Shot Crete is frequently used against vertical soil or rock surfaces, as it eliminates the need for

formwork.

GLASS:- float glass with double glass is used in tall buildings .

Tempered glass is used in tall buildings instead of plain glass, as that would shatter at such height.

Materials used for high rise buildings: concrete, steel, glass, cladding material, high alumina cement used for roofs & floors. It contains bauxite instead of clay, cement, Portland cement of lime stone, silica.

http://en.wikipedia.org/wiki/Image:Curing-concrete-columns.jpg

http://en.wikipedia.org/wiki/Image:Curing-concrete-columns.jpg

ANALYSIS OF MULTISTORY FRAME FOR WIND LOAD

o Wind is essentially the large scale

Horizontal movement of free air.

o It plays an important role in design of tall

structures because it exerts loads on

Building.

o High Rise Building-A building Having

height more then 15m As per National

Building Code 2005 of India is called

High Rise Building.

WHAT IS WIND?Wind means the motion of air in the atmosphere. The response of structures to wind depends on the characteristics of the wind

Imperial Towers Mumbai

WIND ISSUES FOR STRUCTURAL DESIGN

o Structural integrity under ultimate loads

o Deflections under service loads

o Building motions and occupant comfort

o Uncertainties in building structural properties

(stiffness, damping)

o Uncertainties in wind loading

o Uncertainties in wind climate

o Codes and standards

o Computational Fluid Dynamics

The Porsche Design Tower is one of the tallest Residential Buildings in the USA according to Forbes

VARIATION OF WIND VELOCITY WITH HEIGHT

o Near the earth’s surface, the motion is

opposed, and the wind speed reduced, by

the surface friction.

o At the surface, the wind speed reduces to

zero and then begins to increase with

height, and at some height, known as the

gradient height, the motion may be

considered to be free of the earth’s frictional

influence and will attain its ‘gradient

velocity’.

o Gradient Height 300 m for flat ground& 550

m for very rough terrain

HOW WIND FORCE GOVERNING FOR

TALL STRUCTURE?

WITH increase height of building

• Construction cost per unit area

decrease

• Increasing lightness in weight per

unit area

• More danger against high velocity

of wind force at high level

PRESENTATION OUTLINE

Definition of shear wall

Position

Design provisions

Behavior

Case studies

201

RC STRUCTURAL WALLS

Known as shear walls

Designed to resist lateral forces

Excellent structural system to resist earthquake

Provided throughout the entire height of wall

Practicing from 1960s for medium and high rise

buildings (4 to 35 stories high)

202

ADVANTAGES OF SHEAR WALLS

Provide large strength and stiffness in the direction of

orientation

Significantly reduces lateral sway

Easy construction and implementation

Efficient in terms of construction cost and

effectiveness in minimizing earthquake damage

203

PLACEMENT OF SHEAR WALLS

204


Located symmetrically to reduce ill effects of twist

Symmetry can be along one or both the directions

Can be located at exterior or interior

More effective when located along exterior perimeter

of building

205

206

Fig. 2 Reinforced concrete shear wall (Murthy C.V.R. ,2005)


Located symmetrically to avoid ill effects of twisting

Symmetry can be along one or both the directions

Can be located at exterior or interior

More effective when located along exterior perimeter of building

6

DESIGN CONSIDERATIONS

Thickness 150 – 400 mm

Minimum reinforcement 0.25% of gross area in each direction

Diameter shall not exceed 1/10 th thickness of section

Reinforcement provided in two curtains when:

Factored shear stress exceeds or

Wall thickness exceeds 200 mm

9

0.25 ckf

SEISMIC BEHAVIOUR OF WALLS

Factors governing seismic behavior of shear walls:

Ductility

Stiffness

Soil structure interaction effects

Period of structure

15

SEISMIC BEHAVIOUR CONTD…

Ductility

Ratio of displacement at maximum load to that at

yield

Highly desirable property for shear walls

Stiffness

Property of element to resist displacement

More stiffer wall need more force to deflect it

16

SEISMIC BEHAVIOUR CONTD…

Soil- structure interaction

Structural damage directly related to depth of

soil overlying the rock and period of vibration of

soil

Understanding relationship between period of

vibrations of soil and structure is important

18

CONCLUSIONS

Shear walls are efficient in resisting earthquakes

More efficient with increased ductility

Soil structure interaction studies are important

ALR ratio has adverse influence on seismic

performance of shear walls

Shear walls with staggered openings are more effective

than walls with regular openings 41

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