Large Span Structures

Presented by : FAIRUZ Barch/8008/10

Large Span Structures :

•Used in roofs for halls & hall type structures.•Composed of steel in the form of truss system.•Have load transfer mechanism•Quiet strong in nature•Unique because of their aesthetic properties..• Used in airport, railway station, stadium, assembly hall, godown & temple etc.

Large Span Structures:•Shell structures.•Folded plate.•Steel space frame.•Coffered slab•North light roof•Patent glazing

Shell Structures: •Is a curved surface structure.•Transmits load more than 2 directions to support.•Highly efficient.•Shaped, proportioned & supported•Transmits load without bending or twisting.•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.

Shell Structures: 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

1. Dome :•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 domesSmooth shell domes Ribbed shell domes

Different Types Of Dome :

Spherical dome

Rectangular domeCylindrical dome

Triangular dome

2. 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

Multi barrel vault

North light barrel vault

Short span vault

Cantilever barrel vault

Different Types Of Shell Vault :

3. 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•

Cylindrical Shell

•Sliding curve is straight.•Sliding and stationary curves can have any geometrical shape.

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.

4. Ruled Surface Shell :•Is a type of shell structure.•Obtained by moving a straight line so that it ends lie on two fixed vertical curve.•Vertical curves can be similar or different types.• When 2 curves are of similar nature , then cylindrical shell is obtained.•When one of the curve is elliptical, circular & other a horizontal straight line parallel to the base line of the vertical curve then the shell formed is called Conoid.•Have a saddle surface.

Cylindrical Shell

Conoidal Shell Cone Shell•Cone is a special case of conoid

•Horizontal line is a point.

•Curve is circular.

•Hyper paraboloid is also a ruled surface shell.

•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.

Folded Plate Structures:

•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 .

Steel Space Frame Structures:

Different Types Of Space Frame Structures:

Braced barrel vault structure

Hipped end structure

Polygonal dome structure

Geodesic dome structure

Ribbed dome structure

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.

North light structure: • Is a structure Used to take natural day light from north side.•Glazing bars, bolts & nuts, shoe stop, tension clips & washers are made of aluminum.•It requires no painting.•Saves energy used in consumption of tube lights etc.• Cost saving.•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.•It can be used for spans from 20-30m.•Used for industrial buildings, drawing rooms etc

Patent Glazing:

Is a is a non-load bearing framing system.•Used in overhead glazing system.• Can also be used in vertical situations.• Is a drained and ventilated system of dry glazing comprising a series of longitudinal support members, known as ‘Patent Glazing Bars’ , fixed to the building structure, and glass infill's, either single- or double-glazed.• Does not rely necessarily for its water tightness upon external glazing seals.• Is an economic alternative to four edge support curtain walling.• Slim profiles allow the full use of natural light in the building.• Found in railway stations, shopping malls, atria, schools, canopies, roofs & north light glazing.

The End

! ! ! THANK YOU ! ! !