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SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

Nov 28, 2015

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Remya R. Kumar

advanced construction
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Page 1: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt
Page 2: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

Thin-shell structures are light weight constructions using shell elements . These elements are typically curved and are assembled to large structures.

A thin shell is defined as a shell with a thickness which is relatively small compared to its other dimensions and in which deformations are not large compared to thickness.

A shell structure is a thin, curved membrane or slab, usually of reinforced concrete.

It functions both as structure & covering. This structure derives it’s strength & rigidity from the

curved shell form.

A primary difference between a shell structure and a plate structure is that, in the unstressed state, the shell structure has curvature as opposed to plates structures which are flat.

Lattice Shell of the Shukhov Tower

Page 3: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

A barrel shells acts as a beam in the long direction and as an arch in the curved area. The arch is supported by internal shears.

The area of reinforcing is , the force divided by the allowable stress.

A = Force / Stress The force in the reinforcing is equal to the bending moment divided by the effective depth.

The edge spans of the shell should be supported by intermediate columns. The stiffness of a barrel shell at the outside edges is simply not stiff or strong enough to carry the

required loads. The shell reinforcing at the edge members acts more like a typical arch and should be reinforced with two layers of bars.

Page 4: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

The design of folded plate roof structures follows the design of barrel shells, but is much simpler because the elements are all essentially beams.

Support the folded plate at its longitudinal

edges by frequent columns

Folded plate north light is usually achived for this roof

Z – shape folded plate ,there are windows between the tilted z shaped for natural light.

Page 5: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

There will be some bending moment at

the junction of the shell and the ring

beam, so it is usual to gradually increase

the thickness at this point and add moment reinforcing.

Page 6: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

Advantages:• Like the arch, the curved shapes often used for concrete shells are naturally strong structures, allowing wide areas to be spanned without the use of internal supports, giving an open, unobstructed interior.

• structure may be immensely strong and safe.

• Numbers of designs and shapes are possible, because of introduction of modern technology and construction techniques.

Disadvantages:

• Labour Intensive as skilled labour is needed.

• Faulty design may prove more costly with respect to Shell Constructions.

• Much more Centering / Formwork is required. Also any defect or wrong method of FormworkErection may result in total collapse of the structure.

• Placing concrete in shells is hard work for the placing crew who must work on a sloping surface and often shovel heavy concrete uphill, so every effort should be made to make the operation simple and convenient, with an adequate number of workers and finishers

Page 7: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

• The construction of a reinforced concrete shell involves many problems, the design and construction of forms, reinforcement selection and placing, concrete materials and placing, and curing and decentering. All of these problems must be understood in order to make the structure safe and economically feasible.

• More than almost any other structural system, shells depend upon the ability of the architect and engineer to foresee the design problems and upon the ingenuity of the contractor to solve the mechanical problems of construction.

Page 8: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

The term folded structure defines a folded form of construction, including structures derived from elements which form a folded structure by their mutual relationship in space.

• The basic idea of creating this type of construction is striving to achieve more constructive height and greater rigidity and reduce the net weight of the structural element.

• The strength and stiffness of folded construction is achieved primarily by proper design of the structure, and to a lesser extent, by thickness and dimension of the elements that form it.

• Engineer Eudene Freyssinet performed the first roof with the folded structure in 1923as an aircraft hangar at Orly Airport in Paris.

• In technological terms this folded construction is made of prefabricated elements, with pre-stressed structure, which is a remarkableengineering undertaking of the time. Based on the application of this pre-stressedstructure Eudene Freyssinet has been called "the father of pre-stressed concrete.

• The large range of full plate becomes too thick and heavy, and as such is not economical. If we form the folded structure of the inclined panels, their vertical projection becomes the height of the folded construction, and thus enables the smaller thickness of the structural element.

• By the use of folded structures far greater ranges can be overcome than by the application of a full flat plate.

Page 9: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

• Folded structures differ in: geometric form, the form of a base over which they are performed, the manner of performance, methods of forming stiffness, function and position in the building, and the material they are made of.

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

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

Based on geometric shape folded structures can be divided into (Fig. 1): folded plate surfaces, folded plate frames, spatial folded plate structures.

Page 10: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

Folded structures in the plane are the structures in which all the highest points of theelements and all the elements of the lowest points of the folded structure belong to twoparallel planes.

Page 11: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

Frame folded structures represent constructional set in which the elements of eachsegment of the folds mutually occupy a frame spatial form.

This type of folded structure is spatial organization of two or more folds in the plane.

Page 12: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

Spatial folded structures are the type of a structure in which a spatial constructive setis formed by combining mutually the elements of a folded structure.

Page 13: SHELL-ROOF-AND-MEMBRANE-STRUCTURES1.ppt

The shape of folded structures affects the transmission of load and direction of relyingof folded structures. Based on these parameters we can do the division in

linear folded plate structure, radial folded plate structure, spatial folded plate structure.