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.
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.
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.
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
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.
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.
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Numbers of designs and shapes are possible, because of introduction of modern technology and construction techniques. •
Disadvantages: •
Labour Intensive as skilled labour is needed.
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Faulty design may prove more costly with respect to Shell Constructions.
Much more Centering / Formwork is required. Also any defect or wrong method of Formwork Erection 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 •
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 up on 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. •
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 1923 as 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 remarkable engineering undertaking of the time. Based on the application of this pre-stressed structure Eudene Freyssinet has been called " the father of pre-str essed 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. •
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 shapes and 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.
Folded structures in the plane are the structures in which all the highest points of the elements and all the elements of the lowest points of the folded structure belong to two parallel planes.
Frame
folded structures represent constructional set in which the elements of each segment 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.
Spatial
folded structures are the type of a structure in which a spatial constructive set is formed by combining mutually the elements of a folded structure.
The shape of folded structures affects the transmission of load and direction of relying of folded structures. Based on these parameters we can do the division in linear folded plate structure, radial folded plate structure, spatial folded plate structure.
