Shell roofs have been proved to be very useful for covering the large structures. RCC shell roofs are becoming very popular these days. A shell structure is a thin curved membrane or slab usually made up of reinforced concrete, which can function both as a roof covering and structure. Shell roofs typically composed of concrete panels curved, cylindrically or spherically to achieve greater strength.
Shell roof is basically the modification of a pitched roof and covers large areas of the building. Moreover, shell roof is three-dimensional structures consisting of thin membrane slabs, curved in one or more directions which transfer the loads on points of support, i.e. columns, beams, walls etc. Shell roofs are built with several materials such as in situ reinforced concrete, timber, steel sheets, ceramics, glass, plastics, hard board, lattice and composite structure etc.
Shell roofs are used for covering large span structures with a single storey, e.g assembly halls, recreation centers, theatres, factories, research labs etc. A shell roof is commonly used in public building because shell roof is aesthetically pleasing. When the inside of the building is required to be open without any walls or pillars then the shell roof is very useful than flat or even pitched roof. The shells roofs are lighter in weight and save reinforcing steel and concrete.
Singly-curved shell and doubly-curved shell are the types of shell roofs. The thickness of singly-curved shells should not be less than 5 cm. Double curved shells are structurally more efficient than single curved shells. However, preparation of the centring work of doubly-curved shell roof is more difficult. Shell units are effectively used for replacing solid slabs.
In shell roof construction, the slope of the roof and the curve of the arc must be carefully designed so that the building remains stable. Shell roof is not suitable where the roof is required to be at different levels, as the entire structure of the roof must be built at a single level. In shell roof construction, lighting and ventilation arrangement are also difficult to install.
The design of shell roof is difficult, expensive and need skilled and experienced personals. A shell roof is relatively thin and does not require support beams. The costs of materials for these types of roofs are lower than the materials required for either a flat or a pitched roof.
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