ANALYSIS AND DESIGN OF FLAT SLAB BUILDING WITH BRACINGS IN SEISMIC ZONES

Abstract

Flat slabs are favoured by both architects and clients because of their aesthetic and economic advantages. Though this form of reinforced concrete construction gives several advantages over frame structures, they also present some disadvantages because of brittle punching failure and large lateral deformations. Many researchers recommend that flat slab should be designed to resist only gravity loads when used in higher seismic zones and lateral loads should be carried by lateral resisting system. This study is inclined towards the seismic response of a flat plate — braced frame system. Braces are used as structural elements and they do resist lateral forces with substantial structural action. Slab-column connections are the first point of yielding in case of buildings without braces. The shear capacity of this connection reduces drastically in the presence of lateral loading and hence, in such type of buildings should be carefully designed. In case of models with braces, yielding takes place in braces and then subsequently in slab-column connections. Trussed frames are expected to be more efficient in resisting lateral loads. Therefore, RC braced frame building should also be explored for its structural economy in resisting lateral load. The meaning of structural economics is restricted to comparison of the structural cost of the material i.e., the cost of reinforcement steel and concrete required for slabs, beams, columns and braces in building. The cost of foundations is not included in the computation of structural cost. It also does not include the cost of labour and cost of scaffolding. IS 1893 (Part 1):2002 [3]* does not specify that braced frames could also be designed as lateral load resisting system in RC flat slab buildings. Therefore, in this dissertation, an attempt has been made to study about the bracings in building when subjected to earthquake and the structural economics of RC Flat slab building with and without bracings. In the present study, a regular RC flat slab building is analysed and designed for zone IV resting on medium soil strata as per IS 1893(Part 1): 2002 with certain modifications (design of beam in the perimeter of the building and two types of braced frames). Modifications with additional construction elements improve lateral strength, stiffness and improving seismic behaviour of flat-slab construction system [25]. Selected results from the analysis are presented.