SEISMIC RESPONSE OF FLAT SLAB INFILL WALL .SYSTEM

Abstract

The flat slab system is a special structural form of reinforced concrete construction though having several advantages, has some serious issues of concern, like potentially large transverse displacements, low transverse stiffness and brittle punching failure. Therefore, it was recommended that in regions with high seismic hazard, flat-slab construction should only be used as the vertical load carrying system in structures braced by frames or shear walls responsible for the lateral capacity of the structure. In spite of the above concerns, flat-slab systems are often adopted as the primary lateral load-resisting system and their use has proven popular in seismically active regions. But the response under moderate earthquakes indicates extensive damage to non-structural elements even when the code provisions for drift limitation are satisfied. This observation emphasizes the necessity of investigating the vulnerability of flat-slab construction, since the structure exhibits distinct response modes, as compared to conventional moment-resisting frames. This study is inclined to study the seismic response of a flat plate infill wall system. The pushover analysis clearly shows that the slab column connections are the first point of yielding in case of a model without infill walls. The shear capacity of this connection reduces drastically in lateral loading and hence in all buildings these should be carefully designed. However after addition of uniformly distributed unreinforced masonry infills, first yielding was always observed in the infill panels. Though infill provide stiffness to the structure, which initially keeps the drift values very low but after few infills fail, a soft storey effect is induced, which subsequently makes the structure more vulnerable to lateral forces. Hence brick masonry infills when added to a flat plate structure in a place which is located in the zone of high seismicity, though make the structure stiff initially however make it more vulnerable to seismic force and hence should be used only after extensive precautions at design as well as at construction level.