Seismic performance of stairs as isolatedand built-in rc frame building

Abstract

Stairs are vulnerable part of buildings subjected to earthquakes while stair elements have low ductile capacity and may be subjected to brittle failure. Also in analysing a RC building for gravity and seismic loads, its presence is not considereddue to modelling complexity instead its weight is transferred to supportingbeams or walls. Thus, design of stairs is of keen interest. Normally stair slabs are supported on wall or cast monolithic with the floor beam provided along or across the direction of flight. These supports provide rigidity in the stair slabs and impart hogging moments at corners and near supports. Also, as part of building frame, the loads are transferred from the stair slab to the supporting beams, hence a considerable reduction in the deflection and moments in the stair slabs. The behaviour of stair slab is further changed when subjected to seismic loads. Presently, the behaviour of reinforced concrete stair slab is investigated considering differentsupport arrangements with and without seismic effects, and values of moments arecompared as obtained in conventional design methods based on specifications of standard codes of practices.