Seismic Behaviour of Setback Buildings
Milind V. Mohod 1, Nikita A. Karwa 2
Assistant Professor, Department of Civil Engineering, PRMIT & R, College, Badnera, Maharashtra, India
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A common type of vertical geometrical irregularity in building structures arises from abrupt reduction of the lateral dimension of the building at specific levels of the elevation. This building category is known as the setback building. Various researchers have studied the behavior of setback buildings by taking into account different approaches, which revolve mainly around geometric, mass, stiffness and different methods of seismic analysis. But the value of critical setback ratio for which the structure is less prone to earthquake forces has not been reported. Hence, a need has risen to study and specify some improvements in codal provisions for understanding the behavior of setback buildings. Reference structure results were adopted for validation of results obtained from all these models, which helped us to reach the desired output of the task. Nodal displacement and storey drift criteria was considered for ascertaining the optimum value of critical setback ratios. The optimum value of setback ratio came out to be RA=75% and RH=6/5, where the nodal displacement and storey drift values are affecting structure in negligible amount as in comparison to other setback ratio values. Hence, as we go through seismic code, the revision of seismic codes provisions for geometric vertical irregularities seems to be essential to stipulate more restrictive limits or apply more accurate analytical procedures to predict the seismic performance of setback structures under the seismic excitations, especially for structures with critical setback ratios.