SEISMIC PERFORMANCE EVALUATION OF IRREGULAR RC RESIDENTIAL BUILDINGS

Abstract

The building construction works is increasing massively after the Gorkha earthquake due to reconstruction works as well as necessity of the new houses due to internal conflict, urbanization and increasing population. People are constructing building in rush manner in the area where they have got space for the construction. Most of the site available are of irregular in shape so the construction is done in such a way that it feels comfortable according to the site. But according to the code for the well performed building, one should have the regular configuration. This condition does not meet in the actual field practice so people are compelled to construct the irregular configuration. Sometimes the house owner also loves the artistic view with the irregular effects or shape in the building which brings the irregular configuration and might leads to danger situation on seismic action. This study focused mainly on the irregular configuration with non-parallel lateral load system i.e. trapezoidal and triangular shapes. For the study these building configuration are taken because most of the irregular building configuration available are very close to these shapes and if not then can be converted in such shapes as well. Other shapes such as L, T, U, C. H are already studied by many authors but the main shapes available in actual field are the trapezoidal and triangular. So the response and performance of these building shapes are felt necessary for the study. The objective of the study is to identify the responses of the selected building and then identify the performance limit of them. Altogether 21 buildings models with 7 regular, 7 trapezoidal and 7 triangular building configuration are compared to each other with static linear analysis and dynamic response spectrum analysis. For each shapes the number of bays are varied and also the number of stories are changed to observe the differences. The base shear, time period, displacement, drifts of each building are compared to each other as well as torsion irregularity check was done and then the pushover analysis was done to know the performance limit of these buildings. From the study, it can be concluded that the base shear from static linear is more than the base shear from response spectrum method and time period from code is less than the time period from analysis and does not depend on the irregular configuration. In fact, base shear depends on the load application and area of its coverage and time period depends on the mass and stiffness of the building rather than the height of the buildings. The displacement and drifts have direct relation with the building story and the number of bays. As the building story or number of bays increases the displacement and drift also increases. Among 3 building shapes, regular and triangular shapes have no any torsion whereas trapezoidal buildings are found to be in torsion. Finally, after observing the performance limit through pushover analysis in design based earthquake, all the buildings are within the life safety range and are safe in the design basis earthquake.