Seismic assessment of RC frame building designed using gross and cracked sections

Abstract

Bangladesh is situated in a seismically active region with a moderate seismic risk. The country has been divided into four seismic zones following the concept of Maximum Considered Earthquake (MCE) with a return period of 2475 years. A number of infrastructures have already been built in order to fulfill the increasing demand of urban population. Bangladesh National Building Code (BNBC) has been updated to a draft BNBC 2017 to consider the realistic design guidelines. The code considers the cracked section properties for designing a structure at a factored load level. A comprehensive study is conducted in the current thesis to assess the seismic performance of buildings considering cracked section properties of the structural members. For comparative seismic assessment, a regular plan of 6-, 10-, and 15-storey RC frame buildings designed with gross section and cracked section (BNBC-2017 draft) properties of RC members using conventional force-based design approach. All the considered buildings are analyzed using nonlinear static pushover analysis. The obtained results show that the inter-storey drift at design load of RC frames designed using gross section property is well within the prescribed limit of maximum permissible inter-storey drift while that of cracked section properties is beyond the maximum permissible inter-storey drift limit. The higher column reinforcement demand is shown for buildings with cracked sections that those of gross sections and this value is higher for exterior and corner columns (27.4% increase for 6-storied) than those of the interior columns. Response reduction factors of the buildings with gross section properties result higher values than those of the cracked section buildings. R values always fall below the design R for the cracked section buildings and it is obtained 3.23 instead of R value of 5 for the considered 6-storied building.