PUSHOVER ANALYSIS OF RC BUILDING FRAMES WITH SYMMETRICAL SETBACK

Abstract

Multi-storey moment-resisting frames should have sufficient capacity to resist damage under earthquake excitations. The main parameters that affect the seismic capacity are stiffness, mass, and strength. Due to modern architectural design demands, geometrical irregularities have become one of the most practical problems for structural engineers. These irregularities can be in either plan or elevation. The most common reason for the irregularities in elevation is the presence of setbacks. A lot of research has been performed to study the seismic capacity of structures with setbacks and derive methods to improve their seismic performance.

The pushover analysis is a non-linear static technique used to evaluate the seismic capacity of structures. Standard pushover analyses stated in ATC-40, EC8, and FEMA-356 are limited for buildings with regular geometry. Investigating the capacity and performance of buildings with setbacks using the standard pushover analysis may not be possible as it does not take into account the contribution of higher modes. There is limited research in the literature using the pushover analysis methods for buildings with setbacks. In order to investigate and provide a solution for this practical problem, the performance of standard pushover analysis, and other advanced pushover methodologies for buildings with the setbacks, have been examined.

In this thesis, the seismic capacity and performance of several reinforced concrete multi-storey moment-resisting RC frames with setbacks are investigated using four pushover analysis methods: the mass proportional uniform pushover analysis, the mass proportional triangular pushover analysis, the method of modal combinations, and the improved upper bound method. Also, the non-linear time-history analysis using seven scaled earthquakes is applied to determine the mean values and standard deviations for the seismic responses. The results of the storey drifts for serviceability, inter-story drifts for damage and the base shear for strength determined by the pushover analysis methods are compared with the mean results determined by the non-linear time-history analysis. Results from this comparative study showed that the improved upper bound in investigating the seismic capacity and inter-storey drifts gives a good estimate compared with those determined by the non-linear dynamic analysis. The mass proportional uniform pushover method can be applied to estimate the base shear capacities of buildings for practical purpose.