Seismic behavior and response reduction factors for concrete moment-resisting frames

The existing seismic provisions across the world account the non-linear response of a structure in a linear elastic design implicitly using a constant behavior factor, or response reduction factor (R). However, this factor (R) does not address the effects of changes in structural configurations, which eventually alters the dynamic behavior of the structure. Hence, the adequacy of prescribing a constant factor to account for the variable dynamic characteristics of structural systems always appears contentious. Further, seismic analysis of RC buildings usually ignores the interaction of the infill wall with the structural frame leading to inappropriate evaluation of dynamic characteristics of the structure. Hence, in the present research, it is attempted to investigate the sufficiency of the code-based 'R' factor in assessment of seismic behavior using non-linear static analysis (NLS) and non-linear dynamic analysis (NLD) for the structural models considered. Moreover, the results obtained, clearly envisages the influence of structural configuration changes and interaction of the infill wall with the RC MRF on dynamic characteristics in terms of ductility and over strength values. It can be clearly observed that, the code specified constant 'R' for a particular structural type appears erroneous, emphasizing the need for its adequate estimation. This should involve consideration of the dynamic characteristics of the structure resulting in a realistic assessment of seismic demand, thereby contributing to a safe, functional and economical design configuration.