A General Procedure for Selecting and Scaling Ground Motion Records for Nonlinear Analysis of Asymmetric-Plan Buildings

In performance assessment and design verification of complex structural systems including base-isolated buildings, high-rise structures and structures utilizing advanced lateral force resisting components (e.g., viscous dampers), nonlinear response history analysis (RHA) is now a common engineering tool to estimate seismic demands. Today, majority of ground motion selection and scaling methods are suitable for symmetric plan buildings with first-mode dominant response. There is, therefore, a need for a robust method to select and scale records for nonlinear RHAs of asymmetric-plan buildings with significant torsional response. Presented here is a generalized ground motion selection and scaling procedure called modal pushover-based (MPS) procedure. The proposed procedure explicitly considers structural strength, determined from pushover curves, and determines a scaling factor for each record to match a target value of roof displacement. The accuracy and efficiency of the procedure is evaluated by using computer models of symmetric-and asymmetric-plan buildings subjected to one or two horizontal components of ground motions. Analyses for one component of ground motions were conducted for five existing symmetric-plan buildings of 4, 6, 13, 19 and 52 stories; for two components of ground motion, 48 single-story systems and 10 multi-story buildings were analysed. Also examined here is the ASCE/SEI 7 scaling procedure for comparison purposes. This study clearly shows that the MPS procedure provides much superior results in terms of accuracy [true estimates of expected median engineering demand parameters (EDPs)] and efficiency (reduced record-to-record variability of EDPs) than the ASCE/SEI 7 scaling procedure.