Estimating dynamic response from pushover type analysis through a semi-empirical approach

Performance evaluation of buildings against a given level of seismic hazard is usually carried out using a displacement-based approach, called pushover analysis. Among its several variations, Modal Pushover Analysis (MPA) has become increasingly popular owing to its ability of accounting for the recorded ground motion explicitly. Structural performance parameters are usually expressed in terms of displacement and drifts. However, structures are often equipped with non-structural elements which are sensitive to the design response parameters like acceleration, velocity etc. Pushover analysis does not provide any information on the likely dynamic response parameters. In such a case, Incremental Dynamic Analysis (IDA) can be considered as a viable approach, which however is computationally expensive and rarely practiced in a routine job. In this thesis, a semi-empirical method is proposed which uses the modal pushover response to predict an approximate estimate of design dynamic response parameters such as, acceleration and velocity. While doing so, frequency at each analysis stage (i.e., Peak Ground Acceleration (PGA) level) is first estimated from the pushover curve. Variation of maximum absolute acceleration across the height is estimated semi-empirically using the response of linear time history analysis, and frequency and base shear calculated in MPA. Variation of absolute maximum velocity across the height is estimated in an analogous way using that of the absolute maximum displacement response, frequency and modal mass participation factor at the stage of analysis considered. In order to illustrate the methodology, three test-beds are considered: 1) a ten-storeyed building designed conforming to Indian seismic code 2) a seven- storyed existing building located in seismic zone-IV of India and 3) a ten storey unsymmetric building designed as per Indian seismic code. Three seismic events recorded at the Large Scale Seismic Testing (LSST) array in Lotung, Taiwan are used for the purpose of illustration. Absolute acceleration and velocity distributions across the height using the proposed approach are found in well agreement with that from rigorous IDA.