Simplified seismic demand estimation for existing tall buildings in Thailand

Abstract

A study of the performance evaluation of non-seismically designed buildings in Thailand is summarised and a simple methodology for quicker estimation of their seismic demands is presented. Using six case study high-rise buildings (20 to 44 storeys) and different types of input ground motions, it was found that the peak inelastic displacements of taller structures (with natural periods >1 s) can be significantly higher than their elastic counterparts, especially for ground motions with peak spectral acceleration occurring at longer periods. In such cases, use of the equal-displacement assumption may result in significantly non-conservative estimates of seismic demands. A simplified modal pushover analysis was then applied to the case study buildings. The combined seismic demands were determined by combining the peak modal demands obtained from a series of pushover analyses. The target displacement of the first vibration mode was determined by directly applying a modifying factor to the corresponding elastic displacement, while higher vibration modes were assumed to remain elastic. The seismic demands obtained from the detailed non-linear response history analysis procedure were used as benchmarks. The simplified analysis procedure was able to predict overall seismic demands and individual modal contributions of the case study buildings with reasonable accuracy. The method provides a relatively quick analysis option for performance evaluation of a large number of non-seismically designed existing high-rise buildings in Thailand.