DEVELOPMENT OF SEISMIC DESIGN REQUIREMENTS FOR BUILDINGS IN BANGKOK AGAINST THE EFFECTS OF DISTANT LARGE EARTHQUAKES

摘要

Even though Bangkok is located at a remote distance from seismic sources, a recent seismic hazard study shows that Bangkok is still at risk from damaging ground motions induced by distant large earthquakes. The risk is primarily caused by the ability of thick soft surficial deposits in Bangkok to amplify earthquake ground motions about 3 to 4 times. Furthermore, by the near-periodic, long-period, and long-duration nature of the amplified ground motions, tall buildings with fundamental periods near the predominant period of ground motions are likely to be significantly affected due to the resonant amplification of building responses. Three research studies are currently being carried out with an aim to develop appropriate seismic design requirements for buildings in Bangkok against the effects of distant large earthquakes. The first study is a preliminary seismic microzonation of Bangkok and neighboring provinces. Ambient vibrations on the ground surface at more than 150 sites are measured and analyzed by the Nakamura's H/V method. The results show that the predominant period of ground motions varies from notably high values (1.0 s to 1.2 s) at sites near the gulf of Thailand to low values (around 0.4 s) at the boundary of the Bangkok basin. The second study is an ambient vibration survey of nearly 50 buildings with heights varying from 20 m to 210 m in order to identify their dynamic properties. Relationships between building natural periods and building height are obtained. The third study is an evaluation of inherent seismic capacity of several typical non-seismically designed buildings in Bangkok by pushover analysis. Parallel to the analysis work, several quasi-static cyclic loading tests of RC specimens are also conducted to gain more accurate knowledge on seismic performance of typical nonductile RC columns, beam-column joints, and flat slab-column connections.