Seismic Performance Evaluation of Reinforced Concrete Moment Resisting Frames with Various Ductility in Low Seismic Zone

Abstract

Problem statement: Bangkok, the capital of Thailand, is at moderate risk for distant earthquake due to the ability of soft soil to amplify ground motion about 3-4 times although it locates in low seismic zone. In addition, before the enforcement of seismic loading for buildings in the Ministerial Law in 2007, many existing reinforced concrete buildings in Bangkok may have been designed without consideration for seismic loading and did not incorporate the special detailing provisions that required for ductile concrete frames. Now, guidelines for seismic loading of buildings of Thailand (DPT 1302-52) have been recently improved by adopting ASCE7-05. Approach: This study is focused on the effects of the new guidelines on cost estimates and the seismic performance of a nine-story reinforced concrete apartment building with various ductility by the nonlinear static and nonlinear dynamic analyses compared with a Gravity Load Designed (GLD) building. Five selected ground motion records are investigated in the analyses. In order to examine the influence of design ductility classes, the seismic forces on moment resisting frame buildings are defined according to the newly proposed seismic specifications of Thailand with ductility from 8, 5 and 3, corresponding to Special Ductile (SDF), Intermediate Ductile (IDF) and Ordinary Ductile (ODF) frames, respectively. The various frames are assumed to have collapsed if the local drift exceed of 3, 2.5, 2 and 1% for SDF, IDF, ODF and GLD, respectively. Results: SDF is more ductile than that of ODF, however, the strength of SDF is less than ODF. For inelastic designs, SDF decreases stiffness and increases deflection of structures. As for the effect on cost estimates, ODF is the most expensive among ODF, IDF and SDF. Costs of SDF and IDF in Bangkok are quite similar. The study found that the average PGAs for the failure state for SDF, IDF, ODF and GLD are 0.76, 0.60, 0.50 and 0.29g, respectively. Moreover, for the failure state of GLD with volumetric ratio of horizontal confinement within joint panel less than 0.003, the average PGA is only 0.15g. Conclusion/Recommendations: These various frame designs are predicted to just achieve the Immediate Occupancy (IO) performance level. The results also indicate that all frames including GLD are able to withstand a design earthquake. The SDF and IDF are the two best options in consideration of cost and seismic performance.