Assessment of Seismic Deficiency of Existing Reinforced Concrete Buildings in Bangkok

Abstract

This paper presents a result of assessment of seismic deficiency of buildings in Bangkok. The target buildings are mid-rise reinforced concrete beam-column frames having 5-15 stories. The occupancy type is essential and assembly facilities including schools, university, governmental offices and apartments. Many of these buildings with more than 6 stories are usually provided with reinforced concrete lift core. The seismic evaluation methodology consists of demand to capacity ratio determination (DCR), reinforcement detailing check and failure mode investigation. Eight buildings are examined. The seismic deficiency is checked against earthquake loading specified in No.49 Ministerial Law [1] and the ACI [2] requirements for Intermediate Moment Resisting Frame. The region of interest is the first floor sub-frame where the lateral shear is supposed to be highest. The moment frames in both transverse and longitudinal directions are considered. The result shows that all eight buildings do not satisfy reinforcement detailing criteria. Five out of eight buildings do not satisfy DCR criteria. Based on the failure mode investigation, the result shows 44% of beam flexural failure, 41% of joint shear failure and 15% of beam shear failure. It is seen that shear failure covers 66% of the total. The majority of failure is found in beams. The reason why the DCR criteria is not critical is due to traditional working stress design approach for RC structures in Thailand with lower allowable compressive strength of concrete and steel compared to more modern ultimate strength design codes. Another reason is the presence of lift core that reduces the forces transmitted to beam-column frame.