A thesis submitted in partial fulfillment of requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 2004

Recent studies have shown that Thailand is at higher seismic risk than one ever expected although Thailand located in a low to moderate seismicity seismic region and there has never been any severe earthquake damage in this country. There is a raise in the level of awareness about the possibility of seismic hazard. In addition, reinforced concrete structures in Thailand are usually designed without the consideration of seismic loading since building design code and construction practice in Thailand do not include modern seismic provisions. Therefore, the deficient detailing of the members can lead to questionable structural performance during seismic activity. Reinforced concrete beam-column frames are found to be typical in many low-rise to mid-rise buildings in Thailand and beam-column joint regions in such frame are of special interest because they are usually non-seismically detailed including no transverse reinforcement at joints, lap splice in column just above joint level, and construction joints just above and below the beam level. In this research, the quasi-static cyclic loading test was conducted on a beam-column subassemblage that is considered to be one of the most critical members against a seismic action. Structural indices, which indicate the seismic behavior of the beam-column subassemblages, were calculated based on the design documents of ten mid-rise RC mid-rise frame buildings. From the structural indices, interior beam-column subassemblages in Thailand normally are the strong column-weak beam type and can be separated into three groups based on tributary area of each subassemblage. Some might have a poor seismic performance but some might have a good seismic performance depend on the bond index and maximum joint shear stress over joint shear strength ratio. Three specimens representing typical RC mid-rise frame buildings were carefully designed based on the range of structural indices. The experimental results show that if bond condition along the beam bars passing through the interior joint is good enough, the so called joint shear failure shift to the ductile flexural failure in beam. However, almost specimen failed in joint shear failure mode because of the occurrence of bar slip. Bond deterioration along the beam longitudinal bars passing through the interior joint was considered to be the main cause of the degradation in strength and initial stiffness while high diagonal compressive force in joint caused the severity of diagonal crack in joint. If joint shear failure occurred, poor seismic performance could be observed through the experimental force-story drift relationship. For the specimens that failed in the joint region, the strength of specimen decreased more than 20% of peak resistance at 3.00% drift and further reduced approximately 45-60% of peak resistance at 5.00% drift. The peak resistance was found at 1.50%-1.75% drift while the peak strength of specimen that failed in the critical beam section was obtained at a story drift of 4.60% and then the strength dropped to approximately 60% of peak resistance at a story drift of 5.00%.