ScienceAsia 34 (2008): 049-058 Nonlinear Finite Element Analysis of Non-Seismically Detailed Interior Reinforced concrete Beam-Column Connection under Reversed Cyclic Load Teeraphot Supaviriyakit a , Amorn Pimanmas a* and Pennung Warnitchai b a School of Civil Engineering and Technology, Sirindhorn International Institute of Technology, Thammasat University, Thailand. b Asian Institute of Technology, Thailand. * Corresponding author, E-mail: amorn@siit.tu.ac.th Received 2 Mar 2007 Accepted 19 Oct 2007 ABSTRACT: This paper presents a nonlinear finite element analysis of non-seismically detailed reinforced concrete (RC) beam-column connections under reversed cyclic load. The test of half-scale nonductile reinforced concrete beam-column joints was conducted. The tested specimens represented those of the actual mid-rise reinforced concrete frame buildings designed according to the non-seismic provisions of the American Concrete building code (ACI). The test results show that the specimens representing small and medium column tributary area failed in brittle joint shear while the specimen representing large column tributary area failed by ductile flexure though no ductile reinforcement details were provided. The nonlinear finite element analysis was applied to simulate the behavior of the specimens. The finite element analysis employed the smeared crack approach for modeling beam, column and joint, and employed the discrete crack approach for modeling the interface between beam and joint face. The nonlinear constitutive models of reinforced concrete elements consisted of coupled tension-compression model to model normal force orthogonal and paralleled to the crack and shear transfer model to capture the shear sliding mechanism. The finite element model (FEM) shows good comparison with test results in terms of load-displacement relations, hysteretic loops, cracking process and the failure mode of the tested specimens. The finite element analysis clarified that the joint shear failure was caused by the collapse of principal diagonal concrete strut. KEYWORDS: beam-column connection, nonlinear analysis, joint shear failure, diagonal compressive strut, reinforced concrete plate element. doi: 10.2306/scienceasia1513-1874.2008.34.049 INTRODUCTION Although many cities in South East Asia are considered as being located in low to moderate seismic zone due to a relatively long distance from active earth faults, they are not absolutely exempt from seismic hazard. Bangkok, for example, is founded on a soft basin of marine clay of several ten-meter depths. This soil characteristic has a potential to amplify the seismic wave up to 3-4 times 1 . The soft ground condition is quite similar to that of Mexico City, which was devastated by 1985 Mexico earthquake with almost 10,000 death toll. Recently, the 2004 Sumatra earthquake in the Andaman Sea recorded at a magnitude of 9.3 on Richter Scale, caused violent shaking of many highrises in Bangkok though the epicenter was more than 800 kilometers away. The quake has prompted a serious public concern on seismic safety of buildings. Many tall buildings, though not designed for seismic loads, usually have shear walls to resist wind forces, and consequently may not be vulnerable to the overall collapse under the earthquake 2-3 . On the contrary, many low-rise and mid- rise buildings of up to 10 stories are rigid frame without shear walls. The frame structures mainly resist lateral forces through bending of beams and columns. Most of these frame structures were designed for gravity load only according to the American Concrete building code (ACI) in Thailand, and British code (BS) in Singapore and Malaysia 4 . As a result of the lack of seismic consideration in structural design, the reinforcement details of these frame buildings are usually weak against earthquake loading. As shown in Fig. 1, the deficiencies of reinforcement details are characterized by (a) little or no confining reinforcement in beam-column joint, (b) lap splice of longitudinal column bars immediately above floor level, and (c) widely-spaced column ties and beam stirrups. Under lateral force, the joint has to carry a large horizontal shear force (Fig. 2(a)) in order to equilibrate moments acting on the joint in the same direction by framing beams. Concurrently, the longitudinal beam bar in the joint is also subject to a large bond stress. As a result of these forces, the joint commonly fails by either joint shear or bar pull-out failure.