Anchorage Effects of Discontinuity Reinforced Bar in Bean-Column Joints

• Main Authors: Jun-Xian Huang, 黃峻賢
• Other Authors: 廖國偉
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/71992042799858434092

碩士 === 淡江大學 === 土木工程學系碩士班 === 97 === The objective of this study is to investigate the influence of the discontinuous beam flexural reinforcements, in the area of beam-column joint, on the seismic performance. According to the ACI 318-08 and Taiwan’s Concrete Engineering Design Specification and Commentary (401-96) provisions, “the 90-degree hook shall be located within the confined core of a column or of a boundary element”, indicating that 90-degree anchoring hooks should be directed to the joint core if the beam flexural bars have to be ended in this region. Also, based on the strut and tie model, when the 90-degree hooks is arranged within the core region, the confinement effect will be better with the consideration of shear force limit state, and thus have better performance. In this study, we conduct eight full size experiments (five of them are interior beam-column connections and three of them are exterior beam-column connection) to investigate the influence of the location of the 90-degree hooks’ on the performance of beam-column joints. The shear strength of the specimens are designed based on the recommendation of the ACI 318-08 code and the strut and tie model. The method of displacement control is used during each test. Three tests fail to reach the design target due to the early anchor damaged, on the other hand, plastic hinges are found in the end of beam which is in the vicinity of the beam-column joint in the remaining five tests. Note that the development moment strengths of these five tests are close with identical positive and negative flexural reinforcement ratio, indicating that there is no apparent effect due to the different location of 90-degree hooks. The shear force requirement in the joint area is not very high could be the reason. Tests also show that more cracks and shear deformation are found in the beam-column joint area, in which the 90-degree hooks is directed to outside region of joint. In the end, we calculate the initial flexural stiffness of each beam by offset 0.5% deformation. From the calculated results, the initial stiffness is about 22-32% of the elastic stiffness. We also found that the initial stiffness is linear with the reinforcement ratio. This study also proposed a simplified tri-linear model to predict the plastic hinge mechanism in the beam area nearby the joint.