A Study of Shear Strength of Reinforced Concrete Beam-Column Joints for Earthquake Resistance

• Main Authors: Hung-Jen Lee, 李宏仁
• Other Authors: Shyh-Jiann Hwang
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/42733424064159354423

博士 === 國立臺灣科技大學 === 營建工程系 === 88 === A rational model for determining the shear strengths of the reinforced concrete beam-column joints for earthquake resistance is proposed. This analytical model, termed as the softened strut-and-tie model, includes the influential parameters of shear strengths of beam-column joints. On the basis of analytical and experimental studies, a simplified procedure for the design of the shear strengths of the beam-column joints is also recommended. Beam-column joints of moment-resisting frames are geometrical discontinuity regions subjected to very high horizontal and vertical shears under earthquake-introduced loading. The joints are assumed to resist diagonal compression force and to fail in crushing of concrete. The proposed model simulates the shear-resisting mechanisms of joints with the strut-and-tie concept, which satisfies equilibrium, compatibility, and constitutive laws of cracked reinforced concrete. In the proposed model, web reinforcement plays two roles. One is to form tension ties and to provide shear-transferring paths. The other is to control the crack widths and to retard the softening process of the cracked concrete. The strength condition of the diagonal compression failure is defined as the crushing of concrete strut in the model. The proposed model could analyze the shear strengths not only for beam-column joints, but also for similar discontinuity regions failing in diagonal compressions, such as deep beams, corbels, and squat walls. Test Results of 10 high strength concrete exterior beam-column joints indicated that the shear capacity of joint is the most significant parameter for the seismic performance. If the shear capacity of joint is adequate, the great reduction of joint hoop reinforcement from the ACI Code requirement is possible with little or no influence on the seismic behavior of the specimens. However, test results also indicated that elastic hoop reinforcement maintains the integrity and retards the decay of joint strength during large cyclic reversals of displacements. The joint reinforcement is found to be effective as horizontal or vertical ties if sufficient anchorage or development length of the reinforcement is provided. A proposed simplified method predicts the shear strengths of discontinuity regions with the same accuracy of the detailed approach. The proposed simple method is inversed to be a design procedure. Beam-column joints designed with proposed procedure have the same level of shear strengths but less amount of hoop reinforcement in comparison with ACI 318-95 Code. The proposal provides more degrees of freedom for engineers to change design parameters and to avoid the possible congestion of reinforcement in a beam-column joint. Integrated and simplified design procedure, which incorporates the actual shear resisting mechanisms as postulated by the softened strut-and-tie model, has been formulated to improve the current shear design regulations for discontinuity regions in reinforced concrete members.