Shear Strength Degradation Model for Performance-Based Design of Short Coupling Beams

Copyright © 2022, American Concrete Institute. All rights reservedUnder earthquake load, as the inelastic deformation increases, the shear strength of reinforced concrete coupling beams is degraded by diagonal cracking. In the present study, for the performance-based design of short coupling beams (l/h ≤ 2.5), a shear strength degradation model based on diagonal strut and truss mechanisms was developed, addressing the effects of the target chord rotation, longitudinal reinforcing bar ratio, length-to-height ratio, ratio and details of transverse reinforcement, distributed longitudinal web bars, and diagonal bars. Based on the proposed method, a simplified moment-rotation relationship of plastic hinges was developed for the nonlinear numerical analysis of coupling beams. For verification, the proposed method was applied to existing coupling beam specimens with a conventional reinforcing bar layout, distributed longitudinal web bars, and/or diagonal reinforcement. The predicted moment-rotation relationships generally agreed with the test results. Thus, the proposed plastic hinge model is applicable to the nonlinear analysis of short coupling beams to describe the shear strength degradation after flexural yielding. Design recommendations for the practical application of the proposed method were discussed. The proposed model revealed that the use of distributed longitudinal reinforcement and diagonal reinforcement is effective for high ductility.N