Mechanism of shear strength degradation of a reinforced concrete column subjected to cyclic loading

Abstract

The purpose of this study was to investigate the mechanism of shear strength degradation of a reinforced concrete (RC) member under cyclic loading. First, the shear failure after flexural yield of tension reinforcing bars of a RC column designed as bridge pier under cyclic loading was simulated by the method of three-dimensional rigid-body-spring-model (3D RBSM) and the shear strength degradation was quantitatively evaluated by a numerical approach. Afterward, based on the shear resistant mechanism, the degraded shear strengths after each load cycle were decoupled into the contributions provided by beam action and arch action, with the use of the numerical local stress results. As the important finding, the mechanism of shear strength degradation due to cyclic loading of the RC column was concluded as with the increase of deformation level, the arch action first degraded gradually whereas the beam action maintained its original capacity; then after losing most capacity of the arch action, the beam action began to decrease rapidly, which caused the shear failure. K E Y W O R D Sarch action, beam action, cyclic loading, RC column, shear strength degradation | INTRODUCTIONIn the seismic design of a reinforced concrete (RC) member, one of the basic requirements is that brittle shear failure is prevented and the shear strength exceeds the shear demand corresponding to the flexural strength. 1-3Although a well-designed RC member under monotonic loading ordinarily suffers flexural failure and shows good deformation performance, if subjected to cyclic loading, the load-bearing capacity often decreases within a relatively small displacement ductility after the flexural yield of the tension reinforcing bars and ultimately shear failure occurs (called shear failure after flexural yield in this study). Because the deformation ability of a RC member under cyclic loading is significant in seismic deformationbased design, many researchers have investigated the influences of several factors such as web reinforcement ratio, tension reinforcement ratio, axial load, and shear span-to-depth ratio for the ultimate deformation ductility of RC members by numerical and experimental methods. [4][5][6][7][8] As shown in Figure 1, the reason for shear failure after the flexural yield of a RC member has been conceptually explained as that the shear strength degrades gradually with the increase of displacement level and ultimately becomes less than the shear demand corresponding to the flexural strength, which leads to a decrease of loadbearing capacity. Corresponding to this failure mode, the relationship between degraded shear strength and displacement ductility (also called the shear capacity degradation curve) was proposed for the first time by the ATC seismic design guidelines. 9

Experimental assessment of the effects of biaxial bending moment and axial force on reinforced concrete corner columns

“…9 The bilinear elasto-plastic reinforcement model with kinematic strain hardening was used for steel reinforcement. Previous studies [10][11][12][13][14][15][16][17] are also referred to for modeling of the specimen. Figure 18 shows a comparison of the hysteretic curves of the column specimens between the experimental results (solid line) and the analytical results (dashed line).…”

Effect of Various Structural Factors on Shear Strength Degradation after Yielding of RC Members under Cyclic Loads

“…Moreover, their results confirmed that the initial shear strength of a RC column will degrade remarkably under cyclic load with the increasing displacement ductility, whereas will not be significantly affected under one-side repeated load. On the basis of this work, Fu et al (2017) attempted to explain the degradation mechanism of shear strength of a standard RC column discussed in the research conducted by Nakamura et al (2015). Combining the theory of beam and arch actions and 3-D RBSM numerical method, they developed a practical procedure to decouple the beam and arch actions, truss action and concrete contribution for beam action separately from the initial or residual shear strength at each displacement ductility.…”

“…In this study, based on the research works of Nakamura et al (2015) and Fu et al (2017), the individual effect of structural factors on the degradation behavior of shear strength was separately evaluated, and meanwhile the corresponding effect mechanism was clearly explained by the analysis of beam and arch actions. Attributed to the reveal of the shear resistance mechanism for each structural factor, this study will contribute to discussion of more accurate degradation curves of concrete shear contribution, evaluation of the deformation capacity considering the mechanism and the practical improvement method of deformation capacity, all of which were useful knowledge in terms of the shear failure of RC member after flexural yielding under cyclic loads.…”

Numerical evaluation of localization and softening behavior of concrete confined by steel tubes

“…The rigid elements are discretized using the Voronoi diagram to represent the heterogeneity of concrete and eliminate bias in the initiation of crack direction and propagation. The model has been proven effective in simulating various concrete engineering problems such as cracking, localization, and failure behaviors of reinforced concrete members . The confining steel tube, on the other hand, is modeled using a nonlinear isoparametric shell element which can simulate the local buckling effects in the steel tube.…”

“…The model has been proven effective in simulating various concrete engineering problems such as cracking, localization, and failure behaviors of reinforced concrete members. 11,12 The confining steel tube, on the other hand, is modeled using a nonlinear isoparametric shell element which can simulate the local buckling effects in the steel tube. Surface-based interface elements predefined on RBSM surfaces in contact with shell elements provide the load-transfer interaction between RBSM and shell FEM.…”