Study On Seismic Performance Considering Shear Effects And Residual Deformations Of Reinforced Concrete Columns

Aiming at the problems that a large number of existing reinforced concrete columns, piers and piles with poor seismic details are vulnerable to flexural-shear failure (or shear failure) during earthquakes, and the seismic design method for reinforced concrete structures (or members) according to the current codes is still not perfect (e.g., lack of reasonable mechanical analytical model for columns failed in flexural-shear, lack of available post-seismic performance evaluation method for reinforced concrete structures, and lack of specified requirements on repairability for reinforced concrete structures, etc.), this study is focused on the deterioration mechanism of seismic performance for flexural-shear failure columns under two different loading schemes, the influences of shear behavior on seismic performance of reinforced concrete columns, and the post-seismic residual deformation prediction of reinforced concrete columns. The details are listed as follows:1. To study the effects of two different loading schemes (i.e., monotonic and cyclic loading) on seismic failure modes, horizontal load carrying capacity, and deformation performance of reinforced concrete columns, ten groups of column specimens (each group consisted of two same columns) with different shear span ratios and stirrup ratios were designed and tested under monotonic and low frequency cyclic loading respectively. The comparison results of the above two kinds of tests indicate that the degradation degree of shear capacity and stiffness with the increasing of lateral deformation is more remarkable, and the final failure modes are prone to flexural-shear (or shear) when the column subjected to cyclic loading. The deformation properties of the column under cyclic loading reduce due to the effect of cyclic deterioration triggered by the cumulative damage and hysteretic energy dissipation, and the degree of reduction enhances with the increasing of the number of loading cycles and displacement amplitude, especially in the post-peak loading region. Also, a model for modeling the relationship of lateral load-deformation curves of flexural-shear failure columns subjected to monotonic and cyclic loading is developed based on the experimental data analysis in this paper.2. Considering the contributions of three deformation components (i.e., flexural deformation, slip deformation, and shear deformation) to total lateral deformation of the column, the models for evaluating the lateral loads and deformations corresponding to three key damage state points (i.e., flexural yielding, peak lateral load, and flexural-shear failure) of columns failing in flexural-shear are suggested based on the test results in this study. Then, a simplified method for modeling lateral load-deformation curve for the flexural-shear failure column is developed according to the predicted key damage state points.3. Based on the analyses of the mechanical characteristics and available experimental data of flexural-shear failure columns subjected to seismic loads, a model for modeling the load-deformation curves of columns failed in flexural-shear during earthquakes is developed from the practical perspective. In the model, the flexural deformations and slip deformations are predicted by existing analytical models such as the traditional fiber analysis model and slip deformation computational model suggested by Lehman and Moehle, and the shear deformations are evaluated by the proposed modification formulas including shear effects.4. Based on the analyses of the hysteretic behavior and test results of flexural-shear failure columns under cyclic loading, a calculational method for determining the equivalent damping ratio of flexural-shear failure columns is presented. Furthermore, a modified capacity spectrum method (MCSM) for assessing the maximum displacement seismic response of flexural-shear failure columns under seismic loading is also proposed. In this method, the "demand curve" of the column is developed using the proposed method of equivalent damping ratio, and the corresponding "capacity curve" of the column is developed using the model of load-deformation relationship suggested in Content3in this study.5. Based on the statistical analyses of elastic-plastic seismic response (including maximum elastic-plastic deformations and residual deformations) of single degree of freedom (SDOF) systems subjected to seismic excitations, the effects of main parameters such as natural period, system stiffness ratio, relative yield force coefficient, peak ground acceleration, as well as hysteretic model on post-seismic residual deformations of structures are investigated, and a probabilistic prediction model for residual deformations of reinforced concrete SDOF systems (or reinforced concrete columns) is presented combining the theoretical analysis in this research.