Study On Failure Modes And Seismic Behavior Of Reinforced Concrete Columns

Reinforced concrete (RC) columns are often used as the main vertical load-bearing elements in building structures, highway bridges and so on. They play a crucial role in overall structural performance and easily fail in earthquake. In China, which is a multi-earthquake-happening country, many structures are located in regions with moderate and high seismicity. From the view of earthquake disaster prevention, the structure still need reconstruction even if it does not collapse because the damage of support columns in structure is so serious that it is difficult to get them repaired. Therefore, investigations on the failure modes and seismic performance of RC columns are necessary. Effective measures should be taken to ensure that the columns develop sufficient bearing capacity and ductility to prevent failure in earthquake. The seismic performance of RC columns is studied in the paper by experimental and theoretical analysis. The main content and conclusion are listed as follow:1. The monotonic loading tests on ten RC columns and cyclic horizontal loading tests on twenty-four RC columns were carried out. Failure modes and seismic performance of RC columns were studied. Also the contributions of flexura deformation, anchorage slip deformation, and shear deformation, to the total deformation of columns were measured and investigated, respectively. Experimental results show that RC columns under cyclic loading may exhibit three failure mechanisms:flexural failure, flexure-shear failure and shear failure. With the decrease of span-to-depth ratio or transverse steel ratio, or the increase of axial load ratio, specimen failure models are changed from flexural to flexure-shear and shear with poor energy dissipation capacity and ductility, and more obvious pinch can be seen from the hysteresis loops. With the increase of total displacement, the contribution of flexure deformation to the total deformation is reduced; the contribution of shear deformation is increased; and the contribution of anchorage slip deformation keeps at about30%-40%2. According to the anti-seismic test data of RC columns at home and abroad, the influences of span-to-depth ratio, axial load ratio, transverse reinforcement ratio, longitudinal reinforcement ratio, concrete compressive strength and reinforcement strength on failure modes of column were analyzed. Considering these influence factors, a probabilistic estimation method was developed to identify column failure mode, and an equation of discriminant parameter for columns failure modes was proposed. 3. Based on test results of columns failed in flexural-shear, the effects of axial load, span-to-depth ratio and stirrup ratio on shear capacity and displacement ductility were estimated, and equations for predicting shear capacity and displacement ductility factor were proposed.4. Based on analytical and experimental results, approaches were developed for predicting the cracking, yielding and failure loads, as well as corresponding deformations, for RC columns failed in flexural-shear. And then according to three feature points, a simplified method was proposed to describe the backbone curve of restoring force model for RC columns in flexural-shear under seismic loads.5. RC circular columns were tested under combined cyclic lateral displacement excursions and constant axial load after being subjected to accelerated corrosion tests. The controlled variables in the test were corrosion level and axial load ratio. Based on the test results, degradation models for loading capacity, stiffness, ductility and energy dissipation capacity of columns were proposed. Test results show that higher corrosion levels or higher axial loads may result in worse energy dissipation capacity and ductility, and the failure mode of columns damaged seriously by reinforcement corrosion may change from flexure to flexure-shear or shear.