Investigating the Response Mechanism of Vertical Concrete Structures to Alternating Horizontal and Lateral Loads

The improper performance of columns in concrete buildings designed and built in the past years has caused concern and attention to their vulnerability to collapse. The investigation of the damages caused to the structures after various earthquakes and the research conducted during these years have caused changes in the design practices to achieve ductile behavior in the columns. Most of the efforts have been made in these years to improve the design criteria, but the effect of the axial force or the loss of the axial capacity of the columns in the existing buildings built in the past years is still unknown. Most of these columns have transverse reinforcements with large distances, which provide little lateral resistance for the longitudinal reinforcements and also little confinement for the concrete in seismic loads. Many of these columns are not accepted according to the rules of today's regulations. In these columns, not only determining the shear capacity but also the ability of the column to withstand the axial force after the shearing is of great importance. The failure of such columns is due to shear deformations that lead to shear failure and then axial failure. At first, a comprehensive review is done of the studies of other researchers. In this review, we try to collect the analytical and laboratory studies available in the technical literature. These studies are related to the testing of concrete columns until the time of gravitational collapse and the behavior models of the columns until this limit state. Then, according to the collected information and their analysis, several columns will be designed and built for laboratory study. These columns are designed to represent the condition of columns in old concrete buildings. The comparison between the analytical and laboratory results of the 6 tested column samples shows a good agreement between them. As a result, the proposed method has sufficient accuracy and efficiency to determine the effective stiffness of columns.