Seismic behaviors of columns in ordinary and intermediate moment resisting concrete frames

The objective of this study was to investigate the seismic behaviors of columns in Ordinary Moment Resisting Concrete Frames (OMRCF) and Intermediate Moment Resisting Concrete Frames (IMRCF). For this purpose, two three-story OMRCF and IMRCF were designed according to the minimum design and reinforcement detailing requirements specified in ACI 318-02. This study assumed that the building was located in seismic zone 1, as classified by UBC. According to ACI 318-02 the reinforcement detailing requirements for OMRCF are less stringent than those for either IMRCF or SMRCF (Special Moment Resisting Concrete Frames). Tests were carried out to evaluate the seismic behaviors of OMRCF and IMRCF columns using 2/3 scale model columns. Each column was considered as consisting of an upper part and lower part divided at the point of inflection. Quasi-static reversed cyclic loading was applied to the specimens with either constant or varying axial forces. The test variables of this experimental study were the type of axial force (constant and varying, and low and high), the existence of lap splices (with or without lap splice) and type of moment resisting concrete frame (OMRCF or IMRCF). It was observed that all OMRCF and IMRCF column specimens had strength larger than that required by ACI 318, and they had drift capacities greater than 3.0% and 4.5%, respectively. However, the drift capacity of specimens varied with respect to the existence of lap splices and the spacing of lateral reinforcement at column ends.