Seismic Risk of Low-Rise Steel MRF of Built-Up Batten Columns in Moderate Seismicity Regions

In the last couple of decades, the built-up sections, instead of standard wide-flange profiles in the shortage, have been widely used in the columns of steel frames in Iran. However, the seismic behavior of these columns has yet to be adequately studied, and the performance of these frames in the earthquake is not known. This study attempted to analyze the performance of steel R.C. frames with these columns in the moderate seismicity region. For this purpose, two steel moment-resistant frames with two- and four-story heights were chosen. Both frames were designed using batten and conventional sections. The cyclic behavior of standard and batten columns is obtained by FEM modeling and used to model the frames in OPENSEES. Furthermore, the probabilistic seismic behavior of frames is evaluated and used to develop the fragility function of frames. The frames' failure probability and mean annual losses are estimated in a moderate seismicity region. The results showed that the moment capacity and ductility of the columns with standard sections are 14–30% higher than those of batten columns. Also, the ductility of the batten columns connection is 33–43% lower than that of standard sections. Additionally, the mean drop in the post-failure strength of columns with standard and batten sections is 17–40%, respectively. From the viewpoint of the general behavior of frames, using the batten columns increases the probable loss of frames, especially in four-story frames, which reaches up to two times that of standard columns, indicating the destructive effect of using batten columns in medium and high-height structures, especially in high and very high seismic region.