Damage Evaluation of Steel Moment and Buckling Restrained Braces Frames under Critical Successive Earthquakes

In the seismic active zones, structures are often exposed to successive earthquakes. Seismic sequence phenomenon refers to the occurrence of repeated earthquakes with significant PGA shortly after the first earthquake. Vulnerability of steel structures with buckling restrained brace (BRB) subjected to successive earthquakes consist of main-shock and critical aftershocks indicates that the effect of consecutive earthquakes, depending on their intensity, has significant effects on structural failure. For this purpose, 2D steel moment and buckling restrained brace frames with 3, 7 and 11-story are designed based on Iranian Standard 2800 (Fourth Edition). In the following, studied frames are implemented in OPENSEES software and analyzed under single and critical successive earthquakes after verification. Based on the results of nonlinear dynamic analysis, the Park-Ang damage index was calculated for all frames and after processing the output results in MATLAB software, the final results were reported. The results show that in all frames, successive earthquakes increased the damage index due to the accumulation of damage in the elements due to stiffness and strength degradation. It has also been observed that the ratio of increased damage in the steel moment frame caused by consecutive to single case was higher compared to the BRB frames. That is, considering the BRB has reduced the ratio of this failure under consecutive earthquakes.