SEISMIC RETROFIT OF A HIGH-RISE STEEL STRUCTURE CONSIDERING LONG-PERIOD AND LONG-DURATION GROUND MOTIONS

Considering the influence of long-period and long-duration ground motions, a high-rise steel structure is retrofitted and its seismic performance is assessed. The high-rise steel structure located in Shinjuku, Tokyo of Japan, experienced “3·11” earthquake and its acceleration data was recorded by a strong earthquake monitoring system. To make it an emergency shelter, we proposed 2 retrofit schemes to improve its seismic performance. The recorded data is analyzed by a spectrum analysis method and a time-frequency domain analysis method, and it is revealed that the earthquake has an obvious far-field long-period and long-duration characteristics and the long-period component lasts for 300 s before gradually weakening. Inelastic characteristics and potential damage distributions are analyzed using Ai-distribution seismic design forces, and then the static analysis method based on storage stiffness is used for optimized damping design. We selected long-period and long-duration ground motions including the recorded data and one normal ground motion to conduct inelastic dynamic analysis and damage assessment. Compared with the normal ground motion, the damping effect of the high-rise structure subjected to long-period and long-duration ground motions is more obvious. The optimized retrofit scheme makes the vibration decay quickly, which reduces the maximum response of the structure and the damage degree of the structural members. As for steel braces, the cumulative axial strain which can examine local buckling is significantly larger subjected to long-period and long-duration ground motions than that of the normal ground motion. Therefore, we should pay more attention to the local buckling of braces when considering long-period and long-duration ground motions.