Response study of the tallest California building inferred from the Mw7.1 Ridgecrest, California earthquake of 5 July 2019 and ambient motions

Abstract

The newly constructed tallest building in California, the 73-story Wilshire Grand in Los Angeles, California, is designed in conformance with performance-based design procedures. The building is designed with concrete core–shear walls, three outriggers with buckling restrained braces (BRBs) located along the height, and two three-story truss-belt structural systems. The building is equipped with a 36-channel accelerometric seismic monitoring array that recorded the recent Mw7.1 Ridgecrest earthquake of 5 July 2019, as well as the Mw6.4 Ridgecrest earthquake of 4 July 2019. In this article, only the Mw7.1 event of 5 July 2019 is studied because of a larger response of the subject building during that earthquake. The earthquake records of 5 July 2019 are specifically studied to determine its dynamic characteristics and building-specific behavior. The structure exhibits torsional behavior most likely due to abrupt asymmetrical changes in the thickness and size in-plan of the core–shear walls. The translational and torsional modes during the earthquake are not closely coupled, which does not lead to a beating effect even though there is an appearance of it in the records. Available ambient records are used only to identify modal frequencies of the building and compare them with those from the Mw7.1 event of 5 July 2019. Due to the relatively low amplitude of shaking during the earthquake, the drift ratios are too small to cause any damage. It is expected that during stronger shaking levels likely to be caused by future events, these characteristics may change and the effect of BRBs can be better assessed.