Seismic retrofit of steel tall buildings with bilinear oil dampers

This paper presents retrofit solutions for existing tall buildings by utilizing supplemental damping devices, namely oil dampers with relief valve (bilinear oil dampers). To this end, multiple retrofit schemes are presented for a benchmark 40-story steel moment-resisting frame building designed in 1970s in North America. This building has a high collapse risk based on the regional seismic hazard and rigorous nonlinear response history analyses that were conducted with state-of-the-art nonlinear building model representations. Nine retrofit schemes are designed based on three damping levels and three vertical damping distribution methods (i.e. effective, direct and balanced shear force proportional damping distributions). The oil dampers are designed with the aid of a multi-degree of freedom (MDF) performance curves tool. A balanced distribution method is proposed to provide an alternative vertical damping distribution method for frames that exhibit yielding. To assess the proposed retrofit schemes, rigorous nonlinear response history analysis of the retrofitted schemes are carried out in accordance to ASCE 41-13 recommendations. The results suggest that supplemental damping can significantly reduce the collapse risk and control the drift distribution along the building height. The effectiveness of the vertical damping distribution methods is strongly influenced by the extent of frame inelasticity, which in turn depends on the supplemental damping level. Although damper velocity demands may exceed the expected values in a low probability of occurrence seismic event, the corresponding damper forces remain relatively constant. In addition, a large amount of linear supplemental damping is provided at low and moderate ground shaking intensities.