Seismic Retrofit of Existing High-Rise Buildings With Supplemental Energy Dissipation Devices

Abstract eng:
The Pacific Earthquake Engineering Research (PEER) Center has expanded its Tall Building Initiative project to include the seismic performance of existing tall buildings. A candidate 35-story steel moment resisting frame with representative details from that era was analyzed. It was identified that the selected building failed to meet the performance objectives suggested by the U.S. code, and had a number of seismic vulnerabilities that endangered its structural integrity under a major earthquake. Therefore, retrofit strategies should be explored to upgrade the building’s seismic performance and address its major vulnerabilities. The retrofit intent is to reduce the number of beam-to-column connection failure to an extent that it would not jeopardize the building’s overall stability under a basic safety earthquake, level 2 (BSE-2E) per ASCE 41. In addition, the cost-effectiveness of each proposed retrofit strategy will be examined. In this paper, a two-stage retrofit plan is proposed, with a focus on the 2nd stage. In “Stage-1” plan, the widespread brittle column splices are fixed and the heavy exterior cladding is removed. Additionally, “Stage-2” retrofit further improves the structural behaviors by including various supplemental energy dissipation devices in the building. Three devices are selected in this paper, including fluid viscous dampers, viscous wall dampers and buckling restrained braces. The retrofit design starts by selecting locations to install supplemental devices within architectural and functional constraints. Four exterior frames are chosen considering their less interaction with occupants and interior components. The total effective damping ratio needed at each horizontal direction is estimated based on a target roof displacement at corresponding direction. A damping scale factor is used to facilitate the estimation of total effective damping ratio. To compare the effectiveness of each scheme to meet the target performance objective, an equal quantity of devices are used, and they are installed at the same specified locations in the building. Besides, devices at each location are sized in a way to have a commensurable energy dissipation capacity. Their control effects are compared under BSE-2E using nonlinear response history analysis procedure. Three nonlinear response analyses are used to streamline the design, and the maximum responses are compared. To gain more insights into the cost-effective of each scheme, a probabilistic cost analysis is conducted in the framework of performance based earthquake engineering (PBEE) methodology. Performance assessment calculation tool (PACT) is utilized to estimate the probability of the building having irreparable residual drift and unsafe tagging, and the total repair cost of each retrofit scheme. Among the three designs using different devices, the fluid viscous dampers are the most effective to control structural responses and reduce the repair cost and other negative impacts after a major seismic event. Consequently, they are demonstrated as the most promising solution to improve the seismic behavior of the selected building.

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