“Existing Tall Buildings: Case Study Project,” led by former PEER Director Steve Mahin, received a 2016 Excellence in Structural Engineering Award from the Structural Engineers Association of California (SEAOC) in the category of Study/Research/Guidelines.
Sponsored by PEER and Cal-OES, the case study project investigated the seismic evaluation and retrofit study of a 35-story steel building designed in 1968. Major seismic vulnerabilities were identified and considered indicative of potential vulnerabilities in similar existing tall buildings built between 1960 and 1990 on the west coast of the United States.
Two primary earthquake hazard levels were used for the evaluations. Additionally, several different numerical models with high fidelity were developed in accordance with recommendations of ASCE 41-13 and other relevant guidelines, and analyses were performed using the program “Open System for Earthquake Engineering Simulation” (OpenSees). Analysis results were evaluated using methodologies and performance criteria outlined in guidelines ASCE 41-13, FEMA 351, and FEMA P-58. More than 300 sets of sophisticated structural analyses were performed to evaluate the building’s seismic behaviors, and to assess the efficacy of retrofit strategies.
Several retrofit strategies were explored, including conventional methods such as fixing brittle connections and replacing the heavy exterior cladding with a lightweight curtain wall, and state-of-the-art techniques incorporating supplemental energy dissipating fluid viscous damping devices, to improve the building’s seismic performance in a cost-effective manner.
This case study project serves as a comprehensive demonstration of how to assess an existing tall building using guidelines ASCE 41-13, FEMA 351 and FEMA P-58. Modeling techniques of critical structural components and connections provide the engineering profession with better tools for structural analysis. The research conducted provides valuable and conclusive data to encourage seismic performance upgrades of problematic buildings, thus providing benefit to a community’s safety, economy and resilience.
The SEAOC Award jury noted that “this is a really important study. There is a lot of uncertainty about this. This raises awareness.”