PRESENTATION: “Seismic Performance Assessments for Modern and Existing Concrete Buildings” by Abbie Liel

Presentation

When: Thursday 3 December 2015 //

Abstract

This talk will describe seismic performance assessments we have conducted to predict the risk associated with concrete structures in the U.S. The first part of the talk will describe work to assess seismic collapse safety of reinforced concrete frame buildings, examining nonductile moment frames that are representative of those built before the mid-1970s in California, modern U.S. code-compliant reinforced concrete frames for high seismic zones, and nonductile moment frames that have been retrofitted. The probabilistic assessment relies on nonlinear dynamic simulation of structural response to calculate the collapse safety. The results indicate that nonductile RC frame structures have a mean annual frequency of collapse that is approximately 40 times higher than corresponding results for modern code-conforming special RC moment frames. These metrics demonstrate the effectiveness of ductile detailing and capacity design requirements, which have been introduced over the past 30 years to improve the safety of RC buildings. Comparisons are also made between earthquake-induced losses for the different types of buildings, demonstrating that U.S. codes have made more significant improvements in safety (relatively to 1970s era buildings) than in reducing repair costs and damage. Data on comparative safety between nonductile and ductile frames may also inform the development of policies for appraising and mitigating seismic collapse risk of existing RC frame buildings.

Faced with evidence that some older nonductile concrete buildings may pose a significant risk of structural collapse, potentially endangering life safety, some municipalities are considering legislation mandating identification, evaluation and, in some cases, retrofit of these structures. The second part of the talk will describe a new methodology is being developed to expeditiously evaluate a concrete building and determine whether it is an “exceptionally high seismic risk” building. These exceptionally high seismic risk buildings are candidates for more detailed evaluation and, possibly, retrofit. The methodology is intended to be simple and inexpensive, relying primarily on hand calculations. The challenges of developing simple systematic evaluation procedure will also be described.

Bio

Abbie is an Associate Professor of Civil, Environmental and Architectural Engineering at the University of Colorado, Boulder. She earned undergraduate degrees in Civil Engineering, and the Woodrow Wilson School of Public Policy, at Princeton University. She started her graduate studies in the United Kingdom on a Marshall Scholarship, where she received a M.Sc. in Civil Engineering and a M.Sc. in Building and Urban Design and Development. Abbie did her Ph.D. at Stanford University, under the guidance of Professor Gregory Deierlein, focusing on collapse risk of older non-ductile concrete frame structures. At CU, Abbie has worked on problems related to performance of concrete buildings, snow loads on structures, and flood damage in the 2013 Boulder, CO floods. She recently received the Shah Family Innovation Prize from the Earthquake Engineering Research Institute.