Design for Lateral Loads/Systems

Single Abstract

342022 - Collapse Risk Analysis for Reinforced Concrete Walls with Openings and Sensitivity to Modelling Parameter Uncertainties

Friday, April 20
11:00 AM - 12:30 PM
Location: 204AB

Reinforced concrete (RC) walls are used commonly as part of the lateral-force resisting system for buildings in earthquake prone regions. In buildings, RC walls are typically placed near stairwells, elevators, and mechanical duct shafts that often require access through vertical wall openings. These openings may result in significant changes in wall stiffness and strength and, as a result, affect wall performance under earthquake load. ASCE 7 provides criteria for classifying wall systems as “irregular” if a vertical pattern of openings results in significant story-to-story variation in wall stiffness or strength, and places additional design requirements on irregular structures. ACI 318 provides guidance for design to develop force transfers around openings.
This study investigated the changes in collapse risk due to openings that reduce story stiffness in idealized RC walls buildings of 8-, 12-, and 20-stories. The buildings were designed for sites in ASCE 7 seismic design categories of B and D. Wall openings were sized to reduce story stiffness by either 25% or 50%, and the wall story with the opening was designed to have approximately the same strength as the stories above and below. The openings were placed in locations of high moment demand (1st story and 1st and 2nd story) and locations further up the wall where the moment demands are lower (5th story and 8th story).
The walled buildings were modeled in OpenSees using methodologies that were validated using experimental data. The OpenSees models were further verified using the results of nonlinear continuum-type analysis conducted using the non-linear finite element software ATENA. For each building design, an incremental dynamic collapse analysis was performed and the collapse risk was found to be 2 to 3 times larger for buildings with openings than for buildings with continuous walls. In some design configurations, the openings could lead the structure to reach a 10% probability of collapse under the maximum considered earthquake.
This study also investigated the sensitivity of collapse risk to various modeling assumptions. The calculated collapse risk was found to be highly sensitive to the concrete’s calculated confined strength, the concrete post-crushing residual strength, and the assumed loss of strength of the steel reinforcement at buckling. The results are presented considering these modeling uncertainties.

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Kamal Ahmed

PhD Student
University of Washington

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Dawn E. Lehman

Professor
University of Washington

Dawn Lehman is a Professor of Civil and Environmental Engineering at the University of Washington. Her research expertise lies in seismic engineering of structural systems (http://www.ce.washington.edu/people/faculty/faculty.php?id=24).
She has conducted research on a range of systems including reinforced concrete walls and frames, steel braced frames, and concrete-filled-tube, precast and reinforced-concrete bridge systems. Her research results have been implemented in codes, design manuals and provisional structural engineering recommendations, including AASHTO, AISC, WSDOT BDM, Caltrans SDM, and ASCE 41. She has authored over 120 research articles. (Many are available on Research Gate https://www.researchgate.net/profile/Dawn_Lehman).

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Laura Lowes

Professor
University of Washington

Laura Lowes has a BSCE from the University of Washington and MSCE and PhD from the
University of California, Berkeley. She is the William M. and Marilyn M. Conner Professor and Associate Chair in the Department of Civil and Environmental Engineering at the University of Washington in Seattle, WA where she teaches classes on structural design and analysis, finite element methods, and nonlinear analysis. Dr. Lowes’ research seeks to advance structural engineering through the development and application of numerical simulation. Recent and ongoing research projects address the earthquake performance, assessment and design of concrete and steel-plate shear wall buildings. Her research has resulted in a number of component models that are appropriate for use in simulating the earthquake response of buildings and bridges as well as recommendations for using commercial and research software to assess structural performance. Dr. Lowes is a member of the management team for the NSF-sponsored NHERI SimCenter, DesignSafe.ci and UW RAPID facilities. Dr. Lowes is a Fellow the American Concrete Institute and member of ACI Committees 318-C, 318-N, 369 and 447.

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342022 - Collapse Risk Analysis for Reinforced Concrete Walls with Openings and Sensitivity to Modelling Parameter Uncertainties



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