Analysis, Design and System-Level Performance of Repairable Precast Concrete Buckling-Restrained Braced Frames under Seismic Loads

University Of Notre Dame, Notre Dame IN

Investigators

Abstract

The scale of losses from previous earthquakes has demonstrated the need for buildings that can rapidly restore their essential functions after a natural disaster. This concept is called functional recovery. This project will contribute to the nation’s functional recovery objectives by creating and examining a repairable precast concrete buckling-restrained braced (BRB) frame structure with a new type of non-proprietary diagonal brace. The new brace will have low-cost features that permit practical replacement after an earthquake. This project will generate fundamental knowledge on the seismic design and performance of this building system. Data will be generated from numerical analyses, testing of isolated braces and their connections, and culminating tests on the seismic performance and repair of a three-story building utilizing the six-degree-of-freedom Large High-Performance Outdoor Shake Table operated by the University of California, San Diego, as part of the NSF-funded Natural Hazards Engineering Research Infrastructure (NHERI). The project will emphasize diversity and inclusion, will engage undergraduates from underrepresented groups in education and mentoring programs, and will create engineering learning modules for pre-college students. Precast industry partners will provide specimens and technical guidance emphasizing the project’s focus on industry-preferred structural details for practical acceptance. Engagement with the broader engineering community will be achieved through a competition to predict the building response on the shake table. Data generated from this project will be archived and made publicly available in the NHERI Data Depot (https://www.DesignSafe-CI.org). This award will contribute to NSF's role in the National Earthquake Hazards Reduction Program (NEHRP). There is currently no comprehensive U.S.-based research on the seismic performance of precast BRB frame structures. This project will fill this research gap by 1) designing and characterizing the behavior of a novel, replaceable concrete brace, 2) evaluating the design and modeling of multi-story braced frames, and 3) evaluating the seismic behavior of these frames within a building. The new brace will achieve ductile and stable behavior by structurally efficient details incorporating energy-dissipating reinforcing bars crossing gap-joints at the brace ends and spliced with threaded couplers and upsized bars to minimize damage in the beam and column members. This threaded gap-joint connection will permit damaged precast braces to be replaced with cast-in-place concrete braces after an earthquake. Detailed numerical models will be developed and experimentally validated to predict three-dimensional stress gradients and damage conditions that could lead to premature failure of the brace, and to evaluate efficient design-basis models for multi-story braced frames. The modeling and design methods will be validated with the first system-level testing of a precast braced frame building on the six-degree-of-freedom shake table. These culminating tests will demonstrate the performance of the braced frames, their connections, and brace replacement under multi-directional demands. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.