Inelastic behavior and seismic collapse prevention performance of low-ductility steel braced frames

Seismic-force-resisting systems (SFRSs) in areas of low and moderate seismicity such as the east coast of the United States have minimal ductility. Unlike high-ductility systems, whose design encompasses extensive seismic detailing and proportioning requirements to provide said ductility, the analogous requirements for low-ductility steel SFRSs are minimal, and in some instances nonexistent. Ordinary concentrically-braced frames (OCBFs) have requirements that are intended to provide a small level of ductility, and steel SFRSs designed with a response modification factor R = 3 have no specific seismic requirements. Rather than relying on ductility for post-elastic performance, these systems—that have received almost no research attention—must prevent collapse through other means that are not explicitly defined or considered in the design process. Reserve capacity, or additional lateral force resisting capacity following incipience of inelastic and often brittle behavior within the SFRS, has been shown through post-earthquake reconnaissance to be the probable mechanism by which low-ductility concentrically braced frames (CBFs) provide collapse prevention. Aside from these anecdotal cases, however, the inelastic behavior and seismic collapse prevention performance of low-ductility CBFs remain untested and unsubstantiated, and these topics are not yet understood at a fundamental level to the extent of high-ductility systems. In this dissertation, the inelastic behavior and seismic collapse prevention performance of low-ductility CBFs are examined through a combination of numerical simulations and full-scale experimental testing. Sources of reserve capacity are systematically identified and evaluated through numerical simulations. The impact of common design choices, such as system type and system configuration, on reserve capacity is evaluated through full-scale tests of an R = 3 CBF in the chevron configuration and an OCBF (R = 3.25) in the split-x configuration. Test results and numerical simulations indicate that the chevron configuration is more suitable for providing reserve capacity, and that while some of the minor seismic detailing requirements of the OCBF provision improve performance, others are detrimental and lead to uneconomical designs. The knowledge gained from the initial numerical simulations and full-scale experimental testing inspired the development of a new low-ductility system for use in areas of low and moderate seismicity which provides collapse prevention through primary system ductility and intentional reserve capacity mechanisms: the R = 4 OCBF. In a reliability-based performance assessment this new system shows an improvement in behavior over the two primary low-ductility CBF SFRSs—the R = 3 CBF and the OCBF (R = 3.25)—while also minimizing design costs and complexity. This R = 4 OCBF concept is proposed for consideration in the upcoming 2022 AISC Seismic Provisions.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Civil Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2017

Author dc:creator

• Sizemore, Joshua G

Contributors dc:contributor

• Fahnestock, Larry A.
• Abrams, Daniel P.
• LaFave, James M.
• Tremblay, Robert
• Hines, Eric M.

• Buildings
• Earthquake-resistant design
• Concentrically braced frames
• Moderate seismic regions
• Low-ductility systems
• Reserve capacity
• Full-scale testing
• Nonlinear analysis
• Metal and composite structures

Statement dc:rights

• Copyright 2017 Joshua G. Sizemore

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/97388

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/97388