Date of Award
Spring 2023
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Civil, Construction, and Environmental Engineering
First Advisor
Sen, Andrew
Second Advisor
Baolin, Wan
Third Advisor
Huang, Qindan
Abstract
Special concentrically braced frames (SCBFs) are efficient lateral-force-resisting systems that are specifically detailed for steel buildings in regions with high seismic hazard. Current design standards for SCBFs intend to ensure inelastic deformation capacity through strict ductile and capacity-based design requirements. Braces are intended to yield in tension and buckle in compression to dissipate seismic energy. The current standards apply expected brace forces to all framing elements and connections to concentrate yielding in the braces. In these standards it is conservatively assumed that brace yielding and buckling simultaneously occur on all stories, and columns are designed considering the accumulated brace demands along the building height. Little prior research has been conducted on the consequences of such demands and post-column buckling response of CBFs; thus, the understanding of the prevalence and consequences of column buckling is limited. Nonlinear response-history analyses were performed on eight (8) SCBFs to investigate their vulnerability to seismically induced column buckling and subsequent system response. SCBFs were designed in accordance with ASCE/SEI 7-16 and AISC 341-16 for a site in Seattle, WA with varying building heights and bracing configurations. Bracing configurations include chevron, multi-story-X, and paired single diagonal (V and inverted-V). Nonlinear models were developed in OpenSees and the SCBFs were subjected to suites of ground motions scaled to hazard levels corresponding to 10%/50-year, 2%/50-year, and 1%/50-year probabilities of exceedance. Column buckling did not occur in any of the nonlinear analyses and all cases of collapse were caused by excessive drift demands. As such, SCBF column design axial loads have the potential to be relaxed without compromising vertical resistance and stability. Recommendations are developed for SCBF column capacity-based design procedures that reflect more realistic brace forces.