Date of Award
Master of Engineering Science
Civil and Environmental Engineering
Dr. F. Michael Bartlett
Components proportioned using Capacity-Based Design have resistances that exceed the forces that can be generated by adjacent elements, particularly ductile elements in seismic-load- resisting systems. This thesis investigates the reliability indices for compression braces in Eccentrically Braced Frames (EBF) proportioned using Capacity-Based Design. The primary research objectives are: (1) to develop statistical models for link overstrength due to strain hardening and probable yield strengths; (2) to examine, using these models, the reliability indices obtained using the current Capacity-Based Design provisions for EBFs in CSA SI6-09 (CSA, 2009); and (3) to calibrate the resistance factor for a proposed new overstrength model to replace the link overstrength criteria in CSA SI6-09. The statistical models for link overstrength account for the effect of the normalized link length, the plastic link rotation, the ratio of ultimate to yield strength and the normalized web stiffener spacing and are determined using a database of 77 EBF tests performed by others.
The statistical model for higher-than-nominal yield strength is determined using a database of 7717 tests of coupons from Class 1 sections presented by Schmidt (2000). Reliability indices,/?, are computed using the First Order Second Moment (FOSM) method. The reliability indices for the current code provisions vary from 1.30 to values above 5.0 for typical ranges of link parameters. A new design equation is proposed that provides much more uniform reliability. Compression braces designed using the proposed design equation require the resistance factor 0 be decreased to 0.75 from the current value of 0.9 to achieve acceptable reliability levels.
Vemuri, Jaya Prakash, "RESISTANCE FACTORS FOR ECCENTRICALLY BRACED STEEL FRAMES PROPORTIONED USING CAPACITY DESIGN" (2011). Digitized Theses. 3499.