Experimental and Numerical Evaluation of Older Chevron Concentrically Braced Frames with Hollow and Concrete-Filled Braces

Abstract

Detailed seismic provisions for concentrically braced frames have evolved continuously since 1988. Thus, vintage-era braced frames, especially those designed prior to 1988, may be prone to a number of significant deficiencies. These deficiencies include interdependent failures at the braces, connections, and beams, making them difficult to predict without system-level tests. An experimental study was undertaken to evaluate current retrofit provisions’ ability to predict the seismic response of pre-1988 existing braced frames. A nearly full-scale test specimen—representative of a 1985 chevron braced frame—was subjected to cyclic lateral loading. The specimen was subsequently upgraded with concrete-filled braces and retested. Test results demonstrate that pre-1988 braced frames are highly susceptible to weak-story behavior and local failure modes. Numerical models using standard nonlinear static methods predicted some, but not all, of these failures. Accordingly, recommendations to improve the efficacy of these numerical models are presented.