Upgrading of Braced Frames for Potential Local Failures

Abstract

This study concerns a type of local failure that was observed during the 1989 Loma Prieta earthquake: a brace-to-beam connection in concentric braced frame structures due to lack of adequate lateral support to both flanges of the beam. Experimental and analytical studies were carried out to investigate the failure. Field observed local failure of the brace-to-beam connection was reproduced in the laboratory test specimen. The hysteretic loops of the locally failed specimen showed excessive “pinching” when compared to those of bracing members with adequate lateral support. Local failure was confirmed by a finite element analysis. Several upgrading schemes were evaluated by the finite element analyses. The analyses showed that the specimen with a diagonal stiffener in the beam web along the centerline of the brace member axis performed best. The effectiveness of diagonal web stiffeners was verified experimentally.