SEISMIC PERFORMANCE OF CONCENTRICALLY BRACED FRAMES CONSIDERING THE BRACE FRACTURE AND GUSSET PLATE EFFECT

The concentrically braced frame (CBF), which shows good seismic performance with a low cost, is a popular seismic resistant structural system. Generally, CBFs are designed to meet the ductility requirement to ensure that the braces buckle in compression or yield in tension. As observed in previous major earthquakes, the ultimate failure mode of CBFs is the fracture of the braces. However, CBFs are often idealized as trusses in a frame analysis or design, considering the boundary of braces as pinned or fixed connections and ignoring the fracture behavior of the braces. In this paper, a numerical model using OpenSees considering the brace fracture and gusset plate effect was proposed. A single-brace model, a one-story frame model and a three-story frame model were simulated to verify the reliability of the numerical model. The simulated results showed good agreements with the corresponding experimental results. The calibrated three-story frame model was then adopted for an incremental dynamic analysis. The results indicated that the collapse margin ratio of the frame was overestimated if the brace fracture was not considered. It is strongly recommended that the brace fracture and gusset plate effect should be considered for the design and detailing of CBFs to reasonably evaluate the seismic performance.