Seismic design of midspan beam connection of chevron-configured special concentrically braced frames

This paper reveals and addresses the misconception in capacity-based seismic design of midspan beam connections in chevron braced and multi-story X-braced frames. Under the capacity-based seismic design approach, the structural safety and reliability of concentrically braced frames are assumed to be ensured by significant yielding and inelastic deformation of fuse elements such as brace buckling, tensile yielding, and post-buckling deformation. However, under strong earthquakes, the inelastic structural response may not be as expected. In this study, parametric studies are performed to identify critical issues in the beam and midspan connection design of both chevron braced and multi-story X-braced frames. It is revealed that traditional design methods for midspan gusset connections, which rely solely on stress calculation, are insufficient for capturing the true seismic behavior, necessitating updated approaches that incorporate inelastic deformations. It is recommended to use vertical stiffeners at midspan beam connection where the beam web is thinner than the gusset plate to reduce inelastic deformations and ensure the integrity of the structure during large seismic events.