Seismic Evaluation of Bolted Connections in Non-Seismic Concentrically Braced Frames

Steel concentrically braced frames (CBFs) resist lateral load through braces that concentrically frame into the centerline of the beam-to-column joint or into an opposing brace, typically with gusset plate connections. Current design specifications for special concentrically braced frames (SCBFs) require a number of special ductile detailing requirements to encourage increased drift capacity and ductility in the system. Often in areas of high seismicity the brace-to-gusset plate connections are welded. Although bolted connections provide an attractive alternative in terms of constructability, few tests have investigated seismic performance of bolted SCBF connections. Prior to the early 1990s, CBFs were not designed to meet ductile detailing and design requirements and engineers more commonly employed bolted brace-to-gusset plate connections. Yet these older systems also have not been widely investigated. An experimental research program was undertaken to study the seismic performance of older bolted CBF connections. The experimental results were analyzed to draw conclusions on the seismic performance of old CBF bolted connections and to identify deficiencies of systems utilizing older CBF bolted connection details. The data was used to create an initial approach to evaluating and retrofitting CBFs on a subsystem level using ASCE 41.