Replaceable Brace Modules for Concentrically Braced Frames: Test Results from Substructure with Moment-Resisting Beam-Column Connections

In current practice for concentrically braced frames (CBFs), a gusset plate is typically used to join the brace to the frame elements. Using a linear clearance to accommodate the out-of-plane deformation of the buckling brace can have negative implications for both construction and seismic performance. An alternative connection approach, intended to be more seismically resilient, has recently been developed based on a replaceable brace module (RBM). This connection uses shop welded/field bolted connections to facilitate erection and make the brace replaceable by confining all damage to the RBM. This paper presents results from 70%-scale testing of a concentrically braced frame with RBMs and moment-resisting beam-column connections. The experimental program consisted of two phases. In Phase I, the frame was subjected to quasi-static cyclic loading up to brace fracture. In Phase II, the damaged RBMs were replaced with new RBMs, and the behaviour of the frame was investigated under the same loading protocol. The tests demonstrate that the frame performance was at least equivalent to what would be expected with more traditional connections, while also allowing site welding to be avoided, brace buckling to be limited to the in-plane direction, and the brace modules to be easily replaced. The moment-resisting beam-column connections functioned as intended, with minimal damage up to brace fracture during the first tests, and similar behaviour during the Phase II tests with replaced RBMs. In this way, the testing demonstrated the viability of the proposed new approach to detailing concentrically braced frames to facilitate more rapid repair.