Influence of Types of End Connections and Detailing of End-Protected Zones on Seismic Performance of SCBFs

Abstract

This paper presents an experimental investigation to study the influence of the type of end connections as well as the detailing of end-protected zones on the seismic performance of special concentrically braced frames (SCBFs). Depending on the plane of the brace buckling and the location of plastic hinges, three types of end connections are considered in this study: the in-plane buckling brace system, the out-of-plane buckling brace system, and the direct-connection brace system. Five large-scale braced frame subassemblages are tested under quasi-static reversed cyclic loading. The main parameters studied are the energy dissipation, postbuckling strength, fracture ductility, and failure modes of test specimens. Test results showed that the fatigue performance of the brace specimen is increased by increasing the flexibility of the secondary hinges and a higher fracture ductility can be achieved for the restraint-free rotation of hinge plates. The higher flexibility of the secondary hinges resulted in the spreading of inelastic strain along the brace length. Lower postbuckling strengths of the braces resulted in higher fracture ductility. Test results highlighted the importance of the end-protected zones in the prediction of the fracture ductility of braces for the collapse-performance assessment of the braced frames. Based on this study, recommendations on the design and detailing of end-protected zones have been proposed considering the critical limit states to achieve the desired yield hierarchy of SCBFs.