Experimental Investigation of Buckling Restrained Braces for Bridge Bidirectional Ductile End Diaphragms

Quasi-static experiments were conducted to subject buckling restrained braces (BRBs) to a regime of relative end displacements demands to investigate if the BRBs' end connections could be able to sustain the required displacement demands when installed in bidirectional ductile end diaphragm systems (EDS). The loading protocols included the bidirectional displacement histories to be applied to the specimens for the cyclic inelastic test and the uniaxial displacement histories for the low-cycle fatigue test caused by temperature changes. Two types of BRBs with flat end plates and unidirectional pinholes, namely BRB-1 and BRB-2, were designed and tested. Four specimens of each type of BRB were tested under combinations of different displacement protocols, and the resulting BRBs' hysteretic behaviors were studied and compared. All the BRB specimens tested developed cumulative inelastic deformations of more than 200 times the BRB's axial yield displacement. The specimens were able to sustain multiple years of severe temperature cycles in addition to meeting the seismic qualification test criterion. Ultimately, as expected, all BRBs failed in tension after extensive cycles of inelastic deformations. No undesirable end-plate failure or instability was observed. A recommended design procedure for the EDS with BRBs in both straight and skew bridges was developed based on these experimental results.