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

Abstract

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.

Low-Cycle Fatigue of Buckling Restrained Braces in Bidirectional Ductile End Diaphragms Due to Temperature-Change Effect on Bridge Superstructure

“…The analytical results in this paper have been used to experimentally investigate the BRBs' behaviors in the bidirectional EDS application in Wei and Bruneau (2018). Eight BRB specimens were subjected to an extensive set of quasi-static experiments consisting of a regime of combined relative end displacement histories, representative of the displacement demands induced by earthquakes as well as the thermal changes on the bridges presented in this study.…”

“…Based on the total low-cycle fatigue life empirically obtained from test results, it was recommended that BRBs installed in bridges be replaced after 35 years of service to ensure adequate performance under the expected seismic demands; guidance was provided to indicate how longer service life could be achieved. Information of the comprehensive experimental work and corresponding design and detailing recommendations are also presented in Wei and Bruneau (2018).…”

“…This information was used in combination with the seismic displacement demands to investigate the experimental performance of the BRBs under different displacement protocols considered. This experimental work, along with the information on BRB design and detailing recommendations for the current purpose, was presented in Wei and Bruneau (2018). Future study may investigate the effect of braking forces on the previously mentioned findings.…”

Finite Element Modelling of Buckling Restrained Braces under Combined In-Plane and Out-of-Plane Loading

“…The steel property (S275 JR) is shown in Figure 2 where the total elongation of the specimen is around 50% [9]. According to ANSI/AISC 341-16 [10,11], the loading protocol presented in Figure 3 Bruneau and Wei [12,13] introduce a biaxial S-type displacement to evaluate the BRB bidirectional response, where a complete large loop is composed of four small loops.…”