Published February 25, 2019
Graduate Students: Xiaone Wei
Principal Investigator: Michel Bruneau
Project Completion Date: 07-18-2016
Buckling Restrained Braces application to provide more resilient bridges have been subjected to cyclic displacement histories representative of yearly thermal demands and of earthquake excitations. One of SEESL’s shake-table was used to apply displacement histories.
Two prospective applications of implementing BRBs as Structural Fuses (SFs) into new and existing bridges structures have been considered: (i) added between columns of a bridge bent, and; (ii) inserted in the end-diaphragms of slab-on-girder steel superstructures. Design procedures have been proposed for designing BRBs in both applications based on analytical and experimental results. Dynamic nonlinear time history analyses were performed on the bridge models to investigate its global behavior after adding the BRBs, and to understand the magnitude of local demands on the BRBs and other bridge members. Analytical and experimental studies were conducted for BRB’s gusset plates welded to CFT columns, to investigate the connection strength for seismic applications. Quasi-static experiments were performed to subject two types of BRBs to a regime of relative end displacements representative of the displacements demands when BRBs are implemented in the ductile diaphragms.
The tests have demonstrated that BRBs having specially designed end connection details are able to sustain extensive cycles of inelastic deformations without end-plate failure or instability. Tests up to low cycle fatigue failure on eight BRBs have demonstrated that the BRB specimens developed cumulative inelastic deformations of more than 200 times the BRB’s axial yield displacement value, under different sequences of bidirectional and temperature-induced axial displacement test protocols designed to simulate demands when used in bidirectional ductile diaphragms. The analytical and experimental work has demonstrated the feasibility of implementing bidirectional ductile diaphragm in bridges using BRBs. A corresponding design procedure has been formulated to design BRBs in ductile diaphragms, and to establish when they should be replaced during the life of the bridge, using the cumulative ductililty of 250 times the yield displacement as a performance basis. However, the design procedure also specifies a test protocol that can be used to extend this limit, as it is foreseen that other BRBs designs/detailing could allow reaching significantly greater cumulative ductilities.
This project was sponsored by the California Department of Transportation (Caltrans) under research Contract No. 65A0432, and by the Transportation Research Board of the National Academies under the TRB-IDEA Program (NCHRP-172). The donation of Buckling Restrained Braces specimens from Star Seismic, and steel circular hollow sections from Atlas Tube used in this research work is also greatly appreciated..