Buckling Restrained Braces Applications for Superstructure and Substructure Protection in Bridges
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Two prospective applications of implementing Buckling Restrained Braces (BRBs) as Structural Fuses (SFs) into new and existing bridges structures are considered: (i) added between columns of a bridge bent, and; (ii) inserted in the end-diaphragms of slab-on-girder steel superstructures. The objective of the SF is to protect the bridge’s structural elements, such as to leave these other structural elements with minimal damage or even intact in the event of the earthquake. After the earthquake, the intent is that a SF should be relatively easily removed and replaced. A design procedure is proposed for designing BRBs inserted in bridge bents. Two design configurations are considered, including: (i) a two-column bent with BRBs in single-inclined and inverted-V configurations (which provide SF only in the bridge’s transverse direction and would have to be combined with other energy dissipating devices in the longitudinal direction), and; (ii) four-column box piers with BRBs in both the transverse and longitudinal directions. Nonlinear pushover and time history analyses are performed on the bridge bents to verify the effectiveness of adding BRBs to the bridge bents in reducing the seismic demands. Connection details are investigated to connect the BRBs to other members of the bridge bent (to establish feasibility when using certain conventional types of connections). Analytical and experimental studies are conducted for gusset plates welded to Concrete Filled steel Tube (CFT) columns, to investigate the connection strength for seismic applications. For BRBs to be implemented in the End Diaphragm Systems (EDS), parametric nonlinear time history analyses are conducted on benchmark skew and nonskew bridges, which allows investigating the impact of these parameters on global behavior, as well as understanding the magnitude of local demands and the extent of bi-directional displacements that the BRBs must be able to accommodate while delivering their ductile response. The long-term service life of BRBs installed across expansion joints and subjected to bridge thermal expansion histories is also investigated. Quasi-static experiments are performed to subject the BRBs to a regime of relative end displacements representative of the results predicted from the parametric analytical studies. Two types of BRBs are designed, and four specimens of each type of BRB are tested under different combinations of displacement protocols. The protocols include the bi directional displacement histories applied to the specimens for the cyclic inelastic test, and the uniaxial displacement histories for the low cycle fatigue test due to temperature changes. The BRB’s hysteretic behaviors under different displacement protocols are studied and compared. A recommended design procedure for the EDSs in both nonskew and skew bridges is developed based on the paramedic analysis and experimental results.