The National Academies

NCHRP IDEA 20-30/IDEA 215 [Active (IDEA)]

Achieving Resilient Multi-Span Bridges by using Buckling-Restrained Braces

  Project Data
Funds: $100,000
Staff Responsibility: Ianm jawed
Research Agency: University at Buffalo
Principal Investigator: Michel Bruneau
Fiscal Year: 2018

This will expand and validate the Bidirectional Ductile Diaphragm concept, developed in an earlier IDEA project (NCHRP-172) for application in common multi]span bridges. The design strategy relies on Buckling Restrained Braces (BRBs) used at the span ends of multi-span bridges to provide seismic resilience at low cost while keeping displacement within allowed limit. Work in Stage 1 will focus on dynamic analysis of chosen configurations. Multi-span bridges with the proposed ductile diaphragm concept will be investigated to establish their seismic performance, considering various layout and implementation strategies. A parametric study using modal analyses will consider variations in various key parameters that define response. This will be done for various BRB layouts. Nonlinear time-history analyses will be performed for bridges being considered using simplified bilinear inelastic hysteretic models to identify trends in response and considering suites of ground motions accelerations. Selected nonlinear time-history analyses will be conducted for those bridges but using the Bouc-Wen inelastic hysteretic model generally used to model the behavior of BRBs to identify changes in trends identified in the earlier tasks of the project. These analyses will allow determining the level of complexity required to adequately predict the bridge response. The dynamic analyses from earlier tasks will be used to establish the magnitude of the local demands and, more specifically, the extent of bidirectional displacements that the hysteretic devices must be able to accommodate while delivering their ductile response. Response from these numerical studies will be compared and used to develop proposed simple design methods. Work in Stage 2 will involve testing and bidirectional qualification of BRB concepts. Results from Stage 1 will be used to finalize the design the specimens and test set-up. Drawings will be produced and BRBs will be obtained from the supplier. The set-up to test each BRB will be built along with the development and implementation of the instrumentation plan. Testing will be performed at the University at Buffalo's Structural Engineering and Earthquake Simulation Laboratory. It is anticipated that a first specimen will be subjected to an adapted qualification hysteretic test protocol (expanded to 3-D). A second will be subjected to strings of earthquake displacement histories (obtained from the analyses in Stage 1). A third will combine cycles of seismic and thermal expansion demands to represent life-cycle demands. Two different BRB connection details will be considered. The test protocol will be repeated on each specimen until failure to establish its ultimate hysteretic energy capacity. Experimental results will be documented.

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