Analytical and experimental research was conducted to expand and validate the Bidirectional Ductile End Diaphragm (BDED) concept, developed in an earlier IDEA project (NCHRP-172), for application in common multi-span bridges. Buckling Restrained Braces (BRBs) were used as fuse elements located at the end of a superstructure’s floating span for this purpose. This innovative system can provide seismically resilient bridges with damage-free piers at low cost while minimizing displacement demands to levels that can be easily accommodated by conventional expansion joints. The nonlinear behavior of bridges designed using various methods was assessed by subjecting them to suites of earthquake motions using non-linear time-history analyses. One proposed design procedure based on Equivalent Lateral Forces (ELF) was shown to be particularly expedient and effective. It was also determined that, according to fatigue index calculations, it is not necessary to replace BRBs after an earthquake. The proposed design procedures were shown to be adequate for different seismic hazards, BRB geometries, and many irregular bridges. They were used to design BRBs in BDED in a 5-span prototype bridge, then used to design a test specimen that considered various BRB configurations, BRB end-connections to gusset plates, BRB connections to concrete (with details applicable to new structures and/or retrofitted ones), and BRB to steel girder connections. The bridge specimen was supported on two shake tables able to apply both unsynchronized and synchronized excitation representing the demands at the ends of the span. The bridge specimen was tested with different BRB configurations and was subjected to displacement sequences representing thermal expansion demands, design level seismic demands, and strong motions to represent different types of motions (near field, far field, pulse-type motions, and motions in soft soils). Each BRB configuration was tested until failure. Results from this study showed that BDED can provide seismic resilient bridges and that thermal expansion is not controlling the design of this system. It also demonstrated that pier damage could be prevented and that span displacement demands were small (i.e., of a magnitude that can be accommodated by conventional expansion joints). This research made the BDED concept ready for adoption by bridge design specifications.
The final report is available.