This project, a follow-on activity of an earlier IDEA project (NCHRP-65), focused on the application of shape memory alloy (SMA) restrainers to improve the resistance of highway bridges to seismic damage. Work in the initial stage involved developing cost- effective and mechanically stable SMAs for bridge rehabilitation that included ternary alloys of Ni and Ti doped with Fe or Cr. The results show that the binary form of SMAs (NiTi) exhibited superior performance as compared with the ternary NiTiCr or NiTiFe alloys. The performance of SMAs was optimized by thermo-mechanical processing. The effect of temperature on the superelastic cyclic properties of selected alloys was also evaluated in order to establish the optimum performance temperature range.
SMA-based prototype restrainers were fabricated and evaluated in dynamic laboratory and shake table tests. The restrainers were found to be superior to steel restrainers in limiting relative hinge displacements, with maximum hinge displacement being about half of steel restrainers (Figure 1). The restrainers also showed minimal residual strain after repeated cycling and, unlike steel, could undergo many loading cycles with little degradation of properties. Further, with equivalent restrainers under identical earthquake motion, the SMA restrainers produced lower block acceleration as compared to steel restrainers and reached only their yield level while the steel restrainers failed. Full-scale tests on bridges are needed to demonstrate the applicability of the technology in the field. The final report is available from the National Technical Information Service (NTIS # PB 2005-109518).
