3. Superelastic SMA Seismic Bridge Restrainers

Strong earthquakes can cause excessive displacements at bridge joints, possibly leading to unseating the bridge superstructure. Steel restraining cables are typically used to mitigate this type of failure. However, due to their inelastic behavior, steel restraining cables are not always effective in preventing this damage. The superelastic behavior of shape memory alloys (SMAs) is sought in this chapter to develop bridge-restraining devices with no or negligible inelastic deformations. The chapter first discusses the impact of the hysteretic properties of superelastic SMAs on their efficacy in limiting hinge opening in bridges. Another critical factor discussed is ambient temperature effects. Since the superelastic behavior of SMAs is highly dependent on the alloy’s temperature, a sensitivity study is carried out using a thermomechanical SMA model to assess how temperature variability affects the effectiveness of SMAs as seismic restrainers for bridges. Finally, the efficacy of SMA restrainers compared to other conventional seismic retrofit devices is evaluated.