Large scale testing of nitinol shape memory alloy devices for retrofitting of bridges

Abstract

A large scale testing program was conducted to determine the effects of shape memoryalloy (SMA) restrainer cables on the seismic performance of in-span hinges of arepresentative multiple-frame concrete box girder bridge subjected to earthquakeexcitations. Another objective of the study was to compare the performance of SMArestrainers to that of traditional steel restrainers as restraining devices for reducing hingedisplacement and the likelihood of collapse during earthquakes. The results of thetests show that SMA restrainers performed very well as restraining devices. Theforces in the SMA and steel restrainers were comparable. However, the SMArestrainer cables had minimal residual strain after repeated loading and exhibited theability to undergo many cycles with little strength and stiffness degradation. Inaddition, the hysteretic damping that was observed in the larger ground accelerationsdemonstrated the ability of the materials to dissipate energy. An analytical study wasconducted to assess the anticipated seismic response of the test setup and evaluatethe accuracy of the analytical model. The results of the analytical simulationillustrate that the analytical model was able to match the responses from theexperimental tests, including peak stresses, strains, forces, and hinge openings.