This project demonstrated the feasibility of using shape memory alloy (SMA) devices (restrainer cable and core elastomeric bearings) for seismic rehabilitation of highway bridges (Figure 1). By concentrating energy dissipation in controlled locations, these devices can be used to limit the relative hinge displacement and reduce the demand on individual frames in typical bridges. The research evaluated the characteristics of nickel-titanium shape memory alloy rods and wires under compression-tension cycles as a function of diameter size, loading frequency and temperature in order to establish their suitability for bridge rehabilitation. SMA restrainer bars, 1 in. in diameter, were subjected to uniaxial tension, in full-scale tests. The bars were also subjected to cyclical strains up to 8% with minimum residual deformation. The effectiveness of SMA restrainer bars in bridges was further evaluated by an analytical study of a simply supported multi-span bridge. The relative hinge displacement in a bridge was compared for retrofits for conventional steel restrainer cables and SMA restrainer bars. The comparison showed that the SMA restrainers reduced the relative hinge displacements at the abutment much more effectively than conventional steel cable restrainers. In addition the superelastic properties of the SMA restrainers resulted in energy dissipation at the hinges. Finally, the evaluation of the multi-span simply supported bridge subjected to near-field ground motion showed that the SMA bars were very effective in limiting the response of bridge decks to near field ground motion. The increased stiffness of SMA restrainers at large strains provided additional restraint to limit the relative openings in a bridge.
There are thousands of bridges in the United States that are in need of seismic retrofit. The state of California alone has spent nearly $750 million in seismic retrofit since the 1989 Loma Prieta earthquake. Many other state DOT's are now beginning to initiate similar retrofit programs, including New York, Tennessee, Illinois, and South Carolina. Should this technology prove effective and cost efficient, it can become a widely used seismic retrofit technology. Once the technology has been proven effective in reduced-scale experimental tests, the products will be developed and tested in full-scale. Representatives from various DOTs will be provided with the test results and will be invited to participate in future full-scale tests. Collaboration with Shape Memory Alloy manufacturers and end-users is essential to ensure the transfer of the research results to practice. The final report is available from the National Technical Information Service (NTIS # PB2002-103441).
