Seismic Rehabilitation of Bridges Using Nitinol Cables

A Nitinol-based recentering cable device is developed for applications in bridges subjected to earthquake loads.  The device is made by wrapping 320-wire cable using 0.711 mm diameter wire.  The composition of the wire is binary Nickel-Titanium, with 50.8 Atomic % Nickel. This composition yields Nitinol which has a transformation temperature near 0C and is thus superelastic at room temperature.  Testing of the wire shows that it exhibits nearly perfect superelastic and good energy dissipating behavior when subjected to cyclical strains of over 10%.  The cables were made by looping many turns between commercial end attachment hardware then fastening the turns to the hardware with wire wrap.  The wire strands were not twisted but were restrained in elastomer tubing to create cable lengths.

The efficacy of the new recentering devices is assessed through analytical evaluation and large-scale experimentation.  The device is connected between the deck and the abutment in an attempt to limit the hinge opening in the bridge.  Shake table testing allow for large-scale validation of the use of SMA recentering devices in a one quarter-scale, four-span bridge.  Experimental evaluation in a test specimen at this scale, and with a bridge system-level focus, provides a unique opportunity to evaluate the viability of this retrofit device and advance the adoption of this new class of materials for applications in structural dynamics and earthquake engineering.