A new bridge being built in downtown Seattle is the first to feature shape memory metals in an infrastructure. The bridge, a small exit ramp in downtown Seattle, is supported by two reinforced concrete columns that feature the new materials. The project is a collaboration between the Washington Department of Transportation and researchers at the University of Nevada, Reno; the developmental work was funded by the U.S. National Science Foundation among other government agencies. The bridge features nickel-titanium (NiTi) shape memory alloy rods in the top third of the columns, which are both superelastic and enable the recovery of the pillar to its original shape. The columns also use traditional steel rebar. The concrete used in the columns features a high loading chopped fiber reinforcement to enhance flexibility. The bridge is designed not just to survive earthquakes, but remain in service after an earthquake without the need for repairs. The bridge materials and design demonstrated recovery of up to 9% deformation in full-scale testing.
The development of this smart material enabled bridge has many potential consequences: improved flow of emergency responders after earthquakes, a substantial reduction in repair costs, and substantially larger consumption of fiber reinforcement, nickel, and titanium. While important, these impacts will likely only affect a few segments. That does not mean that this is not an important development, however. Readers in every industry should view this development as a case study for adoption and development of smart materials.
- Use of an established material in a novel application: NiTi alloys are far from new. Researchers first developed these materials in 1959, and many products such as medical stents, eyewear, and actuators have used smart materials. All of these applications have been for small size components, however. This is the first application that uses these as structural elements in infrastructure, and uses NiTi at such a large size.
- Long times between identification and initial application. The group at the University of Reno began their work on shape memory alloy reinforcement in 2007, about a decade before the first bridge is scheduled to be completed. This long time from identification to initial adoption is characteristic of other smart materials, such as magnetocalorics and piezoelectrics.
- Overall system design must be modified to accept the smart material. If the shape memory alloy reinforcement was placed into a standard column, the system would still fail in an earthquake. Conventional concrete is not flexible enough to withstand the deformation sustained by the NiTi without cracking and pulling away from the reinforcement. The designers recognized this, and the other material systems in the column have been changed to enable the enhanced performance.
The development of this smart material has so far followed the key trends across the smart material space. If the installation in Seattle is a success, expect this technology to follow the last trend of smart material commercialization: rapid commercial adoption after initial deployment. In the case of piezoelectrics, the technology went from niche to mainstream when the electronics industry discovered its suitability for small-scale actuation. Readers should monitor the success of this project closely, both to gain insight into smart material commercialization and for its potential to impact infrastructure construction in years to come.
By: Anthony Schiavo