May 22, 2017
Rods of a super-elastic nickel-titanium alloy, commonly called Nitinol, containing about 55% nickel and bendable concrete composites have been used for the first time, in downtown Seattle, USA. A bridge that bends in a strong earthquake and not only stays standing, but remains usable, is making its debut in its first real-world application as part of a new exit bridge ramp on a busy downtown Seattle highway.
Modern bridges are designed not to collapse during an earthquake, and this new technology takes that design a step further. In the earthquake lab tests, bridge columns built using shape memory nickel-titanium rods and a flexible concrete composite returned to their original shape after an earthquake as strong as a magnitude 7.5.
“We’ve tested new materials, memory-retaining metal rods and flexible concrete composites, in a number of bridge model studies in our large-scale shake table lab. It’s gratifying to see the new technology applied for the first time in an important setting in a seismically active area with heavy traffic loads,” explained Saiid Saiidi, civil engineering professor and researcher at the University of Nevada, Reno. “Using these materials substantially reduces damage and allows the bridge to remain open even after a strong earthquake.”
Saiidi, who pioneered this technology, has built and destroyed, in the lab, several large-scale 200-ton bridges, single bridge columns and concrete abutments using various combinations of design and innovative materials including the nickel-titanium rods in his quest for a safer, more resilient infrastructure.
“We have solved the problem of survivability, we can keep a bridge usable after a strong earthquake,” Saiidi said. “With these techniques and materials, we will usher in a new era of super earthquake-resilient structures.”
“This is potentially a giant leap forward,” Tom Baker, bridge and structures engineer for the Washington State Department of Transportation, said. “We design for no-collapse, but in the future, we could be designing for no-damage and be able to keep bridges open to emergency vehicles, commerce and the public after a strong quake.”