What if you could build a bridge that could not just stand up to an earthquake but flex back into shape after the shaking stopped?
That’s the promise of a new bridge in Seattle, Washington, built with the help of new super-elastic materials. It represents a seismic step forward in bridge construction.
The SR 99 Alaskan Way Viaduct Replacement South Access–Northbound Off-Ramp has been honored by ASCE as a finalist for the 2019 Outstanding Civil Engineering Achievement award, the Society’s preeminent project honor.
All five OCEA finalists will be recognized at ASCE’s 2019 OPAL Gala, March 14, in Arlington, VA, with the OCEA winner revealed at the end of the event.
The bridge, part of a larger program to replace an aging viaduct with a modern tunnel, is part of an exit ramp from State Route 99 into downtown Seattle. It is the first bridge in the world built with columns made of shape memory alloy (SMA) and engineered cementitious composite (ECC). To the eye, the bridge looks like most others. But inside the columns, the SMA and ECC form a connective tissue with the potential to revolutionize bridge construction in earthquake-prone areas.
At the heart of the Washington State Department of Transportation project is nickel titanium, or Nitinol. For decades, scientists and engineers have moved shapeshifting materials out of science-fiction and into military, then civilian use – for example eyeglass frames or orthodontic braces. But those uses involve thin wires. The bridge uses five-foot long bars of alloy surrounded by an elastic concrete at the top of its two support columns to achieve flexibility in a much more profound way.
“After an earthquake is when you need bridges the most,” says M. Saiid Saiidi, a civil engineering professor whose lab work at the University of Nevada, Reno, led 15 years of the materials’ design and testing, including on shake-tables.
FEMA estimates that as many as 1,000 bridges in Washington and Oregon could collapse or be severely damaged in a strong earthquake. And even if a bridge doesn’t collapse, it doesn’t mean it’s usable. Traditionally, a bridge is deemed successful if left standing. But the new design aims to achieve a “no damage” standard so that bridges also remain open.
When such technology and materials are commonplace, the current six percent additional cost added to the building of a structure could be more than offset when rebuilding in the case of disasters.
The Northbound Off-Ramp Bridge of the SR 99 Alaskan Way Viaduct – the first one that flexes and snaps back when the ground stops shaking – is scheduled to open this February.
Learn more about the 2019 OPAL Gala.
