Imagining a better, more resilient bridge
By using unconventional materials in bridge engineering, Mehdi Saiidi has designed a bridge that can withstand an earthquake, raising the bar for bridge engineering in seismic zones.
For the past decade or so, Mehdi “Saiid” Saiidi has been leading something of a revolution in the field of bridge engineering.
For years, bridges in seismically active zones have been designed with the primary goal of saving lives in the event of an earthquake. As a result, bridges were designed to withstand collapse but were generally unusable after an earthquake, hampering rescue and recovery efforts by taking out key transportation infrastructure. Now, using innovative materials, Saiidi has designed a bridge that can withstand severe shaking and still be usable.
During testing on the University of Nevada, Reno shake tables in February of this year, a two-span bridge using shape memory alloys survived multiple simulated earthquakes while showing few signs of stress. Shape memory alloys, which snap back to their original shape after deformation, allow bridge columns to absorb shaking from an earthquake and return to an upright position.
“You don’t have to replace the bridge. Not only that, you don’t even have to shut it down to traffic,” Saiidi said. “The bridge will be standing upright. What these innovative materials do is keep it serviceable.”
Innovative materials change paradigm for bridge engineering
With that accomplishment, Saiidi has ushered in a new era in bridge engineering. But despite the impressive results Saiidi has achieved experimentally, he has been surprised at how quickly new materials have been embraced in the engineering community.
“I’ve been amazed how fast people have taken note of this and are willing to embrace it,” Saiidi said. “I thought maybe 10 years from now they will be ready for it, but it looks like they are ready now.”
They are certainly ready in Seattle, where Saiidi is working with the Washington Department of Transportation to build a bridge using nickel-titanium shape memory alloys. The bridge is currently under construction and should be open to traffic in 2016.
“This is not a little bridge somewhere in a backroad or rural area where no one sees it. This is downtown, very visible,” Saiidi said. “I’m glad we have those kind of engineers. Let’s talk about how we can break loose from the same old and do something different and exciting.”
Before starting that conversation, Saiidi first had to demonstrate to the somewhat skeptical bridge engineering community that innovative materials could work. His first tests of nickel-titanium shape memory alloys in bridge columns, back in 2005, came under a program devoted to funding high-risk, potentially high-return ideas funded by the National Cooperative Highway Research Program.
When that project returned promising results, Saiidi received additional grants to expand testing to full bridge models and more recently to bridges built using prefabricated elements that are assembled on site. He held a workshop in 2011 to bring researchers, materials scientists and engineers together to explore ways innovative materials could be leveraged in bridge engineering, planting the seeds for implementation of real-world bridges in the engineering community.
Design guidelines for innovative materials under developmentNow, Saiidi is developing design guidelines for bridges using new materials that would pave the way for widespread implementation of bridges designed with innovative materials. The idea to use shape memory alloys – an innovation in materials science – in structural engineering was one Saiidi stumbled across by chance while at a conference in Japan for another project listening to researchers that use the material for mechanical devices.
“Creative ideas come when you combine things from different fields,” Saiidi said. “Faculty who are involved in innovative material research convey a fundamental message to students – be open minded. Just because something has been done certain ways in the past doesn’t mean it has to be done that way in the future.”
Saiidi is taking his own advice to heart. Even as bridges based on his latest breakthroughs are starting to enter engineering design standards, he is thinking about how to transform the field further. This summer, he traveled to Japan to meet with materials researchers and manufacturers who produce a new generation of shape memory alloys that are more cost effective, and Saiidi is hoping this material could be the future of next-generation bridges.