Modern bridges in areas where earthquakes occur frequently are being built in such a way that they do not collapse during an earthquake. However, the way this is done currently, the bridges become permanently damaged and cannot carry traffic anymore after the earthquake. Saiid Saiidi, civil engineering professor and researcher at the University of Nevada (Reno, US), has tested new materials that can bend to build an earthquake-resistant bridge that also remains usable. A pilot project is currently being built on a busy downtown Seattle highway.

On a large-scale shake table lab, Saiidi has tested various materials by making 200-ton bridges, single bridge columns and concrete abutments and exposing them to ‘earthquakes’ with a higher frequency than what is expected in the Seattle area. In these tests, bridge columns built using memory-retaining nickel/titanium rods and flexible concrete composite returned to their original shape with an earthquake equal to 7.5 on Richter scale.

For the most part, the earthquake-resistant bridge consists of the same materials many bridges are made of: concrete, rebar and pre-stressed concrete beams to hold up the road deck. The joints, however, are designed to be flexible.

By reinforcing bars with a metal alloy made from a mix of nickel and titanium, they will flex and snap back into their original shape when the earthquake is over. The concrete is made with small polyvinyl fibres that are coated to bind with the concrete and limit cracking. The concrete has to be made in small badges.

The top one and a half metres (five feet) of the bridge columns that support the beams are made with a combination of the special concrete and reinforced bars. Thanks to these materials, the bridge will remain in shape and usable by for example emergency services during an earthquake.

The bridge is built in a collaboration between the University of Nevada, the Washington State Department of Transportation and the Federal Highway Administration. The bridge should be finished in early April, but cannot be used until a connecting tunnel is finished in 2019.