Instant bridges: New system allows light, strong structures in three days

The University of Maine has unveiled a system for building highway bridges in just 72 hours using composite material girders and precast concrete deck panels.

The lightweight, stackable girders are twice as strong as steel and concrete girders, and the system can be erected with common rental cranes, say researchers at the university’s Advanced Structures and Composites Center.

As well as being a logistical breakthrough – up to four bridges can be transported on a single flatbed truck, researchers said – the system is durable and easily maintained: girders are designed to last 100 years and the precast deck can be easily replaced.

The system can be used for for short- to medium-span highway and pedestrian bridges, and by the military, the university said. The design allows for up to 80-foot unsupported spans.

Last month a bridge girder was strength-tested in the laboratory using hydraulic equipment that simulated the heaviest highway truck loads.

The test proved design modelling predictions and showed the bridge system can withstand the loading specified in the American Association of State Highway and Transportation Officials (AASHTO) Bridge Design Specifications.

"Today’s bridge test exceeded our expectations. The composite bridge withstood forces equivalent to more than 80 cars stacked on top of each other, and more than 5 times the HL 93 design load specified by AASHTO," said Dr. Habib Dagher, executive director of the center.

He called it "a truly a remarkable engineering achievement".

The US Army Corps of Engineers sponsored research on the system, which is patent-pending.

Dagher continued: "This bridge system takes advantage of the unique properties of both composite materials and precast concrete, and it is designed with construction logistics in mind. The bridge girders weigh only 1-2 tons for 40- to 80-foot spans, so that they can be erected with locally-sourced common rental cranes, making them easy to deploy in most locations."

The university is working with a company, AIT Bridges, to commercialise the system. After the strength test its chief executive, Brit Svoboda, said "today’s event allowed us to showcase this new technology with potential investors as well as DOT partners and executives. We’re ready to go to market."

Image: University of Maine performs test on bridge girder made of composite materials (University of Maine)