Reducing pier pressure

A US engineer claims to have developed a design for an earthquake-proof bridge that can also withstand the impact of a terrorist bomb strike.

Prof Michel Bruneau, an earthquake engineering expert at New York State’s University, Buffalo, said that there is a need to protect bridges from both events since as well as being terrorist targets they are also often located in areas of moderate or high seismic activity.

Intended primarily for small and medium sized bridges, Bruneau’s concept focuses primarily on the design of the bridge piers.

Bruneau said that most existing bridges are supported by conventional reinforced concrete columns which, in the event of a major blast, would breach, causing the bridge to collapse.

In his design, the piers are made from corrosion-resistant steel tubes filled with concrete, but without reinforcing bars. The steel and concrete bind together, forming a composite structure, which is claimed to give the piers superior strength and ductility.

Bruneau said that this means they will bend without breaking when subjected to significant blast and seismic forces. For the pier’s footing, additional structural shapes are embedded in concrete to resist the large bending forces developing at the base of the piers.

During trials carried out by the US Army, quarter scale prototype piers were subjected to blast forces similar to those that would be experienced if the bridge were attacked with a car bomb. Bruneau said that while software modelling indicates that a traditional concrete bridge pier would have broken, the prototype was relatively unscathed.

He added that while the design is primarily intended for new bridges, future research will focus on the development of systems that could be retrofitted to existing ones.