The new ‘rocking footing’ design is intended to improve performance for better resistance to earthquakes with less damage and faster on-site construction.
"The design of reinforced concrete bridges in seismic regions has changed little since the mid-1970s," said Professor John Stanton, who developed the concept underlying the new design. Researchers from both Washington University and the University of Nevada have developed the design.
Until now the majority of bridge bents have been made using concrete that is cast in place, said Stanton. Prefabricating speeds on-site construction but means that the pieces need to be connected on-site, and therein lies a major difficulty. "It is hard enough to design connections that can survive earthquake shaking, or to design them so that they can be easily assembled, but to do both at once is a real challenge," he said.
An key feature of the new system is that the columns are pre-tensioned with high-strength steel cables. The system’s ‘re-centering’ action ensures that, directly after an earthquake, the bridge columns are vertical. This means that the bridge can be used straightaway by emergency vehicles.
When the columns rock during an earthquake, they experience high local stresses. To counteract the possibility of crushing, the researchers have protected the ends of the columns with short steel jackets that confine the concrete.
On 14-15 July, the team will test a complete bridge built with the system. The test will be conducted at 25% full-scale on three of the four earthquake shaking tables at the University of Nevada, Reno, earthquake engineering laboratory.
The research findings are included in a paper being presented in Alaska later this month during Quake Summit 2014, as part of the 10th US national conference on earthquake engineering.
