Civil engineers in the US have developed a new way of fixing bridge columns that cuts the repair time from weeks to days.
Researchers led by University of Utah civil and environmental engineering professor Chris Pantelides have developed a new process of fixing columns, outlined in a paper in the American Concrete Institute Structural Journal.
Following earthquakes, if bridge columns are damaged, including internal steel rebar snapping, engineers usually remove concrete, replace rebar and steel hoops, and pour concrete into a new steel cast – a process which takes weeks.
However the system developed by Pantelides involves creating concrete donuts known as repairs, that are lined with a composite fibre material built around the bottom and top of each column. The material is a carbon fibre-reinforced polymer made of fibres and resin that is stronger than concrete and steel. The system has been designed for post-earthquake bridge repairs, but could also be used as a retrofit solution to make bridges more robust in the event of an earthquake.
It works by drilling a number of steel rebars with heads into the foundation around the column and securing them with an epoxy. Then two halves of a circular shell made of the composite fibre, just millimetres thick, are placed around the column and rebar and spliced together. Concrete is poured around the column and over the rebar with the composite fibre acting as a mould. The result is a repaired column with approximately the same structural integrity as the original column, according to Pantelides.
He said: “The circular shape gives you the best strength for the amount of material you are using. The stresses are distributed equally all around the periphery. With this method, if there are future earthquakes or aftershocks the bridge will survive and damage will happen adjacent to the donut. This gives the bridge a second life.”
The team has filed for a patent on the system although it is available for use immediately in earthquake-struk areas. The research was funded by the Utah, New York and Texas departments of transportation and the Mountain Plains Consortium.