It takes a major earthquake less than a minute to inflict debilitating damage to bridge structures – in particular their support columns, which can in turn disrupt the functioning of key roadways that are essential to the functioning of modern society as well as emergency operations.
In stark contrast, the repair work needed to restore damaged bridges to a usable state can take multiple weeks, during which time the provision of key services will be severely impeded.
University of Utah engineers believe the new repair process they’ve developed, which was detailed in a paper published in the American Concrete Institute Structural Journal, will reduce the time needed to fix damaged bridge columns from weeks to mere days, helping to restore earthquake-blighted cities to a functional condition in a far shorter period.
The conventional method for repairing the damaged columns of bridges involves cutting away at the concrete in order to access their interiors, and then replacing any rebar or other steel structural parts which have been damaged or deformed. The whole column is then encased in a steel cast, which is used as a mould for the pouring of new concrete.
The entire process is costly and requires a copious amount of time, leaving bridges out of operation for multiple weeks. This is a major dilemma for earthquake-hit areas where the functioning of roadways is of key importance to emergency operations.
The method developed by University of Utah civil and environmental engineering professor Chris Pantelides make use of donut-shaped concrete structures called "repairs," each of which is lined with a carbon-reinforced polymer that possesses greater strength than steel.
Engineers first drill steel rebar with heads into the foundation of the column before fixing them in place using epoxy. The donut-shaped "repair" is then attached to the column and the rebar, with the composite fibre serving as a mould for the pouring of new concrete.
According to Pantelides, once the concrete is set, the repaired column should possess almost the same structural integrity as it did prior to incurring damage.
"The circular shape gives you the best strength for the amount of material you are using," said Pantelides. "The stresses are distributed equally all around the periphery.
“With this design and process, it is much easier and faster for engineers and crews to rebuild a city ravaged by an earthquake so that critical roadways remain open for emergency vehicles.
"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."
In addition to repairing damaged bridges, the donuts can also be retrofitted to bridges to make them stronger and more earthquake resistant.