Earthquakes don’t just wreck buildings. They smash and destabilize the infrastructure needed for rescue and for the recovery of the area afterwards. Bridges are a particular problem—they’re vulnerable, and by definition, they bridge routes that are are otherwise impossible to pass. Repairing a bridge after an earthquake can take weeks of painstaking work.
A new method of bridge repair, from University of Utah professor Chris Pantelides, can cut repair time down to days.
Regular bridge repair involves a long process of inspecting the columns, and then hacking away the existing concrete to get to the rebar and steel hoops inside. The rebar is replaced, the column is wrapped in a steel cast, and new concrete is poured. It takes forever.
Pantelides's method isn’t pretty, but it’s fast, and the resulting structure is as strong as the original. Holes are drilled into the ground around the broken column, and rebar is glued into them. Then a thin, donut-shaped composite shell is placed around the whole lot, and concrete is poured in. In principal, it’s like wrapping the broken column in gaffer tape, only the result is a lot more permanent. The donut shell itself is made from a carbon fiber-reinforced polymer that is stronger than the steel and concrete it contains.
"The circular shape gives you the best strength for the amount of material you are using," Pantelides said in a press release. "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."
Even a layperson can tell that Pantelides's method—published this week in the American Concrete Institute—is way faster than the old way.
The method is just as suitable for other kinds of column as it is for bridge supports. Damaged buildings can be repaired, and the donuts could even be used to add extra earthquake protection to undamaged structures.
The repair can’t save every bridge. If the columns are too far gone, even a stack of his donuts won’t be enough, and the bridge will have to be demolished and replaced. But in the aftermath of an earthquake, his quick-fix "patches" could make a big difference to rescue operations in the disaster area.