A bridge too weakDetecting a silent bridge-killer

Published 12 November 2009

New York State failed to make ultrasonic test of concrete piers, which could have avoided Champlain Bridge closure; a $10,000 high-tech ultrasonic test of the piers could have provided an early warning of lurking rot and given time to make repairs to stabilize the piers before the bridge became unsafe

New York state engineers were shocked to learn the 80-year-old massive concrete piers that hold up the half-mile-long Champlain Bridge were quickly rotting away unnoticed just below the waterline. A $10,000 high-tech ultrasonic test of the piers — something the state did not perform — could have provided an early warning of lurking rot and given time to make repairs to stabilize the piers before the bridge became unsafe, according to a national engineering expert on bridge failures.

Times Union’s Brian Nearing writes that the bridge was abruptly closed as structurally unsafe on 16 October, detonating an economic bombshell in lake-shore communities in New York and Vermont. Now, people who depend on the bridge are dealing with what will be months of long, costly detours, and the state faces a possible $50 million price tag for a new span if the old one can’t be saved. Even a stopgap temporary bridge could cost $500,000.

Underwater diving inspections of the piers done every five years — most recently in 2005 — gave no advance hint at the rapid deterioration to come, said Skip Carrier, a state Transportation Department spokesman.

In those four years, the amount of missing and rotted concrete in two of the 10-foot-thick piers went from 10 inches to 3 feet. “It is not something we expected to see,” he said.
A test may have been able to find the problem before it got so bad, said Norbert Delatte, a professional engineer and professor at Cleveland State University in Ohio.

 “An ultrasonic pulse test is not cheap, but it is a lot cheaper than what is going to have to happen now,” Delatte said. “This kind of ultrasonic test would give a general idea of the soundness of remaining concrete.”

Delatte is an expert on bridge failure, and is the editor of the American Society of Civil Engineers Journal of Professional Issues in Engineering Education and Practice. He reviewed DOT diving inspection records for 2000, 2003, and 2005 provided by the Times Union.

 An ultrasonic pulse acts like a kind of sonar. An electrical transmitter is placed against concrete and emits a sound wave, which travels through the concrete and bounces back to a receiver. An engineer can analyze the resulting signal to determine the condition of the concrete.

 DOT is aware of ultrasonic pulse technology, but did not use it on the Champlain Bridge, said Carrier. “We use it in other ways