Erosion triggers most bridge collapses, so a Pitt engineer buried an alarm
Michael Rothfuss buried 15 PVC tubes packed with batteries and radios around a remote bridge that spans a small creek in Armstrong County more than two years ago.
He hasn't heard from them since.
Rothfuss, who has a Ph.D. in electrical engineering from the University of Pittsburgh, placed the tubes as part of a Pitt RFID Center of Excellence project. It was to help PennDOT improve erosion monitoring around underwater support structures of remote, rural bridges.
Bridge scour — or erosion caused by a stream, river or lake around a bridge's supports — is the most common cause of bridge collapses in the country.
The erosion can happen over years, eating away at the bridge's stability. Or it can happen rapidly during a flood or high water after heavy rains.
Between 1966 and 2005, scour was the cause in about 60 percent of 1,502 bridge collapses, according to data Pitt used.
“If it tears away enough of the supporting material for certain types of bridge foundations, you can have the bridge collapse,” said Timothy Panzigrau, a civil engineer working on bridges in PennDOT's District 10 office, which covers Armstrong, Butler, Clarion, Indiana and Jefferson counties. Panzigrau worked with Pitt on the project.
A New York Thruway bridge near Amsterdam, N.Y., collapsed in 1987 because of scouring. Two years earlier, a bridge over the Chickasabogue River near Mobile, Ala., collapsed.
There are 27 bridges in Allegheny County and two in Westmoreland County that state and local officials are inspecting for scour after recent heavy rains and flooding, according PennDOT data.
With so many bridges and a limited number of PennDOT inspectors, the agency is hard pressed to examine the structures frequently.
“We're just always looking for a better way of doing things,” Panzigrau said.
The state has nearly 1,200 bridges in Allegheny County. About 14 percent are classified as structurally deficient.
PennDOT has 735 in Westmoreland County. About 16 percent of those are structurally deficient, according to PennDOT data.
Statewide, about 14 percent of PennDOT's 25,361 bridges are structurally deficient.
Ten years ago, about 23 percent of PennDOT's bridges were structurally deficient.
To check for scour, crews probe the material around bridge piers or abutments. Large bridges or large bodies of water require divers.
“The Minnesota event was the catalyst for this project,” Rothfuss said, referring to the collapse of the Interstate 35W bridge in Minneapolis 10 years ago.
On Aug. 1, 2007, the eight-lane highway bridge over the Mississippi River collapsed, killing 13 people.
The Federal Highway Administration asked the National Transportation Safety Board to look into bridge scouring as a potential cause of the bridge collapse as part of its preliminary investigation. Five months after the collapse, federal investigators determined a metal plate that was too thin was the culprit.
Despite the findings of the Minneapolis bridge collapse, PennDOT asked Pitt to develop a way to monitor scour remotely, without sending crews or divers.
“They came to us because there was a need,” Ervin Sejdic, a Pitt assistant professor and associate director of the RFID Center of Excellence.
That's where Rothfuss' tubes — called float-out devices — come in.
The tubes, sealed to be waterproof and designed to last 20 years, were buried at different depths up to 9 feet around a bridge crossing a small stream on Route 1028 in Armstrong County.
If enough erosion occurs to uncover a buried tube, it will float to the surface, at which point, a switch inside the tube will trigger, sending a radio signal to a nearby receiver, alerting PennDOT that bridge scour has occurred.
Someone from PennDOT would still have to venture out to the receiver and check the control panel for an indication a tube was unearthed, but that's easier than poking around in the mud.
In June 2015, Rothfuss buried his tubes. And waited.
Rothfuss shrugs when asked what to make of the fact that the receiver — powered by solar panels — hasn't received a signal. He's not sure if that means there's been no erosion or if his tubes have floated to the surface and floated away without making contact.
Panzigrau said there has been issues with maintaining power, but he didn't label the project a failure.
He doubts PennDOT will move forward with it.
“It didn't prove a typically dramatic result for us,” Panzigrau said, adding later, however, “We're just always looking for a better way of doing things.”
That hasn't deterred Rothfuss. He is already imagining improvements.
“The next goal is to do it over wireless,” Rothfuss said, thus eliminating the need for PennDOT crews to visit bridges.
Aaron Aupperlee is a Tribune-Review staff writer.