Safety of metal plates examined

By Pam Sohn

Staff Writer

The National Transportation Safety Board is advising states to check bridges held together with steel plates and rivets, and Tennessee and Georgia officials confirm there are many in the area.

Officials with both states, however, said residents should not be concerned.

Although the exact cause of the Interstate 35W bridge collapse in Minneapolis is not known, some engineering experts have said the failure of steel plates -- often called gussets -- that hold together steel beams where they intersect could have brought it down.

The recently reopened Chief John Ross (Market Street) Bridge still contains some gusset plates with rivets.

Staff Photo by Angela Lewis

The Aug. 1 collapse killed at least seven people, and at least six others are missing, according to The Associated Press.

Hamilton County has 46 bridges with steel plate gussets and rivets, including the newly refurbished Market Street Bridge and two McCallie Avenue bridges over Dodds Avenue and Willow Street, said Jennifer Osborne, spokeswoman for the Tennessee Department of Transportation.

"The rivets in the Market Street Bridge are perfectly sound," said Ed Wasserman, head of the structures division of TDOT.

"We'll take a look at it," he said, "but the bottom line is that there are many old bridges in Tennessee, and there are many with riveted connections. Not one of them has ever failed (because of rivets) to my memory."

Georgia has up to 35 highway deck truss bridges with steel gussets, including three in Catoosa, Murray and Chattooga counties, Georgia Department of Transportation spokeswoman Crystal Paulk-Buchanan said. She could not immediately say how many of those bridges were riveted together and how many were bolted together.

Ms. Paulk-Buchanan said Peach State bridges similar to the Minneapolis bridge are inspected annually, not every other year as required by federal law.

She said the three area truss bridges with steel gussets are Catoosa County's Jays Mill Road bridge over West Chickamauga Creek, Chattooga County's Lyerly Dam Road bridge over the Chattooga River and Murray County's Old Federal Road bridge over Mill Creek. Those bridges were built in 1901, 1957 and 1918, respectively, Ms. Paulk-Buchanan said.

The National Transportation Safety Board's Wednesday advisory to states cited a "design issue" with the Minneapolis bridge gussets, but NTSB officials on Thursday said people "have run maybe a little bit too far" with the statement on gussets.

"Simply by finding a piece of metal that's been sheared or twisted doesn't necessarily mean it's a critical piece of the puzzle," said Bruce Magladry, director of the NTSB's Office of Highway Safety. "We see a lot of steel that's damaged because of the bridge collapse. What we need to ferret out is what's an initial cause of damage versus what's a secondary cause."

In Tennessee, similar bridges are inspected every other year, Ms. Osborne said.

"Rivets were phased out of bridge construction in Tennessee in the 1960s," she said. "But now in the inspections, they give bridges with rivets extra attention. We're looking again at all of them in the area."

Bridge builder Jerry Britton of Mountain States Contractors said travelers should not be leery of the recently reopened Market Street Bridge, which he and his workmen refurbished.

"We replaced some gusset plates on the bridge that were bad, and in those we used bolts," he said.

Mr. Britton, like Tennessee highway officials, said it is premature to be concerned about remaining riveted bridge connections.

"Younger engineers lean more toward bolts because they don't have experience with rivets," he said, "but it's hard to say one is better than the other."

Mr. Britton said the holding strength of bolted connections can be measured, while the holding strength of riveted connections cannot. An advantage with rivets, however, is that the heat used to seal them fills the connection joints with molten metal that later hardens, he said. In bolted connections, empty spaces remain.

Bridge experts say corrosion from rain and other weather elements seeps into cracks in worn or unsealed bridge areas and contributes to deterioration.

The Associated Press contributed to this story.

E-mail Pam Sohn at psohn@timesfreepress.com