Valpo prof tries to crack case of MLK bridge defects

INDIANAPOLIS | A Valparaiso University engineering professor says there are at least two likely causes for the cracked concrete beams on the now-closed Martin Luther King Drive bridge over the Borman Expressway in Gary.

The first possibility is that something went wrong when the bridge's concrete beams were poured off-site about six years ago, said Karl Zimmerman, assistant professor of engineering.

"It seems like what has happened with M.L. King is there was something that went wrong in the casting yard. I have no idea what that would be," Zimmerman said. "But there were four bridges on that section that were all built at the same time, and I think to the same specifications. Three of them are fine. One of them is not."

The bulb-T concrete bridge beams for the shuttered bridge were cast by Prestress Services Industries at its facility in Decatur, Ind., according to the Indiana Department of Transportation. A PSI employee in Decatur referred questions to the company's Henderson, Ky., office, where an official there said he was not willing to speak about the situation because he was not aware of problems in Gary.

INDOT closed the bridge May 19 after inspectors found diagonal shear cracks in the bridge beams and longitudinal cracking in the beam flange. There also was excessive cracking on the driving surface of the bridge deck, which led engineers to doubt the bridge's load-carrying capacity, said Will Wingfield, spokesman for the state transportation agency.

Zimmerman said the cracks on the bridge deck indicate a second possible reason for why the concrete beams cracked. It may be due to land settling under the abutments on either side of the bridge or under the pier in the middle of the expressway, he said.  

"If one of those three has shifted a little bit, dropped down a little bit, or moved laterally a little bit, it could put stresses on those beams that they didn't anticipate," Zimmerman said. "They're not supposed to get out of line."

The possible settling may have been caused by the massing near the bridge of heavy equipment being used in the reconstruction of the nearby intersection of the Borman Expressway and Interstate 65, Zimmerman said. 

Similarly, the August 2007 collapse of the Interstate 35W bridge in Minneapolis, which killed 13 people, was caused by the weight of construction equipment on the bridge aggravating a design flaw in the bridge's gusset plates, according to the National Transportation Safety Board.

"It may be that when INDOT completes their investigation, they'll say there were about a dozen things that happened to this bridge," Zimmerman said. "The main thing that they did right was they closed it as soon as they had any doubts."

INDOT inspects every bridge in the state every other year and is conducting its own investigation as to what caused the bridge's concrete beams to crack.

Wingfield said the agency does not have a set date that it expects to report on its findings, only that "how quickly discussions progress with the companies responsible will determine the scope and time frame of the investigation."

Representatives of the bridge designer, RQAW Corp., of Indianapolis, and the bridge builder, Superior Construction Co. Inc., of Gary, did not respond to requests for comment from The Times.

The $21.3 million bridge carried an average of 4,100 vehicles a day last year. The span was designed for traffic volume 20 years out, estimated at 13,440 vehicles a day in 2023. The overall life expectancy of a well-maintained bridge of similar design is 50 to 75 years, according to INDOT.

The design of the King Drive bridge, a precast concrete bulb-T beam bridge with a continuous composite deck, was selected because it is cost-effective and normally performs well, Wingfield said.

Indiana has 126 bridges of this design, including five that span the Borman Expressway. Inspections of those Borman bridges in May did not find concrete cracking problems similar to those that required shutdown of the King Drive bridge.