The safety board is expected Friday to issue a formal finding of probable cause in the accident. But investigators honed in Thursday on the insufficient review process to catch the bridge design flaws and the absence of standards regarding the stockpiling of construction equipment and materials.
"Nobody is aware of the (bridge-loading) process because there is none," safety board member Steven Chealander said, referring to how the Minnesota Department of Transportation issued overweight permits to Progressive Contractors Inc., the company conducting a bridge deck resurfacing project.
"Somebody missed the whole idea that we are going to put 287 tons of equipment on that bridge," Chealander said.
The Federal Highway Administration is formulating new standards for balancing weights on bridges during construction.
The Minneapolis bridge was loaded to the point of collapse at its weakest spot in the middle of the span, investigators determined.
"This was the approximate weight of a 747 on a small spot," Rosenker said. "This is truly a very heavy, concentrated load."
Machinery and paving materials were parked and stockpiled on the center span at the time.
The original weight of the deck truss when the bridge opened in 1967 was 18.3 million pounds. Ten years later, 3 million pounds of weight was added when the bridge deck was thickened. A barrier and a deicing system were later installed, adding another 1.2 million pounds, investigators said.
Licensed professional engineers are liable in very specific ways and the licensing is part of that process--and helps to ensure that those practicing both have the requisite skills and experience as well as take the issue seriously.
The bridge had a design flaw, but I don't think that negates the value of licensing.