Minneapolis ABC Television outlet Channel 5 (KSTP) has reported that the Minnesota Department of Transportation (MNDot) conducted a study in 2006 which rated the I-35 bridge as “low to moderate” and stated that there was fatigue cracking of the deck. In addition, “there was out of plane bending of an approach span girder.”
This report was backed up by a statement from the White House, which said today, Thursday, that an inspection two years ago found structural deficiencies in the highway bridge that buckled during evening rush hour in Minneapolis.
White House press secretary Tony Snow said the Interstate 35W span rated 50 on a scale of 120 for structural stability.
"This doesn't mean there was a risk of failure, but if an inspection report identifies deficiencies, the state is responsible for taking corrective actions," he said. The bridge was 40 years old.
In a 2005 abstract, The Journal of Constructural Steel, says there is a complex interaction between bridge components (deck plate, ribs and floorbeams) and also by the interaction between the structure, the pavement and the vehicle’s wheels tires. “Stress concentration resulting from out-of-plane bending of deck components at typical welded joints can make these structures quite susceptible to traffic-induced fatigue cracks.”
There are two basic types of bending in bridge members: in-plane and out-of-plane. When in-plane bending occurs, the cross section of the support resists the load according to the design and undergoes nominal elastic deformation.
Out-of-plane bending implies that the cross section of the member is loaded in a plane other than that for which it was designed and undergoes significant elastic deformation or distortion, according to industry definitions.
In a press conference the evening of the collapse, Governor Tim Pawlenty stated that he saw reports from 2005 and 2006 that said the bridge was structurally intact.
