State workers inspected part of the I-35W bridge in May, intending to finish the job after resurfacing work was complete.
Only three months before the Interstate 35W bridge collapsed, the Minnesota Department of Transportation decided not to use a consultant it had hired to help inspect the structure for potentially fatal flaws.
In what would be the doomed bridge's final inspection, MnDOT staff members used visual and ultrasonic methods in May to check slightly more than half of a critical section of the bridge, taking 15 pages of handwritten notes and more than 200 pictures.
The department then suspended its inspection, with plans to resume in the fall after a resurfacing job on the bridge was finished. A meeting about the partial inspection had been scheduled for Aug. 20 when the bridge collapsed Aug. 1, killing 13 people and injuring more than 100.
The unfinished inspection of the I-35W bridge leaves questions about why MnDOT didn't complete the examination in the spring or use its consultant, URS, after awarding it a contract for that purpose.
"The inspectors who were going through it did not have need for assistance," MnDOT chief bridge engineer Dan Dorgan said in an interview last month. "I talked to the inspectors sometime after May. Pretty brief. 'Did you find any problems?' And the answer was no."
Although the initial focus of the special inspection was to be on the south end of the bridge, the part now believed to have collapsed first, MnDOT inspectors instead started on the north end.
State defends last inspection
MnDOT, at the request of the Star Tribune, recently released notes taken by its workers who performed the partial inspections in May. The agency declined to make the inspectors or other officials involved in the work available for interviews.
In written responses to questions, MnDOT defended its handling of the inspection, and said it had not revealed any major problems with the bridge. Ronald Low, a spokesman for URS, said Tuesday that the company would not comment on any aspect of MnDOT's May inspection and referred all questions to the agency.
"The bridge inspection is one of the many things that we're looking at as part of this investigation," said Terry Williams, a spokesman for the National Transportation Safety Board, which is leading the main probe into the collapse. "We're still in the early stages."
The recommendation for a special inspection of the I-35W bridge near downtown Minneapolis grew out of an extensive study completed in January by URS of crucial steel beams considered susceptible to cracking. MnDOT's bridge office had chosen to do the special examination, over and above the regular annual inspection, after deciding against reinforcing the 40-year-old bridge.
An amendment to MnDOT's contract with URS signed April 5 said "the state is in need of Contractor assistance in the inspection of superstructure steel welds" of the bridge. The amendment went on to say that "Contractor will assist MnDOT as it conducts an in-depth fracture critical inspection of the superstructure welds."
The document says the inspections would be performed by MnDOT employees and begin in the spring. "The south truss span will be the first unit inspected," it specified.
Contractor not used
About midway through the south truss span inspections, MnDOT was to hold a progress meeting. URS was expected to be on site at least two days prior to the progress meeting "to observe inspection procedures and the progress of inspections, and to review all inspection reports completed to date. Contractor will attend and participate in the progress meeting."
Less than a month after signing the contract, MnDOT inspected segments of the bridge on May 1-4 without help from URS. The agency never paid URS any of the $21,563 authorized under the amendment.
A written statement from MnDOT spokeswoman Lucy Kender said, "Although we had a contract for URS to participate in the inspections in May 2007 if needed, we did not have a need to utilize them. ... Our staff had the necessary equipment and training to perform the inspections ... no issues were found during the inspections that required URS services."
In rejecting help from URS in May, the agency also opted for an inspections procedure that differed from one outlined in its contract with the consultant.
Instead of beginning with the south truss, as the contract amendment specified, MnDOT inspectors began on the north end of the bridge and worked south. The agency did not inspect all of the targeted trusses on the south end.
Asked about the change, Kender wrote, "When the amendment was written we assumed inspections would be done from below with manlifts to minimize disruption to traffic." Instead, inspectors used a "snooper" vehicle, "to provide better access for the inspectors. Logistically, it made more sense to inspect one complete side of the bridge at a time, starting at the traffic approach end and traveling in the direction of traffic to the traffic departure end, north to south in the west lane, and then moving to the other side."The order of inspections was set by ease of access; there was no engineering reason to inspect one end or side before the other."
Asked why the agency couldn't inspect the entire bridge in May, Kender said the agency had intended to inspect only some of the critical bridge elements in May, then review the inspection procedure in late August before completing the task in the fall. She said URS would have participated in the August review of the May inspections.
The special inspections in May concentrated on critical elements of the bridge identified by URS. MnDOT had scheduled its regular annual inspection, held in recent years in June, for September.
The handwritten notes from the May inspection -- accompanied by close-up photos of the bridge -- give no indication that MnDOT found serious problems at the time, and are couched in technical language. The partial inspection, according to explanatory notes provided by MnDOT, "only looked at certain truss members (called chords), those identified in the URS study as critical."
Corrosion but no cracks
An accompanying drawing of the bridge, with its many trusses numbered in sequence, shows that workers initially concentrated on the bridge's west side, starting from the north end.
The notes offer glimpses of what was found. For example, notes referring to truss L2' West, plate 2-2', on the bridge's north end, state that workers found "full length welds, bottom flange corroded 1/2 length of bottom weld -- up to 3/32" loss."
The notes indicate that inspectors did ultrasonic testing for undercut and porous areas in the welds and found some. "No crack noted."