Corrosion, cracking may have caused collapse

News Roads & Bridges August 03, 2007
Printer-friendly version

A day after the tragic collapse of the 35W bridge in Minneapolis, theories
of exactly what caused it began pouring out of the Twin Cities area.
Perhaps the most disturbing piece of news surfacing is the fact that
Minnesota Department of Transportation (Mn/DOT) officials knew there was
serious corrosion on bearings and steel but still deemed the bridge fit to
hold traffic. Experts say that corrosion could have restricted the structure
from moving freely as it was designed to do. Officials also knew of decay
and fatigue cracking in the deck truss and other places.

Attempts to reach Mn/DOT over the past couple of days have been
unsuccessful.

It also was suggested that the contractor doing deck resurfacing work at the
time of the collapse may have been linked to the accident. Witnesses on and
around the bridge reported hearing a jackhammer and then feeling heavy
vibrations before the span crumbled. Officials, however, stated yesterday
that all jack-hammering and grinding of old concrete was done hours before.
“We did not do any work on the steel structure,” Tom Sloan, vice president
at Progressive Contractors, told the Chicago Tribune. “We simply repaired
the concrete deck by removing deteriorated concrete, patching and
resurfacing.”

A security video showing the entire collapse as it happened also was
released yesterday and should help investigators pinpoint the exact cause.
Before the video, officials were literally grasping at straws in an attempt
to determine a breaking point. A computer model of the bridge also should
serve as a valuable aid.

The NTSB hopes to salvage crucial parts of the downed bridge and reassemble
them over the next few weeks. Hardcore conclusions, however, could take
months to develop.

Overlay Init