I-35W Bridge Collapse - Week 51

Week 51 by Ivy Chang | September 28, 2010

NTSB releases evidence from bridge investigation

A laboratory report from the National Transportation Safety Board said a corroded gusset plate in the L-11 East gusset node had fractured partially along a line of corrosion on the I-35W bridge and broke apart from compression forces in the bridge truss that led to the bridge collapse.

That plate was recovered in five pieces from the Mississippi River during cleanup efforts.

The report indicated that Minnesota Department of Transportation officials had not repaired the corrosion since at least 1993 and did not replace the gusset plate. It also said secondary impacts did not cause the bridge to collapse.

Paving of Second Street is nearly complete while crews work on the Second Street Bridge. Photo by Ivy Chang.

NTSB also released a frame-by-frame study of videotape on the west side of the bridge from a surveillance camera installed at the lock and dam next to the bridge. Images showed the first movements before the collapse occurred near L-11 and U-10 gusset plates on the downtown Minneapolis end of the bridge.

The study also said the center span over the river fell flat into the water in about three seconds.

This is not the final report and does not draw conclusions about the causes, said NTSB officials.

Concrete pours, paving for roadway continue

Crews continue to pave approach roadways on either end of the bridge; install railings and signs; paint stripes on roadways; paint sides of the bridge; and begin landscaping near ramps to the roads.

During the week of July 28, construction workers finished replacing traffic signals and light poles near the I-35W entrance ramp from University Avenue north of the bridge approach. In addition, they poured concrete for the freeway and entrance and exit ramps at University Avenue on the north side and at Washington Avenue on the south side of the bridge.

Concrete pours began for the curbs, gutters and sidewalks on Second Street, near the University Avenue ramps.

Construction crews build forms for "pier ears," concrete covers that protect bearings on top of the piers. Photo by Ivy Chang.

Falsework under Span 3, north of the river, continues to be dismantled while a crew builds forms for "pier ears," concrete covers that protect bearings on which the bridge rests on top of the piers. Crews also are building barrier rails and curbs on the sides of the main span.

Concrete trucks continue to travel through the project site, delivering concrete to more areas around the bridge. Crews began cutting expansion joints in the freeway concrete and will sandblast concrete surfaces at night.

Work stopped on August 1 between 3 p.m. and 9 p.m. in observance of the one-year anniversary of the bridge collapse.

Hospital receives national award

Hennepin County Medical Center, the downtown public hospital closest to the I-35W bridge, received the President’s Award from the National Association of Public Hospitals and Health Systems for its response to the bridge collapse.

HCMC, as it is know locally, was operating at near capacity but opened 10 operating rooms and 25 intensive-care beds to care for 31 victims brought to the facility. Eight people were in critical condition and some were hospitalize for up to two months. Twin Cities’ hospitals treated 126 victims of the bridge collapse on August 1, 2007.

The award was last presented in 2002 to the New York City Health and Hospitals Corp. for its response to the September 11 terrorist attacks.