The I-35W bridge in Minneapolis days after the collapse (AP)
St. Clound, MN (written by Kari Petrie & Kirsti Marohn/St. Cloud Times)
Wednesday marks the five-year anniversary of one of the worst manmade disasters in Minnesota history -- the collapse of the Interstate 35W bridge in Minneapolis.
On Aug. 1, 2007, under stress from 287 tons of construction material and rush-hour traffic, the bridge's center span shuddered, then collapsed, dragging other spans into the river. Thirteen people were killed, and 145 were injured.
The disaster sparked a nationwide examination of the safety of America's bridges, including more inspections and an increase in funding to repair or replace some of the most critical structures.
A bridge is considered structurally deficient if at least one component -- the deck, superstructure or substructure -- is in poor condition and needs to be scheduled for repair or replacement. It does not necessarily mean a bridge is unsafe although it's one of the factors used to determine which bridges qualify for federal money.
State and county engineers say the I-35W disaster raised awareness of bridge safety, tightened inspection and reporting requirements and made it easier to get state and federal money to repair or replace aging bridges.
"Bridges only last for so long," said bridge engineer Jim Hallgren of Minnesota's Department of Transportation District 3 . "And we need to take care of them."
The National Transportation Safety Board, which investigated the collapse, said one of the chief lessons of the tragedy is that state transportation officials may not have probed deeply enough into the design details of their bridges.
Since the collapse, the state transportation department has made several changes to its bridge program and how bridges are maintained and designed, said Tom Styrbicki, bridge construction and maintenance engineer. It has added 55 new positions in bridge inspection and maintenance divisions statewide.
The investigation into the I-35W bridge collapse uncovered a design flaw, leading to new national standards for reviewing bridge designs. The state now requires an independent peer review for major bridges.
"It's like the belt and suspenders," Styrbicki said. "It adds that level of safety."
The NTSB found that the failure of undersized, steel gusset plates likely caused the collapse. Styrbicki said the state now has new standards for inspecting gusset plates. Instead of describing any corrosion, inspectors take measurements.
Another factor in the collapse was the amount of equipment on the bridge, which was under maintenance. Styrbicki said while the state always had regulations, it has tightened those specifications. Every bridge project now includes restrictions about how much equipment can be on the structure.
"We were doing the right things but weren't doing it in a systematic way," Styrbicki said.
Right after the I-35W collapse, Stearns County Engineer Jodi Teich fielded calls from motorists wondering about the safety of the bridges they drive on every day.
"I think a public that's very aware is a good thing," Teich said.
Most bridges were built when the highway system was booming in the 1960s. Since most bridges have a 70-year lifespan, many of those are coming to the end of their lives.
While most areas have grown rapidly in the past 10 years, Hallgren said the additional traffic volume doesn't hurt the bridges. The increased volume becomes a problem when crews start work on a bridge and limit traffic flow.