There have always been problems, but bridge safety has been brought to the public forefront by the collapse in Minnesota.

If something good can come from the collapse of the I-35 bridge in Minneapolis last year, it might be a new national focus on bridge safety.

"There have always been problems, but bridge safety has been brought to the public forefront by the collapse in Minnesota," said Jessica Newlin, an assistant professor of civil and environmental engineering. "Civil engineers have been aware of it for a while, but I think generally the public really started worrying when that happened."

Surprisingly enough, one problem with bridge safety may be too much rather than too little data. Most bridges in the public road system are supposed to be inspected every two years. The condition of everything from the approach roadway to the bridge abutments and piers to the river flowing below is recorded in the National Bridge Inventory. Having this data is one thing, making sense of it is quite another.

"Managers are faced with this huge database of information and I can't imagine how you would go about trying to find the worst possible thing and what needs to be fixed first," Newlin said. "There is not enough money to fix everything. You have to prioritize."

To help managers prioritize repairs, a sufficiency rating is computed from the data – for example, the Minneapolis bridge scored 50 out of 100 points. A lower sufficiency rating means a higher priority for repairs. However, boiling so much information down into one number might not be the best way to look at such a complex issue. Newlin has been looking for better ways to interpret and use the data.

"Any state manager is probably going to have from a thousand to tens of thousands of bridges that they are responsible for, and it is easiest to look at one number and rank by that one number," Newlin said. "But it's more important to get at why that number is what it is."

Newlin came to the issue of bridge safety from her background in stream channel hydraulics and sediment transport. One of the primary factors that can cause a bridge to fail is scouring by sediment being carried along by the river.

"The foundation, the piers and the abutments are all in danger of being undermined by the stream channel processes," Newlin said.

Posted Sept. 22, 2008

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