Thoughts on the Engineering Industry

A blog covering engineering, technology and business topics

“Fracture Critical” Bridges and Other US Infrastructure Issues

Removal of the fallen Interstate 5 bridge over the Skagit River begins Monday, after barges carrying heavy cutting and lifting equipment from Atkinson Construction arrived in Mount Vernon. After removing the fallen span from the river, final inspections can begin before WSDOT can begin designing a preferred option for repairing the bridge and reopening the interstate.

Hello everyone.  I hope y’all are doing well.  Nothing new has really happened with me; just enjoying summer and my family visiting – all the summer type things.  Today I want to discuss “fracture critical” bridges and the issues in regards to US infrastructure in regard to the bridge collapse of the I-5 bridge in Seattle, Washington.  A recent article I read from the Associated Press, “Thousands of Bridges at Risk of Freak Collapse”, has discussed some of the statistics related to the issue.

The article opens with this quote to describe the bridge category of “fracture critical”: “Thousands of bridges around the United States may be one freak accident or mistake away from collapse, even if the spans are deemed structurally sound.”  In essence, this means that these bridges have no extra level of strength or redundancy incorporated into their design.  Further more these bridges carry millions of drivers every day.  This is the stated reason for the I-5 bridge collapse a couple weeks ago.  Recently, the government has focused on repairing bridges in the “structurally deficient” category – this means that portions of these bridges are poor condition or worse.  The most recent bridge failure in the “fracture critical” category was the I-35W bridge failure in Minneapolis which had a much higher passenger injury rate and even some deaths.  A study performed in the wake of that bridge failure revealed that only a few “fracture critical” bridges fail overall.  However, the government still builds these type of bridges in the belief that they won’t fail – the reason this design is still being used instead of the more conservative redundant design methods is monetary issues.  18,000 “fracture critical” bridges have been built from 1950 to 1980.  On a similar note, 30% of the bridges in the US fall into the “structural deficient” and “functionally obsolete” category; the “functionally obsolete” means that the design of the bridge is not suitable for it’s current usage.  The current spending on these repairs is $28.5 billion and this spending is double that of the budget in 1998.  However, this increase has barely kept up with the demand for repairs and while public officials agree something has to be done, they have not agreed on any solutions to effectively increase the bridge repair budget.  Currently, progress is being made by states in that they are trying to increase state budget investment using toll roads, gas taxes and sales tax.  Along with that, $3 billion of the $27 billion stimulus went to bridge repair budget as well.  Washington state Rep. Judy Clibborn states that “We can’t possibly do it all in the next 10 years, but we’re going to do the first bite of the apple.”

There are several things that can be learned from this bridge collapse.  The main one is that the analyzation of a bridge structure is more complicated than being structurally safe or unsafe.  While some of the bridges that get the most concern are the ones that aren’t structurally safe, there are a lot more that fall into that gray zone.  The secondary thing in relation to that is that in order to understand the complexity politicians need to have a better understanding of bridge design philosophy – especially the importance of redundancy and increased strength.  There also needs to be understanding by the population and politicians alike that there needs to be an increase in budgeted time and money to implement these concepts in order to construct the best quality bridges for our infrastructure.  What are your opinions on how to implement this?  What do you think are the best ways to increase the budget in regards to time/money and improve design/construction methods?  Thanks for your time and have a good week.

“Thousands of bridges at risk of freak collapse”, Associated Press, May 26th, 2013,

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