America's infrastructure is vast. And much of it is past its prime.
Of the roughly 600,000 bridges in the U.S., approximately %40 are over 50 years old. And while there's much talk by politician about the need to inject more money and effort into building new bridges and replacing old ones, the approach has been piecemeal to date and the sheer volume of work required is overwhelming.
Luckily, in many cases, full replacement isn't necessary and steel bridges can see their lives extended through rehabilitation of certain ares or components. Here, I'll present some considerations and advice on rehabilitation steel bridges to bring them back to full strength and keep them that way for as long as possible.
Cast or Band Aid?
Rehabilitation becomes necessary when even our best efforts of maintenance and preservation are not enough to win the battle against nature, or it may become required simply due to increased weight and traffic volume over time. When considering rehabilitation, the first question to ask is if this will be a long-term rehab or a temporary solution until replacement is possible. Knowing what your expectations are for a bridge will keep you from taking unnecessary steps and incurring additional expenses or minimizing the risk of having to implement a series of Band-aid solutions. This requires an evaluation of not just the bridge in question, but also the remainder of the system using the bridge. If a replacement is inevitable for other reasons in 15 to 20 years, then the scope for the rehab project should be adjusted accordingly. Similarly, if the desired timeline for additional bridge life is 40 to 50 years or even beyond (100?) do the best with what is known, but keep in mind that technology and material science will be advancing during the upcoming decades.
Rehabilitations often arise due to low load ratings, but sometimes there are also deterioration issues that don’t show up in a rating because they are not in the direct load-carrying path. This shouldn’t minimize the need to address these items, and it’s often best to take care of these serviceability-related issues before they lead to a strength-related problem, and to include them in the rehab scope of work.
This article was written by Dan McCaffrey, PE, and first appeared in Modern Steel Construction magazine. Find the full article here: http://bit.ly/mscsteelbridgerehab