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Foul play with the Murray Morgan bridge?

Post by David Seago on Nov. 5, 2007 at 5:36 pm |
November 5, 2007 5:36 pm

From the horse’s mouth, here are some rebuttals to accusations that the state Department of Transportation neglected the Murray Morgan bridge to death over the last 15 years.


When transportation chief Paula Hammond came in in last week, we asked a lot of conspiratorial-minded questions about why her agency lost interest in repainting the bridge.


Paint is a bridge’s chief protection against corrosion. The Murray Morgan – now ruined by corrosion – was repainted at what appear to have been roughly 10-year intervals until 1983. Then the brushes were stowed for good.


Another suspicious question: Why did the Murray Morgan’s “sufficiency rating” fall precipitously from 44.64 in 1998 to 2 – that’s right, 2 – in 2001.


Below are WSDOT spokesman Stan Suchan’s answers to the questions we asked. As for the first response, I can’t help noting that some Roman bridges are still standing – and carrying traffic – after 2,000 years. Can’t we do better than 75 years?


What is the life expectancy of a bridge?


The design life of a bridge we build today is generally accepted to be 75 years. When the Murray Morgan Bridge was built the design life of a bridge was generally accepted to be 50 years.



How long does bridge paint last and why wasn’t the Murray Morgan Bridge painted after 1983?



Bridge paint is expected to last around 15 years. This indicates that the next paint job on the Murray Morgan Bridge would occur sometime around 1998 (1983+15 years). During the years leading up to this date, the state, city and port planned to rehabilitate the bridge, which would have included a variety of improvements including a paint job. As a result, we did not pursue a stand-alone painting project. Since that time we haven’t been certain about the future of the bridge—rehabilitation, replacement or removal—so painting did not seem to be a wise investment.



When we paint a bridge we prepare and paint the surface. We do not remove every bit of rust from every nook and cranny, for example, from every bridge member, joint and bearing. When we paint we are coating and protecting the overall structure from degradation. Once corrosion starts in the nooks and crannies, only a serious rehabilitation effort can stop the corrosion and repair the damage.



If WSDOT painted the bridge every five years since 1980, would that have protected it from deterioration? Would it be open to traffic today?


As described above, bridges have a lifespan. Painting a bridge combats corrosion but doesn’t prevent it and does not repair previous damage.



According to Jugesh Kapur, State Bridge Engineer, painting is just one of the maintenance activities required to extend the life of the bridge. Painting the bridge more frequently since 1980—for example, every five years—might have helped us keep the bridge open to traffic a few more years, but only if we also completed additional preservation work such as cable repairs and structural, electrical and mechanical rehabilitation. Ultimately, no amount of paint could have significantly extended the life of the Murray Morgan Bridge.



Why did the sufficiency rating drop in 1999 from 44.64 to 14.49, and drop again in 2001 to 2.00?


In 1998, the state performed a load rating of this bridge. A load rating is a comprehensive analysis of traffic loads the bridge can carry safely. This analysis revealed that the carrying capacity of the bridge was low. When we considered this factor the sufficiency rating dropped from 44.64 to a 14.49.



During the 2000 inspection, the condition rating for the superstructure (for example, girders, deck and truss) dropped from 4 to 3 and for the substructure (piers, columns and foundation) dropped from 5 to 4. This caused the overall sufficiency rating to drop from 14.49 to 2.00.



Condition ratings range from a high of 8 to a low of 0. A condition rating of 2 generally indicates a need to close the bridge.

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