August 28, 2008
Update on Bay Bridge Repairs
We warned you yesterday about emergency repairs the Maryland Transportation Authority announced for the Chesapeake Bay Bridge, starting today. WTOP has a bit of an update on the situation for Labor Day travelers. MTA is assigning extra staff members to help with traffic over the long weekend, and will make sure there are enough EZ-Pass and cash toll booths open to accommodate the heavy traffic, though it's probably still a good idea to find alternate routes to your destination if you can. Asking why the damage to the bolts in the concrete parapet wasn't found earlier, MTA Secretary John Pocani said, "This is something that's not detectable through normal inspection procedures and it's something that has occurred slowly over time," but that the bridge as a whole is structurally sound.
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well, if this is something that wouldn't be found normally, maybe they need to change their definition of "normal" to something that will ensure that they will find structural problems like this. we don't need another minneapolis bridge incident because a DOT is cutting corners.
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In all fairness to the Maryland Transportation Authority, the Bay Bridget failure was not due to cutting corners. The part that failed was not inspected because the design of the bridge made it impossible, at least until recently. MdTA used ground penetrating radar on the bridge to find the problem. GPR was developed in the 1970s by the military, long after the first span of the Bay Bridge was completed in 1952. It is not an ordinary method of inspecting a bridge. Furthermore, the parts of the Bay Bridge that failed had not previously been known to be subject to failure.
Unfortunately, sometimes we learn lessons the hard way. We learned a lot about suspension bridges from the Tacoma Narrows bridge in 1940, the pin and hangar style bridge from the I-95 bridge collapse in 1983, and about gusset plates on arch/truss bridges from the I-35W bridge in 2007.
The plan to reinforce the wall on the Bay Bridge will not stop the corrosion inside inaccessible parts of the Bridge, but will strengthen the wall by providing additional points of attachment to the bridge structure. MdTA plans to periodically inspect the Bridge with GPR to monitor the corrosion inside the wall. If engineers feel it is becoming unsafe, MdTA will take need to take corrective action to maintain the Bridge's safety.
Remember the part of the bridge that failed was put under extraordinary stress. A semi, loaded with chicken, hit the wall at a sharp angle, jumped onto the wall and skidded on top for several yards before the wall collapsed. That's not really the kind of load the wall is designed to handle. It is designed to shove vehicles moving essentially parallel back onto the roadway. In addition, the vast majority of the bridge maintained its structural integrity. It did not have a catastrophic collapse.