The collapse of an I-5 bridge into the Skagit River in Washington reminds us, again, that our bridges are literally falling down around us. There are an estimated 66,000 structurally deficient across the country. In Georgia, there are 941, which ironically is quite good, placing the state 42nd in total number of structurally deficient bridges. But the news is not quite grounds for celebrating.
There are three bridges in Georgia like the I-5 Bridge that collapsed. They are functionally obsolete and fracture critical. This means they are well beyond their design thresholds for the number of vehicles they carry and the weight of those loads. This increases the risk of car accidents, which as the I-5 Bridge demonstrated, can bring the structure crashing down.
The problem is many of these bridges were built as inexpensively as possible. They have no structural redundancies, so if a single girder or truss fails, it can cause the collapse of the entire bridge. This is what is meant by "fracture critical."
Most of these bridges were built in the 1950s and the life expectancy of the average bridge is 50 years, meaning that a significant number of bridges are operating on borrowed time. Even with inspections, crashes and accidents can trigger catastrophic collapses.
As the deaths of 13 people on the I-35W Bridge collapse in Minneapolis showed, these collapses have been deadly. The cost of replacing bridges is high as is the political inertia. No one wants to pay higher taxes to replacing what appears to be a perfectly functional bridge. So, it is likely that some people will pay a much higher price for our neglect.
Source: CBSAtlanta.com, "Georgia has three bridges similar to the collapsed Washington bridge," Jennifer Mayerle, May 24, 2013