A review of Illinois Department of Transportation records found that 400 out of 3,460 bridges in the six-county area are considered “structurally deficient,” meaning that they are in need of repair or possibly replacement. That’s nearly 12 percent. Problem bridges include heavily traveled spans like the Lake Shore Drive bridge over the Chicago River, which is just north of the stretch that closed Monday, and the I-80 bridges over the Des Plaines River in Joliet.