Overhead, an El train rumbles across Chicago's Devon-Sheridan viaduct. Below, amid cracks, spalls and exposed rebar, a network of strain gauges measures the amount of stress that has shifted from the original concrete structure to new supplementary steel shoring.
As the structure continues to deteriorate, primarily from exposure to deicing chemicals, the steel columns and their concrete footings are expected to absorb more of the loading imposed by trains, the roadbed and the structure itself.