Catastrophic Sliding of a Concrete Deck during Its Launching on the Steel Girders of a Composite Bridge

The concrete deck of a 340-m long composite bridge having a general slope of 6.5% was built by increments of 20 m. Forming and concreting were done behind the upper abutment. Increments were successively pushed over the steel girders with cast iron shoes inserted between concrete and steel at regular intervals. As the third increment was in place, it was noticed that the concrete ribbon was slightly curved and laying somewhat eccentrically over the girders. The deformation of the steel flanges induced transverse weight components. Moreover, launching is always accompanied by dynamical effects, which were not correctly understood. As the 10th increment was being pushed, an arresting plate holding the steel structure at the upper abutment in the longitudinal direction failed and transverse weight components helped setting the deck in motion, which then began sliding.