Self-launching erection machines for precast concrete bridges

Construction of precast concrete bridges with spans ranging from 100 to over 600 ft is mostly based on use of self-launching machines. The launching units are complex and delicate structures that resist high loads on long spans under the same constraints that the obstruction to overpass exerts on the final structure, and are also adaptable for reuse on different projects. However, little has been written on these machines in spite of their cost, complexity, and sophistication. This article aims to illustrate the main features of self-launching bridge erection machines, and also offers some lessons learned during 27 years of the author's practice in the bridge industry and as an independent design-checker of launching units. Sections are devoted to: launching gantries, wheeled carriers for full-span precasting, design loads, modeling, support member instability, launch and lock systems, and load testing.