Robustness and Stability of Launching Gantries and Movable Shuttering Systems - Lessons Learned

Launching gantries are frequently used in the erection of precast segmental and I-beam bridges, while movable shuttering systems (MSS) are used for in situ span-by-span and balanced-cantilever construction. The use of launching units is therefore frequent in most types of medium-span, prestressed concrete bridges. Launching gantries and MSS are complex and delicate structures. They resist huge loads during bridge erection and overtake long spans during self-launching. They are light—i.e. designed for high stress levels in different load and support conditions, which make them prone to instability. And they are reused many times, on different projects and by different crews. As a matter of fact, a number of launching units have collapsed in recent years, with many fatalities and extreme delays on the project schedule. As a consequence, the launching units are almost always leased or purchased on the basis of stringent technical specifications, and their design is subjected to independent checking. Design and operational failures detected by the author within numerous independent design check assignments are discussed in the paper and recommendations and suggestions are provided to prevent failures and assure adequate robustness of launching units. Owing to the legal proceedings surrounding such events, only general causes of collapse are discussed in this paper and no photographs of gantry collapses are included, and the photographs do not refer to collapsed units.