Self-launching gantries are frequently used in the erection of precast segmental and I-beam bridges. Movable scaffolding systems (MSS) are used for in-place span-by-span and balanced-cantilever construction. The use of self-launching erection equipment is frequent in most types of medium-span prestressed concrete bridges.
Self-launching gantries and MSS are complex and delicate structures. They resist huge loads during bridge construction and overtake long spans during self-launch. They are light—i.e. designed for high stress levels in different load and support conditions, which make them potentially prone to instability. And they are reused many times, on different projects and by different crews.
As a matter of fact, a number of self-launching units have collapsed in recent years, with fatalities and extreme delays on the project schedule. For these reasons, self-launching bridge construction equipment is often leased or purchased on the basis of stringent technical specifications, and its design is subject to independent checking.
Robustness and Stability of Self-Launching Gantries and Movable Scaffolding Systems – Lessons Learned (2007, IABSE Structural Engineering International) discusses design and operational failures detected by the author within numerous independent design check assignments. Recommendations and suggestions are provided to prevent failure and assure robustness and redundancy of self-launching units.
Owing to the legal proceedings surrounding such events, only general causes of collapse are discussed in this paper, no photographs of gantry collapses are included, and the photographs do not refer to collapsed units.