Chapter 4: The Construction Process of Segmental Bridges
(1982) provide a sample calculation for the effect of stress redistribution with consideration of time-dependent effects.
4.2.2 Cantilever Erection Equipment
Different erection equipment is used in bridge construction. With the specific focus on cast-in- place and precast cantilever segmental bridges, form travelers and launching girders will be introduced in the following sections. Other equipment that can be used for placement of precast segments is e.g. cranes.
184.108.40.206 Form Travelers
Cast-in-place cantilever construction requires formwork that is attached to the tip of the growing cantilever for casting. The following paragraphs will deal with girder cross-sections only. As the cantilever grows the forms travel are set forth in steps. These form travelers give shape to the segment, support the weight of the newly cast concrete until it has gained enough strength to be post-tensioned to the previous cantilever segments, and transfer the segment weight to the already existing superstructure. Determining for the capacity of the form travelers is the maximum size and initial weight of the biggest segment in the bridge superstructure, including other construction loads.
Form travelers available in today’s construction industry are made by specialized manufacturers and are reusable and very flexible (Levintov 1995) with respect to changing geometry of the bridge superstructure and its alignment, including camber. They can be enclosed in a heated tent to enable concrete placement and curing to proceed during adverse weather conditions, especially low temperatures. In comparison with a precasting yard, form travelers often offer the less costly solution, since transportation and storage of prefabricated segments is avoided, and they integrate all the functions of the precasting plant into a relatively small device. Fletcher (1984) notes that by use of form travelers the formwork is reused several times, while adjustments to variable