Four-phase span-by-span casting saves costs, shortens the span cycle time and simplifies the operations of long-span MSS. The pier tables are precast in-place at the end of pier construction to extract complex activities from the critical path and to simplify critical-path operations and the front support systems of the MSS. The span is cast in two phases within the MSS: the U-span is cast first, and the top slab is cast in a second time to simplify removal of the inner forms.
The side wings are cast with forming carriages that travel along the central box core. This removes additional activities from the critical path and diminishes the design load and the cost of the MSS. Early creep of concrete facilitates stress redistribution within the cross-section. Mild post-tensioning may be necessary for the second-phase U-span to control the stiffness interaction with the MSS during casting of the top slab.
The courses that Dr. Rosignoli teaches for the Continuing Education Program of the American Society of Civil Engineers and on-site, on-demand in the offices of bridge owners, designers and constructors explore modern bridge design and construction technology.
- Mechanized Bridge Construction (2 days) examines all modern construction methods for medium- and long-span prestressed-concrete bridges.
- Movable Scaffolding Systems (1 day) is addressed specifically to span-by-span and balanced cantilever casting with MSS.
You will learn under which circumstances is span-by-span casting a competitive alternative to incremental launching and precast segmental construction, will compare the use of telescopic MSS for macro-segmental balanced cantilever bridges with in-place casting with form travelers, and will explore bridge design and detailing for effective use of MSS.
The course also explains configurations, operations, loads, kinematics, performance, productivity, structure-equipment interactions and industry trends of overhead, OPS and underslung MSS for span-by-span casting, telescopic MSS and form travelers for balanced cantilever casting, and forming carriages for segmental slab casting on steel girders.
The eManuals of BridgeTech integrate the courses to provide exhaustive coverage of the topic. Introduction to Mechanized Bridge Construction (44 pages) explains the reasons for the industry trend toward mechanized construction, discusses its principles, means and methods, and explores the different types of bridge construction machines and their influence on the design and construction of the bridge.
Movable Scaffolding Systems (MSS): Introduction (41 pages) is specifically addressed to span-by-span casting of prestressed-concrete bridges. The eManual compares span-by-span casting with MSS with the other construction methods for medium-span prestressed-concrete bridges. It explores one-phase casting of box girders and ribbed slabs with double-T section, two-phase casting of box girders (with and without first-phase post-tensioning) and three- and four-phase casting.
For each span casting method, the eManual explores the prefabrication techniques for the rebar cage and their impacts on the span cycle time, the filling sequences for the casting cell, the design of post-tensioning, and staged application of post-tensioning to control structure-equipment interaction. With extensive illustrations, the eManual introduces the different types of MSS and provides exhaustive guidance on the choice of the most appropriate type. It also explains how to design bridge piers, abutments and superstructures for effective use of MSS technology in relation to the staged casting process selected for the span.