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Precast concrete is a construction product produced by casting concrete in a reusable mold or "form" which is then cured in a controlled environment, transported to the construction site and maneuvered into place; examples include precast beams, and wall panels, floors, roofs, and piles.
Underslung (lower-beam) launching gantry used for Skyline guideway construction (2015). A launching gantry (also called bridge building crane, and bridge-building machine) is a special-purpose mobile gantry crane used in bridge construction, specifically segmental bridges that use precast box girder bridge segments or precast girders in highway and high-speed rail bridge construction projects.
Hollow-core slabs, also known as voided slabs, initially appeared as one-way elements in Europe during the 1950s, and are still commonly manufactured in precast form for applications where fast construction and low self-weight are required. [2] [6] Waffle slabs are a common type of hollow-core slab which use the same principle as voided biaxial ...
By the 1960s, prestressed concrete largely superseded reinforced concrete bridges in the UK, with box girders being the dominant form. [41] In short-span bridges of around 10 to 40 metres (30 to 130 ft), prestressing is commonly employed in the form of precast pre-tensioned girders or planks. [42]
A box girder or tubular girder (or box beam) is a girder that forms an enclosed tube with multiple walls, as opposed to an Ɪ-or H-beam. Originally constructed of wrought iron joined by riveting , they are now made of rolled or welded steel, aluminium extrusions or prestressed concrete .
"Form blowouts" also occur when under-designed formwork bends or breaks during the concrete pour (especially if filled with a high-pressure concrete pump). Consequences can vary from minor leaks, easily patched during the pour, to catastrophic form failure, even death. Concrete exerts less pressure against the forms as it hardens.
Single box girder bridge , flyover above eastern approach of the San Francisco–Oakland Bay Bridge. A box girder bridge, or box section bridge, is a bridge in which the main beams comprise girders in the shape of a hollow box. The box girder normally comprises prestressed concrete, structural steel, or a composite of steel and reinforced concrete.
Schematic cross section of a pressurized caisson. In geotechnical engineering, a caisson (/ ˈ k eɪ s ən,-s ɒ n /; borrowed from French caisson 'box', from Italian cassone 'large box', an augmentative of cassa) is a watertight retaining structure [1] used, for example, to work on the foundations of a bridge pier, for the construction of a concrete dam, [2] or for the repair of ships.