BeamsProducts
A prestressed bridge girder is a precast concrete beam, made in the plant with steel strands tensioned before casting, that carries the deck of a bridge or viaduct. It spans between supports in one piece, so the bridge is built quickly without falsework below.
A prestressed bridge girder is a precast load-bearing member in which high-strength concrete is cast around steel strands that have been tensioned beforehand. Once the concrete has gained enough strength, the strands are released and their tension is transferred into the concrete as compression. This built-in compression limits cracking under service loads and lets the same section span further.
Girders are placed side by side between the abutments and piers and form the main load-bearing element of the deck. A reinforced concrete deck slab is cast in place on top and tied to the girders by reinforcement projecting from them, so girder and slab carry traffic loads together. The girders sit on elastomeric bearings on the supports.
The I-section is the most common shape for bridge girders. Depth and flange width vary with span, deck width and loading. Girder length, section, number of strands and their arrangement are set in the structural design of the bridge. Prestressing gives the girder a slight upward curve, known as camber, which is allowed for when deck levels are calculated.
Girders are made on long prestressing beds in steel moulds. The strands are tensioned between anchorages at the ends of the bed, links and other reinforcement are fixed, and the concrete is placed and compacted by vibration. Curing is controlled so that the concrete reaches the strength needed to take the strand force, and the strands are not cut until test specimens confirm it. Every girder is checked for dimensions, camber and surface finish as it leaves the mould.
Long, heavy girders are delivered to site on specialist long-load vehicles, with the route and lifting points planned in advance. They are usually lifted by two cranes working together and set down on their bearings. Because no falsework is needed beneath the bridge, rivers, roads and railways below are disrupted as little as possible. The deck slab, surfacing and parapets are completed after erection.
Because precast girders can be made in the plant while the piers and foundations are being built, they shorten the overall construction programme. When girder type, bearing details, deck slab and joint layout are considered together at the start of the design, production, delivery and erection follow on smoothly. The transport length and weight of the girders are assessed alongside site access and the crane capacity available.
Dimensions, reinforcement and load capacity are set by structural design for each project; contact us for technical details.
Infrastructure Elements
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Perimeter and Protection Elements
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Facade and Floor Elements
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