Prestressed concrete in the context of Compression (physics)


Prestressed concrete in the context of Compression (physics)

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⭐ Core Definition: Prestressed concrete

Prestressed concrete is a form of concrete used in construction. It is substantially prestressed (compressed) during production, in a manner that strengthens it against tensile forces which will exist when in service. It was patented by Eugène Freyssinet in 1928.

This compression is produced by the tensioning of high-strength tendons located within or adjacent to the concrete and is done to improve the performance of the concrete in service. Tendons may consist of single wires, multi-wire strands or threaded bars that are most commonly made from high-tensile steels, carbon fiber or aramid fiber. The essence of prestressed concrete is that once the initial compression has been applied, the resulting material has the characteristics of high-strength concrete when subject to any subsequent compression forces and of ductile high-strength steel when subject to tension forces. This can result in improved structural capacity or serviceability, or both, compared with conventionally reinforced concrete in many situations. In a prestressed concrete member, the internal stresses are introduced in a planned manner so that the stresses resulting from the imposed loads are counteracted to the desired degree.

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Prestressed concrete in the context of Reinforced concrete

Reinforced concrete, also called ferroconcrete or ferro-concrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement is usually, though not necessarily, steel reinforcing bars (known as rebar) and is usually embedded passively in the concrete before the concrete sets. However, post-tensioning is also employed as a technique to reinforce the concrete. In terms of volume used annually, it is one of the most common engineering materials. In corrosion engineering terms, when designed correctly, the alkalinity of the concrete protects the steel rebar from corrosion.

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Prestressed concrete in the context of Lintel

A lintel or lintol is a type of beam (a horizontal structural element) that spans openings such as portals, doors, windows and fireplaces. It can be a decorative architectural element, or a combined ornamented/structural item. In the case of windows, the bottom span is referred to as a sill, but, unlike a lintel, does not serve to bear a load to ensure the integrity of the wall.Modern-day lintels may be made using prestressed concrete and are also referred to as beams in beam-and-block slabs or as ribs in rib-and-block slabs. These prestressed concrete lintels and blocks can serve as components that are packed together and propped to form a suspended-floor concrete slab.

An arch functions as a curved lintel.

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Prestressed concrete in the context of Beam bridge

Beam bridges are the simplest structural forms for bridge spans supported by an abutment or pier at each end. No moments are transferred throughout the support, hence their structural type is known as simply supported.

The simplest beam bridge could be a log (see log bridge), a wood plank, or a stone slab (see clapper bridge) laid across a stream. Bridges designed for modern infrastructure will usually be constructed of steel or reinforced concrete, or a combination of both. The concrete elements may be reinforced or prestressed. Such modern bridges include girder, plate girder, and box girder bridges, all types of beam bridges.

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Prestressed concrete in the context of Cantilever bridge

A cantilever bridge is a bridge built using structures that project horizontally into space, supported on only one end (called cantilevers). For small footbridges, the cantilevers may be simple beams; however, large cantilever bridges designed to handle road or rail traffic use trusses built from structural steel, or box girders built from prestressed concrete.

The steel truss cantilever bridge was a major engineering breakthrough when first put into practice, as it can span distances of over 1,500 feet (450 m), and can be more easily constructed at difficult crossings by virtue of using little or no falsework.

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Prestressed concrete in the context of Beam and block

Beam and block is a construction method to support flooring, especially for ground floors as well as multi story buildings. It is made of cast concrete, one piece of which is a prestressed concrete beam, which can be an inverted T-shaped beam, or lintel, the other piece being a simple rectangular block. The beams are placed at regular intervals and the blocks placed between them. They form a support for the next layer of flooring materials.

Beam and block is also referred to as rib and block or lintel and block in some countries. Certain countries incorporate the use of temporary propping for 21 days while other rib and block systems use propless systems. Systems where props are used incorporate lighter beams while the prop line allows for structural cross support. Propless systems used heavier inverted T beams to compensate for the exclusion of props.

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Prestressed concrete in the context of Railroad tie

A railroad tie, crosstie (American English), railway tie (Canadian English) or railway sleeper (Australian and British English) is a rectangular support for the rails in railroad tracks. Generally laid perpendicular to the rails, ties transfer loads to the track ballast and subgrade, hold the rails upright and keep them spaced to the correct gauge.

Railroad ties are traditionally made of wood, but prestressed concrete is now also widely used, especially in Europe and Asia. Steel ties are common on secondary lines in the UK; plastic composite ties are also employed, although far less than wood or concrete. As of January 2008, the approximate market share in North America for traditional and wood ties was 91.5%, the remainder being concrete, steel, azobé (red ironwood) and plastic composite.

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Prestressed concrete in the context of Box girder 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. The box is typically rectangular or trapezoidal in cross-section. Box girder bridges are commonly used for highway flyovers and for modern elevated structures of light rail transport. Although the box girder bridge is normally a form of beam bridge, box girders may also be used on cable-stayed and other bridges.

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Prestressed concrete in the context of Box girder

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.

Compared to an Ɪ-beam, the advantage of a box girder is that it better resists torsion. Having multiple vertical webs, it can also carry more load than an Ɪ-beam of equal height (although it will use more material than a taller Ɪ-beam of equivalent capacity).

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Prestressed concrete in the context of Piling

A pile or piling is a vertical structural element of a deep foundation, driven or drilled deep into the ground at the building site. A deep foundation is a type of foundation that transfers building loads to the earth farther down from the surface than a shallow foundation does to a subsurface layer or a range of depths.

There are many reasons that a geotechnical engineer would recommend a deep foundation over a shallow foundation, such as for a skyscraper. Some of the common reasons are very large design loads, a poor soil at shallow depth, or site constraints like property lines. There are different terms used to describe different types of deep foundations including the pile (which is analogous to a pole), the pier (which is analogous to a column), drilled shafts, and caissons. Piles are generally driven into the ground in situ; other deep foundations are typically put in place using excavation and drilling. The naming conventions may vary between engineering disciplines and firms. Deep foundations can be made out of timber, steel, reinforced concrete or prestressed concrete.

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Prestressed concrete in the context of Eugène Freyssinet

Eugène Freyssinet (French: [øʒɛn fʁɛsinɛ]) (13 July 1879 – 8 June 1962) was a French structural and civil engineer. He was the major pioneer of prestressed concrete.

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