Traditional reinforced concrete is based on the use of steel reinforcement bars, rebar, inside poured concrete. Prestressed concrete, invented by Frenchman Eugène Freyssinet in 1928, is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. Prestressing tendons (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a compressive stress that offsets the tensile stress that the concrete compression member would otherwise experience due to a bending load. Prestressing can be accomplished in three ways: Reinforced concrete at Sainte Jeanne dArc Church (Nice, France): architect Jacques Dror, 1926–1933 Reinforced concrete, also called ferroconcrete in some countries, is concrete in which reinforcement bars (rebars) or fibers have been incorporated to strengthen a material that would otherwise be brittle. ... The steel cable of a colliery winding tower. ... Rebar is common steel reinforcing bar, an important component of reinforced concrete and reinforced masonry structures. ... Concrete being poured, raked and vibrated into place in residential construction in Toronto, Ontario, Canada. ... Motto: Liberté, Égalité, Fraternité Liberty, Equality, Fraternity Anthem: La Marseillaise Metropolitan France() – on the European continent() – in the European Union()  —  [] Capital (and largest city) Paris Official languages French Government Unitary republic  -  President Jacques Chirac  -  Prime Minister Dominique de Villepin Formation  -  Celtic Gaul 1200 BC   -  Franks 11 BC   -  Kingdom of France... Eugène Freyssinet (13 July 1879 – 8 June 1962) was a French structural engineer. ... Year 1928 (MCMXXVIII) was a leap year starting on Sunday (link will display full calendar). ... Tension is a reaction force applied by a stretched string (rope or a similar object) on the objects which stretch it. ... A statically determinate beam, bending under an evenly distributed load. ... A hardwood floor (parquetry) is a popular feature in many houses. ... A log bridge in the French Alps near Vallorcine. ... Span is a section between two intermediate supports of a bridge. ... Tension is a reaction force applied by a stretched string (rope or a similar object) on the objects which stretch it. ... The steel cable of a colliery winding tower. ... 6 or 15cm outside diameter, oil-cooled cables, traversing the Grand Coulee Dam throughout. ... Compressive stress is the stress applied to materials resulting in their compaction (decrease of volume). ... Tensile stress (or tension) is the stress state leading to expansion; that is, the length of a material tends to increase in the tensile direction. ... Columns Ionic column base A compression member is a general class of structural elements of which a column is the most common specific example. ...

Pre-tensioned concrete

Pre-tensioned concrete is cast around already tensioned tendons. This method produces a good bond between the tendon and concrete, which both protects the tendon from corrosion and allows for direct transfer of tension. The cured concrete adheres and bonds to the bars and when the tension is released it is transferred to the concrete as compression by static friction. However, it requires stout anchoring points between which the tendon is to be stretched and the tendons are usually in a straight line. Thus, most pretensioned concrete elements are prefabricated in a factory and must be transported to the construction site, which limits their size. Pre-tensioned elements may be balcony elements, lintels, floor slabs, beams or foundation piles. An innovative bridge construction method using pre-stressing is described in stressed ribbon bridge. Friction is the force that opposes the relative motion or tendency toward such motion of two surfaces in contact. ... This article or section does not cite its references or sources. ... A balcony comprising a balustrade supported at either end by plinths. ... Pre-fabricated, pre-tensioned concrete lintels spanning garage doors. ... Look up Pile in Wiktionary, the free dictionary. ... A log bridge in the French Alps near Vallorcine. ... A stressed ribbon bridge is a tension structure (similar in many ways to a simple suspension bridge) in which the roadway follows a catenary arc between supports. ...

Bonded post-tensioned concrete

Bonded post-tensioned concrete is the descriptive term for a method of applying compression after pouring concrete and the curing process (in situ). The concrete is cast around a plastic, steel or aluminium curved duct, to follow the area where otherwise tension would occur in the concrete element. A set of tendons is fished through the duct and the concrete is poured. Once the concrete has hardened, the tendons are tensioned by hydraulic jacks that react against the concrete member itself. When the tendons have stretched sufficiently, according to the design specifications (see Hooke's law), they are wedged in position and maintain tension after the jacks are removed, transferring pressure to the concrete. The duct is then grouted to protect the tendons from corrosion. This method is commonly used to create monolithic slabs for house construction in locations where expansive soils (such as adobe clay) create problems for the typical perimeter foundation. All stresses from seasonal expansion and contraction of the underlying soil are taken into the entire tensioned slab, which supports the building without significant flexure. Post-stressing is also used in the construction of various bridges, both after concrete is cured after support by falsework and by the assembly of prefabricated sections, as in the segmental bridge.The advantages of this system over unbonded post-tensioning are: Physical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume. ... In situ is a Latin phrase meaning in the place. ... The steel cable of a colliery winding tower. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Standard atomic weight 26. ... Hydraulics is a branch of science and engineering concerned with the use of liquids to perform mechanical tasks. ... {{{{{{}}}}}}{{{{}}}}ûûûûûÏ€€€€ ... Hookes law accurately models the physical properties of common mechanical springs for small changes in length. ... Technically a portable double inclined plane, a wedge is a simple machine used to separate two objects, or portions of objects, through the application of force, perpendicular to the inclined surfaces, developed by conversion of force applied to the wide end. ... Grout is a construction material used to embed rebars in masonry walls, connect sections of pre-cast concrete, fill voids, and seal joints (like those between tiles). ... See corrosive for the hazard. ... Renewal of the surface coating of an adobe wall in Chamisal, New Mexico Adobe is a natural building material composed of sand, sandy clay and straw or other organic materials, which is shaped into bricks using wooden frames and dried in the sun. ... The Gay Head cliffs in Marthas Vineyard are made almost entirely of clay. ... Falseworks are temporary structures used in the building of bridges and other arched structures in order to hold the item in place until its building is sufficiently far advanced to support itself. ... As its name implies, a segmental bridge is a bridge built in short sections (called segments), i. ...

• 1. Large reduction in traditional reinforcement requirements as tendons cannot destress in accidents.
  2. Tendons can be easily 'weaved' allowing a more efficient design approach.

Unbonded post-tensioned concrete

Unbonded post-tensioned concrete differs from bonded post-tensioning by providing each individual cable permanent freedom of movement relative to the concrete. To achieve this, each individual tendon is coated with a grease (generally lithium based) and covered by a plastic sheathing formed in an extrusion process. The transfer of tension to the concrete is achieved by the steel cable acting against steel anchors embedded in the perimeter of the slab. The main disadvantage over bonded post-tensioning is the fact that a cable can destress itself and burst out of the slab if damaged (such as during repair on the slab). The advantages of this system over bonded post-tensioning are: General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/grey Standard atomic weight 6. ... Extrusion is a manufacturing process used to create long objects of a fixed cross-sectional profile. ... Repair and Maintenance is fixing any sort of mechanical or electrical device should it get out of order or broken (repair) as well as performing the routine actions which keep the device in working order (maintenance) or prevent trouble from arising (preventive maintenance). ...

• 1. The ability to individually adjust cables based on poor field conditions (For example: shifting a group of 4 cables around an opening by placing 2 to either side).
  2. The procedure of post-stress grouting is eliminated.
  3. The ability to de-stress the tendons before attempting repair work.

Applications

Prestressed concrete is the predominating material for floors in high-rise buildings, foundations for residential buildings in soft soil areas, bridges and in the construction of water towers and water tanks. Post-tensioning is also used to reinforce the large concrete chambers in nuclear reactors. This article or section does not cite any references or sources. ... A foundation is a structure that transmits loads from a building or road to the underlying ground. ... Loess field in Germany Surface-water-gley developed in glacial till, Northern Ireland Technically, Soil forms the pedosphere: the interface between the lithosphere (rocky part of the planet) and the biosphere, atmosphere, and hydrosphere. ... The mushroom-shaped concrete water tower of Roihuvuori in Helsinki, Finland was built in the 1970s. ... Chemical, Elevated, Hydropneumatic and Ground Storage Water Tanks shown together in one installation. ... Nuclear power station at Leibstadt, Switzerland. ...

Unbonded post-tensioning is commonly used in parking garages as barrier cable. Also, due to its ability to be stressed and then de-stressed, it can be used to temporarily repair a damaged building by holding up a damaged wall or floor until permanent repairs can be made. A multi-storey car park is a building or part thereof which is designed specifically to be for vehicle parking and where there are a number of floors on which parking takes place. ...

The advantages of prestressed concrete include lower construction costs; thinner slabs - especially important in high rise buildings in which floor thickness savings can translate into additional floors for the same (or lower) cost and fewer joints, since the distance that can be spanned by post-tensioned slabs exceeds that of reinforced constructions with the same thickness. Increasing span lengths increases the usable unencumbered floorspace in buildings; diminishing the number of joints leads to lower maintenance costs over the design life of a building, since joints are the major locus of weakness in concrete buildings.

The first prestressed concrete bridge in North America was the Walnut Street Bridge in Philadelphia, Pennsylvania. It was completed and opened to traffic in 1949. World map showing North America A satellite composite image of North America. ... The Walnut Street Bridge is a prestressed concrete girder bridge in Philadelphia, Pennsylvania designed by Gustave Magnel of Belgium. ... Nickname: City of Brotherly Love, Philly, the Quaker City Motto: Philadelphia maneto (Let brotherly love continue) Location in Pennsylvania Coordinates: Country United States State Pennsylvania County Philadelphia Founded October 27, 1682 Incorporated October 25, 1701 Mayor John F. Street (D) Area    - City 369. ... 1949 (MCMXLIX) was a common year starting on Saturday (the link is to a full 1949 calendar). ...

See also

• Lake Pontchartrain Causeway
• Prestressed concrete structures
• Structural engineering
• Concrete
• Stressed ribbon bridge

Lake Pontchartrain Causeway Heading south on the Causeway toward New Orleans The Lake Pontchartrain Causeway consists of two parallel bridges that are the longest bridges in the world by total length. ... Concrete being poured, raked and vibrated into place in residential construction in Toronto, Ontario, Canada. ... Taipei 101, the worlds tallest building as of 2004. ... Concrete being poured, raked and vibrated into place in residential construction in Toronto, Ontario, Canada. ... A stressed ribbon bridge is a tension structure (similar in many ways to a simple suspension bridge) in which the roadway follows a catenary arc between supports. ...

External links

• Prestressed Concrete Institute
• Post-Tensioning Institute
• Post-tensioned concrete comes of age - Comprehensive article on post-tensioned concrete, thought to be from Concrete Construction magazine.
• Prestressed Concrete Association of Pennsylvania
• Suncoast Post-Tension, LP - One of the largest post-tensioning companies in the United States, their website contains several photos and brochures on post-tensioning.
• VSL Ltd - Worldwide post-tensioning company, their website contains multiple explanations on this technology.
• Schwager Davis - American post-tensioning company, used in many bridges.
• Dywidag-Systems International - Worldwide post-tensioning company, their website has newsletters showing past projects.