prestressed concrete bridges design and construction by nigel r hewson pdf

Prestressed concrete bridges design and construction by nigel r hewson pdf

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Precast Prestressed Concrete Bridge Design Manual Third Edition

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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.

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.

Prestressed concrete is used in a wide range of building and civil structures where its improved performance can allow for longer spans , reduced structural thicknesses, and material savings compared with simple reinforced concrete. Typical applications include high-rise buildings , residential slabs, foundation systems , bridge and dam structures, silos and tanks , industrial pavements and nuclear containment structures.

First used in the late-nineteenth century, [1] prestressed concrete has developed beyond pre-tensioning to include post-tensioning , which occurs after the concrete is cast. Tensioning systems may be classed as either monostrand , where each tendon's strand or wire is stressed individually, or multi-strand , where all strands or wires in a tendon are stressed simultaneously. While pre-tensioned concrete uses tendons directly bonded to the concrete, post-tensioned concrete can use either bonded or unbonded tendons.

Pre-tensioned concrete is a variant of prestressed concrete where the tendons are tensioned prior to the concrete being cast. Pre-tensioning is a common prefabrication technique, where the resulting concrete element is manufactured remotely from the final structure location and transported to site once cured.

It requires strong, stable end-anchorage points between which the tendons are stretched. These anchorages form the ends of a "casting bed" which may be many times the length of the concrete element being fabricated. This allows multiple elements to be constructed end-to-end in the one pre-tensioning operation, allowing significant productivity benefits and economies of scale to be realized. The amount of bond or adhesion achievable between the freshly set concrete and the surface of the tendons is critical to the pre-tensioning process, as it determines when the tendon anchorages can be safely released.

Higher bond strength in early-age concrete will speed production and allow more economical fabrication. To promote this, pre-tensioned tendons are usually composed of isolated single wires or strands, which provides a greater surface area for bonding than bundled-strand tendons.

Unlike those of post-tensioned concrete see below , the tendons of pre-tensioned concrete elements generally form straight lines between end-anchorages. Where "profiled" or "harped" tendons [8] are required, one or more intermediate deviators are located between the ends of the tendon to hold the tendon to the desired non-linear alignment during tensioning. Straight tendons are typically used in "linear" precast elements, such as shallow beams, hollow-core planks and slabs; whereas profiled tendons are more commonly found in deeper precast bridge beams and girders.

Pre-tensioned concrete is most commonly used for the fabrication of structural beams , floor slabs , hollow-core planks , balconies , lintels , driven piles , water tanks and concrete pipes. Post-tensioned concrete is a variant of prestressed concrete where the tendons are tensioned after the surrounding concrete structure has been cast.

The tendons are not placed in direct contact with the concrete, but are encapsulated within a protective sleeve or duct which is either cast into the concrete structure or placed adjacent to it. At each end of a tendon is an anchorage assembly firmly fixed to the surrounding concrete. Once the concrete has been cast and set, the tendons are tensioned "stressed" by pulling the tendon ends through the anchorages while pressing against the concrete.

The large forces required to tension the tendons result in a significant permanent compression being applied to the concrete once the tendon is "locked-off" at the anchorage. Tendon encapsulation systems are constructed from plastic or galvanised steel materials, and are classified into two main types: those where the tendon element is subsequently bonded to the surrounding concrete by internal grouting of the duct after stressing bonded post-tensioning ; and those where the tendon element is permanently de bonded from the surrounding concrete, usually by means of a greased sheath over the tendon strands unbonded post-tensioning.

When the tendons are tensioned, this profiling results in reaction forces being imparted onto the hardened concrete, and these can be beneficially used to counter any loadings subsequently applied to the structure. In bonded post-tensioning, tendons are permanently bonded to the surrounding concrete by the in situ grouting of their encapsulating ducting after tendon tensioning.

This grouting is undertaken for three main purposes: to protect the tendons against corrosion ; to permanently "lock-in" the tendon pre-tension, thereby removing the long-term reliance upon the end-anchorage systems; and to improve certain structural behaviors of the final concrete structure.

Bonded post-tensioning characteristically uses tendons each comprising bundles of elements e. This bundling makes for more efficient tendon installation and grouting processes, since each complete tendon requires only one set of end-anchorages and one grouting operation. Ducting is fabricated from a durable and corrosion-resistant material such as plastic e. Fabrication of bonded tendons is generally undertaken on-site, commencing with the fitting of end-anchorages to formwork , placing the tendon ducting to the required curvature profiles, and reeving or threading the strands or wires through the ducting.

Following concreting and tensioning, the ducts are pressure-grouted and the tendon stressing-ends sealed against corrosion. Unbonded post-tensioning differs from bonded post-tensioning by allowing the tendons permanent freedom of longitudinal movement relative to the concrete. This is most commonly achieved by encasing each individual tendon element within a plastic sheathing filled with a corrosion -inhibiting grease , usually lithium based.

Anchorages at each end of the tendon transfer the tensioning force to the concrete, and are required to reliably perform this role for the life of the structure. For individual strand tendons, no additional tendon ducting is used and no post-stressing grouting operation is required, unlike for bonded post-tensioning.

Permanent corrosion protection of the strands is provided by the combined layers of grease, plastic sheathing, and surrounding concrete. Where strands are bundled to form a single unbonded tendon, an enveloping duct of plastic or galvanised steel is used and its interior free-spaces grouted after stressing. In this way, additional corrosion protection is provided via the grease, plastic sheathing, grout, external sheathing, and surrounding concrete layers. Individually greased-and-sheathed tendons are usually fabricated off-site by an extrusion process.

The bare steel strand is fed into a greasing chamber and then passed to an extrusion unit where molten plastic forms a continuous outer coating. Finished strands can be cut-to-length and fitted with "dead-end" anchor assemblies as required for the project. Both bonded and unbonded post-tensioning technologies are widely used around the world, and the choice of system is often dictated by regional preferences, contractor experience, or the availability of alternative systems.

Either one is capable of delivering code-compliant, durable structures meeting the structural strength and serviceability requirements of the designer. Long-term durability is an essential requirement for prestressed concrete given its widespread use. Research on the durability performance of in-service prestressed structures has been undertaken since the s, [13] and anti-corrosion technologies for tendon protection have been continually improved since the earliest systems were developed.

The durability of prestressed concrete is principally determined by the level of corrosion protection provided to any high-strength steel elements within the prestressing tendons. Also critical is the protection afforded to the end-anchorage assemblies of unbonded tendons or cable-stay systems, as the anchorages of both of these are required to retain the prestressing forces.

Failure of any of these components can result in the release of prestressing forces, or the physical rupture of stressing tendons. Prestressed concrete is a highly versatile construction material as a result of it being an almost ideal combination of its two main constituents: high-strength steel, pre-stretched to allow its full strength to be easily realised; and modern concrete, pre-compressed to minimise cracking under tensile forces.

Building structures are typically required to satisfy a broad range of structural, aesthetic and economic requirements. Significant among these include: a minimum number of intrusive supporting walls or columns; low structural thickness depth , allowing space for services, or for additional floors in high-rise construction; fast construction cycles, especially for multi-storey buildings; and a low cost-per-unit-area, to maximise the building owner's return on investment.

The prestressing of concrete allows "load-balancing" forces to be introduced into the structure to counter in-service loadings. This provides many benefits to building structures:. ICC tower , Hong Kong m Sydney Opera House Kai Tak Terminal Hong Kong Ocean Heights 2 , Dubai m Eureka Tower , Melbourne m Torre Espacio , Madrid m Concrete is the most popular structural material for bridges, and prestressed concrete is frequently adopted. Concrete dams have used prestressing to counter uplift and increase their overall stability since the mids.

Such anchors typically comprise tendons of high-tensile bundled steel strands or individual threaded bars. Tendons are grouted to the concrete or rock at their far internal end, and have a significant "de-bonded" free-length at their external end which allows the tendon to stretch during tensioning. Tendons may be full-length bonded to the surrounding concrete or rock once tensioned, or more commonly have strands permanently encapsulated in corrosion-inhibiting grease over the free-length to permit long-term load monitoring and re-stressability.

Circular storage structures such as silos and tanks can use prestressing forces to directly resist the outward pressures generated by stored liquids or bulk-solids.

Horizontally curved tendons are installed within the concrete wall to form a series of hoops, spaced vertically up the structure. When tensioned, these tendons exert both axial compressive and radial inward forces onto the structure, which can directly oppose the subsequent storage loadings.

If the magnitude of the prestress is designed to always exceed the tensile stresses produced by the loadings, a permanent residual compression will exist in the wall concrete, assisting in maintaining a watertight crack-free structure.

Prestressed concrete has been established as a reliable construction material for high-pressure containment structures such as nuclear reactor vessels and containment buildings, and petrochemical tank blast-containment walls.

Using prestressing to place such structures into an initial state of bi-axial or tri-axial compression increases their resistance to concrete cracking and leakage, while providing a proof-loaded, redundant and monitorable pressure-containment system. Nuclear reactor and containment vessels will commonly employ separate sets of post-tensioned tendons curved horizontally or vertically to completely envelop the reactor core.

Blast containment walls, such as for liquid natural gas LNG tanks, will normally utilise layers of horizontally-curved hoop tendons for containment in combination with vertically looped tendons for axial wall prestressing. Heavily loaded concrete ground-slabs and pavements can be sensitive to cracking and subsequent traffic-driven deterioration.

As a result, prestressed concrete is regularly used in such structures as its pre-compression provides the concrete with the ability to resist the crack-inducing tensile stresses generated by in-service loading. This crack-resistance also allows individual slab sections to be constructed in larger pours than for conventionally reinforced concrete, resulting in wider joint spacings, reduced jointing costs and less long-term joint maintenance issues.

Gateway Bridge Brisbane, Aust. Incheon Bridge South Korea. Autobahn A73 Itz Valley, Germany. Ringhals nuclear plant Videbergshamn, Sweden. Worldwide, many professional organizations exist to promote best practices in the design and construction of prestressed concrete structures. It is important to note that these organizations are not the authorities of building codes or standards, but rather exist to promote the understanding and development of prestressed concrete design, codes and best practices.

Rules and requirements for the detailing of reinforcement and prestressing tendons are specified by individual national codes and standards such as:. From Wikipedia, the free encyclopedia. Form of concrete used in construction. Unbonded slab post-tensioning. Above Installed strands and edge-anchors are visible, along with prefabricated coiled strands for the next pour. Below End-view of slab after stripping forms, showing individual strands and stressing-anchor recesses.

World Tower , Sydney m Ostankino Tower Moscow, Russia. CN Tower Toronto, Canada. Norcem silos Brevik, Norway. Roseires Dam Ad Damazin, Sudan. Wanapum Dam Washington, US. Retrieved 26 August American Concrete Institute. Retrieved 25 August

Precast Prestressed Concrete Bridge Design Manual Third Edition

Workshop Organizer: William Nickas, P. Prestressed concrete decks are commonly used for bridges with spans between 25m and m and provide economic, durable and aesthetic solutions in most situations where bridges are needed. Concrete remains the most common material for bridge construction around the world, and prestressed concrete is frequently the material of choice. Design manual, precast and prestressed concrete, Third Edition. Canadian Prestressed Concrete Institute. Environmental benefits of life cycle design of concrete bridges, 3rd International Conference on Life Cycle Management Zurich, Switzerland, 27 August , pp. Prestressed piles can double as foundations and piers, thus reducing the amount of on-site forming and concreting.

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. 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. Prestressed concrete is used in a wide range of building and civil structures where its improved performance can allow for longer spans , reduced structural thicknesses, and material savings compared with simple reinforced concrete. Typical applications include high-rise buildings , residential slabs, foundation systems , bridge and dam structures, silos and tanks , industrial pavements and nuclear containment structures. First used in the late-nineteenth century, [1] prestressed concrete has developed beyond pre-tensioning to include post-tensioning , which occurs after the concrete is cast. Tensioning systems may be classed as either monostrand , where each tendon's strand or wire is stressed individually, or multi-strand , where all strands or wires in a tendon are stressed simultaneously.

Views 13 Downloads 2 File size 36MB. Page iii Prestressed Concr. Bridgc Division. Edited by M. Ryall, G.


Prestressed Concrete Bridges - Nigel Hewson - Free ebook download as PDF File .pdf), Text File .txt) or read book online for Download as PDF, TXT or read online from Scribd Concrete Bridges,Design and Construction.


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IRAQ UNIVERSITY COLLEGE

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Prestressed concrete has the great advantage that it can be designed and constructed to ensure that deformations due to impact disappear almost completely, whereas a reinforced concrete structure. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. It can be accomplished in three ways: pre- tensioned concrete, and. Normal-Weight and Lightweight Concrete [Rev.

Views 4 Downloads 1 File size 30MB. Prestressing of concrete is now a well-established technique in all countries, with a wide portfolio of bridge types and span lengths constructed, ranging from major sea crossings to urban viaducts, motorways, rail structures and footbridges. For all these structures, the principles behind the design and construction of prestressed concrete bridges remain the same, which is to combine the tensile strength of the prestressing with the compressive strength of the concrete to create a balanced enhanced structure.

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Prestressed concrete decks are commonly used for bridges with spans between 25m and m and provide economic, durable and aesthetic solutions in most situations where bridges are needed. Concrete remains the most common material for bridge construction around the world, and prestressed concrete is frequently the material of choice. Extensively illustrated throughout, this invaluable book brings together all aspects of designing prestressed concrete bridge decks into one comprehensive volume. Back to Book Listing. Authors: Nigel R. View Chapters.

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2 comments

  • Lothair J. 02.06.2021 at 12:30

    Prestressed Concrete Bridges Design and Construction by Nigel hondapeople.org is a very elaborate source on this subject. Concrete remains the most popular.

    Reply
  • Tesira V. 06.06.2021 at 21:08

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