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Comparison of non-prestressed beam (top) and prestressed concrete beam (bottom) under load: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.[1][2]:&#;3&#;5&#;[3] It was patented by Eugène Freyssinet in .[4]
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.[5] 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.[1]:&#;52&#;59&#; 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 and/or serviceability compared with conventionally reinforced concrete in many situations.[6][2]:&#;6&#; 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.
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 concrete slabs, foundation systems, bridge and dam structures, silos and tanks, industrial pavements and nuclear containment structures.[7]
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.[6] Tendons may be located either within the concrete volume (internal prestressing) or wholly outside of it (external prestressing). While pre-tensioned concrete uses tendons directly bonded to the concrete, post-tensioned concrete can use either bonded or unbonded tendons.
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Pre-tensioning processPre-tensioned concrete is a variant of prestressed concrete where the tendons are tensioned prior to the concrete being cast.[1]:&#;25&#; The concrete bonds to the tendons as it cures, following which the end-anchoring of the tendons is released, and the tendon tension forces are transferred to the concrete as compression by static friction.[6]:&#;7&#;
Pre-tensioned bridge girder in precasting bed, with single-strand tendons exiting through the formworkPre-tensioning is a common prefabrication technique, where the resulting concrete element is manufactured off-site 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.[6][8]
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.[6]
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[9] 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.[1]:&#;68&#;73&#;[6]:&#;11&#; Such deviators usually act against substantial forces, and hence require a robust casting-bed foundation system. Straight tendons are typically used in "linear" precast concrete elements, such as shallow beams, hollow-core 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 slabs, balconies, lintels, driven piles, water tanks and concrete pipes.
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Forces on post-tensioned concrete with profiled (curved) tendon Post-tensioned tendon anchorage; four-piece "lock-off" wedges are visible holding each strandPost-tensioned concrete is a variant of prestressed concrete where the tendons are tensioned after the surrounding concrete structure has been cast.[1]:&#;25&#;
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.[1]:&#;25&#;[6]:&#;7&#; The method of locking the tendon-ends to the anchorage is dependent upon the tendon composition, with the most common systems being "button-head" anchoring (for wire tendons), split-wedge anchoring (for strand tendons), and threaded anchoring (for bar tendons).[1]:&#;79&#;84&#;
Balanced-cantilever bridge under construction. Each added segment is supported by post-tensioned tendonsTendon 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 debonded from the surrounding concrete, usually by means of a greased sheath over the tendon strands (unbonded post-tensioning).[1]:&#;26&#;[6]:&#;10&#;
Casting the tendon ducts/sleeves into the concrete before any tensioning occurs allows them to be readily "profiled" to any desired shape including incorporating vertical and/or horizontal curvature. 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.[2]:&#;5&#;6&#;[6]:&#;48&#;:&#;9&#;10&#;
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Multi-strand post-tensioning anchorIn 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.[10]
Bonded post-tensioning characteristically uses tendons each comprising bundles of elements (e.g., strands or wires) placed inside a single tendon duct, with the exception of bars which are mostly used unbundled. 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.g., polyethylene) or galvanised steel, and can be either round or rectangular/oval in cross-section.[2]:&#;7&#; The tendon sizes used are highly dependent upon the application, ranging from building works typically using between 2 and 6 strands per tendon, to specialized dam works using up to 91 strands per tendon.
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.[6]:&#;2&#;
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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.
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.[10]:&#;1&#;
Unbonded post-tensioning can take the form of:
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.[10]:&#;1&#;
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.
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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.[10]:&#;2&#;
The benefits that bonded post-tensioning can offer over unbonded systems are:
The benefits that unbonded post-tensioning can offer over bonded systems are:
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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,[14] and anti-corrosion technologies for tendon protection have been continually improved since the earliest systems were developed.[15]
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.
Modern prestressing systems deliver long-term durability by addressing the following areas:
Several durability-related events are listed below:
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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.[1]:&#;12&#; Its wide range of application is reflected in its incorporation into the major design codes covering most areas of structural and civil engineering, including buildings, bridges, dams, foundations, pavements, piles, stadiums, silos, and tanks.[7]
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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:
Some notable building structures constructed from prestressed concrete include: Sydney Opera House[24] and World Tower, Sydney;[25] St George Wharf Tower, London;[26] CN Tower, Toronto;[27] Kai Tak Cruise Terminal[28] and International Commerce Centre, Hong Kong;[29] Ocean Heights 2, Dubai;[30] Eureka Tower, Melbourne;[31] Torre Espacio, Madrid;[32] Guoco Tower (Tanjong Pagar Centre), Singapore;[33] Zagreb International Airport, Croatia;[34] and Capital Gate, Abu Dhabi UAE.[35]
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Concrete is the most popular structural material for bridges, and prestressed concrete is frequently adopted.[36][37] When investigated in the s for use on heavy-duty bridges, the advantages of this type of bridge over more traditional designs was that it is quicker to install, more economical and longer-lasting with the bridge being less lively.[38][39] One of the first bridges built in this way is the Adam Viaduct, a railway bridge constructed in the UK.[40] By the s, 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] Medium-length structures of around 40 to 200 metres (150 to 650 ft), typically use precast-segmental, in-situ balanced-cantilever and incrementally-launched designs.[43] For the longest bridges, prestressed concrete deck structures often form an integral part of cable-stayed designs.[44]
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Concrete dams have used prestressing to counter uplift and increase their overall stability since the mid-s.[45][46] Prestressing is also frequently retro-fitted as part of dam remediation works, such as for structural strengthening, or when raising crest or spillway heights.[47][48]
Most commonly, dam prestressing takes the form of post-tensioned anchors drilled into the dam's concrete structure and/or the underlying rock strata. 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.[49]
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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.[50][51][52]:&#;61&#;
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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 pre-stressing 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.[53][54][55]:&#;585&#;594&#;
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 utilize layers of horizontally-curved hoop tendons for containment in combination with vertically looped tendons for axial wall pre-stressing.
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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.[55]:&#;594&#;598&#;[56] Initial works have also been successfully conducted on the use of precast prestressed concrete for road pavements, where the speed and quality of the construction has been noted as being beneficial for this technique.[57]
Some notable civil structures constructed using prestressed concrete include: Gateway Bridge, Brisbane Australia;[58] Incheon Bridge, South Korea;[59] Roseires Dam, Sudan;[60] Wanapum Dam, Washington, US;[61] LNG tanks, South Hook, Wales; Cement silos, Brevik Norway; Autobahn A73 bridge, Itz Valley, Germany; Ostankino Tower, Moscow, Russia; CN Tower, Toronto, Canada; and Ringhals nuclear reactor, Videbergshamn Sweden.[53]:&#;37&#;
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Worldwide, many professional organizations exist to promote best practices in the design and construction of prestressed concrete structures. In the United States, such organizations include the Post-Tensioning Institute (PTI) and the Precast/Prestressed Concrete Institute (PCI).[62] Similar bodies include the Canadian Precast/Prestressed Concrete Institute (CPCI),[63] the UK's Post-Tensioning Association,[64] the Post Tensioning Institute of Australia[65] and the South African Post Tensioning Association.[66] Europe has similar country-based associations and institutions.
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:
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We supply seven wire pc strand with ASTM / US standard as following details.
A 416/A416M - 06 Standard Specification for Steel Strand, Uncoated Seven-Wire for Prestressed Concrete
This standard is issued under the fixed designation A 416/A416M.
1. Scope*
1.1 This specification covers two types and two grades of seven-wire, uncoated steel strand for use in pretensioned and post-tensioned prestressed concrete construction. The two types of strand are low-relaxation and stress-relieved (normal- relaxation). Low-relaxation strand shall be regarded as the standard type. Stress-relieved (normal-relaxation) strand will not be furnished unless specifically ordered, or by arrangement between purchaser and supplier. Grade [250] and Grade [270] have minimum ultimate strengths of MPa [250 ksi] and MPa [270 ksi], respectively, based on the nominal area of the strand.
1.2 The values stated in either inch-pound units or SI units are to be regarded as standard. Within the text, the inch-pound units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the specification.
1.3 The supplementary requirements in S1 shall be specified for 15.2-mm [0.600-in.] diameter uncoated seven-wire steel strand if needed for applications in prestressed ground anchors.
2. Referenced Documents
2.1 ASTM Standards:2
A 370 Test Methods and Definitions for Mechanical Testing of Steel Products
A 981 Test Method for Evaluating Bond Strength for 15.2 mm (0.6 in.) Diameter Prestressing Steel Strand, Grade 270, Uncoated, Used in Prestressed Ground Anchors
E 328 Test Methods for Stress Relaxation for Materials and Structures
2.2 U.S. Military Standards:
MIL-STD-129 Marking for Shipment and Storage 3
MIL-STD-163 Steel Mill Products Preparation for Ship-ment and Storage 3
2.3 U.S. Federal Standard:
Fed. Std. No. 123 Marking for Shipments (Civil Agencies) 3
1 This specification is under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel, and Related Alloys and is the direct responsibility of Subcommittee A01.05 on Steel Reinforcement. Current edition approved April 1, . Published April . Originally approved in . Last previous edition approved in as A 416 - C 05.
2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at . For Annual Book of ASTM Standards volume information, refer to the standard's Document Summary page on the ASTM website.
3 Available from Standardization Documents Order Desk, Bldg. 4, Section D, 700 Robbins Ave., Philadelphia, PA -.
3. Terminology
Definitions of Terms Specific to This Standard:
Strand, n-a group of wires having a center wire enclosed tightly by six helically placed outer wires with uniform pitch of not less than 12 and not more than 16 times the nominal diameter of the strand.
The direction of lay may be either right- or left-hand, however, strands of different lays should not be spliced together.
4. Ordering Information
4.1 Orders for seven-wire low-relaxation or stress-relieved (normal-relaxation) strand under this specification should in- clude the following information:
4.1.1 Quantity (meters [feet]),
4.1.2 Diameter of strand,
4.1.3 Grade of strand,
4.1.4 Type of strand,
4.1.5 Packaging,
4.1.6 ASTM designation and year of issue, and
4.1.7 Special requirements, if any.
Note 1 - Atypical ordering description is as follows: 25 600 m [84 000 ft], 13 mm [0.5 in.], Grade [270] low-relaxation strand, in -m [12 000-ft] reelless packs to ASTM A 416/A 416M- _________.
5. Materials and Manufacture
5.1 Base Metal-The base metal shall be carbon steel of such quality that when drawn to wire, fabricated into strand, and then thermally treated, shall have the properties and characteristics prescribed in this specification.
5.2 Wire -The wire from which the strand is to be fabricated shall be round and have a dry-drawn finish.
Note 2-This product is a composite of seven wires and is produced to mechanical properties only. The chemical composition of all wires or any individual wire is not pertinent to this application, and heat identity is not necessarily maintained. It is possible that wire from more than one heat may be used in the manufacture of a reel or pack. Traceability is based on pack identity as maintained and reported by the manufacturer.
5.3 Treatment-After stranding, low-relaxation strand shall be subjected to a continuous thermal-mechanical treatment to produce the prescribed mechanical properties. For stress- relieved (normal-relaxation) strand, only thermal treatment is necessary. Temper colors which result from the stress-relieving operation are considered normal for the finished appearance of this strand.
6. Mechanical Properties
6.1 Methods of testing for mechanical properties are de- scribed in Annex A7 of Test Methods and Definitions A 370.
Low-relaxation strand shall also be tested as prescribed in Methods E 328.
6.2 Breaking Strength - The breaking strength of the fin- ished strand shall conform to the requirements prescribed in Table 1.
6.3 Yield Strength - Yield strength in kN [pounds] shall be measured at 1 % extension under load. The minimum yield strength shall be 90 % for low-relaxation strand and 85 % for stress-relieved (normal-relaxation) strand of the breaking strength listed in Table 1. Initial loads for the test and minimum yield strengths are listed in Table 2.
6.3.1 The extension under load shall be measured by an extensometer calibrated with the smallest division not larger than 0. mm/mm [0. in./in.] of gage length.
6.4 Elongation- The total elongation under load shall not be less than 3.5 % using a gage length of not less than 600 mm [24 in.]. It shall be permissable to determine the total elonga- tion value by adding, to the 1.0 % yield extension, the percent extension or movement between the jaws gripping the strand after yield determination. The percent is calculated on the new base length of jaw-to-jaw distance.
6.5 Relaxation Properties - Low-relaxation strand shall have relaxation losses of not more than 2.5 % when initially loaded to 70 % of specified minimum breaking strength or not more than 3.5 % when loaded to 80 % of specified minimum breaking strength of the strand after h tested under the conditions listed in 6.5.1 through 6.5.7.
6.5.1 If required, relaxation evidence shall be provided from the manufacturer's records of tests on similarly dimensioned strand of the same grade.
6.5.2 The temperature of the test specimen shall be main- tained at 20 6 2°C [68 6 3.5°F].
6.5.3 The test specimen shall not be subjected to loading prior to the relaxation test.
6.5.4 The initial load shall be applied uniformly over a period of not less than 3 min and not more than 5 min, and the gage length shall be maintained constant; load relaxation readings shall commence 1 min after application of the total load.
6.5.5 Over-stressing of the test specimen during the loading operation shall not be permitted.
6.5.6 The duration of the test shall be h or a shorter period of at least 200 h, provided it can be shown by records that an extrapolation of the shorter period test results to h will provide similar relaxation values as the full h test.
6.5.7 The test gage length shall be at least 60 times the nominal diameter. If this gage length exceeds the capacity of the extensometer or testing machine, then it shall be permitted to substitute a gage length of 40 times the nomimal strand diameter.
7. Dimensions and Permissible Variations
7.1 The size of the finished strand shall be expressed as the nominal diameter of the strand in millimetres [inches].
7.2 The diameter of the center wire of any strand shall be larger than the diameter of any outer wire in accordance with Table 3.
7.3 Permissible Variations in Diameter:
7.3.1 All Grade [250] strand shall conform to a size tolerance of 60.40 mm [60.016 in.] from the nominal diam- eter measured across the crowns of the wires.
7.3.2 All Grade [270] strand shall conform to a size tolerance of +0.65, - 0.15 mm [+0.026, - 0.006 in.] from the nominal diameter measured across the crowns of the wire.
TABLE 1 Breaking Strength Requirements
Strand Designation No. Diameter of Strand, mmTABLE 2 Yield Strength Requirements
StrandTABLE 3 Diameter Relation Between Center and Outer Wires
Strand 7.3.3 Variation in cross-sectional area and in unit stress resulting therefrom shall not be cause for rejection provided that the diameter differences of the individual wires and the diameters of the strand are within the tolerances specified.
7.4 It shall be permitted to furnish, under this specification, specially dimensioned low-relaxation and stress-relieved (normal-relaxation) strands with nominal diameters up to 19 mm [0.750 in.]. The breaking strength shall be defined, and the yield strength, as defined in 6.3, shall not be less than 90 % and 85 % of the specified minimum breaking strength for low- relaxation and stress-relieved (normal relaxation) strands, re-spectively. All other requirements shall apply.
8. Workmanship, Finish, and Appearance
8.1 Joints:
8.1.1 There shall be no strand joints or strand splices in any length of the completed strand unless specifically permitted by the purchaser.
8.1.2 During the process of manufacture of individual wires for stranding, welding shall be permitted only prior to or at the size of the last thermal treatment, for example, patenting or controlled cooling. There shall be no welds in the wire after it has been drawn through the first die in the wire drawing except as provided in 8.1.3.
8.1.3 During fabrication of the strand, butt-welded joints are permitted in the individual wires, provided there shall not be more than one such joint in any 45-m [150-ft] section of the completed strand.
8.1.4 When specifically ordered as "Weldless," a product free of welds shall be furnished. When "Weldless" is specified, the strand is produced as one continuous length with no welds as allowed by 8.1.3.
8.2 The finished strand shall be uniform in diameter and shall be free of imperfections not consistent with good com- mercial strand practices.
8.3 When the strand is cut without seizings, the wire shall not fly out of position. If any wire flies out of position and can be replaced by hand, the strand shall be considered satisfactory.
8.4 The strand shall not be oiled or greased. Slight rusting, provided it is not sufficient to cause pits visible to the unaided eye, shall not be cause for rejection.
Note 3 - Guidance for evaluating the degree of rusting on prestressed concrete strand is presented in Sason. 4
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4 Sason, A.S., "Evaluation of Degree of Rusting on Prestressed Concrete Strand,'' PCI Journal, Precast/Prestressed Concrete Institute, Vol. 37, No. 3, May-June , pp 25 - C30. Reprints of this paper are available from the Precast/ Prestressed Concrete Institute, 209 West Jackson Blvd., Suite 500, Chicago, IL .
9. Sampling
9.1 Test specimens cut from either end of the strand package are permitted. Any specimen found to contain a wire joint shall be discarded and a new specimen obtained.
10. Number of Tests
10.1 One specimen for test shall be taken from each 18-Mg [20-ton] production lot of finished strand, and tested for breaking strength, yield strength, and elongation.
11. Inspection
11.1 If outside inspection is required, the manufacturer shall afford the inspector representing the purchaser all reasonable facilities to satisfy that the material is being furnished in accordance with this specification. All tests and inspections shall be made at the place of manufacture prior to shipment, unless otherwise agreed upon at the time of purchase, and shall be so conducted as not to interfere unnecessarily with the operation of the works.
Note 4 -The purchaser should state, at the time of order, whether outside inspection is required or waived.
12. Rejection
12.1 Failure of any test specimen to comply with the requirements of the specification shall constitute grounds for rejection of the lot represented by the specimen.
12.2 The lot shall be resubmitted for inspection by testing a specimen from each reel or pack and sorting out non- conforming material.
12.3 In case there is a reasonable doubt in the initial testing as to the ability of the strand to meet any requirement of this specification, two additional tests shall be made on a specimen of strand from the same reel or pack, and if failure occurs in either of these tests, the strand shall be rejected.
13. Certification
13.1 If outside inspection is waived, a manufacturer's certification that the material has been tested in accordance with and meets the requirements of this specification shall be the basis of acceptance of the material. The certification shall include the specification number, year-date of issue, andrevision letter, if any.
13.2 The manufacturer shall, when requested in the order, furnish a representative load-elongation curve for each size and grade of strand shipped.
13.3 When the modulus of elasticity of a seven-wire strand is provided, the cross-sectional area used to compute that modulus also shall be provided. The area provided in the certification shall be the area used to calculate the modulus of elasticity.
13.4 A material test report, certificate of inspection, or similar document printed from or used in electronic form from an electronic data interchange (EDI) transmission shall be regarded as having the same validity as a counterpart printed in the certifier's facility. The content of the EDI transmitted document must meet the requirements of the invoked ASTM standard(s) and conform to any existing EDI agreement be- tween the purchaser and the supplier. Notwithstanding the absence of a signature, the organization submitting the EDI transmission is responsible for the content of the report.
NOTE 5 -The industry definition as invoked here is: EDI is the computer-to-computer exchange of business information in a standard format such as ANSI ASC X12.
14. Packaging and Marking
14.1 The strand shall be furnished on reels or in reelless packs having a minimum core diameter of 610 mm [24 in.], unless otherwise specified by the purchaser. Lengths on reels or in reelless packs shall be as agreed upon at the time of purchase. The strand shall be well protected against mechani- cal injury in shipping as agreed upon at the time of purchase. Each reel or reelless pack shall have two strong tags securely fastened to it showing the length, size, type, grade, ASTM designation A 416/A 416M, and the name or mark of the manufacturer. One tag shall be positioned where it will not be inadvertently lost during transit, such as the core of a reelless pack. The other tag shall be placed on the outside for easy identification.
14.2 For Government Procurement Only - When specified in the contract or order, and for direct procurement by or direct shipment to the U.S. government, material shall be preserved, packaged, and packed in accordance with the requirements of MIL-STD-163. The applicable levels shall be as specified in the contract. Marking for shipment of such material shall be in accordance with Fed. Std. No. 123 for civil agencies and MIL-STD-129 for military agencies.
SUPPLEMENTARY REQUIREMENTS
Supplementary requirements shall apply only to 15.2-mm [0.600-in.] diameter strand, Grade 270 used in prestressed ground anchors or similar applications and shall be specified at the time of order placement. These requirements are not applicable to strand used in prestressed concrete applications.
S1. Bond Capacity
S1.1 The results of bond-capacity tests performed in accor- dance with Test Method A 981 shall be submitted to the purchaser. The strand specimens, on which tests were per- formed, shall be from different lots and shall be representative for the strand ordered.
S1.2 The average pull force from six pull tests, performed in accordance with Test Method A 981, required to reach the 0.25-mm [0.01-in.] displacement described therein shall be at least 35.6 kN [ lbf], with the individual minimum test value not less than 30.2 kN [ lbf]. For any future retests, without changes in the manufacturing method and materials used, three tests shall be considered as adequate.
S1.3 Retests - If the test specimens fail to satisfy S1.2, six additional tests shall be performed, and the results shall satisfy the acceptance criteria. Strand that failed the retest shall not be considered acceptable for the use in prestressed ground an- chors.
S1.4 Annual Tests - The pull tests shall be performed annu- ally as a minimum or repeated when, in the opinion of the producer, a process change is made which is believed could decrease the bond capacity of the strand.
SUMMARY OF CHANGES
Committee A01 has identified the location of the following changes to this standard since the last issue (A 416/A 416M - C05) that may impact the use of this standard. (Approved April 1, .)
(1) Sections 6.4, 7.4, and 13.2 were revised to eliminate permissive language.
(2) Revised Table 1, Table 2, and Table 3 to include Strand Designation No. 14 and No. 18.
(3) Editorial changes were made throughout.
Committee A01 has identified the location of the following changes to this standard since the last issue (A 416/A 416M - C02) that may impact the use of this standard. (Approved June 1, .)
(1) Revised Table 1, Table 2, and Table 3 to include Strand Designation No. 13a.
This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and if not revised, either reapproved or withdrawn. More information, go to the ASTM website (www.astm.org).
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