Especificaciones técnicas

3. The minimum elongation of unbonded strand in an anchorage assembly, during the test load, shall not be less than 2% when measured in a gauge length of 10 ft. (3 m).

3. Elongation based on tests with a gauge length less than 10 ft. (3m) should not be cause for rejection.

Anchorage castings shall be non-porous and free of sand, blow holes, voids, and other defects. For wedge type anchorages, the wedges shall be designed to preclude premature failure of the prestressing steel due to a notch or pinching effect.

Anchorages of any type may be used provided the basic requirements noted herein are demonstrated by an acceptable test program.

Sheathing for bonded post-tensioned tendons shall be strong enough to retain shape, resist unrepairable damage during production, and prevent the entrance of cement paste or water from the concrete. Sheathing material left in place shall not cause harmful electrolytic action or deteriorate. The inside diameter shall be at least 1/4 in. (6 mm) larger than the nominal diameter of a single wire, bar, or strand tendon. In the case of multiple wire, bar, or strand tendons, the inside cross-sectional area of the sheath shall be at least twice the net area of the prestressing steel.

Sheaths shall be capable of transmitting forces from the grout to the surrounding concrete. Sheaths shall

Different requirements are imposed upon sheathings for bonded and unbonded tendons. In unbonded tendons, the sheathing does not transmit bond stresses from the prestressing steel to the concrete. Therefore, the sheathing must provide freedom of movement of the prestressing steel and form an adequate cover over the coated tendon. In bonded tendons, bond stresses will be transmitted through the sheathing. Accordingly, the sheathing must be of such material and/or configuration to effectively allow this stress transfer.

The void in the concrete in which the tendon is to be located may also be formed with inflatable and

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Standard Commentary

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have grout holes or vents at each end and at all high points, except where the degree of tendon curvature is small and the tendon is relatively level.

removable tubes. The tendon is subsequently pulled through and no additional sheathing is required.

Grout shall consist of a mixture of cement and water unless the gross inside cross-sectional area of the sheath exceeds four times the tendon cross-sectional area. In such cases, a fine aggregate may be added to the mixture. Fly ash and pozzolanic mineral admixtures may be added at a ratio not to exceed 0.30 by weight of cement. Mineral admixtures shall conform to ASTM C618. Approved shrinkage-compensating material, which is well dispersed in the other admixtures, may be used to obtain 5 to 10%

unrestrained expansion of the grout. Admixtures containing more than trace amounts of chlorides, fluorides, zinc, or nitrates shall not be used. Fine aggregate, if used, shall conform to ASTM C404, Size No. 2, except that all material shall pass the No. 16 sieve. The grout shall achieve a minimum comp-ressive strength of 2500 psi (17.2 MPa) at 7 days and 5000 psi (34.5 MPa) at 28 days when tested in accordance with ASTM C1107. The grout shall have a consistency that will facilitate proper placement. Water content shall be the minimum necessary for proper placement, and the w/cm shall not exceed 0.45 by weight.

Sheathing for unbonded tendons (monostrand post-tensioning system) shall be polypropylene, high-density polyethylene, or other plastics which are not reactive with the concrete, coating, or steel. The material s hall be waterproof and have sufficient strength and durability to resist damage and deterioration during fabrication, transport, storage, installation, concreting, and tensioning. The sheath shall have a coefficient of friction with the strand of less than 0.05. Tendon covering shall be continuous over the unbonded length of the tendon. It shall prevent the intrusion of water or cement paste and the loss of the coating material during concrete placement. The sheath material shall not become brittle or soften over the anticipated exposure temperature and service life of the structure. The minimum wall thickness of sheaths for non-corrosive conditions shall be 0.04 in. (1 mm). The sheathing shall have an inside diameter at least 0.030 in. (0.76 mm) greater than the maximum diameter of the strand.

Tendons shall be lubricated and protected against corrosion by a properly applied coating of grease or other approved material. Minimum weight of coating material on the prestressing strand shall not be less

Due to variations in the manufacturing process, slight variations may occur concentrically in the wall thickness.

The sheathing should provide a smooth circular outside surface and should not visibly reveal the lay of the

than 2.5 lbs (1.1 kg) of coating material per 100 ft (30.5 m) of 0.5 in. (12.7 mm) diameter strand, or 3.0 lbs (1.4 kg) of coating material per 100 ft (30.5 m) of 0.6 in. (15.2 mm) diameter strand. The amount of coating material shall be sufficient to ensure essentially complete filling of the annular space between the strand and the sheathing. The coating shall extend over the entire tendon length. Coatings shall remain ductile and free from cracking at the lowest anticipated temperature and shall not flow out from the sheath at the maximum anticipated temperature. Coatings shall be chemically stable and non-reactive with the tendon, concrete, or sheath.

strand.

3.2.3 Hardware and Miscellaneous Materials All hardware, connection items, inserts, lifting devices, or other apparatus shall be clearly detailed in the project documents showing size and yield strength for architect/engineer approval.

C3.2.3 Hardware and Miscellaneous Materials

Hardware shall be made from materials that are ductile. Plates and angles shall be low carbon (mild) steel. The steel for anchors shall be of a grade and strength similar to the hardware material in which it anchors, to minimize potential welding complications.

Brittle materials, such as low shock resistant, high carbon steels or gray iron castings, shall not be used.

Malleable cast iron is, however, satisfactory.

Materials used in ferrous items that are to be embedded in the concrete connecting precast elements, attaching to adjacent materials, or attaching equipment, shall conform to the requirements of the following specifications:

Precautions should be taken to ensure that hardware elements to be welded together are compatible.

Structural Steel−ASTM A36/A36M (for carbon steel connection assemblies) except that silicon (Si) content shall be in the range of 0 to 0.04% or 0.15 to 0.20%.

Phosphorus (P) content shall be in the range of 0 to 0.02% for materials to be galvanized. Steel with chemistry conforming to the formula, Si + 2.5P< 0.09, is also acceptable.

Stainless Steel − ASTM A666, Type 300 series, Grades A or B, (stainless steel anchors for use when resistance to staining merits extra cost).

Carbon Steel Plate − ASTM A283/A283M, Grades A, B, C, or D.

Malleable Iron Castings − ASTM A47/A47M, Grades 32510 or 35028.

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Standard Commentary

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Carbon Steel Castings − ASTM A27/A27M, Grade 60-30 (for cast steel clamps).

Anchor Bolts − ASTM A307 (carbon steel) or A325/

A325M (high strength steel for low-carbon steel bolts, nuts, and washers).

Carbon Steel Bars − ASTM A675/A675M, Grade 65 (for completely encased anchors).

Carbon Steel Structural Tubing − ASTM A500, Grade B (for rounds and shapes).

High-strength Low-alloy Structural Steel − ASTM A572/A572M except that silicon (Si) content shall be in the range of 0 to 0.04% or 0.15 to 0.20%. The phosphorus (P) content shall be in the range of 0 to 0.20% for materials to be galvanized. Steel with chemistry conforming to the formula, Si + 2.5P<0.09, is also acceptable.

Welded Headed Studs − ASTM A108 Grades 1010 through 1020 inclusive for low carbon steel or ASTM A276/A493 for stainless steel with the mechanical property requirements shown in Table 3.2.3.

Table 3.2.3 Minimum Mechanical Property Requirements for Studs

All metallic hardware surfaces that are exposed to, or within 1/2 in. (12 mm) of concrete surfaces that are exposed to the weather, corrosive conditions, or condensation, shall be protected against corrosion or be made of non-corrosive materials. Hardware shall be properly cleaned prior to application of protective treatment.

The degree of protection from corrosion required depends on the actual conditions to which the connections will be exposed in service. The most common condition requiring protection is exposure to climatic conditions. Connection hardware generally needs protection against humidity of a corrosive environment. Corrosion can cause subsequent rusting and marring of adjacent elements or failure of the unit connection. The use of oil based primers containing lead may be restricted due to local environmental regulations.

Protective coatings should be applied in a manner to ensure against embrittlement. Additionally, loss of connection strength or reinforcement bond should not occur unless otherwise anticipated and allowed for in the design. Often, final finishing of the product causes the protective finish of the hardware to be damaged. When this occurs, a final touch-up coating of the original protective material is required. This work should be performed in accordance with the recommendations of the coating material manufacturer. Since the final connection of a unit to a structure may require a field weld, the protective coating (zinc-rich or epoxy paint) should be applied according to the manufacturer’s requirements after final welding and cleaning.

Corrosion protection, when required, shall consist of one of the following:

1. Shop primer paint − FS-TT-P-645 or 664, or SSPC Paint 25.