511 ALASKA 2020 SECTION 721 PRESTRESSING STEEL A ND FITTINGS
721-2.01 SCOPE. Prestressing steel and fittings used in pre- tensioned and post -tensioned
concrete construction.
721-2.02 PRESTRESSIN G STEEL. Meet the following:
Steel Strand AASHTO M 203 Uncoated Stress -Relieved Steel Wire AASHTO M 204. Do not use oil -tempered wires. High Strength Steel Bars AASHTO M 275
721-2.03 POST -TENSIO NING SYSTEM. Use only post -tensioning systems that utilize tendons
fully encapsulated in anchorages and ducts. Systems that transfer prestress force by bonding the prestress steel directly to concrete are not allowed. Use only post -tensioning systems that are approv ed by the Engineer and meet the following requirements:
1.Anchorage and Distribution. Secure prestressing steel at the ends by means of approved permanent type anchoring assemblies. Use anchorage devices for post -tensioning that hold the prestressing steel at a load producing a stress of not less than 95 percent of the guaranteed ultimate tensile strength (GUTS) of the prestressing steel, when tested in an unbonded state, without exceeding the anticipated set. Distribute the load from the anchoring assemblies to the concrete by means of approved devices or bearing plates that will effectively distribute the load to the concrete. Construct the bearing plate and wedge plate from ferrous metal. For bending stresses in the bearing plates or assemblies induced by t he pull of the prestressing steel, do not exceed the yield point of the material or cause visible distortion in the bearing plate when 95 percent of the GUTS of the tendons is applied as determined by the Engineer. Do not exceed 3500 psi directly underneat h the bearing plate or assembly for the final unit compressive stress on the concrete. Galvanize the body of the anchorage assembly in accordance with AASHTO M 111. Other components of the anchorage assembly including wedges, wedge plate and local zone reinforcement need not be galvanized. Construct anchorage assemblies with grout vents suitable for post -grouting inspection access as approved by the Engineer. Equip all anchorages with a grout cap that is vented and bolted to the anchorage. Recess the anchor ing assemblies so that the ends of the prestressing steel and all parts of the anchoring assemblies will be at least 3 inches inside of the end surface of the members, unless shown otherwise on the plans. After post -tensioning all tendons, fill the recesses with concrete conforming to the provisions for the structure and then finished flush with the abutment end diaphragm.
2.Strand Couplers . Do not use strand couplers.
3.Enclosures for Post -tensioning. Use rigid ferrous metal duct enclosures for prestressing st eel that are galvanized, mortar tight, and capable of withstanding concrete pressures without deforming. Use rigid ducts with smooth inner walls that can be curved to the proper configuration without crimping or flattening and have sufficient strength to m aintain their correct alignment during placing of concrete. Do not use semi -rigid ducts. Fabricate ducts with either welded or interlocked seams. 512 ALASKA 2020 Connect sections of rigid ducts using galvanized ferrous metal couplings that are mortar tight and do not resu lt in angle changes at the joints. Do not use split metal couplings. Use waterproof tape to seal all connections to the duct. Connect ducts to anchoring assemblies using transition couplings that are galvanized ferrous metal or polyethylene, mortar tight, and of sufficient strength to prevent displacement of the ducts during concrete placement. Use ducts for multi -strand tendons with a minimum diameter that provides an inside area at least 2.5 times the net area of the prestressing steel in the tendon. Do not use ducts with diameters that exceed 0.4 times the least gross concrete thickness at the duct location. Use duct enclosures with vents for the injection of grout after post -tensioning.
4.Grout Vents . Use vents with positive means for allowing the escapem ent of air, water, grout, and bleed water out of the vents, injecting grout through the vents, and sealing to prevent grout leakage from the vents. Use 3/4 inch minimum diameter standard pipe or suitable plastic pipe vents with positive shut -off designed t o withstand the grouting pressure. Do not crimp or bend the vent pipe. Use metallic or plastic structural fasteners to connect the vent with the duct. Do not use plastic components that react with the concrete or enhance corrosion of the prestressing steel , or contain water -soluble chlorides. Make all vents mortar tight, taped as necessary. Make vents with sufficient length out of the concrete member to allow proper closing of the vents. Remove ends of vents at least 1 inch below the roadway surface after grouting has been completed. Place vents at the following locations:
a.At anchorages.
b.At the high points of the duct, when the vertical distance between the highest and lowest point is more than 20 inches.
c.At a location down flow from all high point vents where the duct is approximately one- half duct diameter lower than the crest, but not to exceed 3 feet downstream.
d.At the lowest point of the duct.
e.At major changes in the cross -section of the duct.
f.At other locations designated by the Engineer.
5.Grout Caps . Use grout caps that completely cover and seal all exposed ends of prestressing steel at the anchorage. Seal the cap with neoprene “O” ring seals and place a grout vent on the top of the cap. Use caps rated for a minimum pressure of 150 psi.
721-2.04 Certific Ation .
1.Prestressing Steel . Furnish a Certified Test Report from the manufacturer or an independent testing laboratory containing a list of dimensional, chemical, metallurgical, electrical, physical, and other required test results of the specified materia l certifying that the product or assembly has passed all specified tests. Include the following:
a.the project name and number;
b.the manufacturer's name;
c.the name of the product or assembly; 513 ALASKA 2020 d. a complete description of the material;
e.country of origin;
f.the lot, heat, or batch number that identifies the material;
g.all required test results for the specified material from the same lot, heat, or batch defined in Subsection 721- 2.04.1.f; and,
h.a statement, signed by a person having legal authority to act for the manufacturer or the independent testing laboratory, that the test results show that the product or assembly to be incorporated into the project has been sampled and tested and the samples have passed all specified tests. Tag, stencil, stamp, or otherwise mark al l materials or assemblies furnished under certification to the project with the lot number, heat number, batch number, or other appropriate identification, which can be readily recognized and legible, and is identical to the accompanying Certified Test Report.
2.Post-Tensioning Systems . Submit certified test reports to the Engineer that shows the post - tensioning system meets all the requirements specified herein. Submit the certified test reports with the shop drawing submittal. If any component of the post -tensioning system is modified or replaced, the entire system must be retested and resubmitted to the Engineer for approval. Ensure that all components of a system are stamped with the supplier’s name, trademark model number and size corresponding to catalog designation. Submit certification stating the manufacturer's minimum guaranteed ultimate tensile strength of all prestressing steel used for this project. Assign an individual lot number for each manufactured reel of prestressing steel to be shipped to the site. Tag each reel in such a manner that each lot can be accurately identified at the site. All unidentified prestressing steel received at the site will be rejected. Assign and tag each lot of anchorage assemblies to be installed at the site. Tag eac h anchorage assembly in such a manner it can be accurately identified at the site. All unidentified anchorage assemblies received at the site will be rejected. 514 ALASKA 2020 SECTION 722 BRIDGE RAILING
722-2.01 Bridge Rail Ing.
Steel tube rail elements ASTM A500, Grade B Steel Thrie Beam elements AASHTO M 180, Class B, Type II Posts ASTM A709, Grade 36 Machine bolts, cap screws, nuts and washers ASTM A307 High strength bolts, nuts and washers Subsection 716- 2.03 Anchor bolts ASTM F3125, Grade A325 or ASTM A449, Type 1 Welded studs AASHTO M 169, Grade 1015 or 1020 Bent anchor rods ASTM A709, Grade 36 Shims, plates, angles and sleeves ASTM A709, Grade 36 Plate Washers and Tapered Plate Washers ASTM F436 Galvanize steel portions of railing AASHTO M 111 or M 232 and Subsecti on after fabrication. 716-2.07
722-2.02 CERTIFICATI ON. Furnish a certified test report from the manufacturer or an
independent testing laboratory containing a list of dimensional, chemical, metallurgical, electrical, physical, and other required test resul ts of the specified material certifying that the product or assembly has passed all specified tests. Include the following:
1.the project name and number
2.the manufacturer's name
3.the name of the product or assembly
4.a complete description of the material
5.count ry of origin
6.the lot, heat, or batch number that identifies the material
7.all required test results for the specified material from the same lot, heat, or batch defined in Subsection 722- 2.02.6
8.a statement, signed by a person having legal authority to act f or the manufacturer or the independent testing laboratory, that the test results show that the product or assembly to be incorporated into the project has been sampled and tested and the samples have passed all specified tests. Tag, stencil, stamp, or othe rwise mark all materials or assemblies furnished under certification to the project with the lot number, heat number, batch number, or other appropriate identification, which can be readily recognized and legible, and is identical to the accompanying certi fied test report.
Source: Alaska Standard Specifications for Highway Construction, 2020 Edition. Pages 539–541 of 584.