507 ALASKA 2020 SECTION 720
720-2.01 ELASTOMERIC BEARING PADS . Elastomeric bearing pads include plain pads,
consisting of elastomer only, and laminated pads with steel laminates.
1.General . Meet AASHTO M 251, with the following revisions: 4.1 Properties of the Elastomer Delete the first sentence and replace with the following: Use elastomeric compound in the construction of the bearings containing only virgin natural polyisoprene (natural rubber) as the raw polymer. Do not use neoprene. Properties and requirements elsewhere in AASHTO M 251 pertaining solely to polychl oroprene (neoprene) do not apply. Add the following: Use elastomer compound classified as low temperature Grade 5 and meeting the requirements of paragraph 8.9.1.
5.FABRICATION Add the following paragraph: 5.5. Fabricate pads over 3/4 inch thick with alternating laminations of elastomer and metal or fabric reinforcements. The outside laminations must be metal or fabric with a minimum elastomer cover as shown on the Plans. Table 2 – Tolerances. Delete Item 6 and replace with the following:
6.Top, bottom, and edge cover of embedded laminates or connection members - 0, +1/8 inch.
2.Certification. Furnish a Certified Test Report from the manufacturer or an independent testing laboratory containing a list of dimensional, chemical, metallurgical, electrical, ph ysical, and other required test results of the specified material 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;
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 720- 2.01.2.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. 508 ALASKA 2020 Tag, stencil, stamp, or otherwise 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 l egible, and is identical to the accompanying Certified Test Report.
720-2.02 EPOXY ADHESIVE FOR ELASTOMERIC BEARING PADS. Meet AASHTO M 235,
Type IV, Grade 3.
720-2.03 POLYTETRAFL UOROETHYLENE (PTFE) BEARINGS. PTFE bearing assemblies
consist of elastomeric bearing pads, polytetrafluoroethylene surfacing, and stainless steel and steel plates.
1.Materials . Elastomeric Bearing Pads Subsection 720- 2.01 Stainless Steel Plates ASTM A 240, Type 304 Steel Plates ASTM A 709, Grade 36 Use PTFE from virgin material (n ot reprocessed) meeting the requirements of ASTM D 4894 or D 4895, and Table 720- 1.
2.Fabrication. Fabricate the PTFE sliding surface with lubricant dimples having a maximum diameter of 0.32 inch, a minimum depth of 0.08 inch and a maximum depth of one half of the PTFE sheet thickness. Distribute the dimples uniformly within the area ¼ inch from the edges of the PTFE sheet and occupying between 20 percent and 30 percent of the PTFE sheet area. For welding of structural steel, conform to the requirements of S ection 504. TABLE 720 -1 POLYTETRAFLUOROETHYL ENE (PTFE) Bond the PTFE to steel substrate under controlled conditions according to the written instructions of the manufacturer of the adhesive system. Use adhesive material meeting the requirements of the PTFE manufacturer. Uniformly roughen th e contact surfaces of PTFE sheet and steel plate to be bonded to a minimum roughness height value of 250 microinches. Factory treat the side of the PTFE sheet to be bonded by the sodium naphthalene or sodium ammonia process, after the contact surface is r oughened. Fully bond the PTFE sheet in the recess. Ensure the PTFE surface is smooth and free from bubbles after completion of the bonding operation. PTFE sheets that are delaminated will be rejected. Perimeter seal weld the stainless steel plate to the s teel sole plate. Use stainless steel electrodes in accordance with the requirements of the electrode manufacturer. After the completion of the weld operation, ensure the stainless steel plate is smooth and free from waves. Test Requirements ASTM Method Specific Gravity 2.13 - 2.19 D792 Peak Melting Temperature 623oF (±2oF) D4894, D4895, or D5977 Tensile strength (Minimum) 2800 psi D638 or D2256 Elongation (Minimum) 200% D638 or D2256 509 ALASKA 2020 Control the flatness of the beari ng elements such that upon completion of the bearing assembly the PTFE/stainless steel sliding interface is in full bearing. Provide a mating surface of the stainless steel plate with the PTFE surfacing with a surface finish of less than 8 microinches root -mean- square (rms), determined according to ASME B46.1. Do not exceed a first movement static coefficient of friction of 0.05 for the sliding element of the production bearings, when tested without the coating of silicone grease. Fully vulcanize elastomer ic bearing pads to the steel plates under factory controlled conditions. Provide a bond with a peel -strength of at least 30 pounds per inch as determined by AASHTO M 251, Appendix X2. Prepare and paint metal surfaces, except stainless steel surfaces, of bearings exposed to the atmosphere in the completed work. Prepare and paint the surfaces according to Section 504. After installation of the bottom portion of the bearing assembly, apply a 1/16 inch thick coating of silicone grease to the entire PTFE surface and reassemble the bearing without damage to the mating sliding surfaces. Use silicone grease conforming to SAE AS8660. At your expense and without contract extension time return damaged bearings and bearings with scratched mating surfaces to the factory for replacement or resurfacing. Prior to proof testing, permanent die stamp all individual components on 2 of 4 sides with markings consisting of bearing number and contract number. Provide each bearing with a unique bearing number and match marks on plate edges to insure correct assembly at the job site.
3.Testing. Proof test and evaluate full sized PTFE bearings for compression and coefficient of friction in the presence of the Engineer, unless otherwise directed. Perform proof tests on samples randomly se lected by the Engineer from the production bearings to be used in the work. Perform proof tests at an approved independent laboratory. If proof tests are not performed at the specified load, perform additional physical tests in the presence of the Engineer , unless otherwise directed, to demonstrate that the requirements for proof testing at the specified load are satisfied. Give the Engineer at least 7 working days notice before beginning proof testing. Proof test one bearing per lot of production PTFE bearings. A lot is defined as 25 PTFE bearings or fraction thereof of the number of PTFE bearings shown on the Project Plans. Clean the bearing surfaces prior to testing. Proof test bearings after conditioning specimen for 12 hours at 75o ± 5oF. Perform the tests with the dead load as specified in the Contract for the bearing with the test load applied for 12 hours prior to friction measurement and the following: Arrange the tests to allow measurement of the static coefficient of friction on the first movem ent of the bearing. Measure the first movement static and dynamic coefficients of friction at a sliding speed not exceeding one inch per minute and do not exceed the specified coefficient of initial static friction. Subject the test bearings to a minimum of 100 movements of at least one inch of relative movement at a sliding speed not exceeding 12 inches per minute. After cycling, measure again the first movement static and dynamic coefficients of friction at a sliding speed not exceeding one inch per minute and do not exceed the specified coefficient of initial static friction. 510 ALASKA 2020 The proof tested bearings are to show no visible sign of: (1) bond failure of bearing surfaces,
2.separation or lift -off of plates from each other or from PTFE surfaces, (3) other defects. When a proof tested bearing fails to comply with the Contract Documents, test each bearing in that lot for acceptance. Proof test results are to be certified correct and signed by the testing laboratory personnel who conducted the test and int erpreted the test results. Include the bearing numbers of the bearings tested on the proof test results. Test a minimum of one pad per lot for bond strength per AASHTO M 251. Test specimens are to show no indication of deterioration of elastomer or loss of bond between the elastomer and steel laminates. Protect all PTFE and stainless steel surfaces from contamination and weather damage.
4.Certification. Furnish a Certified Test Report from the manufacturer or an independent testing laboratory containing a l ist of dimensional, chemical, metallurgical, electrical, physical, and other required test results of the specified material 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;
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 720- 2.03.4.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 all materials or assemblies furnished under certification to the project with the lot number, heat number, batch number, or other appro priate identification, which can be readily recognized and legible, and is identical to the accompanying Certified Test Report. 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.
Referenced in this section
BEARINGS in other states
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Source: Alaska Standard Specifications for Highway Construction, 2020 Edition. Pages 535–538 of 584. View official source ↗