M 41-10 Page 9-209 Fabricated Bridge Bearing Assemblies 9-319-31 Fabricated Bridge Bearing Assemblies
9-31.1 Steel Plates and Bars
Steel plates and bars, including anchor array templates, shall conform to ASTM A 36. Recessed steel surfaces retaining PTFE shall have an average surface roughness of 250-microinches or less. Steel surfaces in contact with pre-formed fabric pad or polyether urethane disc shall have an average surface roughness of 250-microinches or less. Steel surfaces in contact with stainless steel sheet, or with the bearing block of a pin bearing assembly, shall have an average surface roughness of 125-microinches or less. All other steel surfaces in contact with other fabricated bridge bearing assembly components shall have an average surface roughness of 250-microinches or less.
9-31.2 Stainless Steel
Stainless steel sheet shall conform to ASTM A 240 Type 304L. Stainless steel in contact with PTFE shall be polished to a Number 8 mirror finish. Stainless steel sheet for fabric pad bearing assemblies shall have a thickness greater than or equal to 14-gage. Stainless steel countersunk screws shall be hexagon socket type conforming to the geometric requirements of ANSI B 18.3 and shall conform to ASTM F 593 Type 304L.
9-31.3 Bearing Blocks and Keeper Rings
Bearing block forgings for pin bearing assemblies shall conform to Section 9-06.11 , including AASHTO M 102 Supplemental Requirement S4. The grade shall be Grade F. The bearing block forging surfaces in contact with other pin bearing assembly components shall have an average surface roughness of 63-microinches or less. All other bearing block forging surfaces shall have an average surface roughness of 250-microinches or less. Keeper ring forgings for pin bearing assemblies shall conform to Section 9-06.11 , and the grade shall be Grade H. All keeper ring surfaces shall have an average surface roughness of 125-microinches or less.
9-31.4 Pin Assembly
Pins shall conform to ASTM A 276 UNS Designation 21800. The pin surfaces in contact with the bearing block shall have an average surface roughness of 63-microinches or less. Nuts shall conform to ASTM A 563 Grade DH. Nuts with a thread diameter equal to or less than six-inches shall have a minimum Rockwell Hardness of HRc 24. Nuts with a thread diameter greater than six-inches shall have a Rockwell Hardness between HRc 20 and HRc 30. Washers shall conform to ASTM A 572 Grade 50. Cotter pins shall be stainless steel.
9-31.5 Welded Shear Connectors
Welded shear connectors shall conform to Section 9-06.15 .
9-31.6 Bolts, Nuts and Washers
Bolts, nuts and washers shall conform to Section 9-06.5(3) .
9-31.7 Anchor Array Rods, Nuts and Washers
Anchor array rods, nuts and washers shall conform to Section 9-06.5(4) . The top 1’-0”, minimum, of the exposed end of the anchor rods, and the associated nuts and washers, shall be galvanized in accordance with AASHTO M 232 or ASTM F 2329 as applicable. Pipe sleeves for anchor array templates shall conform to ASTM A 53 Grade B Type E or S, black. Page 9-210 M 41-10
9-31 Fabricated Bridge Bearing Assemblies9-31.8 Bearing Pads
9-31.8(1) Elastomeric Pads
Elastomeric pads shall conform to the requirements of AASHTO M251 unless otherwise specified in the Plans or Special Provisions. The elastomer shall be low-temperature Grade 3 and shall not contain any form of wax. Unless otherwise specified in the Plans or Special Provisions, the elastomer shall have a shear modulus of elasticity of 165 psi at 73°F. All elastomeric pads with steel laminates shall be cast as units in separate molds and bonded and vulcanized under heat and pressure. Corners and edges of molded pads may be rounded at the option of the Contractor. Radius at corners shall not exceed ⅜ inch, and radius of edges shall not exceed ⅛ inch. Elastomeric pads shall be fabricated to meet the tolerances specified in AASHTO M251. Shims contained in laminated elastomeric pads shall be mill rolled steel sheets not less than 20 gage in thickness with a minimum cover of elastomer on all edges of: ¼ inch for pads less than or equal to 5 inches thick and, ½ inch for pads greater than 5 inches thick. Steel shims shall conform to ASTM A1011, Grade 36, unless otherwise noted. All shim edges shall be ground or otherwise treated so that no sharp edges remain.
9-31.8(2) Polytetrafluoroethylene (PTFE)
PTFE shall be unfilled (100-percent virgin) PTFE or fiberglass fiber filled PTFE (or woven fabric PTFE for disc or spherical bearing assemblies) conforming to Section 18.8 of the AASHTO LRFD Bridge Construction Specifications , and the following additional requirements:
1.PTFE shall be unfilled (100-percent virgin) PTFE except where filled PTFE is specified in the Plans.
2.Filled PTFE shall be composed of PTFE resin uniformly blended with 15-percent maximum fiberglass fiber.
3.The substrate shall limit the flow (elongation) of the confined PTFE to not more than 0.009-inch under a pressure of 2,000 psi for 15-minutes at 78°F for a two-inch by three-inch test sample.
4.Unfilled PTFE shall have a hardness of 50 to 65 Durometer D, at 78°F, in accordance with ASTM D 2240.
5.The PTFE may be dimpled.
9-31.8(3) Pre-formed Fabric Pad
Pre-formed fabric pads shall be composed of multiple layers of duck, impregnated and bound with high-quality oil resistant synthetic rubber, compressed into resilient pads. The pre-formed fabric pads shall conform to MIL C 882 and the following additional requirements:
1.The pre-formed fabric pad shall have a shore A hardness of 90 ± 5 in accordance with ASTM D 2240.
2.The number of plies shall be as required to produce the specified thickness after compression and vulcanization. M 41-10 Page 9-211 Fabricated Bridge Bearing Assemblies 9-319-31.9 Polyether Urethane Polyether urethane shall be a molded polyether urethane compound conforming to the following properties: Physical Properties Specification Hardness, Type D durometer ASTM D 2240 45 55 65 Minimum tensile stress, ksi At 100-percent elongation At 200-percent elongationASTM D 412 1.5 2.81.9 3.42.3 4.0 Minimum tensile strength, ksi ASTM D 412 4.0 5.0 6.0 Minimum ultimate elongation, percent ASTM D 412 350 285 220 Maximum compression set (22 hours at 158°F) Method B, percentASTM D 395 40 40 40 Required minimums for tensile stress at specific elongations, tensile strength, ultimate elongation, and compression set may be interpolated for durometer hardness values between 45 and 55, and 55 and 65.
9-31.10 Silicone Grease
Silicone grease for use with dimpled PTFE shall conform to SAE AS 8660.
9-31.11 Epoxy Gel
Epoxy gel shall be Type 1, Grade 3, Class A, B, or C, conforming to Section 9-26.1 .
9-31.12 Resin Filler
Resin filler shall be a two-component, resin and catalyst, liquid thermoset material, with the following properties:
1.The viscosity of the resin-catalyst mixture shall be 35,000 ± 5,000cP at 75°F immediately after mixing.
2.The flash point shall be 100°F minimum.
3.After mixing, the resin-catalyst mixture shall be pourable for a minimum of 8-minutes at 60°F and shall harden in 15-minutes maximum. Heating of the mixture to a maximum temperature of 250°F after placement is permissible to obtain a full cure. The properties of the cured resin-catalyst mixture shall be:
1.The fully cured compressive strength shall be 12,000 psi, minimum.
2.The maximum allowable shrinkage shall be 2-percent. To control shrinkage, an inert filler may be used in the resin provided the specified viscosity requirements are met.
3.The hardness shall be between 40 and 55 in accordance with ASTM D 2583. The resin and catalyst components shall be supplied in separate containers.
Source: Washington Standard Specifications for Road, Bridge, and Municipal Construction, 2024 Edition. Pages 1119–1121 of 1,151.