SECTION 237—STRUCTURE BEDDING MATERIAL AND BEARING P ADS
237.01 Description
These specifications cover material used under bearing devices of structures.
237.02 Detail Requirements
a.Elastomeric Bearing Pads: The elastomer portion of pads shall be new neoprene compound. Pads shall be cast under heat and pressure and may be individually molded or cut from pressure-cast stock. Variations from the dimensions shown on the plans shall be not more than the following: thickness, ±1/16 inch; width, –1/8 to +1/4 inch; length, –1/8 to +1/4 inch. Tolerances, dimensions, finish and appearance, flash, and rubber-to-metal bonding shall conform to A 4-F3-T.063-B2, Grade 2, Method B, in accordance with the RMA Rubber Handbook. Pads shall be furnished in one piece and shall not be laminated unless otherwise specified. Pads shall be furnished in identifiable pack - ages. Adhesive for use with elastomer pads shall be an epoxy-resin compound, compatible with the elastomer, having sufficient shear strength to prevent slippage between pads and adjacent bearing surfaces. Laminated pads shall consist of alternate laminations of elastomer and hot-rolled steel sheets molded together as a unit. The bond between the elastomer and metal shall be such that failure shall occur in the elastomer and not between the elastomer and steel when tested for separation. Material having a nominal durometer hardness of 70 and 50 shall be used for nonlaminated pads and laminated pads, respectively. Test samples shall be prepared from finished pads. Samples of each thickness will be taken from 2 full-size pads from each shipment of 300 pads or less, with 1 additional pad for each additional increment of 300 pads or fraction thereof. Samples shall comply with the following physical requirements when tested in accordance with the ASTM methods designated.
1.Original physical properties: Test results for tear resistance, tensile strength, and ultimate elongation shall be not more than 10 percent below the following specified value: 236.02 Nominal Hardness Property 50 70 Min. tear resistance, ASTM D624, 180 200 Die C (lb/in of thickness) Hardness, ASTM D2240 (points) 50 ± 5 70 ± 5 Min. tensile strength, ASTM D412 2,500 2,500 (average psi of longitudinal and transverse) Min. ultimate elongation (%) 400 300 The compressive deflection tested in accordance with ASTM D575, Method A, shall be as follows:
a.Laminated pads: The maximum compressive deflection shall be 7 percent of the total rubber thickness at the total load given in the plans. The maximum shear resistance shall be 50 pounds per square inch of the plan area at 25 percent shear deformation at –20 degrees F . Test pads shall be subjected to a compressive load of 1.5 times the maximum design load given in the plans without visible damage.
b.Nonlaminated pads: When loaded within 300 to 800 pounds per square inch, material shall show a compressive deflection within 20 percent of that given in the charts of VTM- 23, interpolating for actual measured hardness.
2.Changes in original physical properties: When pads are oven aged 70 hours at 212 degrees F in accordance with ASTM D573, changes shall be not more than the following: Property V alue Hardness (points change) 0 to +15 Tensile strength (% change) ±15 Ultimate elongation (% change) -40
3.Extreme temperature characteristics: Compression set under constant deflection in accordance with ASTM D395, Method B, 22 hours at 212 degrees F , shall be not more than 35 percent. When tested in accordance with the low temperature brittleness test, ASTM D746, breaks shall not occur above –20 degrees F .
4.Ozone cracking resistance: Upon exposure to 100 parts per million of ozone in air by volume at a strain of 20 percent and a temperature of 100 ± 2 degrees F in a test conducted otherwise in accordance with ASTM D1149, cracks shall not develop within 100 hours. Samples shall be wiped with solvent before the test to remove traces of surface impurities.
5.Oil swell: The volume change shall be not more than +120 percent when tested in accordance with ASTM D471 with ASTM Oil No. 3, 70 hours at 212 degrees F .
b.TFE Bearing Surfaces:
1.TFE resin shall be virgin material conforming to ASTM D1457. The specific gravity shall be 2.13 to 2.19. The melting point shall be 623 ± 2 degrees F . 237.02
2.Filler material shall be milled glass fibers, carbon, or other Department approved inert filler materials.
3.Adhesive material shall be an epoxy resin conforming to FS MMM-A-134, FEB film or Department approved equal.
4.When tested in accordance with ASTM D1457, finished unfilled TFE sheets shall have a tensile strength of at least 2,800 pounds per square inch and an elongation of at least 200 percent.
5.Filled TFE sheets shall contain inert filler material uniformly blended with TFE resin. Finished filled TFE sheets containing glass fiber or carbon shall conform to the following: ASTM Method 15% Glass Fibers 25% Carbon Min. tensile strength D1457 2,000 psi 1,300 psi Min. elongation D1457 150% 75% Min. specific gravity D792 2.20 2.10 Melting point D1457 621 ± -50°F 603 ± -50°F
6.Fabric containing TFE fibers shall be manufactured from oriented multifilament TFE fluorocarbon fibers and other fibers as required by specific designs. When tested in accordance with ASTM D2256, the tensile strength of TFE fibers shall be at least 24,000 pounds per square inch and the elongation shall be at least 75 percent.
7.Where TFE sheets are to be epoxy bonded, one surface of the sheet shall be factory treated by an approved manufacturer using the sodium naphthalene or sodium ammonia process.
8.Stainless steel mating surfaces shall be at least 16 gage in thickness and shall conform to ASTM A240, T ype 304. The mating surface shall be a true plane surface with a Brinnel hardness of at least 125 and a surface finish of at least No. 8 mirror finish in accordance with ASTM A480. Stainless steel mating surfaces shall be polished or rolled as necessary to conform to the friction requirements specified herein. The stainless steel shall be attached to the sole plate by means of a seal weld around the entire perimeter of the facing material.
9.The coefficient of friction for the completed bearing assembly shall be not more than the following: Bearing Pressure Material 500 psi 2,000 psi 3,500 psi (3.447 MPa) (13.790 MPa) (24.132 MPa) Unfilled TFE, fabric containing TFE fibers, .08 .06 .04 TFE perforated metal composite Filled TFE .12 .10 .08 Interlocked bronze and filled TFE structures .10 .07 .05
c.Sheet Lead and Common Desilverized Bedding Material: Material shall conform to ASTM B749 and shall be furnished in single sheets of the specified thickness.
d.Preformed Fabric Bedding Material: Material shall be composed of multiple layers of 8-ounce cotton duck impregnated and bound with high-quality natural rubber or its equivalent and equally 237.02
Referenced in this section
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Source: Road and Bridge Specifications, 2020 Edition. Pages 272–274 of 1,065. View official source ↗