5-142 Shear modulus tests shall be carried out using the apparatus an d procedure described in Annex A of the ASTM D4014 specifications.
523.22 Fabrication All components of Laminated Elastomeric Bea rings shall be molded
as an integral unit. Plain Elastomeric Bearings may be molded individually, cut from previously molded slabs, or ext ruded and cut to length. Cut ed ges shall have an ANSI 250 mils finish. Steel laminates shall be abrasive blast cleaned t o an SSPC SP-6 and protected from contamination. The Fabricator must be on the Departments Qualified Supplier List.
523.23 Testing The following testing shall be performed prior to delivery of the
bearings:
1.Ambient Temperature Tests on the Elastomer (This test is re quired for each elastomer formulation) The bond to the reinforcement shall develop a minimum peel stre ngth of 40 pounds/inch. Peel strength tests shall be performed in accordance with ASTM D429, Method B.
2.Low-Temperature Test on the Elastomer (This test is require d for each elastomer formulation) Low-temperature tests shall be performed in accordance with the requirements of Section 711.11; the compound shall satisfy all criteria for its grade. The manufacturer may choose to provide certificates from low-temperature crystalliza tion tests performed on identical material, within the last year, for Grade 3 to Grade 5 material.
3.Visual Inspection of the Finished Bearing Each laminated be aring shall be inspected for compliance with dimensional tolerances and for overall qual ity of manufacture. In steel reinforced bearings, the edges of the steel shall be protected everywhere from corrosion.
4.Short-Duration Compression Tests on Bearings Each laminated bearing shall be loaded in compression to 150% of t he Bearing Design Load. The load shall be maintained for 5 minutes and released. The same load shall be reapplied a nd maintained for a second period of 5 minutes. The bearing shall be examined visually du ring the second loading. If the load drops below the required value during either applicati on, the test shall be performed again. The bearing shall be rejected if: The bulging pattern suggests laminate parallelism outside of th e specified tolerance, A layer thickness is outside the specified tolerances, A poor laminate bond exists, or Three or more separate surface cracks greater than 0.08 inch wi de and 0.08 inch deep exists. 5-143
5.Long-Duration Compression Tests on Bearings (This test is r equired on 10% of each type and size of laminated bearing furnished) The long-term compression test shall be performed as specified in item 4 above, "Short- Duration Compression Tests on Bearings", except that the second load shall be maintained for 15 hours. The bearing shall be visually examined at the en d of the tests while still under the load. If any patterns or cracks specified in section 4, ab ove, occur, all bearings from that lot shall be rejected, unless the manufacture elects to test ea ch bearing of the lot. If the additional testing does not reveal any rejectable defects as no ted in item 4, above, the bearings will be accepted.
6.Shear Modulus Tests on Material from Bearings (This test is required for each elastomer formulation) The shear modulus of the elastomer in the finished bearing shal l be evaluated by testing a specimen cut from it using the apparatus and procedure descri bed in Annex A of the ASTM D4014 specifications, amended where necessary in Tables A or B; or at the discretion of the Fabrication Engineer, a comparable nondestruc tive stiffness test may be conducted on a pair of finished bearings. The shear modulus sh all fall within the specified range. If the test is conducted on the finished bearings, the material shear modulus shall be computed from the measured shear stiffness of the bearings, tak ing due account of the influence on shear stiffness of bearing geometry and compressiv e load. Shear modulus tests performed on a sample of the same material as was used to fabricate the bearings will be acceptable. Shear modulus testing shall b e performed using the apparatus and procedure described in ASTM D4014, Annex A. POT or DISC BEARINGS
523.30 Design Pot or Disc bearings shall be designed for the l oads and movements
given on the Plans. Configurations and dimensions shall confor m to AASHTO/NSBA G 9.1, Steel Bridge Bearing Design and Detailing Guidelines. Con figurations and dimensions other than those given on the P lans or AASHTO/NSBA G 9.1 may be accepted subject to the approval of the Fabrication Engineer. Design calculations to substantiate all the requirements stated in this specification shall be submitted as part of the Working Drawings and shall be stamped and signed by a Professional Engineer lice nsed in the State of Maine. Except where indicated on the Plans, the design shall also incl ude the connections between the bearings and the superstructure, and the bearings a nd the substructure, along with adequate provisions for hold- downs equal to the tensile st rength of the anchor rods. The bearings shall be designed to accommodate a rotation of not less than 0.015 radians. The static coefficient of fric tion between the PTFE and the sta inless steel surface, for each size and type of bearing, shall not exceed 0.20 at the ave rage unit bearing pressure for the minimum vertical load indicated on the Plans. 5-144 The bearings shall be designed for a horizontal force at least equal to 10% of the vertical capacity of the bearing. No more than two bearings, with guide bars, per bearing line, s hall be considered to be carrying the total maximum lateral horizontal load as indicated on the Plans. Bearing friction shall not be cons idered when the horizontal lo ad capacity of guided or fixed bearings is calculated. The PTFE sliding surface for pot or disc bearings shall be desi gned to meet the following:
1.The average unit pressure shall be 3,500 psi, -5%, +0%, for the maximum vertical load indicated on the Plans.
2.Unfilled PTFE shall have a minimum thickness of ⅛ inch with half of its thickness recessed into the piston.
3.Filled PTFE shall be a minimum of 1/16 inch thick and shall be bonded to the surface of the piston and to the guide bar.
4.The maximum thickness of the PTFE, filled or unfilled, shal l be 3/32 inch, except, if recessed it shall be 3/16 inch. The stainless steel sliding surface shall be designed to meet t he following:
1.The stainless steel shall cover the PTFE in all operating p ositions such that the stainless steel will have a minimum of 1 inch edge clearance be yond the PTFE.
2.The thickness shall be not less than 0.040 inch or greater than 0.090 inch.
3.When a center guided key is utilized, a recess shall be mac hined in the sole plate and the vertical sliding surfaces of the recess shall be covered wi th stainless steel. The guide bars shall be designed to meet the following: 1. The guide bars shall be designed for the maximum horizontal load, as indicated on the Plans, but not less than 10% of the vertical capacity of th e bearing.
2.The guided member shall be within the guide bars at all ope rating positions.
3.The overall width of the guide bar and the PTFE sliding sur faces shall be ⅛ inch less than the clear width of the keyway in the guided member. 5-145
4.A PTFE sheet, 1/16 inch minimum thickness, shall be bonded to the sliding contact surfaces of the guide bars. The sheets shall be filled PTFE. Pot Bearings: A. The elastomeric discs shall be designed to meet the followin g:
1.The average unit pressure shall be 3,500 psi, -0%, +10%, fo r the maximum vertical load indicated on the Plans.
2.The average unit pressure shall not be less than 700 psi fo r the minimum vertical load.
3.When utilizing flat brass sealing rings, the upper edge of the discs shall be recessed to receive the brass rings.
4.A PTFE sheet, filled or unfilled, 1/16 inch minimum thickness and the same diameter as the design diameter of the disc, shall be placed below the d iscs. The pot shall be designed to meet the following: 1. The depth of the cavity shall be equal to or greater than: Twice the design rotation plus 0.1 inch plus the thickness of the elastomeric disc and th e PTFE sheet.
2.The inside diameter shall be the same as the design diamete r of the elastomeric disc.
3.The pot shall be mounted, to pr ovide a tight fit, in a ⅛ in ch minimum depth recess in the steel masonry plate or distribution plate and shall be capa ble of being removed for inspection and repairs.
B.The piston shall be designed to meet the following: 1. The outside diameter shall be 0.03 inch less than the insid e diameter of the pot.
2.The minimum thickness shall be not less than 0.08 times the design diameter.
3.When utilizing round brass sealing rings, the lower outside edge shall be beveled to accept and retain the brass ring and to permit full design rota tion.
4.Laterally restrained pot bearings shall have a keyway in th e sole plate. The top surface of the piston shall have a keyway slot and a cold finis hed steel guide bar press fitted into it and welded at the ends.
5.A PTFE sheet, filled or unfilled, 1/16 inch minimum thickness and the same diameter as the bottom surface of the piston, shall be bonded to the bot tom surface of the piston. 5-146
C.The elastomer sealing rings shall be brass and shall be desi gned to meet the following:
1.Flat brass sealing rings, if utilized, shall: a. Have a width of ⅜ inch minimum, with bearings up to a 1,000 kip capacity and a ½ inch width, with bearings over a 1,000 kip capacity.
b.Have a minimum thickness of 0.050 inch. c. Have two rings with a bearing capacity up to 1,000 kip, thr ee rings with a bearing capacity over 1,000 kip, but less than 3,000 kip, and four ring s with a bearing capacity of over 3,000 kip.
d.Have the ends cut at 45° with a minimum gap in the installe d position of 0.050 inch and shall fit the inside diameter of the pot snugly.
e.Have the ring gaps staggered 180° apart. 2. Round brass sealing rings, if utilized, shall: a. Be of one piece with the ends brazed to make a solid ring. b. Have the outside of the ring fit snug in the inside diamete r of the pot. Disc Bearings: A. The elastomeric discs shall be made from a compound based of polyether urethane using only virgin materials.
B.The disc shall be designed such that: 1. Its instantaneous deflection under total load does not exce ed 10% of the thickness of the unstressed disc and the additional deflection due to creep does not exceed 8% of the unstressed disc.
2.The components of the bearing do not lift off each other at any location.
3.The average compressive stress on the disc does not exceed 5.0 ksi. If the outer surface of the disc is not vertical, the smallest plan area sha ll be used for computing stress.
523.31 Materials Materials shall conform to Section 523.02, Ma terials, and the
following: Sealing rings shall be brass. Flat rings shall conform to the requirements of ASTM B36, half hard. Round sealing rings shall conform to the requirement s of Federal Specification QQB626, Composition 22, half hard. Elastomeric Disc hardness shall be: 5-147 Shore A Durometer scale, between 50 and 60, for Pot Bearings Shore D Durometer scale, between 45 and 65, for Disc Bearings 523.32 Fabrication Bonding of PTFE sheets to the piston shall be under factory- controlled conditions and in accordance with written instructio ns of the manufacturer of the adhesive. After completi on of the bonding operation, the PTFE surface shall be smooth and free from bubbles. PTFE surfaces shall not be polished, but sh all be wiped clean using a solvent appropriate for the material. The stainless steel sliding surfaces shall be seal welded aroun d the entire perimeter. The surfaces shall be smooth and flat and the back of the stainless steel shall remain in intimate contact with the sole plate. Pots shall be machined from a solid plate or fabricated by weld ing a cut shape to a plate. Fabricated pots shall be 100% ultrasonically tested at the insi de weld and magnetic particle tested at the exterior weld. The elastomeric discs in pot bearings shall be manufactured fro m no more than three pieces. Each bearing shall be assembled at the plant and, following ass embly, shall be sealed at the joint between the piston and the pot with a continuous ¼ in ch, minimum, bead of a flexible silicone rubber sealing compound approved by the Fabri cation Engineer. Each bearing shall have permanent match marks to indicate the n eutral 45 °F position of the bearing. Each bearing shall also be marked for identificat ion by die stamping on all steel parts (edge of sole plate, piston, masonry plate, and top edge of pot). Each bearing shall be shipped and stored in moisture-proof and dust-proof covers until they are to be erected.
523.33 Fabrication Tolerances Tolerances shall comply with Sec tion 523.06,
Fabrication Tolerances, and as noted below. Brass sealing rings shall have finished surfaces of less than 6 3 mils (ANSI B 46.1).
523.34 Testing and Certification The manufacturer of the pot o r disc bearings shall
furnish test facilities for testing and inspection of the compl eted bearings. The Fabrication Engineer, or an authorized representative, shall be allowed fre e access to the manufacturer's plant and test facility. The Fabrication Engineer will select two completed bearings for testing. The test shall be arranged so that the static coeffic ient of friction on the first movement can be determined. The test shall first be conducted at an average bearing pressure of 3,500 psi on the PTFE surface with the test load ap plied continuously for not less than 12 hours nor more than 14 hours prior to measuring th e friction. The first movement static coefficient of friction shall then be determine d. The above test shall then 5-148 be repeated for the minimum vertical load indicated on the Plan s for the bearings selected. The results shall not exceed that specified for the design. A proof load test shall also be performed on each test bearing by applying a load equal to 150% of the maximum vertical load indicated on the Plans for the bearings selected for a period of one hour. The test bearings shall show no sign of fa ilure or other defects while under load or subsequently upon disassembly and inspection. Before testing, the testing equipment and procedure shall be su bmitted to the Fabrication Engineer for review.
523.40 thru 523.49 Reserved - Spherical Bearings
523.50 Method of Measurement Bearings will be measured for pay ment by each unit,
tested and accepted. Bearing installation will be measured for payment by each unit in place and accepted.
523.51 Basis of Payment Bearings will be paid for at the contr act unit price each, which
price shall be full compensation for the design, fabrication, t esting, and delivery. Bearing installation will be paid for at the contract unit price each w hich price shall be full compensation for installation, including all materials, equipme nt, labor and incidentals necessary for installing the bearings in accordance with the Pl ans and this specification. Removal of the existing bearings , if present, including all mat erials, equipment, labor and incidentals necessary for jacking the superstructure, removal o f the existing bearings and preparation of the bridge seat in accordance with the Plans and this Specification, shall be considered incidental to bearing installation. Payment will be made under: Pay Item Pay Unit
523.52 Bearing Installation E a c h
523.5301 Steel Bearings, Fixed, Sliding Plate E a c h 523.5302 Steel Bearings, Expansion, Sliding Plate Each 523.5303 Steel Bearings, Fixed, Rocker E a c h 523.5304 Steel Bearings, Expansion, Rocker E a c h 523.5401 Laminated Elastomeric Bearings, Fixed Each 523.5402 Laminated Elastomeric Bearings, Expansion Each 523.5403 Plain Elastomeric Bearings E a c h 523.5551 Pot or Disc Bearings, Fixed E a c h 523.5552 Pot or Disc Bearings, Expansion E a c h 523.5601 Spherical Bearings E a c h SECTION 524 - TEMPORARY STRUCTURAL SUPPORTS
Source: Maine Standard Specifications for Road and Bridge Construction, 2020 Edition. Pages 434–440 of 817.