- 573 - SECTION 712 -- FIXED BEARINGS AND EXPANSION BEARINGS, PTFE TYPE
712.01 Description
1.The Contractor shall furnis h and install fixed bearings and polytetrafluoroethylene (PTFE) type expansion bearings at the locations shown in the contract.
2.The fixed bearings and expansion bearings, PTFE type, shall consist of the upper and lower assemblies shown in the contract. Prior to fabrication, the Contractor shall submit shop drawings to the Engineer for review.
712.02 Material Requirements
1.Fixed Bearings:
a.Upper Assembly: (1) The upper assembly shall consist of a sole plate conforming to the requirements of ASTM A709/A709M grade 50W (345W ) weathering steel. All flame cut edges of the sole plate shall be ground to reduce hardness. All corners of the so le plate shall be rounded to a 1/16 inch (1.5 mm) radius.
2.As an alternate, the sole plate may be ASTM A36/A36M grade 36 (250) steel, metallized. If the ASTM A36/A36M grade 36 (250) alternate is used, all flame cut edges of the sole plate shall be ground to reduce hardness and facilitate blast cleaning. All corners of the sole plate shall be rounded to a 1/16 inch (1.5 mm) radius. All exposed surfaces shall be blast cleaned to a near white finish and zinc metallized with a minimum thickness of 8 mils (200 mm). Zinc metallizing must be performed in accordance with American Welding Society Specification AWS C2.2.
b.The lower assembly shall consist of a cotton duck reinforced elastomeric pad (CDP) conforming to the requirements of the current AASHTO LRFD Specifications for Highway Bridges and the Department of Defense Specificat ion MIL-C-882.
2.Expansion Bearings, PTFE Type:
a.Upper Assembly:
1.The upper assembly shall consist of a sole plate conforming to the requirements of ASTM A709/A709M grade 50W (345W) weathering steel with an ASTM A240/A240M Type 304 stainless steel plate (at least 16 gauge when the maximum dimension of the surface is less than or equal to 12.0 in. and at least 13 gauge when the maximum dimension of the surface is larger than 12.0 in.) atta ched to the lower surface. All flame cut edges of the sole plate shall be ground to reduce hardness. All corners of the sole plate shall be rounded to a 1/16 inch (1.5 m) radius.
2.As an alternate, the sole plate may be ASTM A36/A36M grade 36 (250) steel, metallized. If the ASTM A36/A36M grade 36 (250) alternate is used, all flame cut edges of the sole plate shall be ground to reduce hardness and facilitate blast cleaning. All corners of the sole plate shall be rounded to a 1/16 inch (1.5 m) radius. All exposed surfaces shall be blast cleaned to a near white finish and zinc metallized with a minimum thickness of 8 mils (200 mm). Zinc metallizing must be performed in accordance with American Welding Society Specification AWS C2.2.
712.02 Fixed Bearings and Expansion Bearings, PTFE Type
- 574 - (3) The face of the stainless steel plate in contact with the PTFE sheet shall be polished or rolled as necessary to provide a No. 8 mirror finish as established by the American Iron and Steel Institute Committee of Stainless Steel Producers “F inishes for Stainless Steel” at the completion of fabrication.
4.The stainless steel plate shall be attached by welding around its full perimeter.
5.Welding may be done with the shielded metal arc welding process using an AWS E308L-15 electrode, the gas metal arc welding process using an AWS ER308L electrode, or the gas tungsten arc welding process using an AWS ER308L filler metal.
6.The weld shall not extend into the area of contact between the upper and lower assemblies.
b.Lower Assembly: (1) The lower assembly shall consist of a CDP pad with a 94 mil (2.38 mm) thick, low friction, vi rgin, unfilled, polytetrafluoroethylene (PTFE) sheet bonded to the upper surface.
2.Bonding of the PTFE shall meet the peel test requirements (ASTM D 903) of 25 lb/in (0.45 kg /mm) at an angle of 180 degrees.
3.Bonding must be complete and without air gaps under the PTFE sheet to seal out moisture and provide a smooth, flat, slide surface.
4.The PTFE sheet shall c onform to the requirements of the current AASHTO LRFD Bridge Design Specifications and the Standard Specifications for Highway Construction.
c.Flatness of the bearing surfaces shall be determined by the following methods:
1.A precision straightedge longer than the nominal dimension to be measured shall be placed in contact with and as parallel as possible to the surface to be measured.
2.An attempt shall be made to insert a feeler gauge equal to the tolerance allowed and having an accuracy of ± 0.001 inch (0.025 mm).
3.Bearing surfaces are "acc eptable" if the feeler gauge does not pass under the straightedge.
4.Flatness tolerances for the PTFE sheet and the stainless steel plate shall be 0.0005 x "Nominal Dimension."
5.The "Nominal Dimension" shall be the actual dimension, in inches (millimeters), under the straight edge where the straightedge is not parallel to any plan dimension of the sheet or plate being measured.
3.Certification: a. All components for the beari ng assemblies shall be fabricated, assembled, and certified by the manufacturer for the complete assembly. The assemblies shall be suitably packaged to prevent damage during shipment and storage.
b.The certification shall include all required test reports indicating that the static and kinetic coefficient of friction between the sliding surfaces Fixed Bearings and Expansion Bearings, PTFE Type 712.05 - 575 - does not exceed 0.08 at the pressure of 500 psi (3.5 MPa) and shall state that all materials used in the fabric ation of the bearing assemblies comply with the requirements of this Specification.
c.Testing shall be in accordance with the AASHTO Standard Specifications for Highway Bridges . The Engineer shall be allowed to witness all testing and approve the test ing agency or other parties involved in the testing operation.
4.Anchor bolts, nuts, and washers shall conform to ASTM A 307 and shall be galvanized in accordance with ASTM A 153.
5.The manufacturer of the fixed or expansion bearings shall provide to the Engineer all appropriate certified mill test reports for all materials used in the manufacturing process.
712.03 Construction Methods
1.The Contractor shall provide and install the bearing assemblies as described in the contract.
712.04 Method of Measurement
1.The fixed bearings and expansion bearings are assembled units that are measured by the each.
712.05 Basis of Payment
1.Pay Item Pay Unit Fixed Bearing Each (ea) Expansion Bearing, PTFE Type Each (ea) 2. Payment is full compensation for all work described in this Section. - 576 - SECTION 713 -- CONFINED EL ASTOMERIC BEARING DEVICES (POT BEARINGS)
713.01 Description
1.This work shall consist of furnishing and installing confined elastomeric bearing devices at the locations shown in the contract. Bearing devices furnished under this Specific ation shall adequately provide for thermal expansion and contraction, ro tation, camber changes, creep, and shrinkage of structural members, where applicable.
713.02 Material Requirements
1.Unless otherwise specified in the contract, the pot bearings shall be designed in accordance with the appl icable requirements of the AASHTO LRFD Specifications for Highway Bridges .
2.Before fabrication, the Contract or shall submit shop drawings to the Engineer for review. The shop drawings shall show complete details for inspection and construction purposes, detailed by the manufacturer with all appropriate notations and instructions for field installation.
3.Confined elastomeric bearing devices shall be supplied as fixed bearings, guided expansion bearings, and non-guided expansion bearings as shown in the contract.
a.Fixed Bearings: (1) Fixed bearings shall allow rotation but no longitudinal or transverse movement.
2.Fixed bearings shall consist of an elastomeric rotational element, confined and sealed by a steel piston and steel base pot.
b.Guided Expansion Bearings:
1.Guided expansion bearings shall allow rotation and longitudinal movement, but transve rse movement shall be restricted.
2.Guided expansion bearings shall consist of an elastomeric rotational element, confined and sealed by a piston and steel base pot.
3.To allow longitudinal movement, the upper surface of the steel piston shall be faced with a pol ytetrafluorethylene (PTFE) sheet and support a sliding steel top bearing plate.
4.The mating surface of the sliding steel bearing plate shall be faced with polished stainless steel.
5.Guided expansion bearings shall be designed to resist a transverse load of 10% of the rated capacity of the device.
6.To restrict transverse movement, either a guide bar or keyway system shall be used.
7.The guide bar or keyway systems and their mating steel surfaces shall be faced with strips of filled or unfill ed PTFE, per AASHTO specifications, and stainless steel.
c.Non-guided Expansion Bearings: (1) Non-guided expansion bear ings shall allow rotation and longitudinal and transverse movement in the bearing plane.
Source: Nebraska Standard Specifications for Highway Construction, 2017 Edition. Pages 607–609 of 1,048.