SECTION 907 – BEARING ASSEMBLIES
907.01 Structural Bearing Assemblies
907.01.01 General Requirements
Provide high-load multi-rotational (HLMR) or seismic isolation bearing assemblies conforming to the loads shown on the Plans. Provide the design from the manufacturer for each HLMR or seismic isolation bearing assembly. Ensure that the materials and fabrication o f bridge bearing assemblies conform to Section 18 of the AASHTO LRFD Bridge Construction Specifications. Ensure that the fabricating plant is certified under the AISC Quality Certification for Simp le Steel Bridge Structures . Consider steel bridge bearings and HLMR bearing assemblies to be main load carrying members. Perform welding and ensure that welders are qualified according to the ANSI/AASHTO/AWS D1.5 Bridge Welding Code. Unless otherwise specified, provide hot -dipped galvanized steel bearing compone nts as specified in 912.02.01. When painting of steel surfaces is required, paint as specified in 906.06.
907.01.02 Types
A.High-Load Multi-Rotational (HLMR) Bearing Assemblies. HLMR bearings consist of a rotational element of the pot type, disc type, or spherical type when used as a fixed bearing and that may, in addition, have sliding surfaces to accommodate translation when used as an expansion bearing. The Contractor may use g uide bars to constrain translation to a specified direction. Fabricate HLMR bearing assemblies according to Section 18 of the AASHTO LRFD Bridge Construction Specifications.
B.Seismic Isolation Bearing Assemblies.
1.Assembly Requirements. Use seismic isolation bearing assemblies consisting of seismic isolation bearing s (isolators), sole plates, masonry plates, mounting plates, lead core, steel shims, bolts, washers, and anchor bolts. Fabricate seismic isolation assemblies according to Section 18 of the AASHTO LRFD Bridge Construction Specifications. Use one of the following types of isolation bearing assemblies:
a.Elastomeric Type. The isolator consists of alternate layers of natural rubber and steel plates with a preformed hole at the center of the unit filled tight with a pure lead plug core. For the isolator, use elastomer type NR, Grade 3, according to ASTM D 4014. Use lead for t he core that is a minimum of 99 percent pure.
b.Sliding Type. The isolator consists of polytetrafluoroethylene (PTFE) stainless steel surfaces that are to be used in conjunction with an optional spring/damping assembly. Use polyether urethane for the elastomer of the sliding bearing.
2.Testing Requirements. Provide the ME with the required test load for each isolator type. Determine the test load for each isolator type from the maximum design dead load plus the live load that is to be applied to that particular isolator type. Identify all isolator test results by the supplier identification number. During the compression and combined compression/shear tests on completed isolators, closely inspect each isolator for indications of a lack of rubber to steel bond, laminate placements fau lts, or for the appea rance of 3 or more separate surface cracks that are wider or deeper than 1/16 inch. Do not use isolators showing such indications. Evaluate the results of each isolator test for the following performance requirements:
1.The effective stiffness (Keff) falling within a range of ±15 percent of the predicted value.
2.The slope of the loading curve (K) being greater than or equal to 90 percent of the predicted value.
3.The average value of energy dissipated per cycle being greater than or equal to 90 percent of the predicted value.
3.Certification. Submit certifications of compliance, as specified in 106.07, for the isolators . Submit the following data for acceptance of the isolators:
1.Test results as defined in the AASHTO Guide Specifications for Seismic Isolation Design.
2.Copy of the manufacturing specifications.
3.The name of the firm manufacturing the system.
4.Shake table test results demonstrating viability of the complete system.
5.Analytical results showing maximum seismic forces and displacements at all locations, according to the AASHTO Guide Specifications for Seismic Isolation Design.
6.Conformance to the design and construction requirements specified in Section 14 of the AASHTO LRFD Bridge Design Specifications and Section 18 of the AASHTO LRFD Bridge Construction Specifications.
907.01.03 Marking, Packaging, Shipping, and Handling
Mark each structural bearing in indelible ink on 2 sides with the Department Project number, the structure number, location, orientation, order number, lot number, bearing identification number, and elastomer type and grade. For seismic isolation bearings, make a permanent mark on 2 of the 4 sides of each isolator, consisting of an isolator number specified by the supplier, the date of fabrication (month and year), the isolator type, and the supplier (name and address). Ensure that the bearings are packaged to be protected against damage from handling, shipping, and storage. Securely bolt, strap, or otherwise fasten to prevent all relative movement. Wrap the bearings in moisture resistant and dust resistant material to protect them from weather. When providing seismic isolation bearing assemblies, assemble the isolators and their mounting plates at the shop. Provide temporary assembly ties so that the entire assembly is shipped, in protective packaging, as a unit. Provide th e RE with elastomeric bearing test results for both compression stiffness and combined compression and shear according to Section 15 of the AASHTO Guide Specifications for Seismic Isolation Design. Enclose a copy of the materials, fabrication, and testing compliance certifications with each shipment. Supply a separate sheet showing the materials, critical dimensions, and clearances for each bearing.
907.01.04 Quality Control and Acceptance
Notify the ME, in writing, at least 21 days before the start of fabrication, so that arrangements for inspection may be made. Ensure that quality control inspectors are AWS Certified Welding Inspectors, qualified according to the provisions of AWS QC1. Test and inspect structural bearing assemblies according to Sectio n 18 of the AASHTO LRFD Bridge Construction Specifications. Provide test results to the ME at the time of inspection. Provide to the ME certifications of compliance, as specified in 106.07, for all non-ferrous metals, PTFE, adhesives, dowel bars, and bolts. Include with the certifications mill test reports for all steels used and material test reports for all elastomeric components.
907.02 Reinforced Elastomeric Bearing Assemblies
Provide reinforced elastomeric bearings conforming to the requirements shown on the Plans. Reinforced elastomeric bearing assemblies consist of circular or rectangular reinforced elastomeric bearings that are Grade 3 with a durometer hardness of 60. Fabr icate reinforced elastomeric bearing assemblies according to Section 18 of the AASHTO LRFD Bridge Construction Specifications. Ensure that the materials and fabrication of bridge bearing assemblies conform to Section 18 of the AASHTO LRFD Bridge Construction Specifications. Enclose a copy of the materials, fabrication, and testing compliance certifications with each shipment. Supply a separate sheet showing the materials, critical dimensions, and clearances for each bearing. Provide to the ME certifications of compliance, as specified in 106.07. Include material test reports.
907.03 Bearing Pads
Provide elastomeric pads conforming to the requirements shown on the Plans. Provide elastomeric bearing pads that are a Grade 2 with a durometer hardness of 60 according to Section 18.2 of the AASHTO LRFD Bridge Construction Specifications.
Referenced in this section
Bearing Assemblies in other states
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Source: Standard Specifications for Road and Bridge Construction, 2019 (rev. 2022-12-21) Edition. Pages 505–506 of 651. View official source ↗