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From page 447... ... 445 10.1 introduction Bearings are a critical element within overall bridge systems. Although they represent only a small part of the overall structure cost, they can potentially cause significant problems if they function improperly or if possible maintenance, retrofit, or replacement strategies are not envisioned and well planned at the design stage. Read the entire page →
From page 448... ... 446 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 10.2.1 Elastomeric Bearings: Plain and Reinforced Elastomeric bearings have become the most common type of bearing in recent years because of their desirable performance characteristics, durability, low maintenance requirements, and relative economy. Elastomeric bearings have no moveable parts. Read the entire page →
From page 449... ... 447 Chapter 10. BRiDGE BEARiNGS Figure 10.1. Read the entire page →
From page 450... ... 448 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 10.2.3 Sliding Bearings 10.2.3.1 Polytetrafluorethylene When horizontal movements become too large for elastomeric bearings to reasonably accommodate in shear, PTFE sliding surfaces can be used to provide additional capacity (see Figure 10.2) Read the entire page →
From page 451... ... 449 Chapter 10. BRiDGE BEARiNGS Sliding surfaces develop a frictional force that acts on the superstructure, substructure, and bearing. Read the entire page →
From page 452... ... 450 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE and unlubricated MSM and plain PTFE specimens at high movement rates. Unlubricated specimen tests showed MSM to have significantly greater wear resistance than plain PTFE, but with a greater coefficient of friction. Read the entire page →
From page 453... ... 451 Chapter 10. BRiDGE BEARiNGS Figure 10.3. Read the entire page →
From page 454... ... 452 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Disc bearings are reasonably economical, but widespread use has been limited because of their originally patented and proprietary status, which made them available only from a single source. Now that there are additional bearing manufacturers that can supply disc bearings, their use has increased. Read the entire page →
From page 455... ... 453 Chapter 10. BRiDGE BEARiNGS 10.2.4.3 Spherical and Cylindrical Bearings Spherical bearings are used primarily for accommodating large rotations about multiple or unknown axes. Read the entire page →
From page 456... ... 454 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Figure 10.7. Fabricated steel bearings with rocker expansion and fixed conditions. Read the entire page →
From page 457... ... 455 Chapter 10. BRiDGE BEARiNGS Figure 10.8. Read the entire page →
From page 458... ... 456 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Deﬁciency of Bridge System–Related Items Due to Production/ Operation Defects Leaking Deck Joints Inadequate Inspectability Improper Bearing Orientation Inadequate Replaceability Figure 10.9. Bridge system–related deficiencies. Read the entire page →
From page 459... ... 457 Chapter 10. BRiDGE BEARiNGS Bridges wider than three lanes can experience significant transverse thermal movement. Read the entire page →
From page 460... ... 458 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Due to Loads Traﬃc-Induced Loads SystemDependent Loads Element Wear/ Fatigue Element Overload Figure 10.10. Load-related factors affecting service life. Read the entire page →
From page 461... ... 459 Chapter 10. BRiDGE BEARiNGS 10.3.1.2.2 Bearing Deficiency Due to Natural or Man-Made Hazards Figure 10.11 illustrates factors affecting service life due to natural or man-made hazards. Read the entire page →
From page 462... ... 460 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Figure 10.12. Production and operation defects affecting service life. Read the entire page →
From page 463... ... 461 Chapter 10. BRiDGE BEARiNGS of these parameters at the design stage can result in bearings that are subject to excessive rotation, higher stresses, greater wear, and, ultimately, reduced service life. Read the entire page →
From page 464... ... 462 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 10.3.2.1.1 Improper Design In rare occurrences, improper design has led to overloaded pads or pads subjected to excessive lateral movement, causing excessive bulging, splitting, or delamination. The following paragraphs describe various potential failure modes and other issues with elastomeric bearings and how they are addressed within current AASHTO design provisions. Read the entire page →
From page 465... ... 463 Chapter 10. BRiDGE BEARiNGS updated (2010b) Read the entire page →
From page 466... ... 464 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE process. Section 14.7.5.3.5 of the LRFD specifications provides requirements for the thickness of steel reinforcement and considers both strength and fatigue. Read the entire page →
From page 467... ... 465 Chapter 10. BRiDGE BEARiNGS CDP thickness. Read the entire page →
From page 468... ... 466 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Thus, plain PTFE should not be used as a sliding surface for bearings subject to relatively high sliding speeds and low temperatures. Relatively thin layers of PTFE, from 1/16 to 3/16 in., are commonly used in the United States, but engineers in other countries often use thicker PTFE layers to accommodate wear. Read the entire page →
From page 469... ... 467 Chapter 10. BRiDGE BEARiNGS • The thickness of the elastomeric pad also affects rotational capacity. Read the entire page →
From page 470... ... 468 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Currently, both circular cross-section and flat brass rings are permitted in the specifications. Current design and manufacturing in accordance with the LRFD specifications have greatly resolved past issues with sealing rings and leakage of elastomer. Read the entire page →
From page 471... ... 469 Chapter 10. BRiDGE BEARiNGS 10.3.2.6 High-Load Multirotation Spherical Bearings Although a very robust system, HLMR spherical bearings have had service life problems, most often associated with production or operation defects relating to design and manufacturing. Read the entire page →
From page 472... ... 470 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Corroded expansion bearings can lock up or freeze, subjecting beams and the substructure elements below to additional load and potential damage. Read the entire page →
From page 473... ... 471 Chapter 10. BRiDGE BEARiNGS 10.3.2.7.3 Production and Operation Defects Lack of maintenance has been a contributing factor to reduced service life for steel bearings in many instances. Read the entire page →
From page 474... ... 472 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE tABLE 10.2. SoLutionS For Service LiFe ProbLemS cAuSed by bridge SyStem–reLAted deFiciencieS: ALL beAring tyPeS Service Life Problem Solution Advantages Disadvantages Leaking deck joints (Bridge systems with deck joints can have deterioration of bridge elements below deck caused by drainage through leaking deck joints carrying deicing salts and other debris.) Read the entire page →
From page 475... ... 473 Chapter 10. BRiDGE BEARiNGS or operational defects and, more specifically, due to design and details of components within the overall bridge system. Read the entire page →
From page 476... ... 474 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE • Continuous superstructure systems that avoid or minimize the number of deck joints include fully continuous, continuous for live load, or continuous deck slabs (link slabs) Read the entire page →
From page 477... ... 475 Chapter 10. BRiDGE BEARiNGS • For large skew bridges, one approximate solution is to consider the major axis of thermal movement along the diagonal from the acute deck corners caused by thermal movement of the bridge deck. Read the entire page →
From page 478... ... 476 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE can be cut, but doing so requires equipment that may be cumbersome in the space available. Grinding may also be needed to produce a surface flat enough for installing the new bearing. Read the entire page →
From page 479... ... 477 Chapter 10. BRiDGE BEARiNGS for calculating live load rotations, and the Guide was developed according to the methods used in several states. Read the entire page →
From page 480... ... 478 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 10.4.2.1.1 Improper Element Design Resulting in Excessive Shear Deformation and Excessive Bulging, Splitting, or Delamination Excessive bulging, splitting, or delamination can be avoided by following recent provisions (2010) in the LRFD specifications for either Method A or B Read the entire page →
From page 481... ... 479 Chapter 10. BRiDGE BEARiNGS surface offers a practical solution. Read the entire page →
From page 482... ... 480 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE tABLE 10.4. SoLutionS For Service LiFe ProbLemS: cdPS Service Life Problem Solution Advantages Disadvantages Improper pad design resulting in interlayer splitting and delamination Avoid with proper design, manufacturing, and installation. Read the entire page →
From page 483... ... 481 Chapter 10. BRiDGE BEARiNGS 10.4.2.3.1 PTFE Wear Due to Cyclic Truck Load As mentioned throughout this section, the use of higher-wear-resistant sliding surface materials is recommended, when possible, when surfaces are subject to the fast sliding speeds associated with cyclic truck load. Read the entire page →
From page 484... ... 482 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE • Dimpled and lubricated PTFE has been shown to provide both improved wear resistance and reduced coefficient of friction; however, the long-term effectiveness of lubrication is uncertain. • Woven or glass-filled PTFE greatly improves wear resistance, but it has a higher coefficient of friction. Read the entire page →
From page 485... ... 483 Chapter 10. BRiDGE BEARiNGS 10.4.2.4.1 Improper Design and Manufacturing Causing Various Deficiencies Various recommendations by Stanton et al. Read the entire page →
From page 486... ... 484 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE increased damage under cyclic rotation. In highly corrosive environments, stainless steel should be considered, but this affects cost greatly. Read the entire page →
From page 487... ... 485 Chapter 10. BRiDGE BEARiNGS 10.4.2.5.1 Improper Design and Manufacturing Causing Fatigue, Abrasion, and Overrotation Various performance conclusions and recommendations were made by Stanton et al. Read the entire page →
From page 488... ... 486 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 10.4.2.6 High-Load Multirotation Spherical and Cylindrical Bearings Table 10.8 summarizes solutions for various service life issues identified in Section 10.3.2.6 for HLMR spherical and cylindrical bearings. Issues have most often been related to production or operation defects relating to design and manufacturing. Read the entire page →
From page 489... ... 487 Chapter 10. BRiDGE BEARiNGS 10.4.2.6.4 Load-Induced Sliding Surface Wear PTFE sliding surfaces are subject to wear from truck loads or thermal loads. Read the entire page →
From page 490... ... 488 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 10.4.2.7.2 Corrosive Environment For bearings in corrosive environments, the use of stainless steel can avoid the potential of corrosion on exposed surfaces and on contact surfaces. Galvanizing, metalizing, or high-performance paint systems can serve to mitigate the potential for surface corrosion, but a maintenance plan for the longer term will still be required. Read the entire page →
From page 491... ... 489 Chapter 10. BRiDGE BEARiNGS long-term data collection regarding bearing performance will be necessary for developing more accurate service life predictions. Read the entire page →
From page 492... ... 490 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Figure 10.19. Process flowchart for bearing selection and design for service life. Read the entire page →
From page 493... ... 491 Chapter 10. BRiDGE BEARiNGS Table 10.10 provides a format for identifying various demand requirements, and Steps 1.1 to 1.4 summarize the process. Read the entire page →
From page 494... ... 492 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE tA B LE 1 0 .1 0 . Read the entire page →
From page 495... ... 493 Chapter 10. Read the entire page →
From page 496... ... 494 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Step 2. Identify Suitable Bearing Options The options step involves comparing demand requirements with supply parameters for various bearing types and determining which types are suitable. Read the entire page →
From page 497... ... 495 Chapter 10. Read the entire page →
From page 498... ... 496 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE B ea ri n g Ty p e Lo ad a n d M o ve m en t P er fo rm an ce V al u es D u ra b il it y Fa ct o rs Avoidance or Mitigation Requirements Li fe -C yc le C o st s Service Life Potential Load (kips) Rotation (radians) Read the entire page →
From page 499... ... 497 Chapter 10. BRiDGE BEARiNGS B ea ri n g Ty p e Lo ad a n d M o ve m en t P er fo rm an ce V al u es D u ra b il it y Fa ct o rs Avoidance or Mitigation Requirements Li fe -C yc le C o st s Service Life Potential Load (kips) Read the entire page →
From page 500... ... 498 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE The following steps summarize the process for evaluating service life requirements: Step 3.1. For potential bearing alternatives, evaluate factors affecting service life and identify required avoidance, mitigation, or acceptance options. Read the entire page →
From page 501... ... 499 Chapter 10. BRiDGE BEARiNGS It is recommended that bridge inspections and inspection data collection for bearings be expanded to identify bearing types, specific conditions, and other relevant data. Read the entire page →
From page 502... ... 500 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE • Elastomeric bearings should be checked for – Overrotation; – Excessive shear deformation; – Splitting or tearing; – Excessive bulging; and – Sliding or walking out. • PTFE and stainless steel surfaces should be checked for – PTFE fragments indicating wear; – Migration of PTFE surface; – Scratching, paint, or other contamination (exposed stainless steel surfaces) Read the entire page →
From page 503... ... 501 Chapter 10. BRiDGE BEARiNGS actual longitudinal bearing movements caused by girder end rotations under traffic load could be useful in understanding and predicting the service life of sliding surfaces. Read the entire page →

From page 447...

... 445 10.1 introduction Bearings are a critical element within overall bridge systems. Although they represent only a small part of the overall structure cost, they can potentially cause significant problems if they function improperly or if possible maintenance, retrofit, or replacement strategies are not envisioned and well planned at the design stage.