Standard Specifications and Code of Practice for Road Bridges, Section IX — Bearings, Part I: Metallic Bearings

IRC 83 - Scope Summary

The Scope section (Clause 1) of IRC 83 defines the applicability of the code to design, material specification, manufacture, and installation of bridge bearings, including:

• Types covered: Fixed, guided, rocker, elastomeric, and sliding bearings (PTFE/UHMWPE sliding surfaces).
• Materials: Concrete, steel, PTFE (Polytetrafluoroethylene), UHMWPE (Ultra High Molecular Weight Polyethylene), composite materials.
• Loads considered: Vertical loads, horizontal forces, rotations, creep effects.
• Design conditions: Ultimate Limit State (ULS) and Serviceability Limit State (SLS).
• Key parameters:
  • Modulus of elasticity: Concrete (0.5 E), Steel (210000 MPa)
  • Friction coefficients (μ): e.g., 0.4 for steel on steel, 0.6 for steel on concrete.
  • Safety factors (Ym, Yms) for materials and sliding surfaces.
  • Dimensions and geometry parameters for sliding surfaces and restraining rings.

Key Formulas & Parameters

Reference Tables & Annexures

• Annexure A: Properties of PTFE/UHMWPE sliding materials.
• Annexure E: Anchorage design rules.
• Annexure F: Permissible stresses on adjacent concrete.

flowchart LR
    A[Scope: Bridge Bearings] --> B[Material Specification]
    A --> C[Design Requirements]
    A

IRC 83 - Terms and Definitions: Key Points

1. Basic Definitions:

• Top/Bottom Steel Plates: Interface plates with concrete/steel structure.
• Sliding Surface: Hard, smooth surface (stainless steel, chrome-plated) sliding against PTFE/UHMWPE.
• Sliding Interface: Combination of sliding and mating surfaces enabling low-friction movement.
• Projection: Metallic part locking bearing movement perpendicular to sliding.

2. Materials:

• PTFE: Polytetrafluoroethylene, low friction sliding material.
• UHMWPE: Ultra High Molecular Weight Polyethylene, similar use as PTFE.

3. Key Symbols & Notations:

4. Important Relationships:

• Reduced Contact Area: [ A_r = A \times c ] where (c) is a coefficient to account for reduced contact area due to deformation.

• Sliding Resistance: [ F = \mu \times N ] where (N) is the normal load on the sliding surface.

• Modulus of Elasticity for Permanent Loads: [ E_{concrete, perm} = 0.5 \times E_{concrete} ]

5. Approvals:

• Only internationally

IRC 83 - Design Requirements Key Points

1. Material Properties

• Modulus of Elasticity:
  • Concrete (permanent load): ( E_c = 0.5 \times E )
  • Steel: ( E_s = 210,000 , \text{MPa} )
• Strength Parameters:
  • ( f_{fl} ): Characteristic compressive strength of sliding surface (PTFE/UHMWPE)
  • ( f_y ): Specified minimum yield strength of steel
  • Tensile strength as per material specs

2. Sliding Surface & Bearing Dimensions

• Reference diameter: 300 mm (flat/projected concave sliding surface)
• Length of sliding surface strip: ( L_S )
• Length of guide bar: ( L_x )
• Thickness:
  • Backing plate thickness ( t_b )
  • Restraining ring depth ( h_{rr} )
• Radius of curvature:
  • Curved sliding surface ( r )
  • Contact surface with restraining ring ( r_{rr} )

3. Forces & Loadings

• Horizontal force ( F_h )
• Design load/force:
  • Ultimate Limit State (ULS): ( F_{ULS} )
  • Serviceability Limit State (SLS): ( F_{SLS} )
• Force lever arms:
  • Restricting ring lever arm (Fig. 6)
  • Guide bar lever arm (Fig. 8)

4. Friction & Anchorage

• Coefficient of friction:
  • Primary sliding surface ( \mu )
  • Secondary sliding surface ( \mu_s )
  • Bearing-substrate ( \mu_K = 0.4 ) (steel on steel), ( 0.6 ) (steel on concrete)
• Total sliding resistance: [ R_{total} = R_{anchorage} + \mu \times N ]
• Design anchorage resistance in shear

5. Safety Factors

• Partial safety factor for sliding: ( Y_{ms} )
• Partial safety factor for materials: ( Y_m )
• Weld correlation factor: 0.9

Useful Formula Summary

| Parameter | Symbol | Typical

IRC 83: Materials and Corrosion Protection Key Points

Corrosion Protection System (Clause 4.10, 5.5, 6.9)

• Use protective coating per ISO 12944 standards.
• Durability & Corrosivity Categories (ISO 12944-5:2007):

Special Cases

• Stainless steel sheets welded continuously to backing plates: backing plate behind sheet needs cleaning but no full coating.
• Stainless steel sheets attached by screws/rivets: full corrosion protection on backing plate required.
• Bolts, fasteners, washers: adequate corrosion protection mandatory.
• Sliding surfaces: use removable protective devices (wiper seals, rubber aprons).

Maintenance

• Inspect coatings regularly.
• If corrosion found, wire brush rust + reapply coating immediately.

Protective Coating Thickness (Typical)

flowchart TD
    A[Steel Surface] --> B{Attachment Type}
    B -->|Continuous Weld| C[Clean backing plate; no full coating]
    B -->|Screws/Rivets| D[Full corrosion protection on backing plate]
    A --> E[Bolts/Fasteners]
    E --> F[Adequate corrosion protection]
    A --> G[Sliding Surfaces]
    G --> H[Install removable wiper seals/rubber aprons]

Summary: Follow ISO 12944 coating systems tailored to site corrosivity; ensure full protection on exposed steel except welded backing plates; maintain and inspect

Design Verification for Sliding Surfaces (IRC 83 - Clause 5.4 & 6.3)

1. Curved Sliding Surface Capacity Check

The horizontal force capacity ( V ) resisted by the curved sliding surface must satisfy:

[ V \leq T_T \times 12 \times O_{gs} \times \sin^2(\theta - \beta - \alpha_d) \times \sin \beta \times \sigma_{xy,sk} ]

Where:

• ( V ) = Resultant horizontal force in SLS
• ( T_T ) = Thickness factor or a constant (context-specific)
• ( O_{gs} ) = Projected area of the curved sliding surface (perpendicular to rotation axis)
• ( \theta = \sin^{-1} \left(\frac{L}{2r}\right) ) (semi-angle subtended by the curved surface)
• ( \beta = \tan^{-1} \left(\frac{V}{N}\right) ) (angle between vertical and resultant load)
• ( \alpha_d ) = Maximum design rotation in ULS
• ( \sigma_{xy,sk} ) = Maximum average contact stress permitted on the sliding surface
• ( r ) = Radius of curvature
• ( N ) = Permanent vertical load in SLS

2. Thickness and Protrusion (Clause 6.3, Table 7)

• ( L ) = Diameter of the projected sliding surface area (mm)

3. Material & Design Parameters

• Friction coefficients:
  • Steel on steel: ( \mu = 0.4 )
  • Steel on concrete

IRC 83: Dimensional Limitations & Tolerances for Steel Bearings

1. Dimensional Tolerances (Table 5)

2. Curved Backing Plate (Clause 6.2)

• Minimum thickness: 12 mm
• Minimum side space on radius: 20 mm
• Recess shoulders: Sharp, square edges; root radius ≤ 1 mm
• Sliding surface fit tolerance (Table 6):

• Surface flatness deviation (Az): ≤ max(0.0003 × d, 0.2 mm)
• Protrusion tolerance (h): ±0.2 mm (L ≤ 750 mm), ±0.3 mm (L > 750 mm)
• Sliding surface sheet thickness tolerance:
  • Diameter < 750 mm: +0.3 / -0.0 mm
  • Diameter ≥ 750 mm: +0.5 / -0.0 mm

3. Sliding Surface Sheets

• Circular, may be subdivided into:
  • Disc: ≥ 1000 mm diameter
  • Annulus: Width ≥ 50 mm, subdivided into max 4 equal segments
• Separating ring width ≤ 10 mm

IRC 83: Guide Bars and Restraining Rings Key Points

1. Design & Construction

• Monolithic construction of restraining rings and guide bars with the parent component is preferred to ensure strength and reduce complexity.
• If monolithic construction is impractical (due to size, cost, or material wastage), welded connections are allowed under strict conditions:
  • Positioning & locking via tongue and groove machining or Allen-key bolts.
  • Continuous welding on all sides to resist horizontal forces (see Fig. 14).
  • Weld size must be designed for combined effects: shear, bending, tension.

2. Weld Design Check (Clause 5.4.1.7)

For fillet welds connecting restraining rings to base plates:

[ \text{Weld strength} \leq \frac{f_y}{B} \times 13 \times Y_m ]

• (f_y): Yield strength of weld material
• (B): Width of weld throat
• (Y_m): Material safety factor

3. Guide Bars (Clause 5.5.3)

• When monolithically constructed, guide bars must satisfy structural expressions for strength under horizontal forces (refer to Clause 5.5.3 for detailed formulas).

4. Quality Requirements

• Welded restraining rings must be fabricated by certified manufacturers (EN 1090-2 / ISO 3834-2 / AISC).

Summary Diagram: Guide Bar Weld Connection

graph LR
A[Parent Component] -- Tongue & Groove --> B[Restraining Ring/Guide Bar]
B -- Locked by --> C[Allen-key Bolts]
B -- Welded Continuously --> A

Note: Always verify weld sizes and dimensions per applied loads and combined stress modes for safety and durability.

IRC 83 - Stress Verification & Load Calculations for Sliding Surfaces

1. Compressive Stress Verification (Clause 5.4.2)

Verify under ultimate limit state (ULS):

[ N_{sd, max} \leq k \cdot A^* \cdot f_k / \gamma_m ]

• (N_{sd, max}): Design axial force at ULS
• (f_k): Characteristic compressive strength (Table 1)
• (\gamma_m = 1.4): Partial safety factor for materials
• (k): Reduction factor (Clause 4.3)
• (A^* = A \cdot \eta): Reduced contact area
• (A): Contact area (flat or projected curved surface)
• (\eta = 1 - 0.75 \cdot \frac{e}{L}): Coefficient for eccentricity (e) and length (L)

2. Contact Area for Curved Sliding Surface

[ A = \frac{\pi L^2}{4} ]

• (L): Projected length of sliding surface (Fig. 5)

3. Horizontal Force Capacity (Curved Sliding Surface, Clause 5.4)

[ V \leq \pi \times L^2 \times \sigma_{sk} \times \sin^2(\theta - B - \alpha_d) \times \sin B ]

• (V): Resultant horizontal force (SLS)
• (\sigma_{sk}): Max average contact stress permitted
• (\theta = \sin^{-1}\left(\frac{L}{2r}\right)): Semi-angle of curved surface
• (B): Angle between vertical and resultant load
• (\alpha_d): Max design rotation (ULS)
• (r): Radius of curvature

4. Material Properties

Welding and Fabrication Standards - IRC 83 Key Points

• Welding Codes:

  • Follow IS:816 and IS:9595 for welding procedures.
  • Use electrodes as per IS:814 (suitable grade).
  • Preheating and post-weld stress relieving are mandatory when necessary.

• Backing Plate:

  • Must extend beyond Stainless Steel sheet edges to accommodate welds.
  • TIG welding is recommended for Stainless Steel sheets.

• Material Properties:

  Property	Value/Note
  Modulus of Elasticity (E)	210,000 MPa
  Min. Yield Strength (f_y)	As per steel grade
  Min. Tensile Strength (f_t)	As per steel grade
  Weld Co-relation Factor (u)	0.9
  Partial Safety Factor (W)	As per design requirements

• Effective Weld Size (a):

  • Takes throat thickness into account, critical for strength calculations.

• Typical Weld Connection Types:
  Refer Fig. 7 (IRC 83) for restraining ring to base plate weld types.

Typical Weld Strength Formula:

[ F_w = u \times f_y \times A_w ]

Where:

• (F_w) = Weld strength
• (u = 0.9) (correlation factor)
• (f_y) = Yield strength of base metal (MPa)
• (A_w) = Effective weld area (mm²)

Notations Summary:

flowchart LR
    A[Steel Plate] -->|Weld| B[Backing Plate]
    B -->|Support| C[Base Plate]
    C -->|Load Transfer| D[Restraining Ring]
    style A fill:#f9f,stroke

IRC 83: Lubricants for Bearings (Clause 4.8)

Key Requirements for Lubricants:

• Must reduce friction and wear of low friction sliding materials (PTFE/UHMWPE).
• Properties must be retained over the service temperature range.
• Silicon Grease properties should comply with IS: 14383.

Table 3: Physical & Chemical Properties of Lubricants

Maintenance & Inspection Highlights (Clause 9.2)

• Bearings should be virtually maintenance-free.
• Keep bearing surroundings clean and dry.
• Inspect annually for first 5 years, then every 2 years.
• Inspect movement, dimensions, corrosion, locked conditions.
• Record and classify inspection results for action.

Summary Diagram of Lubrication & Maintenance Process

flowchart TD
    A[Lubricant Selection] --> B{Properties Check}
    B -->|Meets Table 3| C[Apply Lubricant]
    B -->|Fails| D[Select Alternative Lubricant]
    C --> E[Install Bearing]
    E --> F[Periodic Inspection]
    F --> G{Condition Assessment}
    G -->|Good| H[Continue Service]
    G -->|Minor Issues| I[Clean & Re-lubricate]
    G -->|Major Issues| J[Repair or Replace Bearing]

Note: Always refer to IS: 14383 for Silicon Grease specifics and ensure lubricant compatibility with bearing sliding materials (PTFE/UHMWPE).

IRC 83: Anchorage Design Rules Key Points

1. Anchorage Arrangement (Clause 4.9, 5.7)

• Bearings must be positively anchored using bolts, dowels, headed studs, or steel plates.
• Anchorage must resist sliding under horizontal forces at Ultimate Limit State (ULS).
• In seismic zones IV & V, friction is ignored (μ = 0) due to dynamic load fluctuations.

2. Design Verification (Clause 1.25)

• Design horizontal force at ULS:

[ V_{pd} = n \times C_1 \times f_u \times A / \gamma_m ]

Where:

• (V_{pd}) = Design horizontal force

• (n) = Number of anchors

• (C_1) = Coefficient (depends on anchor type)

• (f_u) = Ultimate tensile strength of anchor material

• (A) = Cross-sectional area of anchor

• (\gamma_m) = Partial safety factor

• Total resistance to sliding:

[ R = V_{pd} + \mu \times P_k ]

Where:

• (\mu) = Friction coefficient (0.4 steel-steel, 0.6 steel-concrete)
• (P_k) = Minimum vertical load at ULS acting on bearing

Summary Table: Friction Coefficients (μ)

flowchart LR
    A[Horizontal Force on Bearing] --> B[Anchorage System]
    B --> C{Resistance}
    C --> D[Anchor Strength (n*C1*fu*A/γm)]
    C --> E[Friction (μ*Pk)]
    style E stroke:#f66,stroke-width:2px
    note right of E: Ignored in seismic zones IV & V

Ensure anchorage design accounts for both anchor capacity and friction unless seismic conditions apply.

IRC 83: Service Life & Operating Conditions - Key Points

Service Life:

• PTFE bearings: ~30 years
• UHMWPE bearings: ~50 years
• Operating temperature range: -15°C to +50°C

Reduction Factor for Creep Effects (k):
Used to reduce characteristic compressive strength for long-term loads.

Modulus of Elasticity:

• Concrete (permanent load): ( 0.5 E_c )
• Steel: ( 210,000 , \text{MPa} )

Maintenance & Inspection Summary (Clause 9.2)

• Bearings designed for virtually maintenance-free operation.
• Keep bearings clean and dry.
• Inspect yearly for first 5 years; then every 2 years or as agreed.
• Inspect after unusual events (earthquakes, floods, etc.).
• Inspection elements:
  • Measure movement (compare with design values).
  • Measure dimensions.
  • Check for locked/jammed parts.
  • Check corrosion; clean & coat if needed.
  • Inspect adjacent structure.

Formula for Design Strength Reduction due to Creep

[ f_{design} = k \times f_x ] where ( k ) = reduction factor for creep effects, ( f_x ) = characteristic compressive strength.

flowchart TD
    A[Service Life] --> B[PTFE: 30 years]
    A --> C[UHMWPE: 50 years]
    D[Operating Temp] --> E[-15°C to +50°C]
    F[Inspection] --> G[Yearly for 5 years]
    F --> H[Every 2 years after]
    F --> I[After unusual events]

References: IRC 83-2014 Clause 4.3, Clause 9.2, Table 1.

IRC 83: Approval Documents and Certification

Key Points from Clause 7.7 - Certification

• The Approving/Accepting Authority issues a Certificate of Conformity after verifying product quality.
• The certificate confirms compliance with IRC 83 specifications.
• Only after certification, the manufacturer is permitted to ship bearings to the site.

Important Specifications

• Certification ensures product meets:
  • Material standards (Clause 4)
  • Design requirements (Clause 5)
  • Manufacturing quality (Clause 6)
• Certification includes marking and acceptance as per Clause 7.

Recommended Documentation

• Certificate of Conformity should state:
  • Product identification
  • Compliance with IRC 83
  • Date and authority signature

Summary Table: Certification Process

For detailed design and testing parameters, refer to Annexures A-F in IRC 83.

flowchart LR
    A[Manufacturing] --> B[Quality Inspection]
    B --> C{Satisfactory?}
    C -- Yes --> D[Certificate of Conformity Issued]
    C -- No --> E[Rework/Reject]
    D --> F[Shipment Clearance]
    F --> G[Site Installation]

This ensures traceability and compliance for bridge bearing products.

IRC 83 Annexure-E: Bearings Anchorage Design Rules - Key Points

1. Anchorage Types

• Bolts passing through bearing components anchored to:
  • Dowels (IS 2062 Grade E250 min)
  • Headed stud connectors (ISO 13918 SD1/SD2)
  • Steel distribution plates embedded in concrete
  • Intermediate steel plates welded to adjoining steel structures

2. Design Verification (Clause 5.7)

• Check anchorage safety against sliding under horizontal forces at the Ultimate Limit State (ULS).
• For seismic zones IV & V, do not consider friction (take friction coefficient, μ = 0).

3. Bolt Specifications (Clause 8.8)

• Use bolts of property class 8.8 or 10.9 (IS 1367).
• Steel dowels: Rolled steel, IS 2062 Grade E250 minimum.
• Headed studs: ISO 13918 SD1/SD2.

4. Design Formula (Typical Sliding Check)

[ \text{Sliding resistance} = \mu \times N + \sum F_{\text{anchor}} ] Where:

• ( \mu ) = friction coefficient (0 in seismic zones IV & V)
• ( N ) = normal force on bearing
• ( \sum F_{\text{anchor}} ) = sum of anchorage forces resisting sliding

Summary Table: Anchorage Material & Properties

flowchart LR
    A[Bearing Component] --> B[Bolts]
    B --> C[Dowels / Headed Studs]
    B --> D[Steel Distribution Plates]
    C & D --> E[Anchorage in Concrete/Steel Structure]
    E --> F[Resistance to Sliding Forces]

This ensures positive anchorage and safety against horizontal sliding forces per IRC 83 Annexure-E

IRC 83 (2014) Key References & Specifications Summary

Key Terms & Symbols (Clause 3.2)

• E (Concrete): Modulus of elasticity for concrete (short-term) ≈ 5000√fck (MPa)
• E (Steel): Modulus of elasticity = 210,000 MPa
• f_fl_k: Characteristic compressive strength of sliding surface (PTFE/UHMWPE)
• f_y: Specified minimum yield strength of material
• μ: Coefficient of friction (typical steel on steel = 0.4; steel on concrete = 0.6)
• A: Geometrical or projected sliding surface area
• L, Lo: Length dimensions of rocker strip or sliding surface
• r: Radius of curvature of sliding surfaces
• Y_m, Y_ms: Partial safety factors for materials and sliding respectively

Important Tables & Annexures

Typical Design Parameters

Formula: Reduced Contact Area (A_r)

[ A_r = A \times c ] where (c) = coefficient reducing creep effects on sliding surface

Design Checks Include:

• Anchorage bolt shear resistance
• Sliding resistance including friction and anchorage
• Permissible contact stress on PTFE/UHMWPE surfaces
• Deflection and rotation limits under service and ultimate loads

flowchart LR
    A[Load Applied] --> B[Sliding Surface (PTFE/UHMWPE)]