Standard Specifications and Code of Practice for Road Bridges, Section VI — Composite Construction (Limit States Design) (Third Revision)

The scope of IRC 22 covers design and specifications for steel bridges including concrete filled tubular sections, composite columns, fatigue strength, and materials properties. Key formulas include the bending capacity of concrete filled tubular sections, e.g., for major axis bending:

h = A.P_ck - A'st (2p_st - P_ck) / (2b & P_ck + 4t(2p_y - P_ck))

where for circular sections, b = d (diameter) (Clause 1.2).

Material properties for structural steel are standardized as:

• Young's Modulus = 2.0 x 10^5 MPa
• Shear Modulus = 0.77 x 10^5 MPa
• Poisson's Ratio = 0.30
• Coefficient of Thermal Expansion = 0.0000117 /°C (Annexure-III).

Symbols used in design are comprehensively listed in Clause 600.4, including areas, dimensions, moduli, and safety factors.

Fatigue strength design uses detail categories with stress ranges adjusted for number of cycles, e.g., for normal stress range:

• f = f_5x10^6 / N_sc^0.5 when N_sc ≤ 5x10^6
• f = f_5x10^6 / N_sc^0.25 when 5x10^6 < N_sc ≤ 10^8 (Clause 605.2).

Detail categories for fatigue are tabulated in Tables 4 and 5, classifying welded and non-welded details with constructional descriptions.

This scope ensures comprehensive coverage from material properties to fatigue design and structural detailing for steel bridges.

Sources: Clause 1.2, Annexure-III, Clause 600.4, Clause 605.2, Table 4, Table 5

As per IRC 22 Clause 601.4, the partial safety factors (Ym) for materials under Ultimate Limit State (ULS) and Serviceability Limit State (SLS) are given in the following table for strength assessment:

Additionally, Annexure-III specifies material properties such as:

• Young's Modulus of Steel = 2.0 x 10^5 MPa
• Shear Modulus = 0.77 x 10^5 MPa
• Poisson's Ratio = 0.30
• Coefficient of Thermal Expansion = 0.0000117 /°C

These factors and properties are essential for design calculations under ultimate and serviceability limit states, ensuring safety and performance. Partial safety factors apply to both yield and ultimate stresses as noted.

Symbols for areas and moduli used in design are listed in Clause 600.4.

For fatigue design, Clause 605.3 introduces partial safety factors against fatigue failure (Ymft) and limits stresses to not exceed elastic limits under cyclic loading.

Sources: Clause 601.4, Annexure-III, Clause 600.4, Clause 605.3

Design for Ultimate Limit State (ULS) in IRC 22 is defined as the state when, under the worst combination of factored loads, the structure or its components reach design strength and collapse or become unstable, requiring checks for both strength and stability as per Clause 601.2.3. The partial safety factors (γm) for materials used in ULS are specified in Table 601.4, reproduced below for clarity:

These factors are applied to material strengths to ensure safety under ultimate loads (Clause 601.4).

Additionally, Clause 603 discusses design of composite girders at ULS, where the neutral axis position (in slab, flange, or web) affects design calculations.

Summary:

• ULS checks strength and stability under factored loads (Clause 601.2.3).
• Use partial safety factors from Table 601.4 for material strength reduction.
• Composite girder design considers neutral axis location (Clause 603).

This answer is based on IRC 22: 601.2.3, 601.4, and 603 only.

Sources: Clause 601.2.3, Clause 601.4, Clause 603

Design for Serviceability Limit State (SLS) in IRC 22 ensures that the structure remains functional and comfortable during use without damage or excessive deformation. As per Clause 601.2.1, SLS is reached when any of the following occur:

• Stress in structural steel reaches the prescribed limit
• Deflection exceeds the allowable limit
• Concrete crack width surpasses permissible values
• Slip at steel-concrete interface exceeds limits
• Excessive vibration, especially on overhanging foot or cycle paths

While the exact numerical limits for stress, deflection, crack width, slip, and vibration are not provided in the retrieved context, these parameters must be checked against the code's specified permissible values to ensure serviceability.

For detailed formulas and tables, refer to the relevant sections of IRC 22 that specify limits for deflection (e.g., span/250), crack width (typically 0.3 mm for exposure conditions), and steel stress limits under service loads.

Sources: Clause 601.2.1

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For composite girder design per IRC 22 Section VI (Limit State Design), key specifications include partial safety factors for materials as per Clause 601.4 Table 1. These factors are:

The composite girder neutral axis (N.A.) location varies and may lie in the concrete slab, steel top flange, or steel web (Clause 603). Design must consider these positions for moment capacity and shear transfer.

Refer to Annexure-III for material properties and Annexure-I for detailed design procedures.

This summary covers material safety factors and neutral axis considerations essential for composite girder design and detailing under IRC 22.

Sources: Clause 601.4, Clause 603

Key formulas and specifications for composite columns per IRC 22 are as follows:

• Composite Column Types:

  • Fully and partially concrete encased columns (Fig. 14a)
  • Concrete filled hollow sections (Fig. 14b)

• Axial Compression Resistance (Clause 607.7):

  • Buckling check not required if:
    • Axial force < 0.1 P_or (elastic buckling load)
    • Non-dimensional slenderness λ < 0.2
  • Plastic resistance to compression is P_p (Clause 607.3).
  • Buckling safety check involves: [ x = \phi + \sqrt{\phi^2 - \lambda^2} ] where ( \phi = 0.5[1 + \alpha(\lambda - 0.2) + \lambda^2] )

• Imperfection Factor α (Table 11):

• Buckling Curves Selection:

  • Curve a: Concrete filled tubular sections with steel reinforcement < 3%
  • Curve b: Fully/partially concrete encased I-sections buckling about strong axis (x-x) and concrete filled tubular sections with steel > 3%
  • Curve c: Fully/partially concrete encased I-sections buckling about weak axis (y-y)

• Steel Contribution Ratio (Clause 607.1):

  • Must satisfy 0.2 ≤ ρ ≤ 0.9

These provisions apply to isolated composite columns with steel grade per IS 2062 and concrete strength M25 to M90 (Clause 607.1).

Sources: Clause 607.1, Clause 607.3, Clause 607.7, Table 11

Key formulas and specifications for shear connectors and load transfer per IRC 22 are as follows:

• Shear connectors transmit longitudinal shear between concrete and steel, ignoring natural bond (Clause 606.1).
• Shear connectors can be mild or high tensile steel; flexible types are preferred (Clause 606.1).
• Design strength of stud connectors (Qu) depends on diameter (d), height (h), concrete strength (fck), and partial safety factor (γv = 1.25). The design strength formula involves parameters like d, h, and concrete modulus (Clause 1.0).
• Channel connectors design strength Q4 depends on channel dimensions (length b, height h) with limits: h ≤ 20×web thickness or 150 mm max; b ≤ 300 mm; top flange clearance ≥ 30 mm; weld leg length ≤ half plate thickness (Clause 606.1).

Table of Stud Connector Design Strengths (N) for various diameters and heights:

| Nominal Diameter (mm) | Overall Height (mm) | Design Strength (N) for stud diameters 25 | 30 | 40 | 50 | |-----------------------|---------------------|--------------------------------------------| | 25 | 100 | 112 | 125 | 149 | 156 | | 22 | 100 | 87 | 97 | 115 | 120 | | 20 | 100 | 72 | 80 | 95 | 100 | | 16 | 75 | 68 | 76 | 91 | 100 | | 12 | 65 | 46 | 51 | 61 | 64 |

• For rolled angle and tee connectors, channel connector values apply if height is at least equal (Clause 606.1).
• Spacing and design of shear connectors must ensure full transfer of longitudinal shear and uplift resistance (Clause 606.4).
• Longitudinal shear outside load introduction areas should be verified and shear connectors provided if design shear exceeds design shear strength t, which can be taken from Table 13 (Clause 607.9.2).

These provisions ensure safe load transfer between steel and concrete in composite construction.

Sources: Clause 606.1, Clause 606.4, Clause 607.9.2, Clause 1.0 Table

For fabrication and inspection procedures of steel sections in IRC 22, the provisions of Section 513 of IRC:24-2010 apply as per Clause 610.1. Key points include ensuring props in propped construction do not yield and providing adequate bracing for prop stability.

Fatigue design (Clause 605.2) uses standard S-N curves with fatigue strength formulas:

• For normal stress range when Nsc ≤ 5×10^6: f = f_5x10^6 / Nsc^0.5
• For 5×10^6 ≤ Nsc ≤ 10^8: f = f_5x10^6 / Nsc^0.6
• For shear stress range: T_f = T_fm / Nsc^0.5

Partial safety factors for fatigue strength depend on inspection and failure consequence (Table 3):

Detail categories for fatigue strength classification are given in Tables 4 and 5, distinguishing non-welded and welded details with specific fabrication requirements such as grinding edges and weld quality.

Structural steel and consumables must comply with relevant IS standards listed under Clause 2.0, including IS:808, IS:2062, IS:814, IS:822, IS:1024, and others for welding and fasteners.

These ensure quality fabrication, inspection, and fatigue performance of steel structures per IRC 22 requirements.

Sources: Clause 610.1, Clause 605.2, Table 3, Table 4, Table 5, Clause 2.0

For buckling and stability of composite columns per IRC 22 Clause 607.7, key points are:

• Buckling check can be omitted if axial force P < 0.1 P_cr (elastic buckling load) or non-dimensional slenderness λ < 0.2.
• Plastic resistance P_p is used for compression capacity (Clause 607.3).
• Non-dimensional slenderness λ is calculated per Clause 607.6.
• Imperfection factor α depends on buckling curve (a, b, c) selected by section type and bending axis:

• Buckling curves:

  • Curve a: Concrete filled tubular, reinforcement <3%
  • Curve b: Concrete encased I-section strong axis or tubular with >3% reinforcement
  • Curve c: Concrete encased I-section weak axis

• Moment factor Cm for lateral-torsional buckling depends on moment distribution:

• Simplified Cm values:

  • 0.85 for ends restrained against rotation
  • 1.0 for ends unrestrained

• Elastic lateral buckling moment M_cr can be calculated using section properties and effective flexural stiffness.

• Steel properties (Young's modulus E = 2.0×10^5 MPa, Shear modulus G = 0.77×10^5 MPa) are used in calculations.

These formulas and tables govern buckling resistance and stability checks for composite columns in IRC 22.

Sources: Clause 607.7, Table 11, Table 12, Clause 607.3, Clause 607.6, Annexure-III

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Per IRC 22 Clause 607.9, mechanical shear connection ensures load sharing between steel and concrete at load introduction points, especially where transverse shear and end moments act. For axially loaded columns, longitudinal shear outside load introduction zones can be neglected. Shear connectors must be provided where the design shear strength t (from Table 13) is exceeded at the steel-concrete interface, calculated from sectional force changes within the introduction length, which should not exceed 2d or L/3 (d = minimum transverse column dimension, L = column length) as per Clause 607.9.1.

Table 13: Design Shear Strength (t) (N/mm²)

For shear connectors, Clause 606.5 and Table 1 specify stud and channel connector design strengths, e.g., stud connectors with diameters 12-25 mm and heights 65-100 mm have design strengths depending on diameter and concrete strength. Channel connectors have limits on height (≤150 mm or 20×web thickness) and width (≤300 mm), with weld leg length ≤ half plate thickness.

These provisions ensure proper load transfer and shear resistance at steel-concrete interfaces in composite columns and compression members.

Sources: Clause 607.9, Clause 607.9.1, Table 13, Clause 606.5, Table 1

As per IRC 22 Clause 604.5, temperature effects in steel structures should be considered referring to Section 215 of IRC:6-2014. Key material properties relevant to temperature effects from Annexure-III include:

• Young's Modulus (E) = 2.0 x 10^5 MPa
• Shear Modulus = 0.77 x 10^5 MPa
• Poisson's Ratio = 0.30
• Coefficient of Thermal Expansion = 0.0000117 /°C per unit length

These properties are essential for calculating thermal stresses and deformations due to temperature changes.

Symbols related to cross-sectional areas and dimensions (Clause 600.4) are used in temperature effect calculations, such as A (area), b (width), d (depth), and E (modulus of elasticity).

For fatigue design under cyclic temperature variations, Clause 605 provides fatigue strength formulas and detail categories, but temperature effect design primarily refers to IRC:6-2014 Section 215.

Summary:

• Use material properties above for thermal strain and stress calculations.
• Refer to IRC:6-2014 Section 215 for detailed temperature effect design procedures.

No explicit temperature effect formulas or tables are given in IRC 22 itself.

Sources: Clause 604.5, Annexure-III, Clause 600.4

The key formulas and specifications for fatigue design per IRC 22 Clause 605.2 are:

• Capacity reduction factor for thickness > 25 mm: ( u = (25/t_p)^{0.25} \leq 1.0 ), where ( t_p ) is the thicker plate thickness in mm.

• Fatigue assessment exemption: Fatigue check not required if stress ranges ( f ) satisfy: ( f \leq \frac{f_{m5x10^6}}{Y_m Y_{mf}} ) or number of cycles ( N_{sc} < 5 \times 10^6 Y_m f )

• Partial safety factors for fatigue strength (( Y_{mf} )) depend on inspection and fail-safe nature:

• Fatigue strength for normal stress range:

  • For ( N_{sc} \leq 5 \times 10^6 ): ( f_p = f_{m5x10^6} \times (5 \times 10^6 / N_{sc})^{0.1} )
  • For ( 5 \times 10^6 < N_{sc} \leq 10^8 ): ( f_p = f_{m5x10^6} \times (5 \times 10^6 / N_{sc})^{0.2} )

• Fatigue strength for shear stress range: ( T_p = T_{m5x10^6} \times (5 \times 10^6 / N_{sc})^{0.1} )

• Detail categories for fatigue strength are given in Tables 4 and 5, classifying non-welded and welded details respectively, with illustrations and descriptions.

• Stress determination: Elastic analysis ignoring local stress concentration effects but including geometric effects not characteristic of the detail.

These provisions apply under mild corrosion, temperature <150°C, and regular inspection conditions as per Clause 605.2.

Sources: Clause 605.2, Table 3, Table 4, Table 5

Key formulas, tables, and specifications from IRC 22 Annexures and Reference Tables include:

1. Concrete Filled Tubular Sections (Clause 1.2): Major axis bending moment capacity formula:

[ h = \frac{A.P_{ck} - A'{st} (2p{st} - P_{ck})}{2b} \quad & \quad P_{ck} + 4t(2p_y - P_{ck}) ]

• For circular tubes, substitute b = d.
• Minor axis bending uses the same formula interchanging h and b, and subscripts x and y.

2. Material Properties (Annexure-III):

3. Limiting Width-to-Thickness Ratios for Compression Elements (Clause 603.1.4, Table 2):

4. Symbols (Clause 600.4): Defines key symbols such as A (area), As (steel area), bf (flange width), d (web depth), E (modulus of elasticity), M (moment), etc., essential for design calculations.

These tables and formulas provide the basis for design and classification of steel and composite bridge elements per IRC 22. For detailed design, refer to the specific clauses and annexures mentioned.

Sources: Clause 1.2, Annexure-III, Clause 603.1.4 Table 2, Clause 600.4