IS 800:2007 vs IRC:24-2010: Clause-by-Clause Comparison for Steel Bridge Design

IS 800:2007 and IRC:24-2010 apply the same limit-state design philosophy to steel members — the formulations for tension, compression, bending and shear are essentially common — but the clause numbers, table numbers and page references are completely different. IS 800 is the general code for steel structures; IRC:24 is Section V of the IRC bridge code, written specifically for steel road bridges. A designer moving between a building project and a bridge project is not learning new mechanics. They are re-learning where to find the same equations.

That difference matters more than it sounds. Submissions get queried, and calculation sheets get sent back, because a designer cited IS 800 Clause 6.3.3 in a bridge report where the checking authority expected IRC:24 Clause 506.1.2.3 — for the identical rupture check. This article maps the two codes clause by clause for the checks a steel bridge designer uses most.

1. Which code applies to which structure

IS 800:2007, General Construction in Steel – Code of Practice (Third Revision), is the Bureau of Indian Standards code for steel structures generally. It introduced limit state design as the primary method in Indian steel practice.

IRC:24-2010, Standard Specifications and Code of Practice for Road Bridges, Section V – Steel Road Bridges (Limit State Method), is the Indian Roads Congress code for steel road bridges. It carries the limit-state member-design provisions across into the bridge context, alongside bridge-specific matters — fatigue, load combinations from IRC:6, and detailing for bridge components — that IS 800 does not address in the form a bridge needs.

2. Quick clause map: IS 800:2007 to IRC:24-2010

Clause mapping compiled from side-by-side working notes on IS 800:2007 and IRC:24-2010. Verify each number against the current edition of the code held in your office before using it in a submission — clause numbering has shifted across revisions of both codes.

3. Design of tension members

Both codes state the same governing requirement: the factored design tension T in the member shall satisfy T ≤ T_d, where T_d is the design strength of the member, taken as the lowest of three values.

3.1 Yielding of the gross section

T_dg = A_g · f_y / γ_m0

where A_g is the gross area of cross-section, f_y the yield stress of the material, and γ_m0 the partial safety factor for failure governed by yielding. IS 800 takes γ_m0 from Table 5; IRC:24 from Table 1.

3.2 Rupture of the critical section

T_dn = 0.9 A_nc f_u / γ_m1 + β A_go f_y / γ_m0

with the shear lag factor

β = 1.4 − 0.076 (w/t)(f_y/f_u)(b_s/L_c) ≥ 0.7

and an upper bound of (f_u γ_m0)/(f_y γ_m1). The approximate net-section value for preliminary sizing is T_dn = α A_n f_u/γ_m1. IS 800 places this at Clause 6.3.3; IRC:24 at Clause 506.1.2.3.

3.3 Block shear

Block shear strength T_db is taken as the lesser of:

• T_db = [A_vg f_y / (√3 γ_m0)] + 0.9 A_tn f_u / γ_m1
• T_db = [0.9 A_vn f_u / (√3 γ_m1)] + A_tg f_y / γ_m0

IS 800 Clause 6.4.1; IRC:24 Clause 506.1.3.1.

The design strength T_d is the lowest of the three, and the efficiency of the member — η = T_dg/T_d — tells you immediately which limit state is controlling. An efficiency well below one on a tension member almost always points to the connection, not the section: too few bolts in line, an inadequate connection length L_c, or a gusset detail driving block shear. That is a detailing fix, not a heavier member.

4. Design of compression members

The design compressive strength of a member is given in both codes as:

P_d = A_e · f_cd

where A_e is the effective sectional area and f_cd the design compressive stress, subject to P ≤ P_d. IS 800 Clause 7.1.2; IRC:24 Clause 507.1.2.

The design compressive stress follows the Perry–Robertson form used across both codes:

f_cd = (f_y/γ_m0) / [φ + (φ² − λ²)^0.5] = χ f_y/γ_m0 ≤ f_y/γ_m0

with

• φ = 0.5 [1 + α(λ − 0.2) + λ²]
• λ = non-dimensional effective slenderness ratio = √(f_y/f_cc) = √[f_y(KL/r)²/π²E]
• f_cc = Euler buckling stress = π²E/(KL/r)²
• χ = stress reduction factor = 1/[φ + (φ² − λ²)^0.5]
• α = imperfection factor, corresponding to the buckling class of the section

The mechanics are identical. The imperfection factor table is where the numbering diverges: IS 800 gives α in Table 7; IRC:24 gives it in Table 3. This is one of the most common transcription errors in mixed-source calculation sheets, because both tables are short, look similar, and are keyed to buckling class rather than to section designation.

Our free steel I-section and composite section designer and steel box section designer carry out these checks directly, and the section properties calculator is useful for getting A_e, I_y and r right before you start.

5. Design strength in bending

5.1 Laterally supported beams

Where the compression flange is restrained, the factored design moment M must satisfy M ≤ M_d. The value of M_d depends on whether the section is also carrying high shear.

Case (i): low shear, V ≤ 0.6 V_d

• M_d = β_b Z_p f_y/γ_m0
• with M_d ≤ 1.2 Z_e f_y/γ_m0 for a simply supported beam
• and M_d ≤ 1.5 Z_e f_y/γ_m0 for a cantilever

where β_b = 1.0 for plastic and compact sections, and Z_p/Z_e for semi-compact sections. IS 800 Clause 8.2.1.2/8.2.1.3; IRC:24 Clause 509.2.1.2.

Case (ii): high shear, V > 0.6 V_d

The moment capacity is reduced to M_dv:

• For plastic and compact sections: M_dv = M_d − β(M_d − M_fd) ≤ 1.2 Z_e f_y/γ_m0, with β = (2V/V_d − 1)²
• For semi-compact sections: M_dv = Z_e f_y/γ_m0

where M_fd is the plastic design strength of the area of cross-section excluding the shear area, considering the partial safety factor γ_m0. IS 800 Clause 8.2.1.3 read with Clause 9.2.2; IRC:24 Clause 509.2.1.3 read with Clause 510.2.

5.2 Laterally unsupported beams

Where the compression flange is not restrained, the design bending strength becomes:

M_d = β_b Z_p f_bd

with f_bd = χ_LT f_y/γ_m0, and the bending stress reduction factor

χ_LT = 1/{φ_LT + [φ_LT² − λ_LT²]^0.5} ≤ 1.0

φ_LT = 0.5 [1 + α_LT(λ_LT − 0.2) + λ_LT²]

where α_LT is the imperfection parameter for lateral torsional buckling, distinguishing rolled from welded sections, and

λ_LT = √(β_b Z_p f_y/M_cr) ≤ √(1.2 Z_e f_y/M_cr) = √(f_y/f_cr,b)

For a simply supported prismatic member, the elastic critical moment is:

M_cr = (π² E I_y h_f / 2 L_LT²) · {1 + (1/20)[(L_LT/r_y)/(h_f/t_f)]²}^0.5 = β_b Z_p f_cr,b

and for a prismatic member made of a standard rolled I-section, f_cr,b is read directly from IS 800 Table 13 or IRC:24 Table 10. Here:

• I_t = torsional constant = Σ b_i t_i³/3 for an open section
• I_w = warping constant
• I_y, r_y = moment of inertia and radius of gyration about the weak axis
• L_LT = effective length for lateral torsional buckling, taken from IS 800 Clause 8.3.1 Table 15, or IRC:24 Table 10a under Clause 509.2.2

6. Design shear strength and web buckling

6.1 Nominal plastic shear resistance

The factored design shear force V must satisfy V ≤ V_d, where V_d = V_n/γ_m0. For plastic shear resistance, V_n = V_p, with

V_p = A_v f_yw / √3

where A_v is the shear area and f_yw the yield strength of the web. IS 800 Clause 8.4/8.4.1; IRC:24 Clause 509.4/509.4.1.

The shear area A_v depends on the section and the axis of bending:

6.2 Resistance to shear buckling

Shear buckling of the web must be checked when the web slenderness exceeds the code limit:

• d/t_w > 67ε — for a web without stiffeners
• d/t_w > 67ε √(K_v/5.35) — for a web with transverse stiffeners

where ε = √(250/f_y) and K_v is the shear buckling coefficient:

• K_v = 5.35 when transverse stiffeners are provided only at supports
• K_v = 4.0 + 5.35/(c/d)² for c/d < 1.0
• K_v = 5.35 + 4.0/(c/d)² for c/d ≥ 1.0

with c and d the spacing of transverse stiffeners and the depth of the web respectively. IS 800 Clause 8.4.2; IRC:24 Clause 509.4.2.

For the simple post-critical method, the nominal shear strength V_n = V_cr = A_v τ_b, where τ_b is the shear stress corresponding to web buckling:

• τ_b = f_yw/√3 when λ_w ≤ 0.8
• τ_b = [1 − 0.8(λ_w − 0.8)] (f_yw/√3) when 0.8 < λ_w < 1.2
• τ_b = f_yw/(√3 λ_w²) when λ_w ≥ 1.2

and the non-dimensional web slenderness ratio for shear buckling is

λ_w = √[f_yw / (√3 τ_cr,e)]

with the elastic critical shear stress of the web

τ_cr,e = K_v π² E / [12 (1 − μ²)(d/t_w)²]

where μ is Poisson's ratio.

7. What this means in practice

• Pick one code as the basis and state it on the cover sheet. For a steel road bridge that is IRC:24-2010 with IRC:6 loads. Anywhere you fall back on IS 800, say so and say why.
• Do not copy clause numbers across from a building job. The equations survive the move; the references do not. Clause 6.3.3 in a bridge report is a query waiting to happen.
• Watch the table numbers, not just the clause numbers. The imperfection factor (Table 7 versus Table 3), the partial safety factors (Table 5 versus Table 1) and the effective length for lateral torsional buckling (Table 15 versus Table 10a) are the three most commonly mis-cited.
• Remember what IRC:24 adds. Fatigue, bridge-specific load combinations and component detailing are the reason IRC:24 exists as a separate document. The member-design clauses covered here are only part of what a bridge submission has to satisfy.
• Verify against the edition in your office. Both codes have been revised, and a clause number quoted from memory or from an old set of notes is the single most avoidable error in a steel design submission.

For steel superstructure design, proof checking or a second opinion on a member-check methodology, see our ROB and RUB design and elevated and flyover structures practice areas, the wider detailed engineering services, or the full set of free structural design tools.

On the same theme of getting the codal trail right in a submission, see our companion guides to IRC and IS codes for bridge hydrology and hydraulics and to preparing a bridge and cross-drainage structures inventory.

8. Frequently asked questions

9. References

• IS 800:2007, General Construction in Steel – Code of Practice (Third Revision), Bureau of Indian Standards.
• IRC:24-2010, Standard Specifications and Code of Practice for Road Bridges, Section V – Steel Road Bridges (Limit State Method), Indian Roads Congress.
• IRC:6, Standard Specifications and Code of Practice for Road Bridges, Section II – Loads and Load Combinations, Indian Roads Congress.
• IRC:22, Standard Specifications and Code of Practice for Road Bridges, Section VI – Composite Construction, Indian Roads Congress.