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IS 800 : 2007

General Construction
in Steel Code of Practice

The definitive code for structural steel design in India using the Limit State Method. Covers design of tension, compression, and flexural members, connections, stability, and fabrication requirements.

Published: September 2007
Replaces: IS 800 : 1984 (Working Stress)
Method: Limit State
Steel Grades: E250 to E450

Overview & Philosophy

IS 800:2007 provides guidelines for the design of structural steel using the Limit State Method. This replaced the old Working Stress Method (WSM) in 2007, bringing Indian practice in line with international standards (Eurocode 3, AISC). Cl. 1

🛡️
Limit State Philosophy Design for Ultimate Limit State (strength) and Serviceability Limit State (deflection, vibration) separately. Safety factors applied to loads and materials.
⚖️
Partial Safety Factors Load factors: 1.5 for DL+LL. Material factor (γm0): 1.1 for yielding, 1.25 for ultimate rupture.
📐
More Accurate LSM considers actual failure modes (buckling, yielding) rather than elastic stress limits. More economical designs possible.
🌍
Harmonized Based on reliability theory. Consistent with modern global practices and codified in Eurocode 3.
⚠️
Important Note IS 800:2007 applies only to ordinary welded, bolted, riveted, and pinned construction. For special structures (bridges, towers, offshore), refer to specific codes like IRC/IR/PI.

Materials & Properties

Structural steel must conform to relevant Indian Standards (IS 2062, IS 961, etc.). Common steel grades are classified by yield strength. Cl. 5.2

Grade Yield Strength fy (N/mm²) Ultimate Strength fu (N/mm²) Typical Use
E250250410–480Ordinary structures
E350350490–600Medium/high rise buildings
E410410530–620Industrial structures
E450450550–660Heavy industrial

Material Constants:

  • Modulus of Elasticity (E): 2 × 10⁵ N/mm²
  • Poisson's Ratio (ν): 0.3
  • Density (ρ): 7850 kg/m³
  • Shear Modulus (G): 0.769 × 10⁵ N/mm²
Partial Safety Factors:
• γm0 = 1.10 (for yielding)
• γm1 = 1.25 (for ultimate rupture)
• γmb = 1.25 (for bolts)
• γmw = 1.25 (for fillet welds, shop)
• γmw = 1.50 (for field welds)

Section Classification

Cross-sections are classified into 4 types based on their ability to reach plastic moment capacity and rotate without local buckling. Cl. 3.7

Class 1: Plastic
Full plastic capacity achievable
Can form plastic hinges
Class 2: Compact
Plastic capacity achievable
Limited rotation available
Class 3: Semi-Compact
Only elastic capacity
Local buckling before yield
Class 4: Slender
Reduced effective section
Elastic with local buckling

Classification Depends On:

  • Width-to-thickness ratio of flange ($b/t_f$)
  • Depth-to-thickness ratio of web ($d/t_w$)
  • Yield strength of steel ($f_y$)
Element Class 1 Limit Class 2 Limit Class 3 Limit
Flange (outstand)9.4ε10.5ε15.7ε
Web (axial load)42ε42ε42ε
Web (bending)94ε105ε126ε

Where ε = √(250/fy) — standardization factor.

Tension Member Design

Tension members include cables, rods, angles, and channels used in trusses, bracing, and hangers. Cl. 6.2

Governing Failure Modes

  1. Yielding of Gross Section:
  2. Rupture of Critical Section: At holes or notches
  3. Block Shear Failure: Along bolt line paths
Design Strength due to Yielding
Tdg = (fy × Ag) / γm0
Eq. 3
Design Strength due to Rupture
Tdn = (0.9 × fu × An) / γmb
Eq. 4
Design Strength due to Block Shear
Vdb = min[(Avg×fy)/(√3×γm0) + (0.9×Atn×fu)/γmb, ...]
Eq. 5 & 6

Slenderness Limit:

  • Compression members under reversal: λ ≤ 180
  • Tension members subjected to dynamic loading: λ ≤ 300

Compression Member Design

Columns, struts, and braces must be checked for buckling about both principal axes. Effective length depends on end conditions. Cl. 7.1

Design Compressive Strength
Pd = fcd × Aeff
Eq. 7
Design Compressive Stress (fcd)
fcd = (χ × fy) / γm0
Where χ = reduction factor

Reduction Factor (χ):

χ = 1 / [φ + √(φ² − λ̄²)] where φ = 0.5[1 + α(λ̄ − 0.2) + λ̄²]

The value of α (imperfection factor) depends on the buckling curve (a, b, c, d).

Axis h/tf ≤ 40 h/tf > 40
x-x axis (major)Buckle Curve 'a'Curve 'b'
y-y axis (minor)Buckle Curve 'b'Curve 'c'

Effective Length Factor (K):

End Condition Theoretical K Recommended K
Fixed-Fixed0.500.65
Fixed-Pinned0.700.80
Fixed-Free2.002.10
Pinned-Pinned1.001.00

Flexural Member Design

Beams are designed for bending moment capacity and shear capacity. Lateral torsional buckling (LTB) must be checked for unrestrained beams. Cl. 8

Design Bending Moment Capacity
Md = βb × Zp × fy / γm0
For plastic/compact sections

For semi-compact sections, use elastic section modulus Ze instead of Zp.

Lateral Torsional Buckling Check
Md = Zp × fbd / γm0
Where fbd = design compressive stress due to LTB
Design Shear Strength
Vd = (fyw × Av) / (√3 × γm0)
Where Av = shear area
⚠️
High Shear Check If V > 0.6Vd, reduce moment capacity: Md = Md,p − β(Md,p − Md,f).

Connections

Bolted Connections

Common types include bearing bolts and high-strength friction grip (HSFG) bolts. Cl. 10

Shear Capacity per Bolt (Bearing Type)
Vdsb = (fub × Anb) / (√3 × γmb)
Without threads in shear plane
Bearing Capacity per Bolt
Vdpb = 2.5 × kb × d × t × fu / γmb
kb = min(e/(3d₀), p/(3d₀)−0.25, fu/fub, 1.0)

Welded Connections

Fillet welds are most common. Butt welds used for full-penetration connections. Cl. 10

Design Strength of Fillet Weld
Rw = lw × tt × fwd
Where fwd = fu / (√3 × γmw)
Minimum Fillet Weld Size
Min throat = 3mm (for t ≤ 10mm), increases for thicker plates
Table 21
[Diagram: Bolt Spacing Limits]
Min Pitch = 2.5d • Max Pitch = 16t or 200mm (comp.)
Min Edge Distance = 1.7d • Max Edge = 12t

Stability & Buckling

Overall structural stability requires checking for sway, second-order effects (P-Δ), and member buckling. Cl. 5 & 8

Sway Frame vs Non-Sway Frame

  • Non-Sway: Braced frames where lateral deflection is negligible.
  • Sway: Unbraced frames requiring P-Δ analysis.
Simple Rules for Sway:
• If horizontal loads cause drift > H/500, treat as sway frame.
• P-Δ moments may require magnification factor for columns.

Design Considerations

  • Diaphragm Action: Floor slabs provide lateral restraint to beams.
  • Bracing: Required for stability during construction and service.
  • Connection Rigidity: Simple vs rigid connections affect frame behavior.
🏗️
Construction Safety During erection, ensure temporary bracing is installed. Never rely on final connections before permanent bracing is in place. Follow IS 800 Cl. 11 for erection procedures.

IS 800 works in conjunction with several supporting standards:

IS 2062 : 2011
Steel Plates, Sheets, Sections for Structural Engineering.
IS 875 (Parts 1-5)
Design Loads — Dead, Live, Wind, Snow loads for steel structures.
IS 1893 : 2016
Earthquake loads on steel frames (especially for braced frames).
IS 816 : 1969
Code of Practice for Use of Metal Arc Welding.
IS 1161 : 1998
Steel Tubes for Structural Purposes.
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