IS 802 (Part 2) : 2000Code of Practice for Use of Structural Steel in Overhead Transmission Line Towers, Part 2: Fabrication, Galvanizing,Inspection and Packing
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IS 802:2000 (Part 2) is the Indian Standard (BIS) for use of structural steel in overhead transmission line towers, part 2: fabrication, galvanizing,inspection and packing. This code specifies the technical requirements for the fabrication, hot-dip galvanizing, inspection, and packing of structural steel components used in overhead transmission line towers. It is heavily utilized by fabricators and QA/QC engineers to ensure structural fit-up tolerances and long-term corrosion protection before site dispatch.
Code of Practice for Use of Structural Steel in Overhead Transmission Line Towers, Part 2: Fabrication, Galvanizing,Inspection and Packing
Overview
Status
Current
Usage level
Specialized
Domain
Structural Engineering — Structural Engineering and Structural Sections
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! Unlike IS 800 working stress design, IS 802 applies the factor of safety (reliability/load factors) on the load side in Section 1. Therefore, the permissible tensile stress in Section 2 is typically taken directly as the yield stress (Fy) of the material.
! Accurate calculation of the effective slenderness ratio (KL/r) is critical. The K-factor depends on the end restraint conditions, bolting patterns, and whether the member is a leg, bracing, or redundant.
! Using higher grade steel (HT) increases tensile capacity but does not improve the buckling strength of slender members (where KL/r > Cc), as elastic buckling depends only on the Modulus of Elasticity (E).
ASCE 74-2020American Society of Civil Engineers (ASCE), USA
HighCurrent
Guidelines for Electrical Transmission Line Structural Loading
Specifies structural loads, load combinations, and loading requirements for transmission lines.
IEC 60826:2017International Electrotechnical Commission (IEC), International
HighCurrent
Design criteria of overhead transmission lines
Covers design criteria including climatic loads and load cases for overhead transmission lines.
EN 50341-1:2012CENELEC (European Committee for Electrotechnical Standardization), Europe
HighCurrent
Overhead electrical lines exceeding AC 1 kV - Part 1: General requirements - Common specifications
Provides a comprehensive framework for line design, including actions (loads) and material requirements.
Key Differences
≠IS 802 is primarily based on the Allowable Stress Design (ASD) philosophy, using factors of safety on material strength. Most modern international standards like ASCE 74 and IEC 60826 are based on Limit State Design (LSD) or Load and Resistance Factor Design (LRFD), which apply factors to loads and resistances separately.
≠For wind loading, IS 802 uses a simplified Gust Factor approach. In contrast, ASCE 74 specifies a more sophisticated Gust Response Factor (GRF) which accounts for the dynamic interaction between wind gusts and the structure's natural frequency.
≠IS 802 provides a specific wind zone map of India with basic wind speeds. International standards provide methodologies to determine wind speeds from local meteorological data but do not contain country-specific maps.
≠Reliability and security against cascading failures in IS 802 are primarily addressed through 'broken wire' conditions. Modern standards like ASCE 74 and IEC 60826 offer more nuanced reliability levels and anti-cascading provisions, which can include containment towers or longitudinal load analysis.
Key Similarities
≈All standards use a 'basic wind speed' derived from meteorological data for a specific return period (e.g., 50 years) as the foundation for calculating wind loads.
≈The principle of combining various loads (e.g., dead load, wind load, ice load, temperature effects) to determine the most critical design condition is fundamental to IS 802 and its international counterparts.
≈All standards recognize the effect of ground roughness on wind profiles and define different 'terrain categories' to adjust wind pressures based on the surrounding environment (e.g., open sea, open country, suburban).
≈The concept of designing for a security load case, such as a broken conductor or ground wire, is a common feature across all standards to ensure the line does not suffer a progressive collapse.
Parameter Comparison
Parameter
IS Value
International
Source
Design Philosophy
Allowable Stress Design (ASD) with safety factors.
Limit State Design (LSD) / Load and Resistance Factor Design (LRFD) with partial factors.
ASCE 74-2020 / IEC 60826:2017
Factor of Safety (Normal Condition, Wind)
2.0 (on stresses)
Not directly comparable; uses Load Factors (e.g., 1.0 for wind) and Resistance Factors.
ASCE 74-2020 (LRFD)
Basic Wind Speed Return Period
50 years
Variable, based on specified Reliability Level (e.g., 50, 100, 300+ year return periods).
ASCE 74-2020
Terrain Categories for Wind
3 categories defined based on terrain roughness.
4 categories (A, B, C, D) defined based on surface roughness.
ASCE 74-2020
Gust Loading Method
Gust Factor (specified values, e.g., 2.0 for conductors).
Calculated Gust Response Factor (GRF) based on structure dynamics and turbulence.
ASCE 74-2020
Standard Ice Density (Glaze)
Not explicitly defined in the standard, typically 913 kg/m³ is used in practice.
900 kg/m³ is the standard value for glaze ice.
IEC 60826:2017
Temperature Range for Design
Specifies a map for minimum and maximum temperatures in India.
Provides methodology based on local meteorological data; does not provide regional maps.
IEC 60826:2017
⚠ Verify details from original standards before use
Key Values7
Quick Reference Values
permissible axial tensionEqual to the minimum guaranteed yield stress (Fy)
max slenderness ratio leg members120
max slenderness ratio other members200
max slenderness ratio redundant members250
modulus of elasticity E200,000 MPa (approx 2.0 x 10^5 N/mm2)
permissible bearing stress bolts1.5 times the ultimate tensile stress of the bolt material
bolt hole clearance1.5 mm for bolts up to 24 mm diameter
Key Formulas
Fa = Fy [1 - 0.5 * (KL/r / Cc)^2] — Permissible compressive stress for KL/r <= Cc
Fa = (π^2 * E) / (KL/r)^2 — Permissible compressive stress for KL/r > Cc
Cc = π * √(2E / Fy) — Limiting slenderness ratio demarcating elastic and inelastic buckling
Tables & Referenced Sections
Key Tables
No tables data
Key Clauses
Clause 3 - Permissible Stresses in Axial Tension
Clause 4 - Permissible Stresses in Axial Compression
What is the permissible tensile stress for steel members under IS 802?+
It is taken as the minimum guaranteed yield stress (Fy) of the steel, because loads are already factored in Section 1.
What are the maximum allowed slenderness ratios (L/r)?+
120 for leg members and ground wire peaks, 200 for other members carrying computed stress, and 250 for redundant members.
How is the permissible compressive stress calculated?+
It is based on the effective slenderness ratio. For short/intermediate columns, a parabolic formula is used. For long, slender columns, the Euler buckling formula is used.
What clearance is allowed for bolt holes in transmission towers?+
Typically, the bolt hole diameter is made 1.5 mm larger than the nominal diameter of the bolt.