IS 802:2000 (Part 1) is the Indian Standard (BIS) for use of structural steel in overhead transmission line towers, part 1 materials,loads and permissible stresses, section 1: materials and loads. This standard provides the criteria for selecting materials and calculating loads (including wind, dead, broken wire, and construction conditions) for the design of self-supporting overhead electrical transmission line towers. It is heavily utilized by structural and power engineers to ensure power grid stability under extreme weather and mechanical failures.
Code of Practice for Use of Structural Steel In Overhead Transmission Line Towers, Part 1 Materials,Loads and Permissible Stresses, Section 1: Materials and Loads
Key reference values — verify against the current code edition / project specification.
| Reference | Value | Clause |
|---|---|---|
| Method | Working/permissible-stress, tower-specific load cases | Basis |
| Load cases | Normal + broken-wire + construction/maintenance | Loads |
| Tower types | Suspension (A) / tension-angle (B,C,D) / dead-end | Types |
| Slenderness | Role-specific limits: leg < bracing < redundant | Cl. |
| Tension members | Bolted angles — design on NET section | Design |
| Protection | Hot-dip galvanized to IS 4759 (40-yr exposure) | IS 4759 |
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
IS 802 Part 1:2000 is the code of practice for use of structural steel in overhead transmission line towers — Part 1 covers materials, loads and permissible stresses (Sec 1 materials & loads, Sec 2 permissible stresses). It is the governing structural code for lattice steel transmission/communication towers in India.
It is read with the tower/transmission stack:
Transmission towers are wind-and-tension governed lattice structures designed by working/permissible-stress method in IS 802 Part 1:
Member: a tower leg, ISA angle in compression, carrying factored axial from the worst (broken-wire + wind) case.
Step 1 — load tree: resolve the governing load case (e.g. broken ground-wire + transverse wind) into member axial forces via the tower analysis.
Step 2 — slenderness: leg λ = KL/r kept within the IS 802 limit for *leg members* (lower limit than redundant/bracing members).
Step 3 — permissible compressive stress: from IS 802 Part 1 Sec 2 for the computed λ → allowable axial capacity = σ_allow × net area; verify ≥ demand.
Step 4 — connection: bolt group checked for shear + bearing on the angle; net-section (deduct bolt holes) governs the tension members on the same tower.
Step 5 — galvanizing: all members hot-dip galvanized to IS 4759 (towers are exposed for 40+ years). Repeat for tension members (net-section) and bracing (relaxed slenderness).
1. Skipping the broken-wire load case. Suspension and especially tension/dead-end towers are frequently governed by unbalanced longitudinal pull, not normal-condition wind — omitting it under-designs the tower.
2. Wrong slenderness limit by member role. IS 802 sets *different* λ limits for leg / bracing / redundant members; applying one limit everywhere is unsafe (legs) or uneconomic (redundants).
3. Gross-section tension design. Bolted angle tension members must be checked on net section with the connection-eccentricity allowance.
4. Treating it like a building (IS 800 limit state). IS 802 Part 1 is permissible-stress with tower-specific load cases — don't blend methods.
5. Under-specifying galvanizing. Transmission towers must survive decades exposed; full HDG to IS 4759 and proper bolt/nut/washer protection is part of the design, not an extra.
IS 802 is the working code for the hundreds of thousands of lattice towers across the Indian grid; it is reaffirmed and is what utilities (POWERGRID/state transcos) and tower vendors design and proof-test to (Part 4 covers full-scale tower testing). It remains permissible-stress + discrete tower load cases, which is appropriate for the highly repetitive, type-tested nature of tower families — don't try to 'modernise' it into an IS 800 limit-state analysis.
The practitioner essentials: get the load tree right (especially broken-wire and the right tower type), respect the role-specific slenderness limits, design bolted angles on net section, and treat galvanizing as a 40-year durability requirement. Tower failures in service are overwhelmingly broken-wire/cascade, foundation, or corrosion problems — not member-stress arithmetic — so the discipline is in the load cases and the detailing, which IS 802 codifies precisely.
| 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 |