IS 4923 : 1997Hollow Steel Sections for Structural Use - Specification

IS 4923 is the specification for hollow steel sections (HSS) for structural use — circular, square, and rectangular hollow sections (CHS, SHS, RHS) used in structural framing, trusses, columns, racking, fences, handrails, and architectural elements. HSS combines high torsional + flexural stiffness, clean appearance, and uniform strength in all directions — increasingly replacing traditional I-beams and channels in modern Indian construction.

Use IS 4923 sections when designing: - Industrial / warehouse columns and roof trusses - High-rise composite columns (HSS infilled with concrete — composite design per IS 800:2007) - Architectural exposed steel (clean tubular profiles, no visible flanges) - Pre-engineered building (PEB) main framing - Steel pedestrian bridges, walkways - Light-gauge cold-formed structures (warehouse mezzanine, racking) - Marine / coastal structures (galvanised hollow sections) - Furniture / fitments / handrails / fencing - Solar PV mounting structures

IS 4923 covers hot-finished hollow sections (mainly larger sections, thicker walls). Cold-formed welded hollow sections are covered by IS 1161:2014. Both are acceptable for IS 800:2007 structural design; choice depends on size availability and cost.

Common HSS designations: - CHS (Circular Hollow Section) — outer diameter × wall thickness (e.g., 168.3 × 5.0) - SHS (Square Hollow Section) — outer width × wall thickness (e.g., 100 × 100 × 5) - RHS (Rectangular Hollow Section) — outer width × outer height × wall thickness (e.g., 150 × 100 × 4)

Material grades (per IS 4923):

| Grade | Yield strength (MPa) | Tensile strength (MPa) | Use | |---|---|---|---| | YST 210 | 210 (min) | 330 (min) | General structural | | YST 240 | 240 | 410 | Higher-strength structural | | YST 310 | 310 | 450 | High-strength structural |

IS 800:2007 design uses these strength values for capacity calculations.

Standard sizes (CHS, partial table):

| Outer dia (mm) | Wall thickness (mm) | Mass (kg/m) | |---|---|---| | 21.3 | 2.0-3.2 | 0.95-1.46 | | 33.7 | 2.6-4.0 | 1.99-2.92 | | 60.3 | 3.6-5.0 | 5.01-6.85 | | 88.9 | 4.0-6.3 | 8.39-12.83 | | 114.3 | 4.5-8.0 | 12.18-21.05 | | 168.3 | 5.0-10.0 | 20.18-39.05 | | 219.1 | 6.0-12.5 | 31.50-63.69 | | 273.0 | 7.1-12.5 | 46.55-80.39 | | 323.9 | 7.1-12.5 | 55.50-96.10 |

Standard sizes (SHS, partial):

| Section | Mass (kg/m) | Section modulus (cm³) | |---|---|---| | 50 × 50 × 4 | 5.45 | 7.50 | | 80 × 80 × 5 | 11.10 | 25.30 | | 100 × 100 × 6 | 16.90 | 47.80 | | 150 × 150 × 8 | 33.50 | 142.00 | | 200 × 200 × 10 | 56.30 | 304.00 |

Standard length: 6 m or 12 m typically.

Tolerances: - Wall thickness: ±10 % (≤ 5 mm); ±0.5 mm (> 5 mm) - Outer dimension: ±1 % (CHS); ±1 % SHS / RHS - Length: ±100 mm on standard length - Straightness: ≤ 0.2 % of length - Squareness of cut ends: ≤ 1° from perpendicular

Surface condition: - Hot-finished: black mill scale - Galvanised (per IS 4759 hot-dip): 70-100 µm zinc coating; specified for marine / outdoor exposure - Powder-coated (architectural) - Pickled + oiled (for further fabrication)

Connection types: - Welded (most common): butt weld, fillet weld - Bolted (with end plates, gusset plates, or chord plates) - HSS-to-HSS direct welded (T, K, X, Y joints — design per IS 800 + AISC HSS connection guidelines) - Mechanical (clamps, splice sleeves) for non-structural / temporary

Section classification (Clause 3.7 of IS 800): - Compact (Class 1): full plastic moment capacity, no local buckling concern - Compact (Class 2): same plastic moment but limited rotation capacity - Semi-compact (Class 3): yields in extreme fibre but no local buckling - Slender (Class 4): local buckling governs; reduced effective section

For HSS: - CHS: D/t ≤ 88 (Class 1), 252 (Class 3) for fy = 250 MPa - SHS / RHS: b/t ≤ 33 (Class 1), 42 (Class 3) for fy = 250 MPa - HSS at YST 310 grade has tighter limits (lower b/t)

Buckling resistance (IS 800 Clause 7): - HSS columns: very efficient due to high radius of gyration in both axes - Buckling curve: typically 'a' (most favourable) for hot-finished HSS

Composite design (concrete-filled HSS — IS 800 + IRC:22): - HSS provides confinement for concrete; concrete provides stiffness for HSS against local buckling - Effective composite strength ~10-30 % above sum of individual strengths - Common in tall building columns, bridge piers

Connection design: - Welded T / K / X joints: chord wall thickness governs; use AISC HSS connection design or IS 800 direct - Bolted with end plates: standard bolt design per IS 800 - HSS-to-HSS by gusset plate: simplifies geometry but adds material

• IS 800:2007 — code of practice for general construction in steel (the design code).
• IS 1161:2014 — steel tubes for structural purposes (cold-formed welded counterpart).
• IS 2062:2011 — hot-rolled medium and high-tensile structural steel (the source steel for HSS manufacture).
• IS 1786:2008 — high-strength deformed reinforcement (used in composite HSS columns).
• IS 808:1989 — dimensions for rolled steel sections (the I-beam, channel, angle alternative).
• IS 875 Parts 1-5 — loads on structures.
• IS 1893 Part 1:2016 — earthquake resistant design.
• IS 9595:1996 — recommendations for metal arc welding (HSS welding).
• IS 4759 — hot-dip galvanising of iron and steel (HSS surface treatment).
• IS 10987:1992 — glossary of terms relating to hot-rolled and hot-finished steel sections.
• IS 16700:2017 — tall building design (HSS columns common in modern tall buildings).
• IRC:22:2008 — composite construction (concrete-filled HSS bridge piers).
• IRC:24:2010 — steel road bridges.
• AISC HSS Connection Design Manual — international reference for HSS-to-HSS connections.

1. Specifying CHS / SHS / RHS without grade. Same dimensions in YST 210 vs YST 310 have very different strengths. Always specify grade (e.g., 'CHS 168.3 × 5.0 YST 240'). 2. Section classification not checked. Slender sections (Class 4) need effective-section reduction; using gross-section properties overestimates capacity. 3. HSS-to-HSS welded T-joint without chord wall thickness check. Punching shear failure at chord; weld failure at branch. Design per AISC or IS 800 connection rules. 4. No corrosion protection on outdoor HSS. Plain mill-scale steel rusts; structural integrity degrades. Specify galvanised (hot-dip) or paint system per exposure. 5. Internal corrosion of hollow section in coastal exposure. Salt-laden moisture enters via end open or weld pinhole. Seal ends with welded plate or fill with concrete. 6. Composite HSS column designed without confinement effect. Higher capacity available; under-designed conservative. 7. Connection simulation in software not matching actual fabrication. Software may model nodes as rigid; actual welded HSS joints have flexibility. Use semi-rigid models for important structures. 8. Galvanised HSS welded without surface preparation. Zinc burns off near weld; localised corrosion within weeks. Re-coat post-welding with zinc-rich paint. 9. Wrong dimensions ordered (mass per metre check). CHS 168.3 × 5.0 is 20.18 kg/m; supplier may deliver 168.3 × 4.5 (1 mm thinner — substantial weight saving for them, undersized for design). Verify mass per metre at delivery. 10. No fire protection on exposed HSS. Steel softens at 550 °C; structural failure in fire. Provide intumescent coating, board cladding, or concrete encasement. 11. Wrong size shown on drawing — fabricator substitutes. Catalogue gaps mean unavailable size; fabricator substitutes nearest. Specify alternates explicitly or coordinate with available stock. 12. Bolted connections at HSS without clearance for nuts inside. Cannot tighten from inside hollow; either use through-bolt with nut accessible from outside, or use weld-only connection.

Steel structure design with HSS:

1. Conceptual design — frame layout; HSS column / beam / bracing options. 2. Loads (IS 875, IS 1893) — dead, live, wind, seismic. 3. Section sizing (IS 800:2007) — flexure, axial, shear, combined. 4. Material specification (this code, IS 4923 + IS 1161) — grade, dimensions, surface treatment. 5. Connection design — welded / bolted; chord wall capacity check. 6. Fire protection design — passive (intumescent / cladding) or active (sprinkler). 7. Detailed drawings — fabrication shop drawings, erection drawings, BOQ. 8. Procurement: - Mill test certificate per delivery (verify grade, dimensions, mass) - ISI mark on each section - Inspection at supplier yard for major projects 9. Fabrication: - Welding per IS 9595:1996 - Welder qualification + WPS qualified - NDT (UT, MT, RT) per project spec 10. Erection — handling, alignment, bolt-up, weld-out. 11. Surface protection — galvanise, paint, intumescent coating. 12. Inspection + handover — final NDT, paint thickness, fire-rated coating verification.

HSS has emerged as the dominant section type in modern Indian PEB and architectural steel construction. The combination of clean appearance + structural efficiency + fabrication ease makes it the default choice for many applications where I-beams were standard 20 years ago.