Hollow Section vs I-Beam Weight and Section Modulus Compared

The hollow section vs I-beam weight comparison comes up constantly in fabrication — whenever a designer or contractor asks "which is better, SHS or I-beam?" the honest answer is: it depends entirely on whether the member is a column or a beam. Hollow sections win on columns. I-beams win on beams. The table below gives the numbers that make this concrete, using nearest-equivalent pairs from IS:4923:1997 and IS:808:1989.

The Core Structural Difference — Columns vs Beams

A column resists axial (compressive) loads. Its critical failure mode is buckling, and buckling resistance is governed by the radius of gyration (r) — the higher the radius of gyration, the more buckling-resistant the section for a given weight. Because an SHS distributes material equally in all directions from the centroid, it has the same radius of gyration about both axes. An I-beam has a high radius of gyration about its strong axis but a low one about its weak axis — which is why unbraced I-beam columns buckle sideways.

A beam resists bending loads. Its critical measure is the section modulus (Z) — the higher the section modulus, the more bending moment the section can carry before yielding. I-beams concentrate material at the top and bottom flanges, far from the neutral axis, which maximises section modulus per kilogram of steel. For example, a standard ISMB 250 at 37.3 kg/m or ISMB 300 at 46.1 kg/m provides a much higher section modulus than a similar-weight hollow section. Hollow sections spread material uniformly and cannot match this efficiency for pure bending.

This is why you see SHS columns and ISMB beams in the same mezzanine structure — each section is doing what it does best.

Key Section Properties — Formula Definitions

Radius of gyration: r = √(I / A)

I

Second moment of area (moment of inertia), in cm⁴ — measures how far the cross-sectional area is distributed from the neutral axis.

A

Cross-sectional area, in cm² — directly proportional to weight per metre for a given steel grade.

r

Radius of gyration, in cm or mm — the key parameter for column buckling per IS:800:2007 (Limit State Method).

Section modulus: Z = I / y

I

Second moment of area about the bending axis, in cm⁴.

y

Distance from neutral axis to the extreme fibre, in cm — half the depth for symmetric sections.

Z

Elastic section modulus, in cm³ — the key parameter for beam bending capacity per IS:800:2007.

Hollow Section vs I-Beam — Side-by-Side Comparison Table

The table below pairs nearest-equivalent sections from IS:4923:1997 (SHS/RHS) and IS:808:1989 (ISMB) to show weight, section modulus, and radius of gyration side by side. Hollow section vs I-beam weight aur structural properties ek saath compare karein.

ISMB properties per IS:808:1989. SHS/RHS properties per IS:4923:1997. rx = radius of gyration about strong axis; ry = about weak axis. Weights and properties from Tata Steel and APL Apollo published section tables. Verify against current mill certificates for structural design.

Worked Example — 3-Metre Column, SHS vs ISMB

A mezzanine structure requires internal columns at 3-metre height carrying an axial load of 150 kN. The designer is choosing between SHS 100×100×4 and ISMB 100. Here is the comparison:

Option A — SHS 100×100×4 (IS:4923:1997):
Weight = 11.9 kg/m → 3-metre column = 35.7 kg
ry = 39.0 mm (same in both axes — no weak direction)
Slenderness ratio (KL/r) at 3 m = (1.0 × 3000) / 39.0 = 76.9
This falls well within the IS:800:2007 limit of 180 for compression members.

Option B — ISMB 100 (IS:808:1989):
Weight = 8.9 kg/m → 3-metre column = 26.7 kg
ry (weak axis) = 14.6 mm — this is the governing direction for buckling
Slenderness ratio (KL/r) at 3 m = (1.0 × 3000) / 14.6 = 205.5
This exceeds the IS:800:2007 limit of 180. The ISMB 100 fails the slenderness check as an unbraced column at 3 metres.

Conclusion: The ISMB 100 is 25% lighter and therefore cheaper in material cost, but it cannot be used as a 3-metre unbraced column without lateral bracing at mid-height. The SHS 100×100×4 — though heavier at 11.9 kg/m vs 8.9 kg/m — passes the slenderness check in both axes with no bracing required. For columns, hollow section aur I-beam ka weight difference se zyada radius of gyration matter karta hai.

To get the weight of any hollow section or I-beam section instantly, use our free Metal Weight Calculator. For a full SHS and RHS weight reference, see our Hollow Section Weight Calculator article.

Quick Selection Guide — Column or Beam?

Use this as a practical rule of thumb on site or in a fabrication quote:

Choose SHS or RHS (hollow section) when: The member is primarily a column carrying axial compression; the member is exposed and appearance matters (hollow sections paint and finish better); the member needs to resist loads from multiple directions; or the span is short and torsional stiffness is required.

Choose ISMB (I-beam) when: The member is primarily a beam carrying bending loads over a long span; the member sits on brackets and the web can carry shear efficiently; weight and material cost per unit of bending strength is the primary constraint; or the section will be encased in concrete or hidden behind cladding.

In practice, most mezzanine structures use SHS 100×100×4 or SHS 120×120×5 for columns and ISMB 200 or ISMB 250 for primary beams — a combination that gives good structural efficiency at a competitive fabricated cost.