Amogh N P
✦ In loving memory of Amogh N P — Architect · Designer · Visionary ✦
A steel-framed structure under erection — I-section beams and columns bolted into a frame.
Unit IV25ART202 · Concept of Building Structures

Steel Building Components

Rolled sections, tension members and the columns that can buckle.

≈ 35 min + study task

Steel is the other great structural material — strong in tension and compression, ductile, and light for its strength. It comes in standard rolled sections shaped to put material where the stress is, and its members do one of two jobs: they pull (tension) or they push (compression) — and the two fail very differently.

Learning objectives

By the end of this lesson, you will be able to — mapped to the course outcomes for Concept of Building Structures:

1
CO4 · Understand

Identify the common rolled steel sections and where each is used.

2
CO4 · Understand

Explain the properties that make steel a structural material.

3
CO4 · Analyse

Distinguish a tension member from a compression member and how each fails.

4
CO6 · Apply

Recognise why slender compression members buckle and must be braced.

The shapes

Structural steel & its sections

The I-section (ISMB) is the beam — its flanges sit far from the neutral axis where bending stress is greatest. The channel (ISMC), the angle (ISA, for trusses and bracing) and the hollow tube complete the family.[1, 2]

Rolled steel sections I-section (ISMB) — beams channel (ISMC) angle (ISA) — trusses hollow tube (SHS / RHS)
DiagramRolled steel section cross-sections: the I-section for beams, the channel, the angle for trusses, and the hollow square tube

Rolled steel sections

Hot-rolled standard shapes: the I-section (ISMB beam) for bending, the channel (ISMC), the angle (ISA, for trusses and bracing), and hollow tubes. The shape puts material where the stress is — flanges far from the neutral axis.[1, 2]

A steel-framed structure under erection — I-section beams and columns bolted into a frame.
PhotoA steel-framed structure under erection — I-section beams and columns bolted into a frame.PortlandAppraisalBlog · CC BY-SA 4.0 · via Wikimedia Commons
A steel roof truss, its slender members alternately in tension and compression.
PhotoA steel roof truss, its slender members alternately in tension and compression.Didi43 · CC BY-SA 4.0 · via Wikimedia Commons
How members fail

Tension vs compression

A tension member simply stretches and uses its whole cross-section — the most efficient use of steel. A compression member can buckle: a slender column bows sideways and fails far below its crushing load. That is why columns are kept stocky or braced — the slenderness ratio governs.[1, 2]

Tension stretches — compression can buckle tension member stays straight — uses the full section slender compression member bows out & buckles — slenderness governs
DiagramA tension member stays straight and stretches; a slender compression member bows out and buckles sideways
AspectTension memberCompression member
Force carriedTension member: pullCompression member: push
How it failsyielding / rupturebuckling (if slender)
Cross-section usedfully effectiveeffectiveness falls with slenderness
Governed byarea & connectionslenderness ratio (length/radius of gyration)
Examplestruss bottom chord, ties, bracingcolumns, struts, truss top chord
Apply it

Study task

Sketch a simple roof truss and mark each member T (tension) or C (compression). Identify the most slender compression member — the one most at risk of buckling — and suggest how to brace it.

Check your understanding

Self-assessment

1. Why is the I-section so efficient in bending?

2. A long, slender steel column is most likely to fail by —

3. Compared with concrete, a key advantage of steel is its —

In a nutshell

Recap

Rolled steel sections — I-beam, channel, angle, hollow tube — put material where the stress is.
Steel is strong in tension and compression, ductile and light for its strength, but corrodes and weakens in fire.
A tension member simply stretches and uses its full section; a compression member can buckle.
The slenderness ratio decides whether a column is crushed or buckles — slender ones must be braced.
The evidence

References & further reading

  1. [1]IS 800:2007 — General Construction in Steel — Code of Practice. BIS. https://archive.org/details/gov.in.is.800.2007
  2. [2]S.K. Duggal, Limit State Design of Steel Structures. McGraw-Hill Education.
  3. [3]N. Subramanian, Design of Steel Structures. Oxford University Press.
  4. [4]IS 808:1989 — Dimensions for Hot Rolled Steel Beam, Column, Channel and Angle Sections. BIS.
  5. [5]R.K. Bansal, A Textbook of Strength of Materials. Laxmi Publications.

Further reading

  • N. Subramanian, Design of Steel Structures.
  • S.K. Duggal, Limit State Design of Steel Structures.
  • Angus J. Macdonald, Structure and Architecture.

Sources gathered and fact-checked June 2026. Published values vary by source, sample and method — treat as indicative and confirm against the cited standard before structural use.