Amogh N P
✦ In loving memory of Amogh N P — Architect · Designer · Visionary ✦
An RCC frame showing columns, beams and a cast slab — the components working as one skeleton.
Unit III25ART202 · Concept of Building Structures

RCC Building Components

Beams, slabs, columns, footings and stairs — and the beam that bends.

≈ 40 min + calculator

Reinforced concrete is the Indian workhorse, and an architect must read its parts fluently — which member carries which load, and why. This unit walks the components from footing to staircase, then puts a beam under load so you can watch its bending moment and shear change.

Learning objectives

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

1
CO3 · Understand

Name the RCC components of a building and the job each one does.

2
CO3 · Apply

Tell a one-way slab from a two-way slab by how it spans.

3
CO3 · Apply

Compute the maximum bending moment and shear in a simply-supported beam.

4
CO6 · Evaluate

Read which component carries which load in a building frame.

Footing to staircase

The RCC components

Beams carry slab loads to columns in bending (plinth, lintel, roof, cantilever); slabs carry floor loads to beams; columns carry compression down; footings spread it onto the soil; and the staircase is an inclined slab between landings.[1]

The parts of an RCC frame footings column plinth beam floor slab on beam lintel over opening staircase
DiagramAn RCC frame labelled with footings, columns, a plinth beam, a floor slab on beams, a lintel over an opening, and a staircase

Beams

Horizontal members that collect slab loads and carry them to columns in bending. Plinth beam (at plinth, ties columns), lintel (over openings), roof/floor beam, and the cantilever beam (fixed one end, free the other).[1, 4]

An RCC frame showing columns, beams and a cast slab — the components working as one skeleton.
PhotoAn RCC frame showing columns, beams and a cast slab — the components working as one skeleton.macrolepis · CC BY 3.0 · via Wikimedia Commons
An RCC dog-legged staircase, the inclined waist slab spanning between landings.
PhotoAn RCC dog-legged staircase, the inclined waist slab spanning between landings.August Geyler · CC BY-SA 4.0 · via Wikimedia Commons
How a slab spans

One-way & two-way slabs

A slab spans the short way first. If the long side is more than twice the short, it acts essentially one-way; if the sides are closer (ratio ≤ 2) it spans two-way, sharing load to all four beams.

One-way vs two-way slab one-way (long : short > 2) spans to two beams two-way (ratio ≤ 2) spans to all four beams
DiagramOne-way versus two-way slabs in plan — a long slab spanning one way to two beams, and a near-square slab spanning both ways to four beams
AspectOne-way slabTwo-way slab
SpanningOne-way: one directionTwo-way: both directions
Length:breadth ratio> 2≤ 2
Main steelalong the short spanin both directions
Load goes totwo opposite beamsall four edge beams
Economygood for narrow roomsgood for near-square rooms
Try it

The bending beam

A simply-supported beam under a uniform load w over span L has its greatest bending moment at midspan, wL²/8, and its greatest shear at the supports, wL/2. Change the span and load and watch the diagram.

Simply-supported beam · uniform load

Max bending moment M = wL²/8; max shear V = wL/2.

0.0 kNm

Max bending moment

0.0 kN

Max shear force

Bending moment diagram (sagging parabola)

Apply it

Study task

For a 5 m beam carrying 25 kN/m, compute the maximum bending moment and shear by hand, then check yourself with the calculator. Sketch where the steel should go to resist the sagging.

Check your understanding

Self-assessment

1. For a simply-supported beam of span L carrying a uniform load w per metre, the maximum bending moment is —

2. A rectangular slab with a long-to-short side ratio of 3 will behave as a —

3. Which component spreads a column's load safely onto the soil?

In a nutshell

Recap

RCC components: beams (plinth, lintel, roof, cantilever), slabs, columns, footings and the staircase.
A one-way slab (ratio > 2) spans one way; a two-way slab (ratio ≤ 2) spans both and shares load to four beams.
For a simply-supported beam with UDL w over span L: max BM = wL²/8, max SF = wL/2.
Columns carry compression to footings, which spread it onto the soil.
The evidence

References & further reading

  1. [1]IS 456:2000 — Plain and Reinforced Concrete — Code of Practice. BIS. https://law.resource.org/pub/in/bis/S03/is.456.2000.pdf
  2. [2]B.C. Punmia, Ashok K. Jain & Arun K. Jain, Reinforced Concrete Structures. Laxmi Publications.
  3. [3]IS 1904:1986 — Design and Construction of Foundations in Soils — General Requirements. BIS. https://law.resource.org/pub/in/bis/S03/is.1904.1986.pdf
  4. [4]S. Ramamrutham, Design of Reinforced Concrete Structures. Dhanpat Rai & Sons.
  5. [5]Pillai & Menon, Reinforced Concrete Design. McGraw-Hill Education.

Further reading

  • Pillai & Menon, Reinforced Concrete Design — the standard Indian text.
  • B.C. Punmia et al., Reinforced Concrete Structures.
  • S. Ramamrutham, Design of Reinforced Concrete Structures.

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.