## Introduction

This steel section calculator allows the user to obtain key properties and assess the structural integrity of standard steel sections to ensure compliance with the Australian Standard AS 4100:2020. The calculation will identify the design capacities of steel sections to meet axial and flexural design requirements to Ultimate Limit State (ULS) methods.
❗This calculation has been written in accordance with AS 4100.

## Calculation

### ⬇️ Inputs

﻿
﻿
Design bending moment in x, M*x
:20.0
﻿
﻿
﻿
Design bending moment in y, M*y
:10.0
﻿
﻿
﻿
Design shear in x, V*x
:50.0kN
﻿
﻿
﻿
Design shear in y, V*y
:50.0kN
﻿
﻿
﻿
Design axial force, N*
:45.0kN
﻿
Positive N* is compression, negative N* is tension

## Explanation

Steel is an alloy of iron and carbon. Iron is present in the earth’s crust as oxidised iron in the form of rock, called “iron ore”, which is what we mine. After mining, iron ore must undergo “reduction”, which means to loose its oxygen so it converts into iron. When iron is combined with carbon, scrap steel and small amounts of other elements, it becomes steel.
Steel is commonly used to construct building frames, including columns, beams and trusses. These elements provide the necessary structural support for the building. Steel's high strength-to-weight ratio, durability and ductility make it an ideal material for various applications.
Ultimate Limit State (ULS) design for steel includes the following checks against failure phenomena.

### Compression Check

Section capacity, Ns checks against compressive yielding (squashing) and local buckling.
﻿
1. Only 'stocky' compression members fail by yielding, that is, to have a slenderness ratio l/r < 25 approximately.
2. The form factor is the ratio of the effective to the gross area of the section. If the local buckling form factor, kf = 1.0 then yielding will occur before local buckling, if kf < 1.0 then local buckling will occur before yielding.
Member capacity, Nc checks against flexural buckling (or column buckling or Euler buckling).
﻿
1. Flexural buckling can only occur in slender compression members, that is, when l/r >= 25 approximately.
2. The theoretical buckling load, Nom, is given by the Euler Equation. The slenderness reduction factor, αc reduces the Euler equation to account for residual stresses and imperfections.
﻿

### Flexural Check

Section capacity, Ms checks against yielding and local buckling of the compression flange or compression part of web.
﻿
1. Effective section modulus, Ze is based on the slenderness classification of a section as either 'slender', 'compact' or 'non-compact'. The classification is used to understand whether the elastic or plastic material limits should be used. Slender sections should use an elastic approach to prevent buckling, whereas a compact section is allowed to develop full plastic capacity. All standard UB and UC sections have been sized such that they not slender.
Member capacity, Mb checks against flexural-torsional buckling which is where the beam bends in it's minor axis and twists, as this behaviour is the least stiff bending failure.
﻿
1. The elastic flexural-torsional buckling equation, Mo assumes a perfectly elastic and perfectly straight member with a uniform bending moment. The moment modification factor, αm and the slenderness reduction factor, αs reduces the equation to account for non-uniform bending moment and to account for how restraints impact deformations, respectively.
2. Flexural-torsional buckling won't occur in minor-axis bending as it is already bending in the less stiff axis and it won't occur in CHS or SHS sections since Ix and Iy are equal from symmetry.
﻿
﻿

## Comparison of Steel and Concrete

### Concrete

2,400 kg/m3
2-5MPa
20-50MPa
Brittle
Generally lower
Inherent in cover
Inherent in cover

### Property

Density
Tensile strength
Compressive strength
Failure mechanism
Construction cost
Fire resistance
Durability

### Steel

7,850 kg/m3
500MPa
250MPa
Ductile
Generally higher
Not inherent, needs intumescent paint
Subject to weather and rust
﻿