Verified by the CalcTree engineering team on July 20, 2024
This calculator designs a standard steel section by computing the flexural and axial design capacities to Ultimate Limit State (ULS) methods.
All calculations are performed in accordance withAS4100-2020.
Common steel sections
📃 List of symbols used on this page
Calculation
Assumptions
Inputs
Steel Properties
Section
:100 PFC
fy
:320MPa
L
:5 m
Loads
Modification Factors
Output
Section Properties
Member Properties
Capacity checks
Φ
:0.9
Compression Capacity
Ns=kfAnfyCl 6.2.1Nc=αcNsCl 6.3.3
Ns
:339kN
Major axis
αc,x
:0.304
Nc,x
:103
φNc,x
:93kN
N* < φNc,x
:PASS
Minor axis
αc,y
:0.059
Nc,y
:20
φNc,y
:18kN
N* < φNc,y
:FAIL
Flexural Capacity
Ms=fyZeCl 5.2.1Mb=αsαmMsCl 5.6.1.1
Major axis
Ms,x
:13kN m
Minor Axis
Ms,y
:4kN m
αs
:0.31
αm
:1
Mb
:3.9885167029982043
φMb
:4kN m
M*x < φMb
:FAIL
👉Note, Mb,x = Mb,y hence a single Mb is reported
Combined Compression and Bending - Section Capacity
Mr=Ms(1−ϕNsN∗)Cl 8.3.2 & Cl 8.3.3
Major axis
φMr,x
:10kN m
M*x < φMr,x
:FAIL
Minor axis
φMr,y
:3kN m
M*y < φMr,y
:FAIL
Combined Compression and Bending - In-plane Member Capacity
Mi=Ms(1−ϕNsN∗)Cl 8.4.2.2
Major Axis
φMi.x
:6kN m
M*x < φMi,x
:FAIL
Minor Axis
φMi,y
:-5kN m
M*y < φMi,y
:FAIL
Combined Axial and Bending - Out-of-Plane Member Capacity
Mox=Mbx(1−ϕNcyN∗)Cl 8.4.4.1
φMo.x
:-6kN m
M*x < φMo,x
:FAIL
Explanation
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.
Ns=kfAnfyCl 6.2.1
Only 'stocky' compression members fail by yielding, that is, to have a slenderness ratio l/r < 25 approximately.
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).
Nc=αcNsCl 6.3.3
Flexural buckling can only occur in slender compression members, that is, when l/r >= 25 approximately.
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 (Euler) Buckling
Flexural Check
Section capacity, Ms checks against yielding and local buckling of the compression flange or compression part of web.
Ms=fyZeCl 5.2.1
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.
Section behaviour based on slenderness classification
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.
Mb=αsαmMsCl 5.6.1.1
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.
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.