Module 02
Design basis, actions and combinations
The same combination rules as any other material — and a set of cases that only bite steel, because steel structures are light.
What this module covers
- Apply ULS and SLS combinations, and say which one a check belongs to
- Identify when a permanent action is FAVOURABLE, and use the right factor
- Carry out an uplift check on a light roof
- Explain why snow drift is worse for a purlin than uniform snow
- Calculate the force in a restrained member under temperature change
- Explain why crane dynamic factors belong to the action, not to the safety margin
Lessons
Most of this is shared with every other material. The part that is not is knowing when a load is on your side.
Start lesson →Drifted snow, restrained temperature and crane dynamics — three cases where the obvious calculation is not the governing one.
Start lesson →
Module checkpoint
Check what you have taken in
6 questions
Question 1
A roof weighs 0.30 kN/m² and the characteristic wind suction is 1.00 kN/m². What is the net design action, in kN/m², taking downward as positive?
Question 2
A fully restrained member of 3000 mm² sees a 50 K temperature change. What force develops, in kN? Take E = 210 000 N/mm², α = 12 × 10⁻⁶/K.
Question 3
By how much does a free 30 m steel member move under a 45 K change, in mm? Take α = 12 × 10⁻⁶/K.
Question 4
A crane's static wheel load is 40 kN self-weight plus 120 kN hoisted. With dynamic factors of 1.1 and 1.3, what is the amplification ratio of dynamic to static total?
Question 5
A transverse crane force of 18 kN acts 400 mm above the beam's shear centre. What torque does it apply, in kNm?
Question 6
A member's full-restraint thermal force is 400 kN. Its axial stiffness is 2000 N/mm and the restraint's is 2000 N/mm. What force actually develops, in kN?