Structural Steel Design / module 1
Structural steel as a material
What steel actually does when you load it, and why almost every surprising rule in steel design traces back to one fact: the grade changes the strength and leaves the stiffness alone.
What you will understand
- Explain why steel is used structurally, and what it is bad at
- Read a stress–strain curve and say what each region allows a designer to do
- Explain why a higher grade helps some members and almost none of the others
- Describe residual stresses and say where they come from
- Explain why thicker product is weaker
- Recognise toughness, brittle fracture and lamellar tearing as separate problems
Lessons
What steel does when you load it
The stress–strain curve, region by region, and what each one lets a designer get away with.
Residual stress, thickness and toughness
Three properties that are invisible in a tensile test, absent from most calculations, and responsible for a surprising share of what goes wrong.
Module summary
- E is the same for every structural grade — only the strength changes
- So deflection, buckling and local buckling barely improve with a higher grade
- The yield PLATEAU is what makes plastic design possible
- Steel reaches yield at about 0.17% strain and fails near 15% — a reserve of roughly eighty
- Residual stresses come from uneven cooling and are locked in before any load arrives
- Thicker product cools more slowly and does not develop the same yield strength
- Toughness falls with temperature; brittle fracture is a separate failure mode from yielding
- Steel's weaknesses are fire, corrosion and fatigue, and all three are detailing problems
Teaching basis and review status
These are educational models and exercises. Check their assumptions before using the results. The full technical content and every diagram have not yet been independently verified.
Concrete and steel calculations retain their stated first-generation Eurocode teaching basis. Use the standards and amendments specified for your project; do not mix generations without an appropriate design basis.
Read the lesson register and outstanding review notesCheck your understanding
Practice
What is the strain at first yield for S275 steel, as a percentage? Take E = 210 000 N/mm².
Practice
A beam in S275 fails its deflection check by 20%. It is changed to S460. By what percentage does the deflection improve?
Practice
What is ε for S355 steel at a thickness of 20 mm?
Practice
A section has residual compression at the flange tips of 0.3 fy. Expressed as a fraction of the squash load, at what load does the section begin to lose stiffness?
Practice
S460 steel fails at about 15% strain. By what factor does it stretch past its elastic limit? Take E = 210 000 N/mm².
Practice
In pure shear, at what fraction of fy does steel yield on the von Mises criterion? Give the fraction.