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LecturesModule 3

Steel Material Properties and Shapes

ASTM steels, stress-strain behavior, and W/HSS/L/C shape families.

AISC Reference Box
  • AISC 360-22 — Specification chapter governing this topic
  • AISC Manual 16th Ed. — Design tables and worked examples

Lecture Notes

This module introduces steel material properties and shapes. Lecture content here covers the governing physics, LRFD philosophy, and how the relevant AISC 360-22 chapter organizes the limit states.

Instructors can replace this text in Admin Mode. Each section is structured around: (1) behavior, (2) failure modes, (3) AISC limit-state equations, (4) design workflow, (5) detailing requirements.

A short comparison to ASD is included only where the resistance factor / safety factor relationship clarifies the LRFD design check.

Project case study — Cardinal Square — 4-story braced-frame office

Every chapter's worked example is one step in the design of the same building: Plan: 4 bays N–S × 3 bays E–W, each 30 ft × 30 ft. Stories: 4 @ 13 ft (52 ft roof). Composite floor: 4.5 in NW concrete on 3 VLI20 deck. Roof: 1.5 in B-deck + insulation + membrane. Materials: Wide-flange members A992 (Fy = 50 ksi, Fu = 65 ksi). Plates A572 Gr. 50. HSS bracing A500 Gr. C. Bolts A325-N 7/8 in dia. Welds E70XX. Concrete f'c = 4 ksi. Anchor rods F1554 Gr. 36.

Chapter 3 — Material selection
Project-wide steel grades and shape families
Demand carried forward
All flexural and axial demands listed above.
This chapter contributes
Commits to A992 W-shapes, A572 Gr. 50 plates and A500 Gr. C HSS for bracing — sets Fy / Fu used in every subsequent capacity calc.
Feeds into next chapter
Fy = 50, Fu = 65 ksi propagate to Chapters 4–13.
Strain ε (in/in)Stress σ (ksi)Fy = 50 ksiεy ≈ 0.0017Fu = 65 ksiElastic (E = 29,000 ksi)Yield plateauStrain hardeningNeckingRupture
Mild-steel σ–ε curve: elastic, yield plateau, strain hardening, necking, rupture.
W-shapeHSSL (angle)C (channel)
Rolled shape families: W, HSS, single angle L, and channel C.

Formula Sheet

NameEquationAISC Ref
Design strengthφ Rn ≥ RuAISC 360-22 B3.1

Worked Example

Steel Material Properties and Shapes

Given
Replace with project-specific given data (loads, geometry, material).
Load combination
Controlling LRFD load combination from ASCE 7.
Required strength
Compute required strength Ru from the controlling combination.
Limit states
  • Limit state 1
  • Limit state 2
AISC reference
AISC 360-22 — applicable chapter
Solution steps
  1. 1. Required strength
    Compute Ru.
  2. 2. Trial section
    Pick a trial from AISC shape tables Instructor should verify with official AISC Manual.
  3. 3. Check each limit state
    Apply φ Rn ≥ Ru for every governing limit state.
  4. 4. Iterate
    Resize until the most economical section satisfies all checks.
Final design decision
Select the lightest section that satisfies all LRFD limit states.
Common mistakes in this example
  • Skipping a limit state
  • Using the wrong φ factor
  • Forgetting serviceability checks

FE-Style Worked Examples (6)

Each example mirrors the NCEES FE Civil Reference Handbook style: brief givens, a labeled figure, AISC section reference, step-by-step numeric solution, and a single boxed answer.

Given
HSS8×8×1/2 rectangular column.
AISC Reference
AISC Manual Table 2-4
Step-by-step solution
  1. Default
    HSS rectangular → ASTM A500 Gr C: Fy=50, Fu=62 ksi.
Answer A500 Gr. C, Fy = 50 ksi.
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Practice Problems

  1. [E] List Fy and Fu for A36, A992, A572 Gr 50, A500 Gr C HSS, A325 bolt.
  2. [E] Define E, G, υ for structural steel (E = 29,000 ksi, G = 11,200 ksi, υ = 0.30).
  3. [E] Sketch a mild-steel σ–ε curve labeling proportional limit, yield plateau, strain hardening, Fu, rupture.
  4. [E] State the preferred A-spec for modern W-shapes and explain why (A992).
  5. [E] Name the four most common shape families with one application each (W, HSS, L, C).
  6. [M] W14x90 (A992): look up Ag, Ix, Sx, Zx, rx, ry. Compute shape factor Zx/Sx.
  7. [M] Determine if a W12x30 web is COMPACT for flexure: h/tw vs 3.76√(E/Fy).
  8. [M] Identify the most efficient shape family for: 24 ft floor beam; 12 ft interior column; single-angle tension diagonal; stair stringer with bolted flange.
  9. [M] HSS 8x8x1/2 (A500 Gr C) column, K = 1.0, L = 14 ft. Compute KL/r.
  10. [M] A992 vs A36: compute % increase in φPn for a 1.0 in² tension yield section.
  11. [H] W18x35 carries Mu = 220 k-ft. Look up Zx, Sx; determine controlling moment if Lb ≤ Lp.
  12. [H] Discuss strain-hardening's impact on cold-formed vs hot-rolled steel design and AISI 100 vs AISC 360 reliability.
  13. [H] Column 13 ft, K = 1.0, Pn ≥ 800 k required. Try W12x96 (A992); verify Fcr from Table 4-1.
  14. [H] Built-up 2L4x4x3/8 SLBB: compute combined rx and ry for 3/8 in. gusset spacing.
  15. [H] Discuss Charpy V-notch requirements for thick (≥1.5 in.) tension members vs thinner plates (AISC §A3.1c).
Structured Clues
  • A992 is the default for modern W-shapes (Fy = 50, Fu = 65).
  • Shape factor Zx/Sx ≈ 1.10–1.15 for W-shapes.
  • Always look up section properties in AISC Manual Part 1 (Tables 1-1 to 1-10).
Code References
  • AISC 360-22 §A3
  • AISC Manual Part 1, 2
  • ASTM A992 / A36 / A500

Quiz

1. Which AISC 360-22 chapter primarily governs steel material properties and shapes?
2. In LRFD, the basic design inequality is:

Common Student Mistakes

  • Mixing ASD and LRFD load combinations in the same problem.
  • Using nominal strength Rn instead of design strength φRn.
  • Forgetting to check every limit state listed in the AISC chapter.

"Professor Explains" Script

Today we're talking about steel material properties and shapes. Think of this topic as one step in the LRFD workflow: identify the demand, identify the limit states from the relevant AISC chapter, then check that φ·Rn is at least equal to Ru. We'll walk through the failure modes, the equations, and a worked example. Pay close attention to where the resistance factor changes — that's where students lose points on exams.