S
Admin
LecturesModule 13

Welded Connections

Fillet, groove, weld symbols, and effective throat.

AISC Reference Box
  • AISC 360-22 §J2 — Welds

Lecture Notes

This module introduces welded connections. 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 13 — Welded connection at the gusset
Fillet weld of brace gusset to column flange
Demand carried forward
From Chapter 4: brace force Tu ≈ 100 k.
This chapter contributes
Sizes weld leg w using φRn = 0.75 · 0.60 · FEXX · 0.707 · w · Lw (AISC §J2.4). Confirms minimum size per Table J2.4.
wLw — Fillet weld lap joint
Fillet weld: effective throat te = 0.707·w; φRn = 0.75·0.60·FEXX·te·Lw (AISC §J2.4).

Formula Sheet

NameEquationAISC Ref
Fillet weld strengthφRn = 0.75 · 0.60 · FEXX · te · LwAISC §J2.4
Effective throatte = 0.707 · w (for equal-leg fillet)AISC §J2.2

Worked Example

Welded Connections

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 (7)

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
1/4" fillet, E70 electrode (FEXX=70 ksi).
AISC Reference
AISC §J2.4 Eq. J2-4
Step-by-step solution
  1. te
    0.707 × 0.25 = 0.177 in
  2. φRn / in
    0.75 × 0.60 × 70 × 0.177 = 5.57 k/in
  3. Rule of thumb
    ≈ 1.392·D (D in 1/16") = 1.392×4 = 5.57 k/in ✓
Answer 5.57 k per inch of 1/4" fillet.
wLw — Fillet weld lap joint

Textbook — Aghayere & Vigil (2009)(4 worked examples with figures + numerical answers)

Worked examples scanned directly from the CEGR 436 course textbook. Each card shows the original page (figure + full step-by-step solution) and adds an FE-style numerical multiple-choice prompt with answer key.

Chapter summary

Chapter 10 covers fillet, groove, and plug welds. Fillet welds are governed by shear on the effective throat (te = 0.707·w for equal-leg). The base metal must also be checked — weld design rarely controls when E70 electrodes are matched with A36/A992 base.

  • Fillet weld: φRn = 0.75·0.60·FEXX·te·Lw, FEXX = 70 ksi (E70).
  • te = 0.707·w (equal-leg); for full-penetration groove, te = thickness of thinner part.
  • Min fillet leg per Table J2.4 (driven by thicker part — 1/8 in to 5/16 in).
  • Max fillet for ≥ 1/4 in plates: t − 1/16 in.
  • Strength per inch of E70 fillet: 1.392·w (kips/in, w in 1/16) — handy formula.
  • Eccentrically loaded weld groups: use Manual Tables 8-4 to 8-11 (or elastic vector method).
Setup
5/16-in E70 fillet weld.
AISC Reference
AISC §J2.4
Numerical practice
Design shear strength per inch?
Textbook page 483 — Fillet weld strength per inch
Aghayere & Vigil (2009), p. 483 — full worked solution & sketch.

Interactive Calculator

Fillet Weld Strength

AISC §J2.4
te = 0.707·w0.177 in
φ Rn = 0.75·0.6·FEXX·te·L33.4 kipsNG

Longitudinal loading only. Use Instantaneous Center / directional strength increase for angled loads.

Practice Problems

  1. [E] State φ for fillet welds (0.75).
  2. [E] Compute te for a 5/16 in. equal-leg fillet (te = 0.707·w).
  3. [E] State FEXX for E70 (70 ksi).
  4. [E] State min and max fillet size rules (Table J2.4).
  5. [E] Sketch AWS symbol for a 1/4 in. fillet, both sides, 6 in. long.
  6. [M] 5/16 in. fillet, 8 in. long. Compute φRn (E70).
  7. [M] Lap splice 1/2 in. A36 plate with fillet top + bottom, total 12 in. Compute φRn.
  8. [M] L4x4x3/8 welded to gusset. Find Lw to develop Pu = 120 k.
  9. [M] Base-metal shear rupture check for 5/16 fillet on 1/2 A36 plate.
  10. [M] Eccentric weld group: use Table 8-4 IC method, 6 x 4 in. L-pattern, ex = 3 in.
  11. [H] Design CJP groove weld for flange splice in W21x62, Mu = 320 k-ft. Specify electrode, prep, NDT.
  12. [H] Fillet weld around HSS truss joint: design weld for Pu = 95 k tension diagonal.
  13. [H] Two-line fillet at a moment-tab connection; size for combined moment + shear.
  14. [H] 5/16 fillet 1/16 in. undersized over 20% length: compute % capacity reduction.
  15. [H] Base-plate weld: design 5/16 fillet on a 16 x 16 in. plate with Pu = 400 k, Mu = 75 k-ft.
Structured Clues
  • te = 0.707·w for equal-leg fillet weld.
  • Min size from Table J2.4 depends on thicker connected part.
  • Check base-metal shear rupture in addition to weld metal.
Code References
  • AISC 360-22 §J2
  • AISC Manual Tables 8-1 to 8-12

Quiz

1. Which AISC 360-22 chapter primarily governs welded connections?
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 welded connections. 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.