S
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LecturesModule 15

Moment Connections

Welded and bolted fully-restrained moment connections.

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 moment 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.

Mu, VuFR welded-flange / bolted-web (continuity plates)
Fully-restrained moment connection: CJP flange welds + bolted shear tab + continuity plates.

Formula Sheet

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

Worked Example

Moment 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 (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
Beam Mu=300 k-ft, d≈18 in.
AISC Reference
AISC §J10 / Manual Part 12
Step-by-step solution
  1. Fpr
    Mu/(d − tf) = 300×12/(18 − 0.5) = 206 k (flange tension or compression)
Answer Each flange transmits ~206 k.
Mu, VuBolted FR moment connection

Practice Problems

  1. [E] Distinguish FR from PR connections.
  2. [E] List two common FR moment connections.
  3. [E] AISC chapter and Manual part covering moment connections (Ch. J, Part 12).
  4. [E] Define the panel zone.
  5. [E] §J10 limit states for concentrated forces at a column.
  6. [M] Design bolted end-plate FR moment conn for Mu = 180 k-ft, Vu = 40 k.
  7. [M] Welded flange / bolted web FR: design CJP flange welds for Mu = 250 k-ft.
  8. [M] Compute panel-zone shear: W14x132, ΣMb,u = 700 k-in at joint.
  9. [M] Column flange local bending check (§J10.1) for a 200 k flange force.
  10. [M] Continuity-plate sizing for W14x120 column with W21x62 beam framing in.
  11. [H] Pre- vs post-Northridge welded moment conn: compare details; why backing-bar removal.
  12. [H] Design 4-bolt unstiffened extended end-plate per AISC DG-4 / AISC 358 prequalified.
  13. [H] Panel-zone yielding in seismic: check Σh·V > 0.4·ΣMy per AISC 341.
  14. [H] Doubler plate for W14x120 with insufficient web thickness.
  15. [H] Prequalified RBS connection per AISC 358 §5: locate the cut; verify flexural strength.
Structured Clues
  • Designate the connection as FR or PR per AISC §B3.4.
  • For directly-welded flange moment connections, the panel-zone shear is Mu/(0.95d).
  • Check column flange flexural yielding and web crippling at the beam flanges.
Code References
  • AISC 360-22 §B3, J10
  • AISC Manual Part 12, 13

Quiz

1. Which AISC 360-22 chapter primarily governs moment 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 moment 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.