| name | connection-design |
| description | AISC steel connection design — bolted shear/tension, slip-critical, bearing, welded connections, moment connections, shear tabs, seated connections, LRFD/ASD. |
| metadata | {"priority":6,"promptSignals":{"phrases":["connection design","bolted connection","shear connection","moment connection","AISC connection","bearing strength","slip critical"],"minScore":4}} |
Steel Connection Design (AISC) — Complete Skill
Bolt Design (AISC J3)
Bolt grades: A307 (low strength), A325/A490 (ASTM F3125 Gr A325/A490)
A325: F_ub = 120 ksi (dia ≤ ¾"), 105 ksi (dia > ¾")
A490: F_ub = 150 ksi
Nominal Strengths (per bolt, LRFD):
Shear (bearing-type): φR_nv = φ × F_nv × A_b
F_nv = 54 ksi (A325N, threads in shear plane), 68 ksi (A325X, threads excluded)
F_nv = 68 ksi (A490N), 84 ksi (A490X)
φ = 0.75
Tension: φR_nt = φ × F_nt × A_b
F_nt = 90 ksi (A325), 113 ksi (A490); φ = 0.75
Combined tension + shear (AISC J3-2):
F'_nt = 1.3F_nt - F_nt/φF_nv × f_rv ≤ F_nt
Slip-critical (AISC J3-8):
φR_n = φ × μ × D_u × h_f × T_b × n_s
μ = 0.35 (Class A surface), 0.50 (Class B)
D_u = 1.13 (factor), h_f = 1.0 (standard holes)
T_b = pretension (27 kips for ¾" A325, etc.)
φ = 1.00 (serviceability), 0.85 (strength level)
Bearing on Connected Material (AISC J3-6b):
φR_n = φ × 2.4 × F_u × d × t (standard hole, without deformation limit)
φR_n = φ × 1.2 × L_c × t × F_u ≤ 2.4F_u × d × t (deformation limit at ≤ ¼")
φ = 0.75
L_c = clear distance from edge/hole to next hole
Tearout: φR_n = φ × 1.2 × L_c × t × F_u ≤ 2.4 F_u × d × t
Block Shear (AISC J4-5)
φR_n = φ × [0.6F_u × A_nv + U_bs × F_u × A_nt] ≤ φ[0.6F_y × A_gv + U_bs × F_u × A_nt]
φ = 0.75
A_nv = net shear area, A_nt = net tension area
U_bs = 1.0 (uniform tension), 0.5 (non-uniform)
Simple Shear Connections
Shear Tab (Single Plate): AISC Table 10-9
- Design: bolt shear + block shear + plate shear yielding + plate shear fracture
- Min/max spacing: 3d ≤ s ≤ 12t or 6" (bearing limit)
- Edge distance: 1.5d ≤ L_e ≤ 12t
All-Bolted Double Angle: AISC Table 10-1
- Gage = 2½" standard for angle legs
- OSL (outstanding leg): min 4" for framing
Welded/Bolted Shear Tab:
- Weld to support: E70, min 5/16" fillet to column/beam web
- Bolts through supported beam web
Moment Connections
Flange forces from moment: F_flange = M / d_beam (approx, d = beam depth)
Flange plates: design for T = F_flange in tension + compression
FR Moment Connection (fully restrained):
- Tension flange: bolts or CJP weld
- Shear: web plate
- Compression flange: direct bearing or bolts
SMF Pre-Qualified Connections (AISC 358):
- BFWY: Bolted Flange Welded Web
- WUF-W: Welded Unreinforced Flange-Welded Web
- RBS: Reduced Beam Section (dog bone) — reduces flange width by 20-50%
- WUF-B: Welded Unreinforced Flange-Bolted Web
Continuity Plates: required when web + flange combination insufficient
Fillers, shims per AISC commentary
Weld Connection (AISC J2)
Fillet weld: φR_nw = φ × 0.6F_EXX × A_we
For E70XX: φ × 0.6 × 70 = 0.75 × 42 = 31.5 ksi on throat area
Throat = 0.707 × leg size (45° fillet)
Minimum fillet size (AISC Table J2-4):
t ≤ ¼": min weld = 1/8"
¼ < t ≤ ½": min = 3/16"
½ < t ≤ ¾": min = ¼"
t > ¾": min = 5/16"
Max weld size = t - 1/16" (for t < ¼": max = t)
Directional strength increase (AISC J2-5):
φR_nw = φ × 0.6F_EXX × A_we × (1 + 0.5sin^1.5(θ))
θ = angle between force and weld axis: θ=0° (parallel): factor = 1.0; θ=90° (transverse): factor = 1.5
High-Strength Bolt Installation
Pre-tensioning methods: turn-of-nut, twist-off type, direct tension indicator (DTI), calibrated wrench
Snug-tightened (no pretension): only for bearing-type, Category 1 only
Min bolt pretension (AISC Table J3-1): varies from 12 kips (5/8") to 51 kips (1")
LRFD vs. ASD
LRFD: φRn ≥ ΣγᵢQᵢ (factored loads)
ASD: Rn/Ω ≥ ΣQᵢ (service loads)
Relationship: φ × LRFD ≈ ASD × Ω (Ω = 1/φ × 1.5 for ASD)
φ = 0.90 (yielding), 0.75 (fracture, fasteners), 1.00 (slip-critical, SLS)
Output
Provide: bolt size + grade + quantity + layout, φR_n per bolt [kips], critical limit state, weld size [in], block shear check, governing failure mode.
