Canadian End Plate Connection Design — CSA S16 Moment Connection

Complete reference for end plate moment connection design per CSA S16-19. Covers 4-bolt unstiffened and 8-bolt stiffened end plates, bolt prying action, plate bending design, weld design (flange welds vs web welds), and a step-by-step worked example for a W410x60 beam.

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CSA S16 End Plate Design Framework

End plate connections transfer moment through:

Bolts in tension (above beam flange on tension side)
Bolt prying action (additional tensile force from plate bending)
End plate bending (plate thickness must be adequate)
Flange compression (below beam flange on compression side)
Column flange bending (must be checked for stiffener requirements)
Welds (flange groove welds or fillet welds; web fillet welds for shear)

Connection Types

Type	Bolts	Application	Moment Capacity
Unstiffened — 4 bolt	2 rows of 2	Light moment, beams up to W530	Up to 200 kN·m
Stiffened — 8 bolt	4 rows of 2	Moderate moment, beams W410-W690	200-600 kN·m
Extended — 8 bolt	2 rows inside + 2 rows outside flange	Moderate moment, deeper beams	300-800 kN·m
Extended — 12 bolt	3 rows inside + 2 rows outside + 1 row outside	Heavy moment, large beams	500-1200 kN·m

Bolt Prying Action

Per CSA S16 Clause 13.12.4, bolts in end plate connections are subject to prying action — additional tension from plate flexure:

Prying Force Equation

Q = (M_plate / (p - t_w/2)) / 2

Where:

Q = prying force per bolt row (kN)
M_plate = moment in end plate at bolt line per unit width
p = bolt pitch (distance between tension bolt rows)
t_w = beam web thickness

Prying Factor Alpha

alpha = (ln(bf/2) / ln(p)) × (tp^2 × Fy × Bp) / (6 × Tf × p)

Where:

bf = beam flange width
tp = end plate thickness
Bp = effective plate width per bolt
Tf = factored tension force per bolt

Simplified Prying Check

If tp ≥ (0.5 × Tf × bf / (0.90 × Fy × p))^0.5, prying effects are negligible.

For typical connections with tp ≥ 20 mm, prying action increases bolt tension by 20-40%.

End Plate Thickness Design

Per CSA S16 Clause 13.5 (plate bending):

Mr_plate = phi × Z_plate × Fy per unit width of plate

The factored moment in the plate at the bolt line:

Mf_plate = (Tf_per_bolt × p) / (2 × b_eff)

Required plate thickness per unit width for plastic moment:

tp_req = sqrt(4 × Mf_plate / (phi × Fy))

Minimum End Plate Thickness

Beam Depth	Connection Type	Min tp (350W)	Typical tp
W310-W410	4-bolt unstiffened	12 mm	16-20 mm
W410-W530	4-bolt unstiffened	16 mm	20-25 mm
W410-W530	8-bolt extended	16 mm	20-25 mm
W530-W690	8-bolt extended	20 mm	25-32 mm
W690-W920	12-bolt extended	25 mm	32-38 mm

Weld Design

Flange Welds

Per CSA S16 Clause 13.13, flange welds must develop the flange force:

Ff = Mf / d_beam (flange force from moment)

Flange Force (kN)	Required Flange Weld	Typical Detail
≤ 500	8 mm fillet each side	FJP not required
500-1000	10 mm fillet each side	Usually okay
1000-1500	12 mm fillet each side	Consider CJP
> 1500	CJP groove weld required	Full joint penetration

Web Welds

Per CSA S16, web welds must transfer the factored shear:

Vr_web = 0.67 × phi_w × Xu × 0.707 × D × L_weld

For a W410x60 beam with Vf = 200 kN, using E48XX electrodes: Required D per side (two web welds) = Vf / (2 × 0.67 × phi_w × Xu × 0.707 × L_web) = 200 × 1000 / (2 × 0.67 × 0.67 × 480 × 0.707 × 350) = 1.9 mm → use 6 mm minimum weld.

Worked Example — 4-Bolt Unstiffened End Plate

Given: W410×60 beam (350W) to column W360×216 flange. Moment Mf = 150 kN·m, shear Vf = 120 kN. Four A325M M24 bolts outside the beam tension flange. Plate 350W.

Step 1 — Bolt Design: Flange force: Ff = 150 × 10^6 / (407 - 16.3) = 150 × 10^6 / 390.7 = 384 kN Tension per bolt: Tf = Ff / 4 = 96 kN (assuming equal sharing, no prying — check later) Bolt tension capacity: Tr = 0.75 × phi_b × Ab × Fu = 0.75 × 0.80 × 452 × 830 / 1000 = 240.4 kN 96 ≤ 240.4 kN. OK.

Step 2 — Prying Check: For M24 bolts, p = 100 mm (vertical), bf = 178 mm (beam flange) Conservative Tf_adjusted = 1.25 × 96 = 120 kN (including ~25% prying effect) Check: 120 ≤ 240.4 kN. OK.

Step 3 — End Plate Thickness: Assuming Mf_plate governs at bolt line: tp_req = sqrt(4 × (120,000 × 50) / (0.90 × 350 × 178/2)) = sqrt(24,000,000 / 28,035) = sqrt(856) = 29.3 mm Try 32 mm plate.

Step 4 — Weld Design: Flange welds: Ff = 384 kN, use 10 mm fillet each side. Vr_flange_weld = 2 × (0.67 × 0.67 × 480 × 0.707 × 10) × 178 / 1000 = 543 kN ≥ 384 kN. OK.

Web welds: Vf = 120 kN, use 6 mm fillet each side per CSA W59 minimum. Vr_web = 2 × 0.67 × 0.67 × 480 × 0.707 × 6 × 350 / 1000 = 548 kN ≥ 120 kN. OK.

Step 5 — Column Flange Check: Column flange: W360×216, tf = 25.9 mm. Need to check local flange bending per CSA S16 Clause 14.3. p = 100 mm > tf + k = 25.9 + 32 = 57.9 mm. Stiffener not required if: Tf ≤ 0.60 × phi × tf^2 × Fy_col × (12 × B_flex / (4 × p^2 - t_w_col^2))^0.5 = 0.60 × 0.90 × 25.9^2 × 350 × (12 × / (4 × 100^2 - 12.3^2))^0.5 ≈ 1124 kN ≥ 120 kN. OK (no column stiffeners required).

Result: 4-M24 A325M bolts, 32 mm end plate, 10 mm flange fillet welds, 6 mm web fillet welds. No column stiffeners required.

Column Stiffener Requirements

Per CSA S16 Clause 14.3.2, column stiffeners are required when:

Flange local bending: Tf > available capacity from column flange bending formula
Web local yielding: Ff > capacity of column web (t_w_col × (tf_col + 5k_col) × Fy_col)
Web crippling: Ff > Br capacity per Clause 14.3.2

For W360×216 column: tw = 12.3 mm, tf = 25.9 mm, k = 32 mm.

Check	Capacity	Tf/Ff	Stiffeners Needed?
Flange local bending	~1124 kN	120 kN	No
Web local yielding	~500 kN	384 kN	No
Web crippling	~400 kN	384 kN	No

When stiffeners are required, use full-depth stiffeners (doublers) welded to column web and flanges.

Frequently Asked Questions

What is prying action in end plate connections? Prying action is the additional tensile force in bolts caused by flexural deformation of the end plate. As the plate bends under load, it bears against the bolt head/nut at the outer edges, creating a lever action that amplifies the bolt tension. For unstiffened 4-bolt connections, prying can increase bolt tension by 20-40%. Per CSA S16 Clause 13.12.4, the prying effect must be considered in bolt design.

When are column stiffeners required in Canadian end plate connections? Column stiffeners are required when the column flange or web lacks sufficient capacity to resist the concentrated flange forces from the beam. Per CSA S16 Clause 14.3, check: flange local bending (Tf from bolts), web local yielding (Ff from beam flange compression), and web crippling. For heavy moment connections with W360 or smaller columns, stiffeners are commonly needed. W460+ columns typically resist these forces without stiffeners for moderate moments.

What is the difference between 4-bolt and 8-bolt end plate connections? A 4-bolt unstiffened end plate has two rows of bolts entirely outside the beam tension flange. It is limited by end plate thickness (prying action increases with plate flexibility). An 8-bolt extended connection has additional bolts inside the flange, distributing the tension force more evenly and reducing prying. 8-bolt connections can resist 2-3× the moment of 4-bolt connections with the same plate thickness.

Do end plate welds require full joint penetration groove welds? For flange forces below approximately 1000 kN, fillet welds each side of the flange are adequate per CSA S16. For forces exceeding 1500 kN, complete joint penetration (CJP) groove welds are typically specified. The transition depends on weld size availability: the maximum practical fillet weld is 12 mm (16 mm in heavy fabrication), providing approximately 1.83 kN/mm with E48XX. If Ff/bf > 1.83 kN/mm, a CJP groove weld is needed.

This page is for educational reference. End plate connection per CSA S16-19 Clauses 13.12-13.14. Verify column stiffener requirements per Clause 14.3. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent PE/SE verification.

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