Canadian Shear Tab Connection Design — CSA S16 Single Plate Connection
Complete reference for shear tab (single plate) connection design per CSA S16-19. Covers bolt shear at beam web, weld design at the support interface, plate bending, block shear, eccentric load effects, and a step-by-step worked example for a 4-bolt shear tab in 350W steel.
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CSA S16 Shear Tab Philosophy
A shear tab (also called a single plate or fin plate connection) is a steel plate welded to a support and bolted to the beam web. Per CSA S16-19, the connection must be designed for:
- Bolt shear at the beam web (eccentric, because the bolt line is offset from the support face)
- Plate bearing at the bolt holes
- Plate bending (corbel action)
- Plate block shear
- Weld capacity at the support interface
- Gross section yielding of the plate
Eccentricity in Shear Tabs
The eccentricity e in a shear tab connection has two components:
e = a + b/2
Where:
- a = distance from support face to bolt line (weld eccentricity)
- b = distance from bolt line to beam web face (plate thickness + gap)
Total eccentricity is typically 50-80 mm for standard connections, creating a torsional moment on the bolt group.
Bolt Group Design for Shear Tabs
Per CSA S16 Clause 13.12, bolts in shear tabs are eccentrically loaded:
Bolt Vertical Spacing
| Bolt Row Spacing | Typical | Min (CSA S16) | Used For |
|---|---|---|---|
| 75 mm | Standard | 3d for M20 | Convenient layout (75 mm = 3 inch legacy) |
| 80 mm | Standard for M24 | 3d | Heavy shear tabs |
| 100 mm | Wide spacing | 3d | Seismic connections |
Number of Bolts
The number of vertical bolt rows depends on the shear demand. The elastic vector method is conservative. For a concentrated load on the connection, the IC method (CISC Handbook) provides more accurate capacity.
Weld Design
Per CSA S16 Clause 13.13, the weld between shear tab and support must develop:
- Direct shear: Vf from beam reaction
- Eccentric moment: Vf × e (e = distance from support face to bolt line)
The resultant stress on the weld group is the vector sum of direct and torsional components.
Weld Size from Demand
For a typical shear tab with Vf = 200 kN, plate width = 200 mm, e = 60 mm:
M_weld = 200 × 60 = 12,000 kN·mm
Weld section modulus: S_w = 2 × (0.707 × D) × L^2 / 6 = 0.707 × D × L^2 / 3
For D = 6 mm E48XX: Vr_weld = 0.915 kN/mm per fillet leg (from weld capacity table)
Total weld capacity per vertical mm: 2 × 0.915 = 1.830 kN/mm (both sides of plate).
Plate Design
Per CSA S16 Clause 13.5, the shear tab must be checked for:
Plate Thickness
Minimum plate thickness per CSA S16 Clause 22.3: tp ≥ 0.5 × d_bolt (for M20, tp ≥ 10 mm).
| Bolt Dia | Min tp | Typical tp | Used For |
|---|---|---|---|
| M16 | 8 mm | 10 mm | Light shear |
| M20 | 10 mm | 12-16 mm | Standard |
| M24 | 12 mm | 16-20 mm | Heavy shear |
Plate Bending (Corbel Action)
Per CISC Handbook, the shear tab must resist the moment from the eccentric shear force:
Mf_plate = Vf × e_bending
Where e_bending = distance from weld line to the bolt line (typically a).
Required plate thickness for bending: tp_req = sqrt(6 × Mf_plate / (phi × Fy × L_plate))
Block Shear
Per CSA S16 Clause 13.2:
Tr_block = phi_u × (Atn × Fu + 0.60 × Avn × Fu) ≤ phi × (Atg × Fy + 0.60 × Avg × Fy)
The block shear path goes through the bolt holes on the net shear planes and tension plane.
Worked Example — 4-Bolt Shear Tab
Given: Vf = 180 kN (factored), W410×60 beam, 350W steel. Shear tab welded to W360×216 column flange. 4-M20 A325M bolts (AA — threads intercepted).
Step 1 — Bolt Group Check: Vertical spacing = 75 mm (3 rows at 75 mm = 225 mm bolt group height) Eccentricity: a = 10 mm (weld leg) + 10 mm (gap) = 20 mm. b/2 ≈ 20 mm. Total e = 20 + 20 = 40 mm.
Elastic vector method: n = 4, centroid at mid-height of group. r_max = 112.5 mm for top and bottom bolts. sum(r_i^2) = 2 × 112.5^2 + 2 × 37.5^2 = 28,125 mm^2
Direct shear: 180/4 = 45 kN Torsional shear at critical bolt: V_to = 180 × 40 × 112.5 / 28,125 = 28.8 kN Resultant: V_res = sqrt(45^2 + 28.8^2) = 53.4 kN
Vr AA per M20 A325M = 81.3 kN 53.4 ≤ 81.3. Ratio = 0.66. OK.
Step 2 — Plate Design: Try 12 mm plate, 350W. Gross yielding: Tr = phi × A_g × Fy = 0.90 × 12 × 240 × 350 / 1000 = 907 kN. OK. Plate bending: Moment at weld line = 180 × 20 = 3,600 kN·mm. Z_plate = 12 × 240^2 / 4 = 172,800 mm^3 Mr = 0.90 × 172,800 × 350 / 10^6 = 54.4 kN·m ≥ 3.6 kN·m. OK.
Step 3 — Block Shear Check: Net tension area: Atn = (60 - 22) × 12 = 456 mm^2 Net shear area: Avn = 2 × (225 - 3.5 × 22) × 12 = 2 × 148 × 12 = 3,552 mm^2 Tr_block = 0.75 × (456 × 450 + 0.60 × 3,552 × 450) / 1000 = 0.75 × (205,200 + 959,040) / 1000 = 873 kN Gross section: Tr_gross = 0.90 × (60 × 12 × 350 + 0.60 × 2 × 225 × 12 × 350) / 1000 = 0.90 × (252,000 + 1,134,000) / 1000 = 1,247 kN Tr_block = min(873, 1247) = 873 kN ≥ 180 kN. OK.
Step 4 — Weld: 6 mm fillet weld, E48XX, both sides of plate (240 mm vertical): Vr_weld = 2 × 0.915 × 240 = 439 kN (direct) Moment at weld: M = 180 × 20 = 3,600 kN·mm S_w = 0.707 × 6 × 240^2 / 3 = 81,485 mm^3 Vr_weld_moment = 0.67 × 0.67 × 480 × 81,485 / (240 × 1000) = 365 kN Resultant: V_weld = sqrt(180^2 + (3600/240)^2) / 439 ratio = 0.41. OK.
Result: 4-M20 A325M AA bolts, 240×12 mm shear tab (350W), 6 mm fillet weld both sides, E48XX.
Standard Shear Tab Configurations
| Beam Size Range | No. of Bolts | Plate Size (mm) | Weld | Shear Capacity (kN) |
|---|---|---|---|---|
| W250-W310 | 3-M20 | 200×10×350 | 6 mm fillet | 120 |
| W310-W410 | 4-M20 | 240×12×350 | 6 mm fillet | 180 |
| W410-W530 | 5-M20 | 280×12×350 | 8 mm fillet | 220 |
| W530-W610 | 6-M20 | 320×16×350 | 8 mm fillet | 270 |
| W610-W690 | 8-M20 | 380×16×350 | 10 mm fillet | 350 |
Frequently Asked Questions
What is the eccentricity in a shear tab connection? The eccentricity e is the distance from the bolt line to the weld line (support face). It typically comprises: weld leg + gap between plate and support (10-15 mm total) plus the distance from the bolt line to the plate surface. Total e ranges from 50-80 mm for standard connections. This eccentricity creates a moment on both the bolt group and the weld, which must be included in design.
What thickness should a shear tab plate be for M20 bolts? Minimum 10 mm per CSA S16 Clause 22.3 (tp ≥ 0.5 × d_bolt = 10 mm for M20). Typically 12-16 mm for standard shear tabs. The plate thickness must also satisfy bearing and block shear checks. Thicker plates (16 mm) increase the connection stiffness and reduce rotation demand on bolts.
How do you calculate block shear for a shear tab? Block shear per CSA S16 Clause 13.2 considers shear failure along the bolt hole lines combined with tension failure across the end. For a shear tab, the shear planes are vertical through the bolt lines, and the tension plane is horizontal at the bottom. The net area (deducting holes) is used for rupture, gross area for yielding. The lesser of the two capacities governs.
When should a shear tab be used instead of an end plate? Shear tabs are used for simple (shear) connections where no moment transfer is required. End plates are used for moment connections. Shear tabs are: cheaper to fabricate, allow for beam end rotation (simple beam assumption), easier to erect (beam can be lowered into place), and require less precision. End plates are used where moment continuity is needed (moment frames, seismic connections).
Related Pages
- CSA S16 End Plate Connection
- CSA S16 Bolt Bearing & Tearout
- CSA S16 Bolt Spacing & Edge Distance
- CSA S16 Weld Capacity
- CSA S16 Gusset Plate Design
- Bolted Connection Calculator
- All Canadian References
This page is for educational reference. Shear tab design per CSA S16-19. Verify connection rotation capacity for simple beam assumption. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent PE/SE verification.
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