Bolted Connection Types — CSA S16 Clause 22.3
CSA S16:24 recognizes three connection types:
| Type | Serviceability | Bolt Grade | Surface Prep | Application |
|---|---|---|---|---|
| Bearing-type (threads included) | Slip permitted | A325 / A490 | As-rolled | Standard connections |
| Bearing-type (threads excluded) | Slip permitted | A325 / A490 | As-rolled | Shear-critical, thicker plates |
| Slip-critical | No slip at service | A325 / A490 | Class A/B/C faying surface | Fatigue, vibration, oversized holes |
This guide focuses on bearing-type connections — the most common type in Canadian building construction.
Shear Resistance — Clause 13.12.1.2
Factored shear resistance per bolt, threads included in shear plane:
Vr = 0.60 x phi_b x 0.70 x Ab x fu
Where:
- phi_b = 0.80 (bolts)
- 0.70 = reduction factor when threads intercept the shear plane
- Ab = nominal bolt body area (pi x d^2 / 4)
- fu = specified minimum tensile strength (830 MPa for A325 <= 1", 725 MPa for A325 > 1")
Threads excluded (body in shear plane): Vr = 0.60 x phi_b x Ab x fu (no 0.70 reduction)
The 0.70 reduction accounts for the reduced shear area when threads are in the shear plane — the root diameter is approximately 0.84 x nominal diameter, giving a stress area ratio of approximately 0.75-0.78. CSA uses 0.70 to be conservative.
Tension Resistance — Clause 13.12.1.3
Factored tensile resistance per bolt:
Tr = 0.75 x phi_b x Ab x fu
No thread-plane distinction for tension — the threaded portion always governs due to stress concentration at the thread root.
Combined Shear-Tension — Clause 13.12.1.4
For bolts subjected to simultaneous shear and tension:
(Vf / Vr)^2 + (Tf / Tr)^2 <= 1.0
This elliptical interaction accounts for the reduced shear capacity when tension is present and vice versa. The exponent of 2 is less conservative than a linear interaction (which would be Vf/Vr + Tf/Tr <= 1.0).
Bolt Design Capacities — CSA S16:24 (A325, phi = 0.80)
| Bolt Diameter | Ab (mm^2) | Vr Threads In (kN) | Vr Threads Out (kN) | Tr Tension (kN) |
|---|---|---|---|---|
| 1/2" (12.7) | 127 | 31.9 | 45.7 | 45.7 |
| 5/8" (15.9) | 198 | 49.9 | 71.3 | 71.3 |
| 3/4" (19.1) | 285 | 71.8 | 102.6 | 102.6 |
| 7/8" (22.2) | 387 | 97.5 | 139.3 | 139.3 |
| 1" (25.4) | 507 | 127.7 | 182.5 | 182.5 |
Note: A325 fu = 830 MPa for d <= 1". For d > 1" (1-1/8" and 1-1/4"), fu = 725 MPa — capacities reduce approximately 13%.
Bearing Resistance at Bolt Holes — Clause 13.12.1.1
When bolt shear capacity exceeds the connected plate bearing capacity, bearing failure governs. The bearing resistance per bolt hole:
Br = 3.0 x phi_br x tp x d x Fu (for standard holes, deformation permitted)
Where:
- phi_br = 0.80 (bearing)
- tp = minimum connected plate thickness (mm)
- d = bolt diameter (mm)
- Fu = plate tensile strength (MPa, e.g., 450 MPa for 350W)
For connections where deformation at service load is not permitted (slip-critical or long slotted holes with load perpendicular to slot): Br = 2.4 x phi_br x tp x d x Fu
Tearout Resistance — Clause 13.12.1.1
When the bolt-to-edge distance is small, tearout (end pull-out) governs:
Br = 1.5 x phi_br x a x tp x Fu (for a < 2d, standard holes)
Where a is the clear distance from the bolt hole to the edge of the plate in the direction of load, measured perpendicular to the bolt line.
Worked Example: Beam-to-Column Shear Tab Connection
Problem: Design a shear tab (single plate) connecting a W460x67 beam to the web of a W310x158 column. Factored shear Vf = 380 kN. Beam web thickness = 8.8 mm. Use 3/4" A325 bolts, threads included, in CSA G40.21 350W plate (Fu = 450 MPa). Shear tab plate thickness = 10 mm.
Step 1 — Bolt shear capacity: For 3/4" A325, threads included: Vr = 71.8 kN per bolt.
Number of bolts required = Vf / Vr = 380 / 71.8 = 5.3 — use 6 bolts.
Step 2 — Bolt layout (CSA S16 Clause 22.3.2):
- Minimum spacing: 2.67d = 2.67 x 19.1 = 51.0 mm — use 75 mm centres (3d typical)
- Minimum edge distance (sheared edge): 1.5d = 1.5 x 19.1 = 28.7 mm — use 35 mm
- 6 bolts in a single column at 75 mm pitch: total depth = 5 x 75 + 2 x 35 = 445 mm
Step 3 — Bearing check (10 mm plate, Fu = 450 MPa): Br = 3.0 x 0.80 x 10 x 19.1 x 450 / 1000 = 206.3 kN per bolt
Bearing capacity per bolt (206.3 kN) >> shear per bolt (380/6 = 63.3 kN). Bearing is not critical.
Step 4 — Beam web bearing (8.8 mm web): Br_web = 3.0 x 0.80 x 8.8 x 19.1 x 450 / 1000 = 181.5 kN >> 63.3 kN. OK.
Step 5 — Shear tab plate shear (gross section, Clause 13.4): Plate cross-section at bolt line: Ag = 10 x 445 = 4,450 mm^2 Vr_plate = 0.90 x 0.66 x 4450 x 350 / 1000 = 925 kN >> 380 kN. OK.
Step 6 — Shear tab plate shear (net section at bolt holes): Net area: A_net = 10 x (445 - 6 x 21.5) = 10 x 316 = 3,160 mm^2 (21.5 mm = 19.1 mm bolt + 2.4 mm clearance for standard hole) Vr_net = 0.90 x 0.66 x 3160 x 450 / 1000 = 845 kN >> 380 kN. OK.
Step 7 — Weld to column: The shear tab is fillet welded to the column web. Weld size = 6 mm (matching plate thickness standard for 10 mm plate). Weld length = 445 mm (plate depth).
Weld capacity per unit length per CSA S16:24 Cl 13.13.1: Vr_weld = 0.67 x phi_w x 0.707 x a x Xu Where phi_w = 0.67, a = 6 mm leg size, Xu = 490 MPa (E49XX electrode). Vr_weld / mm = 0.67 x 0.67 x 0.707 x 6 x 490 / 1000 = 0.933 kN/mm.
Total weld capacity = 0.933 x 445 x 2 (both sides) = 830 kN >> 380 kN. OK. 6 mm fillet weld is adequate.
Final design: 6 x 3/4" A325 bolts at 75 mm pitch. 10 mm x 445 mm deep shear tab. 6 mm fillet weld both sides to column. Specify "threads included in shear plane" on fabrication drawings.
Frequently Asked Questions
What is the practical difference between bearing-type and slip-critical? Bearing-type connections are standard for static building frames — they allow some slip into bearing at factored loads, which is acceptable for strength design. Slip-critical is required for: (a) connections with oversize or slotted holes where slip would affect the structure's performance, (b) connections subjected to fatigue or significant load reversal, (c) connections with combined shear + tension where the faying surface is critical. The cost premium for slip-critical is 15-30% due to surface preparation requirements.
When should threads be excluded from the shear plane? Threads excluded (body in shear plane) is preferred when: (a) bolt is short enough that the threaded portion stays outside the grip, (b) shear is the dominant force (pure shear tab, splice plate), or (c) the bolt count is being minimized (higher capacity per bolt). For typical beam end connections with standard grip lengths (< 50 mm), the threads will be partially in the shear plane — specify threads included for conservative design unless thread location is explicitly controlled.
How do I check for combined shear-tension in a moment connection? In moment end plate connections, the tension bolts (upper rows) also carry some shear from the beam reaction. The interaction per Clause 13.12.1.4: sum (Vf/Vr)^2 + (Tf/Tr)^2 per bolt. The bolt with the highest tension (top row) typically governs. A common rule of thumb: if Tf/Tr < 0.30, combined effects can be ignored in favour of separate shear and tension checks.
This page is for educational reference. Bolt design per CSA S16:24 Clause 13.12. Verify bolt capacities against CISC Handbook Tables 3-35 through 3-40. All structural designs must be independently verified by a licensed Professional Engineer. Results are PRELIMINARY — NOT FOR CONSTRUCTION.