Steel side and knife plate connections
Bolts or drift pins through a wood member with steel plates. The plates are two side plates, one side plate, or one knife plate let into a kerf in the wood. The calculation covers the fasteners in the wood (NDS 2024 Chapters 11 and 12), the local stresses in the wood around the group (11.1.2 and Appendix E) and the steel plate (AISC 360-22 J3 and J4). LRFD or ASD.
Inputs of the connection #
- Arrangement:
- Two steel side plates on a wood main member: double shear.
- One steel side plate: single shear.
- One knife plate in a kerf: double shear, with the plate as the main member and the wood on each side of the kerf as the side members.
- Fastener:
- Bolts, with the bolt grade for the steel shear check, or drift pins at 75 % of a bolt (12.3.10).
- Diameter 1/2 in. to 1 in., and the bending yield strength Fyb (45,000 psi for bolts).
- Plate: thickness, width, kerf width (usually the plate plus 1/8 in.), Fy and Fu. Fu sets the dowel bearing strength of the steel, Fe = 1.5 Fu.
- Pattern:
- Rows across the member and fasteners in each row along it, with the spacing in a row and between rows.
- Staggered rows: alternate rows have one fewer fastener, offset by half the spacing.
- The end distance in the wood, whether the member is in tension or compression at that end, the edge distance of the outer rows, and the plate end distance.
- Wood member:
- Sawn lumber (Douglas Fir-Larch, Hem-Fir, Spruce-Pine-Fir or Southern Pine, Select Structural to No. 2).
- A glulam stress class (Table 5A) or axial combination (Table 5B), with its thickness and width.
- Or Ft, Fv, E and G entered.
- For glulam, the shear reduction factor Cvr = 0.72 at connections (NDS 5.3.10) is on by default.
- Loads: dead, live, snow and wind along the member, combined by ASCE 7-22, and the load angle to grain.
- Service: moisture (Table 11.3.3), temperature (Table 11.3.4), and the local stress check (NDS 11.1.2, on by default). Load duration factors and the time effect factor are in the code options.
Auto-design (editor toolbar) varies the fastener diameter, the fasteners per row and the rows. The arrangement, plate, member and spacings stay as entered. Objective: the least fastener steel, or the fewest fasteners.
Checks performed #
| Check | Basis |
|---|---|
| Kerf at least the plate, wood left on each side | Input |
| Rows fit the member and the plate | Edge distances and row spacing |
| Reference Z of one fastener | NDS Table 12.3.1A yield modes (single or double shear), steel Fe = 1.5 Fu, wood Fe by Hankinson, Rd with Kθ (Table 12.3.1B) |
| Adjusted group capacity n Z' | CD (≤ 1.6) or KF φz λ (λ ≤ 1.0), CM, Ct, Cg (Eq. 11.3-1, γ = 270,000 D^1.5 wood to metal), CΔ (Tables 12.5.1A, 12.5.1B), drift pins × 0.75; every load combination |
| End distance, spacing, edge distance, row spacing | Tables 12.5.1A to 12.5.1D; the 5 in. limit between outer rows (12.5.1.3) as a note |
| Net section tension of the wood | Appendix E, Eq. E.2-1, every row deducted, net of the kerf |
| Row tear-out | Eqs. E.3-1 to E.3-3: n F'v t s_critical per row, s_critical the lesser of the end distance and the spacing |
| Group tear-out | Eq. E.4-1: half of each outer row's tear-out plus F't on the net area between the outer rows |
| Bolt shear | AISC 360-22 J3.7, Table J3.2, per shear plane |
| Bolt bearing and tear-out in the plate | J3.11(a)(1): 1.2 lc t Fu ≤ 2.4 d t Fu per bolt; each of two side plates takes half the load |
| Plate tension yielding and rupture | J4.1 (holes 1/16 in. over the standard hole, U = 1.0) |
| Plate block shear | J4.3 along the two outer bolt lines |
The drawings are the joint elevation (the member end, the plate, the fasteners, end distance, spacing, edge distances and the load) and a section through a row (plates, wood, kerf and fastener).
Limitations #
- Not designed:
- Two or more knife plates (multiple shear planes, 12.3.8). Lag screws and dowels driven into blind holes.
- The plate's connection beyond the joint (welds, other bolts) and the plate in compression (buckling between bolts).
- The member away from the joint.
- Local stresses (Appendix E) are for load parallel to grain. With a load at an angle, check the member's shear at the connection (3.4.4) and splitting in the member's own calculation.
- Our readings:
- With staggered rows, every row is deducted for the net section, as Appendix E sample E.7 does.
- For Cg, Am and As are divided by the number of rows.
- Staggered rows closer than a quarter of the distance between their nearest fasteners act as one row (11.3.6.3).
- The member's F't and F'v use the connection's CD (at most 1.6) or λ (at most 1.0): conservative where a member could take more.
- Edge distance: checked with the parallel-to-grain requirement for loads along the member. The loaded edge requirement (4D) applies when the load has a perpendicular component.
Verification examples #
Verification status: 16 values compared in 4 examples (1 published, 3 hand calculations from the cited equations): 16 within tolerance, 0 recorded deviations. Thin: only 1 published example. Code basis: not yet recorded for this module.
The published example is NDS 2024 Appendix E sample solution E.7 (pp. 176-177): staggered 1 in. bolts through a combination 2 Douglas Fir glulam with 1/4 in. steel side plates. It checks Z, the row tear-out of each row and in total, the net section and the group tear-out. The example rounds F'v to 191 psi, 0.1 % above the unrounded 190.8 psi.
The default knife plate's yield modes, a sawn member with two side plates, and the default plate's AISC checks are hand calculations. No published knife-plate example is on disk.