Timber rivet connections
Timber rivets (glulam rivets) driven through steel side plates into structural glued laminated timber, by NDS 2024 Chapter 14 with the adjustment factors of Chapter 11. LRFD or ASD.
Inputs of the rivet connection #
- Rivets and plates:
- Rivet length: 1-1/2, 2-1/2 or 3-1/2 in., the lengths of Tables 14.2.1A to 14.2.1F. The penetration is p = length − plate thickness − 1/8 in. (14.2.1).
- Rows across the grain and rivets per row along the grain: for a load along the grain these are the code's nR and nC. For a load across the grain the roles swap: the rows parallel to the load run across the grain.
- Spacing along the grain sp: 1 or 1-1/2 in., the values the tables give. The code minimum is 1 in. (14.3.1).
- Spacing across the grain sq: 1 or 1-1/2 in. The code minimum is 1/2 in., but Tables 14.2.1A to 14.2.1F are for 1 in. and Table 14.2.2A for 1 or 1-1/2 in.
- Side plates: one plate, or plates on opposite faces. The plate thickness is ASTM A36, at least 1/8 in. A plate thinner than 1/4 in. reduces the rivet capacity by Cst (Table 14.2.3).
- Member: Douglas Fir-Larch or Southern Pine glulam, the only members Chapter 14 covers (14.1.1).
- Thickness: with plates on both faces, the tables are entered with the thickness; with one plate, with twice the thickness.
- Depth at the joint: across the grain. With the unloaded edge distance and the rows, it gives the far edge distance.
- Load angle to grain.
- End distance: from the member end to the nearest row.
- Unloaded edge distance ep: for a load across the grain it also sets the geometry factor CΔ (Table 14.2.2B).
- Loads: dead, live, snow and wind on the connection, combined by ASCE 7-22.
- Service conditions:
- Moisture: CM = 0.8 in service wet (Table 11.3.3). Table 11.3.3 gives no factor for rivets fabricated wet, so that case is not feasible.
- Temperature: Ct of Table 11.3.4.
- Load duration: the load duration factors and the live-load time effect factor are in the code options.
Auto-design (editor toolbar) varies the rivets per row, the rows and the rivet length. Objective: the fewest rivets, then the shorter rivet. The member, plates, spacings, distances and loads stay yours.
Checks performed #
| Check | Basis |
|---|---|
| Rivet capacity parallel to grain | Pr = 188 p^0.32 nR nC (Eq. 14.2-1), per plate |
| Wood capacity parallel to grain | Pw from Table 14.2.1A to 14.2.1F by rivet length and sp, member dimension (thickness, or twice it with one plate), rivets per row and rows; linear interpolation as the tables' note permits |
| Rivet and wood capacity perpendicular to grain | Qr = 108 p^0.32 nR nC (Eq. 14.2-2); Qw = qw p^0.8 CΔ (Eq. 14.2-3) with qw from Table 14.2.2A and CΔ from Table 14.2.2B at ep / ((nC − 1) sq), interpolated |
| Metal side plate factor | Cst (Table 14.2.3) only when the rivet capacity controls; CΔ only on the wood capacity (Table 11.3.1 footnotes 4 and 5) |
| Load at an angle to grain | N' = P'Q' / (P' sin²θ + Q' cos²θ) (Eq. 14.2-4) |
| Connection capacity | Plates × N' against the load, every combination with CD (≤ 1.6) or KF φz λ (λ ≤ 1.0); no group action factor (Table 11.3.1) |
| Penetration | At most 70 % of the member thickness (14.1.3.2); with plates on both faces the points must not overlap |
| Plate thickness | At least 1/8 in. (14.1.2.2) |
| Spacing | Outermost rows at most 12 in. apart across the grain (14.3.1) |
| End and edge distances | Table 14.3.2: end distance ap (parallel) or aq (perpendicular) by the number of rows, unloaded edge ≥ 1 in., loaded edge ≥ 2 in. |
The drawings are the joint elevation (the plate over the rivet group, the rows, end and edge distances, the load) and a section through the member with the plates and the rivet penetration.
Limitations #
- Not designed:
- the steel side plates and their connection to the rest of the structure (14.2.6; AISC 360);
- the member's net section and local stresses (Appendix E);
- the member itself.
- Not offered: rivets in end grain (14.2.5) and rivets from opposite faces whose points overlap (14.1.3.3).
- Tabulated values only: spacings, rivet lengths and group sizes outside the tables are not feasible. This includes a load across the grain with sp other than 1 in. (Table 14.2.2A is for sp = 1 in.). The tables are not extrapolated.
- Geometry factor: CΔ is interpolated linearly between the rows of Table 14.2.2B. This is our reading: the code gives the table without saying how to read between rows.
- Scope of Chapter 14: Douglas Fir-Larch and Southern Pine glulam only. Sawn lumber and CLT are outside it.
Verification examples #
Verification status: 17 values compared in 8 examples (5 published, 3 hand calculations from the cited equations): 17 within tolerance, 0 recorded deviations. Code basis: not yet recorded for this module.
Published values: the NDS 2024 tables themselves, read from the page images of the 2024 scan:
- Pw of Tables 14.2.1A and 14.2.1C, including one plate entered with twice the member thickness;
- qw of Table 14.2.2A;
- CΔ of Table 14.2.2B;
- Cst of Table 14.2.3;
- the end distance of Table 14.3.2.
Hand calculations: the rivet capacity Pr, the wood capacity Qw, interpolation between member dimensions, a 3/16 in. plate, a load at 45° and the default connection in ASD and LRFD.
Neither the NDS nor its Commentary has a worked timber rivet example. AWC's Structural Wood Design Examples are listed as needed.