Embed plate
Checks a steel plate with welded headed studs, flush in a concrete face, taking an attached member's moment, shear and tension. ACI 318-19 Chapter 17 for the studs, strength design. The plate is checked for bending and the concrete for bearing under the compression. The studs act as a welded group.
Inputs of the embed plate #
- Plate: width B along x, height H along y (the direction of the moment), thickness, Fy.
- Attached member depth and width: the depth places the compression force and the tension flange. The width sets the other way's plate bending.
- Studs: diameter, effective embedment, head, fya, futa and grid. For a flush plate, hef = stud length + plate thickness − head thickness − the weld burn-off of 3/16 in., as SP-17(14) does; check the product. No stud at the center leaves an odd grid's middle clear.
- Concrete: f'c, λa, member thickness, cracked, the distance from the outer stud to each edge (0 = no edge), and the cover. Supplementary reinforcement changes φ by Table 17.5.3(b); you detail it. Edge reinforcement sets ψc,V.
- Loads: by load type or factored. M puts the +y side in tension; My the +x side; V acts toward the −y side; N pulls off the concrete. Shear distance from the concrete face: V times this adds to the moment; leave it at 0 if your moment already has it.
- Stud forces: your choice of model. By default elastic over the group while every stud stays in tension; otherwise the compression sits under the compression flange and tensions grow with the distance from it. That second model is SP-17(14) Example 14's assumption, not a code rule. You can force either.
Auto-design varies the stud diameter, embedment and count, and the plate thickness. The plate's outline, spacing, concrete, loads and member stay yours.
Checks performed #
| Check | Basis |
|---|---|
| Stud forces | 17.2.1, elastic analysis with the plate stiff; the choice above |
| Steel in tension, in shear | 17.6.1 and 17.7.1 (Eq. 17.7.1.2a, without the 0.6 of a bolt); stud shank area; futa at most 1.9 fya and 125 ksi |
| Concrete breakout, pullout, side-face blowout | 17.6.2, 17.6.3, 17.6.4, on the studs in tension |
| Breakout in shear, pryout | 17.7.2 Case 2 for a welded group (the farthest row), 17.7.3 |
| Interaction | 17.8 |
| Plate bending | The moment of the studs past the tension flange, and past the member's side, against φ Fy S (elastic, so the rigid plate assumption holds) |
| Stud size | AISC 360-22 I8.1: at most 2.5 t |
| Bearing | 22.8: the length under the flange at φ 0.85 f'c |
| Spacing, edges | Table 17.9.2(a), 20.5.1.3 |
Limitations #
- Headed studs only. Deformed bar anchors are not offered: Chapter 17 has no path for a bar without a head, and treating it as a developed bar is a different design that the PCI Handbook covers.
- The weld of the member to the plate is not designed. Use Weld group.
- Anchor reinforcement (17.5.2.1) and seismic requirements (17.10) are not part of this. Use Anchors in concrete for 17.10 on a bolt group. In SDC C to F, check 17.10 by hand.
- Plate bending takes the full width of the plate and ignores two-way action, and the studs' own local plate effects. Keep the plate stiff.
- The compression position is an assumption. If the plate and member are not as Example 14's, choose by the depth entered or by your own analysis.
Verification examples #
Verification status: 73 values compared in 7 examples (5 published, 2 hand calculations from the cited equations): 60 within tolerance, 13 recorded deviations. Code basis: partial. Only some provisions were read in the target edition; the rest rests on older editions, examples or summaries.
| Example | Source | Values |
|---|---|---|
| Eight studs, moment and shear | ACI SP-17(14), Anchorage Example 14, pp. 806 to 817 (318-14) | Stud forces 6.79, sum 26.2 kips; plate moment 61 kip-in.; φNsa 14.9; Ncbg 75.5 kips; and with deviations φNpn 27.6, Vcbg 49.3 kips, interaction |
| Six studs, eccentric tension | SP-17(14), Example 16, pp. 830 to 836 | T 10.9; φNsa 21.5; Ncbg 41.6 kips |
Three things differ on purpose in Example 14. Its pryout takes the breakout area of the top row alone; this type uses the group's. Its pullout uses 0.75, the factor of 318-14; 318-19 has 0.70. Its Vb takes the load-bearing length as hef, past the limit of 8 da in 17.7.2.2.1, so this type's shear breakout is about 6 % lower and the interaction slightly higher. Example 16 prints one stud at −205 lb; this type sets a stud in compression to zero, so the sum differs slightly. No published example is on disk to ACI 318-19: ACI MNL-17(21) comes after wave 7 and would confirm these. The plate's side bending, the bearing check, biaxial moment in the flange model and I8.1 are hand checked or read from the code.