Cold-formed steel jamb studs
The studs beside a wall opening: the wind on their tributary width, the gravity load the header brings down, the jamb's strength as one stud or a pack, its deflection and its connection to the track at the head and the base. To AISI S100-16 (with S2-20) and AISI S240-20 B3.2.5.
Inputs of the jamb studs #
- Stud and jamb: an SSMA designation or custom dimensions, Fy, and the jamb: one stud (with what faces the opening), two to four studs side by side (each counted alone, braced like the others), two back to back (S100 I1.2 with the connector spacing a), or a box (with your confirmation that the connections close it).
- Wall and loads: the stud height (simple span), the opening width and the stud spacing. The tributary width for wind is half the opening plus half the stud spacing, as usual practice takes it; enter another value if your opening frame says otherwise. The wind is the components and cladding pressure at the strength level. The header reaction and any load from above go in the axial table by load type.
- Bracing and deflection: bridging spacing (0 for sheathing on both flanges), Kx, Cb, distortional buckling with kφ, the wind factor for deflection (0.42, S240 B1.1.2) and the limit (L/360 prefilled for brittle finishes at openings; IBC Table 1604.3 lists the others).
- Head and base: a track (stud-to-track by S240 B3.2.5.1), a deflection track at the head (B3.2.5.2), or a clip designed elsewhere; the track's thickness, Fy, Fu and flange, the screw, whether both stud flanges are screwed.
Auto-design varies the stud (lightest first) and, for studs side by side, their number. The opening, wind, loads, tracks and Fy (unless unlocked) are kept.
Checks performed #
| Check | Basis |
|---|---|
| Compression | S100 E2, E3 (and I1.2 for back to back and box) |
| Distortional buckling, compression and bending | S100 E4, F4 |
| Bending | S100 F2, F3 |
| Shear, bending and shear | S100 G2, H2 |
| Compression and bending | S100 H1.2 with B1 (C1.2.1.1, Cm = 1.0) |
| Connector spacing | S100 I1.2(a) |
| Deflection under wind | IBC Table 1604.3 (limit entered), S240 B1.1.2, S100 L1 |
| Stud to track at the head and base | S240 Eq. B3.2.5.1-1, Table B3.2.5.1-1 (at an opening) |
| Track at back-to-back jamb studs | S240 Eq. B3.2.5.1-3, Table B3.2.5.1-4 |
| Outside those ranges, or one flange screwed | S240 B3.2.5.1(e): S100 G5, halved next to an opening |
| Deflection track at the head: stud web crippling | S240 B3.2.5.2.1 |
Limitations #
- The window or door frame's loads are taken as a uniform wind on the tributary width; the frame's anchor points are not modelled.
- Studs side by side are not in Table B3.2.5.1-1: their track check is S100 G5, halved next to an opening.
- A deflection track at a jamb carries the jamb's reaction over a short length, which Eq. B3.2.5.2-1 does not cover: check it with the cold-formed steel track type, or use a clip.
- The I1.2(b) and (c) end and tie connections of a back-to-back jamb are checked by the built-up member type, not here.
- The header, its connection to the king studs, the sill and the track anchors are not designed.
Verification examples #
Verification status: 9 values compared in 2 examples (0 published, 2 hand calculations from the cited equations): 9 within tolerance, 0 recorded deviations. No published example: every value is a hand calculation. That checks the program against this reading of the code, not the reading itself. Code basis: not yet recorded for this module.
No published worked example of jamb studs is in the free library. The values are hand calculations from the cited equations: the tributary width and wind line load, the reactions, the moment and S240 Eqs. B3.2.5.1-1 and -3. The member strengths come from the libraries the stud and header types verify against the SSMA tables. A CFSEI technical note or AISI D110 example would replace them.