Cold-formed steel bridging
The intermediate bracing of wall studs: the brace force at a stud, its build-up along a run, and the strap, screws and anchor that carry it. To AISI S240-20 B3.4.1, with AISI S100-16 C2.2.1 and Chapter J.
Inputs of the cold-formed steel bridging #
- Studs: an SSMA designation, stud spacing, and the spacing of the brace rows a. In S100 C2.2.1 W takes the load within 0.5a each side of the brace.
- Studs between anchors: each stud adds its brace force on the way to the anchor. Where you put blocking or struts is your layout.
- Bridging: flat straps on both flanges, or U-channel through the web punchouts.
- Each strap's share of the axial brace force: S240 gives 2 % of the compression per brace. How two straps share it is your judgment. 0.5 is prefilled. 1.0 puts it all on one.
- Strap: width, thickness, Fy and Fu. Screws: size, how many at each stud, how many at the anchor.
- Channel: its nominal strength with its factors, entered from the product's data.
- Loads: by load type on a stud: axial compression per stud, and a pressure across the wall.
Auto-design varies the strap thickness and width, the screws at each stud and at the anchor. Studs, the run between anchors and loads are kept.
Checks performed #
| Check | Basis |
|---|---|
| Brace force, bending | S240 B3.4.1.1; S100 C2.2.1, Eq. C2.2.1-3 |
| Brace force, axial | S240 B3.4.1.2, 2 % |
| Brace force, combined | S240 B3.4.1.3 |
| Strap yielding | S100 D2 |
| Strap rupture at a screw | S100 J6.2 |
| Screws at each stud and at the anchor | S100 J4.3.1, J4.3.2 |
| U-channel axial strength (entered) | Product data |
Limitations #
- Strength only. The provisions read give a force and no stiffness requirement.
- A uniform load through the web only: Eq. C2.2.1-3. Point loads are not modelled.
- The U-channel's strength is your entry: this type does not compute it, and the clip is taken as 54 mil at 33 ksi for its screws.
- Blocking or a strut at the anchor, its fastening to the stud, and the wall's lateral system are yours.
- With both flanges sheathed, S100 C2.2 asks for no further bracing, and this type is not needed.
- Single anchors at the run's ends: a run anchored at both ends may share the force, which is your entry through the number of studs.
Verification examples #
Verification status: 7 values compared in 6 examples (3 published, 3 hand calculations from the cited equations): 7 within tolerance, 0 recorded deviations. Code basis: the provisions it uses were read in the target edition.
No published worked example of bridging is in the free library. CFSEI Tech Note W400-23 and the AISI Framing Design Guide are paid and would give them.
- Published value: the shear center distance m of three sections against the SSMA Guide (2022). It is the one published number Eq. C2.2.1-3 rests on, and it says nothing about the method.
- Hand calculations: the axial and wind forces, their accumulation and the strap yield strength, from S240 B3.4.1 and S100 C2.2.1, D2. No published value checks these.