Designing a beam web opening
The Beam web opening type (Wizard group Components & calculators, mark prefix WO) checks a rectangular or circular opening in the web of a W-shape beam, without reinforcement or with horizontal bars welded above and below the opening on one or both faces of the web. It follows AISC Design Guide 2, Steel and Composite Beams with Web Openings (Darwin, 1990, revised printing 2003), for non-composite steel beams. The opening is checked at its centreline for the moment and shear there.
| Configuration | What is checked | DG2 example |
|---|---|---|
| Unreinforced rectangular opening (concentric or eccentric) | Mm (Eq. 3-6), Vm of both tees, interaction, guidelines | Examples 1 (LRFD) and 1A (ASD) |
| Bars on one side of the web | Mm (Eq. 3-7 or 3-8), Vm with the bar term μ, one-sided limits, bar welds and extension | Example 2 |
| Bars on both sides of the web | As above, with the bar area at each edge doubled | — |
| Circular opening | The equivalent rectangle of DG2 Eqs. 3-29 / 3-30 | — |
Web opening inputs #
- Loads: the shear V and the moment M at the opening centreline (service dead and live loads, required strengths, ASCE 7 combinations or load cases). Enter the values at the centreline of the opening from your beam analysis.
- Beam: the W-shape and its material, which flange is in compression (it selects the tee for the tee-buckling guideline), and the unbraced length of the compression flange (0 when braced continuously).
- Opening: rectangular (length a0, depth h0, corner radius) or circular (diameter D0); the eccentricity e of the opening centre above mid-depth (negative below); optionally the clear space to the next opening and the distance from the opening edge to the support.
- Reinforcement: none, bars on one side or on both sides of the web; bar thickness and width (projection from the web), material, the gap between the opening edge and the bar, the extension ℓ1 past each side of the opening (0 = the DG2 minimum rounded up to 1/4 in.), the fillet size and electrode, and whether the bar is welded on one edge (the tee side) or both edges within the opening. In the extensions both edges are always welded (DG2).
Web opening checks #
Strength (DG2 Chapter 3):
- Maximum moment capacity Mm at the opening: Eq. 3-6 for unreinforced openings, Eq. 3-7 (tw e < Ar) or 3-8 (tw e ≥ Ar) for reinforced openings, never more than Mp = Fy Z.
- Maximum shear capacity Vm = Vmt + Vmb (Eq. 3-12): each tee carries αv Vp with Vp = Fy tw s / √3 and αv = (√6 + μ) / (ν + √3) ≤ 1 (Eq. 3-13), ν = a0 / s (a0 / s̄ when reinforced), μ = 2 Pr dr / (Vp s) (Eq. 3-14), Pr = Fy Ar ≤ Fy tw a0 / (2√3). Vm is limited to (2/3) V̄p for stocky webs and 0.45 V̄p otherwise (§3.7a2).
- Moment–shear interaction: R = [(Mu / φMm)³ + (Vu / φVm)³]^(1/3) ≤ 1 with φ = 0.90. In ASD, DG2 §3.8 uses φ = 1.00 with a load factor of 1.7 on dead and live load; ILX applies it as Ω = 1.70 on Mm and Vm with your ASD loads, which gives the same ratio 1.7 Ma / Mm.
Guidelines (DG2 §3.7): Fy ≤ 65 ksi; compression flange and bar b/t ≤ 65/√Fy; web (d − 2tf)/tw ≤ 520/√Fy; p0 = a0/h0 + 6 h0/d ≤ 5.6; a0/h0 ≤ 3.0 (2.2 for webs above 420/√Fy); h0 ≤ 0.7 d; each tee at least 0.15 d deep and a0 / s ≤ 12; corner radius ≥ 2 tw and ≥ 5/8 in.; the opening edge at least d from a support; the clear space between openings (Eqs. 3-37 / 3-38). Bars on one side only also need Ar ≤ Af/3, a0/h0 ≤ 2.5, s/tw ≤ 140/√Fy and Mu / (Vu d) ≤ 20 (Eqs. 3-33 to 3-36). Notes: no concentrated load over the opening, the tee-buckling guideline (ν ≤ 4 for unreinforced openings), and the reduction of J for lateral-torsional buckling (Eq. 3-26) when an unbraced length is entered.
Reinforcement (DG2 §3.7b5): the extension ℓ1 ≥ a0/4 and ≥ Ar √3 / (2 tw); the welds within the opening develop φ 2Pr (Eq. 3-31) and those in each extension φ Fy Ar (Eq. 3-32), with the fillet strength of AISC 360-22 J2.4 (longitudinal, kds = 1.0) and the required size in sixteenths; the bar's shear rupture (as DG2 Example 2) and the web's (J4.2); the Table J2.4 minimum and J2.2b(b) maximum fillet sizes; room for a fillet between the opening edge and the bar when both bar edges are welded within the opening.
Web opening drawings #
The elevation shows the beam broken at both ends, the opening with its corner radii (or the circular hole), the bars extended ℓ1 past the opening with their fillets seen face-on and the AWS fillet symbol, the dimensions ℓ1, a0, ℓ1 above the beam, the tee depths and h0 at the right, e from the beam centreline when the opening is eccentric, and the corner-radius note. Section A-A through the opening centre shows the top and bottom tees, the bars on one or both faces of the web and their fillets in true cross-section outside the base metal.
Web opening limits #
- Composite beams (DG2 §3.5b, §3.6b, the slab and shear-connector rules) are not covered; nor are castellated or cellular beams, or several openings acting together (only the spacing guideline is checked).
- The compression tee is not checked as a column (DG2 §3.7a3): ILX flags unreinforced openings with ν > 4.
- The beam's own strength away from the opening (flexure, shear, lateral-torsional buckling) is designed elsewhere.
- Verification: DG2 Examples 1, 1A and 2 (95 published values, LRFD and ASD); other configurations by hand calculations (backend/tests/test_web_opening.py). See research/38_web_openings.md.