Beam Web Design — Shear, Crippling, Local Yielding & Web Openings

The web of a steel beam resists shear force and transfers concentrated loads to the flanges. Four distinct limit states govern web design: shear yielding, shear buckling, web local yielding under concentrated forces, and web crippling. Failing to check any one of these can result in a beam that passes flexural checks but fails locally at a support or load point.

Shear strength of beam webs

AISC 360-22 Section G2 provides the shear capacity for I-shaped members with unstiffened webs. The nominal shear strength is:

Vn = 0.6 × Fy × Aw × Cv1

Where Aw = d × tw (total web area), and Cv1 is the web shear buckling coefficient. For most rolled W-shapes with h/tw ≤ 2.24 × sqrt(E/Fy), Cv1 = 1.0 and phi_v = 1.00 (no buckling reduction). This threshold equals h/tw ≤ 53.9 for Fy = 50 ksi steel, which covers nearly every standard rolled W-shape in the AISC Manual.

For slender webs where h/tw exceeds 2.24 × sqrt(E/Fy), Cv1 drops below 1.0 and phi_v reduces to 0.90. This typically only applies to plate girders or very deep built-up sections.

Worked example — shear check for W18x50

Given: W18x50, A992 steel (Fy = 50 ksi), Vu = 120 kips.

Step 1 — Web properties: d = 18.0 in, tw = 0.355 in, h/tw = 45.2

Step 2 — Check compactness limit: 2.24 × sqrt(29000/50) = 53.9. Since 45.2 < 53.9, Cv1 = 1.0 and phi_v = 1.00.

Step 3 — Nominal shear strength: Vn = 0.6 × 50 × (18.0 × 0.355) × 1.0 = 191.7 kips

Step 4 — Design shear strength: phi_v × Vn = 1.00 × 191.7 = 191.7 kips > 120 kips — OK

Web local yielding (AISC 360-22 Section J10.2)

When a concentrated force is applied to the flange (from a beam reaction or point load), the web must resist the force over a limited bearing length. The nominal strength for web local yielding is:

At interior locations (force applied more than d from the member end):

Rn = Fy × tw × (5k + lb)

At end locations (force applied within distance d from the member end):

Rn = Fy × tw × (2.5k + lb)

Where k = distance from outer face of flange to the web toe of fillet (tabulated in AISC Manual), lb = bearing length, and phi = 1.00.

Web crippling (AISC 360-22 Section J10.3)

Web crippling is a localized buckling failure of the web directly under a concentrated force. It differs from web local yielding because it involves stability, not material strength. The nominal crippling strength at the member end when the force is applied within d/2 of the end:

Rn = 0.40 × tw² × [1 + 3(lb/d)(tw/tf)^1.5] × sqrt(E × Fy × tf/tw)

With phi = 0.75. This low phi factor reflects the sudden, brittle nature of web crippling failure. When Rn is insufficient, bearing stiffeners must be provided.

Bearing stiffeners

When web local yielding or web crippling capacity is exceeded, full-depth bearing stiffeners are welded to the web at the concentrated load point. Per AISC 360-22 Section J10.8, bearing stiffeners are designed as columns using an effective cross-section consisting of the stiffener plates plus a strip of web (25tw for interior stiffeners, 12tw for end stiffeners). The stiffener must extend from flange to flange with tight-fit bearing or welds at the loaded flange.

Minimum stiffener width: bst ≥ bf/3 − tw/2. Minimum thickness: tst ≥ bf/3 × sqrt(Fy/2.48E) to prevent local buckling of the stiffener itself.

Web openings

Web openings for ductwork and piping are common in floor beams. AISC Design Guide 2 addresses both rectangular and circular openings. Key rules:

Code comparison

AISC 360-22 uses the Cv1 approach for shear and separate checks for web local yielding (J10.2), web crippling (J10.3), sidesway web buckling (J10.4), and compression buckling of the web (J10.5). Phi factors range from 0.75 to 1.00.

AS 4100-2020 Section 5.11 checks web bearing yield and web bearing buckling as separate limit states. The bearing buckling uses an effective web compression member with capacity reduction factor phi = 0.90. The bearing yield check uses phi = 0.90 and a dispersion length of bbf + 5tf at interior locations. AS 4100 does not distinguish "crippling" from "buckling" the way AISC does — both are captured under the bearing buckling check.

EN 1993-1-5 Section 6 addresses transverse forces on webs using the resistance to transverse forces method. The effective loaded length is determined from a dispersion model (ss + 2tf for end patches), and the buckling coefficient is calculated from the web slenderness. EN 1993 provides a single unified check with partial safety factor gamma_M1 = 1.00.

Common mistakes engineers make

  1. Forgetting to check web crippling at beam ends. Designers often verify shear and flexure but skip the concentrated force checks at supports. A W-shape that easily passes shear may fail web crippling at a short bearing seat.

  2. Using the wrong k-distance. The k-value in AISC Tables is the distance from the outer face of the flange to the web toe of fillet, not the fillet radius alone. Using the wrong value directly corrupts the web local yielding calculation.

  3. Placing web openings in high-shear zones. Openings near supports create Vierendeel bending in the tee sections above and below the opening. If the tee cannot resist this moment, the beam fails prematurely in a mode that standard beam checks do not capture.

  4. Undersizing bearing stiffeners. Stiffeners must be checked as compression members (columns) using an effective length of 0.75h. Simply welding thin plates to the web without checking local buckling or column buckling of the stiffener assembly is a frequent fabrication-driven error.

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Disclaimer

This page is for educational and reference use only. It does not constitute professional engineering advice. All design values must be verified against the applicable standard and project specification before use. The site operator disclaims liability for any loss arising from the use of this information.