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Steel Web Crippling & Bearing Stiffener Design: End Reactions & Stiffeners
A wide-flange beam end seated on a column-top plate, with a symmetric pair of transverse bearing stiffeners clamped snug against the loaded flange and fillet-welded to the web—this is the detail that stops web crippling at a concentrated reaction.
Steel web crippling bearing stiffener design starts with a simple observation: a column base plate spreads an anchor-bolt reaction into a concrete footing, but a beam end does something different—its thin web gets crushed right under the bearing plate. Overlooked, the web buckles locally well before the beam's bending capacity is reached. The entire field of steel web crippling bearing stiffener design is about one thing: how the beam web survives a concentrated reaction at its end or an intermediate load, and when you must add a bearing stiffener to carry it. The controlling variables are the bearing length N, the fillet distance k, the web slenderness h/t_w, and whether the load lands at the beam end, near the end, or well inside the span.
This guide walks through the failure modes, the AISC 360 formulas for web local yielding and web crippling, the critical-section classifications, and the step-by-step sizing of a pair of transverse bearing stiffeners. Our steel base plate anchor bolt design deep dive covers column-to-foundation behavior. This article is the beam-side equivalent—web bearing at supports and intermediate concentrated loads.
Web Crippling vs Column Base — Where This Applies
It is easy to confuse web bearing with column base plate design because both involve a plate sitting on steel and transferring compression. They are different problems. In a steel column base plate design problem, the element being stressed is the column end plate spreading load into concrete, with anchor bolts taking tension and shear. In web crippling, the element being stressed is the thin vertical web of the beam, squeezed between the loaded flange and the bearing plate. The failure zone is a small patch of web, typically 2 to 4 times the web thickness wide, directly under the reaction.
Three load locations drive steel web crippling bearing stiffener design:
- Beam-end reaction — the beam sits on a bearing plate on a column, wall, or girder seat. Stress can spread only inward from the end, so capacity is the lowest of the three cases.
- Interior concentrated load — a secondary beam frames into the side of a girder, dropping its reaction onto the girder web at a point more than d/2 from the girder end. Stress spreads both ways.
- Near-end reaction (one-end) — the load lands between the end and d/2 from the end; capacity falls between the interior and end cases.
Engineers routinely size a beam for flexure, check deflection, and forget web bearing. When the web slenderness ratio h/t_w is large, local crushing capacity drops sharply—often to less than half the bending strength implied by the section weight. Local plate buckling of the web is the same family of behavior covered in steel member local stability, but here it is driven by compression through the flange into a short deep web strip rather than by overall plate slenderness.
Table 1 — Web Failure Mode Map (typical W-shape, F_y = 345 MPa / 50 ksi)
The failure mode map below is the starting reference for steel web crippling bearing stiffener design: pick the load location, match it to the governing limit state, then decide whether the bare web suffices or a stiffener pair is required.
| Load Case | Location | Governing Limit State | AISC Clause | Notes |
|---|---|---|---|---|
| End reaction | ≤ d/2 from beam end | Web crippling + local yielding | J10.2 / J10.3 | Lowest capacity; stiffener often required |
| Interior reaction | > d/2 from either end | Web local yielding + crippling | J10.2 / J10.3 | Full spreading both directions |
| One-end reaction | Between end and d/2 | Web crippling (intermediate) | J10.3 | Factor between end and interior |
| Wheel load on crane beam | Top flange, moving | Crippling + fatigue | J10.3 + App. 3 | Transverse stiffener at every wheel point |
| Concentrated floor beam | Top flange, interior | Local web yielding | J10.2 | Often stiffener required for heavy reaction |
Web Local Yielding & Web Crippling — The Formulas
Two limit states must be checked at every concentrated load or reaction location. The first, web local yielding, applies when the web is stocky enough that it yields before it buckles. The second, web crippling, applies when the web is slender enough that it buckles under the concentrated compression before yield. Both are in AISC 360 Section J10.
Web local yielding (AISC J10.2). The nominal strength is:
R_n = F_yw · t_w · (C · k + N)
where F_yw is the web yield stress, t_w the web thickness, k the distance from the outer face of the flange to the web toe of the fillet, N the length of bearing along the beam, and C a location coefficient:
- Interior load (load applied at a point more than d/2 from the member end): C = 5.
- End reaction (reaction applied at, or within d/2 of, the member end): C = 2.5.
The factor 5 versus 2.5 is the heart of the end-versus-interior asymmetry. At an interior load, the flange stress spreads diagonally into the web on both sides of the loaded point; at an end, it can spread only inward, so the effective strip is half as long. Load combinations must use the factored reaction from steel structure load combination tables—never service load.
Web crippling (AISC J10.3). When h/t_w is high, the web strip buckles like a short column before reaching yield. The nominal strength formula is more complex and includes t_w², a dimensionless plate-slenderness term, and location coefficients for end, interior, and one-end loading. End loading gives the lowest crippling strength because the stress field cannot spread outward beyond the beam end. AISC uses a 60° spread assumption (roughly 1V:1.7H) and penalizes end loads with a reduction factor. For thin-webbed built-up members, crippling—not yielding—usually controls, and that is precisely where plate girders live; see steel plate girder design deep dive for how transverse stiffeners are laid out along the span.
Table 2 — Web Bearing Capacity Factor by Location (illustrative, F_yw = 345 MPa / 50 ksi)
| Location | Yielding Factor (C·k + N) | Crippling Factor (relative) | Relative Capacity vs Interior | Notes |
|---|---|---|---|---|
| Interior load | 5k + N | 1.00 | 100% | Full two-way spread |
| Near-end (one-end) | 5k + N (modified) | ≈ 0.75 | ≈ 75% | Partial outward restraint |
| End reaction | 2.5k + N | ≈ 0.55 | ≈ 55% | One-way spread only |
| End, unstiffened seat | 2.5k + N | ≈ 0.50 | ≈ 50% | Common failure case |
| End, with bearing stiffener | Web bypassed | Stiffener takes all R_u | ≥ 100% | Designed as compression strut |
The takeaway: an end reaction can be less than 60% as strong as the same load applied at midspan. Designers who copy interior coefficients onto end reactions routinely over-predict capacity by a factor of nearly two.
Bearing Stiffener Design
When R_u > φR_n for either web local yielding or web crippling, AISC J10 requires transverse stiffeners at the concentrated load. They come in pairs, one on each side of the web, and they are designed as a compression strut—like a small column—running from the loaded flange to the opposite flange.
The effective section for compression includes:
- The two stiffener plates (full width, full thickness).
- A strip of web width equal to 12·t_w centered on the stiffener line (J10.4).
Slenderness of the outstanding stiffener plate is checked against λ_r = 0.56·√(E/F_y) to ensure local plate buckling does not precede strut failure. The stiffener must be cut to fit snug against the loaded flange (bearing fit) so the reaction goes into the stiffener by direct bearing, not by welding alone. The pair is fillet-welded to the web on both sides; the weld must transmit the entire reaction that the web itself cannot carry. Stiffeners should avoid intersecting flange-to-web groove welds so residual welding stresses do not stack up—see steel welding distortion control for how to sequence these welds. This is part of the broader steel structure connection design toolkit.
Table 3 — Bearing Stiffener Dimension Schedule (illustrative, Q355B / A992, F_y = 345 MPa / 50 ksi)
| Beam Mass (kg/m / lb/ft) | Factored Reaction R_u (kN / kips) | Suggested Stiffener (mm×mm / in×in) | Fillet Weld Size (mm / in) | Notes |
|---|---|---|---|---|
| 100 / 67 | 350 / 79 | 2 PL 150×12 / 2 PL 6×1/2 | 8 / 5/16 | Stocky web, often not needed |
| 150 / 100 | 550 / 124 | 2 PL 180×14 / 2 PL 7×9/16 | 10 / 3/8 | Typical interior reaction |
| 200 / 134 | 800 / 180 | 2 PL 200×16 / 2 PL 8×5/8 | 10 / 3/8 | Crane beam seat |
| 300 / 200 | 1,200 / 270 | 2 PL 250×20 / 2 PL 10×3/4 | 12 / 1/2 | Heavy column-tree joint |
| 400 / 268 | 1,600 / 360 | 2 PL 300×22 / 2 PL 12×7/8 | 12 / 1/2 | Bridge girders / transfer girders |
Getting a Crushed Web Where a Heavy Reaction Lands?
We check web local yielding and crippling per AISC J10, size the bearing stiffener pair as a compression strut, and detail bearing-fit welds. Tell us your beam section, reaction, and bearing length N.
Crane Runway & Intermediate Load Cases
Crane runway beams are the most demanding application of steel web crippling bearing stiffener design. The wheel load is a moving, repeated concentrated load on the top flange. Because the load cycles, you must check both web crippling (J10.3) and fatigue at the stiffener-to-web weld (see steel structure fatigue design). Each wheel location typically gets a transverse stiffener pair, and because crane runway webs are often slender, crippling governs the section selection—often before bending does. Regular inspection of these stiffeners matters; see steel overhead crane runway maintenance for what to look for during service.
For intermediate loads, the classic case is a secondary beam framing into the side of a main girder. The secondary reaction lands on the girder web at an interior point. If the reaction is small (say, less than the interior R_n), no stiffener is needed. If it exceeds the interior strength, add a pair of transverse stiffeners at the frame point. This is standard practice in overhead crane steel building designs where mezzanine beams, duct hangers, or runway brackets land on the main frame.
Detailing Rules & Engineering Pitfalls
A handful of detailing rules make the difference between a stiffener that works and one that looks like it works:
- Bearing length N must be long enough. At beam ends, a bearing plate narrower than about 2.5·k will trigger end crippling even with moderate reactions. Specify seat plates that extend inward well past the fillet.
- Stiffeners must bear against the flange. "Snug" or "tack-welded only" stiffeners do not transfer the reaction as a compression strut. Fabrication drawings must show cut-to-fit and contact against both flanges.
- Use pairs, not singles. A one-sided stiffener introduces torsion and eccentricity; AISC assumes symmetric pairs.
- Use the end coefficient at the end. Designers sometimes conservatively—but incorrectly—use the interior 5k coefficient at beam ends, which over-predicts strength. The end 2.5k coefficient is mandatory at supports.
- Avoid flange weld intersection. Locate stiffener toes clear of the flange-to-web groove weld to keep residual stresses from stacking.
- Check second-order effects if the beam is part of an unbraced frame. Web bearing is local, but the reaction it feeds into the column interacts with frame drift; see steel structure second order analysis for how local forces couple with global P-Δ effects. Bolted alternatives at these joints are covered in steel high strength bolt connection deep dive.
The most common field failure is a beam end that bulges outward (a "elephant's foot" buckle) within months of loading. It traces back to a beam selected for bending only, with no web crippling check and no stiffener at the seat. By then the retrofit requires shoring the beam and adding welded stiffeners under load—expensive and risky. Done correctly, steel web crippling bearing stiffener design prevents this failure before fabrication even starts.
Conclusion
Steel web crippling bearing stiffener design reduces to a small set of checks: compare the factored reaction against web local yielding and web crippling strength per AISC J10, use the weaker end coefficient at supports, and when R_u exceeds φR_n, add a symmetric pair of transverse stiffeners designed as a compression strut with a 12·t_w web strip included. End reactions are the weakest case; crane wheels are the most repeated; and stiffeners must bear against the loaded flange, not just weld to it. Get the section, reaction, and bearing length N on the table and we will size the stiffener pair for you. Done right, steel web crippling bearing stiffener design is a small, cost-effective insurance policy against a very visible failure mode.
About the Author
Senior Structural Engineer
With over 20 years of hands-on experience in steel structure design and prefabricated building engineering, our in-house senior structural engineer has personally contributed to more than 500 steel building projects—including warehouses, industrial factories, aircraft hangars, agricultural buildings, and commercial structures. The focus is on translating design codes such as AISC 360, ASCE 7, and Eurocode 3 into buildable, cost-effective steel solutions that balance structural performance, fabrication efficiency, and total project cost.
Learn more about our engineering team
Case Example
A crane-equipped manufacturing building in southern Ontario with two 10-ton overhead bridge cranes experienced visible web bulging ("elephant's foot" deformation) at the end bearing seats of four W360×134 crane runway girders within 14 months of commissioning. The root cause was that the girders were selected for flexure and deflection without a web crippling check per AISC J10.3, and the end bearing plate was only 100 mm (4 in) long—well short of the 2.5k minimum bearing requirement at beam ends. The retrofit shored each girder, then welded a symmetric pair of transverse bearing stiffeners (2 PL 180 × 14 mm / 7 × 9/16 in) bearing-fit against the loaded flange, fillet-welded to the web on both sides. The effective compression strut section included the 12·t_w web strip. After two years of continuous crane operation, no further web deformation was observed. For crane runway maintenance inspection, see steel overhead crane runway maintenance.
Frequently Asked Questions
Q1: What is web crippling in a steel beam?
Web crippling is local failure of the thin beam web under a concentrated reaction or load—the web buckles or crushes right under the bearing plate before the beam reaches its bending capacity. It is governed by AISC 360 J10.3 and is most severe at beam ends, where stress can spread in only one direction.
Q2: How do I check web local yielding?
Per AISC J10.2, compare the factored reaction to R_n = F_yw · t_w · (C·k + N), where k is the fillet distance and N the bearing length. The coefficient C is 5 for interior loads and 2.5 at beam ends—ends are roughly half as strong. Apply the resistance factor and compare with R_u.
Q3: When must I add a bearing stiffener?
When the factored reaction exceeds the web's local yielding or crippling strength (R_u > φR_n), add a pair of transverse bearing stiffeners bearing-fit against the loaded flange. Design them as a compression strut, including a 12·t_w-wide web strip, and check outstanding-leg slenderness against 0.56·√(E/F_y).
Q4: Why are crane runway beams prone to web crippling?
Moving crane wheel loads are repeated concentrated loads on a slender web, so web crippling and fatigue govern together. Each wheel location typically needs a transverse stiffener pair, and the end-bearing capacity (the lowest of the three locations) must control the seat design.
Q5: Can I use a one-sided stiffener to save welding?
No. A one-sided stiffener introduces torsion and eccentric compression on the web, and AISC J10 assumes a symmetric pair. Single-sided stiffeners also distort the web under load. Always specify pairs, one on each side of the web, fillet-welded both sides.
Crushed Webs at Heavily Loaded Ends? We Size the Stiffener Pair to Stop It.
We check web local yielding and crippling per AISC J10, design bearing stiffeners as compression struts, and detail crane-runway stiffeners for moving wheel loads. Tell us your beam section and reaction.
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Reference Links
- AISC 360 Specification for Structural Steel Buildings, Section J10 (Flange Local Bending, Web Local Yielding, Web Crippling, and Sidesway Buckling) — the governing US code clauses for web local yielding (J10.2), web crippling (J10.3), and transverse stiffener design (J10.4).
- AISC Design Guides — companion commentary and worked examples for stiffener detailing at beam ends and crane runway seats.
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