When are bearing stiffeners required in steel beams?

Bearing stiffeners are required at locations where a concentrated load exceeds the web's capacity to resist local failure. AISC 360-22 Section J10.8 mandates bearing stiffeners when the web fails any of the following checks: (1) Web local yielding (J10.2) — the web crushes directly under the load because the bearing area is insufficient; Rn = (2.5k + N) * Fyw * tw for interior loads or (1.0k + N) * Fyw * tw for end reactions. (2) Web crippling (J10.3) — the web buckles locally near the loaded flange; capacity depends on the bearing length-to-depth ratio and whether the load is at an interior or end location. (3) Web sidesway buckling (J10.4) — the compression flange buckles laterally due to a concentrated load applied to one flange without sufficient lateral restraint. Bearing stiffeners are also required at all support locations for plate girders regardless of calculated demand, per AISC 360 G2.2. They must be provided in pairs (one on each side of the web) and must bear on or be welded to both flanges. For end reactions, bearing stiffeners must extend the full depth of the web. For interior concentrated loads, they must extend at least half the web depth. The bearing stiffener is designed as a column with an effective section consisting of the stiffener plates plus a strip of web extending 25tw on each side of the stiffener pair (AISC 360 J10.8) — or 15tw per AS 4100. The effective length is 0.75h where h is the clear web depth, reflecting the rotational restraint provided by the flanges. The stiffener plate width-thickness ratio bst/tst must satisfy the compactness limit to prevent local buckling of the stiffener itself. The stiffener-to-web weld must transfer the full bearing force from the stiffener into the web.

How do transverse stiffeners enable tension field action in plate girders?

Transverse stiffeners divide the girder web into rectangular panels, enabling tension field action — the post-buckling shear strength mechanism where the buckled web behaves like a diagonal tension brace. Without intermediate stiffeners, a thin web's shear capacity is limited to the elastic buckling strength (Cv1 * 0.6 * Fy * Aw). Once the web buckles in shear, the diagonal compression band loses stiffness and the panel cannot carry additional load. With properly sized transverse stiffeners at appropriate spacing, however, the web can carry 1.5 to 2 times the buckling strength through tension field action. The mechanism: after the web buckles, diagonal tensile membrane stresses develop along the tension diagonal, while the buckled compression diagonal sheds load. The transverse stiffeners act as compression struts (anchoring the tension field) and the flanges act as tension chords. The stiffener must have sufficient rigidity to enforce a node in the buckled web at the stiffener location — if the stiffener is too flexible, it bends with the web and the tension field cannot develop. AISC 360 Section G2.2 provides the stiffener requirements: (1) Moment of inertia of the stiffener pair about the web centerline: Ist >= a * tw^3 * j where j = max(2.5 / (a/h)^2 - 2.0, 0.5). (2) Minimum stiffener area: Ast >= 0.15 * (Fyw / Fyst) * (1 - Cv1) * rho_st * a * tw * (Vu / (phi_v * Vn) - 1). (3) Stiffener spacing a: for maximum shear capacity, space stiffeners at a/h between 0.5 and 1.0 (closer spacing = higher capacity). Transverse stiffeners are welded to the web but are typically stopped short of the tension flange (1/4 to 1/2 inch gap) to avoid creating a fatigue-sensitive detail at the flange. They must bear on or be welded to the compression flange.

What is the difference between web local yielding and web crippling?

Web local yielding and web crippling are two distinct limit states that govern how a steel beam web resists concentrated forces, and both must be checked independently. Web local yielding (AISC 360 J10.2) is a material yielding failure where the web directly under the load plastically deforms because the bearing area is insufficient to distribute the force. It is essentially a bearing stress check: the web steel yields in compression over the loaded length. The capacity depends on the bearing length N plus a 2.5k (or 1.0k for end reactions) spread distance through the flange and fillet into the web. For a W21x44 with k = 1.0 in, tw = 0.350 in, Fy = 50 ksi, and a 6-inch bearing plate at an interior location: Rn = (2.5*1.0 + 6) * 50 * 0.350 = 8.5 * 50 * 0.350 = 149 kip. Web crippling (AISC 360 J10.3) is a buckling failure — the web buckles locally in a region adjacent to the loaded flange because the compression from the concentrated load causes out-of-plane instability. Crippling capacity depends on the bearing length-to-depth ratio (N/d), the web slenderness (d/tw), and whether the load is interior or at an end. It is more complex and typically lower than the local yielding capacity for thin webs. For the same W21x44 with N = 6 in, d = 20.7 in, tw = 0.350 in, tf = 0.450 in at an interior location: Rn = 0.80 * tw^2 * [1 + 3*(N/d)*(tw/tf)^1.5] * sqrt(E*Fy*tf/tw) = 0.80 * 0.350^2 * [1 + 3*(6/20.7)*(0.350/0.450)^1.5] * sqrt(29,000*50*0.450/0.350) = 0.098 * [1 + 3*0.290*0.707] * sqrt(1,870,714) = 0.098 * 1.615 * 1,368 = 216 kip. Sidesway buckling (J10.4) is a third check — the compression flange buckles laterally if it is not restrained against rotation at the load point, which typically governs when the loaded flange is in compression and the beam is unbraced at the load point. This is checked separately and often controls for crane runway beams and monorails.

What are the stiffener-to-flange weld requirements?

The welding requirements differ for bearing stiffeners vs transverse intermediate stiffeners, and the distinction is driven by fatigue considerations. For bearing stiffeners (at supports and concentrated load points), the stiffener must be welded to BOTH flanges with full load-transfer welds. The weld to the loaded flange transfers the bearing force from the flange into the stiffener, and the weld to the opposite flange transfers the force back out. These welds are sized for the full bearing force. The stiffener-to-web weld (usually a fillet weld on each side of the stiffener) transfers the force gradually from the stiffener into the web along the full depth. For a bearing stiffener at a support reaction of 100 kip with 1/4 inch fillet welds (E70XX electrode, capacity = 1.392 kip/in per 1/16 inch of weld size, so 1/4 in = 5.57 kip/in): required weld length = 100 / 5.57 = 18 inches of weld per side. With double-sided fillets over a 12-inch web depth, this provides 24 inches of weld — sufficient. For transverse intermediate stiffeners (tension field stiffeners), AISC 360 Section G2.2 requires them to be welded to the compression flange to transfer the stiffener force, but they must NOT be welded to the tension flange. The reason is fatigue: welding a transverse stiffener to the tension flange creates a fatigue-sensitive detail (Category C' per AISC Appendix 3) at the point of maximum tensile stress in the girder. By stopping the stiffener short of the tension flange (a 1/4 to 1/2 inch gap), the fatigue category improves significantly. The stiffener force is transferred through the web into the tension field. The minimum fillet weld size for stiffener-to-web connections follows AISC Table J2.4 based on the thinner part joined. For a 1/4 inch stiffener plate to a 3/8 inch web, the minimum fillet weld is 3/16 inch. For stiffener-to-compression-flange welds, size the weld to transfer the stiffener compression force.

When are longitudinal stiffeners required in plate girders?

Longitudinal stiffeners are horizontal stiffeners that run parallel to the flanges along the length of a plate girder. They are required when the web depth-to-thickness ratio exceeds the limit for non-compact webs in bending, and they serve to divide the web into sub-panels to prevent flexural buckling of the compression portion of the web. Per AISC 360-22 Section G2.4, longitudinal stiffeners are needed when h/tw exceeds 5.70 * sqrt(E/Fy) = 137 for Fy = 50 ksi — this is well beyond typical rolled W-shapes. For example, a plate girder with a 72-inch deep web and tw = 3/8 inch would have h/tw = 192, exceeding the limit and requiring at least one longitudinal stiffener. The stiffener is typically placed at a distance of hc/5 from the compression flange, where hc is twice the distance from the neutral axis to the compression flange. This location optimizes the buckling resistance of the compression sub-panel. The longitudinal stiffener must satisfy a minimum moment of inertia requirement about the web centerline: I_st >= h * tw^3 * [0.16 * (a/h) * (b/tw) / (h/tw) - 0.07] where a is the transverse stiffener spacing. For practical design: (1) One longitudinal stiffener at h/5 from the compression flange is sufficient for h/tw up to about 250. (2) Two longitudinal stiffeners (at h/5 and h/3) may be needed for extremely slender webs with h/tw > 250, though such sections are rare in building construction and more common in long-span bridges. (3) The longitudinal stiffener must be continuous — it cannot be interrupted at transverse stiffeners. Transverse stiffeners pass through cutouts in the longitudinal stiffener or are coped around it. (4) The longitudinal stiffener itself must satisfy compactness limits to prevent local buckling. In modern practice, longitudinal stiffeners are uncommon in building plate girders because fabricators prefer to increase the web thickness rather than add longitudinal stiffeners, which add significant fabrication labor. The decision is economic: a thicker web costs more in material (about $0.25-0.40/lb for the additional steel) but avoids the labor cost of fitting, coping, and welding longitudinal stiffeners (which can add $0.50-1.00/lb to fabrication cost). For bridge girders where weight optimization matters more, longitudinal stiffeners are more common and economical.

Stiffener Design — Bearing, Transverse & Longitudinal Stiffeners

Transverse stiffener sizing, bearing stiffener design, and longitudinal stiffeners for plate girders. AISC 360 Chapters G and J provisions, worked examples, and cross-code comparison.

Why stiffeners are needed

Stiffeners are plates welded to the web of a beam or girder to prevent local web failures. Without stiffeners, deep thin webs fail by three mechanisms:

Web local yielding -- the web crushes directly under a concentrated load because the bearing area is insufficient. Governed by AISC 360 Section J10.2.
Web crippling -- the web buckles locally in a region adjacent to the loaded flange. Governed by AISC 360 Section J10.3.
Web sidesway buckling -- the compression flange buckles laterally due to concentrated load applied to one flange. Governed by AISC 360 Section J10.4.

Additionally, deep girder webs (d/tw > 50-60) may require transverse stiffeners to develop the full post-buckling shear strength (tension field action) per AISC 360 Section G2.2, and longitudinal stiffeners to increase the web bending capacity in very slender plate girders.

Types of stiffeners

Bearing stiffeners

Bearing stiffeners are fitted to the top and bottom flanges at points of concentrated load (supports, point loads from columns or beams). They act as short columns transferring the load from the top flange through the web to the bottom flange. AISC 360 Section J10.8 requires bearing stiffeners when the web fails any of the J10.2 through J10.5 checks.

Design the bearing stiffener as a column with an effective cross-section consisting of the stiffener plates plus a strip of web (25tw on each side of the stiffener per AISC, or 15tw per AS 4100). The column effective length is taken as 0.75h (where h is the clear web depth) because the flanges provide rotational restraint.

Transverse stiffeners

Transverse stiffeners are welded to the web (but not necessarily to the flanges) at regular intervals to subdivide the web into panels for shear resistance. They allow the engineer to take advantage of tension field action -- the post-buckling shear capacity where the web acts like a diagonal tension brace after initial web buckling.

AISC 360 Section G2.2 permits tension field action when intermediate stiffeners are provided. Without stiffeners, the web shear capacity is limited to the buckling strength alone. With stiffeners, the capacity can be 1.5 to 2 times the buckling strength.

Longitudinal stiffeners

Longitudinal stiffeners run parallel to the flanges along the length of the girder. They divide the web into two panels for bending compression buckling. Rarely needed for standard rolled sections, but used in deep plate girders (d > 1500 mm) where the web depth-to-thickness ratio exceeds the slender limit.

Bearing stiffener sizing table

Minimum stiffener dimensions for common beams (A36, Fy = 36 ksi)

Beam	d (in)	tw (in)	Min bst (in)	Min tst (in)	Typical Stiffener	Effective A (in^2)
W12x26	12.2	0.230	2.17	0.18	2-1/2" x 1/4"	3.55
W16x40	16.0	0.305	2.33	0.19	2-1/2" x 1/4"	4.33
W18x50	18.0	0.355	2.56	0.21	3" x 1/4"	5.37
W21x62	21.0	0.400	2.58	0.22	3" x 1/4"	5.80
W24x76	23.9	0.440	2.89	0.24	3" x 5/16"	7.51
W24x131	25.4	0.605	2.86	0.24	3" x 5/16"	10.2
W27x94	26.7	0.490	3.11	0.26	3-1/2" x 5/16"	8.72
W30x90	29.5	0.470	3.43	0.28	3-1/2" x 5/16"	8.58
W33x118	33.3	0.550	3.66	0.30	4" x 5/16"	10.9
W36x135	35.6	0.600	3.73	0.31	4" x 3/8"	13.9

bst >= bf/3 - tw/2. tst >= bst / (0.56 * sqrt(E/Fy)). For Fy = 36 ksi, tst >= bst/15.9. For Fy = 50 ksi, tst >= bst/13.5.

Bearing stiffener capacity table

Beam + Stiffener	Effective A (in^2)	KL/r	phiPn (kip)
W18x50 + 2x(3"x1/4")	5.37	3.8	174
W24x76 + 2x(3"x5/16")	7.51	3.2	243
W24x131 + 2x(3"x5/16")	10.2	2.1	330
W30x90 + 2x(3.5"x5/16")	8.58	3.5	278
W36x135 + 2x(4"x3/8")	13.9	2.4	450

All stiffeners very stocky (KL/r < 5), so phiPn is approximately 0.90 _ Fy _ A.

When stiffeners are required

Web checks that trigger bearing stiffeners (AISC J10)

Check	Section	phi	Triggers Stiffeners When
Web local yielding	J10.2	1.00	Ru > phi*Rn (interior)
Web crippling	J10.3	0.75	Ru > phi*Rn
Sidesway buckling	J10.4	0.85	Ru > phi*Rn
Web compression	J10.5	0.90	Ru > phi*Rn
Web panel shear	G2.1	1.00	Vu > phi*Vn

When transverse stiffeners are needed for shear

h/tw Range	Stiffener Requirement	Shear Basis
h/tw <= 2.24*sqrt(E/Fy)	Not required (rolled shapes)	Cv1 = 1.0, full shear
53.9 < h/tw < 260	Optional: use to increase shear capacity	Tension field action
h/tw > 260	Required per AISC G2.2	Panel buckling + TFA
h/tw > 360	Not permitted without longitudinal stiffeners	Code limit

For Fy = 50 ksi: 2.24*sqrt(E/Fy) = 53.9. Nearly all standard W-shapes have h/tw below this threshold.

Transverse stiffener requirements (AISC G2.2)

Minimum dimensions

bst >= d/3 - tw/2   (per side)
tst >= bst / (0.56 * sqrt(E/Fy))
bst/tst <= 0.56 * sqrt(E/Fy)

Spacing requirements

a/h Ratio	Shear Behavior	Notes
a/h <= 1.0	Tension field fully develops	Maximum shear benefit
a/h = 1.5	Partial tension field	Common spacing for girders
a/h = 2.0	Limited tension field	Minimum for TFA credit
a/h = 3.0	No tension field	Buckling-only capacity

Where a = stiffener spacing, h = clear web depth. Closer spacing = higher shear capacity.

Stiffener moment of inertia requirement

Ist >= a * tw^3 * (2.5 / (a/h)^2 - 2) >= 0

This ensures the stiffener is stiff enough to act as a nodal line for the web buckling mode.

Worked example -- bearing stiffener at beam support

Beam: W24x62 (A992), d = 23.74 in, tw = 0.430 in, tf = 0.590 in, h/tw = 50.0. Support reaction Ru = 120 kips. Bearing length N = 3.5 in.

Web local yielding (J10-2, at support): phi*Rn = 1.0 x (2.5 x 1.34 + 3.5) x 50 x 0.430 = 147 kips > 120 kips. OK.

Web crippling (J10-4, at support): phi*Rn = 0.75 x 0.40 x 0.430^2 x [1 + 3(3.5/23.74)(0.430/0.590)^1.5] x sqrt(29000 x 50 x 0.590/0.430) = 0.75 x 0.0739 x 1.316 x 141.8 = 10.3 kips. Far less than 120 kips -- web crippling fails.

Bearing stiffeners required. Try 2 plates, 5" x 1/2" each side, A36.

Effective section: Stiffener area = 2 x 5.0 x 0.50 = 5.0 in^2. Web strip = 25 x 0.430 on each side = 9.25 in^2. Total A = 14.25 in^2.

KL/r = 0.75 x (23.74 - 1.18) / 5.32 = 3.2. Very stocky. phiPn = 0.90 x 36 x 14.25 = 462 kips >> 120 kips OK.

Worked example -- transverse stiffener for plate girder

Built-up plate girder: d = 72 in, tw = 3/8 in (0.375 in), h = 70 in, h/tw = 187. Stiffener spacing a = 42 in (a/h = 0.60).

Stiffener dimensions: bst >= 70/3 - 0.375/2 = 23.1 in... wait, that's for bearing stiffeners. For transverse: bst per G2.2, Ist >= a _ tw^3 _ (2.5/(a/h)^2 - 2) = 42 x 0.375^3 x (2.5/0.36 - 2) = 42 x 0.0527 x 4.94 = 10.95 in^4.

Try single-sided stiffener 4" x 3/8": Ist = 0.375 x 4.0^3 / 3 = 8.0 in^4. Insufficient. Try 5" x 3/8": Ist = 0.375 x 5.0^3 / 3 = 15.6 in^4 > 10.95. OK.

For double-sided stiffeners 3" x 5/16" each: Ist = 2 x (0.3125 x 3.0^3/3 + 0.3125 x 3.0 x (0.375/2 + 1.5)^2) = 2 x (2.81 + 2.43) = 10.48. Close but slightly insufficient. Use 3-1/2" x 5/16" each side.

Weld requirements for stiffeners

Stiffener Type	Flange Connection	Web Connection
Bearing	Full bearing or CJP weld	Fillet weld, both sides
Transverse	Not required (stop short)	Fillet weld, both sides
Longitudinal	Not typically connected	Fillet weld, one side

Minimum fillet weld size per AISC Table J2.4

Thinner Part Thickness	Minimum Fillet Weld Size
1/8" to 3/16"	1/8"
3/16" to 1/4"	3/16"
1/4" to 1/2"	1/4"
Over 1/2" to 3/4"	5/16"
Over 3/4"	3/8"

Fatigue consideration

Welding transverse stiffeners to the tension flange creates a Category C fatigue detail (AISC Appendix 3, Table A-3.1). For crane girders and bridge beams, stop the stiffener 4tw to 6tw short of the tension flange to maintain Category B at the web-to-flange weld.

Multi-code comparison

Provision	AISC 360-22	AS 4100:2020	EN 1993-1-5	CSA S16-19
Bearing stiffener	J10.8	Cl. 5.13 (load-bearing stiffener)	Cl. 9 (transverse forces)	Cl. 14.4
Transverse stiffener	G2.2 (for Vn with TFA)	Cl. 5.11.5 (intermediate stiffeners)	Cl. 9.3 (transverse stiffeners)	Cl. 13.4.1.2
Web strip for column	25tw each side	15tw each side	Per effective width	Similar to AISC
Effective length	0.75h	Panel length x restraint factor	Panel length x buckling curve	0.75h
Stiffener width limit	bst >= d/3 - tw/2	bst >= (d/2 - tw)/5	Cl. 9.2.1 (outstand limits)	Cl. 14.4.1
Stiffener thickness	tst >= bst * sqrt(Fy/E) / 0.56	tst >= bst / 15	bst/tst per Table 5.2	tst >= bst * sqrt(Fy/340) / 15
Tension field action	G2.2 permitted	Cl. 5.11.5 permitted	Not explicitly (uses rotated stress field)	Per S16 Cl. 13.4

Cross-code bearing stiffener capacity: W24x76 + 2x(3"x5/16")

Code	phiPn (kip)	Method
AISC 360	243	Column analogy, KL = 0.75h
AS 4100	~255	Bearing + buckling, phi = 0.90
EN 1993-1-5	~240	Effective column, gamma_M1=1.0
CSA S16	~250	Column analogy, phi = 0.90

Common mistakes

Welding transverse stiffeners to the tension flange in fatigue-sensitive locations. Creates a Category C fatigue detail. For crane girders and bridge beams, stop the stiffener 4tw to 6tw short of the tension flange.
Omitting the bearing check at interior point loads. Engineers often check supports for web crippling but forget that any column or beam bearing on the girder flange applies the same concentrated load. Every point load location needs the J10.2-J10.5 checks.
Using too-thin stiffener plates. Stiffener outstands must satisfy the compactness limit to prevent local buckling before the stiffener reaches its design load. The thickness limit is bst * sqrt(Fy/E) / 0.56 per AISC.
Not fitting bearing stiffeners to both flanges. Bearing stiffeners must be in contact with (or welded to) both flanges to transfer the full reaction. A stiffener welded to the web but not bearing on the flanges is a transverse stiffener, not a bearing stiffener.
Ignoring the web strip contribution. The effective column section includes a strip of web (25tw each side). Forgetting this overestimates the required stiffener area, but ignoring it entirely (designing the stiffener plate alone) is unconservative for the bearing check.
Using single-sided stiffeners for bearing. Bearing stiffeners should be placed on both sides of the web to avoid eccentricity. Single-sided stiffeners introduce bending in the effective column.

Frequently asked questions

When do I need bearing stiffeners? When the required reaction or concentrated load exceeds the web local yielding (J10.2) or web crippling (J10.3) capacity. For W18 and smaller sections with thin webs, stiffeners are often needed at end reactions.

What is the difference between bearing and transverse stiffeners? Bearing stiffeners are fitted to both flanges and resist concentrated loads. Transverse stiffeners are welded to the web only and increase shear capacity through tension field action. They serve different purposes and have different design requirements.

Do standard rolled W-shapes need transverse stiffeners? Almost never. The h/tw ratio for standard W-shapes is below 53.9 at Fy = 50 ksi, giving Cv1 = 1.0 and full shear capacity without stiffeners. Only plate girders and built-up sections typically need them.

What is tension field action? After a web panel buckles in shear, the diagonal buckles form a tension field that acts like diagonal bracing. The transverse stiffeners act as vertical members of this truss. This post-buckling strength is permitted by AISC G2.2 and significantly increases the design shear capacity.

Can I use partial-depth stiffeners? Partial-depth stiffeners are not permitted for bearing stiffeners (must be full depth). Transverse stiffeners may be partial depth in some codes, but AISC G2.2 requires full depth for tension field action.

How are stiffeners attached to the beam? Bearing stiffeners are fillet-welded to the web and either milled-to-bear or welded to both flanges. Transverse stiffeners are fillet-welded to the web, typically with a gap at the tension flange for fatigue.

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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.