Do transverse intermediate stiffeners need to be welded to both flanges of a plate girder?

Not always. AISC 360 and AWS D1.1 allow transverse stiffeners on the tension flange to be stopped short—typically one to six times the flange thickness above the flange—to avoid creating a stress raiser at the weld termination in the tension zone. Bearing stiffeners, by contrast, must bear tightly against the compression flange and are normally welded to it to transfer concentrated loads.

What weld size governs the stiffener-to-web fillet weld in a built-up plate girder?

Minimum fillet weld size is set by AWS D1.1:2025 Table 7.7, using the thinner of the two parts joined as the governing thickness (T) when low-hydrogen processes are used. The designer's required weld size for load transfer may exceed the Table 7.7 minimum; the larger of the two governs what goes on the WPS.

Can the same WPS used for flange-to-web groove welds cover the stiffener fillet welds?

Only if the WPS covers the process, filler metal classification, base metal group, and position range that apply to the stiffener welds. Stiffener welds are almost always fillet welds, while the flange-to-web connection is typically a CJP or PJP groove. A separate fillet weld WPS, or a WPS qualified for both groove and fillet welds under the appropriate essential variables in Table 6.6, is usually needed.

What pre-weld inspection items does the CWI check on bearing stiffeners before welding?

The CWI verifies tight bearing contact between the stiffener plate and the compression flange, correct stiffener height and width to plate width tolerances, cope or clipping at the stiffener corners to clear the flange-to-web weld, and proper material identification (heat number traceability). Gaps between the stiffener and flange wider than permitted by the WPS or project spec must be corrected before welding.

Nov 7, 20267 min read

Plate Girder Stiffener Weld Procedures Under AWS D1.1

Bearing and transverse stiffener welds in built-up plate girders need specific WPS parameters and CWI inspection. AWS D1.1 requirements covered.

WPS AWS D1.1 plate girder stiffener welds structural steel CWI fabrication

New to procedures? Start with WPS welding: what a welding procedure specification is, with a filled-in example.

Built-up plate girders—fabricated from web plate and flange plates joined by continuous longitudinal welds—are workhorses of long-span structural steel construction. Transfer girders, crane runway beams, heavily loaded floor girders, and bridge-type frames all depend on plate girder geometry. Within those assemblies, stiffener plates perform two distinct structural functions that require different WPS treatment: transverse intermediate stiffeners that brace the web against shear buckling, and bearing stiffeners that transfer concentrated loads from the flange into the web at support points and load application locations.

Understanding the distinction matters for WPS development. The fit-up requirements, weld sizes, inspection hold points, and even whether a stud weld to the compression flange is required differ between the two stiffener types. AWS D1.1:2025 governs the welding execution requirements; AISC 360 Chapter G sets the design logic that explains why the requirements differ.

Transverse Intermediate Stiffeners: Web Bracing Against Shear Buckling

Intermediate transverse stiffeners run perpendicular to the girder web between the flanges. Their structural purpose is to provide stiffness that prevents the web from buckling under shear. They are typically single-sided or double-sided flat plates fillet welded to the web. The web panel buckling behavior is what drives how the stiffener is connected.

Stiffener-to-web fillet weld. The fillet weld between the intermediate stiffener plate and the web plate is the primary structural weld. AWS D1.1:2025 Table 7.7 sets the minimum fillet weld size based on the thinner of the two parts being joined (T = thinner part for low-hydrogen processes). For stiffener plates on a 3/8 in [10 mm] web, that minimum is typically 3/16 in [5 mm]; for a 1/2 in [12 mm] web, 3/16 in [5 mm] minimum again; for a 3/4 in [19 mm] web, 1/4 in [6 mm] minimum. The designer's calculated weld size for stiffness may be larger—use the larger of the design requirement and Table 7.7 minimum on the WPS.

Termination at the tension flange. AISC 360 permits transverse intermediate stiffeners on the tension flange to be terminated short of the flange rather than welded to it, to avoid welding directly into the tension zone at a potential fatigue initiation site. The termination distance—typically not less than four times the web thickness and not more than six times the web thickness above the near toe of the tension flange weld—must be maintained consistently and is a CWI inspection item. The WPS should note this detail if the girder will carry cyclic loads, and the inspector should verify the actual termination distance against the design drawing.

Termination at the compression flange. On the compression flange side, intermediate stiffeners may be welded or may bear in tight contact. In fabrication, they are more often welded for assembly stability. The weld here is a small fillet that ties the stiffener to the compression flange; it is not the primary load path and is sized to minimum per Table 7.7.

Corner clips. Stiffener plates must be clipped (coped or notched) at the web-flange junction corners to clear the flange-to-web longitudinal weld. The clip geometry—typically a 1 in [25 mm] square clip or a radius clip—must clear the weld toes while maintaining contact bearing over the full stiffener height less the clips. CWIs should verify that clips are sized correctly and that the longitudinal weld toes are not cut into by an undersized clip.

Bearing Stiffeners: Concentrated Load Transfer

Bearing stiffeners appear at girder ends (at supports) and at points of concentrated load application (column hangers, crane stops, transfer loads). Their structural function is column-like: they transfer a large vertical load from the flange down through the web to the support reaction or into an adjacent structural element. This column action demands tighter fit-up and heavier welds than intermediate stiffeners.

Fit-up to compression flange. Bearing stiffeners must bear tightly against the compression flange plate. AWS D1.1 workmanship requirements and project specifications typically limit the gap between the stiffener end and the flange surface to a few thousandths of an inch for fitted bearing, or require a weld of sufficient size to bridge any gap. CWIs performing the pre-weld fit-up inspection should use feeler gauges to verify bearing contact across the stiffener width. A stiffener that is rocking or has a visible gap requires grinding or shimming before welding proceeds.

Stiffener-to-web fillet weld sizing. The bearing stiffener to web fillet weld carries the full bearing load in shear along the stiffener height. This weld is typically much larger than the minimum Table 7.7 value—the designer calculates it based on the bearing reaction force and the weld allowable shear strength. WPS parameters for these welds should reflect the larger weld size and the multi-pass sequence needed to achieve it. For a plate girder with a 1 in [25 mm] web and a bearing reaction of 500 kips, the stiffener-to-web weld may be 5/16 in or larger on each side; verify against the design drawings, not just the minimum table.

Weld to compression flange. Unlike intermediate stiffeners, bearing stiffeners are normally welded to the compression flange to complete the load path. The weld from the stiffener to the flange must be sized for the full bearing load. Where the stiffener is fitted tight to the flange, the weld is sized for stability and for any eccentric load; where a gap exists, the weld alone must carry the full load. Document this distinction in the WPS.

Bearing stiffener grinding. On crane runway beams and other fatigue-critical girders, bearing stiffener welds may be ground flush or contoured to reduce stress concentration at the weld toes. If the design specifies a particular weld profile at the stiffener base, the WPS should include the grinding or blending requirement and the CWI should verify the final profile.

WPS Development for Stiffener Welds

Most shop fabricated plate girder stiffener welds use FCAW-G or SMAW in the flat (1F) or horizontal (2F) position when the girder web is set up horizontally. The position establishes the qualified range for the WPS; a 1F fillet weld WPS does not cover overhead or vertical position welds that may arise if stiffeners are added after the girder is flipped.

Stiffener welds are almost always fillet welds rather than groove welds. The essential variables that apply are those for the process and filler metal classification under AWS D1.1:2025 Table 6.6, covering process, electrode classification, shielding gas, position, and heat input range. For a typical A572 Grade 50 (Group II per Table 5.6) web and stiffener plate with FCAW-G using an E71T-1C/-9C electrode, a prequalified fillet weld WPS covers the work without a PQR if all Clause 5 limitations are met. See Built-Up Plate Girder WPS Sequence, Camber, and Sweep and Plate Girder Weld Procedure Under AWS D1.1 for the broader girder assembly context.

For A36 stiffeners on A572 Grade 50 webs—a common combination—the base metal combination is an unlisted dissimilar pairing that still falls within the prequalified framework as long as both steels appear in Table 5.6 and the filler metal satisfies the Table 5.4 matching-strength requirement for the higher-strength base metal. A filler metal that matches A572 Grade 50 meets this requirement for the A36 stiffener as well.

Preheat and Interpass Temperature

Bearing stiffener plates are often thick—1 in [25 mm] or heavier—and are welded with high-heat-input multi-pass sequences. For these conditions, minimum preheat requirements from AWS D1.1:2025 Table 5.11 (for prequalified WPS applications) apply based on the base metal category and thickness. A36 and A572 Grade 50 at thicknesses over 1-1/2 in [38 mm] require preheat per the Table 5.11 schedule; verify the specific temperature requirement against the edition and category row governing your material and process.

For tested WPS applications where CVN toughness is required—as may be specified on demand-critical welds or low-temperature service girders—the Table 6.8 supplementary essential variables also apply. Heat input range becomes a qualified range that the production welding must stay within. See CVN Supplementary Essential Variables Under AWS D1.1 Table 6.8 for details on when these variables become mandatory.

CWI Inspection Hold Points for Stiffener Welds

The inspection sequence for plate girder stiffener welds follows the standard pre-weld, in-process, and final visual pattern described in Weld Examination Sequence: CWI Visual and NDE Under AWS D1.1:

Pre-weld. Check stiffener dimensions against shop drawings, verify material heat traceability, confirm corner clips are correct, verify bearing contact (bearing stiffeners), confirm fit-up gap tolerances, verify preheat is applied and measured before arc strike.

In-process. Confirm interpass temperature is within WPS limits before each subsequent pass, verify pass sequence and bead placement on multi-pass bearing stiffener welds, check that weld toes at terminations are clean and that crater fills are complete.

Final visual. Verify fillet weld sizes (gauge measurement), check for undercut, overlap, cracks, or incomplete fusion visible at the weld surface, verify that tension-side stiffener termination distances are as designed, confirm any specified grinding or contouring is complete.

MT or PT when specified. For cyclically loaded girders, fatigue category requirements may trigger MT or PT on stiffener weld terminations. If specified by the design or project weld quality control plan, NDE should be performed after final visual before final acceptance.

Record-Keeping for Plate Girder Stiffener Welds

Each girder should have a weld map or traveler that ties stiffener weld locations to the WPS used, the welder who performed the work, the preheat/interpass temperature records, and the CWI inspection dates and results. This traceability package supports AISC fabricator certification audits and owner turnover requirements. For projects where multiple WPSs cover different stiffener details, the traveler must clearly identify which WPS applies to each weld location.

Rule library based on AWS D1.1:2025; verify against your governing edition.

Managing plate girder stiffener WPS records, welder assignments, and inspection documentation in one place is exactly what the tools at wpswelding.com/pricing are built for.

FAQ

Frequently asked.

Do transverse intermediate stiffeners need to be welded to both flanges of a plate girder?: Not always. AISC 360 and AWS D1.1 allow transverse stiffeners on the tension flange to be stopped short—typically one to six times the flange thickness above the flange—to avoid creating a stress raiser at the weld termination in the tension zone. Bearing stiffeners, by contrast, must bear tightly against the compression flange and are normally welded to it to transfer concentrated loads.
What weld size governs the stiffener-to-web fillet weld in a built-up plate girder?: Minimum fillet weld size is set by AWS D1.1:2025 Table 7.7, using the thinner of the two parts joined as the governing thickness (T) when low-hydrogen processes are used. The designer's required weld size for load transfer may exceed the Table 7.7 minimum; the larger of the two governs what goes on the WPS.
Can the same WPS used for flange-to-web groove welds cover the stiffener fillet welds?: Only if the WPS covers the process, filler metal classification, base metal group, and position range that apply to the stiffener welds. Stiffener welds are almost always fillet welds, while the flange-to-web connection is typically a CJP or PJP groove. A separate fillet weld WPS, or a WPS qualified for both groove and fillet welds under the appropriate essential variables in Table 6.6, is usually needed.
What pre-weld inspection items does the CWI check on bearing stiffeners before welding?: The CWI verifies tight bearing contact between the stiffener plate and the compression flange, correct stiffener height and width to plate width tolerances, cope or clipping at the stiffener corners to clear the flange-to-web weld, and proper material identification (heat number traceability). Gaps between the stiffener and flange wider than permitted by the WPS or project spec must be corrected before welding.