Built-up plate girders — a web plate continuously welded to top and bottom flange plates — are among the highest-volume repetitive weld joints in a structural steel fabrication shop. A single long-span plate girder can require hundreds of feet of web-to-flange fillet weld, multiple transverse stiffeners, and occasional cover plate attachments. Each weld type has distinct WPS requirements, process considerations, and inspection criteria that a CWI needs to manage as a coherent plan rather than disconnected individual joints.

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

Why plate girder WPS planning matters more than W-shape connections

A standard wide-flange (W-shape) beam arrives from the mill with the web-to-flange weld already made at the steel producer's rolling facility under the producer's own procedures. For a plate girder, the fabricator makes those welds — and takes on full responsibility for WPS qualification, process selection, parameter documentation, and inspection.

The practical implications are significant:

Continuous long welds amplify distortion risk. Unbalanced welding sequence on web-to-flange joints causes longitudinal camber and lateral sweep. The WPS should specify the required welding sequence — typically welding opposite flanges in alternating passes or using a jig to balance heat input — not leave it to the welder's judgment.

Process selection drives shop productivity. Submerged arc welding (SAW) is the dominant process for web-to-flange welds in high-production shops because of its deposition rate and consistent bead profile under flux cover. FCAW-G is the alternative when SAW gantry setups are unavailable or for shorter girder runs. SMAW is rarely cost-effective for continuous web-to-flange work.

Thick plate requires preheat discipline. Plate girder webs and flanges often exceed 1 in [25 mm] thickness, bringing AWS D1.1:2025 Clause 5 (prequalified) or Table 5.3 (PQR basis) preheat requirements into play depending on carbon equivalent and base metal specification.

Web-to-flange fillet welds: process selection and WPS parameters

The web-to-flange fillet weld runs continuously along the full depth of the girder on both sides of the web. Process selection affects both the WPS qualification path and daily production performance.

Submerged arc welding (SAW)

SAW is the standard high-production choice. A gantry or positioner runs the girder under a fixed welding head, and twin-wire or tandem setups can deposit both web-to-flange welds simultaneously on a single pass around the web. SAW essential variables under AWS D1.1:2025 Table 6.6 include:

  • Wire classification (a change in AWS A5.17 or A5.23 classification is essential)
  • Flux classification (changes that affect mechanical properties are essential under Table 6.6)
  • Heat input range (travel speed and electrical parameters together set heat input)
  • Wire extension (CTWD)
  • Number of electrodes (single vs. twin vs. tandem — each is a separate qualification)

The SAW WPS must document the qualified travel speed range tightly, because travel speed directly controls weld size and heat input on long continuous welds. A welder who slows down to fix fit-up may inadvertently push outside the WPS heat input range. See SAW essential variables and WPS documentation under AWS D1.1 for a process-specific breakdown.

FCAW-G as an alternative

FCAW-G is used when girders are short enough not to justify SAW equipment setup, when access or positioning limits the SAW head, or in shops without SAW capability. FCAW-G WPS essential variables under Table 6.6 include electrode wire classification, shielding gas composition and flow rate, and heat input range. Note that under the 2025 edition, A5.36 composite electrodes were dropped from the list of FCAW allowed electrode classifications under certain rows of Table 6.6 — verify that your wire classification is still covered by your existing PQR if you've recently changed to an A5.36-classified product.

Weld size and the qualified range

The design engineer specifies the required weld size based on shear flow demand at the web-to-flange interface under the governing load combination. AWS D1.1:2025 sets minimum fillet weld sizes based on the thicker part being joined; this minimum is a code floor. The WPS must document the maximum and minimum fillet weld sizes the procedure covers, bounded by what was tested in the PQR or by Clause 5 limits. The CWI's in-process inspection must gauge each weld to confirm the actual fillet is at or above the design size and within the WPS range. See fillet weld size requirements and WPS documentation for how the inspection criteria interact with the qualified range.

Stiffener welds: bearing, intermediate, and the flange restriction

Plate girders carry transverse stiffeners — vertical plates welded to the web — to control shear buckling and transfer bearing loads. The WPS and joint plan must treat bearing stiffeners and intermediate stiffeners differently.

Bearing stiffeners

Bearing stiffeners transfer concentrated loads (at support reactions and point loads) into the web. They are typically fitted tight to the compression flange and welded on both sides of the web with fillet welds sized to transfer the full bearing load. Bearing stiffener-to-web welds are usually full depth on both sides; the connection detail at the compression flange is either a tight bearing fit (grinding to contact) or a fillet weld, per the EOR's detail.

The WPS for bearing stiffener welds is typically the same process and parameter set as the web-to-flange weld if plate thicknesses are similar and fall within the same qualified range. If the stiffener plate is thicker or thinner than the web-to-flange joint tested in the PQR, check that the thickness is within the qualified range per Table 6.6.

Intermediate stiffeners and the tension flange rule

Intermediate stiffeners (shear stiffeners) control web buckling between bearing points. They carry no direct load — their function is geometric. Their WPS and joint detail have one critical design constraint with direct inspection implications: do not weld intermediate stiffeners to the tension flange in cyclically loaded structures.

AWS D1.1:2025 fatigue provisions (Annex A) assign fatigue stress categories to weld details. A weld termination at the tension flange — a transverse attachment weld — creates a Category E' stress concentration at the weld toe. Category E' carries a substantially lower allowable stress range than the parent plate Category A, which can govern girder capacity under fatigue loading. This is not a conservative formality; fatigue cracking initiated at misapplied stiffener-to-tension-flange welds has caused failures in bridge girders and industrial crane runway beams.

Standard detailing practice:

  • Clip or cope the bottom of the intermediate stiffener 1 to 2 in [25 to 50 mm] clear of the tension flange
  • Terminate the stiffener-to-web fillet weld the same distance above the flange face
  • Omit any weld from the stiffener to the tension flange

The WPS joint plan must explicitly specify this clearance dimension, and the CWI confirms it during in-process inspection before the welder finishes the stiffener run. If the EOR's drawings do not specify the stiffener termination detail — a common omission in preliminary issue drawings — the fabricator should issue an RFI before welding.

See fatigue and cyclically loaded weld requirements under AWS D1.1 for the complete category assignment table and how it applies to other connection types.

Cover plate attachment welds

Cover plates — additional flange plates welded to the bottom flange to increase section modulus in high-moment zones — require continuous longitudinal fillet welds at the flange-to-cover-plate interface. Process selection for these welds is the same as for web-to-flange (SAW or FCAW-G), but the end termination of the cover plate is a fatigue-critical detail that requires separate WPS attention.

At the end of the cover plate, the longitudinal weld terminates in a transverse end weld (or the plate is tapered). AWS D1.1:2025 Annex A assigns fatigue categories to these end configurations based on the weld geometry and whether the end is welded transversely, tapered, or left as a square-cut termination. The EOR must specify the termination detail; the WPS and inspection plan must address the end weld parameters separately from the continuous run weld, since the end weld orientation, size, and profile may differ from the main longitudinal run.

The CWI inspection plan for plate girder fabrication

A CWI inspecting plate girder production in a shop should work from a written plan that maps each weld type to the applicable WPS, the required inspection method, and the acceptance criteria. The minimum inspection checkpoints for each girder:

Pre-weld: Plate identification against CMTRs; joint fit-up — gap between web and flange within AWS D1.1:2025 workmanship tolerances; preheat confirmed if required by the WPS; electrode or wire lot certified and stored per WPS requirements.

In-process: Production welding parameter log confirms amperage, voltage, and travel speed fall within the WPS range; interpass temperature does not exceed the WPS maximum; stiffener bottom clearance above the tension flange confirmed before the stiffener weld is completed.

Post-weld: Fillet weld gauge confirms each weld type meets the design size; visual inspection per AWS D1.1:2025 Clause 9 acceptance criteria (undercut limits, overlap, surface porosity, weld profile); NDE per the project quality inspection plan if required.

For SAW web-to-flange welds, the production welding parameter log is the primary in-process documentation. If the shop does not log travel speed and wire feed rate with timestamps tied to the joint, the CWI has no documented evidence that heat input stayed within the WPS range — a routine finding on plate girder fabrication audit packages. The complete audit packet should include the WPS(s), PQR(s) or prequalified documentation, CMTRs, filler metal certifications, preheat records, in-process parameter logs, and inspection records.

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