Can you use a prequalified WPS for HSS brace-to-gusset plate welds?

Yes, if the joint detail meets the requirements of AWS D1.1 Clause 3 for prequalified fillet welds or groove welds. Most HSS-to-gusset plate connections use fillet welds that fit within prequalified limits, though the dihedral angle between the brace and gusset face must be checked against the prequalified range.

What fillet weld size is required for an HSS brace to a gusset plate?

Minimum fillet weld size is set by AWS D1.1 Table 7.7, based on the thinner part of the joint. For a standard HSS with 3/16 in. to 1/2 in. wall, minimum fillet sizes range from 3/16 in. to 1/4 in. The design engineer specifies the required size from load demand; the WPS must qualify both the minimum structural size and the required size.

Does a round HSS brace to flat gusset plate require a groove weld?

Not necessarily. Fillet welds around the full perimeter of the round HSS are common, but the effective weld area on a curved surface requires careful sizing. Some designers specify a full-perimeter groove weld for heavily loaded connections. Either way, the joint geometry for a round HSS saddle on a flat plate falls outside most standard prequalified joint details and may require PQR qualification.

How does the dihedral angle affect fillet weld leg size on a brace connection?

When the brace meets the gusset plate at an angle other than 90 degrees, the effective throat of the fillet weld changes. AWS D1.1 provides effective throat adjustments for skewed T-joints with dihedral angles that differ from 90 degrees. The WPS should document the dihedral angle range and the effective throat adjustment applied.

Nov 11, 20266 min read

HSS Diagonal Brace-to-Gusset Plate WPS: AWS D1.1

WPS considerations for welding HSS diagonal bracing to gusset plates in concentrically braced frames: fillet vs groove weld selection, dihedral angle fit-up, and essential variable documentation.

WPS HSS bracing gusset plate concentrically braced frame AWS D1.1 fillet weld

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

Diagonal bracing connections—the workhorse of concentrically braced frames (CBF) in industrial and commercial steel buildings—put a specific WPS challenge in front of a shop: the HSS brace hits the gusset plate at an angle. That angle is not 90 degrees. It changes with the building geometry, the brace slope, and the connection layout. The joint is effectively a skewed T, and the prequalified fillet weld details in AWS D1.1 Clause 3 have a dihedral angle range that must be checked before writing a prequalified WPS.

This article covers the WPS qualification path for the most common case: rectangular or round HSS brace welded to a flat gusset plate in a CBF application, non-seismic or low-seismic (SDC A, B, or C), where AWS D1.1 governs without the full AWS D1.8 overlay.

Joint Configuration at the Brace-to-Gusset Connection

The brace-to-gusset plate weld is typically a fillet weld around the perimeter of the HSS end. For a rectangular HSS (square or rectangular tube), the connection geometry depends on whether the brace end is cut square (perpendicular to the brace axis) or notched to lap over the gusset plate. Most fabricated connections use a square-cut HSS end welded to the face of the gusset plate—essentially four fillet welds, one on each flat of the HSS end.

The complication is angle. If the brace slopes at 30 to 60 degrees from horizontal (a typical range for X-brace or K-brace configurations), the HSS end is not parallel to the gusset plate face. The fillet weld on the face of the connection—the weld between the flat HSS wall and the gusset—is a skewed fillet at the dihedral angle formed between the HSS tube wall and the gusset plate. AWS D1.1 defines this as a skewed T-joint, and the prequalified fillet weld details allow dihedral angles from 60 to 135 degrees for prequalified welds.

If the calculated dihedral angle for a brace at a specific slope falls outside that range (which can happen with very steep or very shallow braces), the joint is not prequalified and requires PQR qualification. Check this early in WPS development.

Calculating the Dihedral Angle

For a rectangular HSS brace welded to a vertical gusset plate, the dihedral angle on the face of the connection is:

90° minus the brace slope angle on the uphill face
90° plus the brace slope angle on the downhill face

For a brace at 45 degrees, the uphill face dihedral is 45° and the downhill face dihedral is 135°. Both are within the prequalified range of 60–135°. For a brace at 20 degrees (a nearly horizontal brace), the uphill face dihedral drops to 70°—still within range, but marginal.

When the dihedral angle falls between 80° and 100°, the standard fillet weld geometry applies without effective throat adjustment. For angles outside that band (but still within prequalified limits), AWS D1.1 Annex A provides effective throat adjustment factors for skewed T-joints. The WPS should document the dihedral angle range and reference the effective throat calculation if the design relies on it.

Fillet Weld WPS: Essential Variables Under Table 6.6

For a prequalified or PQR-qualified fillet weld WPS covering HSS brace-to-gusset plate welds, the Table 6.6 essential variables for the applicable process (FCAW-G, GMAW-S, SMAW) all apply as usual. The specific variables that require attention in this application:

Position. An HSS diagonal brace welded in the shop may allow the assembly to be positioned so the brace-to-gusset weld is made in the flat (1F) position. If the assembly must be welded in a fixed position with the brace at angle, some portions of the perimeter weld become overhead or vertical. The WPS must qualify all positions that will be encountered. For shop fabrication, rotating the assembly to maximize flat-position welding is standard practice—but the WPS must reflect the actual positions used.

Joint configuration. The fillet weld WPS must call out the joint type (skewed T-joint) and the dihedral angle range. A WPS written for a 90-degree T-joint does not cover a 60-degree skewed T without an amendment or separate WPS.

Minimum fillet size per Table 7.7. Minimum fillet size is based on the thinner part. For an HSS with 3/8 in. wall thickness welded to a 1/2 in. gusset plate, the thinner part is 3/8 in., putting the minimum fillet at 1/4 in. (for low-hydrogen processes). The required structural weld size from the design engineer will typically exceed this minimum for a loaded bracing connection—but the WPS must state both. See minimum fillet weld size requirements under AWS D1.1 Table 7.7 for the full table lookup.

Base metal group qualification. A500 Grade B/C HSS and A36 or A572 Grade 50 gusset plate are both in Table 6.9 Group I, so a single WPS covers both. If the gusset is A572 Grade 65 or other higher-strength material, check whether both materials are covered by the WPS's base metal qualification range per Table 6.9.

Round HSS Brace to Flat Gusset: Different Challenge

Round HSS (CHS) bracing to a flat gusset plate is a saddle-on-flat geometry. The round tube bears on the flat plate along a curved contact line, not a straight weld line. Fillet welds around the perimeter of a round HSS end on a flat plate are achievable, but the effective throat varies around the perimeter because the tube wall angle relative to the plate face changes continuously.

Most EOR-specified details for round HSS bracing call for either: (a) the HSS end to be cope-cut to a saddle shape that fits flush against the gusset face, then fillet-welded around the perimeter; or (b) the HSS end to be cut square and welded with a full-penetration groove weld. The saddle-cut approach typically requires PQR qualification because the joint geometry falls outside the standard prequalified joint details. See round HSS pipe to plate T-joint weld procedure for detail on round section connections.

Preheat Requirements

For standard A500 or A53 HSS in Group I material at typical wall thicknesses, the preheat requirements from AWS D1.1 Table 5.11 start at 32°F (0°C) minimum for the thinner material categories with low-hydrogen filler metals. At wall thicknesses over 3/4 in. with higher-strength gusset material, preheat requirements increase.

The practical issue on brace connections is joint restraint. A heavily restrained HSS brace connection—common in X-brace configurations where the brace is tightly fitted between two gusset plates—creates residual stress concentration that increases hydrogen cracking risk. Some fabricators increase preheat beyond the Table 5.11 minimum on restrained joints. Document the actual preheat minimum on the WPS; if you are increasing it beyond Table 5.11 for practical reasons, note that in the WPS remarks. See preheat verification methods for the field for the measurement approaches applicable during production welding.

WPS Submittal for Braced Frame Projects

A complete WPS package for a CBF shop fabrication project should identify:

All HSS sizes and gusset plate thicknesses in the project (to verify the minimum fillet size and base metal group coverage)
The dihedral angle range across all brace connections, with confirmation that all angles are within prequalified limits (or supported by PQR if not)
The welding positions present across the connection geometry
Preheat requirements by material thickness group

AISC 303 requires this documentation before fabrication begins. Building it up front—rather than scrambling when an inspector questions whether the WPS covers a particular brace slope—keeps the job moving on schedule.

For a software solution that tracks WPS qualification ranges, preheat requirements, and essential variable coverage across multiple connection types on a project, see wpswelding.com/pricing.

Rule library based on AWS D1.1:2025; verify against your governing edition. For seismic SDC D, E, or F braced frames subject to AWS D1.8, additional essential variables and filler metal requirements apply beyond those shown here.

FAQ

Frequently asked.

Can you use a prequalified WPS for HSS brace-to-gusset plate welds?: Yes, if the joint detail meets the requirements of AWS D1.1 Clause 3 for prequalified fillet welds or groove welds. Most HSS-to-gusset plate connections use fillet welds that fit within prequalified limits, though the dihedral angle between the brace and gusset face must be checked against the prequalified range.
What fillet weld size is required for an HSS brace to a gusset plate?: Minimum fillet weld size is set by AWS D1.1 Table 7.7, based on the thinner part of the joint. For a standard HSS with 3/16 in. to 1/2 in. wall, minimum fillet sizes range from 3/16 in. to 1/4 in. The design engineer specifies the required size from load demand; the WPS must qualify both the minimum structural size and the required size.
Does a round HSS brace to flat gusset plate require a groove weld?: Not necessarily. Fillet welds around the full perimeter of the round HSS are common, but the effective weld area on a curved surface requires careful sizing. Some designers specify a full-perimeter groove weld for heavily loaded connections. Either way, the joint geometry for a round HSS saddle on a flat plate falls outside most standard prequalified joint details and may require PQR qualification.
How does the dihedral angle affect fillet weld leg size on a brace connection?: When the brace meets the gusset plate at an angle other than 90 degrees, the effective throat of the fillet weld changes. AWS D1.1 provides effective throat adjustments for skewed T-joints with dihedral angles that differ from 90 degrees. The WPS should document the dihedral angle range and the effective throat adjustment applied.