Does AWS D1.1 apply to concrete-filled HSS tube columns (CFT)?

Yes. AWS D1.1 governs the structural steel welding at and around concrete-filled tube columns. The concrete fill is a structural element governed by ACI standards, but the beam-to-column welds, through-plate connections, shear tab welds, and any cap plate or base plate welds are subject to AWS D1.1 for the steel work.

What NDE method is best for welds on CFT column connections?

Ultrasonic testing (UT) is the preferred NDE method for most CFT weld connections. Radiographic testing is impractical for round HSS with concrete fill — the filler material creates scatter that makes RT images uninterpretable. Phased array UT (PAUT) works well for CJP groove welds in HSS faces. For fillet welds, MT or PT is used for surface discontinuities. See the UT in lieu of RT article for the AWS D1.1 approval pathway.

What filler metal should I use for welding to A500 Grade C HSS in a CFT column connection?

For standard structural connections using FCAW-G or SMAW, E71T-1 / E71T-9 (FCAW-G) or E7018 (SMAW) class filler metals are typical for A500 Grade C HSS. For demand-critical welds under AWS D1.8, the filler metal must also meet notch toughness requirements — select a CVN-qualified wire designation. Confirm the electrode classification and F-number against Table 5.6 of AWS D1.1:2025.

Can I use a prequalified WPS for the through-plate connection in a CFT column?

A prequalified WPS can cover the groove welds at the tube face if the joint geometry meets Clause 5 requirements. Through-plate connections involve welding the plate to the HSS face and sometimes to the HSS interior face — the interior weld may require a specially designed groove detail and confirmation that the joint fits within prequalified joint geometry limits. If the connection forces a non-standard geometry, qualification by test under Clause 6 is required.

Nov 14, 20267 min read

WPS for Concrete-Filled HSS Column Connections Under AWS D1.1

WPS considerations for welding beam-to-column connections on concrete-filled HSS (CFT) tube columns: joint access, through-plate details, filler selection, and NDT limitations.

WPS AWS D1.1 HSS CFT Structural Fabrication CWI Moment Connections

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

Concrete-filled HSS (CFT) tube columns have become a common choice in mid- and high-rise structural frames, industrial equipment supports, and seismically demanding applications. The concrete fill dramatically increases axial and shear capacity with no increase in column footprint. However, the fill creates real constraints for the structural welder, the CWI, and the engineer selecting connection details.

A WPS written for a standard unfilled HSS column will cover the steel welding process parameters — but it will not automatically address the access, NDT, joint geometry, and thermal considerations that differ when that tube is filled with concrete. This article covers the practical WPS considerations for beam-to-column connections on CFT columns under AWS D1.1.

Rule library based on AWS D1.1:2025; verify against your governing edition — the AHJ or contract may specify 2020 or earlier.

How CFT Changes the Welding Environment

For an unfilled HSS tube column, the common welding considerations are:

Access to the tube face for the beam-to-column connection
Position of the weld (commonly 1G for shop-welded connections, variable for field)
Tube wall thickness and its implications for minimum preheat
CJP vs. PJP groove weld selection based on load demand

When the tube is concrete-filled, additional factors enter the picture:

Heat sink effect. Concrete has significant thermal mass but relatively low thermal conductivity compared to steel. This slows heat dissipation from the weld into the tube, which can slightly elevate the interpass temperature near the fill but does not change the minimum preheat requirement for the steel. The preheat minimum from Table 5.11 of AWS D1.1:2025 applies to the base metal and is not reduced because of the fill.

No access holes possible. For an unfilled tube column, the structural engineer may allow a weld access hole to relieve stress concentration or improve root pass access at a moment connection. With concrete fill, drilling or cutting an access hole in the tube wall would require extensive concrete remediation and is essentially never done. Connection details must work without access holes.

Interior back-weld is not possible. On unfilled HSS tube, it is sometimes possible to access the interior for a back-weld on a groove joint. Concrete fill eliminates that option entirely. All CJP groove welds on CFT column faces must be designed to achieve full penetration from the exterior face only, using either steel backing or a groove joint geometry that allows single-side root access.

UT is the only practical volumetric NDE option. Radiographic testing requires clear X-ray or gamma-ray transmission through the joint cross-section. Concrete fill scatters radiation in a way that makes RT film uninterpretable for the tube wall and groove weld region. Phased array UT (PAUT) or conventional UT is the NDT method of choice. The CWI should confirm UT accessibility before the connection is detailed — some HSS face geometries limit probe placement.

Connection Types and WPS Implications

Shear Tab (Single Plate) Connection

The standard shear tab welded to the face of a CFT column is a fillet weld of the plate to the tube face. This is a common, straightforward connection that does not change with the presence of concrete fill. The WPS for a fillet weld of a plate to an HSS tube face remains valid for CFT columns.

Minimum fillet weld size is determined by the thinner connected part per Table 7.7 of AWS D1.1:2025. The tube wall thickness governs when it is thinner than the plate. The filler metal, process, and essential variables in the WPS apply without modification for the fill condition.

Through-Plate Connection

Through-plate connections are common in CFT columns where high moment or combined load demands require load transfer through the column section. A flat plate is passed completely through the HSS tube — through slots cut in both tube walls — and groove-welded to the tube face on each side. The concrete is poured after the steel connection is complete.

For the WPS perspective:

The groove weld of the through-plate to the tube face follows standard AWS D1.1 groove weld requirements. The joint must be designed to allow CJP groove weld access from the exposed exterior face, using steel backing or a suitable groove detail.
If the slot cut into the tube wall is tight to the plate, the resulting fit-up must be within AWS D1.1 groove root opening tolerances.
Steel backing bars placed at the bottom of the groove (on the interior tube face side) are not removable after concrete is placed. The engineer of record must accept permanent backing for this condition.
The CWI must verify that the slot cut does not introduce notch conditions at the tube corner that would create stress concentration in the final connection.

Cap Plate and Base Plate Connections

Cap plates (top of column) and base plates (bottom of column) are fillet- or groove-welded to the tube end face. These connections are typically made before concrete is placed and are not affected by the fill condition in terms of WPS requirements.

For base plates on CFT columns, preheat requirements follow the standard A500 Grade C HSS requirements in Table 5.11 of AWS D1.1:2025, based on the tube wall thickness. After concrete is placed, the base plate weld is complete and the connection is not revisited.

Field Moment Connection — Welded Flange Plates

In some high-rise applications, beam flanges are welded directly to the CFT tube face with a CJP groove weld for moment transfer. This is the most demanding connection in terms of WPS, NDT, and inspection requirements:

The groove weld must achieve CJP from the exposed exterior face only. This typically uses a steel backing bar tack-welded to the tube face behind the groove.
The root pass is a critical hold point. The CWI must visually verify the root pass before proceeding, as back-gouging from the interior face is not possible.
UT must be performed after welding is complete. The CWI should confirm with the NDT technician that probe access is sufficient on the tube face geometry — round tube faces may require curved probe shoes or PAUT scanning to achieve adequate coverage.
For seismically detailed moment connections under AWS D1.8, the demand-critical filler metal requirements apply. The electrode must meet notch toughness requirements in addition to strength.

NDT Planning for CFT Connections

Because UT is the primary volumetric NDE method for CFT groove welds, the CWI should address UT planning before the connection is fabricated:

Confirm probe access. Round HSS tube faces create curved surfaces that limit flat probe placement. Curved probe shoes matched to the tube OD are commonly used. PAUT with a linear array can accommodate the surface profile more readily.
Identify scan directions. For a groove weld in a rectangular HSS face, transverse scanning from both directions along the weld is feasible. For a CJP groove weld in a round tube face, the scan geometry must achieve adequate coverage per AWS D1.1 UT requirements.
Plan for in-process UT if required. For seismic demand-critical welds, the contract may require intermediate NDE after root pass and after fill passes, not just at completion.
Coordinate timing. UT after welding must meet the minimum postweld NDE delay requirements of AWS D1.1 for the steel being welded. For higher-strength steels, a delay of 24 to 48 hours after completion is common to allow hydrogen diffusion.

Preheat and Interpass for CFT Column Welding

The minimum preheat for A500 Grade C HSS follows Table 5.11 of AWS D1.1:2025, based on the tube wall thickness and base metal group. Typical wall thicknesses for CFT columns range from 1/4 inch to 3/4 inch or more for heavy sections.

Key points for interpass temperature control on CFT columns:

The concrete fill acts as a moderate heat sink. While this keeps interpass temperatures from rising rapidly, it does not replace the need for active monitoring.
Maximum interpass temperature stated on the WPS must be measured and recorded. For A500 tube and standard structural filler metals, a maximum interpass of 450°F to 500°F is typical.
Do not apply preheat to the concrete-filled section with an open flame applied to the tube face for extended periods. The goal is to warm the tube steel, not drive heat into the concrete.
Use a contact thermometer or temperature-indicating crayons to verify preheat. Surface-temperature infrared thermometers have accuracy limitations at metal surfaces that the CWI must account for.

Common WPS Gaps for CFT Projects

1. WPS does not address backing bar permanence. The WPS should explicitly note that steel backing on interior tube faces is permanent (non-removable) and is designed accordingly. The engineer of record must accept permanent backing.

2. WPS does not list the NDT method. The WPS or the inspection plan should identify UT as the volumetric NDE method and confirm that the UT procedure covers the specific tube geometry.

3. WPS was written for flat plate, not for tube face geometry. A fillet weld WPS written for flat material covers the same weld metallurgy on a tube face, but the CWI should confirm the essential variables — position, filler metal, preheat — remain within range for the tube-face joint.

4. Essential variables for seismic not addressed. If the project requires demand-critical filler metal qualification (AWS D1.8), the WPS must call out a CVN-qualified electrode designation. Standard production E71T-1 wire without notch toughness testing does not meet the demand-critical requirement.

For WPS library management tools that track connection types, NDE method requirements, and essential variable compliance across your project portfolio, see wpswelding.com/pricing. For standard HSS tube weld WPS guidance, see HSS Tubular Connection Weld Procedures Under AWS D1.1.

FAQ

Frequently asked.

Does AWS D1.1 apply to concrete-filled HSS tube columns (CFT)?: Yes. AWS D1.1 governs the structural steel welding at and around concrete-filled tube columns. The concrete fill is a structural element governed by ACI standards, but the beam-to-column welds, through-plate connections, shear tab welds, and any cap plate or base plate welds are subject to AWS D1.1 for the steel work.
What NDE method is best for welds on CFT column connections?: Ultrasonic testing (UT) is the preferred NDE method for most CFT weld connections. Radiographic testing is impractical for round HSS with concrete fill — the filler material creates scatter that makes RT images uninterpretable. Phased array UT (PAUT) works well for CJP groove welds in HSS faces. For fillet welds, MT or PT is used for surface discontinuities. See the UT in lieu of RT article for the AWS D1.1 approval pathway.
What filler metal should I use for welding to A500 Grade C HSS in a CFT column connection?: For standard structural connections using FCAW-G or SMAW, E71T-1 / E71T-9 (FCAW-G) or E7018 (SMAW) class filler metals are typical for A500 Grade C HSS. For demand-critical welds under AWS D1.8, the filler metal must also meet notch toughness requirements — select a CVN-qualified wire designation. Confirm the electrode classification and F-number against Table 5.6 of AWS D1.1:2025.
Can I use a prequalified WPS for the through-plate connection in a CFT column?: A prequalified WPS can cover the groove welds at the tube face if the joint geometry meets Clause 5 requirements. Through-plate connections involve welding the plate to the HSS face and sometimes to the HSS interior face — the interior weld may require a specially designed groove detail and confirmation that the joint fits within prequalified joint geometry limits. If the connection forces a non-standard geometry, qualification by test under Clause 6 is required.