What weld type connects a wide-flange column to its base plate?

In most gravity and light lateral designs, double-sided fillet welds connect the column flanges and web to the base plate. For moment-resisting column bases or high-axial-load assemblies, the engineer may specify partial-joint-penetration (PJP) groove welds or complete-joint-penetration (CJP) groove welds to develop larger capacity at the column-to-plate interface.

Does welding a thick base plate require preheat under AWS D1.1?

Yes. Preheat requirements are driven by the thicker of the two members being joined. Base plates are commonly 1.5 in to 4 in thick; these thicknesses push preheat requirements to 150°F–225°F (66°C–107°C) for typical A36 or A572 Grade 50 material, depending on carbon equivalent. Confirm with the applicable preheat table in AWS D1.1:2025.

What filler metal is typically used for wide-flange column base plate welds?

For A36 or A572 Grade 50 base plates, E70XX (SMAW) or ER70S-X/E71T-X (GMAW/FCAW-G) electrodes matching or overmatching the base metal strength are typical. When the base plate or column steel has elevated carbon equivalent (CE > 0.45), a low-hydrogen electrode is required to control hydrogen-induced cracking.

Is a PQR required to weld a wide-flange column to a base plate?

Not necessarily. If the WPS qualifies as prequalified under AWS D1.1 — correct process, filler metal, joint type, preheat, and geometry all within prequalified limits — no PQR test is required. If any variable falls outside the prequalified envelope (thickness, joint geometry, or process), a tested WPS with a supporting PQR is required.

Wide-Flange Column Base Plate Shop Weld Procedure Under AWS D1.1

WPS requirements for welding W-shape columns to base plates in the fabrication shop — fillet sizing, preheat for thick plates, filler metal selection, and CWI checks.

Shop-fabricated column assemblies — a wide-flange section welded to a thick steel base plate — are among the highest-volume structural weld operations in a structural fab shop. Despite their visual simplicity, these welds carry significant consequence: the base plate transfers all column loads (axial, shear, and moment) into the anchor rods and foundation. A deficient weld here is not a rework item — it can be a structural failure waiting to happen.

A CWI reviewing base plate assemblies needs to verify the right WPS is in place, preheat is being applied, and the fillet or groove weld geometry matches the engineering drawing. This article covers what goes into that WPS and what the inspector should check on the floor.

What the Engineer Specifies

The structural drawings should call out:

Base plate dimensions and material grade (A36 or A572 Grade 50 are most common; A572 Gr.65 occasionally in high-rise column stacks)
Fillet weld size around the column perimeter, or specific groove weld type at the flange faces
Whether the weld is shop or field
Any special NDE requirement

Base plate welds shown on structural drawings are almost always shop welds. Field welding a column to a base plate after anchor rod setting is done only in special moment-frame designs; standard column bases are shop-fabricated and shipped to the site as an assembly.

Typical Weld Configuration

For a gravity column or lightly loaded lateral column, the standard connection is:

Double-sided fillet welds at each flange: The column flange rests flat on the base plate. A fillet weld is laid on both the top and bottom (inside and outside) face of each flange-to-plate contact. The weld size is specified on the drawing — commonly 5/16 in to 1/2 in for light columns, larger for heavy sections.
Fillet welds at the web: A fillet weld is placed on both sides of the web where it contacts the base plate. These are shorter runs and tend to be the same size as the flange welds or slightly smaller depending on drawing callout.

For a moment-resisting base (a "fixed" or "pinned moment base"), the engineer may specify:

PJP groove weld at the flange: A beveled groove provides more throat for tension transfer. The weld depth and included angle must match the WPS qualified range.
CJP groove weld at the flange: Full penetration to develop the full flange capacity. This requires a backing bar (typically left in place for shop welds) or backgouge and reweld.

The WPS must specify which joint type it covers. A WPS written for fillet welds does not cover a PJP groove weld on the same joint even if the process and filler metal are the same.

Filler Metal and Process Selection

Most base plate assemblies in a structural shop are welded with one of three processes:

SMAW (Stick): E7018 (low-hydrogen, DCEP) is the standard for manual base plate welding. Good control on heavy single-pass fillet welds, easy to manipulate in the flat or horizontal position typical of base plate assembly. The low-hydrogen requirement matters for thick plate — see preheat discussion below.

GMAW/FCAW-G: ER70S-6 (GMAW) or E71T-1 (FCAW-G) electrodes are used for higher-volume production. FCAW-G with C25 shielding gas (75% Ar / 25% CO₂) is a common shop choice for large fillet welds because it allows higher deposition rates and better out-of-position control than short-circuit GMAW. The WPS must document the gas mixture as an essential variable.

SAW (Submerged Arc): For very large column assemblies (heavy sections with base plates over 3 in thick), SAW may be used for the flat-position flange fillet welds. It offers high deposition rates and excellent metallurgical quality, but setup time and equipment cost make it practical only for repetitive production runs.

Filler metal strength matching is standard: E70xx or ER70S-x electrodes for A36 and A572 Grade 50. For A913 Grade 65 columns, verify the filler metal selection against the base metal and the WPS — you may need E80xx or higher-classification electrodes for proper strength match.

Preheat: The Critical Variable on Thick Plate

This is where most base plate WPS deficiencies arise. Base plates are thick — often 1.5 in to 3.5 in or more for large commercial columns — and thick steel requires elevated preheat to prevent hydrogen-induced cracking in the heat-affected zone (HAZ).

Preheat requirements under AWS D1.1:2025 are driven by:

The base metal group (A36, A572, etc.)
The carbon equivalent (CE) of the specific heat of steel (from the material test report)
The thickness of the thicker member being joined

For the column-to-base-plate joint, the thicker member is almost always the base plate. A 2-in A572 Grade 50 base plate typically requires minimum preheat of 150°F (66°C); a 3-in plate may require 225°F (107°C) or more depending on the heat's CE.

Common mistake: The welder preheats the column flange but not the base plate. AWS D1.1 requires preheat within 3 in of the joint on both members. Because the base plate is a massive heat sink (large surface area, low thermal conductivity for deep sections), it takes time to bring to temperature. A contact pyrometer or temperature-indicating crayons measured on the base plate surface (not just the column flange) is the correct verification method.

The WPS must specify the minimum preheat and maximum interpass temperature. For structural A572 Grade 50 base plate work, maximum interpass temperature of 450°F (232°C) is typical, though the engineer may specify a lower limit for thick plate or highly restrained joints where solidification cracking risk exists.

Joint Fit-Up Tolerances

The flat underside of the column rests on the base plate. Mill tolerance and camber can create gaps at the flange-to-plate interface. AWS D1.1 permits a gap up to 3/16 in (4.8 mm) for fillet welds; beyond this, the effective fillet weld leg size is reduced by the gap, or the gap must be filled before welding.

For CJP welds with steel backing, the backing bar must be in full contact with the base plate surface. Any gap between backing bar and base plate creates a notch at the weld root and may be unacceptable under radiographic or UT inspection. Fit-up verification is a CWI hold point before welding begins.

WPS Essential Variables for Prequalified Base Plate Welds

Under AWS D1.1, a prequalified WPS must fall within the boundaries established in the prequalified joint detail tables and the process-specific requirements of Clause 5. For fillet welds connecting a wide-flange column to a base plate, the prequalified path typically requires:

Process: SMAW, GMAW, FCAW-G, or SAW
Filler metal: AWS classified electrode matching the prequalified process requirements
Joint type: fillet weld in flat (1F) or horizontal (2F) position
Preheat: at or above the required minimum for the material group and thickness
Interpass: within the WPS limit
Fillet weld size: within the range qualified on the WPS (maximum single-pass fillet size varies by process and electrode diameter)

Any deviation from prequalified limits — thicker base plate than the WPS covers, groove weld configuration not on the prequalified list, or a new process not previously qualified — requires a tested WPS with a PQR. See WPS requalification triggers under AWS D1.1 for the full list.

Inspection Checkpoints

Before welding begins:

Confirm WPS is approved, current, and applies to this joint type, process, and base metal combination
Verify preheat has been achieved on both members within 3 in of the joint
Check fit-up gap per AWS D1.1 tolerances
Confirm welder has a current WPQ covering this process and position

During welding:

Interpass cleaning (slag removal between passes for SMAW and FCAW-G)
Interpass temperature measurement between passes
Fillet weld size at root passes (use fillet gauge)

After welding:

Visual inspection per AWS D1.1 acceptance criteria: profile, undercut, cracks, crater fill, weld size
Fillet weld leg and throat measured with appropriate gauge
NDE if specified (MT or PT for surface examination; UT if specified for volumetric)

Documentation Package

The complete base plate weld package for a AISC-certified fabricator includes:

WPS with all applicable essential variables documented
Welder WPQ records confirming current qualification
Preheat records (temperature, method, measured location)
Production weld log linking each column assembly to the WPS and welder
Material test report (MTR) for base plate confirming CE and grade
NDE reports where applicable

For moment-frame base plate assemblies, seismic provisions (AWS D1.8 if the project invokes it) add additional requirements: supplemental CVN testing for filler metal and possibly for the base metal, and specific preheat minimums tied to AWS D1.8 rather than D1.1. Confirm the governing specification with the EOR before writing the WPS.

Rule library based on AWS D1.1:2025; verify against your governing edition. Base plate weld requirements may also be governed by AISC 360, AISC 341 (seismic), and project-specific specifications.

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