Can I use my AWS D1.1 WPS on a bridge fabrication project?

Generally no. AWS D1.5 is the governing code for steel highway bridges on FHWA-funded projects and those built to AASHTO specifications. A WPS qualified under AWS D1.1 is not automatically acceptable under D1.5. The codes have different qualification requirements, base metal restrictions, preheat tables, and fracture-critical member provisions. If your contract references D1.5, your WPS documentation must be qualified under that code.

What is a fracture-critical member and why does it affect WPS requirements?

A fracture-critical member (FCM) is a tension member or tension component of a member whose failure could cause collapse of the bridge. AWS D1.5 has additional mandatory requirements for welds in FCMs, including Charpy V-notch testing of the deposited weld metal to verify toughness. These CVN requirements apply to both the WPS qualification and in some cases to production weld metal from each heat of consumables. D1.1 has no equivalent automatic FCM trigger — CVN testing under D1.1 is invoked by a supplementary essential variable change or owner specification.

Does AWS D1.5 have prequalified WPS provisions like D1.1 Clause 3?

No. AWS D1.1 allows certain process/base metal/joint combinations to qualify as prequalified, meaning no PQR test is required. AWS D1.5 does not have an equivalent unconditional prequalified path. All WPS under D1.5 must be supported by a PQR demonstrating qualification by test. This is one of the most significant practical differences for shops transitioning from building structural work to bridge fabrication.

What base metals does AWS D1.5 permit?

AWS D1.5 limits base metals to those specifically approved within the code, primarily ASTM A709 grades (36, 50, 50W, 70W, HPS 50W, HPS 70W, HPS 100W) and a limited set of equivalents. The code's base metal tables define which A709 grades may be combined with which filler metals. D1.1 has a broader list of approved base metals through its Table 6.9 group system. Shops welding bridge steel must verify that every base metal in their mix falls within the D1.5 approved list.

AWS D1.5 Bridge Welding WPS Requirements vs AWS D1.1

AWS D1.5 governs highway bridge welding with stricter WPS qualification, fracture-critical member rules, and CVN requirements that don't apply under D1.1. Here's what fabricators need to know.

A fab shop that builds structural steel for commercial buildings under AWS D1.1 has a solid foundation — but shifting to highway bridge work under AWS D1.5 introduces a different set of rules. The two codes share a common ancestry and many provisions look similar on the surface, but the differences in WPS qualification requirements, base metal restrictions, fracture-critical member obligations, and CVN testing will catch shops off guard if they treat D1.5 as a minor variant of D1.1.

This article covers the key WPS-related differences from a CWI and QC manager perspective.

Why Two Codes Exist

AWS D1.1 — Structural Welding Code — Steel is the general-purpose code for welded steel structures: buildings, industrial frames, bridges not built under AASHTO jurisdiction, tanks, and similar applications. It is broad by design and balances a large number of base metals, processes, and joint configurations.

AWS D1.5 — Bridge Welding Code is a joint publication of the American Welding Society and the American Association of State Highway and Transportation Officials (AASHTO). Its scope is steel highway bridges. The Federal Highway Administration requires D1.5 compliance on federally funded bridge projects. When a bridge owner's specification or a National Steel Bridge Alliance (NSBA) project document references D1.5, that code governs — not D1.1.

The reason D1.5 exists as a separate document is that bridge structures carry unique demands: fatigue cycling, dynamic loads, fracture-critical consequences of member failure, and a regulatory environment that demands tighter controls than D1.1's flexible baseline.

No Prequalified WPS Path

The most immediately practical difference for shops new to bridge work: AWS D1.5 does not have a prequalified WPS provision equivalent to AWS D1.1's Clause 3.

Under D1.1, a qualified shop can use a prequalified WPS for a broad range of SMAW, FCAW-G, GMAW, and SAW joint configurations without running a formal procedure qualification test (PQR). The prequalified path is one of D1.1's most-used features — it removes the cost of testing for standard structural configurations and lets a new project start immediately.

D1.5 requires every WPS to be qualified by test. A PQR covering the applicable variables — process, base metal, filler metal, joint geometry, position, heat input range, preheat and interpass temperatures — must be on file for every WPS in use on the project. There are no shortcuts for familiar processes or simple joints.

For a shop that has relied on prequalified D1.1 procedures, this means testing costs before the first bridge weld is ever run in production. Shops that want to enter bridge work need to budget qualification testing as part of project mobilization.

Base Metal Restrictions

D1.5 approves a more limited set of base metals than D1.1. The code centers on ASTM A709, which is the bridge-specific standard for structural steel. A709 grades include the standard grades (36, 50, 50W), weathering grades (50W, 70W), and high-performance steel (HPS 50W, HPS 70W, HPS 100W). The code tables define permitted filler metal combinations for each grade.

The high-performance grades — HPS 70W and HPS 100W — are quenched and tempered steels with mechanical properties and weldability characteristics that are distinct from the carbon-equivalent range of A572 or A588. Preheat requirements for HPS grades are different from A709-50, and filler metal matching requirements are more specific. WPS qualification for these grades must be done on the actual HPS grade, not inferred from a lower-strength D1.1 qualification.

D1.1's base metal Table 6.9 includes A709 grades, so a D1.1 WPS technically covers the same steel. But D1.5's additional requirements — FCM CVN testing, code-specific heat input controls — mean that a D1.1 WPS for A709 steel does not meet D1.5 project requirements.

Fracture-Critical Member Requirements

AWS D1.5's fracture control plan (FCP) provisions are the most significant operational difference from D1.1. A fracture-critical member (FCM) is defined as a tension member or tension component whose failure would be expected to cause collapse of the bridge. The designation is made by the bridge designer and called out on project drawings.

For welds in FCMs, D1.5 imposes mandatory Charpy V-notch (CVN) toughness requirements on the deposited weld metal. This means:

PQR testing for FCM WPS must include CVN specimens from the deposited weld metal taken from the procedure qualification test plate or pipe. The CVN results must meet the minimum absorbed energy requirement at the specified test temperature.

Production heat lot testing is required by some owner specifications and project requirements: for each heat or lot of filler metal used on FCM welds, CVN tests from a deposited weld metal sample must confirm toughness before the heat is cleared for production use. This lot testing requirement goes beyond the standard PQR and is enforced contractually rather than directly in the D1.5 code itself, but it is common on major bridge projects.

Under AWS D1.1, CVN supplementary essential variables (Table 6.8) are triggered when the governing specification or owner requirement invokes them — not automatically for every weld. A D1.1 structural shop may never run a CVN program on deposited weld metal if their project specifications don't call for it. A D1.5 bridge shop working on FCMs has no such choice.

Heat Input Controls

D1.5 is more prescriptive about heat input ranges than D1.1. For many weld configurations, the code specifies heat input limits — minimum and maximum — in the WPS. These limits serve two purposes: they control the mechanical properties of the heat-affected zone (grain coarsening and HAZ toughness), and on HPS grades they protect against softening of the quenched and tempered base metal.

Under D1.1, heat input is tracked in the WPS as a function of current, voltage, and travel speed, but the essential variable system of Table 6.6 governs requalification based on changes from qualified values rather than absolute limits. Rule library based on AWS D1.1:2025; verify against your governing edition.

For D1.5 bridge work, the WPS must document the heat input range (minimum and maximum joules per inch), and welders must monitor and record heat input during production. This adds a process control discipline that many building structural shops are not set up to enforce.

Preheat and Interpass Differences

D1.5 preheat tables are more conservative than D1.1 for comparable thicknesses and grades, particularly for high-strength steels. For HPS grades, preheat minimums can be significantly higher than for comparable A572 structural steel under D1.1.

Interpass temperature maximums are also specified and enforced for FCM welds to prevent degrading CVN toughness through excessive heat accumulation. Some HPS grades require interpass temperature to be held below 400°F (200°C) — which in thick-section welds means pausing between passes and waiting for the joint to cool. Production planning must account for this.

CWIs working on D1.5 projects need to be checking and recording preheat and interpass temperatures at each pass on FCM welds, not just at the start of welding.

WPS Documentation for a Bridge Project

A D1.5-compliant WPS package typically includes:

WPS form covering all essential variables required by the code: process, base metal P-number equivalent, A709 grade, filler metal classification, position, heat input range, preheat and interpass temperature minimums and maximums, joint geometry range, and shielding gas (where applicable)
PQR documenting the qualification test results: all mechanical tests required by the code, CVN data for FCM-rated procedures, with test lab certification
FCM designation on the WPS identifying that the procedure is approved for fracture-critical use (when applicable)

The WPS must be available for review at the welding station. CWIs must confirm that the production weld variables (amperage, voltage, travel speed) fall within the WPS heat input range on FCM welds.

Transitioning a D1.1 Shop to D1.5 Work

If your shop is bidding bridge fabrication for the first time, the path forward is:

Review the project's governing specification. Confirm that D1.5 is specifically required, and identify which members carry FCM designations.
Budget PQR testing. Every WPS needs a supporting PQR. Plan for test plates, mechanical testing at an accredited lab, and CVN testing for FCM procedures.
Evaluate filler metals. Confirm your standard filler metals are D1.5-approved for the A709 grades on the project. For FCM work, confirm CVN approval.
Set up heat input monitoring. Welders on D1.5 FCM work need to be monitoring and recording current, voltage, and travel speed so heat input can be verified against the WPS.
Review your QC plan. AISC certification for bridge fabrication (Category BR) has its own audit requirements distinct from the standard building structure categories.

For shops already running D1.1 WPS programs, the WPS vs PQR vs WPQ primer and the CVN supplementary essential variables explainer give solid background. For bridge-specific project estimates, our pricing page covers what a WPS documentation platform looks like for multi-code shops.

D1.5 is a rigorous code, and the extra burden is appropriate given what a bridge failure means. Shops that come in prepared — with their testing done and their QC plan built for bridge work — will find the qualification process straightforward. Shops that assume D1.1 experience transfers without review will be correcting deficiencies on the first FHWA auditor's visit.