AWS D1.5 — Bridge Welding Code
AWS D1.5 is the joint AASHTO/AWS bridge welding code for structural steel highway bridges. It separates fracture-critical from non-fracture-critical members with different preheat tables, mandatory CVN toughness testing, and enhanced inspection for tension members whose failure could cause bridge collapse.
Bridge-specific: D1.5 is referenced by AASHTO LRFD Bridge Design Specifications and by state departments of transportation across the United States. It supplements AWS D1.1 with bridge-specific requirements — where D1.5 and D1.1 conflict, D1.5 governs for bridge work.
What Is AWS D1.5?
AWS D1.5 is the joint AASHTO/AWS Bridge Welding Code governing structural steel highway bridges. It covers both fracture-critical members (FCM) and non-fracture-critical members (NFCM), with significantly stricter requirements for FCM welds including mandatory CVN toughness testing, enhanced NDE, and separate preheat tables (Tables 12.4 through 12.8).
AASHTO/AWS D1.5M/D1.5 — Bridge Welding Code — is a joint publication of the American Association of State Highway and Transportation Officials (AASHTO) and the American Welding Society (AWS). It establishes requirements for welding steel highway bridge components including girders, floor beams, diaphragms, connection plates, gusset plates, bearing assemblies, and other structural elements.
The current edition is D1.5:2025 (9th Edition). The code applies to carbon and low-alloy steels with specified minimum yield strengths up to 690 MPa (100 ksi). D1.5 references AASHTO M270 steel grades rather than ASTM designations, though AASHTO M270 grades have direct ASTM equivalents (M270 Grade 345 = ASTM A709 Grade 50, M270 HPS485W = ASTM A709 HPS70W).
The most significant distinction in D1.5 is the separation of requirements for fracture-critical members (FCM) and non-fracture-critical members (NFCM). This separation affects every aspect of welding — procedure qualification, preheat, inspection, acceptance criteria, and documentation.
Fracture-Critical vs Non-Fracture-Critical
Fracture-critical members (FCM) are steel tension members or tension components of flexural members whose failure would cause collapse of the bridge. Two-girder bridges are the classic example — no load path redundancy exists if one girder fails. FCM welds carry the strictest requirements in D1.5: separate preheat tables (Clause 12, Tables 12.4 through 12.8), mandatory CVN toughness testing, enhanced NDE, and tighter acceptance criteria.
Non-fracture-critical members (NFCM) have structural redundancy such that failure of a single member would not cause collapse. Multi-girder bridges (three or more girders) provide redundancy — if one girder cracks, the remaining girders carry the load while repairs are made. NFCM welds follow the general requirements of D1.5 Clauses 1 through 11, with minimum preheat from Table 6.3 and maximum interpass temperature from Table 6.4.
Preheat Requirements
D1.5 uses two separate preheat systems. Non-fracture-critical members use Table 6.3 for minimum preheat and Table 6.4 for maximum interpass temperature. Fracture-critical members use Tables 12.4 through 12.8, which add hydrogen designator (H4, H8, H16) and heat input as lookup axes beyond steel grade and thickness.
D1.5 has two separate preheat systems, making it more complex than D1.1 Table 5.11:
Non-fracture-critical preheat: Table 6.3 specifies minimum preheat and interpass temperatures by steel grade group and thickness, similar in structure to D1.1 Table 5.11 but referencing AASHTO M270 grades. Table 6.4 specifies maximum interpass temperatures. Together they define the NFC thermal envelope.
Fracture-critical preheat (Tables 12.4 through 12.8): A four-variable lookup that adds hydrogen designator (H4, H8, H16) and heat input band (low, medium, high) as additional axes beyond steel grade and thickness. This means the same steel at the same thickness can require different preheat temperatures depending on the welding process's hydrogen level and the heat input being used. Use our D1.5 Bridge Preheat Calculator to look up both NFC and FC requirements.
CVN Toughness Testing
For fracture-critical members, D1.5 Clause 12 requires Charpy V-notch (CVN) impact testing of weld metal per Clause 12.6.3. The required toughness values depend on the minimum service temperature specified by the engineer and the steel grade being welded.
For non-fracture-critical members, CVN testing requirements follow the base metal specification (AASHTO M270) and the engineer's judgment based on service conditions. The engineer may specify CVN testing for specific NFC connections where service temperatures are extreme or where fatigue loading is a concern.
How D1.5 Compares to Other Standards
D1.5 covers highway bridges while D1.1 covers structural steel buildings. D1.5 adds fracture-critical weld classifications, mandatory CVN toughness testing, and four-axis preheat lookup (steel, hydrogen, heat input, thickness) versus D1.1's two-axis lookup (steel/process, thickness). D1.5 references AASHTO M270 steel grades instead of ASTM.
D1.5 vs D1.1
D1.1 covers general structural steel welding (buildings, industrial structures, equipment). D1.5 covers highway bridge steel welding specifically. D1.5 requires fracture-critical member identification that D1.1 does not have. D1.5 preheat tables are organized by AASHTO M270 steel grades rather than ASTM designations. D1.5 mandates CVN toughness testing for FCM welds. Both codes provide prequalified and qualified WPS paths, but D1.5 has additional essential variables for FCM qualification. A WPS qualified under D1.1 cannot be used for D1.5 bridge work without verifying all D1.5 requirements are met.
D1.5 vs D1.8
D1.8 supplements D1.1 for seismic applications (buildings in earthquake zones). D1.5 covers bridges. Both codes add toughness requirements beyond D1.1 and both designate certain welds as critical (demand-critical in D1.8, fracture-critical in D1.5). The FCM/NFCM distinction in D1.5 is analogous to the demand-critical/non-demand-critical distinction in D1.8, but the specific requirements differ.
| Aspect | D1.5 (Bridges) | AWS D1.1 | ASME IX |
|---|---|---|---|
| Scope | Highway bridges | Structural steel | Pressure equipment |
| Steel grades | AASHTO M270 | ASTM (Table 5.6) | P-number groups |
| Prequalified WPS? | NFC only | Yes (Clause 5) | No |
| Preheat method | Tables 6.3/6.4 (NFC), 12.4–12.8 (FC) | Table 5.11 | Per WPS/PQR |
| CVN toughness | Mandatory for FC welds | Not required | Per construction code |
| Critical weld class | Fracture-critical (FC) | None | None |
Related Standards Guides
Frequently Asked Questions
AWS D1.5 is the joint AASHTO/AWS Bridge Welding Code. It governs the welding of steel highway bridges and is referenced by AASHTO LRFD Bridge Design Specifications and state departments of transportation across the United States. D1.5 covers both fracture-critical and non-fracture-critical members, with significantly stricter requirements for fracture-critical welds including mandatory CVN toughness testing, enhanced NDE, and separate preheat tables.
Fracture-critical members (FCM) are tension members or tension components of members whose failure would probably cause a portion of or the entire bridge to collapse. Non-fracture-critical members (NFCM) have redundancy such that failure of a single member would not cause collapse. D1.5 requires FCM welds to meet stricter requirements: separate preheat tables (Tables 12.4 through 12.8), mandatory CVN toughness testing of weld metal, enhanced nondestructive examination, and tighter acceptance criteria.
D1.5 has two separate preheat systems. Non-fracture-critical members use Table 6.3 for minimum preheat (similar to D1.1 Table 5.11 but referencing AASHTO M270 grades) and Table 6.4 for maximum interpass temperatures. Fracture-critical members use Tables 12.4 through 12.8, which add hydrogen designator (H4, H8, H16) and heat input as additional lookup axes beyond steel grade and thickness. This means FC preheat depends on four variables, not two.
D1.5 references AASHTO M270 steel grades, which are the bridge-specific equivalents of ASTM structural steels. Common grades include M270 Grade 250 (equivalent to A709 Grade 36), M270 Grade 345 and 345W (equivalent to A709 Grade 50 and 50W), M270 HPS345W and HPS485W (high-performance steels), and M270 HPS690W (quenched and tempered, the highest strength grade in the code).
For fracture-critical members, yes. D1.5 Clause 12 requires CVN toughness testing of weld metal for all fracture-critical welds. The required toughness values depend on the minimum service temperature and the steel grade. For non-fracture-critical members, CVN testing requirements follow the base metal specification and the engineer’s judgment based on service conditions.