Bridge Welding (D1.5): Fracture Control and Qualification
What the candidate must understand
D1.5 governs welded steel bridges and is stricter than D1.1 because of cyclic loading and fracture-critical members (FCMs). Candidates must understand the fracture control plan, the definition of an FCM, and the additional qualification, inspection, and documentation those members demand. Know the welding procedure qualification requirements, including essential variables and the role of the Engineer, and the nondestructive testing requirements: typically complete joint penetration groove welds in tension are subject to volumetric examination. Understand the difference between statically and cyclically loaded structures and how that changes acceptance criteria and inspection frequency.
Traps in questions
A common trap is applying D1.1 acceptance criteria to a D1.5 bridge. Another is forgetting that an FCM designation triggers extra requirements: qualified procedures, qualified welders with demonstrated performance, and documented inspections. Watch for questions about who approves procedure changes and whether radiographic or ultrasonic testing is mandatory; answers that make NDT optional for FCM tension welds are wrong. Also expect confusion about the effective throat and weld size for skewed joints.
Worked example / rule of thumb
Rule of thumb: if the member is fracture-critical, everything escalates. Worked example: a stem describes a complete joint penetration groove weld in tension on an FCM. The correct answer includes volumetric NDT and a qualified procedure with documented inspection, not merely visual examination. If a question offers visual only, reject it.
Study approach
Read the fracture control and qualification clauses together, then compare D1.5 and D1.1 side by side to see where the bridge code tightens requirements.