Direct Answer
A crane runway girder (CRG) is a structural steel girder that supports an overhead bridge crane's rail and wheel loads — a high-fatigue application with repetitive dynamic loading. CRGs have special fabrication requirements: mill tolerance on web flatness, continuous flange-to-web welds (no stop/start), strict top-of-rail alignment, and often ultrasonic testing of flange-to-web welds.
Full Explanation
CRG fabrication requirements driven by fatigue: (1) Continuous web-to-flange welds — stop-start locations in the fillet weld are crack initiation sites under cyclic crane loads. AWS D1.1 fatigue provisions (Annex A) govern weld category. (2) Top flange flatness — the crane rail must bear flat on the top flange; any convexity or distortion transfers load to the rail foot rather than the full bearing. (3) Rail attachment — rails are attached via hook bolts, clips, or welded plates; method affects fatigue life. (4) Girder camber — sized to account for crane dead load plus a fraction of live load, so the girder is nearly flat under typical service conditions. AISC Design Guide 7 covers crane runway girder design.
What This Means for Your Shop
CRG fabrication is a specialty — the fatigue requirements, continuous welds, and rail alignment tolerances require experience and procedure knowledge. If you're new to CRGs, visit a shop with CRG experience or hire an experienced superintendent before committing.
Common Mistakes
Using intermittent (skip) welds on the flange-to-web joint of a crane runway girder. Skip welds create stress risers at every weld termination — in a crane runway application, these initiate fatigue cracks under the dynamic loading from crane travel.
Recommended Process
For all CRG work: (1) Use continuous fillet welds on flange-to-web joints, AWS D1.1 Annex A Category B minimum. (2) Check top flange flatness after fabrication with a straightedge. (3) Coordinate rail alignment with the crane supplier before erection — the rail position tolerance is typically ±1/8" from design location.