NHI Bridge Inspection Course 130055 Practice Test

When steel grid deck areas in travel lanes are exposed to heavy, repeated traffic, the welded joints where grid members connect to supports become the stress concentration points that endure the most cycling. Each wheel load causes bending, shear, and vibration at these welds, so over time tiny fatigue cracks can start at the weld toes or roots. With many loading cycles, these cracks grow until the weld can no longer transfer the load, resulting in a broken weld. This fatigue failure of welded connections is a common outcome under high-cycle, real-world traffic conditions, which is why broken welds is the most likely problem.

Other failure modes—like buckling of girders or cracks in the girders themselves—are less directly tied to the repetitive loading at each weld in the grid deck, and simply deteriorating welds without breakage doesn’t describe the typical progressive fatigue that leads to a complete weld fracture.