NHI Bridge Inspection Course 130055 Practice Test

Repeated heavy traffic subjects welded joints in a steel grid deck to many cycles of loading, creating fatigue at the connections. The grid has numerous welds at intersections, and these locations experience high stress concentrations from wheel loads and impact. Over time, tiny cracks begin at the weld toes and grow with each cycle, until the weld can no longer carry the load and breaks. This local failure of welds is more likely than first causing the girders to crack or the entire grid to buckle, because those larger-scale failures require higher or more sustained stresses and are less common under normal heavy-traffic service. So, broken welds at the deck connections are the most probable failure mode under heavy traffic.