Which vehicle type is associated with fatigue cracking in bridges?

• A. Cars
• B. Trucks
• C. Bicycles
• D. Motorcycles

Answer: (B)

Fatigue cracking in bridges is driven by repetitive, high‑amplitude stresses from vehicle loading. Heavy trucks impose larger peak loads and bending moments with each axle pass, creating cyclic stresses at critical details such as welds, joints, stiffeners, and connections. Over many cycles, these small stress reversals can initiate a crack and then grow gradually until failure could occur if not found and repaired. Lighter vehicles like cars or motorcycles do cause cyclic loading, but the stress ranges they produce are typically much smaller, so fatigue cracks at the same critical locations are less likely to develop from those loads alone. Bicycles are far too light to contribute meaningful fatigue damage to bridge members.