NHI Bridge Safety Inspection Practice Exam (Midterm) for In-Service Bridges

Steel is the material most susceptible to fatigue failure primarily due to its mechanical properties and the nature of its stress response. Fatigue failure occurs when a material is subjected to repeated loading cycles over time, which can lead to the development of small cracks that grow progressively until failure occurs.

Steel exhibits a relatively high strength-to-weight ratio, making it a preferred choice for many bridge types. However, it also has a finite number of stress cycles it can withstand before it begins to fail, especially under fluctuating loads and environmental conditions. The cyclic loading can align with the material's microstructure in a way that initiates cracks, particularly at points of stress concentration such as welds or connections.

While other materials, like concrete, wood, and composite materials, can experience fatigue, they generally do not experience it to the same degree or in the same manner as steel. Concrete is primarily designed to handle compressive loads and does not show significant fatigue under tension. Wood has a different failure mechanism and does not often fail through fatigue in the same way as steel. Composite materials, while they can also experience fatigue, usually have designs that mitigate such risks through layering and specific orientation of fibers.

Thus, in terms of a structural application like bridges, steel's propensity for