How does wind create dynamic loads and oscillations in a bridge?

In bridge engineering, wind creates dynamic loads that induce vertical and torsional (twisting) oscillations. Unlike static wind loads, which exert horizontal pressure, dynamic loads occur when wind interacts with a bridge's structure, potentially leading to dangerous vibrations.1

If a bridge deck is thin and lacks sufficient vertical or torsional stiffness, it may fail to resist these aerodynamic forces. A notable historical example is the original Tacoma Narrows Bridge, which collapsed in 1940 because its design did not account for the aerodynamic behavior of its thin deck, causing it to twist and oscillate wildly even in moderate winds.12

To mitigate these risks, modern engineers prioritize aerodynamic design. By shaping the bridge to allow wind to pass through or around the structure with minimal resistance, engineers reduce the likelihood of dangerous oscillations. Additionally, structural reinforcements such as trusses and cable-stays are used to increase a bridge's stiffness and stability against wind-induced motion.12