*3.3.2 Tacoma narrows bridge: a lesson learned*

The suspension bridge located at Tacoma Narrows consists of two main structural steel towers supporting a main cable and the main deck is stiffened by two steel girders. A total length of 5905 feet (1800 m) and a span of 2930 feet (893 m) were covered. It was inaugurated in 1940 and became one of the largest bridges in the world.

The main feature of this bridge was the dramatically collapse of the main deck after a few months of inauguration, due to the oscillating movement with the action of the wind flow. These forces were considered for structural design; however, with a much slower wind velocity, the vibration movement increased with enough speed to make the structure collapse. Looking into **Figure 9**, the oscillating movements of the bridge can be observed.

Under research, the main reason for the collapse of the bridge was the concept of resonance, which means, a range of coincidence between the natural frequency of the structure and the frequency of wind thrust loads. The concept of vibration and resonance is not visible easily and many factors influenced on the event:

**Figure 8.** *Mexicali bridges, road distributor [9].*


After this event, studies on aerodynamics and aero-elasticity topics in the structures increased significantly, developing procedures to simulate these events on structures, including bridges of very large spans.
