Natural Frequency and Buildings
The Tacoma Narrows Suspension Bridge dramatically collapsed in 1940 due to wind-induced vibrations. (left). Today, engineers conduct laboratory research and field studies to reduce vibration on bridges, skyscrapers and other building structures. (right)Copyright Federal Highway Administration, US Department of Transportation http://www.fhwa.dot.gov/publications/publicroads/11janfeb/03.cfm
Students learn about frequency and period, particularly natural frequency using springs. They learn that the natural frequency of a system depends on two things: the stiffness and mass of the system. Students see how the natural frequency of a structure plays a big role in the building surviving an earthquake or high winds.
In order to design buildings (and other human-made structures) to be able to withstand the forces of earthquakes and windstorms, structural engineers compute the natural frequency of buildings. For example, if the frequency of the seismic waves matches the natural frequency of a building, resonance occurs and structure fails. Engineers conduct research and field studies to learn how various structural designs and materials perform under anticipated hazardous conditions, so they can design the safest structures possible. They also design real-time wind and earthquake monitoring systems that include wind, vibration and ground motion sensors to provide early warning of failure.
After this activity, students should be able to:
- Calculate either the frequency or period of a vibration or wave.
- Perform data collection and compare results for the natural frequency of the different systems.
- Describe how resonance and natural frequency can damage buildings and bridges and how technology can be used to avoid this.