Antoine+-+EARTHQUAKE+PROOFING

Back to FORCED OSCILLATION AND RESONANCE =EARTHQUAKE PROOF BUILDINGS=

__ Definition of Key Terms: __ Natural Frequency : The frequency at which a system will oscillate naturally. Forced Oscillations : Oscillations of a system which is being driven at another frequency than its natural one. Resonance : When the driving oscillation has the same frequency as the natural frequency of the system, the amplitude of the system will increase. Damping : The loss of energy of oscillations due to work against friction or viscous medium. Can be heavy, light or critical. __ Problem: __ During earthquakes most “normal” buildings will collapse as there is a possibility that the vibrations caused by the earthquake might result in resonance. This is because resonance means that the buildings will oscillate at their natural frequency thus eventually collapsing. The buildings will crumble when they reach their natural frequency because buildings are made out of “stiff” materials such as concrete which, just like glass, cannot resist high levels of oscillation without “shattering”. In addition, “normal” buildings are generally not damped which means nothing will stop the vibrations of the earthquake from causing resonance. This is a recurring problems in countries located on the border of tectonic plates (eg. Japan) which is why several solutions to this problem have been found. __ Solutions: __ In order to prevent buildings from reaching natural frequency through resonance architects have come up with several building “damping systems”. One of those systems consists of attaching a mass to a rail on the roof of the building. This is because the movement of the mass will be controlled by a lever system which will make the mass slide in the opposite direction that of the one the building is swaying in. This will “break” any oscillation movement by the building and thus prevent it from reaching its natural frequency. Another solution to this problem is to build buildings to be more flexible. That is buildings should be built with less rigid materials such as wood or steel rather than concrete. This is because steel and wood will not snap as fast as concrete if oscillation occurs. In addition, the walls of the buildings should be reinforced in order to be able to withstand the weight of the building when it oscillates and beams and trusses should be placed strategically in order to transfer the effect of the oscillation into the ground. Furthermore, the foundations of the buildings should be built in order to enable the building to “slide” and thus absorb the shocks and movements created by the earthquake. However, it is impossible to build a 100% earthquake proof building as there is always a risk that the building will eventually reach its natural frequency despite the damping.