Final answer:
The swaying of buildings is reduced by tuned-mass dampers and pendulums that counteract the movement. Viscous dampers are used to dissipate the energy of the motion, enhancing the system's efficiency and preventing structural damage. They convert kinetic energy into heat, avoiding excessive damping that could hinder the system's oscillation.
Step-by-step explanation:
The swaying motion of buildings, particularly skyscrapers, is reduced by the use of tuned-mass dampers and physical pendulums. When a building sways due to winds or seismic activities, the pendulum installed at the top of the building moves in the opposite direction. This counteracts the sway and reduces the oscillation of the building. The motion of the pendulum introduces a dynamic force that operates out of phase with the building's sway, thereby mitigating it.
Supporting viscous dampers are included to absorb some of the energy of the swaying motion, which helps in reducing the amplitude over time. They do this by converting the kinetic energy of the oscillations into heat. The purpose of including viscous dampers is to enhance the efficiency of the system in dissipating the energy, which could otherwise lead to excessive strain on structural components and potentially cause damage or failure.
In the case of the Comcast Building, a unique liquid-column mass damper is employed. A 300,000-gallon tank of water serves as a pendulum by oscillating at the building's natural frequency, with the damping provided by adjusting turbulence levels.
This setup is crucial for high-rise buildings because as buildings are built taller, they act like inverted pendulums, susceptible to swaying from natural forces. The role of viscous dampers is to ensure that the damping does not become too large, as this could negatively affect the oscillation frequency and lead to an over-damped system that does not oscillate efficiently.