Ball screws help protect buildings from earthquakes

Constructing buildings and bridges in earthquake-prone regions often necessitates the use of damping techniques. While solutions such as mass spring damping or hydraulic systems provide one method of absorbing dynamic compressive and tensile forces, an alternative is to use vibration dampers featuring high-load ball screws.

NSK has developed its HTF ball screws for typical deployment in industrial machinery, for example on servo presses and plastic injection moulding machines. However, they are also proving to be suitable for use as vibration dampers and absorbers in buildings and bridges, (a development that originated in Japan), where the earthquake risk is high and all structures need to be designed and protected accordingly.

Today, several suppliers of earthquake protection systems are offering solutions based on NSK ball screws. The technique uses a high-load ball-screw drive with a rotating counterweight on the nut. This ball screw (integrated into a structural unit) then takes its place between two load-bearing elements of the building, often in the basement.

Linear movement of the ball screw ensues when one of the two load-bearing elements is set in motion, usually when a high dynamic load occurs for a short period of time, such as during an earthquake or when a heavy train crosses a railway bridge. This linear movement converts into rotary motion of the damping weight. When the direction of rotation changes, the oscillations superimpose each other with opposite amplitudes. The result is an effective damping of the shock load, whereby both dynamic compression and tensile forces are absorbed, providing a safer environment for everyone should an earthquake strike.