Destructive
earthquakes and devastating winds always strike without a warning. They
grant their victims no second chance to react, and then the victims are
down. We are risking at least thousands of lives any moment in a day if we
do not equip the skyscrapers to face the above two major tragedies. The
current technological trend changes from focusing on "earthquake-and-wind
resistant" to "vibration control". Apart from fighting the vertical force of
gravity, skyscrapers also have to deal with the horizontal force of wind and
vibrational force of earthquake. There's when the tuned mass damper system
and MR fluid system comes in. (Refer to
Construction: Obstacles)The tuned mass damper system can be generally classified into 2 groups: TMD (Tuned Mass Damper) and AMD (Active Mass Damper). Both kinds of tuned mass damper systems are driven by oil (or any incompressible fluid) hydraulic systems, which push a 400-ton weight back and forth, balancing the acceleration of the skyscraper (e.g when the building is forced to the right, then the weight is shifted to the left). The only difference is that the TMD is driven by a spring (when the building sways, it sets the spring into motion automatically); while AMD is controlled by a computer system (it monitors the acceleration of the structure, and shift the weight accordingly). Therefore one is passive and the other is active.
The full name for MR fluid is
magnetorheological fluid. It is a special gray, oily liquid, that turns into
solid when magnetized. In the MR fluid damper, the liquid is stored in a
piston, with electromagnetic coils wrap around it. During an earthquake,
sensors in the building send signals to the computer system to magnetize the
coils, which turns the MR fluid to solid. Earthquake vibration would ripple
through the skyscraper, transforming the MR fluid from liquid to solid
thousands of times per second. There can be more than a hundred damper in
the building. The solid form of the MR liquid would compensate for the shock
brought by the earthquakes, keeping the horizontal
displacement of the skyscrapers at or near zero.
