Tokyo
THE same type of antilock sensors that help car drivers to brake without
skidding could also be used to slow down the movement of buildings during
earthquakes. They are at the heart of a braking system developed in Japan by
Mitsubishi Heavy Industries (MHI).
The system consists of a vertical lever, with the upper end attached to one
of the building鈥檚 horizontal structural beams. The lever鈥檚 fulcrum is just below
the beam, held in place by two braces that form an inverted V. As the beam moves
sideways during an earthquake, a microprocessor calculates the direction and
size of the lateral force. It then activates a brake at the lower end of the
lever, which slows down the movement of the beam at the upper end. Every floor
of a building would have four sets of brakes and levers, one on each side.
Advertisement
Most existing anti-earthquake devices, such as metal-rubber 鈥渟prings鈥� fitted
to the foundations, act on the building as a whole. But as last year鈥檚 Kobe
earthquake demonstrated, different floors may experience different stresses
during an earthquake. As in a car鈥檚 antilock brake system, which applies more
brake pressure to wheels that are going faster while easing up on those which
are going more slowly, MHI鈥檚 device can apply just the right amount of braking
to each part of the building. This should reduce stress and lessen the chances
of structural damage.
During tests, MHI found that the maximum lateral displacement at the top of a
40-storey building during a simulated strong earthquake was reduced from 575
millimetres to 203 millimetres鈥攁 reduction of 65 per cent. MHI says its
new system would be good value for money and add only a small percentage to
construction costs.
