A new damped outrigger system to stabilise tall buildings has cut
the cost of a 200m tall residential tower in the Philippines by around
£2M, the designer has claimed.
The system uses small viscous dampers, mounted between the
structure's outriggers and columns to introduce a degree of redundancy
to the frame and allow it to perform better under wind loads.
"With tuned mass dampers, there is only one of them and there
is a lack of redundancy," explained Arup associate, Rob Smith who led
the Philippines projects.
"(Tuned mass dampers) can be used for serviceability conditions, but
you wouldn't want to rely on them for strength, to resist ultimate wind
loading," he said. "With our system, because there are many different
viscous dampers, if one failed there would not be much difference."
He pointed out that the redundancy meant the system could be
designed to take ultimate loads, (loads that might cause yielding or
overturning) as well as service loads (loads that might cause
deflection and vibration). Design loads on the rest of the structure
could therefore be reduced and the structure reduced in stiffness.
"The cost of the dampers is offset by the saving in the structure," said Smith.
The usual method of reducing lateral building movement is to
add significant extra structure to stiffen the building or to install
tuned mass dampers, which act as a pendulum at the top of the building,
swaying in the opposite direction to the building.
Viscous dampers act as energy absorbers, like car shock
absorbers and damp out vibrations. Although not as commonly used in
structures in the UK they have been used in seismic areas such as
California. This is the first time they have been used to reduce a
building's response to wind.
Source : New Civil Engineer
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