John says:
“It’s really exciting because I’ve never
before been involved in a project
where there is such a significant life-
saving dimension to it. We might be
a little way from it just yet, but there
is the potential for something that is
environmentally friendly, sustainable,
affordable in countries where it
matters, and has the potential
to save historic buildings and lives.”
While famous skyscrapers tend to
have built-in earthquake protection
and are designed to sway slightly
above ground, smaller high-rises
and historic buildings are relatively
rigid and still experience movement
below ground. If the agitation of the
earthquake is in sympathy with the
natural properties of the ground
then they accentuate each other,
which causes a slightly more forceful
shaking or vibration at the bottom
of the building known as resonance.
If the natural frequency of the
ground does not match that of
the earthquake then they’re not
working together and instead offset
each other.
“Doing some numerical analysis,
we have seen that we can change
the natural frequency of the soil,
moving it away from the frequency
of the earthquake. It’s not just
about damping the vibration or the
acceleration but also moving it away
from the frequency that’s going to
affect the structure,” says Juan.
Work is set to continue in the
laboratory, including experiments
on large shaking tables, and the team
hope to have a field test of their
installation method in the ground
within three years.
“We can measure the dynamic
properties of the ground through tests
and we can assume something about
the natural frequency of the buildings
from their size and what they’re made
from, for example timber, concrete
or masonry. From those, we can
ascertain meaningful, credible values
that point you in a certain direction
in terms of the installation and the
rubber-sand mixture you’d need to
offset the potential damage from
an earthquake.”
“It’s really exciting because I’ve never before
been involved in a project where there is such
a significant life-saving dimension to it.”
HOW IT WORKS
Dr John McDougall explains that
their innovative earthquake
damping technology can be
explained using the example
of garden swing.
“The solution we’re developing can be
visualised in the motion of a garden
swing. An earthquake creates cyclic
motions in the ground – like a garden
swing oscillating back and forth.
There are two ways you can stop
a swing: abruptly or gently.
An immovable object in the path
of a swing will bring it to an abrupt
stop. And with inevitable damage
to the swing and rider as a result
of the instantaneous deceleration.
It is sudden accelerations and
decelerations of ground motions that
are responsible for the damage to
buildings caused by earthquakes.
If you want to stop the swing gently,
bring your hands to move with the
swing, take hold and gradually
decelerate the swing. You use your
flexibility and mass to absorb gently
the energy of the oscillating swing
and bring it comfortably to rest. By
the introduction of rubber shreds, we
are changing the dynamic properties
of the ground, enabling it to absorb
the energy of ground motions and so
minimise their impact on buildings.“
DR JOHN MCDOUGALL
Interested
in this project?
Dr John McDougall
School of Engineering
& the Built Environment
[email protected]
Watch our video about this project at
www.napier.ac.uk/impact
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