Building 'Belt' Offers Cheap, Quick Repair of Earthquake Damage
A damaged building joint repaired with post tensioned metal straps and tested on a shaking table to the equivalent level of a magnitude 7 earthquake. (Credit: University of Sheffield) |
Four years after the January 2010 earthquake, 145,000 people still
remain homeless in Haiti. A cheap and simple technology to repair
earthquake damaged buildings -- developed at the University of Sheffield
-- could help to reduce these delays by quickly making buildings safe
and habitable.
Recent tests showed that a damaged building repaired using the
technique could withstand a major earthquake -- similar in scale and
proximity to the buildings that collapsed during the Haiti earthquake.
The technology involves wrapping metal straps around each floor of
the building, which are then tensioned either by hand or using
compressed air tools. It is designed for use on reinforced concrete
frame buildings -- a common construction technique around the world,
including countries like Haiti. Unlike other repair methods, it does not
require expensive materials or a high level of technical knowledge,
making it ideal for use in the developing world.
Lead researcher, Professor Kypros Pilakoutas, explains: "The
strapping works very much like a weight-lifter's belt, by keeping
everything tightly compressed to reduce tension on the concrete columns
of the structure.
Concrete works well under compression, but not when pulled under
tension and this is why it has to be reinforced for use in construction.
When the reinforcement is faulty or damaged, it can be very expensive
to repair.
"Our method not only makes the building stable again very quickly,
but it increases the building's ability to deform without breaking,
making it more able to withstand further earthquake movement."
The team tested the technique on a full scale, two-storey building,
built according to an old European standard which has inadequate
reinforcing to withstand earthquakes. This construction is typical of
many buildings in the developing world, as well as many Mediterranean
buildings built before the 1980s.
The building was constructed on a specially designed 'shaking table'
which can simulate ground movement caused by earthquakes. During the
first test, the building was very near collapse following a small
earthquake similar in scale to a magnitude 4 on the Richter scale having
about 10000 times less energy than the Haiti earthquake.
The building was then repaired using the post-tensioned metal straps
and retested. The researchers were unable to make the building fail
during a major earthquake similar in scale to the magnitude 7 Haiti
earthquake at the epicentre and stopped the test at that point.
Professor Pilakoutas hopes the new technology will not only speed up
the response to major earthquakes, but could also prevent the damage
happening in the first place. The cost of the materials for a typical
small building column is about £20 and it would take a crew of two
people around 2 hours to complete the strengthening. For a typical small
dwelling having 6 columns, the seismic rehabilitation would cost around
£200 and could be completed in a few days, rather than cost several
thousand pounds and take months with other traditional rehabilitation
techniques such as jacketing with steel plates or concrete.
"Ideally, governments shouldn't wait until a disaster happens, but
should be identifying buildings at risk and taking steps to make them
strong enough to withstand any future earthquakes," he says. "Because
this method causes minimal disruption and is cheap to apply, it's ideal
for bringing existing buildings up to standard -- both in the developing
world and in earthquake risk areas in Europe as well."
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