FOR RELEASE: March 11, 1997
Contact: Larry Bernard
Office: (607) 255-3651
Internet: [email protected]
Compuserve: Larry Bernard 72650,565
http://www.news.cornell.edu
ITHACA, N.Y. -- This just in: An earthquake hit part of the Cornell campus
on Feb. 26, resulting in severe building damage, broken concrete and a lot
of data. "I would say this building is irreparable. It may be that the
whole building will have to be demolished," said Richard N. White, the
James A. Friend Family Distinguished Professor of Engineering and professor
of civil and environmental engineering.
But don't worry -- it was a simulated earthquake of a 1/4-scale building,
using a shake table in Cornell's "structure lab" in the basement of
Thurston Hall. The earthquake, which would have registered about 8.2 on
the Richter scale -- a severe earthquake -- was part of dissertation
research by Ahmed Abdel-Mouti, a doctoral student sponsored by the Egyptian
government in Cornell's School of Civil and Environmental Engineering.
While his doctoral research is at Cornell, the Ph.D. will be awarded by Aim
Shams University in Cairo. Abdel-Mouti and Timothy Bond, manager of the
George Winter Laboratory of Structural Engineering, built a 1/4-scale
concrete building typical of many buildings in this country and in Egypt --
with a reinforced concrete exterior frame, but with interior, infilled
walls. These walls, basically concrete blocks put together with layers of
mortar such as that used in common construction, generally are not
considered part of the structural integrity of a building, but
Abdel-Mouti's experiment, sponsored by the Egyptian government, is showing
something different.
After a 32-second amplified version of an earthquake on the shake table,
the masonry walls crumbled in parts but did not collapse. The walls made a
difference, although several of the reinforced columns failed. It was the
first such test on an infilled building.
"This is exactly what we had hoped for -- incipient building failure
without collapse. With failure, the building does not function, but it is
still standing," Abdel-Mouti said.
Infilled interior walls make a difference in the integrity of the
structure, and construction standards should consider them in design
calculations, the researchers said.
White, Abdel-Mouti's adviser, said that previous tests of concrete
structures on the shake table, without infilled walls, collapsed at much
less severe earthquake forces. Abdel-Mouti's research, he said, "will
certainly help clarify the beneficial role of infills in buildings. True
dynamic tests on realistic infilled building models have never been done
before. Infills are often ignored in design calculations, but they
certainly have a major role in the strength of the structure. This would
have collapsed without them, at much less load."
It was no easy task. Bond outfitted the shake table to measure every
useful parameter. About 120 sensors measured accelerations, displacements
and loads. Five computers collected data simultaneously, from sensors
making 300 measurements per second per channel for all 120 channels. That
translates, Bond said, "to 9,600 data points per channel" in the
experiment's
32-second duration.
"This will help us characterize the change that occurs when you put walls
in," Bond said. "You can make better analytical tools as a result, to
analyze the response of existing structures."
"This is a typical, common residential building. It is not designed to
resist earthquake or wind damage," Abdel-Mouti said. "We need to know how
the structure will behave and how these walls will perform in an
earthquake. We built this to be exactly like a real building, just a
smaller scale."
The shake table is basically a 5-by-7-foot aluminum plate driven by a
hydraulic actuator powered by high-pressure oil and controlled by
electronics. It sits atop a super-smooth granite slab with a layer of oil
in between to reduce friction to almost zero. During the "earthquake,"
pieces of concrete clearly were jarred loose, leaving gaping holes in the
sides of the building.
"There is severe deterioration with permanent deformations," Abdel-Mouti
said. "The building is just not reparable."
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