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Shake
Table Study Tests Wood-Framed Structure
7/10/2006
By
Tom Nicholson
Earthquake engineers at the State University
of New York at Buffalo performed an unprecedented study June 26-28,
hammering the largest wood-frame structure ever to undergo shake
table testing with the force of a 500-year, 6.9-magnitude temblor.
Researchers say the testing provided new insight about how seismic
dampers, which were installed in the 1,800-sq-ft, two-story townhouse,
may be applied to wood-frame structures.
The dampers “improved the performance
of the structure, no question,” says Michael Symans, professor
of engineering at Rensselaer Polytechnic Institute, the lead researcher.
“And we’ve learned some about how to improve their performance.”
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Technicians monitor shake-table testing of a full-scale, two-story,
wood-frame townhouse. |
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With metal hold-down brackets mounted to
the foundation and metal shear clips connecting sheathing between
the floors to minimize lateral displacement, the house is “typical
of wood-frame structures found in seismic regions like California,”
says Andre Filiatrault, UB professor of engineering, who is supervising
the tests. Researchers noted that connections in the structure shook
loose despite the damping, suggesting structural stiffening to maximize
dampers’ strokes may be part of future wood-frame seismic design.
The 20-in.-long, 3.5-in.-dia dampers were
integrated into the structure in wall modules designed by Symans.
The modules, placed on both floors of the house, consist of shear
wall sections of various dimensions, each with a fluid seismic damper
mounted horizontally and capable of dissipating five tons of force.
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| Shake It. Researchers
Symans and Filiatrault inspect a seismic damper wall module. |
Doug Taylor, CEO of Taylor Devices Inc.,
North Tonowanda, N.Y., which manufactured the dampers used in the
test, envisions a burgeoning market for wood-frame seismic damping.
“Contractors may be able to install prefabricated damper wall
modules,” he says. “It very well may be the future of wood-frame
construction” in seismic zones.
The experiment was conducted on the two 23-ft-square
shake tables at UB’s Structural Engineering and Earthquake
Simulation Laboratory. The research is part of a four-year, $1.24-million
NEESWood project led by the Network for Earthquake Engineering Simulation,
a network of 15 U.S. universities, to establish a benchmark for
wood-frame seismic design and the use of seismic dampering in wood-frame
structures.
“We don’t have accurate physical
data to fully define how wood structures behave in earthquakes,”
says Symans, “We have models, but their accuracy has not been
verified with full-scale tests.”
Integrating seismic dampers into wood-frame
structures is a concept that “has been ignored by engineers,”
says Filiatrault. “Damping technology is used on steel and
concrete structures. Now we need to learn how to apply it to wood.”
In follow-up tests scheduled for this November,
gypsum wallboard will be installed in the house and researchers
will subject it to the violent shaking of a simulated 2,500-year
quake.
(Photos courtesy of the University of Buffalo)
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