BUFFALO, N.Y. -- It takes just seconds for tall buildings to
collapse during powerful earthquakes. Knowing precisely what's
happening in those seconds can help engineers design buildings that
are less prone to sustaining that kind of damage.
But the nature of collapse is not well understood. It hasn't
been well-studied experimentally because testing full-scale
buildings on shake tables is a massive, expensive and risky
That's why researchers at the University at Buffalo and Japan's
Kyoto University teamed up recently to try an innovative "hybrid"
approach to testing that may provide a safer, far less expensive
way to learn about how and why full-scale buildings collapse.
"One of the key issues in earthquake engineering is how much
damage structures can sustain before collapsing so people can
safely evacuate," explains principal investigator Gilberto
Mosqueda, Ph.D., UB assistant professor of civil, structural and
environmental engineering. "We don't really know the answer because
testing buildings to collapse is so difficult. With this hybrid
approach, it appears that we have a safe, economic way to test
realistic buildings at large scales to collapse."
The UB/Kyoto team's positive results could enable engineers to
significantly improve their understanding of the mechanisms leading
to collapse without the limitations of cost, reduced scale and
simplified models necessary for shake table testing in the U.S.
In the unusual "slow motion earthquake" test conducted in late
July, UB and Kyoto engineers successfully used the hybrid approach
(see video at http://seesl.buffalo.edu/projects/hybridmoment/video.asp)
to mimic a landmark, full-scale experiment conducted in 2007 on the
E-Defense shake table at the Miki City, Japan, facility. In that
test (see video of the 2007 test at http://www.youtube.com/watch?v=MV4GcUZyTzo),
a four-story steel building was subjected to a simulation of ground
motions that occurred during the 1995 Kobe earthquake.
But instead of using a full-scale steel building, this time, the
researchers developed a hybrid representation of that test by
combining experimental techniques carried out in earthquake
engineering labs in Buffalo and Kyoto with numerical simulations
conducted over the Internet.
The landmark data from the E-Defense test was used to verify the
effectiveness of the hybrid approach. Only the parts of the
buildings that were expected to initiate collapse were tested
"If this had been a real building, it would have toppled over,"
That presents a real problem in a laboratory.
"You can't allow a structure to collapse completely on a shake
table," he said. "You need to have support mechanisms in place,
like scaffolds, to catch the falling structure."
The building in the original full scale test weighed more than
200 tons. That kind of weight puts shake tables under enormous
stress, Mosqueda explains. It not only forces them to operate at
full capacity, there is the additional potential for the heavy
structure to crash down on the equipment.
"But in this case, we simulated the load with high-performance
hydraulic actuators so the specimen overall was actually pretty
light," explains Mosqueda. "We completely did away with the hazard
of having tons of weight overhead that could come crashing down.
Here, we just shut off the hydraulics and the load
It took the U.S. and Japanese researchers, who were
communicating over the Internet, about two hours to subject the
hybrid model to the powerful ground motions that represented
approximately the first five seconds of the 1995 Kobe quake.
According to Mosqueda, the hybrid test paves the way for
additional experiments that will allow researchers to more
precisely learn about the nature of structural collapse.
"We want to know, for example, what is the probability that a
building will collapse in the next expected earthquake," says
Mosqueda. "First, we need to develop this capability to understand
and simulate how they collapse. Then we can determine how to
improve new construction or retrofit existing buildings so that
they are less likely to collapse."
The experimental part of the test involved a half-scale,
nine-foot-tall structure in UB's Structural Engineering and
Earthquake Simulation Laboratory (SEESL), while a second
experimental component was located at Kyoto University. Together,
the two experimental substructures represented the first
one-and-a-half stories, while numerical simulations represented the
rest of the building.
Mosqueda explains that while reduced-scale models were used in
this preliminary test to evaluate the method, the capacity exists
at UB and other laboratories to apply this approach to full-scale
Mosqueda's colleagues on the test include Maria Cortes-Delgado,
a doctoral student in the UB Department of Civil, Structural and
Environmental Engineering, Tao Wang, Ph.D., of the Institute of
Engineering Mechanics in Beijing, and Andres Jacobson, a doctoral
student, and Masayoshi Nakashima, Ph.D., a professor at Kyoto
These "distributed hybrid tests," were made possible by UB, its
international collaborators at Kyoto University and the Institute
of Engineering Mechanics in Beijing, and the National Science
Foundation's George E. Brown Jr. Network for Earthquake Engineering
Simulation (NEES) Facility, a nationwide earthquake-engineering
"collaboratory" of which UB is a key node.
The project is the result of a prestigious $400,000 Faculty
Early Career Development Award Mosqueda received from the NSF to
develop a hybrid simulation platform for seismic-performance
evaluation of structures that collapse.
The University at Buffalo is a premier research-intensive public
university, a flagship institution in the State University of New
York system and its largest and most comprehensive campus. UB's
more than 28,000 students pursue their academic interests through
more than 300 undergraduate, graduate and professional degree
programs. Founded in 1846, the University at Buffalo is a member of
the Association of American Universities.