Wood splintered, screws flew and columns sheared off from their
bases when a series of earthquakes shook the UCLA campus last
week.
Scale models of college dormitories were put to the seismic test
in an earthquake simulator when seven teams from California
universities competed in the seismic-design challenge Friday during
the 2006 Pacific Southwest Regional Conference of the American
Society of Civil Engineers, hosted by the UCLA Henry Samueli School
of Engineering and Applied Science.
While earthquake-safe building design and drawing up plans may
be nothing new to civil engineering students, participants said the
hands-on construction aspect of the challenge was not exactly
second nature.
“We weren’t particularly adept at woodworking. …
It was a lot of trial and error,” said Jerry Lee, a
fourth-year civil engineering student who designed UCLA’s
entry.
He estimated that UCLA’s seismic-design team spent about
50 hours constructing their model.
Teams were asked to design a three-story scale model of a
dormitory for UCLA Housing, according to cost and land-size limits
for Housing’s master plan, which would guarantee four years
of on-campus Housing to freshmen.
UCLA’s team incorporated three different types of
earthquake reinforcement into their project, including brace frames
to keep columns upright during the violent shaking, and shear walls
which stiffen the structure as a whole, Lee said.
Another element UCLA’s team used were moment frames which
are “stiff connections” that make the scale-model
dormitory move and absorb force as one, rather than act as a series
of walls and columns put together but still functioning
independently.
Designing an earthquake-safe building is about finding the right
balance between strength and flexibility.
“Rigidity is not always good in seismic zones because it
invites more resistance at each point,” said Mike Thompson, a
fifth-year civil engineering student from California Polytechnic
State University, Pomona.
Cal Poly Pomona’s entry included elements similar to those
employed by UCLA and many other teams in the competition: shear
walls, brace frames and moment-resisting connections.
The dorms were subjected to three quakes. The first was an
earthquake of small size where only minor damage is acceptable as
buildings are expected to be immediately reoccupied and fully
operational after the earthquake.
The second test replicated the shaking patterns of the
Northridge earthquake, a 6.7 magnitude tremor that struck Los
Angeles in 1994, causing damage at UCLA.
Models were designed to be “life safe” in the second
phase, according to the design scenario, which would allow
occupants time to exit safely; heavy damage is acceptable as long
as the building does not collapse.
The third optional test, known as “shake it to break
it” among attendees, involved shaking the model dormitory
until it began to break apart.
Most entries withstood 1-2 Gs of force before failing. When the
structural columns dramatically sheared off from the base at this
point on San Diego State University’s entry, the earthquake
simulator’s operators quickly turned off the shake table
before the dorm split in two and crashed into the crowd, much to
the disappointment of the audience who was rooting for its
destruction.
Other entries, such as that of the team from Cal Poly Pomona,
put the shake lab to the test; its heavily damaged structure went
through several full-force charges from the earthquake simulator,
subjecting it to forces of up to 10 Gs, without producing
audience-pleasing levels of destruction.
The shake table, powered by hydraulic pumps, can only create
horizontal motion patterns, according to Robert Keowen, a senior
development engineer in UCLA’s Department of Civil and
Environmental Engineering.
The winning entry was built by the team from UC San Diego.
Entries were judged on three criteria: weight; total story drift,
which is the displacement at the top of the building relative to
the bottom; and the ratio of acceleration from the top of the
building to the bottom.
Participants said the seismic-design competition, along with the
many others taking place at the conference, allowed them to
exercise their theoretic knowledge in realistic scenarios.
“In class, you’re just doing a bunch of math,
analyzing this and that. … When you build it, you actually see
what exactly is going on,” Lee said.