Kerckhoff stands on rubber solesSeismic isolators prepare
building for possible quake
By Patrick Kerkstra
Beneath the gothic and aged Kerckhoff Hall, a modern feat of
engineering is taking place.
As part of the university’s seismic strengthening program,
Kerckhoff is undergoing an innovative structural improvement
process called base isolation.
"When we’re done, this entire building will be mounted on
rubber. The theory is that while the earth shakes, the building
will not. The building will stay relatively still while the earth
is doing its story," said Dan Fearman, project superintendent of
Ray Wilson Co., general contractor for Kerckhoff and Ackerman
Halls.
This technique, which isolates the structure from its
foundation, was chosen for two reasons: to maintain Kerckhoff’s
functionality through construction, and to preserve the historic
building’s appearance.
More conventional retrofitting efforts, such as adding shear
walls, would structurally reinforce existing walls and make the
building more rigid. However this procedure, the same used on
Powell Library, would have forced evacuation of Kerckhoff.
"If we’d gone shear wall, it definitely would have required
everyone to leave the building for as much as two years," said Curt
Ginther, principal project manager for Kerckhoff Hall.
Kerckhoff is not the first historically significant building to
be seismically isolated. Dynamic Isolation Systems, the company
that produced Kerckhoff’s isolators, also renovated Oakland City
Hall, the City and County Building in Salt Lake City and the Old
Parliament Building in New Zealand.
And although the system’s track record in actual earthquakes is
limited, it remains unmarred. For instance, the University of
Southern California’s Hospital is built on isolators, and rode out
the Northridge quake successfully. In addition, the recent Kobe
temblor also provided some evidence of the method’s
effectiveness.
"Similar systems have been used in Japan and the preliminary
information we’re getting is that two buildings with this type of
isolator have performed well, although those structures aren’t in
the immediate Kobe area. They’re about 50 miles away," said Lindsay
Jones, executive vice president of Dynamic Isolation Systems.
The base isolation of Kerckhoff is an expensive venture that
will cost about $15 million, not including renovation of the
building’s spires, officials said.
This cost is scheduled to be paid for through the new student
seismic fee. The $113 annual fee will be assessed after completion
of the renovations, which is scheduled to be in the spring of 1996,
according to a document issued by the associated students.
Currently, Kerckhoff is built on 148 reinforced concrete
foundation columns. The purpose of the retrofitting is to isolate
the building from its foundation by inserting rubber and steel
cylindrical isolator units into the supports.
Each isolator, fabricated in and imported from New Zealand, is
thoroughly tested, said representatives of the company.
"The testing essentially imposes simulated quakes or recorded
motions of real ones on the isolator itself, shearing the top
surface (of the isolator) from the bottom surface," said Jones.
These isolators are the key to the retrofitting efforts.
"(An isolator) is a sandwich of thin sheets of rubber and steel.
In fabrication, the rubber and the steel are compressed in a
process called volcanization to achieve physical bonding," Ginther
said.
This composite will drastically reduce the shaking Kerckhoff
would endure in the next temblor.
Another aspect to Kerckhoff’s retrofitting, is the construction
of an 18-inch moat around the building that will give the structure
room to move in an earthquake.
The moat, in conjunction with the isolators, will allow
Kerckhoff to move in a controlled lateral motion, and about one
foot in any horizontal direction, according to construction
officials.
"There’ll be a decking on top of the moat, so it won’t be
noticeable that there’s a moat there at all. In a large earthquake,
this decking will break away, so the building can move back and
forth in this moat," Otavka said.
The sights and sounds of construction surrounding Kerckhoff are
symptoms of the lengthy process required to install the
isolators.
"From the first time we touch a column to the time we walk away
from it, and it is holding up the building again, you’re looking at
about a three week process," Fearman said.
During the construction, workers build a large frame around each
column, which transfers the weight of the building from the column
to the supporting structure.
"We install our beams and legs, and we put hydraulic jacks on
it, and we literally pick up the building. We move it several
thousandths of an inch," Fearman said.
After the column is cut, a new base for the column is installed,
and the isolator is placed on the base. The column is then extended
and the construction framework removed. The net effect is a column
of essentially the same size with no major aesthetic
differences.
Once Kerckhoff is completed, the ground level of the building
will have a new floor plan, and the spires will be replaced. There
will also be a new addition replacing the old stucco annex that was
demolished on the southwest side of the building.