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Taking the guesswork out of strengthening buildings in quake areas
STANFORD -- The large San Francisco Bay Area employer needed to retrofit its buildings to prepare for earthquakes and proved to be a prime candidate for a developing concept called "risk- balanced design" -- goal-based engineering design rules.
The organization's goals included:
Civil engineers Fouad Bendimerad and Haresh Shah worked with the organization's officers and with advisers who understood its goals, its facility inventory and its operational practices. They added earthquake engineering information applicable to their client's location. Then they calculated the cost of retrofitting existing buildings to meet the goals.
The price: $320 million. However, if the organization would accept a recovery time doubled to two weeks, the cost would be cut in half.
Bendimerad's and Shah's "client" is Stanford University, an 8,200-acre campus with 400 university-owned structures, located four miles from the San Andreas and 15 miles from the Hayward faults. Shah is a professor of civil engineering and Bendimerad is the university's seismic engineering manager, the sort of professional that smaller institutions, companies and homeowners hire as a consultant.
To achieve its risk-mitigation goals, Stanford is developing what Bendimerad calls "risk-balanced" design guidelines for the retrofitting of existing buildings. It will spend approximately $160 million over the next decade on seismic retrofitting, work that has already begun at many locations on campus.
Bendimerad is to explain how the buildings will be rebuilt under the concept of balancing seismic risk at Stanford on Aug. 28 at the Fourth International Conference on Seismic Zonation.
Most civil engineers have not been trained to translate what they know about seismic engineering into the practical risk- balancing considerations needed by owners of existing buildings, he said.
"Civil engineers are trained to design and build new facilities following a process that clearly defines the purpose and liabilities of all parties, one that uses well established building codes and standards," Bendimerad said.
"There are no rules in retrofitting buildings that apply uniformly. In the absence of rules, you might say the general approach is for the engineer to tell the customer: 'I'll do all I can within your pocketbook.' "
The point of the Stanford project is to get around this uncertainty. The first step is to define the institution's earthquake survival goals. Then construction methods and the responsibilities of all parties involved are defined.
"We want all parties -- the owner, designers and contractors - - to work within a well-defined framework that enables us to successfully achieve our goals. That's why the plan establishes several independent reviews of every structure retrofit project, beginning with a 'criteria review' by a panel of civil engineering experts before design development begins," he said.
Before the 1989 Loma Prieta earthquake, Stanford had identified buildings needing strengthening. It placed them in three priority categories based on their physical condition and the number of human occupants.
"We never went through the inventory and said, 'How much will we lose in this location and that location if a severe quake hits close by, and what do we need to survive it?' That is being done now," Bendimerad said.
Stanford hopes to be up and running its teaching and research programs within two weeks of a 7.5 earthquake with an epicenter just four miles away. In 1989, the university was shut down for 24 hours following the 7.1 earthquake centered on the San Andreas fault approximately 30 miles away .
Two weeks is considered the maximum acceptable down-time in Stanford's situation, he said, because "beyond two weeks, it could conceivably cost us the remainder of our academic year's research and teaching. The students would start leaving, and faculty and staff would start looking for other things to do," Bendimerad said.
What does up-and-running mean?
"It doesn't mean that everyone will have their nice, air- conditioned office back or that 100 percent of the research will be functioning, but people would be able to be busy with their duties," he said.
"In order to fit all the classes into two-thirds of our normal teaching space, students would have to take classes until about 8 p.m." Undergraduate classes now aren't normally scheduled for evenings. (A table at the end of this press release shows how much space, by operating function, the university expects to be out of service after a closeby, 7.5-magnitude quake.)
It's possible that Stanford will be able to meet its two-week goal for a closeby quake of no greater than 7.0 magnitude, Bendimerad said. Recent research on the ground motion amplification on two- to five-story buildings close to the epicenter of a quake indicates they may be subjected to more force than earthquake theoretical models now indicate.
"We are modeling to better understand the ground motion at our site in a closeby quake," he said. "It's difficult, because only a handful of data recorded near the epicenter of large-magnitude earthquakes is available from around the world."
The final determination of the size quake that the university can target to survive won't change building retrofitting plans, Bendimerad said, but it will be helpful in making other earthquake contingency plans. Future space allocation and contingency reserve decisions, for example, might be affected by the final determination.
The university's overall approach to earthquake risk management is based on research at its John A. Blume Earthquake Engineering Center and its civil engineering department, where Bendimerad earned his doctorate, working with Shah.
Estimated net square footage (nsf)
that may be lost following a M7.5 earthquake
Type of space Area (nsf) Percent of total nsf
Teaching 86,000-143,000 14-23%
Research 76,000-247,000 6-21%
Administration 101,000-228,000 8-18%
Libraries 11,000-74,000 2-11%
Housing 390,000-439,000 16-18%
Other 85,000-186,000 7-14%
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