September 12, 2007
7 Engineering Wonders: Structural — How to keep it all working after the BIG ONE
By CRAIG OLSON
KPFF Consulting Engineers
Owners ranging from public agencies to financial institutions and research facilities have a need for buildings that can both survive earthquakes and protect valuable contents from destructive shaking. Providing new technologies for a local critical emergency facility proved to be one of KPFF’s most interesting technical challenges and important responsibilities.
KPFF was approached in 1995 to design the state’s Emergency Operations Center (EOC) near Olympia. As the focal point for state responses to emergencies and disasters, the ability of the facility to remain operational throughout a major earthquake directly affects the lives of all Washington residents. We proposed to evaluate the use of base isolation technology to satisfy Washington’s need to have the EOC operational throughout a major earthquake.
Base isolation was pioneered in the 1980s in California as a system to isolate a building from the ground using a mechanical device. KPFF entered the field with the design of the University of Southern California Teaching Hospital, which was completed in 1991. This hospital was the seventh base-isolated building in the U.S. and the first hospital in the world to use this technology.
There were several challenges to overcome to bring this technology to the EOC project. These included:
• Evaluating the need. We worked with the owner and architect to develop an understanding of the need and cost of implementing the system. Considerations included the type and amount of damage a conventional building would sustain in an earthquake, critical building systems, and the ability of contents (i.e. computers) to operate after an earthquake. Costs associated with the isolator system were balanced against the owner’s tolerance of down time in making the decision to isolate the building.
• Designing for infrequent earthquakes. No two earthquakes are identical and regional differences create a huge variation in how the ground surface moves in an earthquake. Base isolation design relies on the ability of the design team to understand reasonably accurately the expected actual earthquake for each site. While base-isolated buildings had already been built in California using its records from frequent earthquakes, the geotechnical engineer for the EOC had to determine probable earthquakes for our region from historic information on Washington’s infrequent large earthquakes.
• Adopting different design procedures. Conventional mid-1990s structural engineering computer analysis software was not suitable for base isolation design. Specialized software was used to predict how the isolators would react to simulated earthquakes. The output of those specialized programs was then used to design the building’s beams and columns in a conventional manner.
• Working with regulatory officials. As the first base-isolated building in Washington, it was understandable that those governing the permitting of such structures would have questions. We worked to develop an understanding of how isolated buildings differed from conventional buildings so that the appropriate approvals could be obtained. Ultimately, the building above the isolators was very similar to conventional buildings.
• Peer reviewing. Base-isolated structures were not a codified building type by the Uniform Building Code then in force. Therefore, to satisfy regulatory officials with the EOC’s design, a peer review process was selected to check the design. Since the peer reviewer had not designed such a building, that person had to be educated in the applicable design procedures.
• Integrating utility systems. In typical buildings, all utility connections (electric, water, sewer, etc.) are simple rigid pipes and wires running through or under the building’s foundation to outside services. In a base-isolated building, those utility connections must allow the building to move relative to the ground outside. We worked with the mechanical and electrical engineers to develop details that would allow their systems to survive the building’s movement.
• Procuring isolators. Regardless of the few companies that make isolators, the EOC, as a public project, was required to follow competitive procurement procedures. To further complicate the process, base isolation building design requires that the actual isolator product be analyzed in the design of the building. A procurement process was created that allowed the state to meet its legal requirements by developing an early bid package.
• Construction issues. No contractor in the state had built an isolated building. We worked closely with the contractor to identify and resolve unique detail issues. By working together, the EOC opened in 1998 to provide a survivable home for the state to direct disaster recovery operation.
On Feb. 28, 2001, the EOC easily survived the magnitude 6.8 Nisqually earthquake, even though it was just 10 miles from the epicenter. Since the completion of the EOC, KPFF has assisted several other local owners with the evaluation and implementation of base-isolated buildings for their critical facilities. Buildings with extremely valuable contents such as financial institutions, research facilities, communication/command centers and historic structures have been successfully isolated from destructive earthquakes, providing owners with the ability to function during and after a major earthquake.
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