Hal Amick, Ahmad Bayat, and Zoltan A. Kemeny
Semiconductor
facilities engaged in development, production, and mask-making for computer
chips are extremely expensive, often with unit costs exceeding $3,000 per
sq ft of cleanroom. The total cost including both building and equipment might
exceed $1 billion, of which 3/4 might be the cost of the delicate equipment
used to make the products (chips, masks, etc.). Much of this equipment is
vibration-sensitive, and building designers go to great lengths to minimize
the vibrations to which the equipment is exposed.
The structures themselves are generally designed to meet or exceed seismic
code requirements. However, the fragile, vibration-sensitive equipment sometimes
equipped with internal pneumatic isolation but without additional seismic
provisions is typically "hard-mounted" to the structure, exposing it to the
full lateral loads of a seismic event. A major earthquake could leave one
or more of these facilities standing but non-functional for quite some time,
posing disastrous economic consequences for an industry center like Silicon
Valley.
The authors present a conceptual approach in which the design objective for
the facility would be that its contents remain operational following an earthquake.
The structure and mechanical systems would be designed for strength and rigidity,
but the most costly portion of a semiconductor facility the cleanroom and
the expensive production tools would be designed to be decoupled from the
building shell using low-compliance isolation and/or dissipative systems.
This concept will be compared and contrasted with base isolation approaches
which might be considered for the building shell by itself.
Reprinted from Proceedings of Seminar on Seismic Design, Retrofit, and
Performance of Nonstructural Components, ATC-29-1, Applied Technology Council,
San Francisco, Jan. 1998, pp 297-312