John Stanton
Professor, Department of Civil Engineering, University of Washington,
Seattle, WA
Dave Seagren
Chief Engineer, Charles Pankow Builders, Ltd.,
Altadena, CA
William Stone and Geraldine Cheok
Research Civil Engineer, National lnstitute of
Standards and Technology, Gaithersburg,
MD
4th Joint Technical Coordinating
Committee on Precast Seismic Structural Systems, Proceedings, May 16-17, 1994, Tsukuba, Japan
Precast concrete frame construction
is not used extensively in seismic regions of the USA. The UBC (ICBO, 1991) currently
permits only certain specific building systems to be used and a precast frame
is not one of them. The reason is that extensive research on cast-in-place
frames has led to the development of reinforcement details that provide
suitable ductility, and these details are now prescribed in the UBC. In most
cases, these details cannot be easily achieved in a purely precast system. The
result is that most precast structures can be made to satisfy the UBC only
under the guise of an “undefined structural system” which must be shown by
technical and test data which establish the dynamic characteristics and
demonstrate the lateral force resistance and energy absorption capacity to be
equivalent to systems listed in Table No. 23-O for equivalent Rw values.
This
requirement makes approval of a precast frame very difficult. In addition,
another UBC requirement calls for “reinforcement resisting earthquaked-induced”
forces to conform to ASTM A 706 and A 615 Grades 40 and 60 specifications which
excludes prestressing steel. Since the advantages of precasting and
prestressing are interlinked, this provision on prestressing inhibits the use
of precast concrete.
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