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Re: 6.2+ earthquake in Seattle

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Charlie Griffes said .   .   .   . "There are various
triggers in the Seattle amendments to the UBC that will require the building
to meet the current code requirements..  My opinion is that this is an
awkward provision since it is very difficult to show that the retrofit has
actually brought the old building into full compliance with current codes.
There seems to always be a compromise of some sort that is reached with
the building official with respect to the scope of the upgrades required."


I don't think it is practical to try to make a URM building comply with the
UBC.  A modern building code requires the use of ductile materials.
Unreinforced masonry is not ductile.

The Uniform Code for Building Conservation, Appendix Chapter One, published
by ICBO, is the appropriate standard for improving the seismic response of
buildings with URM walls.  It recognizes the non-ductile response of URM
walls, and allows appropriate evaluation and use of inherent strengths in
the existing materials.

It is based on research into the seismic response of the components
typically found throughout the U. S. in  buildings with URM walls.  The
research was sponsored by the National Science Foundation in the 1970, and
was documented and published and put into first practice in the City of Los
Angeles in the early 1980's (Old Division 88 of the L.A. City Building
Code).  The 1987 Whittier Narrows Earthquake allowed real-life testing of
its concepts when strengthened and unstrengthened URM buildings could be
compared.  Subsequent modifications resulted in buildings that performed
very well in the Northridge Earthquake of 1994.

Nels Roselund
Structural Engineer