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Re: Upgrading unreinforced quarry stone masonry building ...

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Stone buildings are usually built with walls of unreinforced masonry.  Rules
for seismic strengthening in California are included in the Uniform Code for
Building Conservation, 1997 edition, and the ICBO publication, Guidelines
foe Seismic Retrofit of Existing Buildings -- an updated edition will be
published by ICC.

Using the UCBC, or the GSREB, securing of walls and parapets to the
diaphragms and height-to thickness ratios are most important.  The
development a shear-load-path from the mass of the building to the ground,
and assuring that diaphragms are rigid enough to control displacement but
are flexible enough to limit the response of the buildings are also very
important factors.  [The understanding of the importance of a flexible
diaphragm often seems unconventional and strange -- but it is essential to
an effective retrofit for many unreinforced masonry buildings].

However, there are significant differences between stone buildings and brick
buildings.  Stone buildings in California seem to have no bond units
intentionally placed to provide through-the-wall bonding that would make the
wall act as monolithic during strong shaking -- we install a system of
through-the-wall bond pins embedded in epoxy that engage inner and outer
wythes.  Corners are vulnerable and tend to separate even though other parts
of the walls are anchored to diaphragms -- we install diagonal wall anchors
into the corners.  I know of very little in writing about strengthening of
stone bulildings against winds and earthquakes, but I've had some
experience.  I'll try to answer questions if you'd like.

Nels Roselund
Structural Engineer
South San Gabriel, CA

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