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Re: Stone Buildings

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Barry,
 
The 1997 UCBC, Appendix Chapter One is applicable for seismic strengthening of stone buildings.  The LRFD version of the UCBC [published by ICBO], "Guidelines for the Seismic Retrofit of Existing Buildings is also applicable; it probably has not been adopted by many jurisdictions but will probably be accepted based on its credentials.
 
Testing for mortar quality to establish in-plane shear strength is a problem.  Ashlar stone masonry can be tested using UBC Standard 21-6, but testing of large units dressed only on the exposed face can be very damaging to a wall.  I have not found a satisfactory test procedure for rubble stone masonry.  The exposed face of a stone in a rubble stone wall gives you no clue about its configuration inside the wall; excavation into the wall to evaluate the appropriateness for testing of candidate stones results in many excavations and few appropriate specimens. 
 
The California Historic Building  Code [Title 24, Part 8] provides low arbitrary allowable in-plane shear values that are sometimes high enough to be usable for design.  It also provides for testing to establish mortar strength values based on the force required to pull a stone out of the wall.  However, when you select a stone, you can't tell whether the other end is wider than the exposed face [like an anchor], or smaller and appropriate for pullout testing.
 
Anchor bolts embedded in epoxy adhesive generally provide very good shear and pullout values -- I always do job-specific testing.
 
You are right that there is not much published information.  If you are the only professional on a strengthening project, or if you have a project that does not have a team that includes stone conservation expertise, the engineer may be the one who has to address conservation issues.  In that case, these would be helpful.  Conserving Buildings by Martin Weaver, John Wiley and Sons, and Practical Building Conservation, Volume 1, Stone Masonry by John and Nicola Ashurst, Halsted Press, a Division of John Wiley and Sons.
 
Nels
 
Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net