The Uniform Code for Building Conservation, Appendix Chapter One provides
the appropriate criteria for seismic retrofit for a hollow clay tile
building. I expect that you will find that the 8" + 4" tile wall is
actually made up of interlocked L-shaped or T-shaped tiles, or that the two
wythes of tile are interlocked with a periodically -spaced bond-course of 4"
tiles laid flat through the wall -- I would be surprised to find that the
two wythes are independent.
In-place shear testing in accordance with UBC Standard will need to be
modified somewhat: The jack load will need to be distributed over the end of
the unit to avoid crushing (I like to use large, thick steel plates with a
bed of gypsum plaster (USG Hydrocal, or equivalent) cast between the plates
and the units to distribute the load. The typical mortar bed joint in tile
construction approximated the unit wall thickness -- rarely were the mortar
bed joints laid full. In calculating the mortar strength per formula A6-1,
the Ab needs to be modified to use the net mortar joint widths rather that
the full bed-joint area of the tile unit.
Good wall anchorage capacities can be attained with resin-adhesive anchors
(Hilti, Epcon, Simpson and others), but the design capacity will need to be
determined by testing -- no resin-adhesive manufacturer has ICBO approval
for anchor capacities in hollow tile. I design the anchors to be made with
screen tubes that are partially wrapped with duct tape, to confine the
adhesive, but allow it to form bulbs behind the masonry unit shells.
There is a rumor going around that clay tile explodes, and clay tile walls
can't be strengthened. It looks like a clay tile block explodes if you hit
it with a hammer. But seismic loads aren't like hammer blows. I believe an
effective seismic retrofit can be accomplished using conventional URM
techniques, and at costs comparable to a conventional seismic retrofit on a