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Re: Terracotta Behaviour

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Thor,

Is the terra cotta you are dealing with hollow clay tile?  the following
comments are based on the assumption that it is.

Hollow clay tile in numerous configurations were used in Southern California
in the 1910's through the 1920's, and into the '30's.  They typically have
open cells with webs of about 3/4" thickness.  Cells were sometime oriented
horizontally, sometime vertically sometimes mixed.  Some configurations (T-
shaped and L-shaped) were interlocking through the wall and could be
interlocked in varying patterns that resulted in different wall thicknesses.
Structural wall thicknesses are generally 8" and 12"; nonstructural partition
thicknesses could be 4" or even occasionally 3".  They were typically laid-up
in lime mortar, but some of the later work was done in portland cement mortar.
Bed joints and head were usually about the same width as the cell walls.

The "explosive response of hollow caly tile was also rumored in this areas in
the '80's.  Terra cotta of this kind behaves "explosively" when hit with a
hammer or dropped from the roof.  Earthquake forces do not cause explosive
behavior.  Evaluation and design using the UCBC is appropriate (the UCBC even
says so).  Evaluation of mortar quality by the UCBC procedures should be based
on net mortar-joint  dimensions, not on gross wall thicknesses.  Testing of
mortar quality using the procedures of UBC Standard 21-6 requires bearing pads
of steel plates set in gypsum mortar to distribute jack loads so that the jack
doesn't break through the cell walls.  Effective wall anchors can be made
using all-thread rods embedded in epoxy -- it takes some creative detailing
and careful workmanship to develop epoxy keys into the cells -- but they give
good test results.  Also look into using the Cintek Anchor System
(613-225-3381) (they are Canadian folks) -- I've come across this since my
last hollow clay tile project, and it looks very good.  

Seismic damage to unstrengthened buildings with hollow clay tile walls is
about the same as seismic damage seen in unstrengthened buildings built with
unreinforced brick masonry walls.  

This kind of material is still manufactured to conform with ASTM C-34 and
C112.  The last time I looked (probably the late 80's) the specifications were
essentially unchanged from the same ASTM specifications of the 1920's.

Nels Roselund
Structural Engineer