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clay tile masonry (long)

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Here in the midwest (at least in Iowa), it seems that one can drive around 
out in the country side and see a fair number of silos located on the various 
farms.  In particular, there still are a number of silos that were built 
using clay tile masonry.  These are usually around 25 feet in diameter, 80 
feet or so in height, and have a shiny glazed finish on the masonry units.  
They probably worked just fine until the roofs blew off or rotted away.  It 
does seem that you hardly ever see one that is still in use, or with a roof 
still intact.  The point of this whole long winded description is that I 
thought at one time someone (a state agency or agriculture group) had issued 
a warning to farmers about these structures because they have a nasty 
tendency to suddenly collapse, apparently without too much external 
influence.  I presume any collapse was due to the deteriorated nature of the 
masonry which was probably caused in part by water infiltration once the roof 
was gone.  In addition, I presume the clay tiles get punctured, or the 
glazing becomes deteriorated and really soft from cows rubbing up against 
them.

I wonder about all this because I have just begun an investigation of a four 
story building (condo) here in Iowa, that is constructed with clay tile 
masonry bearing walls.   It was designed by an intern of Louis Sullivan 
around 1908.  It has a cement based stucco finish and some really poor 
details with brick masonry around the perimeter of the building and the 
windows.  It is on the historic register, so we just can't go in and tear out 
the bad and put in the good, because that will change the original appearance 
(heaven forbid).  Or better yet, take a bulldozer to it and eliminate the 
problem altogether.   Instead, I have been hired by an architect who 
specializes in historic restoration.  This means we have to go around and 
look at all the little details, talk in great length about it, agonize over 
every little detail, and then finally just bull ahead with some half-baked 
solution, all in the name of historic preservation. 

This brings me back to the collapsing farm silos.  The clay tiles on the 
condo are really deteriorated at the first floor level underneath that stucco 
finish.  There haven't been any cows loose in this area since around the turn 
of the century, so should I worry about sudden collapse of this building, or 
do we forge ahead and try to deal with the original lousy design details that 
were done by a high-buck architect who is now dead?  Any opinions about clay 
tile masonry??

Les Kuehl, P.E.
NNW, Inc. - Consulting Engineers
Iowa City, Iowa