stone pergola

[Tomas Lipps <tmlipps@zzzzzzzzzzzzz>]

Norman, hello,
some thoughts:

I sent this earlier, but exceeded the minimum of quoted material
allowed so it came back. much of this has already been mentioned but
I'll include it anyway:

what you describe is a stout member and might not exceed the tensile
strength of the material, but you, or he, should ask a materials
engineer about that. I certainly wouldn't recommend it.  also
there's a problem where the horizontal members meet at the corners,
if you mortise each member, they'll be weaker at that point; if
they're stacked it would be unsightly.  holes should be drilled in
the tops of the uprights and corresponding holes in the horizontal
members so everything can be secured with stainless steel pins and
these pins should be anchored with strong compounds.  it might be
mentioned that it IS possible to core drill the entire eleven feet
length and insert a long rod of substantial thickness if your friend
is determined to do it all in stone.

I would recommend using stone pillars but with wooden horizontal
members. (the design might be enhanced aesthetically by effecting a
slow arching curve to the horizontal silhouette between the pillars.
to have stone or wooden "capitals" atop the posts also seems a good
idea).  mortise and pin them with threaded bolts.  also, having these
uprights only a foot in the ground is woefully inadequate.  my
instinct tells me two feet -or more, particularly in areas where
seismic activity is likely.  in this case holes could be drilled
laterally into the bottom of the posts and pins inserted to integrate
of the stone posts with substantial concrete footings below-grade.
core-drilling and inserting rods as mentioned above would stabilize
the uprights in the event of a major earthquake.

hope this helps

Tomas