Lintles

["David J. Holmes" <wolfscrag@zzzzzzzzzzz>]

Hello Dr. Watts,
    I am involved in a similiar project coming up later in the year.
It is a pergola "section" or Stonehenge arch.
Posts 10', 3' x 3' , lintle 16', 2' x 3'. About 8 tons per piece.
I have always worked the lintle capacity from the fulcrum
on top of the post. If there is 3' outboard from the center of the post then
the same weight is 3' inboard....each negating the gravity of the other, a
see-saw,  if not too long....another assumption.
Doubling the weight of that amount for each post and subtracting it from the
overall weight of the lintle at 170 lbs per cube will give you the
actual center gravitational weight in the middle of the lintle.
All that said, that information is worthless because that assumes that you
have an absolutely flawless piece of stone that is a tested commercial
structural architectural granite. Figures for that are available on line
 from the commercial stone people and engineering sites of the major
commercial stones. ( Granite generally. )......and , nno, I don't have them.
I go looking when I need them. I think that common sense,intuition,
observatioon and past experience play a lot in these types of
determinations.
Unfortunately today courts don't always take that into consideration even
though we didn't make the stone.
As to the pins, verticle pins only need to be in the stone 5" or so.
Lintles that size don't normal have any horizontal movement or pin shear
stress unless the joint is poor and/or not plumb. It acts more like a key.
Old 3/4" to 1 1/4", 1 1/2" steel drill rod with the air hole down the center
is about as strong a pin generally available if the joint and hole are
sealed ( rust). Pipe ( or drill rod) is stronger BECAUSE of the hole.
A 6.5 earthquake might cause a problem. For verticle pins stainless is fine.
Keep in mind that the more holes you make, the weaker the stone.
I don't know if they used stainless pins at Stonehenge. Some are still up
and some aren't. I know that most of the destruction of early stonework
throughout the ages came from a simple parable- "Why cut a block when you
can steal it."

Regards to everyone and thanks to Clive for the direction to the list.

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David J. Holmes
Wolf's Crag Sculpture
Plymouth, Maine