dpb wrote, on Thu, 30 Oct 2014 08:13:07 -0500:

I don't need a picture of the big redwood; I'm perfectly willing to
allow as how they can and do get big; I've been through redwood country
a number of times. I was simply noting from the pictures posted near
that point in the thread there didn't seem to be much of any real size
and was more concerned of potential on the root system with the load
than whether the tree itself was sufficient presuming it was.

I apologize that most of my pictures were from the uphill side (where
the suspension bridge is currently forming), where those trees are puny
in comparison to "General Sherman" (which is what we call the big one).

The only time I climbed down the 100 feet to General Sherman was when we
were setting up the cables around it, and I was the gaffer who passed up
tools and supplies.

So my only pictures of General Sherman are the ones I showed, which don't
quite show the massive girth of the thing, especially at the bottom,
because what you see above is already split in two.

When the response to the question regarding angles for trying to
estimate tension needed to provide a given vertical force component
includes the justification that the angle will increase owing to the
tree flexure doesn't lend itself to thinking they're terribly big,
either. Just a "devil's advocate" position raising the question...

I agree with you, that when I first saw the angle stuff, I too wondered
about bending a tree that much to make *any* difference. I'll forward
your comments above on to the owner to see what he makes of that.

From a diagram such as that with a few measurements one could get at
least a reasonable approximation using simple-enough analyses as
outlined in the following (beginning at 7-30ff)--

http://isdl.cau.ac.kr/education.data/statics/ch7.pdf

I will forward that "Chapter 7: Forces in Beams and Cables" PDF to the
owner, who, while he isn't an engineer, he has multiple graduate degrees
and can handle almost anything we throw at him (he was an early Google
exec).