Ok, I got out my old book and did a little trig :-). For a simple
triangular truss with two equal sides and a horizontal crossbar at the base,
the load needs to be applied at the joint at the apex of the angled risers.
That places the angled risers in pure compression and the horizontal bar in
pure tension. You can drop a vertical bar from the apex to the center of
the horizontal beam and apply the load at the base of that, if you want,
just make sure it can support the entire load in tension. If you use two
lift points part way up each angled riser, that adds bending stress and
greatly weakens the assembly. Here are a few equations for you:

length of horizontal beam: L
angle of base of risers with horizontal beam: T
load applied to apex: W

length of each angled riser = L / (2 * cos T)
height of apex = (L * tan T) / 2
compressive force on each angled riser = W / (2 * sin T)
tensile force on horizontal beam = W * cos T

So, if L=15.5'=186", W=1000 lbs, and T=30 degrees:
length of each angled riser = 186 / (2 * cos 30) = 107.4"
height of apex = (186 * tan 30) / 2 = 53.7"
compressive force on each angle riser = 1000 / (2 * sin 30) = 1000 lbs
tensile force on horizontal beam = 1000 * cos 30 = 866 lbs

Using eng. pwr tools, one estimate of the compressive load a slender beam
like 3" square tube 107.4" long can support 8900 lbs with a safety margin of
5x. The cross sectional area of 3" square .120 wall tube is 1.34 in^2 and
if the tensile strength is 35,000 lb/in^2 the horizontal beam can handle
35,000 lb/in^2 * 1.34 in^2 = 47,000 lbs, or 9,000 lbs with a factor of 5
margin. Gosh, one truss like this can handle 9,000 lbs (if you can keep it
upright :-)). Anyway, play with the formulas to find an angle you like.

-----
Regards,
Carl Ijames
"Steve B" wrote in message
. ..


"Carl Ijames" wrote in message
...
The simple beams were within a factor of 2 or 3 of just enough, so my gut
says your truss will be plenty - I just can't back it up with numbers
without looking up some stuff. If I get a chance tomorrow at work I'll
try.

-----
Regards,
Carl Ijames


Appreciate it. Now's the time to do the numbers. This gives me a clear
span under the lift, converts downward bending to compression, and just
stiffens and strengthens in several ways.

Steve