Bill Schwab wrote:
john wrote:
Ned Simmons wrote:
In article ,
says...
Proctologically Violated©® wrote:
How did you determine what an "acceptable" deflection would be?
Building codes?
i personally use the moment and bending stresses , and a safety
factor of 3 to four , with 36000 psi being a standard for most beams
you dont want to get over 9 to 11 k in the bending and moments
The AISC standard uses a factor of safety of 1.67 in most cases,
which results in a working stress of 21.6 ksi for A36 steel.
you will see deflections of less that 1/16 inch for a properly
designed beam , while anything over 1/8 inch you will see the
bending and moment stresses edgeing up into unacceptable levels
That's a huge oversimplification. A deflection much greater than 1/8"
is acceptable in a long beam, and a very short beam may fail,
probably in shear, before it deflects 1/16".
Ned Simmons
On a cantilever beam hoist you want to keep the deflection to a
minumum because with a heavy load it will want to roll down hill in
the direction of the negative deflection. It will take off by itself
when you hoist a load, and that can get exciting.
True enough, but what's "a minimum" in that context? The load needs to
be pinned, held by cable, etc. to restrain the horizontal motion.
Bill
Every cantilever hoist that I have used never had any restraints or
locks for horizontal motion. Most of the heavier ones ( 2 and 3 tons)
have the cantilefer arm with a secondary turnbuckle rod between about
2/3 the was out on the horizontal and back to the upright above the
attachpoint of the horizontal beam forming about a 30 degree triangle.
John