DIYbanter - View Single Post

wrote:
From this, I ran one of the web beam calculators using
as a calculation load 250#, and got just over 1/8" of
bend, and 13.6 ksi bending stress at the receiver.

With a yield stress of 36ksi, A36 would seem to be OK--BUT
it is not unusual for bouncing and other momentary
stresses to cause the actual forces to exceed that, so
a common rule of thumb is to use four times the load for
a safety factor.

If we re-run the calculator for a 1000# load, we get just
over 1/2" of bend and a stress of 54ksi, which would put you
over. So my quick "back of the envelope" calculation would
agree with your other two responses, use the thicker section.

I called it a 30" cantilever beam with a 250 lb load multiplied by four
for bouncing, etc. and get
BeamOut(0 15 30)(30E6,1 I_sqr 2 .25)Beam 0(30 1000)
pos'n pt. couples shear bend. slope def'l
force stress stress

0 -1000 -30000 -1394 36170 0 0
15 0 0 -1394 18080 0.01356 0.113
30 1000 0 0 0 0.01808 0.3617

So I would say even .25" wall is marginal especially since going dirt
biking usually involves going over some pretty rough roads.

Ted