15 Jul 2010 03:17 UTCThu 15 Jul 2010 - 3:17 am UTC
I am building a cart out of rectangular steel tubing that is 6 feet long. It will rest on casters on each end. It will carry a load of about 600 lbs concentrated within 22 inches of one of the ends. I am using the formula D = P x l^3 / 48EI to calculate the deflection which assumes the load is concentrated in the middle however my load is concentrated within 22 inches of the end. How do I adjust the calculation for this.
15 Jul 2010 08:12 UTCThu 15 Jul 2010 - 8:12 am UTC
For clarity, is the 600lb load concentrated within 22 inches of only one of the ends, or is it equally concentrated between points at that distance from both ends?
Either way the deflection will be less than what would occur with loading concentrated at the midpoint of the beam.
15 Jul 2010 14:28 UTCThu 15 Jul 2010 - 2:28 pm UTC
The load is concentrated from one of the ends to 22 inches from that end. There is very little load if any from 22 inches to the other end
15 Jul 2010 14:38 UTCThu 15 Jul 2010 - 2:38 pm UTC
here is a simple drawing.
L is the load and X is the length of the steel beem. I should also clarify that there will be two lengths of steel tube so I think the load for each beam wold only be 300 LBS. I also posted a sketchup drawing at http://files.me.com/kevcoleman/3t6nt1 if you want to look at what I am building. The load, a table saw will rest on the four triangular gussets.
16 Jul 2010 14:31 UTCFri 16 Jul 2010 - 2:31 pm UTC
That explanation helps alot. redhoss, I dont necessarily need a 3 X2 tube, in fact I wouldnt mind a slighly smaller one so long as it doesnt deflect much more than probably 1/16 at the center.
16 Jul 2010 16:22 UTCFri 16 Jul 2010 - 4:22 pm UTC
Also, the thickness is not a contraint. from the looks of available tubing, it is probably 3/16 or could be 1/4. I originally selected 3X2 tubing in 3/16 inch thickness because using the center loaded formula showed that would result in a deflection of around 1/16 inch which is acceptable to me. I am thinking however based on your guys feedback that given the load is at the end, I may be vastly overestimating the size of tubing I will need to limit the deflection.
I did try to use the beam software mentioned but I am not an engineer so I had a hard time figuring out all the inputs.