Cantilever rack load capacity design?

[Amyymd1]

I am supposed to design a cantilever rack made from HSS steel and i am having an issue calculating the load capacity for each arm. I have a reference drawing where i am trying to figure out how they calculated it, the load capacity increases with the length of the arms on this drawing. When i try to calculate the load capacity it decreases with the length of the arms and i can't seem to get the answers they are getting. I am using equations for beams in bending to calculate the load capacity like

https://www.engineersedge.com/beam_bending/beam_bending15.htm.

(the beam/arm is supported in the center). I am using the yield strength as the maximum stress at the center. Can someone direct me to the correct equations or give me a guide to how to calculate the load capacity for a cantilever rack? I know this is simple but i can't figure it out! If anyone could help me out that would be really helpful! For example one rack had an arm that was made from CSA g40.21 50w, HSS 4x4x1/4 70inches long, supported in the middle, and had a load capacity of 7500 for each arm. probably with a safety factor or 1.5. can someone tell me how they got this? thank you so much!

 

[GregLocock]

"the load capacity increases with the length of the arms"

Seems a bit unlikely

" probably with a safety factor of 1.5"

Seems very low indeed.

I'm having trouble envisaging the construction. The key equation for a cantilever is M/I=sigma/y at the root (well actually all the way along).

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[3DDave]

The most probable formula is

https://www.engineersedge.com/beam_bending/beam_bending8.htm

s = Wl/2Z

Z = 4.4 in^3, l = 35 in; s = 50 ksi

W = s*2*Z/l = 50000pounds*in^-2*2*4.4 in^3/35 in = 12,600 pounds per side. 12600/7500 = 1.7 FS.

Why do you think the load increases with the length of the arm based on the drawing?

 

[desertfox]

Hi Amyymd1

Ca you provide a sketch of your problem it's hard to visualise from the description.



“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein