need structural advice 1

[asv4k8]

I am trying to design a parts storage carousel that uses 4 large gears and 2 chains to support "buckets" that hold parts as shown here:

The blue lines designate the roller chain and the red lines designate the buckets (havent got around to mating them all in yet)

I calculated there will be 40 buckets total, all holding steel parts (each bucket loaded with ~250lbs) = 10000 lbs

The roller chain weighs 6.02lbs/ftx40ft= 240lbs

The top two gears weigh 328lbs per gear= 656lbs

This totals up to 10,896lbs that the two channel beams will have to support. I am trying to figure out what the smallest beam is i can safely use. I ran FEA in solidworks 2010 on a 5" beam with a web thickness of .325". I ran it with 5500lbs (roughly half the weight of the total since there are two beams) and solidworks came up and gave me the factor of safety was above 1, i was sceptical so i changed to force to the total weight (10,896lbs) on one beam and it still comes up as not yielding. Materials is ASTM A36.

The displacement is shown here (this beam is 18ft tall) :
Im not as concerned with the displacement because the two beams will be attached to each other at the top.

The vonmises shown here:

I am worried about the stress at that hole (even though it will have a gusset/bushing welded around it at the hole) and the beam buckling... the .325" web makes me uneasy about this. I dont think these factor of safety results are right..

Here are my beam size choices on page 5:

http://www.alro.com/DATACatalog/CatalogPages/004-Structural.pdf#page=6

I know people are going to suggest making a triangle shape out of the beams ect to increase stability but that is not an issue, this will be fastened to the ceiling in a warehouse to a secure point..so assume it to be stable from tipping. my only concern here is the beam supporting that compressive stress for years to come..

Is there anyone that has worked a problem like this before that can advise? Thanks in advance.

 

[asv4k8]

The chain link is US Tsubaki chain with a claimed working load of 9600lbs... since the weight (10,896lbs) is split between two sides I think it is going to be fine.

The hole is a 2.5" diameter and is located ~24" from the top edge if i remember correctly.

I know solidworks is not the end all on stress analysis but I am using it to get an idea of what beam to use just for a project cost proposal, once the project is a go, I will have all the time in the world to run the design through the appropriate tests and get it certified by a PE... thanks again.

 

[rb1957]

10,000 lbs on an area of 5"*0.325" = 1.625"^2 = 6154psi = 42 MPa

bearing on the hole =10000/(D*0.325) ...

be concerned about the rail buckling like a column (at your stress level this isn't a problem, but it could be if you optimise it).

 

[patswfc]

If one chain was to come of the cog all the load would go into the other chain, plus there would be dynamic effects that would increase this load.
I would consider using a stronger chain.

 

[asv4k8]

The chain will have guides to not allow it to come off, and even though I am designing for a total of 10,000 lbs you have to realize that is split 5000 per front and and back, and its also split side by side so each run of chain is only supporting 2500 lbs in reality. There will also be multiple rollers that have centrifugal clutches so if a chain breaks and the unit starts to free fall or exceed its set speed they will catch and stop it like an elevator.

 

[asv4k8]

So FATMANDO, your ansys results are stating that the critical stress has not been exceeded however the buckling factor suggests that is will buckle? is this correct? i am having trouble finding a step by step example of a pinned column buckling problem, lots of formulas but no examples...

 

[asv4k8]

Ok, I ran this problem through by hand using eulers formula and stepped up to an 8" beam

Here is my formula

Fcr = (pi^2 x E x I)/L^2 I used english standard units which i think are correct but see if i am correct here:

E for astm a36= 200gpa = 29007547.54psi
I is my moment of inertia in inches^4 = 1.80621 (using the 8" beam with webs of .487" and spars of 2.527")

Fcr = (3.14^2 x 2907547.54psi x 1.80621in^4 )/216"^2 = 11072.126 lbs before one beam buckles..does this sound right?

As always thanks in advance and if you need ANY automotive engineering or performance advice feel free to email me as I am not on here that often.

 

[rb1957]

except that the load is applied to two beams and are the beams pinned at both ends ... the posted model looks more like a free end cantilever (like a flagpole), c = 0.25 and Pcr = pi^2*EI*c/L^2

 

[asv4k8]

yes but i simplified it to the loading on one beam.... the beam needs to hold half the weight and not buckle...

As always thanks in advance and if you need ANY automotive engineering or performance advice feel free to email me as I am not on here that often.

 

[GregTirevold]

asv4k8,

If you are using a C8x18.75 Channel then
Least I is about Y-Y and is Iy=1.98in^4

Fcr=Pi^2*E*I/Le^2

If you are sure your end conditions are "pin-pin" then your Le equals the normal length so

Fcr=Pi^2*(29E6)*(1.98)/(216^2)
Fcr=12147 pounds for a factor of safety of 1.0

For lifting applications FoS is often 6 or higher, this is something you either have to decide yourself or see if there is any spec you will need to meet that gives a FoS.

Have you looked into HSS tube? Its made to ASTM A500 Grade B and for the same weight per foot you'd get rectangular or square tube with a 45ksi yield and vastly better values of I and r. 6x3x3/8" HSS would give you double shear on each side for your shaft as well. Channel isn't really meant for columns due to its highly directional value of I.

http://www.linkedin.com/in/gregtirevold

 

[asv4k8]

Its been 6 years since i did any classes on beam/column design so bear with me.

Alro steel doesnt carry HSS it but i think i might have to find it elsewhere......any suggestions?

As always thanks in advance and if you need ANY automotive engineering or performance advice feel free to email me as I am not on here that often.

 

[GregTirevold]

Alro has it, check the catalog section 7 pages 2-7.

http://www.linkedin.com/in/gregtirevold

 

[asv4k8]

thanks, i missed that,

so here is what i ran using that tube size I changed things a bit and am using 4 small columns rather than 2 large ones. For this analysis I sketched up the 6 inch tube and associated bracing on which the load would be applied:

force was set at 2500lbs (10000/4 columns) at the point where the gear would sit on the cross brace.

my displacement seems good, only around 1mm I know its not fixed as a pin at either end but i think those fixtures should be fine. Do you see any problem with this? You mentioned factor of safety being 6 for lift applications, solidworks is telling me there is a FOS of 12 on this, but again i want to double check... If that is the case I could go with a smaller tube... but i might keep it where it is just incase there is some kind of incident where one of these legs would be impacted...

As always thanks in advance and if you need ANY automotive engineering or performance advice feel free to email me as I am not on here that often.