top heavy

[rookie37]

I'm trying to calculate this. I have forgotten how. Will somebody please give me a link that explains how to do this?

This link explains what I'm trying to do

http://content.screencast.com/users...10cb-d2a2-4385-8ad5-1d52af69d60b/tip over.png

 

[GregLocock]

moments about the lower left corner

Cheers

Greg Locock


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

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

 

[hydtools]

https://diversity.umn.edu/multicult...edu.multicultural/files/Phys1301CRsolns-2.pdf

See problem 10 b).

Ted

 

[desertfox]

Hi

See page 4 of this link

http://www.kmitl.ac.th/~kbnavaph/food/file/static_chapter8_6_slides_per_page.pdf

 

[chicopee]

Elementary problem if properly presented, however, with lack of sufficient information, problem is unsolvable since no tipping point is given and we have no idea if it is a static or dynamic condition.

 

[rookie37]

This is a pallet rack problem

We have racks similar to the one in the link

I want to remove the bottom shelf so that we can park things under the pallet rack. I'm told that this isn't allowed and wasn't given a reason. I assume it is because the rack will become top heavy. I want to make modification to the rack to compensate.

I.E. If the rack is depending on the bottom shelf to be loaded with 1 tonne, I would like to remove the bottom shelf and anchor down the feet with bolts that will equal 1 tonne tensile strength.

http://www.google.com.au/imgres?imgurl=http://

http://www.triboroshelving.com/pall...act=rc&uact=3&dur=6945&page=1&start=0&ndsp=19

 

[chicopee]

The reason that it may not be allowed is the possibility of the legs buckling if you remove the bottom horizontal members when the rack top shelves are loaded to capacity, so you should ask the rack manufacturer how much unsupported free length between shelves is recommended. The problem otherwise is a basic static problem of an assumed rigid rack on which (one can assume) rack loading and rack weight acting in the middle of the rack depth, the rear legs under compression, front legs under tension and an external horizontal at some height pushing the rack. You'll have to first determine the allowable compressive load that the rear legs can take when you remove the bottom horizontal members either from the manufacturer or from calculations; then sum the vertical forces to find the tensile force that the front legs will be taking; then sum up the moments, taking the fulcrum about the rear legs, to find the horizontal external force that would try to tip the rack; then sum up the horizontal forces to find the shear load imposed on the rack legs in contact to the floor. A free body diagram is always recommended.

 

[rookie37]

I thought of the legs buckling as well. (not as in depth) I would be prepared to add cross bracing.
Our rack is taller and has 3 shelves. I want to remove the bottom shelf so that I can park product under it. Note the blue bracing will be different to the green bracing. I will anchor down the feet better as well.

http://content.screencast.com/users...f340bf2a-184d-42dc-ab11-8c43cdb78806/rack.png

 

[LittleInch]

rookie 37,

I think your idea is fairly sound as I doubt the majority of these things actually bolt the feet to the floor. Removing the lower shelf will raise the centre of gravity of the whole rack, but so long as that C of G doesn't go beyond the outer edge it won't fall over on its own.

Until though you nail down the issues behind the fact that "I'm told that this isn't allowed", you probably won't get very far even though there is presumably no guarantee that the bottom shelf would always be loaded if higher ones were also loaded.

The only other issue is whether in the past they have had accidents either because there was some sort of jolt on the rack and it caused a collapse or if the feet are not fixed, they could splay out or buckle.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Compositepro]

The connection to the horizontal beams is all that provides shear support to the columns (to prevent racking of your racks). Any other type of support will interfere with access to the shelves but can be done if it is calculated correctly and will not again be altered by someone else in the future. This question would be more appropriate in the Structural Engineering forum.

 

[rookie37]

"This question would be more appropriate in the Structural Engineering forum"

Thank you. I'll do that after I have done a bit of homework. I.E.
What are the dimensions of my pallet rack?
What is the weight of the heaviest pallet?
What is the maximum moment of the column?

 

[telecomguy]

Without friction, it'll just slide.

http://xternal.me

 

[TheTick]

I would do two things with this:

1. Make a graph of force vs. angle as the "box" is pushed and rotated around the corner. Force will decrease as CG reaches tipping point. Excel is great for this. You may want to make a series of graphs for various contact points.

2. Calculate the amount of energy needed to raise CG up and past tipping point. This can tell you how long a force must be applied before it's too late to stop.

The buckling issue... do be careful.

 

[rookie37]

I would do two things with this:

1. Make a graph of force vs. angle as the "box" is pushed and rotated around the corner. Force will decrease as CG reaches tipping point. Excel is great for this. You may want to make a series of graphs for various contact points.

2. Calculate the amount of energy needed to raise CG up and past tipping point. This can tell you how long a force must be applied before it's too late to stop.

The buckling issue... do be careful.




This sounds interesting. I partially understand. Will you send me an excel file as an example?




Without friction, it'll just slide.

The feet are bolted down to the floor. It won't slide