Shelf load

[varistor]

Hi all,

New and totally electrical so plese accept my ignorance

Say I have a shelf rated to carry a 100kg load and all it sees is normal gravity. Now, say i subject this to a constant 4g acceleration then i assume the shelf has to withstand 4 x 100kg. But what if I want to make the shelf withstand a 4g very short duration pulse (ie a bump). Does the 4x 100kg stand or would there be some factoring involved, or may be even the shelf would be able to cope designed to 100kg
Hope all that makes sense

 

[rb1957]

first, what does "rated" mean ? ... i mean what use is it rated for ? (in airplanes it could mean 9g forward, or 6g down, or ...) ... you may need to ask the manufacturer

simply put, an impact load is double the effect of a static load.

are you worried about the shelf or its attachment to the rest of the world (or the vehicle carrying it) ? the shelf would see this impact magnified load, the attachment might not (due to flexibility in the shear).

 

[mizzoueng]

Check this thread out.

http://www.eng-tips.com/viewthread.cfm?qid=155771&page=1

Your shelf is "rated" for 100kg. That is the weight it can support vertically. Usually there pull-out forces that are designed for the bolts holding it to the wall it is connected to. Check the bolt sizes and manufacturer and then type "bolt pull out equation" into google.

Also look up the bolt manufacturer and see if they have this information on their website or in their catalog. More than likely it is an anchor and this information is readily available in catalogs.

 

[MiketheEngineer]

Remember - wood and steel behave differently and use far different allowances for impact loads.

 

[rb1957]

i don't go along with mizzoueng.

airplane floor planels are rated for 125 lb/ft2. they don't break when you put 125 lb/ft2 on them, or even 250 lb/ft2, 'cause they're desinged for 125 lb/ft2*loadfactor, loadfactor = 6, 9, whatever. maybe things are differnt if you're stuck on the ground ?

 

[varistor]

Thanks for the responses guys. Maybe I need to be a little clearer in what i am asking

I will give another example:
Ball bearing slides that fit into 19" racks have a static loading (usually for the extended state)
So,
Slides rating 100kg

Scenario 1 - Slides loaded with 80kg in a rack sat in an office

Scenario 2 - Slides loaded with 80kg but in an aircraft subject to 4g for several seconds

Scenario 3 - Slides loaded with 80kg in a car which travels over a pot hole and experiences a shock pulse in the slides of 4g 11ms

So would the design philosophy for scenario 3 be the same as for scenario 2? I am just trying to understand whether the slides would need to be the same size for scenario 3 as scenario 2

 

[zeusfaber]

Case two is clearly overloaded.

Whether case three is overloaded or not depends on how rigidly the loading mass is connected to the weak point of the shelf that determines the permissible load. This will depend on the nature of the mass, the stiffness of the shelf and the location of the weakest point.

If everything is stiff, then the weak point is likely to see most of the load, and the shelf will be overloaded.

If there's a lot of stretch between the mass and the weak point, the full 4g's worth of force won't be transmitted to the weak point until significant deflection has been achieved - and if the acceleration is removed long before this point, it is possible that overload at the original weak point may never be reached.

That doesn't mean that some statically stronger, but closer to the mass, element won't get overloaded instead.

A.