Load Distribution Using Spreaders

[HIGHFLY33]

I have a quick and simple question for you all that is causing somewhat of a dissagrement in our ops department.

The question relates to load distribution calculations whilst using spreaders

http://i60.tinypic.com/6qifkh.png

concerning floor load limitations , surely the 667 kg/m2 is the correct answer ?

pleease feel free to share your views and thoughts on this matter,

Thank you in advance

[Wireless]

I'd say area 667 and running load 667. My thinking of course the contact area is 3 square metres. I suppose to take it to extremes say it was balanced on 2 stiletto shoes of 1cm along each edge it doesn't matter how far apart they were the area load would still be 10millon kg/m2. Don't ask me why I chose stilettos. I guessed the dimensions I don't own a pair, promise. Running/linear of course as you say 2000/3 in that orientation.

[jtt]

Hi,

I'm not a loadie or anything related to aviation, just a simple-minded physicist, so take this with a grain of salt... I'd say you're absolutely right with your 667kg/m^2 - that's the pressure excerted onto the floor in the areas of the spreaders (and in between there's no pressure at all).

Now how best to argue your case? Instead of having spreaders (the name says it all, I guess) consider the case were you had your load on legs with 1x1cm sizes at the extrem edges of were the spreaders are now. Would anyone still argue that the load would be 444kg/m^2, just because that's the area enclosed by the supporting four legs? I guess anyone would see immediately that each of the 4 legs would have to support about 500kg, resulting (with the above assumptiong of a 1x1cm profile) in a pressure of 5000t/m^2 below the legs. Making the area of the legs larger reduces the load, but only when the whole 3x1.5m^2 area is loaded equally you get down to 444kg/m^2.

Of course, if you can show that the spreaders are on top of load bearing structures that can take a lot more things are different, but then you don't talk about load distributions and any "maximum loads" don't make sense anymore.

[Wireless]

How strange you posted an almost identical post at the same time using the same extreme example except you chose pegs. I should have chosen pegs not stilettos shoes! I'll get me coat.

[jtt]

Probably a similar way of thinking - I found that when trying to come up with an intuitive explanation it's often useful to consider "extreme cases" that are really obvious and then start arguing from there;-)

[WASALOADIE]

During my training and career (Military), we always took into account the thickness of the load spreader and increased the footprint through an angle of 45degrees from the contact area of the load to give the effective footprint. Then divide the mass of the load by the new footprint area to give the loading. With 2 battens as per the illustration, the inner edges could not be extended by 45deg .

Load spreading means increasing the contact to reduce the floor loading. You cannot simply add any depth of material just to spread the load without taking into acount the spreading effect (otherwise 3mm ply would suffice??), if you dont take into account the depth of the material then it just becomes floor protection to reduce damage to the floor, but not spread the load.

The use of battens may be to prevent contact with a non-treadway area where the battens rest on the treadway areas (Bridging). In which case they are purely distributing the load to the treadway areas which will have a higher UD load strength limit.

drop me a pm and I'll email you with a diagram of what I'm on about as I cannot seem to get the image onto here

[Wireless]

Yes indeed I like your thinking!

I suppose another way to rationalise it is- the area between the 2 spreaders does not support any mass from above. As mentioned though the boards/pallets have to be of sufficient strength for their dimensions to displace the load imparted evenly over their surface without flexing otherwise you're creating a point load under the part of the board that has the cargo directly above it.

Maybe to be really picky you should add the mass of the spreaders into the mix if on the limit? Not sure about that one though! Thinking about this also if you rachet strap down to vickers rings onto the edge of the maindeck you're effectively adding pressure to the load which is imparted on the floor. Unless strapped directly to a pallet? Don't know again. One again for the loadies. They seem like magicians to me, glad we have them.

[awblain]

Does it matter about the orientation compared with the floor beams, and their spacing?

I can see 667 being a good safest guess, if you have no information about that.

What would you do for a pair of 1000kg boxes that were each 3m x 0.5m?

Are the spreaders stiff enough to distribute the weight evenly right along them? If they flex, then it will cause a peakier pressure. At worst having them splaying and teetering on an inside edge would make it much worse than leaving the red box on the floor.

[WASALOADIE]

As you tie down the load, yes technically you are applying an extra force to the floor but no more mass apart from the mass of the strops.

Yes you need to take into account the mass of the spreaders too.

This is similar to one of the EASA/CAA exam questions that came up a few months ago where it asked for the floor loading but included the mass of the battens in the question. It was not a load spreading question as such but a floor loading question and the dimensions, mass are the same.