Doing my head in!

[tab]

Morning all

After doing a search (and finding a thread i started last year and completely forgot about) can any one help me with this,

How much weight will box section support over a given distance?

For example:
If i have a peice of 50mm sqaure box section with 3mm wall, spanning 1.5metres, how much weight will it hold?

I've seen the links people have posted before such as that superbeam but i cant work out how to use it, are there any good old fashioned calculations i can do to give me an answer?

Any help appreiciated, its sending me nuts trying to work out what material i can get away with using, i dont want to keep going overkill on things which i could make at a lower price if i just used to right materials to start with.

 

[atomant48]

When you say how much weight it needs to be a bit more specific, ie what kind if load (single point or distributed) and what's the use (ie how much deflection is tolerable) etc. with some more details we might be able to help.

 

[tab]

My apologies, i didnt realise it got a bit more complicated.

erm ok, say i was making a weight lifting bench and was after a maximum user weight. People would lie on it (which i guess is distributed weight) or sit on it (which i guess is single point) but then i might aslo get the odd one that will use it for jumping squats which i imagine would increase the stress.

As for deflection i suppose if it bends a bit that wouldnt matter, well as long as it doesnt break 6 months down the line with constant use.

 

[Paul.]

If you applied a 200kg (1.96kn) point load to the centre of a 1.5 metre simply supported 50x 50 x 5 SHS, it would deflect by 3.3mm, well within the acceptable limits for structural steelwork,

The same load evenly distibuted over 500mm in the middle of the section will deflect it by 1.5mm.

the maximum safe loading from a structural point of view works out at around 244kg (2.4kn) central point load, that would give a deflection of 4.1mm.
presumably your loads will be supported by more than one member, so depending on design will give a good safety margin, very often the weak points in structures are the joints and connections rather than the materials.

 

[tab]

Paul thats brilliant thanks, can i ask how you worked that out though so i can apply it to other sizes when i need to

 

[rkde]

Looks like bending moment calculation is what you need

 

[Mick - Ford Focus]

http://www.engineeringcalculator.net/

This May Help

Mick