huangyhg

safe working load of simple rectangular beam
hi guys,
can anyone help me with the following calc i have to perform (i'm sure you'll find it basic.)
i have a rectangular beam positioned vertically to support a load. the beam is made from al al 6082 t6 size: 30mmx60mmx1000mm. the load applied to the top of the beam(30x60 face)is 4500kg.
can anyone show me how to calculate the buckling load, and derive either a fos or the failure criteria?
many thanks guys.
max.

is there any bracing? this will effect the buckling strength. is there any welding? this will effect the yielding strength.
do you have (or can you get your hands on) a copy of the aluminum design manual? there are provisions for allowable stresses based on the section type and b/t ratios. if you have welding, that knocks the fy down significantly within a few inches of the weld.
lesser slenderness as doubly pinned is 115 so it has elastic buckling behaviour and (i don't seem to have the data for your exact 6082 t6 material, but it is t6 what i give as follows) an allowable stress of 85000/115^2 or 6.42 ksi gives about 8.96 kips allowable or 4.05 ton. your load exceeds the allowable by 11% if the formula for the allowable stress in the elastic range is right for your material. seek that formula in the aluminum specs.
disregard the previus entry;
will look a correct allowable stress later. no time at this moment. it seems i am taking a section that doesn' is the correct one.
it seems section 3.4.7 overall buckling behaviour in the elastic range controls, hence
fa=pi^2*10100/(sf*(l/ry))=3.86 ksi, where the safety factor is 1.95 and l/ry=115.
hence the allowable load is 10.76 kips or 4.87 ton.
your load is just safe.
it seems i not only choose a bad section in the book i was searching but multiplied with error by the previous allowable. hurries.
thanks for the excellent response guys.
i'll be documenting this straight away
ishvaaag-
how are you determining that without knowing the bracing conditions?
maxarmstrong,
ishvaaag's calcs are ok considering a pin-pin situation without sidesway. if the top of this column is not restrained adequately, your safety factor effectively disappears.
you might want to have a local structural friend of yours take a look...
if you "heard" it on the internet, it's guilty until proven innocent. - dcs
structural eit, i was just solving a pin pin situation as sweringen noticed, not negating that bracing influences allowable load.
my point is that pins are modeled as infinitely stiff with no moment resistance. i'm curious if his situation really approaches this assumption...
if you "heard" it on the internet, it's guilty until proven innocent. - dcs
certainly, if you do not restrain movements at the tips of the bar, we are in a dangerous situation, 4.5 tons on something that can slip. so, again, assuming pinned ends.

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