huangyhg

lateral force due to stacked round bar?
we have been asked to check the capacity of steel i-beam verticals supporting stacked rebar (in a rebar bending factory). there is a series of pairs of verticals, with the rebar constrained within each pair, the clear space between the pair being about 685 mm.
the question; what is the lateral force exerted on the verticals due to the stacked bars? any suggestions would be appreciated.
john
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very interesting. i suppose you could consider the worse case, and assume the rebar are true cylinders that roll perfectly on each other and are "nested" together with minimum air space between them. then it becomes a "hydrostatic" pressure problem.
assume steel weighs 490 lb/cubic foot and that for any given storage area all the rebar are the same diameter.
with closest packing of cylinders, about 9% of a given volume is air.
then the unit weight of the assumed "rebar fluid" would be:
490 lb/cubic foot x 91% = 446 lb/cubic foot.
with that, the calcs for (worse case) horizontal pressure are straight forward.
i have been analyzing a problem with similar challenges. i work at a ce testing lab. we receive 100s of 4x8 concrete cylinders each week. not all are tested to failure so we end up with a pile of cylinders. some of our folks take home the cylinders and use them at their homes for fill or lanscaping or whatever.
you cant just stack them on their sides cause they will roll out on you, so i looked at the problem analytically. a free-body-diagram shows the cylinder above rests on the two below and the force of gravity is resisted by two normal forces acting 30 degrees to the side of vertical where the cylinders touch. the forces are pointed inwards toward each other so the horizontal components cancel out. the vertical component of each is half the weight of the cylinder above. this is true for the top row of cylinders.
the layers below have the same reactions to resist the applied forces. now, however, you have the weight of the cylinders and the reactions from the layers above. set up your fbd for the bottom layer of rebar, and you will quickly determine the horizontal pressure necessary to keep the stack static.
after you get this load, apply some magnification factor for something being placed on the stack that shouldn't be there or a man standing on the stack or whatever. you don't want a pile of steel starting to flow! the inertia would be impressive.
good luck.

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