Impact Loading of Weight Drop

[eigen21]

To solve sudden drop of weight to the beam

I'm currently utilizing equation in Sec 2.8-3 'Design of Welded Structur' y Blodgett.

F = Wb + sqrt(Wb^2+2*K*Wb*h)

My problem is that actuall 'K' is too big So, I'm getting too big F

supporting strucure is too stiff (depth is 6' slab) also loading is not applied on the almost cornor of the slab causeing too small deflection under unit load
So, this results in very high stiffness

If we use the above equation and assume infinite stiffness, small drop (like 0.1") will cause infinite F !
It does not look make sense to me

This book is saying that 'As the weight of the supporting member (Wm) increase, this impact factor of (2) becomes less'

Do you have any solution or idea how that factor (2) can be decrease? I tried to derive the solution, but that was not succeessful.

My case is Wb = 200k ,h = 0.51", and
K = 20,000 k/in (from FEM model)

If I use the above equation DLF is more than 30!
It's too much to consider that drop of the weight.

Do you know how to handle this proble ?

 

[GregLocock]

I think you need to step back and look at your assumptions. Impact loadings are very difficult in practice, and there have been several threads on them in the past.

The reason you simplistically get infinite stresses from an infinite stiffness is that in effect you have assumed an infinite Young's modulus, and since the beam has to absorb a certain amount of energy it must deflect. You haven't left it many options.

The worst equation in the whole world (possibly an exaggeration) is the one for 'deflections from a suddenly applied load', two times the Force you first thought of. It is not actually wrong in context, but it is not conservative in many cases, and it is misleading.


Cheers

Greg Locock

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