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Re: Finite Element Modeling

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>When using finite element analysis to model a concrete slab on ground,  what 
>would be the advantage of using elastic blocks, rigid blocks, and torsion 
>bars to model the slab rather than shell elements?
The biggest disadvantages are the additional time it takes to figure out 
the individual equivalent stiffnesses and the possibility of making a 
gross error. In doing these kinds of equivalents you also apply an 
certain amount of kentucky windage to determine the effects of 
interactions. This is roughly similar to figuring a stiffened plate using 
an equivalent moment of inertia including a certain width of plate to 
either side of the stiffener. There are several different rules of thumb 
for this equivalent width, depending on the effects to be calculated. 
I've spent much more time discussing this with people who liked to keep 
things 'simple' than I would have just doing a finite element model that 
would include the interactions automatically.

The disadvantage of the finite element model is providing results which 
accord with concrete code practice for client presentations. You need to 
make a reasonably accurate model but including such things as cracks can 
get pretty ugly, since real world cracks are a lot more complex than the 
absence of material.

Christopher Wright P.E.    |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw



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