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Re: Two way slab designed as one way

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As was pointed out by Dick Horning and Walter Sawruk, you *can* design a 12' 
X 16' as a one-way slab, but cracking due to flexure in the long direction 
will occur.

*All* slabs supported on 4 sides will behave as a 2-way slab, however, the 
maximum moments for a slab with a 2:1 aspect ratio or greater will be the 
same as considering the slab as a one-way slab spanning in the short 
direction.  This does not mean that there will no negative bending moment in 
the long direction over the support spanning the shorter distance.  
Therefore, negative moment reinforcing *must* be placed in the slab at that 
support.  A good rule-of-thumb is to use the same negative moment steel as 
used in the short direction and extend it the same distance.  Some positive 
moment steel should also be placed in the long direction as can be recognized 
if a set of yield lines are sketched.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona