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Re: need help with slab

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Neglecting the rotational stiffness of the beams increases the moments but
not to the extent you are saying. The discrepancy in the moments could be
that the concrete weight of the structure was added more than once when you
modeled it the first time.

Hasan Hindawi

> Hello,
> I differ with my boss on the result of a rectangular slab 25x17mts
> (82x58ft) with 70cm (28in) beams on both directions spaced 170cm (67in).
> Uniform surface load, line suport with no rotational stiffness.  First I
> modeled it in Etabs as a system of T shaped beams.  Then I modeled it in
> SAFE as a slab with T shaped beams.  The max moments in the central beam
> were 78.6 t*m and 78.2 t*m (567 kip*ft).  My boss tells me that those
> results are wrong, that the system should be analyzed as a flat slab.  As
> flat slab without beams the max moments in the slab are 30.9 t*m/m (223.5
> kip*ft/ft) which multipied by the beam spacing mean that the middle beams
> would get 30.9*1.7 = 52.53 t*m (380 kip*ft).  Are my results overly
> conservative? Or is my boss's idea unsafe? I don't have much experience,
> any help will be welcome
> thanks in advance
> Tomas Matta