Slab Deflection Results Reading

[faisal.aaouatif]

Good Morning/Evening

Please indicate if the deflection results should be read directly from the RSA display ( see attachement ) or one should substract values under slab supports (Beams in this case) :

1. Defl at center = 1.90 mm

2. Defl at center = 1.90 - 0.81 = 1.09 mm

Thank you

[EduardoMeruvia]

Hi faisal.aaouatif, 

The 1.9mm settlement on your slab at the middle is the total "displacement" of your panel at that point i.e. That is the global displacement of you panel as a whole. 

If you checking your panel/slab for SLS 'Deflections' then the total DIFFERENTIAL deflection is what you should be looking at i.e. the 1.9 - 0.81 = 1.09mm as this is the "TRUE" bowing of your slab. Similar logic can be applied to beam members. 

Hope this helps. 

[faisal.aaouatif]

Thanks for your reply Eduardo ,

This is what i am expecting : deflections is a displacement difference between two points , one point on a support (or not) , the other on the element investigated.

I dont know if it is convenient to talk about deflection in slabs unless we precise in regard to what ( for beams , its a little bit clear because support are identified and are nodal )  , especially for slabs with different supports stiffness's.

My design process is to verify slab "Primary supports" ( horizontal ) deflections in regard to their supports ( vertical ) , especially if they are embedded in the slab ,  and then verify the deflection of the slab itself to these Primary supports, by subtracting their "displacement" from slab's one. ( values displayed in the "Deflections map )

What do you think about that ?

A little Remark to Rafal/Artur , wouldn't be convenient to uniformise terms in this userform and similar ? ( see attachement please )

Thanks a lot.

[EduardoMeruvia · Accepted solution]

I think your approach as outline below is suitable for the checks you are doing. 

The Differential displacements in a slab is its final deflected shape and should be used as such, as more often than not this "differential" deflected shape produces a greater curvature in the slab/beam. See figure below; 

 Slab Deflections

 Of course in two-way slabs such in your case, you would need to check these deflections in both ways respectively. Specially if the slab is rectangular with a large Width to Length Ratio.