RC slab deflection control - wich lenght to take into account

[mar2805]

Hello!
Please see pictrue attached.
My code (EUROCODE) defines that for contoling deflecion of RC slab one must see that the deflections are under the value of L (shortest slab span) divided by 250.
Wich value for L would you take for this scenario?
The walls are made from confided masonry and are 25cm thick.
RC beams are 25/50cm. Slab is 20cm thick

 

[Lomarandil]

The slab will primarily (but not entirely) span back toward the transverse beam and the rest of the building.

So the span in blue is the correct span to use. Check whether Eurocode modifies the L/250 guidance for a cantilever.

 

[rapt]

Deflection for each span of each element should be checked.

For a 2 way slab where there is a single mid-span deflection that is actually the deflection of the slab in both directions, the shorter span L will control.

 

[Struct123ure]

Deflection should be checked for all spans meaning the blue L/250 cantilever should be checked for downward deflection and the span between the columns (Red subtract blue)should be checked for deflection upward.
The deflection limits are given for simply supported beams. For cantilevers the deflection limit is 2 times since a cantilever is half of the simply supported beams. In your case the cantilever limit would be L/125 (see attached).
I believe you are looking at EN.1992.1.1.2004 "Design of concrete structures - General rules and rules for buildings" (maybe the newer version) and deflection control is covered under 7.4. Part 5) says deflections that could damage adjacent parts of the structure should be limited. The reason I bring this up is because at the end of the cantilever you have concrete columns which hold up more structure above(roof). For transfer elements I like to design for L/600, but in Eurocode I guess L/500 would suffice. The reason being if you have a 3m cantilever and it goes down L/125 you are looking at serious cracking and other elements could be pulled out of plumb above.
Using the more stringent L/500 which converts to L/250 for cantilever which is what you have been designing for already.