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[ramu_se]

Dear Sir,

Kindly explain how the load is getting distributed in flat slabs to the supporting columns.

Thanks & Regards,
Ramu.

[vikram.jeet]

Flat slab :- As all we know it is beam less slab, slab in itself act  as beams in two directions .

Slab is treated to be divided into Column strips and middle strips, in both directions  ,Refer code IS 456 .

Every thing is explained in IS.

Though transfer of load becomes two way at columns ,, Bending moments are worked out in each direction assuming one way action since each side strength to transfer loading is dependent on other direction  strength of flat slab.

Slab is assumed to be divided into Column strips and Middle strips

There are two methods of analysis :
Direct Design Method
Equivalent frames method

DDMethod :-
Minimum three spans inbeach dir for this method
Absolute mo Mo:-
W= w*Lx*Ly
Absolute BM x =W*Lnx/8
Absolute BM y = W*Lny/8
In absence of column heads Lnx= Lx and Lny=Ly
In case of drops /col heads = Ln is clear span between drops, brackets but not less than 0.65*L

+ve and  -ve Moment allocation :-
-ve Moment = 0.65*Mo
+ve Moment = 0.35*Mo

Moment allocation to strips :-
Column strips (Acting as concealed beams)
-ve moment:-
-ve moment at support for column strip := 0.75 of (0.65*Mo)
-ve moment for Middle strip  = remaining ie 0.25 of (0.65*Mo

+ve moment

+ve moment for Column strip  = 0.60 of (O.35*Mo)
+ve moment for mid strip = O. 40 of (O.35*Mo)

This above is for Internal Panels,,
For external refer code

(To be continued)