Design of flat slabs by IS: 456 The term flat slab means a reinforced concrete slab with or without drops, supported generally without beams, by columns with or without flared column heads (see Fig. 12). A flat slab may be solid slab or may have recesses formed on the soffit so that the sof fit comprises a series of ribs in two directions. The recesses may be formed by removable or permanent filler blocks. Components of flat slab design: a) Column strip :
Column strip means a design strip having a width of 0.25 I,, but not greater than 0.25 1, on each side of the column centre-line, where I, is the span in the direction moments are being determined, measured centre to centre of supports and 1, is the-span transverse to 1,, measured centre to centre of supports. b) Middle strip : Middle strip means a design strip bounded on each of its opposite sides by the column strip. c) Panel: Panel means that part of a slab bounde d on-each of its four sides by the centre-line of a Column or centre-lines of adjacent-spans. Division into column and middle strip along:
7 Longer span Shorter span L =6.6 m , L =5.6 m 1 2 ( i ) column strip = 0.25L = 1.4 m 2 But not greater than 0.25 L = 1.65 m 1 (ii) Middle strip = 5.6 – (1.4+1.4) = 2.8 m L =5.6 m , L =6.6 m 1 2 ( i ) column strip = 0.25L = 1.65 m 2 But not greater than 0.25 L = 1.4 m 1 (ii) Middle strip = 6.6 – (1.4+1.4) = 3.8 m