BAR BENDING SCHEDULE OF TWO WAY SLAB
FIRSTLY BAR BENDING SCHEDULE OF TWO WAY SLAB We are going to calculate the steel quantity for a two way slab before starting this procedure. We must know how to identify a two way slab. it to a ratio of longer spent to the short span of a slab is less than 2. The slab is Taken as a two way slab . That a one way slab is supported on Beams on two opposite sides and the loads are carried along the short span. In case of two way slab, the supports are provided along all the dimensions. Since the loads are carried along both directions. I am going to show you this method by illustrating it with the help of an example and at the end of this lecture. I will show you how to prepare the table for BBS of to his lab so before starting this process. Suppose we need to calculate the quantity of steel for a slab of length four metre and width three metres, it should be noted that the spans of to be considered by excluding the width of beam from all the sides. Lx is the longer Spam and Ly short span.
SECONDLY GIVEN DATA
1) Size of the room = 4.2m * 5 m
(ii) Edge conditions Simply supported, corners not held down
(iii) Overall depth of the slab 140 mm
(iv) Bearing on Us = 230 mm
(v) Reinforcement
Steel for shorter span = #12 at 220 mm c/c (Alternate bars are cranked at a distance of 400 mm from the face of the support) Steel for longer span = # 10 at 250 mm c/c (Alternate bars are cranked at a distance of 500 mm from the face of the support)
(vi) Covers
Bottom clear cover = 20mm
Top clear cover = 20 mm
Side covers = 25 mm
(vii) Materials
Concrete: M 20 grade concrete
Steel: Fe-415 steel
THIRDLY SCHEDULE OF REINFORCEMENT
(a) Length of straight main straight bar along short span (#12)
=Clear span in shorter direction + 2 x bearings-2x end cover
=4200 + 2 * 230 – 2 * 25 * 4610mm = 4.61m
No of bars=Total length of the slab in longer direction excluding end cover/Spacing of bars+1
[(5000 + 2 * 230 + 2 * 25)/(220 * 2)] + 1 = 13.3Say 14 nos. (Spacing is doubled as alternate bars are cranked)
(b) Length of main cranked bar along shorter span (#12)
=Length of the straight bar 2x crank allowance
=4610 + 2 * 0.414(140 – 2 * 20 – 12) = overline 4610-2*0.414*88
=4683mm = 4.683m
No of bars 14-1= 13 nos.
(c) Length of straight main straight bar along longer span (#10)
=Clear span in longer direction + 2 x bearings2x end cover
=5000 + 2 * 230 – 2 * 25 = 5410mm = 5.41m
No of bars =Total length of the slab in shorter direction excluding end cover/ Spacing of bars+1
=[4200+2×230-2×25/250×2]+1= 10.22 Say 11 nos (Spacing is doubled as alternate bars are cranked)
(d) Length of main cranked bar along longer span (100)
=length of the straight bar + 2 crank allowance
=5410+2×0.414 (140-2×20-10)-5410+2× 0.414 x 90
= 5485 mm 5.485 m
No of bars 11-1=10 nos
(e) Anchor bars to support cranked mein bars along short span (# 8,3 nos on either side)but Length of anchor bårs =length of main bars along the longer span
=5410 mm 5.41 m.
No. of bars 3+3=6
(f) Anchor bars to support cranked main bars along longer span (# 8, 3 nos. on either side)but Length of anchor bars=length of main bars along the shorter span
=4610 mm 4.61 m
No. of bars 3+3=6
FINALLY BAR BENDING SCHEDULE
