5 · Flat Slab Design
Direct design method for an interior panel — Cl. 31 of IS 456:2000.
Design depth, D
slab only
250mm
Effective depth, d
D − cover − ø/2
224mm
Clear span, lnCl. 31.4.2.2
l1 − c1
5.550m
Design load, wu
1.5 (DL + LL) with the flat-slab self weight
18.38kN/m²
Mo = wu·l2·ln²/8Cl. 31.4.2.2
18.38 × 6.000 × 5.550² / 8
424.497kN·m
Negative design moment (0.65 Mo)Cl. 31.4.3.2
275.923kN·m
Positive design moment (0.35 Mo)Cl. 31.4.3.2
148.574kN·m
Strip distribution
Cl. 31.5.5Column strip — negative (75 %)
206.942kN·m
Column strip — positive (60 %)
89.144kN·m
Middle strip — negative
68.981kN·m
Middle strip — positive
59.430kN·m
Column strip widthCl. 31.1.1
2 × 0.25 × min(l1, l2)
3,000mm
Middle strip width
l2 − column strip
3,000mm
Negative moment — top steel
Moment per metre width
column strip moment / strip width
68.981kN·m/m
Ru
1.375N/mm²
pt design
0.3391%
Ast required
759mm²/m
Spacing required
148.9mm
Ast provided
754mm²/mFAIL
Positive moment — bottom steel
Moment per metre width
29.715kN·m/m
Ast required
314mm²/m
Ast provided
754mm²/mOK
Critical perimeter, boCl. 31.6.1
at d/2 from the column face
2,696mm
Punching force, Vu
wu × (tributary area − critical area)
653.15kN/m
τv = Vu/(bo·d)Cl. 31.6.2
1.082N/mm²
βc
short side / long side of the column
1.000
ks = 0.5 + βc ≤ 1.0Cl. 31.6.3.1
1.000
Permissible ks·τc
ks × 0.25 √fck
1.250N/mm²
Verdict
τv ≤ ks·τc
SAFE in punching shearOK
| Location | Bar | Spacing | Ast req. | Ast prov. | Status |
|---|---|---|---|---|---|
| Column strip — TOP over the column | ø12 | 150 mm c/c | 759 mm²/m | 754 mm²/m | REVISE |
| Column strip — BOTTOM at midspan | ø12 | 150 mm c/c | 314 mm²/m | 754 mm²/m | OK |