Structural Concrete - Hassoun

17.12 Equivalent Frame Method 691
Table 17.14
Design of an Interior Flab Slab with Drop Panels
M 0
= 491.6kN⋅ m
M 0
=+0.35M 0
=−319.5kN⋅ m
M p
=+0.35M 0
=+172.1kN⋅ m
Long Direction Column Strip Middle Strip
Moment factor 0.75M 0 0.60M p 0.25M n 0.40M p
M u (kN ⋅ m) −239.6 ±103.3 −79.9 ±68.8
d (mm) 190 110 110 110
Strip width b (m) 2.7 2.7 2.7 2.7
R u = M u
(MPa) 2.46 3.16 2.44 2.10
bd2 Steel ratio, ρ (%) 0.71 0.93 0.7 0.6
A s = ρbd (mm 2 ) 3642 2762 2079 1782
Min. A s = 0.0018bh (mm 2 ) 1070 680 680 680
Bars selected (straight bars) 18 × 16 mm 14 × 16 mm 20 × 12 mm 16 × 12 mm
Spacing (mm) 150 193 135 170
M 0
= 425.2kN⋅ m
M n
=−0.65M 0
=−276.4kN⋅ m
M p
=+0.35M 0
=+148.8kN⋅ m
Short Direction Column Strip Middle Strip
Moment factor 0.75M n 0.60M p 0.25M n 0.40M p
M u (kN⋅m) −207.3 ±89.3 −69.1 ±59.5
d (mm) 180 100 100 100
Strip width b (m) 2.7 2.7 3.3 3.3
R u = M u
(MPa) 2.37 3.30 2.10 1.80
bd2 Steel ratio, ρ (%) 0.69 1.00 0.6 0.5
A s = ρbd (mm 2 ) 3353 2700 1980 1650
Min. A s = 0.0018bh (mm 2 ) 1070 680 832 832
Bars selected (straight bars) 18 × 16 mm 14 × 16 mm 18 × 12 mm 16 × 12 mm
Spacing (mm) 150 195 185 205
I c (for circular column, diameter 400 mm)
= πD4
64 = π 64 (400)4 = 1257 × 10 6 mm 4
K c = 4E cb I c
= 4E cb × 1257 × 106
= 1676 × 10 3 E
l c 3000 mm
cb
Ratio of column stiffness/slab stiffness (Assume E cb = E cs )
= K c
K s
=
1676 × 103
1016 × 10 3 = 1.65
which is greater than α min of 1.15. If I s in the long direction is used, the calculated ratio of column
to slab stiffness will be greater than 1.65. Therefore, the column is adequate.
6. Determine the unbalanced moment in the column and check the shear stresses in the slab, as
explained in Examples 17.8 and 17.9.