Civil Engineering Reference
In-Depth Information
Figure 9.12
Calculation for deflection at the centre of an interior panel of a two-way
slab accounting for creep and cracking (Example 9.5): (a) top view of an
interior panel; (b) bending moments at mid-span of column and middle
strips due to service load 8.4 kN/m
2
(175 lb/ft
2
).
bottom reinforcements in
x
and
y
directions,
d
0.16 m (6.3 in). Modu-
lus of elasticity of concrete at time
t
0
when the load is applied;
E
c
(
t
0
)
=
=
25 GPa (3600 ksi); creep coe
cient
φ
=
2.5; aging coe
cient
χ
=
0.8;
tensile strength of concrete in
fl
exure (modulus of rupture),
f
ct
=
2.0 MPa (290 psi), modulus of elasticity of the reinforcement
=
200 GPa
(29000 ksi).
E
ective moment of inertia of the gross concrete section of a strip of
unit width (Equation (9.48) ) is
ff
(0.2)
3
12(1
694 × 10
−6
m
4
/m.
I
g slab
=
0.2
2
)
=
−
Poisson's ratio is assumed equal to 0.2.
In this example, the basic de
fl
ection can be calculated using coef-
fi
cients from Table 9.2 which gives:
de
fl
ection at centre of panel
ql
4
E
c
I
g slab
0.00482
=
5.60 mm (0.221 in)
De
fl
ection at mid-span of column strip
ql
4
E
c
I
g slab
0.00342
=
3.97 mm (0.157 in)
Search WWH ::
Custom Search