Civil Engineering Reference
In-Depth Information
the simplified design equations along with the partial safety factors
suggested in sections 3.16 and 3.17 have been utilised (Ray, 1980; 1983).
Example: Beam with web opening
Data: symmetrical two-point loading;
L=750 mm, D=750 mm;
X
N
=250 mm;
Bearing width=75 mm;
W
=330 kN;
f
'
c
=22
.
5 N/mm
2
;
f
'
cu
=30 N/mm
2
;
f
'
t
=3 N/mm
2
;
f
sy
=250 N/mm
2
.
Opening size:
a
1
x
=100mm;
a
2
D
=150mm;
Co-ordinates of opening centre:
K
1
X
N
=137.50 mm,
K
2
D
=475 mm.
Design procedure
i) Main steel
A
s
:
Design moment
M
=5775×10
4
Nmm
The design moment should not exceed
(3.49)
From Eqns (3.49) and (3.50) on simplification,
A
s
=778.4614mm
2
. Provide 2
-25 mm diameter bars (981 mm
2
) as main steel.
ii) Beam width: The web opening parameters are shown evaluated in Table
3.1. The shear resistance of concrete alone given by the first part of Eqn
(3.45) is:
Table 3.1
Web opening parameters
It is assumed that the contribution of concrete for resisting shear is about
(0.65×50%) of that of the solid web. That is,
0.65×115.50×10
2
=75.075×10
3
N
Simplifying Eqns (3.51) and (3.52)
b
=239.8322mm;
b
=200 mm (say)
iii) Shear strength of beam with tensile steel only. Using the first two terms
of Eqn (3.45):
(3.52)
(3.53)
