Civil Engineering Reference
In-Depth Information
strength of the concrete to be taken into consideration; as a
result designers can reduce predicted defl ection by increasing
the concrete strength. A fl ow chart describing the process for
checking defl ection is presented in
Figure 17.7
.
Where the stress in the reinforcement is relatively low the
defl ection will be lower, and the modifi er given in Expression
(7.17) allows for this. Eurocode 2 assumes that the stress in
the reinforcement is 310 MPa under quasi-permanent loading.
When the stress is below this level, as it will almost invariably
be, the basic span-to-effective-depth ratio can be increased. The
stress at the serviceability limit state can be calculated from
fi rst principles using a triangular stress block for the concrete,
Column Position
Factor,
β
Internal
1.15
Edge
1.4
Corner
1.5
Table 17.8 Values for
β
Punching shear design
d
eff
d
ef
d
= (
ddd
+
ddd
)/2
= 0.2 (1-
f
ck
f
ck
/250)
f
ck
f
ck
or refer to column 3 of
Determine factor,
β
. from Ta ble 17.8 or
from Expressions in Cl. 6.4.3 of EN
1992-1-1
v
Rd,max
v
Rd,max
Ta ble 17.6)
(
v
Ed
v
Ed
- 0.75v
Rd,c
)
s
r
u
1
1.5f
ywd
A
sw =
Determine shear stress at column face,
v
Ed
where
v
E
v
=
β
V
Ed
V
E
V
/(
uuu d
eff
d
ef
d
)
=
V
Ed
V
E
V
/(
u
1
d
eff
d
ef
d
)
v
Ed
v
E
v
= Design shear stress resistance of concrete
Determine,
v
Rd,max
v
Rd,c
v
Rd,c
v
Rd,max
without shear reinforcement
= Radial spacing of the shear reinforcement
s
r
Is
v
Ed
v
Ed
ax
?
≤
v
Rd,m
v
Rd,m
= length of basic control perimeter, 2
d
from
d
from
u
1
the face of the column
Calculate
v
Rd,c
v
Rd,c
See Ta ble 17.7
= length of column perimeter
u
1
f
wyd
= design strength of the shear reinforcement
Find position of outer control perimeter
(the point at which shear reinforcement
is no longer required) i.e. Distance
from column face,
f
wyd
= (
β
V
Ed
V
E
V
/(
v
Rd,c
v
Rd,c
d
ef
d
)) -
uuu
)/2
π
d
eff
r
out
r
out
Ye s
Punching shear
reinforcement
not required
Is
r
out
r
out
≤
2
ddd
No
Determine the area of punching shear
reinforcement per perimeter,
A
sw
.
This should be provided around every
perimeter within 2
d
Is
r
out
r
out
≥
3.5
d
?
No
Ye s
Additional perimeters required up
to
r
out
r
ou
r
- 1.5
d
from column face.
Calculate
A
sw
for each additional
perimeter
Carry out reinforcement detailing
Figure 17.6 Design process for punching shear reinforcement
