Environmental Engineering Reference
In-Depth Information
according to DIN 1045-1 Table 20 [33]
2
21
214
¼
0
:
r
s
¼
0
:
2
:
21
%
4.8.3 Special aspects of construction with precast concrete elements
Compared with prestressed in situ concrete, higher demands are placed on the
overstressed joints because outside the zones directly affected by the tendons it is
not possible to verify the crack width limitation at the joints.
No tensile stresses are permissible in the load case “G
k
þ
P
m
1
þ
0.4
Q
k,W
” according
to DIN 4228 [15] 6.3 (decompression limit state). Similarly, according to DIN 4227-3
[63], the following applies for this case:
s
c
;
Gk
þ
0
:
9
s
cpm
1
þ
0
:
4
s
c
;
QkW
1
:
0 MPa
According to [63] 7.1, the crack formation limit state must be investigated for the
characteristic load combination (
¼
normal load according to [15]). It is not necessary to
verify the crack width at the joints provided
s
c
;
Gk
þ
0
:
9
s
cpm
1
þ
1
:
0
s
c
;
QkW
2
:
0 MPa
In this case it is to be expected that the tendons, including their ducts, remain
overcompressed for a temperature gradient in the wall amounting to
T
¼
15 K.
Figure 4.24 shows the effect of a temperature gradient over the wall thickness.
D
Fig. 4.24 Restraint stresses as a result of a temperature gradient
:
=
60 E
cm
¼
36800 MPa
Example
C 50
2 36 800 10
5
s
c
;D
T
¼15
=
¼2
:
8 MPa
s
c
;
n
2
:
0 MPa
N
¼ s
c
;
n
b x
ð2 s
c
;D
T
=
b
Þ
x
=
2
0
:
5
0
:
5
ð
x
=
b
Þ¼ðs
c
;
n
=s
c
;D
T
Þ
¼ð2
:
0
=
2
:
8Þ
¼ 0
:
84
Otherwise, Equation (2) in [63] results in the joint crack width in the vicinity of tendons
being effectively limited to w
k
0.04 mm:
d
p
r
Ds
p
10
4
with r
¼
10 according to 1
½
Table 2 for ribbed bars
:
