Environmental Engineering Reference
In-Depth Information
According to DIN 1045-1 [33], the limiting diameter d
s
for a given crack width w
k,cal
is
E
s
f
ct
;
eff
s
d
s
¼
6
w
k
;
cal
sII
Using the bond coefficient
j ¼
0.7 for a ribbed prestressing tendon, the reference value
for the concrete tensile strength f
ct0
¼
3.0MPa and E
s
¼
200 000MPa, we obtain
E
s
j
f
ct
;
eff
Ds
w
k
;
cal
Ds
f
ct
;
eff
f
ct0
d
p
¼
6
w
k
;
cal
¼
252
10
4
p
p
Comparing the coefficients of the formats for d
p
and d
p
on the basis of f
ct,eff
¼
f
ct0
results in the crack width required:
r
¼
10
252
¼
0
w
k
;
cal
:
04 mm
4.9 Fatigue limit state
In prestressed concrete loadbearing structures, fatigue analyses must be carried out for
the concrete, reinforcing steel and prestressing steel (and its anchorages). These
analyses may be performed according to the stipulations of the DIBt Guideline [9]
in line with the method of analysis given in Model Code 90 [66].
The level of prestress should be chosen in such a way that no decompression
occurs under fatigue loads. This approach enables the stress ranges in the prestress-
ing steel to be limited and prevents cracking of the cross-section, which could lead to
damage!
The following equation should be used instead of the quasi-permanent design load case:
s
c
;
Ed
¼ s
c
;
Gk
þ
r
inf
þ c
2
;D
T
s
c
;D
Tk
0
s
c
;
pm
1
þ c
1
;
W
s
c
;
Wk
þ s
c
;
Hs W
ðÞ
where
s
c,Gk
stress in concrete under permanent actions
s
c,pm
1
prestress taking into account the loss of prestress over time at time t
!1
,
with the scatter factor r
inf
according to DIN 1045-1 [33] 8.7.4 (2)
s
c,Wk
stress in concrete under characteristic wind loads (see Sections 4.5.3 or
4.6.4), with the combination factor
c
1,W
¼
0.5 for frequent wind loads
s
c,Hs(Wk)
stress in concrete under the action effect resulting from characteristic sea
state loads for characteristic wind loads with the significant wave height H
s
(V(W
k
)), see Sections 2.5.6 and 4.6.4
s
c,
D
Tk
stress in concrete under characteristic thermal actions, with the combination
factor
c
2,
D
T
¼
0.5 for quasi-permanent action effects (according to DIN
Special Report 101)
Note: The maximum values of the wind loads under the EWM wind conditions (see
Section 2.3.2) should be used as the characteristic wind loads.
