Environmental Engineering Reference
In-Depth Information
Fig. 4.27 Stresses for calculating
h
c
according to Model Code 90 [66]
depth. To what extent stress redistributions take place in thicker cross-sections has not
yet been investigated. The limit laid down in Model Code 90 is therefore to be regarded
as an estimate based on engineering experience.
The design value for the fatigue strength of the concrete f
cd,fat
subjected to compression
loads is determined as follows:
f
cd
;
fat
¼
0
:
85
b
cc
ð
t
Þ
f
ck
ð
1
f
ck
=
250
Þ=g
c
(4.5)
where
b
cc
(t) coefficient for taking into account the increase in the concrete strength over time.
(In the simplified analysis according to Equation 4.1 this should be
b
cc
(t)
¼
1.0
provided the first cyclic load takes placewhen the concrete is
28 days old; but if
the first cyclic load takes place earlier, then the factor
b
cc
(t)
<
1.0 has to be
determined and taken into account in the analysis.)
f
ck
characteristic cylinder compressive strength
g
c
partial safety factor for concrete
The factor of 0.85 in Equation 4.5 takes into account how the permanent load
component affects the concrete compressive strength and the difference between
Fig. 4.28 Stresses in the tower shaft for calculating
h
c
