Loadbearing structures and detailed design - Concrete Structures for Wind Turbines - page 163

The S-N curves for repeated compressive loads are as follows:
When 0 < S cd ; min < 0 : 8, then

log N 1 ¼ð 12 þ 16 S cd ; min þ 8 S cd ; min Þð 1 S cd ; max Þ (4.7)

log N 2 ¼ 0 : 2 log N 1 ðlog N 1 1Þ (4.8)

S (4.9)
The critical numbers of fatigue cycles log N are defined according to Equations 4.10 to
4.13:

log N 3 ¼ log N 2 ð0 : 3 3 S cd;min = 8Þ=D

If logN 1 6 then

logN ¼ logN 1

;

(4.10)

If log N 1 > 6 and D S 0 : 3 3 S cd;min = 8 ; then

(4.11)

log N ¼ log N 2

If log N 1 > 6 and D < 0 : 3 3 S cd;min = 8 ; then

S

(4.12)

log N ¼ log N 3

with S cd;min and S cd;max according to Eqs :ð4 : 2Þ and ð4 : 3Þ:

(4.13)

D S ¼ S cd;max S cd;min

Equation 4.14 applies for the S-N curve for plain concrete subjected to a repeated
tensile load:
logN ¼ 12 ð 1 S td ; max Þ (4.14)

where S td;max ¼ g sd s ct;max = f ctd;fat

(4.15)

and f ctd;fat ¼ f ctk; 0:05 = g c

Figure 4.31 shows the S-N curve for a repeated tensile load.

Fig. 4.31 S-Ncurve for concrete subjected to a repeated tensile load according toModel Code 90 [66]