Concrete Cracking Stress vs. Fatigue
Concrete Cracking Stress vs. Fatigue
(OP)
I didn't get any response in the concrete forum so I'll try here:
In the ACI, there is the value given for modulus of rupture, fr = 7.5 x sqrt(f'c). This is the theoretical stress at which normal weight concrete will crack. For 4000 psi concrete this is about 474 psi.
My question is this. When concrete is stressed to something less than that value, whether it be 100 psi or 300 psi, it isn't supposed to crack. But if that concrete is subjected to repetitions of stress at these lower values, does the concrete fatigue (like steel) and crack at the lower stress levels after so many cycles?
If so, is there any documentation of this anywhere that would suggest acceptable stress levels with repeated loading? Like the AISC fatigue tables for steel stress ranges?
In the ACI, there is the value given for modulus of rupture, fr = 7.5 x sqrt(f'c). This is the theoretical stress at which normal weight concrete will crack. For 4000 psi concrete this is about 474 psi.
My question is this. When concrete is stressed to something less than that value, whether it be 100 psi or 300 psi, it isn't supposed to crack. But if that concrete is subjected to repetitions of stress at these lower values, does the concrete fatigue (like steel) and crack at the lower stress levels after so many cycles?
If so, is there any documentation of this anywhere that would suggest acceptable stress levels with repeated loading? Like the AISC fatigue tables for steel stress ranges?






RE: Concrete Cracking Stress vs. Fatigue
Macgregor and Wight give similar numbers, about 55% of the static strength.
The %'s above are also noted in ACI 215 "Considerations for Design of Concrete Structures Subjected to Fatigue Loading". ACI 215 is also cited by Macgregor and contains some further information, S/N curves and shows the use of the Goodman diagram mentioned in Nilson.
RE: Concrete Cracking Stress vs. Fatigue
RE: Concrete Cracking Stress vs. Fatigue
Edited by Mark Fintel
Van Nostrand Reinhold Company
1974
Section 6.9, page 170, Fatigue of Concrete
Section 22.4.5, page 646, Fatigue
Thees sections discuss fatigue. They include S-N curves, Goodman diagrams and also recommend a limit of 50% of the modulus of rupture as the limiting value for fatigue. Table 22-4 on page 648 shows the % of modulus of rupture and the number of allowable repetitions. Below 50%, unlimited repetitions. The table goes from 51% (400,000 repeitions) to 85% (30 rpetitions).
RE: Concrete Cracking Stress vs. Fatigue
I was looking for information on stress levels with various repetitions (like what eureka indicated).
Non-prestressed.
eureka, does it indicate what repetitions are suggested for 66%?
RE: Concrete Cracking Stress vs. Fatigue