According to EN 1992-1-1 (2004) chapter 7.1.(2) the concrete can be assumed uncracked if the flexural tensile stress is less than fct,eff. In which limit state does one calculate the flexural tensile stress ? In Serviceability Limit State caracteristique, frequent or quasi-permanent ?
"(2) In the calculation of stresses and deflections, cross-sections should be assumed to be uncracked provided that the flexural tensile stress does not exceed fct,eff. The value of fct,eff may be taken as fctm....."
If you are evaluating the ultimate limit state the section can be assumed to be cracked. When you are checking serviceability then the point of cracking will draw the line between linear elastic and inelastic effects or behaviour. Thus typically that check is done for assessing sls such as deflections and crack control.
The SLS Section 7.1(2) deals with the determination of the flexural stiffness EI to be used when computing stresses and deflections. Therefore, I believe it should apply for any load combination relevant in the SLS (Section 5.1.3, and EN 1990 (Sect. 5). Hopefully, this may be of some help.
@Martinez-Vasquez
Thank you for the answer. The question remains : What limit state is the bending moment (= cracking moment) that gives a (flexural) tension of fct,eff in the concrete (just before cracking).
@ Hellesland
One and the same bendingmoment (M = ftm,eff (I/v)) can not be 3 limi!t states at the same time ? or is it ? odd, isn't it ?
Pieter,
The cracking of structural concrete is always checked at the serviceability limit state, as the exceedance of such limit state does not mean the collapse of the structure. Concerning which combination of actions to be considered for the verification of the decompression or cracking limit state, this will depend on the effects of the cracking in the particular structure and is a owner decision. Generally speaking, we can say that if the SLS is irreversible, then you can use the characteristic combination of actions. If the SLS is reversible ( as for instance cracking in prestressed concrete, where the crack closes after removal of the extrnal load), then you can use the frequent combination of actions.
I hope this helps to answer your question
Hello Pieter. The cracking moment is not a limit state itself. The cracking moment is a reference value that tells you when the section will stop an asssumed linear elastic behaviour. Typically you integrate Mcr in deflection control whose limit is a serviceability limit state e.g. L/250. Hope this helps.
@Joan R Casa
Thank you, very interesting approach
@Martinez-Vazquez
"The cracking moment is not a limit state itself" Very well put : I tend to agree with you!
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