A. Pérez Caldentey/H. Corres Peiretti/J. Peset Iribarren/A. Giraldo Soto · Cracking of RC members revisited: influence of cover, φ/ρs,ef and stirrup spacing – an experimental and theoretical study
Fig. 5. The effect of cover on crack spacing: beam 25-20-00 has a mean crack spacing of 13.1 cm, whereas beam 25-70-00 has a crack spacing of 22.7 cm
Model Code 90 [15], are incomplete. From a theoretical point of view, the effect of cover on crack spacing can be understood by the need to transmit tension stresses generated at the bar-concrete interface to the effective concrete area surrounding the bar in order to generate actual cracking. However, this is only part of the explanation of how cover affects crack spacing. Another aspect of the influence of cover on crack spacing has to do with secondary cracks and whether or not these cracks eventually become passing cracks. This topic is addressed in more detail in section 3.2.
2.3.3 Influence of φ/ρs,ef The influence of the φ/ρs,ef ratio on crack spacing is a direct consequence of the definition of the transfer length and can be easily derived from the equilibrium of the bar between a crack and the zero slip section and from the equilibrium of the two sections. The influence of this factor on crack spacing can easily be compared by counting the number of cracks in specimens having the same cover. Fig. 6 shows this comparison. A clear influence can be
Fig. 6. Influence of φ/ρs,ef on mean crack spacing
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seen as the crack spacing increases with the value of φ/ρs,ef. These results seem to show a larger influence of this parameter for a smaller cover. This seems logical since crack spacing can be modelled as the sum of the effect of cover and the effect of φ/ρs,ef, as shown in Eq. (4): sr,m = k1c + k2
φ ρs, ef
(4)
As the cover c increases, so the relative importance of the second term in φ/ρs,ef becomes smaller. In Eq. (4), k1 and k2 are constants.
2.3.4 Influence of stirrup spacing Most cracking tests carried out avoid the presence of stirrups, because they influence the cracking pattern. A good example of this can be seen in the tie cracking tests carried out by Gómez Navarro [16] in Lausanne, shown in Fig. 7. It can be very clearly seen in these tests that cracks form every 10 cm on the sides where stirrups are placed at this distance and at 20 cm in the central part of the tie,