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Figure 7.22. Slenderness limits for total deflection and different total service load to ultimate load ratios

0.C0 5.00 10.00 15.00 20.00 25. OC 30.00 35.00 4C.0C

Figure 7.22. Slenderness limits for total deflection and different total service load to ultimate load ratios

7.4.3.11 Influence of the concrete grade

The influence of the concrete grade on the slenderness limit has been studied in a very detailed manner for many values of the reinforcement ratio. The concrete grades considered are: C30, C40,C60 and C100.

For this comparison, the relationship between total service load and ultimate load has been taken as 51%. This value, is different from the reference value, but, as explained in section 7.4.3.10, agrees well with the values of prEN 1992-1 table 4.14 which are also in accordance with the values of MC-90 and ENV-1992-1-1:1991.

Fig. 7.23 shows the results of this comparison. It can be seen that there is a very significant influence of the concrete grade on the slenderness limit. These curves, also show very well the behaviour for very low steel ratios. There is a clear discontinuity in the curves which separates the point in which cracking does not occur from the point in which the bending moment is greater than the cracking moment. The curves also show that for low steel ratios, much higher slenderness limits can be established. These curves form the basis for the formula proposed for the slenderness limit in prEN 1992-1, which is dependent on the concrete grade, and provides a continuous estimation of the slenderness limit as a function of the reinforcement ratio.

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