Why are there 2 creep factors?

In Diamonds (and ConCrete) you will see two creep factors $\varphi$ :

Creep factor for stress limit $\varphi_{stresses}$ : this factor is taken into account when checking the steel and concrete stresses in SLS. $\varphi_{stresses}$ is calculated so that the ratio
$\frac{E_s}{E_{c,\infty}} = \frac{E_s}{\frac{E_{c,28}}{1+\varphi_{stresses}}} = 15$

$\varphi_{stresses} = \frac{15 \cdot E_{c,28}}{E_s} -1$

For concrete $C25/30$ this becomes

$\varphi_{stresses} = \frac{15 \cdot 30472N/mm^2}{200 000N/mm^2} - 1 = 1.285$
Creep factor for deformation $\varphi_{deformation}$ : this factor is taken into account when calculating the cracked deformation (only if you opted to calculate with creep). $\varphi_{deformation}$ is determined from EN 1992-1-1 Fig. 3.1, $\varphi_{deformation}=2$ is a ‘standard’ value.

If the creep factor for stresses $\varphi_{stresses}$ would be 2, there is a less probability to ever have to add additional reinforcement because the concrete stresses decrease at increasing creep factor. This would lead to discussions about not calculating sufficient reinforcement.

So to be on the safe side, we need different creep factors for stresses and deformation.

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