Rerounding effect

[Bas]

Hi,

In dutch standard NEN 3650-1:2020 C.4.2.5.2.2 it is mentioned that, for specific conditions, usage of horizontal soil support is allowed.
But only without usage of the rerounding effect (frr).

Is it possible to set ffr=1 in PLE?

[Dr. J Foerster]

No, the rerounding effect can tot be disabled in Ple4Win.

But it is actually not necessary as the NEN standard describes the conditions under which horizontal soil support is allowed and what tests to perform to see if it is applicable.

In short, without internal pressure horizontal soil support may always be applied, with pressure a check has to be performed if the ovalisation reduction due to horizontal soil support is larger than the rerounding effect.

[Bas]

..with pressure a check has to be performed if the ovalisation reduction due to horizontal soil support is larger than the rerounding effect.

The way I interpret that chapter:
C.4.2.5.2.3 describes what you said above: When horizontal soil support reduction is larger than the rerounding effect (frr < dy2/dy1) horizontal support is allowed (disregarding water level for now).
In C.4.2.5.2.2: When horizontal soil support reduction is smaller than the rerounding effect (frr > dy2/dy1) horizontal support is also allowed, but only without rerounding.
(In both cases assuming internal pressure)

[ir KW Radder]

In NEN 3650-1:2020 the rerounding effect due to internal pressure is taken into account by multiplying the circumferential stress with frr, a factor < 1. See the equation in D.3.1 on page 187.  So in case of hand calculations the factor frr can be set to 1. In Ple4Win the circumferential stresses due to all cross-sectional loadings including the internal pressure are calculated by means of a 6th order  differential equation through Fourier series. So simply disabling the rerounding effect  is not possible. 

The rerounding results in a reduction of the circumferential stresses. If it is not allowed to include the rerounding in the calculations, a work-around would be to increase the circumferential stresses by multiplying with the value 1/frr. This can be done by a weighing factor for SFIORA in input table SWEIGH in DF6.2.