Seismosoft | Earthquake Engineering Solutions

Hi Tim,
The EC8 Part-3 shear capacity expression (A.12), which has been implemented in SeismoStruct v7) is rather complicated and the combined effect of the different parameters can create confusion in several occasions.

1) The (A.12) formula cannot be employed for sections in the middle of the element of the force-based element. This is because in the middle integration sections the h-x term (i.e. depth of section – compression zone) assumes unpredictable and unrealistic values, as almost all the section is under compression. The result is conservative, but extremely conservative, as you have realised in your project
2) h-x (and consequently the axial force contribution) are zero, when the element is fully under compression. This is reasonable though
3) The plastic ductility demand also plays a significant role and decreases the concrete contribution cosiderably
4) Lv also assumes extreme values when M or are close to zero, as for instance in cantilevers (in A.12 both Lv and 1/Lv are present). In SeismoStruct ther are limits from 0.1L to 2.0L, but still the variation is large
All these mechanisms combined together often give the impression that there is something strange in the implementation

Seismosoft Support

Note that we have made several changes in the upcoming release of SeismoStruct (the development will be completed in 2-3 weeks and it will be published in 3-4 months time), the most important of which is that the axial force contribution is calculated for the entire element (i.e. all the integration sections of the element and not for each section independently). In the tests that we have carried out, we got much more predictable results.

In any case, for you particular project, we would suggest that you simply ignore the results for integration section (b), (c) and (d) as extremely conservative. You will notice that the results at the two edges (a) and (e) make much more sense.

Seismosoft Support

dear all;
i observe that the problem still appears in current edition,
i got very small capacity along section (c) manly
best;

Dear Thaer,

The Seismosoft Support post refers to the SeismoStruct 2016, which is not published yet.