What use has the ‘Pillar design’ option in the special analysis with FAGUS, from STATIK?

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Among the special analyses that we can do with STATIK, we have the reinforced concrete special analysis with FAGUS. On the lower part of the box, we find the ‘Pillar design’ option:

 

The ‘Pillar design’ option only affects the way the tabulated results for the wall pillar elements is given, that is, if the box is checked the information will be given to us depending on how the reinforcements of the cross sections of the elements in CEDRUS are named, and if it is not checked, the results are shown normally. By default, the reinforcements on the ends are called N1 and N2 and the reinforcement spread over both its faces is called W1:

 

If we continue with the example given in this other article:

- Checking the box:

The results output called ‘Wall reinforcement’ will activate and we will see the following:

 

If we do not check the box, we will directly stop seeing the results output, obtaining the standard output only.

 

If we compare the values, for example of bar L1-P1 (distance 0.00), we can see that on the first table we obtain a total longitudinal reinforcement of Astot = 2986 mm2 (N1+N2+W1). If we compare this value with the one on the second table for Aso(M,N) = 2235 mm2, we can appreciate that there is a difference of 733 mm2. This difference is due to the fact that the program adds, on the first case (conservatively), the increment of longitudinal reinforcement needed because of shear. If we control this section with FAGUS and we select the most critical force line:

 

The highlighted value on the previous figure is the necessary longitudinal reinforcement on  only one face due to the shear on the cross section. Multiplying this value by 2 we get the 733 mm2 we mentioned above (if we calculate 367x2 = 734, this is because, truly, the value 367 is a round up of 366.5).

NOTE: if we compare the value of Astot = 2986 mm2 with the one obtained for Aso(M,N,V) = 2936 mm2 we can observe a difference that occurs because to obtain the second value, a different calculating process is carried out. The first one is a direct sum of the necessary longitudinal reinforcement due to shear and the one needed due to the normal stresses on the section. The second one come from calculating the longitudinal reinforcement considering the shear force on the cross section (moment diagram offset).

 

An additional comment that may be of interest in some cases is that, if we look at the previous table we see that, because it is a pillar, we will only be give reinforcement values on one column of the table, and no values will appear on the ‘bottom reinforcement’ column. This indicates that the program assumes the reinforcement will be symmetric in this kind of elements. If we were analysing beams, we would obtain results in both the top and bottom reinforcement columns.