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Figure 6.1. Rectangular section with virtual neutral axis

Indicating respectively by pit and fet the resultant and its position about the whole length x and by (3ib and p2b the similar quantities about the x-h part, the resultant (3 and its position (4 compared to the most compressed edge and in relation with depth h are given by:

The (3 and (4 values for a number of x/h ratios are given in Table 6.3.

Table 6.3. ß3 and ß4 values parabola - rectangle costitutive law

Table 6.3. ß3 and ß4 values parabola - rectangle costitutive law

 x/ fck = 50 N/mm2 fck = 55 N/mm2 fck = 60 N/mm2 fck = 70 N/mm2 fck = 80 N/mm2 fck = 90 N/mm2 /h ¡33 ¡4 ¡3 ¡4 ¡3 ¡4 ¡3 ¡4 ¡3 ¡4 ¡3 ¡4 1,00 0,80952 0,41597 0,74194 0,39191 0,69496 0,37723 0,63719 0,36201 0,59936 0,35482 0,58333 0,35294 1,20 0,89549 0,45832 0,83288 0,43765 0,78714 0,42436 0,72968 0,41022 0,69249 0,40355 0,67720 0,40186 1,40 0,93409 0,47480 0,88197 0,45841 0,84129 0,44724 0,78831 0,43492 0,75381 0,42907 0,73986 0,42761 1,60 0,95468 0,48304 0,91168 0,46990 0,87615 0,46046 0,82826 0,44975 0,79679 0,44461 0,78422 0,44335 1,80 0,96693 0,48779 0,93113 0,47702 0,90007 0,46895 0,85695 0,45954 0,82834 0,45499 0,81702 0,45389 2,00 0,97481 0,49077 0,94460 0,48178 0,91730 0,47478 0,87838 0,46644 0,85234 0,46237 0,84211 0,46140 2,50 0,98550 0,49475 0,96464 0,48861 0,94420 0,48347 0,91348 0,47705 0,89255 0,47385 0,88448 0,47311 5,00 0,99702 0,49893 0,99060 0,49705 0,98285 0,49512 0,96937 0,49234 0,95972 0,49089 0,95622 0,49057

b2) Rectangular diagram

In this case (x > h) EC2 does not give instructions. It is nevertheless possible to write a formula that gives the equivalent depth h* in relation with x, so that it results h* = x ^hh where the k a factor is determined by imposing that for x = h is h* = X • h. It results:

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