By Alexander Meierhofer, Dlubal Engineering Software
With the current RFEM version 4.10.0001 we have released the Austrian NA ÖNORM B 1992-1-1:2011-12 in all add-on modules available for concrete design. The Austrian national annex was introduced on 1st December 2011. Some design rules have been taken over from the German annex so that the safety level has been increased as well for the concrete design according to ÖNORM B 1992-1-1:2011-12. In the following you find a short list of the most significant modifications specified in the new annex ÖNORM B 1992-1-1:2011-12, having a direct influence on the results.
In the serviceability limit state design the following items were modified for the calculation of the minimum reinforcement concerning crack width control acc. to section 7.3.2:
– The limit diameter acc. to table 8 as well as the factor k required to take into account self-equilibrating stresses distributed non-linearly are determined depending on the action types for restraint or loading.
– Limiting the minimum reinforcement for thick structural components is considered additionally.
– The sphere of effectiveness for the reinforcement A_c,eff is calculated in relation to the structural component’s thickness.
In the direct calculation of crack widths acc. to 7.3.4, determining the maximum crack spacing s_r,max acc. to Eq. 7.11 has been adjusted so that now s_r,max depends only on steel stress and reinforcement diameter.
The biggest changes in the Ultimate Limit State were in the proof of punching acc. to chapter 6.4:
– The previously fixed factor kappa equal to 1.65 in the calculation of max. punching shear resistance is now determined as a function of shear reinforcement covered of the flexural reinforcement and the plate thickness.
– The required punching reinforcement acc. to 6.4.5 (1) is increased in the first two perimenters by 60 %.
– For the punching proof of column bases acc. to 6.4.4 (2) has been recognized that the contents of the square bracket of equation 6.51 describes the load increasing factor beta. For this reason, the contents of the square brackets haven’t to be less than the value 1.10 (previously 1.0).
– A punching shear reinforcement is allowed only for plates with a thickness of >= 200 mm.