## 3 Bending of Slab Supported by Column  
In FEM models for slab (as well as shell) structures, the bending moment values obtained at points of discrete supports or connections with columns may be overestimated. These locations are referred to as stress concentration points. The slab's bending moment values increase significantly with mesh refinement. Consequently, they become unreliable for further use, such as in reinforcement design for slabs. This effect can be mitigated by a reduction in moments at the support or column. The objective of this benchmark is to demonstrate the impact of applying a reduction in the post-processing stage on the slab's bending moments at the column connection. Both Midas and Robot software provide this functionality, albeit in different ways. The results of this reduction in the two programs are compared. Additionally, in Robot, the influence of the column's cross-sectional dimensions on the reduction measure is considered, i.e., the change in the values of the slab's bending moment after reduction is studied. In Midas, the reduction domain is directly defined by a certain characteristic distance, and this has also been verified. The ability to adopt a force and moment reduction above columns and walls as well as above nodal and linear supports is crucial. Proper usage of the reduction option for forces and moments at these connection points is beneficial. As the benchmark in this section, the simplest possible model of the connection between the slab and the column has been created. Out-of-plane bending is now studied. The slab is square and supported by the column in the center; see Figure 8. Such geometry indicates that there are four symmetry axes: two along the edges and two along the diagonals. The model could, therefore, be limited to a quarter, but it is intentionally considered for the entire domain to verify whether the symmetry is correctly reproduced. Moreover, a seemingly simple configuration may provoke difficulties during computa  
Figure 7: Contour plots of normal stress \(\sigma_{x}\) for Midas and Robot, medium mesh (FE size is 3 cm). tions due to single-node support and/or discrepancies between the FE dimensions of the slab and the column, which can lead to an ill-conditioned system of equations. Square FEs with a corresponding approximation for out-of-plane bending are applied in both computational programs [9; 10]. The span of the slab is \(L=4.96\) m, and its thickness is \(d=20\) cm. The dimensions of the column are as follows: the height is \(H=3\) m, and the edge size of the square cross-section is \(b=30\) cm. For both the slab and the column, concrete C30/37 is assumed, with the following material properties: [PERSON]'s modulus is \(E=33\) GPa, [PERSON]'s ratio is \(\
u=0.2\), and shear modulus is \(G=13.333\) GPa. The surface transverse load \(\hat{q}_{z}=2\) kN/m\({}^{2}\), uniformly distributed on the whole slab, is applied. The model of the entire configuration can be constructed in two ways. The column is fully represented as a structural element or can be replaced by a fixed nodal support, whereby the column edge size is defined to enable moment reduction. Figure 8 illustrates both options. The computations in Midas are carried out with the full representation of the slab and column. The computations in Robot are performed with the assumption that the support with the additionally specified size at the node corresponds to the full model. The validity of adopting this simplification in Robot is explained below. Figure 9 shows the deformations of the slab obtained in both packages. It is visible that the symmetry is obeyed. At the top, the solution from Midas is depicted. The mesh with \(32\times 32\) elements is employed for the slab, i.e., the FE size equals \(h_{\text{FE}}=15.5\) cm. At the bottom, the results from Robot are demonstrated. The same discretization is adopted. On the left, there is the deformation for the model of the slab and full column. On the right, the counterpart with the nodal support is presented.