## 3 Results and Discussions  
The results obtained for both groups of specimens using the simplified design method, FE analysis, and laboratory experiments were consolidated and compared to validate the proposed simplified method. The focus was on evaluating the maximum vertical displacements and stresses acting in the chords of the posi-josted beam. A graphical representation of the maximum vertical displacement as a function of the applied load for the first group of specimens is depicted in Figure 12. Notably, the OSB and steel lattice were modelled using the SHELL-type FE, as indicated in the description below Figure 12.  
Figure 11: Vertical displacement (**a**) and the scheme of crack development (**b**), obtained for the FE model of the second group of laboratory specimens with a concrete layer. Figure 10: Stresses (**a**) and vertical displacements (**b**) obtained for the FE model of the second group of laboratory specimens with a concrete layer. The obtained dependencies reveal that the average deflections from the experimental results initially surpassed those from theoretical calculations, attributed to residual deformations and creep effects. Beyond a load of 9 kN, the experimental displacement fell below the theoretical design curve. Throughout loading, the vertical displacement curve of the FE model remained consistently below the theoretical curve. The average difference between the results obtained by the simplified method and the experiment exceeded 23.10%. However, the difference between the results obtained by FE analysis and the experiment was more modest, at 6.25%. For the first group of specimens, the maximum value of normal stresses obtained by the simplified method was 13 MPa, while the same value obtained by FE analysis was 12 MPa, resulting in a difference of 7.69%. Similar results were obtained for the second group of specimens with the concrete layer (Figure 13). The chart with a line FE_shell_mod was derived from the FE model, where the OSB, concrete layer, and steel lattice were modelled by the SHELL-type finite element, taking into account the compliance of mechanical bonds (screws) between the top chord of the beam and the OSB layer. Figure 12: Maximum vertical displacement as a function of the applied load for specimens of the first group without concrete layer, by the simplified design method (SDM), FE analyses (FE_shell), and laboratory experiments (LAB_avr). Figure 13: Maximum vertical displacement as a function of the applied load for the specimens of the second group (with concrete layer), by the simplified design method (SDM), FE analyses with three models (FE_shell, FE_shell_mod, and FE_solid), and laboratory experiments (LAB_avr). Bond compliance was assessed based on the experimental results and recommendations from the literature [35]. Comparison of the maximum vertical displacements obtained by the simplified design method and the aforementioned FE model indicated a mean difference of 6.40%. The differences for the FE models using the SOLID and SHELL types, without considering bond compliance, were significantly higher, reaching 63%. Comparing the maximum vertical displacements obtained by the simplified method and the experiment indicated a mean difference of 11.6% for the first loading cycle. The chart shown in Figure 13, depicting the FE_solid line, was generated by modelling the concrete layer using the finite element type SOLID. The chart is interrupted at a load level of 18 kN, where the development of the first cracks was noted. However, in practice, the failure of specimens was observed at an average load level of 45.81 kN for the three considered specimens. Therefore, it can be concluded that the use of the finite element type SOLID for modelling the concrete layer in timber-concrete composite structures with posi-joisted beams does not enable the accurate prediction of the structure's behaviour at all loading stages.