# The Behaviour of Half-Slabs and Hollow-Core Slab in Four-Edge Supported Conditions
## 4 Computational Analysis
### FEM Calculations
Material linearity was based on the assumption of linear-elastic parameters of the material model. The displacement convergence criterion was used in the nonlinear analysis. This means that successive increments were defined as components of the displacement of a specific node. The calculations take into account the actual cross-sectional areas of the structural reinforcement of the panels and the decrease in the stiffness of the structure resulting from cracks. The models were only under the non-uniformly distributed load corresponding to the loading sequences K-11 and L-12 (Figure 11); the deflection caused by the dead weight and initial prestressing was neglected. The numerical models are shown in Figure 22. The models were based on the assumptions that slab corners did not demonstrate any separation and loading of the slabs corresponded to the loading sequence K-11. The summary of test results and FEM calculations are shown in Table 8 and Figure 22.  
in which the joint thickness between the precast units was reduced. This thickness was then 80 mm in the LGR and 40 mm in the RP model. The comparison of results is shown in Figure 23.  
In the models that reflected long-term loading, initial-value boundary conditions were modified following the observations. Due to the detection of rotation and cracks, the stiff connection between the slab and walls was replaced with a hinged connection. Additionally, compression-only supports were used to represent the noticed separation of corners. These models also included a reduced modulus of elasticity of concrete due to creeping at 72% humidity (Figure 19), and the modulus of elasticity was reduced to  
Figure 23: Comparisons of the displacement in the Y-axis between FEM calculation and short-term measurements: (**a**) calculated displacement; (**b**) calculated performance of panels at Y-axis; (**c**) LGR performance; (**d**) RP performance; (**e**) HC panels performance. obs—observed deflection, cal—deflection with a thickness \(\mathsf{h_{red}}\) caused by short-term loading, *cal—deflection with a thickness \(\mathsf{h_{red}}\) caused by short-term loading. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Model** & \(\mathbf{a_{obs}}\) **(mm)** & **h**(mm)** & **h**(mm)** & **a**(mm)** & **a**(mm)** & **a**(mm)** & **a**(mm)** & **a**(mm)** & **a**(mm)** \\ \hline LGR & 1.96 & 200 & 160 & 1.54 & 1.27 & 80 & 2.00 & 0.98 \\ \hline RP & 3.90 & 160 & 120 & 2.74 & 1.42 & 40 & 3.92 & 0.99 \\ \hline HC & 3.57 & 150 & – & 4.29 & 0.83 & – & – \\ \hline \hline \end{tabular}  
* a\({}_{obs}\)—measured displacement; a\({}_{all}\)—calculated displacement; h\({}_{red}\)—slab thickness reduced by a thickness of the precast unit; *h\({}_{red}\)—corrected thickness \(\mathsf{h_{red}}\); *a\({}_{all,FEM}\)—maximum deflection of the model at the reduced thickness of the joint.  
\end{table} 
Table 8: Comparison of results from tests and FEM calculations under short-term loading. E\({}_{\text{c,lt}}\) (Table 2). The long-term effects of prestressing were represented by membrane forces with an orientation consistent with the arrangement of tendons. As there are no explicit guidelines for considering the prestress for composite cross-sections and slabs composed of single prestress units, it was assumed, in accordance with Eurocode [54], that 1/5 of the whole long-term prestressing forces (after the losses) acted on the composite cross-section (for the stored elements up to three weeks before their placement). Compared to the experimental results, the displacements calculated in the LGR and RP models under the above assumptions were underestimated. The maximum calculated value of displacements in the LGR model was 8.78 mm and lower than the measured value by more than 48%. The calculated value of displacements in the RP model was equal to 9.15 mm and lower than the measured value by 31%. A similar scale difference between the calculated and determined results was found for the HC model. In that case, the overestimated values of displacements exceeded 60%.