# Study on Mechanical Properties of Multi-Cavity Steel-Concrete Composite Floor
## 5 Finite Element Modeling Investigation
### Analysis of Influencing Factors  
In order to evaluate the influence of steel thickness, floor thickness, cavity size and span length on bearing capacity and section rigidity of composite floor were studied. In the simulation, the composite floor was not concreted, and other parameters were kept constant. The initial steel thickness, floor thickness and span length were 1.0, 120 and 2500 mm, respectively. The midspan deflection of composite floor and the maximum stress of steel were obtained under the load of 96 kN. The deflection nephogram and stress nephogram are shown in Figures 17-24. The results are summarized in Table 2.  
Figure 19: Deflection nephogram of composite floor with different thickness: (**a**) 120, (**b**) 110 and (**c**) 100 mm.  
Figure 20: Stress nephogram of composite floor with different thickness: (**a**) 120, (**b**) 110 and (**c**) 100 mm.  
Figure 21: Deflection nephogram of composite floor with different cavity size: (**a**) 100, (**b**) 125 and (**c**) 250 mm.  
It can be seen from Table 2 that when the steel thickness increased from 1.0 to 1.5 and 2.0 mm, the midspan deflection decreased by 6.5% and 9.8%, and the maximum stress of steel decreased by 62.1% and 63.4%, respectively. It can be concluded that increasing the thickness of steel can significantly improve the bearing capacity and section rigidity of composite floor.  
When the thickness of composite floor was reduced from 120 to 110 and 100 mm, the mid span deflection of composite floor increased by 8.6% and 27.7%, and the maximum stress of steel increased by 13.6% and 20.9%, respectively. This shows that increasing the thickness of composite floor can improve the bearing capacity and section rigidity of composite floor.  
When the cavity size increased from 100 to 125 and 250 mm, the mid span deflection of composite slab increased by 8.5% and 31.2%, and the maximum stress of steel increased by 7.2% and 9.2%, respectively. This is because when the size of the cavity steel plate of the composite floor increases, the restraint effect of the cavity steel plate on the concrete is reduced. In this case, the load which  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Number**} & **Steel** & **Floor** & **Cavity Size** & **Span** & **Midspan** & **Maximum** \\  & **Thickness** & **Thickness** & **(mm)** & **Length** & **Deflection** & **Stress of** \\  & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **Steel (MPa)** \\ \hline
1 & 1.0 & 120 & 100 & 2500 & 9.61 & 182.7 \\
2 & 1.5 & 120 & 100 & 2500 & 8.98 & 69.2 \\
3 & 2.0 & 120 & 100 & 2500 & 8.67 & 66.8 \\
4 & 1.0 & 110 & 100 & 2500 & 10.43 & 207.6 \\
5 & 1.0 & 100 & 100 & 2500 & 12.26 & 220.9 \\
6 & 1.0 & 120 & 100 & 2000 & 3.85 & 133.5 \\
7 & 1.0 & 120 & 100 & 3000 & 14.80 & 221.0 \\
8 & 1.0 & 120 & 125 & 2500 & 10.43 & 195.9 \\
9 & 1.0 & 120 & 250 & 2500 & 12.61 & 199.5 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Simulation results of composite floor.  
Figure 23: Deflection nephogram of composite floor with different span: **(a)** 2500, **(b)** 2000 and (c) 3000 mm.  
Figure 24: Stress nephogram of composite floor with different span: **(a)** 2500, **(b)** 2000 and **(c)** 3000 mm.  
was burdened by the deformation of concrete and steel plates was exerted to the steel plate at the bottom of the composite floor. In addition, with the increase in the size of the cavity, the number of steel plates in the cavity was reduced accordingly, which reduced the height of the compression zone of the composite floor, thereby reducing the sectional stiffness of the composite floor as a result.  
When the span length of composite floor was reduced from 2500 to 2000 mm, the midspan deflection decreased by 59.9%, and the maximum stress of steel decreased by 26.9%. When the span length was increased from 2500 to 3000 mm, the midspan deflection increased by 54.2%, and the maximum stress of steel increased by 21.0%, which indicates that the bearing capacity and section rigidity of composite floor can be significantly improved by reducing the floor span.