# Study on Mechanical Properties of Multi-Cavity Steel-Concrete Composite Floor
## 4 Results and Analysis
### Load-Deflection Curve  
According to the deflection values at the end, 1/3 and 1/2 span of the floor, the load-deflection curve of the composite floor was drawn, as shown in Figure 10.  
It can be seen from Figure 10 that under a load <96 kN, the deflection increased linearly with the load, and the composite floor was in the elastic deformation stage; when the load reached 96 kN,  
Figure 8: Loading of composite floor.  
Figure 10: Load-deflection curve of composite floor.  
Figure 9: Failure characteristics of composite floor: (a) bending deformation of composite floor; (b) crack between steel plate and concrete on the side of the specimen.  
the deflection of mid span of the composite floor was 10.9 mm; when the load value was greater than 96 kN, plastic deformation occurred and the deflection increased much more rapidly, which was caused by the large deformation of the cavity steel plate on the side of composite floor. As a result, the restrains on concrete were weakened and the stiffness of composite floor was reduced.  
When the load reached 146 kN, the stress of the composite floor did not increase, and the ultimate bearing capacity was reached. The load-deflection curve of the composite floor was close to that of the traditional cast-in-place concrete floor, both of which showed the characteristics of bending deflection. This shows that the cavity steel plate and concrete form a whole through the holes in the cavity steel plate, which has good vertical bearing capacity and shear strength. Thus, they can maintain as a whole under load.  
As seen from Table 1, in [PERSON]'s experimental study on reinforced concrete composite floor, the size of reinforced concrete composite floor was (length) 2500 \(\times\) (width) 1000 \(\times\) (thickness) 120 mm, the concrete strength was C30 and the total weight of steel was 30.2 kg [25]. As can be seen from Figure 11, the maximum bearing capacity of reinforced concrete composite floor was 21.6 kN when the mid span deflection reached 11 mm of normal service limit. The total weight of steel for multi-cavity steel-concrete composite floor with the same size was 52.9 kg, which is 1.75 times of that of the composite floor. However, when the same ultimate deflection was reached, the load it could bear was 4.44 times that of the composite floor. For Cheng Long's precast anchor floor, the size of it was (length) 2500 \(\times\) (width) 1000 \(\times\) (thickness) 120 mm, the concrete strength was C30 and the total weight of steel used was 28.19 kg [26]. When the mid span deflection reached the normal service limit of 11 mm, the maximum load it could bear was 13.6 kN. The total weight of steel for the same size of multi-cavity steel-concrete composite floor was 1.88 times that of the precast floor slab anchored at the pier head. However, when the same ultimate deflection was reached, the load that our composite floor could bear was 7.06 times that of the precast anchor floor. This shows that compared with the two existing precast floors, the total weight of steel used in the multi-cavity steel-concrete composite floor is nearly twice as much as that of the two existing precast floors, but the bearing capacity of multi-cavity steel-concrete composite floor increases to more than four times.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Floor Type** & **Size (mm)** & **Maximum Bearing** & **Total Weight of Steel** \\  & & **Capacity (kN)** & **(kg)** \\ \hline Multi-Cavity Floor & \(2500\times 1000\times 120\) & 96.0 & 52.90 \\ Reinforced Concrete & \(2500\times 1000\times 120\) & 21.6 & 30.20 \\ Composite Floor & \(2500\times 1000\times 120\) & 13.6 & 28.19 \\ Precast Anchor Floor & \(2500\times 1000\times 120\) & 13.6 & 28.19 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Steel consumption of three precast floors.  
Figure 11: Load-deflection curve of three precast floors.