# Dynamic Response and Damage Characteristics of Large Reinforced Concrete Slabs under Explosion
## 3 Results and Discussion
### Damage Characteristics under Different TNT Charges  
Based on the above calculation model with ideal parameters, the damage characteristics of the slabs under 5-40 kg TNT explosions were studied. As shown in Figure 9, under the 5 kg TNT explosion, there was no obvious change in the whole top surface of the slab. A small number of cracks appeared on the bottom surface, the concrete did not fall off, and the steel bar was not exposed. Under the 10-15 kg TNT explosion, obvious ring cracks appeared on the top surface, and the center of the slab was obviously broken. Many longitudinal and annular cracks appeared on the bottom surface, a small amount of the concrete fell off, and the steel bar in the explosion craters was exposed without obvious deformation. Under the 20 kg TNT explosion, a large number of ring cracks appeared on the slab, the concrete fell off in a medium range, and the steel bars in the center of the explosion craters were slightly deformed. Under the explosion of more than 25 kg of TNT, intensive ring cracks appeared on the top surface of the slab, and a large range of concrete fell off and collapsed in the centers of the top and bottom surface positions. The steel bars in the center of the explosion craters were obviously deformed or even broken.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{5}{c}{**Maximum Acceleration/g**} \\ \cline{2-6}
**Position** & \multicolumn{2}{c}{**1.26 m/kg\({}^{1/3}\)**} & \multicolumn{2}{c}{**1 m/kg\({}^{1/3}\)**} & \multicolumn{2}{c}{**0.8 m/kg\({}^{1/3}\)**} \\ \hline Center & 85.1 & –94.6 & 160.4 & –166.7 & 239.2 & –177 \\ Long side (1 m) & – * & – & – & – & 96.3 & –116 \\ Short side (1 m) & 21.1 & –18.4 & 34.7 & –33.2 & 83.2 & –99.6 \\ Diagonal line (1 m) & 16.3 & –15.3 & 38.4 & –48.9 & – & – \\ \hline \hline \end{tabular}  
* Note: “–” means no valid acceleration data were obtained.  
\end{table}
Table 4: Acceleration results.  
Figure 8: Typical acceleration–time history curve (Test 2, 1 kg TNT, 1 m).  
The side damages of the slab were under the 5-40 kg TNT explosions, as shown in Figure 10. Under the 5 kg TNT explosion, a small amount of concrete fell off under the side of the slab, and the slab was slightly bent and deformed. Under the 10-15 kg TNT explosions, the slab showed an overall bending and obvious cracks. Under the 20 kg TNT explosion, more concrete fell off below the side. Under the 25-40 kg TNT explosions, a large number of cracks appeared on the side, and large pieces of concrete fell off.  
When the blast wave reached the surface of the reinforced concrete slab, the compressive stress wave caused damage to the top surface of the slab and propagated to the bottom surface of the slab to form a strong tensile wave, resulting in the spallation and collapse of the concrete. The damage in the tensile area of the reinforced concrete slab was more serious; there were several longitudinal and annular cracks in the longitudinal middle of the bottom surface, and some layer cracks appeared at the bottom. With the increasing TNT charge, the annular and radial cracks of the reinforced concrete slab gradually increased. The failure mode of the slab was mainly when there was an annular crack on the top surface, with the center of the slab as the circle center, and a local failure on the top surface center, accompanied by different degrees of spalling and lamination failure at the bottom. The lamination failure zone also expanded with the increase in the charge amount.  
According to the numerical simulation results, the damage degrees under the explosions of TNT can be classified as shown in Table 5.  
Figure 10: Damage to the short side surfaces (4 m).  
Figure 9: Damage to the top and bottom surfaces.