# Dynamic Response and Damage Characteristics of Large Reinforced Concrete Slabs under Explosion
## 3 Results and Discussion
### Damage Characteristics of the RC Slab  
The state of the RC slab under the 20 kg TNT explosion is shown in Figure 11a-f. On the top surface of the concrete, an explosion crater appeared, as shown in Figure 11a. More than 10 long cracks appeared on the bottom surface, as shown in Figure 11b. The RC slab bent along the centerline, and annular cracks and radial cracks appeared on both the top and bottom of the slab, as shown in Figure 11a,b. The concrete spalling fell off in a medium range in the center of the bottom surface.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Damage Degree** & **Description** & **Charge/kg** \\ \hline Minor damage & There were small cracks on the top surface of the reinforced concrete slab, and a small range of concrete fell off in the center of the bottom of the slab, but the maximum displacement of the slab was small. & 5 \\ Moderate damage & There was obvious residual deflection in the center of the reinforced concrete slab, showing obvious bending failure, certain ring cracks and radial cracks on the top and bottom of the slab, and a small range of concrete spalling off in the center of the bottom of the slab. & 10, 15, 20 \\ Heavy damage & A large number of annular cracks and radial cracks appeared on the top and bottom of the reinforced concrete slab, and the concrete spalling fell off in a medium range in the center of the bottom of the slab, but there was no penetration. & 25 \\ Complete destruction & The reinforced concrete slab was bent and collapsed along the centerline; intensive ring cracks and radial cracks appeared on both the top and bottom of the slab; and large central block spalling, collapse, and penetration occurred in the center of the slab. & 30, 35, 40 \\ \hline \hline \end{tabular}
\end{table}
Table 5: The damage degrees under the explosion of TNT with different charges.  
Figure 11: Damage characteristics of the RC slab: (**a**) the top face after explosion, (**b**) the bottom face with cracks after explosion, (**c**) the length and width of the blast crater, (**d**) the explosion crater of the bottom face, (**e**) a 3D scan figure of the crater of the top face, and (**f**) a 3D scan figure of the crater of the bottom face.  
The explosion crater was elliptical with a size of 1020 mm \(\times\) 760 mm, as shown in Figure 11c, mainly because the 20 kg of TNT used was composed of two 10 kg cylinders. The steel bars were exposed in the blast crater on the top surface with no obvious fracture and being slightly bent. As shown in Figure 11d, the steel bars were also exposed in the blast crater on the bottom surface, and they were obviously bent but not broken. Figure 11e,f show the 3D scan figures of the explosion craters on the top and bottom surfaces, as well as the state of the steel bars in the craters.  
Taking into account the actual material parameters, the average compressive strength of the concrete (37.2 MPa) and the yield strength of the steel bar (405 MPa) were used in the simulation detailed below.  
The recalculation results are shown in Figure 12. Under the 20 kg TNT explosion, the concrete on the surface of the slabs fell off into pits, the rebar was exposed, the concrete slab bent along the centerline, and the top surface of the slab exhibited annular cracks and radial cracks. The maximum size of the short side crater on the top surface was 934 mm, and the maximum size of the long side crater was 906 mm. Compared with the test of 1020 mm \(\times\) 760 mm, the relative errors were 8% and 19%, respectively.