## 3 Numerical Model Validation  
The working conditions of the test section of the literature [3] were simulated; the experimental model is shown in Figure 1a. A scaled-down model of the steel box girder, as shown in Figure 1b, was established, and the test model was subjected to finite element analysis using LS-DYNA. We used 45 g of B explosive (corresponding to 55 g TNT equivalent). For the first working conditions, the explosive center was 50 mm from the roof of the detonation, 525 mm from the longitudinal beam end, and 240 mm transverse. For the main test, structural damage characteristics were examined when the explosion occurred in the absence of transverse bulkheads, longitudinal bulkhead support, and longitudinal U-shaped ribs in the middle. For the second working conditions, the explosive center was 1125 mm from the longitudinal beam end and 180 mm transverse. The main examination was of the role of the partitions in the support of the roof when the explosion occurred at the intersection of the longitudinal and transverse partitions.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \(\rho\)/ (kg/m\({}^{3}\)) & A/ & B/ & **R\({}_{1}\)** & **R\({}_{2}\)** & **\(\omega\)** & **D/ (m/s)** & **E\({}_{0}\)/ (J/kg)** & **P** \\ \hline
1630 & 3.7377 \(\times\) 10\({}^{11}\) & 3.7471 \(\times\) 10\({}^{9}\) & 4.15 & 0.9 & 0.35 & 6930 & 3.681 \(\times\) 10\({}^{6}\) & 2.1 \(\times\) 10\({}^{10}\) \\ \hline \end{tabular}
\end{table}
Table 2: Parameters of JWL equation of state for explosives.  
\begin{table}
\begin{tabular}{c c c c} \hline \(\rho\)/(kg/m\({}^{3}\)) & \(\gamma\) & _e/(J/kg)_ & _Pshift_/Pa \\ \hline
1.225 & 1.4 & 2.0 \(\times\) 10\({}^{5}\) & 0 \\ \hline \end{tabular}
\end{table}
Table 3: Parameters of ideal gas equation of state.  
Figures 2 and 3 show a comparison of the actual and simulated damage patterns. The comparison between the simulated and experimental values of the scaled-down model of the steel box girder shows that in case 1, the deviation between the simulated and real values of the longitudinal length L and transverse width D of the top slab crack was controlled within 5%, while the simulated results of the subsidence depth H around the crack exceeded the experimentally measured values, and the difference was kept in the range of \(-10\%\). In case 2, the differences between the simulated and measured numbers of longitudinal length L and transverse width D of the top slab crack were limited to 10%, while the simulated results of subsidence depth H at the edge of the crack also deviated no more than 10% from their tested values. The measured numbers were limited to 10%, while the simulation results of the subsidence depth H at the edge of the fracture also differed from their tested values by no more than 8%. The specific data are shown in Table 4.  
By summarizing the data analysis of the simulated values and experimental values, the damage characteristics of the steel box girder bridge under the action of explosive load could be simulated more accurately with LS-DYNA software.  
Figure 1: Experimental and simulation models. (**a**) Experimental apparatus and explosion process. (**b**) Simulation mode.  
Figure 3: Simulated damage patterns.  
Figure 2: Actual damage patterns.