# Dynamic Behavior Analysis of I-Shaped RC Beams under Combined Blast and Impact Loads
###### Abstract  
The existing literature mainly focuses on the research of reinforced concrete (RC) beams under a single load such as blast or impact. In this paper, the slab-rib-slab RC beam, a new type of structure widely used in bridge structures, was taken as the research object. The explicit dynamic analysis software LS-DYNA was used to numerically analyze the dynamic response and failure behavior of I-shaped RC beams under combined blast and impact loads. For this reason, an effective numerical analysis model was obtained by carrying out experiments on I-shaped RC beams under contact explosion. The key factors affecting the dynamic response of the structure under combined loads were numerically analyzed. Numerical results showed that different load application sequences have important effects on the dynamic response of the structure. When the impact load was first applied to the structure, more severe concrete damage and deformation occured in the depth direction of the beam. However, when the blast load was first applied to the structure, the concrete at the lower flange was damaged in the span direction of the beam due to tension, and no large-scale concrete spallation occurred in the depth direction. This was mainly due to the different mechanisms of blast and impact loads. In addition, the vulnerability of the I-shaped RC beams varied with some structural parameters, including span, depth, and configuration of reinforcement. At the same time, the results showed that the structure is more sensitive to changes in structural parameters when it is first subjected to impact loads. combined impact-blast load; I-shaped RC beams; dynamic response; failure behavior +
Footnote †: journal: Applied Sciences  
response of the structure [12]. [PERSON] et al. carried out four-point bending experiments of the glass fiber-reinforced polymer (GRFP)-reinforced bar concrete beams under close blast. It was proven that GRCB has a stronger blast resistance through the remaining bearing capacity of the beam [13]. [PERSON] et al. studied the impact of steel fibers on the blasting performance of high-strength concrete beams and carried out related experimental research. The results showed that steel fibers can replace the transverse reinforcement and reduce the shear failure caused by explosion [14]. [PERSON] et al. conducted an explosion test analysis on 10 half-scale beams. At the same proportional distance, the damage of RC beams with a larger blast mass was more serious. At the same time, the empirical formula between the mid-span displacement and the proportional distance was obtained [15]. Compared with blast loads, the existing literature has more sufficient research on RC beams under impact loads. [PERSON] et al. carried out the drop-weight impact test of reinforced concrete beams to study the response changes of the drop-weight height and the amount of longitudinal reinforcement to RC beams under impact loads. It was found that the local and global response of the structure depends on different loading rates [16]. [PERSON] et al. studied the influence of the overall stiffness of the structure on the impact force distribution through LS-DYNA. A two degrees of freedom (2 DOF) analytical model was developed for an RC beam under drop-weight impact by predicting impact forces using a fiber beam section analysis method [17]. [PERSON] et al. used a numerical analysis method to study the effect of impact velocity on the response and failure of RC beams. Analytical equations that predict the failure modes in RC beams from bending to shear were presented [18]. [PERSON] et al. designed the projectile impact experiment of mixed fiber-reinforced concrete beams and found that mixed fibers can improve the energy absorption of beams and improve the impact response of RC beams [19]. [PERSON] et al. used drop-weight tests to study the mechanical properties of RC beams with cushions.