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Reinforced concrete (RC) beams under the impact loading are typically prone to suffer shear failure in the local response phase. In order to enhance the understanding of the mechanical behavior of the RC beams, their dynamic response and shear demand are numerically investigated in this paper. A 3D finite-element model is developed and validated against the experimental data available in the literature. Taking advantage of the above calibrated numerical model, an intensive parametric study is performed to identify the effect of different factors including the impact velocity, impact mass and beam span-to-depth ratio on the impact response of the RC beams. It is found that, due to the inertial effect, a linear relationship exists between the maximum reverse support force and the peak impact force, while negative bending moments also appear in the shear span. In addition, the local response of the RC beams can be divided into a first impact stage and a separation stage. A shear plug is likely to be formed near the impact point at the first impact stage and a shear failure may be triggered near the support by large support forces. Based on the simulation results, simplified methods are proposed for predicting the shear demand for the two failure modes, whereas physical models are also established to illustrate the resistance mechanism of the RC beams at the peak impact force. By comparing with the results of the parametric study, it is concluded that the shear demand of the RC beams under the impact loading can be predicted by the proposed empirical formulas with reasonable accuracy.

Extreme actions, such as impact loads, contain many uncertainties and hence, may not be analyzed by a deterministic approach. In this paper, an effective framework for performance evaluation of reinforced concrete (RC) beams subjected to impact loadings is proposed. For this purpose, a simple yet effective model considering the shear-flexural interaction is developed based on available impact test results. By incorporating the shear effect, both the maximum displacement and impact force are well predicted, by which the proposed model for the impact analysis of RC beams is validated. The joint probability density function (PDF) of two damage indexes, i.e. local drift ratio and overall support rotation, is used to represent the local shear damage degree and the overall flexural damage degree. Taking advantage of the probabilistic framework and the effective model, reliability analysis of the RC beams under different impact scenarios is performed. The damage, described in this study by the joint PDF, is highly affected by the combination of impact mass and velocity. Thus, the mass–velocity ($m$–$v)$ diagrams for various performance levels are generated for the damage assessment of the RC beams. Furthermore, the contribution of the local and global responses to the failure probability is quantified using the proposed probabilistic framework.

During the service life of reinforced concrete beams (RC beams), they may experience impact loadings induced by various falling objects, such as falling rocks and fragments of upper floors. Therefore, the RC beam’s impact resistance is important to its application in structures. This paper investigated the impact mitigation performance of polyurea coatings on RC beams by drop weight impact tests with different impact velocities and hammer shapes. According to the test results, the polyurea coatings can significantly reduce the RC beams’ local damage and midspan displacement. Moreover, it was found that the RC beams’ plateau impact forces were notably increased by the polyurea coatings. Besides, comparisons between impact tests with different impact loads indicated that the polyurea coatings’ protection effect was not noticeably influenced by the hammer shape or impact velocity. Based on the test results, a numerical model was established and validated, and the model was used to study the mechanism and the parameter influence of polyurea coatings. By simulating the response of upper- and lower-side coated beams, it was revealed that the polyurea coating reduced the RC beam’s overall damage by reducing its local damage and increasing its bending moment. Parametric studies showed that the mitigation effect increased with coating thickness and the increase rate decreased with the thickness. In addition, the effect of longitudinal coating length was also studied via numerical simulation, and it was found that the mitigation effect increased with coating length, and it became nearly identical to that of the fully coated beam when the coating length exceeded 60cm.