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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.

A Bayesian methodology to construct probabilistic seismic demand models for the components of a structural system is developed. Existing deterministic models and observational data are used. The demand models are combined with previously developed capacity models for reinforced concrete (RC) bridge columns to estimate the seismic fragilities of bridge components and systems. The approach properly accounts for all relevant uncertainties, including model error. Application to two bridge examples typical of modern California practice is presented.

The effects of the axial load variations on the seismic response of bridges isolated with friction pendulum systems (FPS) are investigated. A series of parametric time history non-linear analyses are performed for different bridge configurations, defined after an extensive investigation on typical existing cases. The influence of both horizontal and vertical components of the ground motion is considered. The behaviour of the pier-isolator-deck system is predicted using two analytical models characterised by hysteretic loops sensitive or insensitive to axial force variations, in order to compare the different responses. Level of axial force, maximum displacements and induced bending moment are investigated, as well as shear and torsion demand, caused by different shear actions acting on the isolator devices. A comparison between demand and resistance capacity of the bridge piers is performed, in order to investigate possible non-conservative approaches in the current design methods and to raise controversial issues on the subject.