A simply supported reinforced concrete (RC) beam only experiences sagging moment under static loads while it might experience both sagging and hogging moments under impact loads due to the inertial effect. In order to investigate inertial effect on the impact behavior of RC beam, a numerical model is developed by using the finite element code LS-DYNA. The strain rate effect of the material is considered in the numerical model. The numerical model is calibrated with the testing results of drop weight impact on RC beams available in the literature. The numerical results show that the prediction is better than some other researchers’ predictions in terms of peak impact force and peak deformation. In addition, inertial effect is quantitatively evaluated by the peak impact force and the peak hogging moment. The relationship between the peak hogging moment and the peak impact force of the beam is investigated by conducting parametric studies with regard to various net spans, impact masses and impact velocities. The empirical formulae are then proposed to predict the peak impact force and the peak hogging moment. The predications by the proposed empirical formulae are compared with the testing results and the predicted results by other formulae available in the literatures.

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This paper describes the detailed development of a mathematical model for determining the effect of moisture on the mechanical properties of concrete at the time of test. Based on the theory of elasticity, it focuses on the stress distribution around spherical cavities in concrete filled with different types of inclusions. Results obtained from the mathematical model have assisted in interpreting a number of experimental phenomena that have been the subject of long-term controversy. In particular the model explains why compressive strength tests yield higher measured values for dry concrete specimens than for otherwise identical wet specimens, while the measured values of static modulus exhibit the opposite effect. It also provides an explanation as to why measured tensile strength values obtained from direct tension, tensile splitting or torsion tests are largely independent of moisture content. The model provides an analytical tool for studying the interdependence between the mechanical properties of concrete and its moisture content. It also yields essential input for the computational simulation of the behaviour of concrete structures that are subjected to large changes of moisture condition. Moreover, it provides a method for analysing the stresses at the surface of any type of inclusion but particularly for cavities filled with incompressible liquids under any stress field.

A two-degree-of-freedom mass-spring model considering the local effect of the contact component is developed to investigate the dynamic responses of reinforced concrete beams under low-velocity impact actions. The local modified coefficient is proposed by parameter regression from drop-hammer impact test results, and then the simplified model is validated by other relevant research. As shown, the simplified model is able to capture the dynamic responses of reinforced concrete beams. In addition, the impact process is simulated and further analysed. The effects of initial impact velocity and the yield criterion of reinforced-concrete beams are investigated. The energy dissipation levels for various cases with the same initial impact energy are compared. An analysis proposal is also developed to predict the dynamic responses of reinforced concrete beams if the impact action case is uncertain.

The dynamic compressive strength of recycled aggregate concrete (RAC) was studied by conducting quasi-static compression tests and high strain rate tests with split Hopkinson pressure bar (SHPB). The RAC specimens with three recycled coarse aggregate (RCA) replacement percentages of 30%, 70% and 100% and the natural aggregate concrete (NAC) specimen were prepared and tested. The effect of various RCA replacement percentages on the compressive strength under quasi-static and dynamic loads was studied. The failure modes of the specimens after testing were recorded and compared, and the dynamic compressive strength was analyzed. Regression formulae for dynamic increase factor (DIF) on the compressive strength for RAC were proposed. In this study, the DIF of compressive strength ranges from 1 to 3, and increases with the increase of RCA replacement percentage. In addition, the Continuous Surface Cap Model (CSCM) for RAC material is calibrated with the SHPB testing data by numerical simulation. The numerical results show that CSCM with strain rate effect can predict the dynamic compression behavior of RAC with a relatively high precision.