Experimental And Numerical Study Of Behaviors Of RC Beams And Columns Under Impact Loadings And Rrapid Loadings

Strong dynamic loads such as earthquake action and impact loading destroy the reinforced concrete (RC) structures, and then lead to a great of casualties and economic loss. Under the strong dynamic loads, the behaviors of RC structures are very different from the behaviors under static load because the strain rate effect of materials is induced in RC structures. Under impact loadings, stress wave propagation and inertia effect exist in the structures and make the behavior more complicated. By now, the experimental and numerical studies on the dynamic behavior of RC columns subjected to rapid concentric compressive loadings and the dynamic behavior of RC columns considering the strain rate effect and the confined effect of stirrups together within the range of strain rate corresponding to earthquake action are very limited. For the studies on the behavior of RC structures subjected to impact loadings, little literature reports the studies on the impact-resistant behavior of RC beam without stirrups, deep RC beam and the RC beam with stirrups in shear failure. Little study investigates the response and distribution of acceleration of the RC beam in details and all-around discussion on the influence parameters such as shear span ratio and stirrup ratio is not conducted. So in this study, the dynamic behaviors of RC columns subjected to rapid loading with the strain rate corresponding to earthquake action and the impact-resistant behaviors of RC beams and deep RC beams are investigated experimentally and numerically. The main contents of this study are summarized as follows:(1) Experimental study and finite element analysis of slender RC columns with two slenderness ratios under concentric rapid loading are carried out. The effects of rapid loading on the axial compressive load-carrying capacity and the corresponding axial deformation of columns with different slenderness ratios are analyzed according to the experimental and numerical results. Finally, the mechanism for dynamic increase in the strength of the slender RC columns under axial rapid loading is investigated, namely the effect laws of strain rate and inertia effect on the behavior of columns with different ratios.(2) An equivalent stress-strain relationship of concrete considering both strain rate sensitivity of concrete materials and confinement effect of stirrups is proposed for the concrete plastic constitutive model in ABAQUS and a FEA model is established to analyze the dynamic behaviour of laterally confined short columns under rapid loadings. With the validation of relative examples, the calculated results using the FEA model are on the whole in good agreement with the experimental results. Based on the proposed analysis model, the influence laws of the following three parameters including the configuration, spacing of stirrups and the ratio of longitudinal reinforcement on the dynamic behaviour of laterally confined short columns considering different strain rate corresponding to earthquake action is studied.(3) Falling-weight impact tests and finite element analysis of RC beams without shear-resistant bars are carried out. In the tests, main attentions are paid to the effect of parameters including the weight of impact mass, impact velocity and impact energy on the failure procedure, crack patterns, the characteristics of shear failure surface, also the characteristics of the time histories of impact force and the time histories of strain of concrete and steel rebar. From the data of strains measured, the distribution characteristic of moments and inertia forces along the beams under impact loading are obtained and then discussion on the single degree of freedom system model for analyzing the behaviors of RC beams subjected to impact load is made. For further study, a FEA model for impact analysis of RC beam without shear rebar is established using LS-DYNA and is validated by the test results. Based on the validated FEA model, the effect of parameters referred to shear span ratio, symmetrical reinforcement and impact velocity is analyzed.(4) Falling-weight impact tests and finite element analysis on a group of RC beams with stirrups are carried out. In the experiment, the effects of impact velocity, impact energy and the impact times on the shear resistant behavior of RC beams under impact loading are investigated. The crack initiation, propagation and the failure patterns, the characteristics of time histories of impact force, reaction forces and displacement, impact force versus displacement curves, reaction force versus displacement curves are described and analyzed in details. Based on the measured response of acceleration at different positions along the length of the beams, the distribution and effect of the inertia force are analyzed, and further analysis is conducted on the mechanism of the diagonal crack forming under different impact level and discussion on evaluation methods of impact-resistant capacity of RC beams is made. Finally, A FEA model for impact analysis of RC beam is established using LS-DYNA and the effect of the stirrup ratio on the impact response of RC beam is investigated.(5) Falling-weight impact tests on simply supported deep RC beams are carried out for the first time and the effects of impact velocity and impact times on two groups of RC deep beams with different static behavior are investigated. The crack initiation, propagation and the failure process, the crack patterns, the characteristics of time histories of impact force and displacement and impact force versus displacement curves are analyzed in details. The evaluation methods of the impact-resistant capacity of RC deep beams under impact loadings are discussed. To investigate the effect of more parameters, a FEA model is established using LS-DYNA to predict the behavior of deep RC beam under impact loading and is validated by the test data. Then the effect laws of stirrup ratio on the impact response of deep RC beams are investigated.