| RC beam is widely used in various building structures.As an important structural component,its brittle shear failure will cause serious consequences.Both steel and concrete materials are rate-sensitive,and concrete exhibits more obvious brittleness under high loading rates.Current research results have shown that the load-bearing capacity,failure mode,crack morphology and cracking speed of reinforced concrete beams are all affected by the loading rate.However,due to the complexity of the shear problem and many influencing factors,there is no universally applicable unified conclusion about the influencing factors of the shear performance of reinforced concrete beams under dynamic loads.Therefore,studying the shear characteristics and cracking characteristics of reinforced concrete members under dynamic loads and their influencing factors has very important theoretical significance and practical reference value.Based on this background,in this paper,the finite element software MSC.Marc is usesd to numerically simulate the force process of reinforced concrete simply supported beams under dynamic loads.Four influencing factors including loading rate,shear span ratio,longitudinal reinforcement ratio and stirrup ratio are considered in the simulation,and the effects of different factors on the shear characteristics and cracking modes of reinforced concrete beams under dynamic loads are studied.The main research contents are as follows:（1）This paper introduces the research background and current research status of the dynamic shear performance of reinforced concrete beams and concrete cracking.Summarize the shearing theory and calculation model of some existing reinforced concrete beams,and the cracking mechanism of reinforced concrete members.（2）This paper introduces the method of nonlinear analysis using MSC.Marc finite element software.Refer to related experiments in the literature to establish a finite element model in the software,and compare the simulation results with the experimental results to prove the feasibility of the numerical simulation analysis.（3）This paper uses MSC.Marc finite element software,a finite element model was established by considering four influencing factors of loading rate,shear span ratio,longitudinal reinforcement ratio and stirrup ratio to simulate the process of monotonic mid-span loading and unidirectional cyclic loading.Analyze the strength growth of reinforced concrete beams under different loading rates.Study the influence of shear-span ratio,longitudinal reinforcement ratio and stirrup ratio on the yield strength,ultimate strength,dynamic increase factor and ductility factor of reinforced concrete beams.（4）This paper introduces the types of cracks in reinforced concrete beams,analyze and propose a method for dividing cracking areas.Compare the crack development process of part of the beam in Chapter 3,summarize the crack types and failure modes that appeared in the simulation,and study the effect of loading rate,longitudinal reinforcement ratio and shear span ratio on the equivalent cracking strain of diagonal shear cracks and vertical bending cracks,respectively Value. |
