The Study Of The Size Effect On Reinforced Concrete Beam Under Impact Loading

Reinforced concrete structure has become the choice for the impact resistance design of current building structures due to its excellent durability,integrity and seismic resistance.However,during the entire life cycle,the building structure may be subject to impact accidents caused by human or natural factors.This poses a great threat to the security and stability of the people,society and country.Therefore,studying the impact resistance of reinforced concrete members and structures has become a hot issue of concern for architects and researchers.It is of great scientific significance and engineering value to the shock safety design of the current building structure.In addition,the size effect of reinforced concrete beams has been studied for more than 6centuries.At this stage,most of the studies on size effect are aimed at the analysis of the nominal strength under static load.The research on the size effect of reinforced concrete beams under impact load is lacking.Therefore,based on the experimental data and theoretical model calculation,the size effect of the RC beam under bending load is studies in this paper.The main research work of this paper is as follows:(1)Firstly,the theory of single degree of freedom(SDOF)and the process of equivalent derivation is shown.Secondly,the resistance parameters of the full response stage in the SDOF model is analyzed and improved.Based on that,the improved single degree of freedom(ISDOF)model is proposed.Finally,the reliability of the ISDOF method is verified and corrected.The optimized ISDOF model is obtained.(2)To begin with,the response characteristics of the RC beam under impact load are analyzed.The impact of various test parameters(such as impact force,supporting force,mid-span displacement,longitudinal strain and concrete strain,etc.)on the impact resistance of the RC beam is studied.At last,the cracking process and failure mode of each beams is summarized.(3)The RC beam test database under concentrated load is established.Based on the impact force and mid-span displacement time history curve,the impact of various factors on the RC beam impact response is analyzed.With the increase of aspect ratio,mass or velocity,the peak impact force,the duration of impact force and the peak displacement of midspanincrease.With the increase of the high-span ratio,the peak displacement of the impact force and the peak displacement of the mid-span increase accordingly.And the duration of the impact force decreases as it increases.Under the influence of various factors,the shape of the impact force time-history curve is not much different.(4)The improved single degree of freedom(ISDOF)model is solved by LS-DYNA structural analysis method.And the calculation results with the test results are compared.Base on that,the impact of dimensionless normalized characteristic parameters such as impact energy,drop weight momentum and beam static bearing capacity is analyzed on the peak displacement of RC beam span.The results show that the impact energy and the drop weight momentum are directly proportional to the peak displacement of the beam span,and the static bearing capacity of the beam is inversely proportional to the peak displacement of the beam span.In addition,the effect of each characteristic parameter on the maximum displacement size effect of RC beams is studied.The empirical formula of the size effect of the nominal peak displacement of the RC beam is obtained by parameter fitting.