Study On Lateral Anti-impact Properties Of The Reinforced Concrete Pier In Drying-wetting Cycles And Chloride Ion Corrosion Environment

For the hydraulics concrete structure in the ocean environment,reinforcement corrosion caused by chloride ion is the most important factor of structure durability.With the rapid development of coastal and cross-sea bridge construction,reinforced concrete structures inevitably face extreme dynamic load in its service period.Frequency of serious ship-bridge collision accident is obviously increasing recently.Therefore,the problem of ship-bridge collision accident is attracting more attention.In general,water level fluctuation part of a bridge is mainly subjected to vessel collision.Besides,water level fluctuation part of a bridge is corroded more seriously than other parts of bridge.However,the research of ship-bridge collision is focused on non-corroded bridge present.Compared to static load conditions,dynamic characteristic of the material and response of structure under impact load are different owing to transient and partial load characteristics of impact load.Bridge pier is the important component of bridge,which performance affects safety and durability of the whole bridge.Hence,it is urgently to carry out a research into the performance of pier under lateral impact load in drying-wetting cycles and chloride ion corrosion environment.Mechanical properties of typical corroded reinforced concrete members were systematically studied in this paper.In the bending classification repeated loading experiment of corroded beams,the corrosion level influence on the mechanical properties of reinforced concrete beam was studied.Through the Electricity accelerated corrosion and drying-wetting cycle corrosion of 15 reinforced concrete pier specimens,drop hammer impact experimenting machine was used to simulate lateral impact of reinforced concrete piers being loaded.Reinforcement corrosion and the dry-wet cycles influence on the properties of pier under lateral impact were analyzed.Based on the general finite element software ANSYS/LS-DYNA,the concrete piers under non-corrosion,chloride ion corrosion and drying-wetting cycle corrosion were simulated to lateral impact load.Numerical simulation result was compared with the experiment results.Besides,various factors’ influence on the mechanical behavior of reinforced concrete bridge piers under lateral impact were analyzed,for example,corrosion level of longitudinal reinforcement,velocity of lateral impact,number of lateral impact,the type of impact contact surface,etc.Mechanical properties of reinforced concrete beam under repeated loading and lateral anti-impact performance of corroded bridge piers are predicted by support vctor machine method.The main results of this study are as follows:1)The relationship between crack width and corrosion rate and the curve of load-deflection of reinforced concrete beam were obtained by experiments.Through amending the reduction factors of corroded reinforced concrete members,the bending bearing capacity calculation model and crack load calculation formula of corroded beam under repeated load was given.2)The failure states of corroded reinforced concrete members in different corrosion level are different.The failure mode of non-corrosion and low corrosion rate specimen is cutting and bending failures collectively controlled by lateral bending crack and skew shearing crack.The failure mode of middle corrosion rate specimen is cutting and bending failures collectively controlled by skew shearing crack.The failure mode of high corrosion rate specimen is suddenly destroyed by several lateral impacts,and is collectively controlled by cutting pressure,bending moment and corrosion-induced expansive pressure.3)The acceleration amplitude of high corrosion rate specimen under lateral impacts is smaller.The acceleration amplitude of middle corrosion rate specimen under lateral impacts is bigger.The structural strength is improved by small amount of rebar corrosion.As corrosion rate improves,the malleability of specimen and the capacity of energy dissipation under lateral impacts have decreased.4)In tensional area of specimen,as corrosion rate improves,the peak strain and average strain of steel rebar in each case reduces.As impact load increases,steel rebar has experienced elastic stage,yield stage strengthen stage strain of increases correspondingly.While steel rebar reaches to the ultimate strain,the strain of steel rebar decreases as the impact load increases.5)The numerical simulation result,base on four types of common concrete constitutive model includes the Johnson Holmquist concrete model,the brittle damage model,continuous surface cap model and concrete damage model rel3,the was compared with the experiment results,and the numerical results are basically consistent with experiment results.The impact phenomenon of concrete could be well described by the Johnson Holmquist concrete model and concrete damage model rel3.6)The initial corrosive cracks along longitudinal steel are pre-set in geometry model,which could well reflects the initial environmental damage of concrete pier by drying-wetting cycles corrosion and chloride ion corrosion.The simulation results agree with the experimental results.7)By modifying the modeling file of LS-DYNA(.KEY file),impact damage of reinforced concrete pier is transmitted to the next impact.The consecutive multiple impact of corroded reinforced concrete pier could be simulated well by using ‘Full restart analysis’ of ANSYS/LS-DYNA.8)Various factors’ influence on the lateral anti-impact performance of corroded bridge piers is different,for example,corrosion level of main longitudinal rebar,diameter of main longitudinal rebar,diameter of stirrup,velocity of lateral impact,number of lateral impact,the type of impact contact surface,etc.The diameter of main longitudinal rebar and number of lateral impact are the major factors.The presence or absence of corrosion has much different effects on anti-impact performance of corroded bridge piers.In low corrosion rate case,the anti-impact performance of reinforced concrete members increases as the corrosion rate increases.9)Maximum crack width,failure load,span deflection and rigidity of corroded beam under repeated load were studied and predicted by the support vctor machine method.The effectiveness and reliability of predicted method was verified by the experiment results.10)The anti-impact performance of corroded bridge piers are predicted by support vctor machines method,such as corrosion rate of steel rebars by chloride ion corrosion drying-wetting cycles corrosion,stable strain of steel and concrete strain after impact.The difficulty of data collection and record and the number limit of data collection could be overcomed by support vctor machines.The present work,which study on lateral anti-impact properties of the reinforced concrete pier in drying-wetting cycles and chloride ion corrosion environment,is provided references for design of new pier and mechanical properties assessment of damaged pier by impacting in littoral environment.