Investigation On Damage Characteristics And Residual Load-carrying Capacity Of RC Beam Under Impact

Bridges are critical nodes and hubs in transportation infrastructure,and various impact actions seriously threaten the service safety of bridge structures.As the basic component of bridge structures,reinforced concrete(RC)beams have important significance for post-disaster assessment of bridge structures by studying their damage characteristics,residual bearing capacity evolution laws,and mechanisms under impact loads.Based on RC beam drop hammer impact tests and in-situ static loading tests after impact,and combined with numerical analysis,this thesis analyzes the dynamic response and damage failure modes of RC beams under impact loads,studies the influence of different factors on the change of bearing capacity of RC beams after damage,and reveals the evolution mechanism of bearing capacity of RC beams after impact damage.The main research work of this paper is as follows:1.In recent years,incidents of vertical impact accidents such as falling rocks and objects on bridge structures have been introduced,highlighting the necessity of the research presented in this article.The current research status of the impact resistance performance and residual performance of RC beams both domestically and internationally have been systematically described,which clarifies the research direction and content of this article.2.In addition,this paper designs and conducts a series of drop hammer impact tests on12 RC beams with two different types of tensile reinforcement,analyzing the dynamic response characteristics of RC beams under impact loads and elucidating the failure modes of RC beams under impact.A numerical analysis model of drop hammer impact on RC beams is established using LS-DYNA,and the accuracy of the finite element model is verified based on the experimental data.The concrete damage in the impact area of the RC beams is severe,and there is an obvious shear wedge at the impact location.The impact response of the RC beams consists of two stages: local response and global response,and impact damage mainly occurs in the local response stage.The maximum impact force is mainly related to the local contact conditions,and factors such as impact energy and reinforcement parameters have a small impact on the maximum impact force.Increasing the reinforcement ratio can not only reduce the maximum impact displacement of RC beams,but also significantly improve the displacement recovery performance of RC beams under impact.3.The in-situ static loading test was conducted on the reinforced concrete(RC)beam after impact damage,and the residual bearing capacity of the RC beam after impact damage was obtained.The restart analysis function of LS-DYNA was used to load the damage model,and the variation of residual bearing capacity of the RC beam under different impact energy,longitudinal reinforcement ratio,transverse reinforcement ratio,and concrete strength parameters was obtained.A formula for predicting the residual bearing capacity of the RC beam was established.During the second stage of the static loading process,the RC beam specimen with impact damage showed a bending-dominated failure mode,and the impact damage cracks further developed.The increase of the compression steel reinforcement ratio and the transverse reinforcement ratio could reduce the degree of bearing capacity decline,while the increase of the tension steel reinforcement ratio not only improved the original bearing capacity of the RC beam but also increased the proportion of the decline in residual bearing capacity.The concrete strength had little effect on the residual bearing capacity of the RC beam after impact damage.4.Fiber section analysis was used to analyze the moment-curvature response of damaged sections and investigate the influence of material damage on the load-carrying capacity of reinforced concrete(RC)beams.The evolution mechanism of the load-carrying capacity of RC beams was studied by combining material damage constitutive analysis.The main reason for the decrease in bending capacity of RC beams is the crushing and spalling of the top concrete at the mid-span.The degree of degradation of the load-bearing capacity of RC beams due to impact damage mainly depends on the failure mode of the RC beams at the ultimate limit state.For the concrete beams that fail under tension,their load-bearing capacity will not be severely affected by impact damage because the reserve compression capacity in the compressed zone can still provide sufficient resistance until the beams fail under tension.In contrast,for concrete beams that fail under compression,their load-bearing capacity will also significantly decrease after being subjected to impact damage.This study further clarifies the dynamic response and damage evolution of RC beams under impact loads,elucidating the evolution laws and mechanisms of the load-carrying performance of RC beams under impact loads.The research results can provide a basis for the anti-impact design of reinforced concrete structures and the evaluation of the residual performance of structures after being impacted.