Research On Impact Performance Of RC Beams With Bending Crack In Chloride Environment

The penetration of chloride ions has become one of the leading causes of reinforcement corrosion in reinforced concrete structures and affect the durability and service life of concrete structures in the offshore areas.Moreover,the situation becomes more serious once the concrete is cracked.The presence of cracks has a significant effects on the penetration of chloride ions.Meanwhile,for reinforced concrete structures in offshore areas,during their service life,In addition to being subjected to quasi-static loads such as self-weight and live loads,these structures may also be subjected to various types of impact loads,such as earthquakes,explosions,tsunamis,etc.,in addition to quasi-static loads such as self-weight and live loads,and all these impact loads can lead to structural damage or even exceed its load-bearing capacity.Therefore,the impact resistance of these structures due to chloride corrosion must be considered in the safety evaluation of reinforced concrete structures in the marine environment.Based on this,this paper conducts a study on the chloride ions penetration characteristics and impact resistance of reinforced concrete beams with bending cracks subjected to continuous loading and chloride ion environment in actual projects,which provides an important theoretical basis for the design,strengthening,and maintenance of future structures in marine engineering.Specifically,the following aspects are included.(1)A total of 15 reinforced concrete beams were tested for two years for chloride ion penetration considering three main parameters: crack width,water-cement ratio,and wettingdrying cycle time.The effects of the three parameters on the distribution of free chloride ion concentration and cross-sectional loss of longitudinal reinforcement,as well as the effects of transverse crack width and wet and dry cycle time on the chloride ion diffusion coefficient are discussed.(2)Considering the effect of loading on chloride ion diffusion,the concrete load influence function F(d)describing the effect of considering crack width on chloride ion transport in concrete is proposed,describing the mechanical damage produced by different crack control levels(0mm,0.1mm,0.2mm)corresponding to the load ratio on concrete,and correcting the chloride ion diffusion coefficient for flexural cracked concrete,then transport model of chloride ions and moisture in rusted reinforced concrete beams under the coupling effect of chloride ion attack and bending load is proposed.Numerical simulations were carried out in the multi-physics field finite element analysis software COMSOL,considering the coupling effect of structural damage factors and chloride ion erosion,establishing the numerical analysis models,and the simulation results were compared with experimental results for parametric analysis studies.(3)The tests of 19 reinforced concrete beams on the flexural bearing capacity were conducted.The effects of various sustained loading grades and drying-wetting cycle periods on the crack distribution,the mass corrosion rate of longitudinal reinforcements,and the flexural behavior of corroded members were studied.(4)Drop hammer impact test(13)and static load test(13)were carried out on corroded beams(26 in total).The effects of four main parameters,corrosion rate,load ratio,wettingdrying cycle time and crack width,on the crack development and impact force/displacementtime curve of the crorroded beams are discussed in the results of the drop hammer impact test.The ultimate load capacity-displacement curves were obtained by static load tests,and the results were compared and analyzed with the test results under the impact load test.(5)A finite element model of reinforced concrete beams with different degrees of corrosion to resist impact effects was developed with the impact loading phenomenon on the frame structure in the offshore areas.Meanwhile,the effects of material strain rate effect and the degradation of mechanical properties of materials due to corrosion are considered,and the bond-slip relationship between reinforcement and concrete is simulated by using spring element to verify the corroded beam test in this paper,and then the dynamic response of reinforced concrete beams under impact loading is investigated.On this basis,the deformation and internal force changes of the corroded reinforced beams during the impacting process are investigated in depth.Parametric analysis is carried out for different impact kinetic energies Ek to explore the force mechanism of corroded reinforced beams under the drop hammer test.(6)Through regression analysis of available test data,an empirical formula for impact resistance design allowing the maximum deflection of the structure is proposed,and the effect of rust rate is considered.