Bond Strength Between Corroded Bars And Concrete Under Monotonic And Cycle Loads

Reinforced concrete structure is one of the most used in the construction field of structure form,which has the advantages of being easy to draw materials,good integrity and fire resistance.In recent years,reinforcement corrosion phenomenon becomes more and more common in different environment of reinforced concrete structure,such as Marine and offshore environment,damp environment and port and other industrial structure in the environmental pollution etc.The durability of the concrete structure growing,it causes the degeneration of the performance of the structure also gradually become the hot topics in the study of civil engineering.For the reinforced concrete structure,reliable bonding is the basis of steel and concrete materials to work together.And corrosion of reinforcement is one of the reasons for bonding performance degradation,its mainly makes the bond strength of steel and concrete lower,damages the structure safety.Therefore,how to evaluate the effects of bond strength of the corroded bars and concrete under monotonic and cycle loading is particularly important.Current research on bond strength of corroded reinforced concrete has accumulated certain results,but there is also insufficient.In theory research,the forecasting model of ultimate bond strength under the monotonic loading is more based on regression of experimental data,its applicability and prediction precision depends on the regression analysis adopted database;in test research,the study of ultimate bond strength under cycle loading is more based on drawing test,the specimen in the test has different stress condition with the real concrete member,so the applicability of the test results exist certain problems.Based on this,the main research work and conclusions of this paper are as follows:(1)Based on the elastic-plastic of thick wall cylinder theory,a analysis model is put forward to predict bonding failure pattern and strength of deformed bars and concrete.The model mainly considers the generalized constraint influence on bonding cleavage crack extension of deformed bars,namely,concrete cover and stirrup.When the material parameters(concrete,steel bar intensity)and geometric parameters(concrete cover,diameter of reinforcing bars and stirrup)are given,the predictions of bonding failure pattern and strength of deformed bars and concrete can be madet.With the comparison and verification with a large number of contrast test data,this model is independent of the existing experimental data,the prediction precision is favorable,and the applied range is more extensive.(2)Lucubrating the theory prediction model of the ultimate bond strength of deformed bars and concrete of this article,considering the mechanism influence of corrosion on bond strength,a theoretical analysis model is proposed which is used to calculate the ultimate bond strength of corroded reinforced concrete.The model consists of a variety of parameters,including concrete strength,steel bar diameter,the thickness of concrete cover,the influence of diameter of stirrup and stirrup spacing,etc.By comparing with the existing experimental data,the predicting model of the ultimate bond strength of corroded deformed bars and concrete with and without stirrup has a good precision.At the same time,the parameters are analyzed,the key parameters for the bond strength of corroded reinforced concrete are studied.(3)A test unit is developed,which is used to make the performance test of the bonding beam spicemen under cycle load realized,using the device can simulate the mechanical characteristics the real component of steel and concrete.The effect on the failure pattern and bond strength of cycle load,the degree of corrosion and the rebar diameter is studied based on the test result.The results show that with the increase of corrosion ratio,the ultimate bond strengths rise after the fall,and the critical corrosion ratio is existed.Under the given corrosion ratio,the bond strength of each cycle is decreased with the increase of cycling times.At the same time,the higher the corrosion ratio is,the more obvious the degradation of the bond strength under manifold cycles with constant amplitude is.