Effect Of Chloride Corrosion On Bending Mechanical Properties Of Composite Box Girder With Corrugated Web Plate And Experimental Study

The composite box girder with corrugated web and bottom plate(hereinafter referred to as the new composite box girder)is a new type of structure in which the concrete bottom plate is replaced by the flat steel bottom plate on the basis of the traditional composite box girder with corrugated web.It has the characteristics of light dead weight,strong bending and seismic resistance,factory prefabrication and assembly construction,and is a new type of composite structure bridge with broad application prospects.Because the new composite box girder structure has been put into production for a short time,domestic and foreign scholars have little research on it,especially considering the durability of the research is not seen.In the future,when the new composite box girder bridge is promoted and applied nationwide,it will inevitably face the corrosion of the structure in some special areas such as saline soil,salt lake and coastal areas.Due to the large amount of chloride ions in the soil,water and aerosol in the environment of such areas,the service life of the new structure will be seriously affected.Therefore,it is of great theoretical significance and practical engineering value to study the effect of chlorine corrosion on the new composite box girder structure.In this paper,based on the scientific research project of Gansu Provincial Department of Transportation "The Whole Life Design and Application Technology Research of Highway Concrete Bridge in Gansu Province(Science and Technology Project 2020-05)",the influence of chloride corrosion on the bending mechanical properties of the new structure was systematically studied by combining theoretical analysis,model test and finite element numerical simulation.It plays a certain reference value for the optimization of design and construction and the improvement of durability of this kind of new composite box girder structural bridge.The main research contents and achievements of this paper are as follows:(1)Using the energy variational method and considering the effects of shear hysteresis comprehensively,the shear hysteresis displacement function in the form of quadratic function is introduced,and two warp displacement functions are set up.The governing differential equation and natural boundary conditions of the vertical bending of composite box girder with corrugated web and steel bottom plate are derived by the principle of minimum potential energy,and the closed solution of the corresponding generalized displacement is obtained.(2)The scaled model test beam was designed and made,and the model test beam was corroded in 6% sodium chloride solution for 517 d by full immersion method.After the corrosion of the model test beam is completed,it is found that the steel members of the beam have serious corrosion phenomenon,but the concrete roof has obvious corrosion phenomenon.Vertical concentrated load tests were carried out on the model test beam before and after corrosion within the elastic range.The results show that the height strain distribution of concrete roof along section is approximately consistent with the "flat section assumption" before and after the corrosion of model test beam.However,the vertical displacement and the normal stress of the top and bottom plate of the model test beam after corrosion are significantly increased compared with that before corrosion,indicating that chlorine salt corrosion reduces the strength,stiffness and bearing capacity of the model test beam.(3)Based on the weight loss method,the average corrosion depth of the corrugated steel web and steel bottom plate of the corroded model test beam was calculated;Then,the loading process of the model test beam before and after corrosion was simulated by ANSYS finite element software using uniform cross-section reduction method.The results show that the theoretical values,experimental values and finite element numerical simulation values before and after the model corrosion are in good agreement,which verifies the correctness of the finite element model,and also shows the reliability of the model test beam after simulating uniform corrosion by using the uniformly reduced section method.(4)The influence of the Marine climate rich in chloride ions on the natural vibration characteristics of the model test beam is analyzed.The corrosion depth of the model test beam exposed to Marine climate was predicted,and then the ANSYS finite element software was used to model the model test beam with different corrosion time and calculate the first 6 order natural vibration frequencies.The results show that the Marine climate can significantly reduce the first 6 order natural vibration frequency of the model test beam,indicating that the Marine climate due to the high content of chloride ions in the aerosol,the model test beam corrosion is serious,deterioration of the beam stiffness,reduce the overall stability of the beam.