Study On Eccentric Compression Of Reinforced Concrete Bridge Columns Under Typical Climate Environment And Sulfate Erosion In Northwest China

Reinforced concrete（RC）column is an important load-bearing member,and its durability has become one of the research hotspots in the field of civil engineering.In the northwest of China,the damage caused by sulfate erosion has become the main reason for the failure of RC column.In this paper,the durability of RC column under the actions of sulfate and other environmental factors was studied,in order to understand the mechanical performance of RC columns in service in northwest China.Based on the experimental results and theoretical analysis,the damage and durability degradation of concrete under the actions of sulfate and other factors were studied.The research results will provide a basis for the durability design and evaluation of RC columns under sulfate multi-factor environment.It has important engineering application value and theoretical significance.This paper studied the durability of RC column under the actions of ’sulfate and wetting-drying cycle’,’sulfate,wetting-drying cycle and freeze-thawing cycle’.The testing plan of the durability of concrete under sulfate multiple factors was designed.Through the experiments under the actions of sulfate and other factors,the microstructure of concrete,compressive stress-strain relationship of concrete,the bonding performance of steel bar and surrounding concrete and the eccentric compressive performance of RC column were studied.The operating system and the coupling effect were produced.Based on the stress-strain curve of concrete,the bonding performance curve of steel bar and surrounding concrete,and current theoretical analysis,the predicting model of ultimate bearing ability of RC column under the actions of multiple factors is established.Furthermore,the performance of RC eccentric compression column in northwest China can be predicted.The main research contents are as follows:（1）In order to analyze the macro phenomenon,microscopic testing methods like scanning electron microscope（SEM）,X-ray diffraction（XRD）were used in this paper.Microstructure morphology,phase composition analysis of concrete under double factors and multiple factors of sulfate were studied.The results showed that the microstructure morphology and phase composition of concrete under the actions of sulfate,dry-wet cycle and freeze-thaw cycle changed greatly and physical crystallization of sodium sulfate appeared in pores.The internal structure of concrete changed from dense to loose.（2）The effects of different factors（the number of drying and wetting cycles,the strength grade of concrete,the concentration of sodium sulfate solution,the mineral admixtures and the number of freeze-thaw cycles）on the stress-strain curve of concrete under uniaxial compression were studied.The influence of freeze-thaw cycles on the corrosion morphology,mass loss rate and dynamic elastic modulus of concrete were detected.The changing rules of compressive stress-strain curve caused by different factors are analyzed,and the relations between the relative peak stress and corresponding strain with the number of dry-wetting cycles and the number of freeze-thaw cycles are established.（3）The bonding performance of steel bar and surrounding concrete under the actions of sulfate and other factors was studied.By considering the number of dry-wet cycles,the strength of concrete,the concentration of sodium sulfate solution,the number of freeze-thaw cycles and mineral admixtures,the central pull test of steel bar and concrete was finished.The test phenomenon,failure modes and the relationship of the average bond stress-slip between rebar and concrete also are analyzed.（4）Six C40 short columns with cow-leg were designed and manufactured.The eccentric distance and the number of wetting and drying cycles were applied to the eccentric compression experiments of RC column.The influences of different design parameters on the failure modes,ultimate bearing capacities,load-midspan deflection curves,load-concrete strain and load-reinforcement strain of the RC column are analyzed.（5）Based on current calculation method of ultimate bearing capacity of RC column,the ultimate compressive strength of concrete and the bonding performance of steel bar and surrounding concrete under the actions of sulfate and other factors,the ultimate bearing capacity model of RC column in the sulfate environment is established.The results show that the model and the testing results are in good agreement.The accuracy of the model is verified.