Research On Stiffness Degradation Of Reinforced Concrete Compression-bending Members Considering Material Degradation

The deterioration of reinforced concrete materials caused by corrosion is an important factor in the deterioration of mechanical properties of reinforced concrete structures.Every year,the phenomena of reducing bearing capacity and excessive deformation of reinforced concrete structures caused by material deterioration occur frequently,which causes huge economic losses and also poses a threat to national security.Nowadays,the research on the reduction of bearing capacity of reinforced concrete structures caused by corrosion has been more in-depth.However,the research on stiffness degradation of reinforced concrete structures due to the deterioration of materials caused by corrosion is still less.Especially,the research on stiffness degradation of arch bridge isobaric bending structure is still in the exploratory stage.Based on the research background of reinforced concrete arch bridge,considering the deterioration of reinforced concrete materials and the influence of different corrosion rates and eccentricities,this paper explores the deterioration status,mechanical characteristics and failure modes of corroded reinforced concrete columns,aiming at obtaining the stiffness degradation law of corroded reinforced concrete eccentric compression structure,which can be applied to actual corroded reinforced concrete arch bridge in the later stage.Lay the foundation.The main contents of this paper are as follows:1.Based on the current research status of material deterioration,accelerated corrosion test methods and stiffness degradation of reinforced concrete structures,and taking reinforced concrete arch bridges as the background,and aiming at reinforced concrete compression-bending structures,the deterioration mechanism and section stiffness theory of reinforced concrete caused by corrosion are analyzed and summarized,which provide theoretical basis for the test of corroded columns and the calculation model of stiffness degradation.2.Considering different corrosion degrees and load conditions,15 reinforced concrete columns with different corrosion rates(0,5%,10%,20% and 30%)and various load conditions(axes,eccentricities e=0.25 h and eccentricitiese=0.4h)were tested by using the encapsulated electrochemical accelerated corrosion method.The effects of different corrosion degrees on the actual corrosion status of steel and concrete were analyzed,and the causes of material deterioration were studied in depth.The variation of bearing capacity,deflection,strain and failure mode provides experimental basis for stiffness degradation calculation model of corroded reinforced concrete under eccentric compression.3.A stiffness calculation model of reinforced concrete compression-bending members based on material deterioration is proposed.Considering the influence of parameters such as reduction of section area of reinforcing bar,reduction of section size of test column and degradation of bond performance between reinforcing bar and concrete caused by material deterioration,a stiffness degradation calculation model of reinforced concrete compression-bending members based on material deterioration is proposed based on the existing stiffness analysis method.The ABAQUS finite element model is established to compare the results of test data,calculation model and finite element model,and to verify the effectiveness of the proposed method.4.The calculation of section stiffness of reinforced concrete structure is extended from two-dimensional section level.A program based on Python language is developed to solve the moment-curvature relationship of section.According to the relationship between moment-curvature curve and section stiffness,several groups of numerical analysis of stiffness degradation of cracked section of reinforced concrete based on corroded steel bars are carried out,and rigidity considering concrete grade and corrosion rate of steel bars is proposed.Degree degradation law has reference value for stiffness analysis of corroded reinforced concrete structures in service.