Study On The Resistance Behavior Of Concrete Eccentric Columns With Corroded Cracks In The Compressive Zone

As the main load-bearing structure of the building,the eccentric column plays a decisive role in the safety of the building.Its durability has always been of concern to the majority of scholars,but the research on the rust-biased column at this stage is not clear and thorough.At present,the studies on concrete eccentric columns are mostly symmetry biased columns,and the root causes of the decline in the resistance performance of concrete eccentric columns cannot be well analyzed.Especially for the biased columns of the rust cracks in the concrete cover,The research conclusions are mostly qualitative analysis and do not give quantitative conclusions.Therefore,it is necessary to study the influence of the rust damage of concrete cover on the resistance performance of the biased column,and to quantify the influence of the damage of the p concrete cover on the resistance performance of the eccentric column,and then the residual bearing capacity of the rust bias column and other resistance performance indicators.The calculation formula is corrected or reconstructed.In this study,a self-designed monolithic concrete column foot adjustment device independently designed by the research group and a new method for attaching the strain gauge to the surface of the steel bar make the placing process of the concrete bias column simple and rapid,and the centering effect is good.At the same time,the method of pasting the strain gauges on the surface replaces the method of pasting the strain gauges by cutting the reinforcing steel bars in the past,so that the difficulty of the test is reduced,and the test accuracy is greatly improved.Fifteen reinforced concrete columns were designed and manufactured.They were tested with a large and small eccentric column and verified by ABAQUS.Through the comparative analysis of physical tests and simulation results,the changing law of cracking load,ultimate load,bending stiffness,cross-sectional strain,and crack development situation of the bias column along with the increase of the degree of damage caused by the rust cracking in the concrete cover was investigated.The calculation formula for the residual bearing capacity of corroded bias columns was revised.The specific conclusions are as follows:1)Regardless of the large bias column or the small bias column,the rust cracking damage of the nip protective layer does not change its final failure mode.The large bias column still yields firstly the longitudinal bars of the tension zone,and then the concrete in the nip area is Crushing,the small biased column still yields first for the compressive bars,then the concrete is crushed.2)The damage of the nip protective layer has significant influence on the cracking load and the ultimate load of the large eccentric column and the small eccentric column,but the degree of influence on the large eccentric column is smaller than that of the small eccentric column.When the nip protective layer was completely peeled off,the cracking load and the ultimate load of the large bias column decreased by 12% and 21%,respectively,and the small bias columns decreased by 33% and 21%,respectively.3)The rust cracking damage of the concrete cover has no obvious effect on the distribution of stress cracks in the bias column,ie,the final number and distribution of stress cracks in the biased column are not changed,but the maximum crack width of the biased column is affected.Obviously,especially the effect of the maximum crack width of the large bias column is greater than the effect of the maximum crack width of the small bias column.4)The rust cracking damage of the concrete cover has no obvious influence on the regularity of the surface strain of the eccentric column,and does not change the change law of the flat section,but with the increase of the degree of rust cracking in the nip,the same position under the same load At the bias column concrete surface strain value is relatively large.5)The rust cracking damage of the compressive cover has a significant influence on the bending stiffness of the biased column.With the increase of the degree of rust cracking in the compressive zone,the mid-span deflection of the biased column under the same load increases continuously.6)Both the cracking load and the bearing capacity of the bias column decrease with the increase of the degree of rust cracking in compressive zone.The degradation of the cohesion force in the compressive zone only has a certain influence on the cracking load of the large eccentric column.The susceptibility to cracking damage in the compressive zone is greater than that of the large eccentric column due to the cracking load and ultimate load of the eccentric column.7)The reduction of longitudinal bars in the compressive zone leads to the reduction of the cross-sectional area,which has little effect on the cracking load and ultimate load of the eccentric column.Considering only the reduction of the cross-sectional area of the longitudinal bar in the compressive zone,the influence on the large bias column and the small bias column is small.When the cross-section area of compressive zone is zero,the corrosion rate of the vertical bar in the nip reaches 100%.At the time,the cracking load and ultimate load of large bias columns were only reduced by 5% and 12%,respectively,and the small bias columns were only reduced by 8% and 15%,respectively.8)At the end of this paper,the effect of corrugation of the concrete cover in the compressive zone on the flexural rigidity of the bias column is considered,and then the mid-span deflection of the biased column is affected.The deflection and eccentricity are corrected,and the rust expansion crack width is introduced.The reduction factor establishes the evaluation formula for the ultimate bearing capacity of the rust bias column.This formula changes the practice of reducing the cross section of the rust bias column during the calculation of the bearing capacity of the original rust-biased column,and the correction method is more straightforward.It can reflect the degree of damage of the crushed zone rust damage to the bearing capacity of the bias column,and has certain reference significance.