Compressive Performance Study Of Preplaced Aggregate Concrete-Filled Circular Steel Medium-length Columns

The preplaced aggregate concrete can give full play to the embedded locking effect and skeleton effect of coarse aggregates,and has the characteristics of low shrinkage,low cementitious material consumption and excellent durability,etc.Its application in steel pipe can solve the problem of reduced restraint effect of traditional steel pipe concrete column due to shrinkage of core concrete on the one hand,and reduce the amount of concrete in steel pipe on the other hand,which can promote the green and low carbon development of steel pipe concrete structure.Based on this,this paper took steel pipe preplaced aggregate concrete medium-length column as the research object,analyzed the factors influencing the axial pressure and bias pressure of steel pipe preplaced aggregate concrete medium-length column through axial pressure and bias pressure mechanical performance test and finite element simulation,and established the formula for calculating the axial pressure and bias pressure bearing capacity of steel pipe preplaced aggregate concrete medium-length column,the main research contents and conclusions were as follows:(1)Designed 11 medium-length columns of steel tube-preplaced aggregate concrete and 3medium-length columns of Steel The research shows that: the damage form of the mediumlength column of steel tube-preplaced aggregate concrete is bending instability damage,which goes through elastic stage,elasto-plastic stage and plastic stage;the load-bearing capacity of the medium-length column of steel tube-preplaced aggregate concrete is comparable to that of the medium-length column of ordinary steel tube-concrete,but the axial stiffness of the steel tube-preplaced aggregate concrete specimen is about 1.2 times of that of the ordinary steel tubeconcrete specimen.For the medium-length column of steel tube-preloaded aggregate concrete,when the diameter-thickness ratio of the specimen is reduced from 39.75 to 19.88,the ratio of the circumferential strain to the vertical strain corresponding to the ultimate load on the compressed side increases from 0.53 to 0.68,and the restraint effect increases,and the bearing capacity of the specimen increases by 15% and 28%;when the length-diameter ratio increases from 6 to 15,the bearing capacity of the specimen decreases by 5% and 20% respectively,and the specimen changes from When the eccentricity ratio increases from 0.25 to 1,the ultimate load decreases by 14%,35% and 50% respectively,and the bearing capacity decreases with the increase of eccentricity ratio.(2)Based on the results of axial pressure and bias pressure tests,a finite element model of steel tube preplaced aggregate concrete medium-length column was established to verify the validity of the finite element model.On this basis,the factors affecting the performance of steel pipe preplaced aggregate concrete medium-length columns were expanded parametric analysis to study the effects of different design parameters on the preplaced aggregate concrete mediumlength columns.The study shows that: all the basic parameters of the specimen have a significant effect on the bearing capacity,but the length-to-diameter ratio is the main factor affecting the stability of the specimen,with the increase of the length-to-diameter ratio,the stability coefficient decreases significantly;the other parameters of the specimen have less influence on the stability coefficient.(3)In order to establish the calculation formula of axial pressure and bias pressure for medium-length columns of steel pipe preplaced aggregate concrete,firstly,we tried to apply the domestic and foreign codes to calculate the bearing capacity of medium-length columns of steel pipe preplaced aggregate concrete,compared and analyzed the calculation results,and then established the calculation formula of bearing capacity of medium-length columns of steel pipe preplaced aggregate concrete based on the limit balance theory.The results show that:GB/T 51446-2021 formula calculation results are closer to the experimental value,followed by JGJ138-2016 formula,ANSI/AISC 360-16 formula calculation results and the largest deviation from the test value.The calculated results of the bearing capacity formula established in this paper were in the best agreement with the experimental results.