Study On Axial Compressive Behavior And Fire Performance Of Square Steel Tubular Columns Filled With Recycled Lump Concrete And High-strength Steel Angles

Concrete filled steel tubular(CFST)column can provide high load-bearing capacity and ductility,but exposure of steel tube causes fire performance of CFST column relatively poor.To solve this problem,this paper presents a novel type of column called square steel tubular column filled with recycled lump concrete and high-strength steel angles.Under the condition that the total steel consumption is unchanged,the column reduces thickness of steel tube and adds high strength steel angle inside.It strives to significantly improve fire performance of CFST column without degrading performance of specimen under axial compression.To provide technical support for engineering application of the column and combine the thought of recycling of waste concrete,the main reseach works are as follows:1.Six square steel tubular columns filled with recycled lump concrete and high-strength steel angles were tested under axial compression,and the influences of the replacement ratio of demolished concrete lumps,yield strength of steel angles,and clearance between the steel angle and steel tube on compressive behavior of these columns have been investigated.It is found that:(1)under the condition that the total steel consumption is almost unchanged,the column's axial load bearing capacity and ductility index can be enhanced to some extent,and the initial stiffness of the column is almost unchanged or improved a little by thinning the steel tube properly,setting high-strength steel angles in the tube,and reserving a certain clearance between them;(2)with the increase of clearance between steel angle and inner wall of steel tube,the initial stiffness of the column decreases gradually and the descending stage is slower,but the axial load bearing capacity changes a little;(3)the improved formulas can predict the axial load bearing capacity of such column well;4)the yield strength of high strength steel angle can be brought into full play by choosing suggested type of steel angle.2.Based on ABAQUS,numerical simulation model of CFST columns filled with recycled lump concrete and high-strength steel angles were modeled.The influences of strength of recycled lump concrete,outer side length of steel tube,ratio of steel angles weight to total steel weight,yield strength of steel angle,clearance between steel angle and inner wall of steel tube and initial width-to-thickness ratio have been analyzed.It is found that:(1)under the condition that the total steel consumption is almost unchanged,axial load bearing capacity and ductility index of the columns are better than CFST columns;(2)with the increase of the ratio of steel angles weight to total steel ranging from 10% to 30%,and the increase of yield strength of steel angle ranging from 500 Mpa to 950 MPa,axial load bearing capacity of the column increases little.(3)with the increase of clearance between steel angle and inner wall of steel tube ranging from 20 mm to 50 mm,axial load bearing capacity of the column changes a little.3.Three specimens were tested for fire resistance.The effects of high-strength steel angles and clearance between the steel angle and steel tube on fire performance of such columns have been examined.It is found that:(1)under the condition that the total steel consumption is almost unchanged,the fire endurance of such column can be remarkably increased by more than 200% by thinning the steel tube properly,setting high-strength steel angles in the tube,and reserving a certain clearance between them.(2)in the case that the steel consumption remains unchanged,the fire resistance of such column can be further enhanced by properly increasing the clear distance from the steel angle to the steel tube.