Effect Of Core Concrete Defects On Mechanical Properties Of Ordinary Circular Steel Tube Concrete Axial Compression Components

Concrete-filled steel tube structures make full use of the advantages of steel tube and concrete working together,so that it has the advantages of high bearing capacity,good plasticity and toughness,strong seismic performance,and so on.However,in the process of construction,due to poor management and the influence of its own structure closure and other factors,the core concrete inside the steel tube will be empty,hole defects and other defects,because the concrete filled steel tube needs the steel tube and the internal concrete to work together,the existence of these defects is bound to affect the structural safety.In the process of pouring concrete into the steel tube,the inner reinforced ring and flange are prone to gas deposition due to poor exhaust,resulting in the circular hole defects in the core concrete.At present,the internal defects of concrete-filled steel tube at home and abroad are mainly studied in the directions of annulus cavitation,spherical crown cavitation and spherical holes.Therefore,it is of great significance to study the mechanical properties of core concrete members with annular hole defects.In this paper,6 specimens with circular hole defects of different shapes and sizes and 1standard specimen were designed and made.The axial compression test was carried out on them.The failure morphology and mechanical properties of different types of specimens were investigated.The contents of this paper mainly include:(1)through the defects with circular holes with different shapes and sizes of steel pipe concrete specimen and zero defect specimen axial compression experiment research,examines the different failure pattern and the bearing capacity of the specimens containing defects weaken degree,defects analysis different shape,different size,and so on the influence of parameters on the mechanical properties of the reinforced concrete member.(2)the load-displacement curve was drawn according to the test data,and the stress changes on the steel tube surface collected by the strain tester were combined to obtain the stress mechanism and failure reasons of the specimens with different degrees of defects through comparison,and the influence law of the hole defects on the mechanical properties of the specimens with concrete filled steel tube column was proposed.(3)on the basis of the verification of the applicability of the finite element software,the finite element software is used to carry out the simulation test and compare with the actual test results to obtain the stress cloud diagram and the load-displacement curve,so as toimprove the analysis of the failure mechanism of the defective specimens.Through the axial compression test and the corresponding simulation analysis,the following conclusions are drawn:(1)the load-displacement curve of concrete-filled steel tubular specimens in axial compression test has developed through three stages: elastic stage,elastic-plastic stage and failure stage.(2)the failure characteristics of concrete-filled steel tubular specimens can be divided into two categories.The first category is local yield failure.The second type is the overall bending failure of the specimen: the steel tube in the middle of the specimen yields,resulting in the overall instability failure of the specimen.However,the ultimate failure form of all specimens in this test is the instability failure of central bending.(3)the existence of defects in core concrete has a significant impact on the ultimate bearing capacity and failure process of concrete-filled steel tube.The ultimate bearing capacity of all specimens with holes and defects is lower than that of non-defective specimens.For circular and semi-circular hole defects,the bearing capacity of concrete-filled steel tubular specimens decreases with the increase of defect size.And under the same defect size,compared with the annular defect,the semi-annular defect weakens the ultimate bearing capacity to a greater extent.(4)due to the lack of core concrete support in the middle of the annular hole defect specimen,the steel pipe in the central position will yield earlier than that in the non-defect specimen.The main failure form is premature bending at the position of the annular hole defect;The failure form of the semi-annular hole defect specimen is mainly typical bending instability.Due to the uneven stress on the core concrete,it bends earlier and the degree of bending deformation is also obvious.(5)an obvious yield platform appeared in the first half of the elastic-plastic stage of yh-1,indicating that the existence of defects makes the concrete-filled steel tube unable to give full play to the advantages of the two working together.(6)the finite element simulation is basically consistent with the failure pattern of the test.The software simulation can effectively verify and supplement the actual test.