Study On Axial Compression Performance Of Circular Steel Slag Concrete Filled Steel Tubes By Steel Jacket

In the initial stage of elasticity of concrete-filled steel tube columns,due to the Poisson’s ratio of steel（about 0.3）is different from that of core concrete（about 0.2）,making the transverse deformation of steel pipe larger than that of concrete when the two are subjected to axial load together,leading to the separation and dehiscence of the two,weakening the restraint effect of steel tube on core concrete,thus leading to a decrease in the bearing capacity of the specimen.Therefore,a form of restraint is needed to improve the bonding interface of the concrete-filled steel tube in the elastic stage.Steel slag is one of the bulk solid wastes with the lowest utilization rate of major steel enterprises,and up to 2020,the accumulated stockpile of domestic steel slag in China is nearly 2 billion tons.With the progress of society and the development of productivity,how to reasonably utilize steel slag has become an imminent social problem.In order to solve the above problems,external restraint in the form of steel jacket is used to limit the lateral deformation of concrete and steel pipe at the beginning of elastic stage,and steel slag is used to make steel pipe steel slag concrete column,and steel jacket restraint is combined with steel pipe steel slag concrete column to form steel jacket restrained round steel pipe steel slag concrete column.The axial compression performance of steel jacket restrained round steel pipe steel slag concrete column is studied by using 1000 t multifunctional structural test system,and the main research results are as follows:（1）Axial compression tests were conducted on the specimens without steel jacket restraint and steel jacket restraint specimens.By comparing the mechanical properties and damage morphology of the two,it was concluded that the damage morphology of the specimens without steel jacket restraint was mainly end buckling,while the buckling of the steel jacket restraint specimens mainly occurred between the two steel jackets.The restraint form with steel jacket can effectively limit the lateral deformation of concrete-filled steel tube and improve the interfacial bond at the beginning of the elastic phase of concrete-filled steel tube.The bearing capacity of the steel sleeve restrained specimens were greater than that of the specimens without steel sleeve restraint,and the bearing capacity of the steel sleeve restrained specimens was increased by 23% at maximum compared with that of the specimens without steel sleeve restraint.（2）The effects of specimen diameter-thickness ratio and core concrete steel slag replacement rate on the mechanical properties of the specimens were analyzed.Comparing the bearing capacity and N-? curve of each specimen,it was concluded that: the steel pipe slag concrete bearing capacity was the largest when the steel slag replacement rate was 75%;the effect of steel jacket on the bearing capacity of specimens was more significant in the specimens with larger diameter-to-thickness ratio（D/t=33.6）,with an average increase of 13.1%,while the average increase in the specimens with smaller diameter-to-thickness ratio（D/t=21,22）was 6.7%.The improvement was 6.7%.（3）The actual value of the bearing capacity obtained from the axial compression test in this paper is compared with the calculated value of the ultimate bearing capacity formula of concrete-filled steel tube domestically and abroad,and it is found that the formula of Zhong Shantong,the formula of Han Linhai,the formula of European code EC4-2004 and the formula of American Institute of Steel Construction AISC3600-16（2016）and the formula of American concrete structure code ACI318（2014）are conservative,while the calculated value of Cai Shaohuai formula is more consistent with the bearing capacity test value of this paper,and the ratio of the calculated value of bearing capacity to the test value is 0.92 on average.On the basis of the axial compression test,the parameters of Cai Shaohuai formula are modified,and the ultimate bearing capacity formula applicable to the specimens of this paper is obtained,and the ratio of the calculated value of the modified formula of bearing capacity to the test value is 0.99 on average.