Experimental Study And Theoretical Analysis On Static Performance Of The Steel Slag Concrete-filled Circular Steel Tube

Concrete-filled steel tube structure has been widely used in practical engineering due to the advantages of high bearing capacity, good ductility and convenient construction and so on. But the shrinkage in the hardening process of core concrete lead to the decrease of bond strength between steel tube and core concrete, and seriously affect the safety and durability of concrete-filled steel tube structure.Because steel slag has the hardness and activity, so it can instead of fine aggregate to mix steel slag expansive concrete, then the steel slag concrete-filled circular steel tube(SCFST) is manufactured by filling the steel slag expansive concrete in the steel tube,which not only can fully play the advantages of two kinds of materials, but also can promote the recycling of solid waste, reduce project cost, and has significant economic and social benefits. Therefore, the experimental study and theoretical analysis on static behavior of SCFST column is developed, which mainly include the following contents:The experimental study on mechanical properties of SCFST columns subject to axial compression are carried out, the effects of aspect ratio, diameter-thickness ratio and expansion rate on mechanical properties of SCFST column such as failure mode,bearing capacity, deformation, stiffness and the stress-strain curve are analyzed, test results show that the failure pattern of short columns subject to axial compression is compression bucking failure, the failure pattern of mid-height columns subject to axial compression is compression bending bucking. With the increment of aspect ratio,the bearing capacity and ultimate compressive strain is gradually decreased, the enhancement degree of bearing capacity is gradually increased, the speed of stiffness degradation and strain increment is gradually accelerated. with the increment of diameter-thickness ratio, the bearing capacity and the ultimate compressive strain is gradually decreased, the speed of stiffness degradation is gradually accelerated, but the speed of strain increment is gradually reduced. Compared with the specimens with steel slag expansion ratio of 3.5×10-4, the enhancement degree of bearing capacity and the ultimate compressive strain with steel slag expansion ratio of 2.8×10-4 is bigger,the speed of stiffness degradation is slower, the elastic stage of stress-strain curves are longer.The experimental study on mechanical properties of SCFST columns subject to eccentric compression are carried out, the effects of aspect ratio, eccentricity andexpansion rate on mechanical properties of SCFST column such as failure mode,bearing capacity, ductility, stiffness and the related load-displacement relationship curves are analyzed, test results show that the failure pattern of short columns subject to eccentric compression is compression bending bucking, the failure pattern of mid-height columns subject to eccentric compression is elastic-plastic instability failure. With the increment of aspect ratio, the bearing capacity and ductility coefficient is gradually decreased, the enhancement degree of bearing capacity is gradually increased, the speed of stiffness degradation and deflection increment is gradually accelerated. With the increment of eccentricity, the bearing capacity and ductility coefficient of specimens is gradually decreased, the speed of stiffness degradation and deflection increment is gradually accelerated. Compared with the specimen with steel slag expansion ratio of 3.5×10-4, the enhancement degree of bearing capacity and ductility coefficient with steel slag expansion ratio of 2.8×10-4 is bigger, the speed of stiffness degradation is slower, the load-displacement relationship curves are longer.Based on the experimental study, considering the effect of self-stress between steel tube and steel slag concrete, the reinforcement coefficient of axial compressive strength of steel slag concrete is introduced to simulate the expansive of steel slag concrete. The calculation formula of bearing capacity and deformation of SCFST columns subject to axial and eccentric compression is deduced, and the related simplified calculation formula is also put forward. Based on the reasonable stress-strain model of materials, using the fiber model method, the MATLAB program is compiled to simulate the full-range analysis of SCFST columns subject to axial and eccentric compression. Based on the compiled MATLAB program, the effects of strength grade of steel slag concrete, steel yield strength, steel ratio and axial compression ratio on stress-strain, load-deflection and moment-curvature of SCFST columns are analyzed, and then the stress-strain, load-deflection and moment-curvature model of SCFST columns are established.Based on the reasonable stress-strain model of material, using finite element analysis software ABAQUS, the finite element analysis model of SCFST columns subject to axial and eccentric compression is established. Based on the finite element analysis model, the effects of strength grade of steel slag concrete, steel yield strength,and steel ratio on the stress-strain, load-deflection and moment-curvature ofSCFST columns are analyzed, and the working mechanism of SCFST columns subject to axial and eccentric compression is revealed.