Study On The Torsion Mechanism Of Partially Encased Concrete-Steel Composite Columns

With the rapid development of urban modernization,steel-concrete composite structure has been widely used because of its good force performance.Partially Encased Composite(PEC column),as a new form of steel-concrete combination,has significantly improved its load-bearing capacity compared with steel columns,while the encased concrete has improved the stability and fire resistance of steel columns.PEC columns are gradually being widely used in engineering.At present,there are few studies on the torsional performance of PEC columns,therefore,the analysis of the torsional performance of PEC column structure under torsion is of great significance to the actual engineering construction.In this paper,the correctness of the finite element model is verified by numerical simulation of the PEC column subjected to torsion test and comparison.On this basis,the numerical models of 48 PEC columns were established by using ABAQUS software to analyze their torsional mechanical properties,and the effects of section flange width-thickness ratio,section yield strength and filler concrete strength on the torsional mechanical properties of PEC columns were investigated respectively.The analysis results show that the ultimate torque of PEC column can be significantly improved by decreasing the flange width-thickness ratio,increasing the steel strength and increasing the filler concrete strength;increasing the filler concrete strength can also improve the torsional stiffness of PEC column.On this basis,the pure torsional stress performance of the PEC column is analyzed in the whole process.In the initial stage,the overall torsional angle of the partially encased concrete-steel combination column is very small,and the torque is mainly borne by the filled concrete at this time.With the increase of torque,the filling concrete torsional effect gradually fails,and the section steel gradually bears the torsional effect.In the later stage,the torque-angle of twist curve of PEC column does not appear obvious decline section,the filler concrete can still play a role in restraining the role of steel,so that the PEC column torsional resistance is given full play.In this paper,according to the torsional calculation theory of steel and reinforced concrete members,based on the existing test conclusions and numerical analysis results,based on the superposition principle,while taking into account the mutual restraint between the steel sections and the encased concrete,a calculation method is proposed which can calculate the cracking torque and ultimate torque of the PEC column under the action of pure torsion,and the calculation results are compared with the test and finite element results,and the results show that The calculated values of the formula agree well with the experimental and finite element results.