Ultimate Bearing Capacity And Blast-resistant Characteristics Analysis Of Square Concrete-filled Steel Tubular With Spiral Stirrups

Explosions occurred frequently in recent years which led to great damage to buildings nearby.Square concrete-filled steel tubular with spiral stirrups was a new type of steel-concrete composite member.The advantages such as high load capacity,good ductility,easy for construction,and good fire resistance performance made it a good choice for structure design in explosion resistance.Existing studies mainly focused on bearing capacity formula using the method of regression analysis.But these formulas often had no theories foundation.And so far,there is no research on dynamic response to blast load reported.In this research,the analysis of bearing capacity under axial compression and dynamic response to blast load has been done with square concrete-filled steel tubular with spiral stirrups.The main jobs and conclusions are as follows:(1)The ultimate bearing capacity formula of square concrete-filled steel tubular with spiral stirrups under axial compression was deduced on the unified strength theory.The area of concrete was divided according to composition of restriction.The restriction from both spiral stirrups and steel tubular has been taken into consideration.The square steel tubular was considered as circular one that had the same areas of steel.A formula was deduced on the base of the unified solution of limit strength of thick wall cylinder using the unified strength theory.And then,the formula was introduced to stub columns of different cross sections.At last,parameter analysis has been done.(2)The theoretical solution to dynamic displacement has been given on the square concrete-filled steel tubular with spiral stirrups subjected to blast load.Three parts of the square concrete-filled steel tubular with spiral stirrups were considered to be same according to the unified theory,and the ultimate moment resistance was obtained.The strain rate effect has been taken into consideration.For simplicity in calculating the dynamic response,the column was considered as equivalent single degree of freedom system,and the blast load curve was considered as descending triangles patterns.(3)Numerical simulation of dynamic response to blast load has been done on the square concrete-filled steel tubular with spiral stirrups.FEM pre-processing was done in Hypermesh,and stress-initialization was set for axial compression before explicit dynamic analysis,and then the problem was solved in LS-DYNA Solver.Finally the results such as displacement,stress,strain,and failure mode was studied.In addition,parameter analysis on dynamic response has been done.The influence of axial compression ratio,material strength,diameter and pitch of the stirrups,proportion distance were discussed,and proposals for design have been given.