Axial Compression Performance And Bearing Capacity Calculation Of Multi-spiral Composite Stirrup Confined Concrete Square Column

Circular spiral stirrups have good constraint effect,but their application in rectangular section columns is still limited.In practical engineering,square section concrete columns are more common.In order to apply the spiral stirrups suitable for cylinders to rectangular columns,scholars have carried out research on multiple spiral stirrups(composite)confined concrete columns,but these studies are mainly concentrated in Taiwan,China.The research in the mainland is rare and lacks relevant design specifications.Therefore,through the test of the research group and the collection of existing test data,this paper analyzes the test data of 66multi-helix composite stirrup confined concrete square columns,establishes the calculation formula of the axial compression bearing capacity of this type of square columns,and uses the finite element software to supplement the axial compression performance of this type of square columns.The main work and conclusions are:(1)Based on the axial compression test of 7 multi-spiral composite stirrup confined concrete square columns and the test data of 59 multi-spiral composite stirrup confined concrete square columns,the effects of stirrup yield strength,volume stirrup ratio and section type on the axial compression performance of multi-spiral composite stirrup confined concrete were analyzed.The results show that the multi-spiral composite stirrup constraint can significantly improve the peak strength,peak strain and ductility of concrete columns.The constraint effect of five-spiral stirrups is better than that of four-spiral stirrups,and both of them are better than the constraint effect of traditional well-shaped composite stirrups.Under the same conditions,the strength and ductility of the specimens increase with the increase of stirrup yield strength or volume stirrup ratio.(2)Combined with the test data,the twin shear unified strength theory was introduced to analyze the constraint mechanism of multi-helix composite stirrups.The calculation formula of axial compression bearing capacity of this type of square column was established and compared with the calculation formula of bearing capacity proposed by different national codes and scholars.The results show that the calculation results of the axial compression bearing capacity formula proposed in this paper are closer to the experimental values.Based on the proposed formula,the influencing factors of the axial compression bearing capacity of this type of column are analyzed.The results show that reducing the stirrup spacing and increasing the stirrup strength or concrete strength can effectively improve the axial compression bearing capacity of the column.While changing the strength of concrete,the spacing and strength of spiral inner hoops,the number of circular spiral inner hoops is 8 to obtain the maximum axial bearing capacity of this kind of column.(3)ABAQUS finite element software was used to numerically analyze the axial compression performance of multi-spiral composite stirrup confined concrete square columns,and compared with the experimental results.The results show that the finite element model can better simulate the stress and deformation characteristics of this type of square columns.At the same time,125 models were established for parametric analysis.The results show that the bearing capacity of multi-spiral composite stirrup confined concrete square columns increases with the increase of concrete strength grade,and the strength enhancement coefficient and deformation enhancement coefficient decrease with the increase of concrete strength.When increasing the strength of the inner and outer stirrups or reducing the spacing of the inner and outer stirrups simultaneously,the enhancement of the constraint effect is the most obvious,the constraint effect of increasing the strength of the spiral inner stirrups or reducing the spacing of the spiral inner stirrups is the second,and the constraint effect of increasing the strength of the rectangular outer stirrups or reducing the spacing of the rectangular outer stirrups is the lowest.For the four-spiral composite stirrup confined concrete square column,increasing the diameter of the spiral inner hoop can effectively improve the strength and ductility of the specimen.For the five-spiral composite stirrup confined concrete square column,reducing the ratio of the diameter of the spiral inner hoop constraint(that is,the ratio of the diameter of the outer spiral inner hoop constraint to the diameter of the central spiral inner hoop constraint)can also improve the strength and ductility of the specimen to a certain extent.The increase of the number of spiral hoops and the interlocking treatment of spiral hoops can effectively improve the strength and ductility of the specimens.