Modeling and analysis of centrally loaded double skin composite columns

Composite columns offer several benefits for the earthquake resistant design. They are produced in a variety of cross-sections and by many methods. However, there are some limitations in the application since the behavior of such members under loading is quite different than traditional steel or concrete members. In this thesis, three new models for calculating the ultimate axial strength of centrally loaded composite columns were developed. For this, totally 103 experimental test results on circular hollow section (CHS) concrete-filled double skin steel tubular (CFDST) composite columns given in the previous studies was employed. The models presented herein were generated by using finite element method as well as gene expression programming and artificial neural network techniques. The yield strength, diameter, and thickness of outer and inner steel tubes, concrete compressive strength, length of test specimen, and ultimate axial strength of the CHS-CFDST columns were adopted as investigation parameters. The usefulness of available codes of ACI, Eurocode 4, and AISC, and some existing empirical models suggested by scientists were also statistically evaluated. Furthermore, to investigate the effect of diameter and thickness of outer and inner steel tubes, and concrete strength on such composite columns, a parametric study was performed through finite element analysis. All results were given and discussed comparatively.