Girma, Zerayohannes (PhD)Melekte, Muluken2021-03-302023-11-112021-03-302023-11-112021-02http://etd.aau.edu.et/handle/12345678/25811Concrete filled double circular steel tube (CFDCST) columns are exceedingly efficient categories of composite columns, which can be considered as modified sorts of circular concrete-filled steel tube (CFST) columns. They also possess the properties of circular CFST columns with extra improvements. The double confinement effect observed in CFDCST short columns is an important aspect, which tremendously improves the load-bearing capacity of the column and the CFDCST‟s performance depends on the constituent material's individual property and combined action effects. These types of short CFDCST columns are importantly used in composite multistory building structures for taking most of the earthquake forces acting on the system and they could be used in slopped grounds as footing columns and also positioned in the requirement of an intermediate beam for supporting heavy compression loads. Despite the CFDCST column‟s vast advantages, very limited researches have been carried specifically in examining the influential factors related to the change in material‟s strength, and geometrical properties. There is also complexity in accompanying finite element (FE) analysis, especially in defining the materials‟ combined action. Therefore, in conducting a parametric study using FE analysis; this paper provides a basic understanding of the axial load performance of CFDCST short columns. Besides, the possible advantages of using CFDCST columns instead of CFSTs are discussed in detail. Possible FE analyzing techniques used in this study were verified by experimentally conducted and published seven CFST and four CFDCST column tests. Moreover, seven basic sections of model specimens are classified to study the axial load behavior of circular CFST and CFDCST short columns in a total of fifty-eight model analyses. Different parameters are also studied regarding the change in material strength and geometrical variations. The analysis result assures that CFDCST columns are much better in providing extra-axial resistance through the development of a higher confinement tendency. It is also found that the insertion of an internal steel tube has a great influence to tolerate the variation in the external D/t ratios, which can be taken as a measure to enhance the capacity of CFST columns. In addition, no immediate failure occurred in CFDCST columns and failure modes tend to develop lower lateral displacement at the average height of the column due to the presence of the internal steel tube.en-USCFST and CFDCST short columnsDual confinement effectThesis