Finite element analysis of large diameter high strength octagonal CFST short columns

Octagonal masonry columns have been broadly used in outstanding architectural heritage due to their aesthetical appearance and to support high loads. Nowadays, concrete-filled steel tubular (CFST) columns have been utilised to carry such high load. However, a recent trend in the construction of the CFST columns is to use the high strength concrete (HSC) to increase the usable floor spaces in different buildings due to the global limited land areas. Therefore, this paper combines the architectural demand of the octagonal column shape with the advantages of the CFST columns by investigating numerically, by means of finite element (FE) modelling, the octagonal CFST short columns. Accordingly, validated FE models for the octagonal CFST short columns are employed to perform parametric studies to widen the available knowledge about their behaviour. The paper is mainly devoted for investigating large diameter columns using extensive series of diameter-to-thickness (D/t) ratios ranging from 40 to 200, most of which filled with HSC up to 100 MPa. The ultimate strengths, based on available experiments in literature and current FE investigation, are compared with the existing design models. This comparison indicates that the existing design models are conservative and their accuracy is affected by the D/t ratios. Therefore, a new design model is suggested based on the existing provisions by taking the D/t ratios of the columns into account. This suggested design model is validated by using the existing experimental results and is found to give excellent results. The important factors that affect the strength and behaviour of the octagonal CFST short columns filled with HSCs are additionally discussed in detail, with new conclusions added to literature for the first time.