Citation: Hassan, M.K.; Saha, S.; Rahnamayiezekavat, P. Behaviour and Design of Innovative Connections of Prefabricated CFST Columns under Tension. Sustainability 2023, 15, 2846. https:// doi.org/10.3390/su15032846 Academic Editor: Baojie He Received: 7 January 2023 Revised: 30 January 2023 Accepted: 31 January 2023 Published: 3 February 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). sustainability Article Behaviour and Design of Innovative Connections of Prefabricated CFST Columns under Tension Md Kamrul Hassan * , Swapan Saha and Payam Rahnamayiezekavat School of Engineering, Design and Built Environment, Western Sydney University, Penrith, NSW 2751, Australia * Correspondence: k.hassan@westernsydney.edu.au Abstract: This paper investigates the tensile behaviour of prefabricated concrete-filled steel tube (PCFST) columns with bolted connections. Innovative bolted column-column (BCC) connections are developed using standard structural bolts to simplify the construction process for the connection of two PCFST columns, especially for the corner, edge, and interior columns. The behaviour of BCC connections in PCFST columns under tension has been investigated, adopting the finite element (FE) modelling approach. Parametric studies are carried out to understand the influence of bolt arrangements (TB = 4, 6, 7, 8), base plate thickness (t bp = 8, 10, 14, and 18 mm), bolt diameters (d b = 16, 18, 20, 24 mm), vertical stiffeners (t hs = 4, 6, 8, 10 mm), horizontal stiffeners (t hs = 10, 12, 13, 15 mm), and yield strength of steel tube (f y,t = 380, 450, and 550 MPa) on the behaviour of PCFST columns with developed BCC connections. The results show that the PCFST columns with the developed BCC connections can attain sufficient tensile strength and satisfy the tensile strength requirements recommended in AS5100 and the robustness requirements in AS1170. The outcome of this paper will be useful to practising structural engineers to design prefabricated CFST columns with BCC connections under tension. Keywords: prefabricated CFST columns; prefabricated column connections; structural bolts; steel-concrete composite structure; tension behaviour; numerical analysis 1. Introduction In practice, prefabricated construction systems are limited to timber, reinforced con- crete (RC) and steel structures. The prefabricated composite structures using concrete-filled steel tubular (CFST) columns are limited. However, CFST columns have high merit in the construction of prefabricated steel-concrete composite structures due to their structural and constructional benefits [1,2]. CFST columns are fabricated without any additional form- work, as the hollow steel tube is used as formwork, which reduces the construction cost and time. Even concrete damage usually observed during the transportation of conventional prefabricated RC columns can be overcome by utilising the steel tubes in the CFST col- umn. Steel tubes effectively protect the inner concrete core of CFST columns from damage during transportation. Extensive research investigations on CFST columns for on-site construction were con- ducted experimentally and numerically under different loading conditions, such as compres- sion [3–17], bending [18–27] and tensions [28–32]. In the conventional construction of CFST columns, welded connections are widely used to connect one steel tube to another steel tube of CFST columns, which is assumed to behave similarly to continuous CFST columns without connections. The tensile behaviour of CFST columns without connections was investigated by Han et al. [28] and compared with the design code of AIJ [33], AISC [34], and EC4 [35]. In recent years, grouted sleeve connections [36–39], base plate connections [40–43] and demount- able connections [44,45] were investigated under either tension or bending. The grouted sleeve connections were proposed for the construction of prefabricated square CFST columns under tension [39], and the demountable connections using blind bolts were proposed for the demountable construction of CFST columns [44]. Sustainability 2023, 15, 2846. https://doi.org/10.3390/su15032846 https://www.mdpi.com/journal/sustainability