Nonlinear Analysis of Double Square Steel Tubular Short CFDST Columns

This report presents a numerical model to investigate the behavior of short concrete-filled double skin tubular (CFDST) columns under axial compression. The research focuses on the performance of these structural components, which are increasingly used in construction due to their improved compressive strength and ductility derived from the combination of steel and concrete. The study aims to develop a predictive model for future design by analyzing the effects of different weight loads, local buckling, and biaxial bending. The report includes an introduction to CFDST columns, their significance, and a review of existing literature, including both numerical and experimental studies. It highlights the importance of considering local buckling effects to avoid overestimation of ultimate loads and potential structural failures. The methodology involves a nonlinear analysis to determine the load-bearing capacity of CFDST columns, with the goal of creating a model for accurate calculations in structural design. The literature review examines research by Liang (2009) and Liang & Uy (2000) on numerical analysis and Ahmed et al. (2018) on experimental analysis of CFDST columns. The report underscores the significance of this research in enhancing the understanding and design of CFDST columns in civil engineering.

College of Engineering and Science
NEF4101 Research Project 1
Extended Project Brief [20%]
Project title: Nonlinear Analysis of Double Square Steel Tubular Short Columns Filled with
Concrete
Student Name:
Student ID:
Supervisor:
Date submitted:
28/02/2020
__________________________________________________________________________________

Abstract
Thin walled squarer concrete-filled double steel tubular (CFDST) columns is designed by
outer square steel column filled with concrete as well as the inner square steel tube. CFDST
increasingly being used in the performance-based design applications in construction projects
around the world. CFDST have become popular because they utilize the inherent
characteristics of two building materials; steel and concrete to improve compressive strength
and ductility. This research aims at performing a numerical model to investigate the
behaviour of short CFDST structural components under axial- compression in order to have a
predictive model for future design. This research is necessary and will add to the body of
existing knowledge due to a dearth of studies on the effects of local buckling, which have
gained scant attention during advanced methods of analyzing CFDST performance.

Introduction and background
A contemporary popular design principle being adopted globally in building is performance-
based design; it allows designers to tailor structural members to specific performance levels
based on need (Liang, 2009). Concrete-filled double skin tubular columns (CFDST) are
structural columns is an example of this principle (Ahmed et al. 2020). CFDST is a
composite structural component made up of two steel layers with a concrete layer in between
them. The inner hollow steel section is the reinforcement and formwork for the concrete and
both materials work in a complimentary manner where concrete delays buckling, improving
its ductility. The concrete core is important in adding compressive strength and stiffness to
the tubular column while at the same time reducing the potential for inward buckling. CFDTS
are popular because of their high strength, good fire and seismic performance, as well as high
stiffness to bending (Ahmed et al. 2018).
Aims and Objectives
The aim of this project is to undertake a numerical model to investigate the behaviour of short
CFDST structural components under different weight loads in order to have a predictive
model for using the components under different axial loads and their biaxial bending.
Objectives
 To perform nonlinear research on the long-term load bearing performance and
strength test of CFDST.
 To use the results to develop a predictive model on the CFDST axial load bearing and
biaxial bending to be used in future design.
Significance
This research is significant because of the effect of steel plates in CFDST buckling when
subjected to various loads and this results in the thin walled concrete filled box columns
having reduced performance when under axial compression. Local buckling effects have not

been given much consideration during advanced methods of analysing CFDST performance.
This results in the ultimate loads for the composite frames and columns being overestimated,
and this can result in structural failures (Liang et al.2006). This research, therefore, seeks to
test the performance of short CFDST columns under different loads and develop a predictive
model for accurate calculation of their load bearing capacity for structural integrity.
Literature Review
Numerical Studies on CFST Columns
Liang (2009) used algorithms and theory to conduct a performance-based analysis for
performance-based design and nonlinear analysis of CFST beam columns for local buckling
effects. According to Liang (2009), the performance-based analysis technique involving the
use of theory as well as algorithms is both accurate and efficient as proven by the research
findings and can be directly used in performance-based design for CFST thin walled bam-
columns. Using the finite element method, Liang and Uy (2000), performed a theoretical
study on post local buckling behaviour for steel plates within welded steel box columns with
concrete filling. They investigated effects of various geometric imperfections, rations of
width to thickness, and residual stresses on post buckling effects in CFST columns. The
authors aver that the proposed method that evaluates initial and post local buckling steel
plates reserve strength with imperfections give accurate results comparable to experimental
methods.
Experimental Studies on CFST Columns
Ahmed et al. (2018) performed a numerical and an experimental study on the behaviour of
thin walled rectangular CFDST columns with a rectangular inner steel tube eccentrically
loaded by carrying out various tests under axial and eccentric loading to evaluate their
responses to different design parameters. Experimental verification of developed computer
models was done, and the results show that the computer model can accurately predict the

CFST short column performance metrics from experimental studies. Experimental studies are
effective tools for analysis because they are based on actual data, even theough the results can
also be accurately predicted using numerical methods.

References
Ahmed, M., Liang, Q., Patel, V. and Hadi, M. (2020). Experimental and numerical
investigations of eccentrically loaded rectangular concrete-filled double steel tubular
columns. Journal of Constructional Steel Research, 167, p.105949.
Ahmed, M., Liang, Q., Patel, V. and Hadi, M. (2018). Nonlinear analysis of rectangular
concrete-filled double steel tubular short columns incorporating local buckling. Engineering
Structures, 175, pp.13-26.
Liang, Q. and Uy, B. (2000). Theoretical study on the post-local buckling of steel plates in
concrete-filled box columns. Computers & Structures, 75(5), pp.479-490.
Liang, Q. (2009). Performance-based analysis of concrete-filled steel tubular beam–columns,
Part II: Verification and applications. Journal of Constructional Steel Research, 65(2),
pp.351-362.
Liang, Q., Uy, B. and Richard Liew, J. (2006). Nonlinear analysis of concrete-filled thin-
walled steel box columns with local buckling effects. Journal of Constructional Steel
Research, 62(6), pp.581-591.