۱- Introduction

۲- Experimental investigation

۳- Finite element modeling

۴- Analytical study

۵- Conclusions

References

Abstract

The use of concrete-filled stainless steel tubular (CFSST) members is relatively innovative and new. CFSST columns can be used for bridge piers, multi-story buildings and other supporting structures. However, a common mode of failure with these type of tubular composite columns is inelastic outward local buckling occurring at the column ends. Therefore, this paper presents the results of experimental, numerical and analytical investigations into the behavior of circular CFSST columns strengthened by carbon fiber reinforced polymer (CFRP) wrap and subjected to axial compression loading. The experimental investigation comprised three series of tests. The main variables tested were the diameter to thickness ratio of the stainless steel tube and the thickness of the CFRP wrap. 3D finite element models (FEMs) were developed for CFRP-wrapped CFSST columns using the ABAQUS software and were validated with experimental results. An extensive parametric study was carried out by using the validated FEMs. It was shown from the experimental and FEMs results that CFRP jacketing was highly effective in improving the axial load carrying capacity and axial shortening capacity of the CFSST columns. Finally, an analytical model based on the FE parametric study results was proposed to predict the axial load carrying capacity of the CFRP-wrapped CFSST columns.

Introduction

Recently, stainless steel material has been used as a construction material, while it was previously only used for special purposes or for decoration due to its advantages over carbon steel which include its aesthetic appearance, high resistance to corrosion, ease of maintenance and high fire resistance. Taking into account the long-term cost, stainless steel material can be selected as a competitive material [1]. In addition, one of the reasons for considering stainless steel as a competitive structural material is its favorable mechanical properties and its high ductility. Stainless steel material exhibits a nonlinear stress- strain relationship with no defined yield point, unlike carbon steel material [2]. Many investigations have been conducted into the structural behavior of unfilled (hollow) stainless steel sections. Important early reported studies exploring the structural performance of hollow stainless steel sections were performed by Rasmussen and Hancock [3]. Subsequently, a series of studies has been performed to understand more about these tubular sections [4–۷]. These studies have contributed greatly to the expansion of information on the structural performance of stainless steel elements and, at the same time, have highlighted some shortcomings in the existing design standards such as American stainless steel design specifications SEI/ASCE-8 and EN 1993-1-4. For the sake of simplification, these existing design standards disregarded some mechanical characteristics observed in stainless steel, such as strong strain hardening and the rounded stress-strain relationship. This simplification method, adopted in the existing standard codes, includes using an elastic perfectly plastic bilinear material model that leads to a significant degree of conservatism. A new, efficient and more rational method has been developed to consider the particular stress-strain characteristics of stainless steel [8–۱۰]. Instead of considering that the maximum design stress limit is the 2% proof stress, as in the existing standards, a new method called the continuous strength method (CSM) [11–۱۶] has been developed as a deformation-based design method to exploit the noticeable strain hardening in the determination of stainless steel cross-section resistances. However, the initial high cost of stainless steel material has limited the extensive use of stainless steel material in structural construction. Hence, concrete-filled stainless steel tube (CFSST) columns have been developed to balance the high initial stainless steel material cost, as well as to enhance the structural behavior.