Behaviour of cold-formed steel-concrete composite columns under axial compression: Experimental and numerical study
Introduction
The extensive use of thin-walled members in constructional industries is mostly due to their high strength-to-weight attributes and superior fabrication versatility. Primarily, hot-rolled steel sections are used for steel–concrete composite structures [1]. However, nowadays cold-formed sections are begin to replace the hot-rolled sections due to their inherent advantages [2]. The composite columns especially hot rolled sections are made by two techniques, one is encased steel section, and the other is Concrete-Filled Steel Tubular (CFST) section. When comparing these two techniques, the confinement effect in CFST section has proven beneficial to withstand larger gravitational loads than its counterpart [3]. Rahnavard et al. (2022) have studied the behaviour column at four different cross sectional shapes and found that steel component withstands higher compressive strength when it is used in composite column than bare steel column.[4] Evirgen et al, 2014 [5] have studied the behaviour of column with various cross-sectional shapes like Circular, hexagonal, rectangular and square sections and found that circular section outstands all. The major limitation of square and rectangular concrete filled composite sections is its inability to withstand the outward buckling of steel tubes [6], [7] which was witnessed in cold formed composite columns also [8]. Ge & Usami, 1994 have increased the performance of square and rectangular column by adopting different stiffening schemes [9]. Huang et al. (2002) proposed a set of four steel bars at regular spacing along the tube axis and it found to increase both strength and ductility [10].
Tao et al (2005) presented the improvement of ductile behaviour of stiffened composite stub columns with various methods as shown in Fig. 1. [11] Their research showed that although all different stiffening methods have potentials to improve the ductility of the stiffened stub columns to some extent, adding fibres to concrete is the most effective and reliable measurement in increasing the ductility capacity.
Nassirnia et al. (2015) studied the effect of corrugation in delaying the local buckling of hollow columns, and it exhibited better compressive strength and energy dissipation. It was found that the ductility increases with the number or width of inner stiffeners.[12].
Usually, in hot rolled members stiffeners can be directly welded to the section. However, such practice is not feasible for thin-walled section as it may lead to generation of residual stresses and geometrical imperfection. Hence stiffening can be achieved by corrugating the flat sheet. The corrugation shape provides continuous stiffening which permits the use of thin sheets. A corrugated sheets can easily be bent in one direction, whereas it retains its rigidity in the other direction. Fabrication costs for elements with corrugated panels are normally lower than those elements with additional stiffeners.
Thus, the present study aims to evaluate the effectiveness of corrugations as web stiffener in the load-carrying capacities of cold formed steel hollow column and cold formed steel concrete composite column. The square cross section was adopted since it would be difficult to make circular section in cold formed steel. The square columns were tested for two conditions with and without stiffeners (ie) column made of flat and corrugated flat sheet respectively. A parametrical study was also carried out by adopting various changes in corrugation. The flat sheets were bent and formed as square section using self-tapping screws. In this study, specimens were tested for with and without stiffener condition in three different slenderness range. Numerical studies were done for various stiffeners and appropriate buckling curve for various slenderness range were presented.
Section snippets
General
An experimental program comprising 36 specimens was undertaken to determine the concentric axial load carrying capacity of square cold-formed plain steel columns (without stiffeners), cold-formed steel profiled columns (with web stiffeners), cold-formed steel plain composite columns, and cold-formed profiled composite columns. The effectiveness of an under-investigated connection system using self-tapping screws is also evaluated in this study.
Test specimens
The column dimension adopted for the experimental
Analytical studies
Design philosophies proposed by some of the prominent codes are used to estimate the axial strength of the test specimens.
Reliability analysis
Reliability analysis was performed to evaluate relative reliability of codal guidelines for performed tests. The analysis was performed as recommended in North American Specification for the design of cold formed steel structural members. The reliability index was calculated using the equation 17. The parameters Mm, Fm, Vm, Vf, were assumed as 1.10, 1.00, 0.10, and 0.05 respectively were determined by statistical analysis. Pm is the mean value included in the Table 4, Table 5. The coefficient
Numerical modeling and validation
A numerical modelling framework was developed in conjunction with the experimental data to conduct a parametric study. Finite element (FE) models were developed for each of the specimens tested experimentally. In this work, the commercial FE software package (ABAQUS) is employed to develop the computational models.
Parametric study
The literature commented on the improved axial behaviour of CFS columns with an increase in the stiffener angle, stiffener dimensions and stiffener numbers [12], [30]. Parametric studies were carried out to assess the effect of the stiffener angles, sizes, and stiffeners on composite columns. The details of the models adopted for numerical analysis are given in Table 7. Nomenclature CM is used for the profiled control model with a 120.96° angle. For the other models, the first number indicates
Buckling curve from numerical studies
The parametric study was extended to a wide range of slenderness range for the length of the column varying between 500 mm and 5000 mm. The reduction factor for buckling, χ (P/Py), is plotted against the non-dimensional slenderness ratio, λ as shown in Fig. 28.
The non-dimensional slenderness ratio is evaluated as:
λ (27).where Py is the plastic resistance of the section,
Pe is the elastic buckling load, EIeff is the effective stiffness of
Concluding remarks
Composite cold-formed steel–concrete columns (CFSCs) exhibit improved strength and ductility characteristics while the introduction of web stiffeners can further enhance their buckling performance. The cold-formed steel tube sections employed in this study were formed using self-tapping screws, a technique which is prevalent is several developed countries.
This study focuses on the effect of stiffeners on the concentric axial load behaviour of composite cold-formed steel–concrete columns with
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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