Cold-formed Steel Hollow Sections Research Articles

Experimental investigation on cold-formed steel hollow sections with moderate heat treatment under combined compression and cyclic lateral loads

This paper presents an experimental investigation on cold-formed steel rectangular and square hollow sections (RHSs and SHSs) with subsequent heat-treatment under combined compression and cyclic lateral loads. A total of 25 specimens designed with different parameters, including slenderness ratios (b/t and d/t) and axial load ratio (n) ranging from 0 to 0.5 were tested. Material tests were carried out to confirm the material ductility requirements stated in Eurocode being reached. Failure modes, moment-rotation curves, secant stiffness, energy dissipation and plastic hinge length presented were analysed. In addition, deformation capacity was evaluated in terms of maximum and ultimate rotations. The comparison results between plastic rotation limits proposed by design codes and the test results indicate that AISC 341-16 is more suitable for the design of cold formed hollow sections with moderate heat treatment under this investigation, though the recommended reduction factor of axial load might be conservative.

Structured light-based dynamic 3D measurement system for cold-formed steel hollow sections

In the cold-formed steel hollow section manufacturing process, one of the key stages is forming an inspection to check whether it meets the requirement. In this paper, a dynamic 3D measurement system based on low-cost structured light was presented, which can be used to measure the dimensions of a cold-formed steel hollow section in real-time. The system is mainly composed of four sets line-structured light inspection device. A temporary coordinate is proposed to assist in solving multi the calibration of structured light plane. An optimisation method of L-M algorithm is proposed to solve the problem of stitching accuracy of point cloud contour. A point cloud simplification processing method is proposed for solving main parameters. The side length measurement error of the system is within ±0.05 mm, and the outer arc radius measurement error is within ±0.45 mm. All parallelisable tasks can achieve an acquisition rate of up to 25 fps.

Simplified models for residual stresses and equivalent plastic strains in cold-formed steel elliptical hollow sections

Abstract The manufacturing process of cold-formed steel members induces cold work which has a significant effect on their structural performance. In order to assess this cold-working effect, residual stresses and equivalent plastic strains need to be quantified. A finite element-based method was recently proposed by the authors for predicting the coexistent residual stresses and plastic strains in cold-formed steel hollow sections. In the present study, this finite element-based method was employed to carry out a parametric study in order to generate numerical data of the residual stresses and coexistent equivalent plastic strains in cold-formed steel elliptical hollow sections (EHS) for a wide range of steel grades (including both normal grade steels and high strength steels) and section sizes. By analyzing these numerical data, simplified models for residual stresses and coexistent equivalent plastic strains in cold-formed steel EHS are proposed. The simplified models can be employed to define the initial states of cold-formed steel EHS members in a nonlinear finite element analysis for their structural performance, and thus can be used to examine the cold-working effect on the member behavior in future studies.

Tests of cold-formed normal and high strength steel tubes under tension

Abstract The construction field has a widespread usage of cold-formed steel tubular members in various types of structures. In recent decades, extensive research studies have been carried out on cold-formed steel hollow sections under various loading conditions. However, there is a lack of research study on the tensile performance of cold-formed steel tubular sections with the whole cross-section under tension. Therefore, the focus of this study is to investigate the structural behavior of cold-formed steel tubular sections with and without circular perforations under pure tension through experimental investigation. Eleven cross-section series made of cold-formed normal and high strength steel were considered. The nominal outer dimensions of hollow steel tubes ranged from 20 to 100 mm and the nominal wall thicknesses ranged from 1.5 to 8 mm. The mechanical properties were determined through tensile coupon tests. The measured 0.2% proof stresses ranged from 323 to 795 MPa. A total of 24 tensile tubular specimens, including twelve specimens with circular holes and the rest without hole, were tested with full cross-section under pure tension. Tensile test results of cold-formed steel tubular sections were discussed and compared with the tensile capacities predicted by the North American Specification, the Australian/New Zealand Standards and the European Code. The comparisons show that the existing design rules provide quite conservative and reliable tensile strength predictions for cold-formed steel tubular sections.

Mechanical properties of YSt-310 cold-formed steel hollow sections at elevated temperatures

This paper presents an experimental investigation into the mechanical properties of YSt-310 cold-formed steel hollow sections, which is one of the most widely used structural steel in India, under steady state elevated temperatures ranging from approximately ambient to 800 °C. Elevated temperature stress–strain curves and reduction factors of key material parameters such as Young's modulus; yield stress; stresses corresponding to 0.5%, 1.5% and 2.0% strains; tensile strength and corresponding strain (%); fracture strain (%) and Ramberg-Osgood parameter are reported. Further, the reduction factors obtained from the current experimental programme are compared with predictions based on current fire design standards as well as those reported in literatures for cold-formed steel at elevated temperature. Statistical analysis was carried out to check the reliability of the elevated temperature reduction factors and it was found that the existing design rules are inaccurate and not applicable to cold-formed hollow steels at elevated temperature. A new set of fire design reduction factors are then proposed for cold-formed steels hollow sections based on lower bound values, considering both the current and previously reported experimental data. The newly proposed reduction factors are shown to offer improved mean (conservative) and reliable predictions and therefore recommended for inclusion in future revisions of fire design codes.

Finite element-based method for residual stresses and plastic strains in cold-formed steel hollow sections

Residual stresses and plastic strains in steel tubes are induced by their manufacturing processes and play an important role in determining their mechanical and structural behaviour. The manufacturing process of cold-formed steel hollow sections can be divided into four main stages: (1) the coiling and uncoiling of a steel strip, (2) the transverse bending of the uncoiled strip into a circular shape, (3) the welding of the circular tube along the longitudinal strip edges, and (4) the shaping of the welded circular steel tube into a specific cross-sectional shape. In this paper, a finite element-based method is presented for predicting residual stresses and equivalent plastic strains in cold-formed steel hollow sections (including elliptical, square, and rectangular shapes of both normal grade steel and high strength steel). In this method, residual stresses and equivalent plastic strains due to the coiling, uncoiling and transverse bending operations are predicted analytically, and applied as the initial state for the subsequent finite element simulations of both welding and shaping operations. Predictions from this method show satisfying agreement with experimental measurements, which demonstrate the validity of the proposed method. This method can predict the distributions of residual stresses and equivalent plastic strains across the thickness and over the cross section, which are too complex to be measured completely in laboratory. The method provides a tool for investigating the effects of different material and forming parameters on the resulting cold work and structural behaviour.

Hot-dip galvanizing of cold-formed steel hollow sections: a state-of-the-art review

A good understanding of the effects of galvanizing on the short- and long-term behaviours of steel components is essential for structural design. This review paper is motivated by a series of recent reports on cracking in galvanized cold-formed tubular steel structures and the limitations of current steel product standards and steel design specifications in this field. The steel-related and galvanizing-related factors, different pre-galvanizing countermeasures for brittle cracking and the available technical documents are summarized. An extensive bibliography is provided as a basis for future research and development in this field.

Post-fire mechanical properties of cold-formed steel hollow sections

Cold-formed steel hollow sections are extensively used in building construction due to their potential benefits over hot-rolled and open cold-formed steel sections. Their performance in fire is important for successful structural applications while their post-fire residual capacities are also important to assess the extent of their fire damage and reusability with and without strength enhancing techniques. This paper presents the details of an experimental investigation on the post-fire mechanical properties of cold-formed steel hollow sections. Tensile tests were performed on coupons exposed to elevated temperatures varying from 100 to 800 °C and then cooled down to room temperature. These coupons were cut from cold-formed steel square and rectangular hollow sections with varying thicknesses and grades. The results from this investigation provided post-fire stress-strain curves, yield strengths, ultimate strengths and elastic modulus, and their reduction pattern. They show that the post-fire mechanical properties of cold-formed steel hollow sections are different to those of open cold-formed channel and hot-rolled sections. New predictive equations were proposed to determine the post-fire mechanical property reduction factors. Post-fire mechanical properties were also compared with their elevated temperature mechanical properties to evaluate their strength gain after cooling down. This paper also evaluates various strength enhancement techniques for use with fire damaged cold-formed steel hollow sections.

Dynamic material performance of cold-formed steel hollow sections: a state-of-the-art review

This paper presents a literature review focused on the material performance of cold-formed, carbon steel, hollow structural sections under impulsive (highly dynamic) loading. Impulsive loading, represented by impact and blast, is characterized by a very rapid, time-dependent loading regime in the affected members and materials. Thus, the effect of high-strain-rate loading is initially reviewed. Next the material toughness, an important energy-absorption property and one measure of a material’s ability to arrest fracture, is considered by means of studying the Charpy V-notch behavior. The response of hollow sections under axial and lateral impact loading is then reviewed.

Elevated temperature material properties of cold-formed steel hollow sections

Elevated temperature material tests on cold-formed steel coupons cut from circular, rectangular and square hollow sections have been conducted, including both steady-state and transient-state tests. The experimental apparatus, methods of testing and results obtained are fully described. Temperature dependent retention factors for stiffness, strength and ductility were determined and compared to those provided in the European Standard EN 1993-1-2:2005 and the Australian Standard AS 4100:1998. It was found that the codified retention factors, despite being derived on the basis of tests on hot-finished material, are also applicable to cold-formed hollow sections. A design proposal from the literature for the prediction of ultimate strain has been also shown to be suitable for application to cold-formed hollow sections. A new expression for predicting strain at fracture has been proposed that provides a lower bound estimate of the test results derived in the current study.

High strain rate behaviour of cold-formed rectangular hollow sections

For blast- or impact-resistant design of steel structures, it is important to use realistic properties of steel under high strain rate. In particular, the substantial rise in yield stress under high strain rate may have important effects on the dynamic behaviour of a steel structure. The high strain rate properties of some steels have been studied in the past; mostly reinforcing bars, plates and hot-rolled sections. The goal of this research is to remedy the lack of knowledge on the high strain rate behaviour of cold-formed steel hollow sections. In this study, four cold-formed Rectangular Hollow Sections (RHS) manufactured by two different cold-forming methods (direct-forming and continuous-forming) have been examined. The dynamic properties of the RHS specimens were determined by performing a total of 166 compressive and tensile Split-Hopkinson Pressure Bar (SHPB) tests at strain rates ranging from 100 to 1000s−1 and their dynamic yield stresses were compared to their static yield stresses, to characterise the strength enhancement of cold-formed RHS under such loading rates.