Search

This paper presents an experimental study on the behavior of low-strength concrete columns confined with cold-formed steel under axial compression. The laboratory test specimens consist of four groups of rectangular concrete stub columns in the size of 130 × 200 mm cross section and 300 mm height; the first group composes of the unconfined specimens, while the other three contain the confined specimens under 0%, 25% and 50% sustained axial loads. The jackets are made of two G450-grade channel cold-formed steel sections of 2.4 mm thickness welded together. No bonding material is used between the core concrete and the steel jacket. From the results, it is found that the cold-formed steel jacketing can increase the axial strengths of the unconfined concrete specimens by approximately 40-65%. The strength increase comes mainly from the confinement action, as only small axial deformation is detected in the jacket. Based on the given amount of prescribed preloads in this study, the presence of preload in the column does not have a significant effect on the increase in strength of the confined concrete columns. The measured strength enhancement ratio and the confinement ratio of the tested specimens are compared using five existing strength predictive equations. The performance of the unbonded cold-formed steel jacketing technique adopted in the stub columns is observed to closely conform with the predictive confinement model of the concrete-filled tubes. [ABSTRACT FROM AUTHOR]

Geometric imperfections play an important role in the strength and behavior of thinwalled metal parts such as those commonly used in cold-formed steel construction. The objective of this paper is to detail a newly developed imperfection measurement platform, where the full-three dimensional (3D) imperfect geometry of a cold-formed steel member can be measured and reconstructed with reasonably high throughput and sufficient accuracy to explore all relevant imperfections. The measurement platform is composed of a two-dimensional laser sensor mounted on rotary and linear stages. Specimens are placed within a rotary ring and along a reference beam. The linear stage provides a means to scan the length of the specimen and the rotary stage a means to scan from any angle. Control of the custom linear and rotary stages are detailed in the paper, and corresponding control accuracies are studied. A procedure for registering the individual scans into the complete 3D model reconstruction (point cloud) is provided by specific calibration tests, from which rotation and translation quantities can be found to transform surfaces measured in local coordinates to a universal global coordinate system. A variety of different imperfection quantities, from basic dimensions and out-of-plane deviations to more advanced spectral and modalbased imperfection magnitudes may be rapidly processed from the 3D model. Accurate understanding of geometric imperfections is critical to the long-term success of analysis-based design paradigms for cold-formed steel constructions. The apparatus detailed herein will be used to provide a broad suite of imperfection information to assist in these new efforts. [ABSTRACT FROM AUTHOR]

In order to increase a stiffness of cold-formed steel (CFS) elements it is practised to built-up the cross-section. In the analysed case, a main element is strengthened by adding extra chord in contact partially along the column. This additional chord acts as a longitudinal stiffener connected with the main section by series of bolts. Authors check whether rules applied over the years, for hot-rolled elements, can be indiscriminately used in the analysed CFS element. The aim of this study is to experimentally and computationally recognize the normal stress distribution in axially compressed CFS built-up column chords and to evaluate the element load-bearing capacity. [ABSTRACT FROM AUTHOR]

Previous research on cold-formed steel (CFS) battened columns has identified the critical factors influencing their performance and accordingly, their limiting values for improved performance have been recommended. However, these studies involved connecting battens to the chords (channels) via their flanges, leaving the slenderest component disconnected from the web. This study introduces a novel hooped-batten (tubular-element) that links both webs and flanges of the chords together, thereby improving the structural integrity of the built-up system and curtailing the half-wave buckling length in the webs. As a result, axial strength and stability in these built-up columns may improve adequately. Firstly, a numerical model of a conventional CFS battened column was developed in ABAQUS and verified against test results on the same reported in literature. Afterward, the validated model was used to simulate the behaviour of CFS built-up columns with hooped-battens. Two key parameters i.e., unbraced chord slenderness and overall column slenderness were varied to explore their influence on the axial behaviour of built-up columns in terms of peak strengths, failure modes and load-displacement characteristics. The performance of the hooped-battened columns was compared with the identical conventional battened columns, which reflects that the former exhibits superior strength and stability characteristics over the latter. [ABSTRACT FROM AUTHOR]

Since cold-formed steel (CFS) elements are susceptible to complex buckling phenomena that decrease their structural capability, many strengthening trends have been developed so far. One of these methods is the use of polystyrene aggregate concrete (PAC) as bracings in order to restrain the global and distortional buckling modes of CFS members, where a new structural system comprising CFS elements encased in PAC has been proposed. In this research, PAC-encased CFS shear panels have been investigated numerically, where a simplified finite element model was developed to predict the structural behavior and capacity of such members. This goal was achieved using ANSYS software, where a geometrically and materially nonlinear analysis with imperfections (GMNI) was used to solve the problem of PAC-encased CFS shear panels. The full detailed volume-contact element-based concrete model was replaced by spring elements perpendicular to the plate’s plane with equivalent properties, and beam elements that could represent the concrete block more accurately regarding the global lateral stiffness and shear resistance. Consequently, for this case, the combination of local and global stiffness of PAC could produce the actual shear behavior of PAC-filled wall panels. The developed model was validated against previous experimental tests from the literature. Parametric studies were conducted in terms of the imperfection amplitudes, the stiffness of springs and the properties of PAC. Finally, the structural performance of PAC-encased panels under combined axial and shear loading was examined, where the effect of different axial load levels on the lateral strength was determined, and an interaction equation was proposed.Article Highlights: An innovative simplified numerical model was developed to predict the shear performance of PAC-encased CFS wall panels. The effect of different imperfection amplitudes and PAC properties on the shear performance of PAC-encased CFS walls were investigated. An interaction curve was proposed to predict the resistance of PAC-filled CFS walls under combined vertical and shear action. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. Studies of blast on hollow sections, most of which fall under the categories of contact/near-field loading or far-field loading are presented. Under large-scale field blast experiments, cold-formed hollow sections have shown excellent behavior. Software for modeling blast loading and structural response, the latter including single degree of freedom analysis and explicit finite element analysis, is described and discussed. [ABSTRACT FROM AUTHOR]

The influence of the moment–rotation characteristic on cold-formed steel (CFS) screwed back-to-back sections with varied beam and gusset plate thicknesses is investigated in this work. Twelve full-scale studies were used to determine their behavior. The results reveal that the moment resistance values increase in direct proportion to the thickness of the beam. In addition, the ratio of beam thickness (“ t ”) to gusset plate thickness (“ t p ”) is critical in calculating rotation capacity, energy dissipation values, and cost-effective design. The ductility of the joint values is also affected by the thickness of the gusset plates. Furthermore, the failure modes of the all-specimens tests show that the gusset plate thickness can be reduced to make the system more cost-effective. [ABSTRACT FROM AUTHOR]

The stable crack growth in thin steel sheets is the topic of this paper. The crack opening was observed using a videoextensometry system, allowing the crack extension determination. JR-curve and δR-curve were established from obtained data. The ductile tearing properties of different thin sheets of steel were determined, including the impact of the specimen orientation, from test performed on compact tension specimens loaded under two conditions. The effect of the material, the rolling direction, and loading rate on the crack growth resistance of thin steel sheets was analyzed. In addition to the crack growth resistance, J-integral values for crack initiation were also estimated. The relation between Ji and J0.2 was assessed using the basic mathematical and statistical methods. This relation was described by a linear regression model. [ABSTRACT FROM AUTHOR]

Texture and microstructure evolution in a ferritic/martensitic 9wt%Cr oxide dispersion strengthened (ODS) steels during heat treatment after cold tube forming are studied via in situ synchrotron X-ray diffraction analysis. The initial textures of cold-formed ODS steel tubes present a well-known α-fiber (< 110 >//RD). During high-temperature heat treatment, this initial sharp fiber texture, inherited from cold forming, is transformed by the phase transition to austenite into a weak < 111 > fiber. During cooling, a texture memory effect is observed with a strong dependency of the fiber intensity on the cooling rate. After quenching into martensite, the < 110 > fiber becomes weaker than in the initial ferrite. By contrast, after slow cooling into ferrite, the < 110 > fiber develops and becomes stronger than initially. For many materials, texture memory effect can be explained by a variant selection phenomenon. Accordingly, experimental results are compared to the double Kurdjumov–Sachs (DKS) model. During heating, a limited texture heritage is exhibited with essentially a Kurdjumov–Sachs (K–S) relation between the two phases. During cooling the DKS relation correctly predicts the texture fiber components. However, the strong enhancement of texture during slow cooling remains not completely explained. A Williamson–Hall analysis of the size and strain evolutions during the heating cycle showed a remarkable stability of the crystallites size which is the same in ferrite, austenite and martensite. [ABSTRACT FROM AUTHOR]

A generic procedure is formulated for the determination of the moment capacity of composite beams having a complex cross-section. The key feature is the use of Fourier series to convert the piecewise functions of the cross-sectional stress distribution into a single-rule function. This eliminates the need for several capacity expressions to cover different stress stages, since the procedure permits the use of the general moment capacity expression. It also eliminates any iteration process when determining the location of the neutral axis since equilibrium of the cross-section can be satisfied explicitly. Numerical examples are given to demonstrate the validation and the applications of the formulation. [ABSTRACT FROM AUTHOR]

In order to improve the longitudinal shear resistance between foam concrete and C-Channels, an investigation is carried out on the shear connectors in foam concrete with cold-formed steel double C-Channels embedment. Twenty-four tests have been carried out in two groups. Two types of connectors: flange connectors and web connectors are installed using self-drilling screws for a rapid construction. The experimental results show that they can effectively improve the longitudinal shear-resist capacity of the concrete. After the experiment, the specimens are dismantled for an interior observation. Based on the observation, the form of damage, the failure mechanism was discovered, and the equation of longitudinal shear capacity was developed. It is concluded that the failure involves independent slippage between two C-Channels and the shear connection fractures. Since the composite structure requires sufficient slip between the two materials, these types of shear connectors will have good enhancement for this type of composite structures subjected to dynamic loads. [ABSTRACT FROM AUTHOR]