Cold-formed Steel Profiles Research Articles

Buckling Behavior of Cold-Formed Studs with Thermal Perforations

Studies have shown that the optimal structural scheme for low-rise buildings that meets all regulatory requirements is a frame system. In this connection, thin-walled cold-formed steel (CFS) profiles seem to be the best material for constructing light steel framed (LSF) walls. The framework of LSF walls is usually constructed from CFS C-shaped profiles. To increase the thermal effectiveness of a wall, CFS profiles usually have thermal perforations and thus are called thermoprofiles. However, these openings have a negative impact on bearing capacity of profiles and require accurate evaluation. In this article a relatively new reticular-stretched thermoprofile with diamond-shaped openings is considered. The article deals with the buckling analysis of perforated CFS C-sections subjected to compression.

Seismic Design Method for CFS Diagonal Strap-Braced Stud Walls: Experimental Validation

AbstractThe search for innovative methods to ensure high structural, technological, and environmental performance is an important issue in the development of new construction. Among the several available building systems, constructions involving the structural use of cold-formed steel (CFS) profiles represent an efficient and reliable solution. In an effort to characterize the seismic response of CFS structures and to support the spread of these systems, a theoretical and experimental research has been carried out. It focused on the all-steel-design solution, in which CFS diagonal strap-braced stud walls are the main lateral resisting system. In order to overcome the lack of information in the current European codes, a critical analysis has been carried out of the requirements for these systems in difference codes for hot-rolled X-braced steel frames (tension-only). On the basis of the design hypothesis outlined from this analysis, a case study has been developed with the aim to define an extended experim...

Seismic response of Cfs strap-braced stud walls: Theoretical study

The use of cold-formed steel (CFS) profiles in low-rise residential buildings has increased in European construction sector. The reason of this interest is related to potentialities offered by this constructive system, which are the high structural performance, lightness, short construction time, durability and eco-efficiency. Nevertheless, the current structural codes, such as Eurocodes, do not provide enough information about the seismic design of this structural typology. In an effort to investigate the seismic response of CFS structures, a theoretical and experimental research has been carried out at University of Naples Federico II, with the main aim to support the spreading of these systems in seismic areas. This study focuses on an “all-steel design” solution in which strap-braced stud walls are the main lateral resisting system. In the present paper the outcomes of theoretical phase are shown with the aim of defining the criteria for the seismic design of such structures. In particular, a critical analysis of the requirements for CFS systems provided by the American code AISI S213 has been carried out by comparing it with those given by Eurocodes for traditional braced steel frames.

Distortional buckling resistance of cold-formed steel

The design of cold-formed steel structures is generally ruled by the ultimate buckling limit state. Most cold-formed steel profiles display open and rather thin-walled cross sections, which means that their structural behavior is strongly affected by buckling. On profiles with stiffened sections, such as C, Zee, rack and hat, there is the occurrence of distortional buckling. However, verifying distortional buckling is not trivial. According to the Brazilian standard, knowledge of the critical load that causes distortional buckling is necessary to design cold-formed steel profiles. Nevertheless, the code does not provide a procedure to obtain this critical load. This paper conducts a brief literature review of the distortional buckling mode and, by means of software for linear stability analysis, developed by the authors, presents the resistances associated with the distortional buckling of various cold-formed steel profiles, enabling structural elements design according to the Brazilian standard.

Finite element analysis of new composite floors having cold-formed steel and concrete slab

In this research, the structural behavior of a new type of composite floor system is explored through finite element modeling. The new composite floor incorporates cold-formed (light-gauge) steel profiles as the joist on bottom, a corrugated steel deck as the formwork for concrete, a continuous hat channel (furring channel) as the shear connector and finally a concrete slab on top. All steel parts in the system are cold-formed and connected together by self-drilling fasteners.In the present study, a comprehensive three-dimensional finite element modeling is performed for this composite floor system. A local bond-slip model is applied to simulate the slip of the shear connector inside the concrete slab. A nonlinear analysis is performed on the composite floor considering all different types of structural nonlinearities and the behavior of the system is monitored from beginning of loading all the way to a defined point of failure. Results of finite element analyses are compared with experimental data.Further, parametric studies are conducted to determine the effect of shear connector’s slip on reducing ultimate strength and initial stiffness of such a floor system.

Computational modelling of flange crushing in cold-formed steel sections

The computational modelling of the flange crushing phenomenon in cold-formed steel profiles is described in this paper, with particular emphasis to the development of shell finite element (SFE) models and performance of quasi-static analyses with an explicit integration scheme. Web crippling failure is widely recognised as the most relevant collapse mode of cold-formed steel members subjected to transverse concentrated loads. However, it has been experimentally and numerically observed that a somewhat different collapse mode may occur, due to the heavy stress concentrations stemming from the adoption of narrow bearing plates. This phenomenon, termed flange crushing, should not be confused with web crippling. Usually, the web crippling phenomenon is numerically investigated by means of non-linear static SFE models with an implicit integration scheme. In this study, SFE models are developed in ABAQUS code to study the flange crushing failure of a plain channel beam subjected to Internal Two Flange (ITF) loading conditions. These models are described in detail, as well as additional modelling concerns regarding quasi-static analyses and the explicit integration method. Different parameters are discussed in this article and the numerical results obtained are commented throughout. Such parameters include the (i) SFE type and mesh, (ii) load rate, mass scaling, adoption of smoothed displacement amplitude curves and control of inertial effects, (iii) contact and friction definitions, (iv) effects of forming cold-work and manufacturing process and (v) geometrical imperfections. Finally, the load–displacement response obtained with the quasi-static model and an equivalent non-linear static analysis are compared with the experimental test curves. It is concluded that very good results are achieved with the quasi-static approach, not only in terms of the ultimate load prediction, but also regarding the post-collapse load–deflection curve and the failure mechanism.

Local bond–slip behavior between cold-formed metal and concrete

Composite action in systems consisting of steel and concrete depends on an effective shear-transfer mechanism between the two materials. Such mechanism for smooth steel surfaces inside concrete will be limited to the bond–slip behavior at the steel/concrete interfaces. This research investigates the bond–slip behavior of galvanized cold-formed (light gauge) steel profiles embedded in normal weight normal strength concrete. A new innovative pull-out test is presented which is convenient to set up and perform and reduces the undesirable parameters to the minimum. Global bond–slip curves for different values of concrete strength are obtained from such tests. Through an innovative procedure, mathematical equations and selected points from the experimental global bond–slip curves are used to develop a bi-linear local bond–slip model which represents the discussed bond–slip behavior. By curve fitting, empirical equations are proposed to determine the suggested model’s parameters based on the concrete compressive strength. Finally, validity of the proposed model is explored by two methods: (1) by comparing the results from analytical equations with test results, (2) by comparing the results from finite element modeling with test results. An excellent agreement has been observed in both verification methods.

Shape Grammar of steel cold-formed sections based on manufacturing rules

This paper formalizes the domain of all and only manufacturable open cold-formed steel (CFS) profiles aimed at improving their strength capability in the development of new products. A Genetic Algorithm is applied over this domain to get a set of best solutions from structural and constructive viewpoints. A basic review is carried out with regard to (i) Shape Grammar, (ii) Finite Strip Method-based elastic buckling analysis, (iii) Direct Strength Method-based structural strength computation and (iv) modified procedure of the Non-dominated Sorting Genetic Algorithm. CFS-manufacturing is defined as a language and its general grammar is presented. This grammar-based model responds to requisites of descriptive power, simplicity of implementation, and customization to specific needs. The CFS grammar has been implemented using scripting languages available in pre-existing CAD and CAE applications. Implementation includes generation, visualization, analysis and improvement capabilities. Results show that innovative shapes with improved strength could be generated from the finite set of allowable manufacturing grammar rules encoded by the grammar.

Experimental analysis on cold-formed steel beams subjected to fire

The great majority of the studies in this area emphasise further the structural behaviour of cold-formed steel members by means of analytical approximation and purely numerical methods. In addition, they generally only take into account the structural behaviour of members with just one profile. On the contrary, this paper reports a series of flexural tests under fire conditions focused on cold-formed galvanised steel beams consisting on compound cold-formed steel profiles which are often used in floors and roofs of warehouses and industrial buildings. The main objective of this research was to assess the failure modes, the critical temperature and the critical time of the studied beams. Other important goals of this research work were also to investigate the influence of the cross-sections, the axial restraint to the thermal elongation of the beam and the rotational stiffness of the beam supports. Finally, the results showed above all that the critical temperature of a cold-formed steel beam might be strongly affected by the axial restraint to the thermal elongation of the beam.

Experimental investigations on composite slabs to evaluate longitudinal shear strength

Cold-formed steel profile sheets acting as decks have been popularly used in composite slab systems in steel structural works, since it acts as a working platform as well as formwork for concreting during construction stage and also as tension reinforcement for the concrete slab during service. In developing countries like India, this system of flooring is being increasingly used due to the innate advantage of these systems. Three modes of failure have been identified in composite slab such as flexural, vertical shear and longitudinal shear failure. Longitudinal shear failure is the one which is difficult to predict theoretically and therefore experimental methods suggested by Eurocode 4 (EC 4) of four point bending test is in practice throughout world. This paper presents such an experimental investigation on embossed profile sheet acting as a composite deck where in the longitudinal shear bond characteristics values are evaluated. Two stages, brittle and ductile phases were observed during the tests. The cyclic load appears to less effect on the ultimate shear strength of the composite slab.

Numerical study of built-up double-Z members in bending and compression

The use of the finite element method (FEM) for the design of composed, thin-walled, structural steel members is considered. The bolted double-Z frame member is an interesting and economical engineering solution, already used in practice [1]. However, the European recommendations for the design of steel structures do not consider built-up members from cold-formed steel profiles. Finite element analysis is used to capture the various buckling effects that shape the response of slender thin-walled members. From the finite element model, the importance of initial imperfections and stiffness of connections is identified. The experimentally validated model predictions show that a non-linear finite element analysis can predict the member behaviour, in terms of failure mode and ultimate load, yield line pattern, overall stiffness and local strain in the cold-formed profiles. To obtain a good prediction, overall and localised initial imperfections should be considered and included in the analysis.

Improvement of the Mechanical Properties of Formed Steel Cross Section Profile for Timber Upgrading

The main objective of this paper is to analyze the behaviour of cold formed steel cross section respect to mechanical characteristics, such as deflection, mainly. A cold formed steel profile with thickness of 1 mm regards is studied to determine its viability as reinforcement of timber upgrading. Thus, temperatures, stresses and strains have been analysed during the manufacturing process of these profiles, and also, the deflection supported, comparing between unreinforced and reinforce pieces. The analysis has been carried out by means of Finite Element Method, using DEFORM 2D software, during the simulation of manufacturing process and COPRA software during the final static computations. Results provide information about the integrity and good behavior of these profiles for timber upgrading.

Design of Built-Up Cold-Formed Steel Columns According to the Direct Strength Method

The (DSM) direct strength method [1] is used in order to predict the axial compression capacity of innovative cross-section shapes for built-up columns from cold-formed steel (CFS) profiles. The proposed four composed shapes have been adapted in order to obtain members of increased strength-to-weight ratio. After excluding various buckling mechanisms from the columns response to compressive loads, highly stable members with reduced sensitivity to initial imperfections are obtained. DSM predictions are validated experimentally for the four built-up cross-sections types. The investigation shows that DSM could easily be extended towards composed members if provisions for members sensitive to global-distortional buckling interaction are included in the method. The good agreement with experiments also indicates that the proposed built-up assemblies are reliable and can be integrated into everyday construction practice.

Experimental Investigation of the Deformation of Built-up Members of Cold-Formed Steel Profiles

Built-up members of cold-formed steel (CFS) profiles were tested in 4-point bending. CFS profiles (generally thin-walled) deform considerably under load, and the deformed configuration is a result of the superposition of different buckling mode shapes. Local buckling propagates through the profile walls; during distortional buckling parts of the cross-section rotate around a web-flange juncture. Alongside the buckling effects, the overall deformation of the member is considerable. To study these slender and relatively long members, a sufficient number of measuring positions on the specimens is needed. Often, this is not feasible with the conventional measuring techniques. An optical measuring device was used to record the movement of a large number of points per specimen. The obtained results are placed in a 3D coordinate system and can be exported for further data processing. The goal of the measurement campaign was to calibrate a Finite Element model that will simulate the tests. The model will be used for the analysis of composed frame members of CFS profiles, whose design is not entirely covered by the European Standard [1]. After calibration, the FEA predicts the performance of these built-up members well.

Optical Measuring Technique for the Investigation of Built-Up Cold-Formed Steel Structural Members

The construction industry uses cold-formed steel (CFS) sheets in the form of galvanised thin-walled profiles and corrugated sheets. In the past decade, CFS profiles have been competing with their hot-rolled counterparts as primary structural members of industrial halls, office buildings and residential housing of up to 3-4 storeys. The spans and column heights achieved with CFS profiles are ever larger. Due to the large slenderness of these members, adequate strength and stability are necessary, as well as reliability in design. Thin-walled members go through buckling during all stages of their working life. Local buckling appears at loads sometimes much lower than the design load. Distortional buckling seriously reduces the member resistance. It interacts with warping and lateral-torsional buckling, being significant for these asymmetric open sections. To restrict these effects, builders employ double sections - usually two standard cold-formed shapes bolted together to form a built-up section. These sections have the advantages of symmetry, higher stability and strength. The design of built-up members involves many uncertainties - although the European standard includes guidelines on the prediction of local, distortional and global buckling, the partial integrity and interaction between the parts of the composed members is still not studied. To study the actual behaviour, built-up members are tested in bending. An optical device for 3D motion analysis measures the displacement of points of interest on the specimen. Two interacting cameras use parallax to obtain the position of an arbitrary number of reflective markers glued to the specimen. The device tracks the movement of the markers in a 3D coordinate system without any contact with the specimen. Standard displacement transducers measure vertical displacements to validate the results. The paper gives an appraisal of the applicability of the method, a summary of the difficulties faced and the outcome of the test campaign.

Analysis of Structural Changes in Cold-Formed Steel Profiles Caused by Production Technology

Because of different production technology, the calculation of cold-formed profiles significantly differs from that of hot-rolled profiles. Formation of various section shapes from the basic sheets induces changes in material mechanical properties, which manifest themselves through different yield point, ultimate tensile strength, modulus of elasticity and reduced elongation percentage. Yield stress distribution over the cross section also changes, the largest values are in the corners of the profile. This paper presents testing results obtained from tensile coupons taken from different regions within profiles and compression tests on complex stub columns. Results are shown on cumulative diagrams and compared with those obtained from the base strip coupons. Before testing, a detailed measurement of real geometric properties of profiles was performed to determine the initial geometric imperfections of samples. The obtained results represent important parameters in determining appropriate buckling curves of centrically compressed members made from cold-formed profiles.

Experimental study of screw connections in CFS-calcium silicate board wall panels

Cold-formed steel (CFS) wall panels with different board materials are used extensively in residential and commercial buildings to resist lateral loads by in-plane shear, in addition to helping the studs resist gravity loads. Generally the screw connection between the board and CFS skeleton frame, which experience shear, dictates the behaviour and strength of such panels. In this paper, details of an experimental study on behaviour and strength of the screw connections between the cold-formed steel profiles and calcium silicate boards, under monotonic and cyclic shear loading, are presented. The objectives of the experimental study are: (a) to develop a new test procedure that realistically represents the behaviour and failure of screw connections in CFS wall panels; (b) to investigate the effect of edge distance of the screws and thickness of the boards on behaviour and strength; (c) to study behaviour under monotonic and cyclic loading; (d) to develop the values of the important parameters that determine the load–deformation behaviour of the screw connection in such wall panels under in-plane shear; and (e) to develop design equation to evaluate the ultimate shear strength and its resistance factor required in load resistance factor design (LRFD).

Light Gauge Cold-Formed Steel Profile for Decks in Housing Units

For the decking of dwellings a new light gauge cold-formed steel channel profile has been developed and applied. It is cold formed from steel sheet. Its design is based on AISI in 1983. Buckling and conditions at the supports are analyzed. Application to a one-family house is shown. Advantages and drawbacks are considered.

Enhanced mechanical properties after cold process of fabrication of non-linear metallic profiles

It is well known that the cold-forming process is likely to significantly enhance the mechanical properties of the profile by strain hardening leading to increased resistance compared to a resistance assessment based on nominal properties. It is thus necessary to accurately determine the mechanical properties after the cold process of fabrication. In this paper, experimental reference data and formulae calculating the increased proof strength in cold-formed stainless steel profiles are reviewed. A new theory-based formula for the evaluation of the actual mechanical properties of stainless steel structural members using the virgin sheet material properties is then established. This formula is dependent upon the radius of curvature to thickness ratio; it is not restricted to a single alloy but is valid for non-linear metallic materials. Prediction efficiency is evaluated against the collected experimental data and particular attention is paid to the set of experimental data related to hollow sections. The main thrust of the predictive model lies in its axiomatic roots in contrast to the traditional empirical formulae found in the literature.

Cold formed steel beams under monotonic and cyclic loading: Experimental investigation

The use of cold-formed thin-walled steel profiles in seismic structures is nowadays strongly penalized by code prescriptions, which impose for this kind of members a q-factor equal to 1, so that the design for the action of a severe earthquake must be carried out practically in the elastic field. On the other hand, some theoretical studies on the seismic performance of such structural systems gave encouraging results. For these reasons, an experimental and theoretical research program on the behaviour of cold-formed members loaded by cyclic loads has been started in the recent past by the authors. In the first phase of the experimental program, tests in bending on coupled channel beams under monotonic and cyclic load have been carried out. In this paper the research program is described, the obtained results are presented and some preliminary consideration is made on the behaviour of these types of members.