Cold-formed Steel Plates Research Articles

Strengthening of Timber Beam with Cold-Formed Steel Plates

This paper describes an experimental program which examined the flexural strengthening of timber beams (50x50x1000 mm) using cold-formed steel (CFS) plates (0.75 mm thick and 30 mm wide). A total of fifteen specimens were tested in three-point bending scheme with a span-depth ratio of 18:1. The effectiveness of the steel plates was evaluated for different strengthening lengths and number of strengthening layers. Test results showed that maximum load carrying capacity and stiffness of the strengthened beams can be improved by up to around 70% and 40%, respectively, relative to that of control unstrengthened beams. The increase in the percentage gain occurred as increasing strengthening length as well as number of the strengthening layers. Control unstrengthened beams demonstrated linear elastic behavior during the test whereas the strengthened beams tended to undergo a pseudo-ductile behavior. Along with it tensile failure in timber was still observed in the strengthened beams.

Investigations on the lateral-torsional buckling of an innovative U-shaped steel beam

An innovative solution of a steel-concrete composite beam was developed for buildings with beam spans between 6 and 12 m, taking into consideration the fire situation and the construction stage. The beam is composed of an U-shaped steel part, connected to a reinforced concrete part. In the construction phase, the beam is supporting the slab and constitutes a formwork for the reinforced concrete part. When casting concrete, the steel beam is filled at the same time as the slab, this allows considerable time savings on site. In the exploitation stage, the beam behaves as a steel-concrete composite beam.The developed U-shaped section is composed of three steel parts; a hot rolled steel plate (180x8x6300 mm, and two cold-formed steel plates (470x4x6300 mm) before folding. The section was assembled together with four self-drilling screws longitudinally spaced of 150 mm.In the construction stage, the U-shaped steel beam without restraints is prone to lateral torsional buckling instability. In this paper, the mechanical behaviour of the steel beam at the construction stage, in particular its lateral-torsional buckling stability, was studied. In order to characterize this instability without lateral support, a four-point bending test was carried out on a life-size specimen. The load introduction system was developed especially for the test to allow for all displacements due to LTB. The test clearly showed the lateral torsional buckling behaviour of the steel beam. The test results are compared with numerical simulations and analytical studies. A parametrical study, covering 200 geometrical configurations of the U-shaped beam, is carried out to validate the use of the curve “b” for the design of the steel beam for lateral torsional buckling according to Eurocodes 3.

A practical numerical model for thin-walled steel connections and built-up members

The interaction between the cold-formed steel members and fasteners in a structural assembly often involves complex stress states, material plasticity, significant in-plane deformations and curling, rendering computational modelling of the resulting structural system challenging. In addition, the presence of initial geometric imperfections and the susceptibility of cold-formed steel members to local instabilities adds a further degree of complexity to the numerical modelling. The behaviour of bolted connections between cold-formed steel members has traditionally been assessed based on physical tests, though these can be time consuming and expensive. In this paper, a practical numerical approach to the simulation of bolted cold-formed steel connections, capturing all the key behavioural features including bolt preload, slippage and bearing, is introduced. Starting from a typical shell finite element (FE) model of a cold-formed steel plate, a small number of solid elements is introduced around the bolt holes, to allow accurate replication of the bolt-ply interaction, with contact pairs defined between the bolts and the surrounding material. An explicit dynamic solver is then employed to solve the geometrically and materially nonlinear problem, both with and without bolt slippage. Validation of the FE model is conducted using benchmark tests reported in the literature. It is shown that the proposed numerical method can accurately capture the structural behaviour of bolted cold-formed steel connections and cold-formed steel built-up sections, while being computationally efficient and numerically stable; the proposed approach is therefore recommended for the numerical modelling of cold-formed steel systems assembled using fasteners.

Effects of corrosion on the strength of self-drilling screw connections in cold-formed steel structures-experiments and finite element modeling

Cold-formed steel (CFS) self-drilling screw connections are popular in construction industry due to rapid fastening and ease of installation. However, the performance of the CFS connections is very critical when they are exposed to corrosive environments such as humid and acidic or chloride-rich environments. The corrosion damage of CFS structures when exposed to these environments can result in significant reduction of mechanical properties, which can affect the safety and durability of such structures. Very limited research is available in the literature to investigate the effect of corrosion on the behaviour of CFS connections. This issue is addressed herein through an experimental investigation. This paper presents a total of 36 new experiments on different types of CFS self-drilling screws (12 and 14 gauge) and steel sheet thickness (2.5 mm). Half of the tests were for corroded specimens and the remaining half were for non-corroded specimens. Further, one to two screws per arrangements connecting the steel sheets having yield strength of 450 MPa, were tested. Screws were immersed for 31 days and the CFS plates were immersed for 8 weeks in corrosion chamber before the tests were conducted. The experimental program was designed to investigate the effect of number of screws on shear strength of corroded specimens. Furthermore, a nonlinear explicit dynamic FE model was developed and validated against the experimental test results. The FE results were in reasonable agreement with the test results, both in terms of connection strength and failure modes.

Experimental study on cyclic shear performance of steel plate shear wall with different buckling restraints

The buckling-restrained cold-formed steel plate shear wall (SPSW) is a new type of shear wall that integrates building and structural functions. It consists of an embedded steel plate, hat-section steel strips, two thermal and sound insulation layers, two oriented strand board (OSB) plates. In order to study the cyclic shear performance of SPSW with different buckling restraints, six SPSW specimens with different buckling restraints and one SPSW specimen without buckling restraints were tested with hinged frame. The test results showed that the hat-section steel strips (i.e. stiffeners) can significantly decrease the outward buckling deformation of the embedded steel plate, thus preventing the formation of tension field on the diagonal direction of SPSW and improving the energy dissipation capacity, ductility and bearing capacity of the SPSW. Among all the specimens, the cross-shaped buckling restraints has the highest efficiency in improving the bearing capacity of the SPSW, followed by the X-shaped. In addition, as the number of steel strips increases, the restraint effect of steel strips, the energy dissipation capacity and the plastic deformation performance of specimens are also gradually improved. Finally, the shear capacities of all SPSW specimens are calculated by according to existing international design standards. As can be seen from the results, the design rule in AISC is the most conservative, while the design method of Eurocode 8 is most accurate.

Experimental study on the seismic behavior of high-performance cold-formed steel plate shear walls

To study the seismic behavior of two types of walls under horizontal reversed-cyclic loading, 6 full-scale cold-formed steel plate shear wall (CFS-SPSW) specimens were designed. They each had three specimens. The effect of the vertical stiffener and the cross-section form of end stud on the seismic behavior of the cold-formed steel center-sheathed shear wall (CFS-C-SW), and the middle stud and peripheral self-tapping screw spacing on the seismic behavior of cold-formed steel skin-sheathed shear walls (CFS-S-SW) were considered. The failure modes, hysteresis and skeleton curves, characteristic values, energy dissipation capacity, stiffness and strength degradations were analyzed. The test results indicated that two types of walls exhibited high shear capacity and stable mechanical behavior. Furthermore, the shear capacity of CFS-C-SW could be improved significantly by setting vertical stiffeners or using hat-section end column. Moreover, the shear capacity and deformation capacity of CFS-S-SW could be improved significantly by reducing the peripheral screw spacing, but changing the middle stud spacing had no significant effect on its seismic performance.

Seismic behavior of thin cold-formed steel plate shear walls with different perforation patterns

Thin perforated Steel Plate Shear Walls (SPSWs) are among the most common types of seismic energy dissipation systems to protect the main boundary components of SPSWs from fatal fractures in the high-risk zones. In this paper, the cyclic behavior of the different circular hole patterns under cyclic loading is reported. Based on the experimental results, it can be concluded that a change in the perforation pattern of the circular holes leads to a change in the locations of the fracture tendency over the web plate, especially at the plate-frame interactions. Accordingly, the cyclic responses of the tested specimens were simulated by finite element method using the ABAQUS package. Likewise, perforated shear panels with a new perforation pattern obtained by implementing Topology Optimization (TO) were proposed. It was found that the ultimate shear strength of the specimen with the proposed TO perforation pattern was higher than that of the other specimens. In addition, theoretical equations using the Plate-Frame Interaction (PFI) method were used to predict the shear strength and initial stiffness of the considered specimens. The theoretical results showed that the proposed reduced coefficients relationships cannot accurately predict the shear strength and initial stiffness of the considered perforated shear panels. Therefore, the reduced coefficients should be adopted in the theoretical equations based on the obtained experimental and numerical results. Finally, with the results of this study, the shear strength and initial stiffness of these types of perforated shear panels can be predicted by PFI method.

Experimental Study on Beam-Column Connections of Concrete Encased Cold-formed Steel Beams to Concrete-filled Steel Tube Columns

Experimental testing was done to investigate the flexural behaviours of internal roof beam-column connections. Four specimens were studied under static loads, one of which was specified as a reference reinforced concrete beam-column connection with regular bars as a conventional reinforcement for beam and column. The other specimens featured cold-formed steel plates with the equivalent area to regular bars as reinforcement, with square steel tube cross-sections filled with concrete used for columns. The results showed an increase in load carrying capacity and toughness for the experimental specimens as compared with conventional reinforcement beam-column connection. The concrete prevented local buckling of the cold-formed steel sections and improved the flexural bending capacity.

An Investigation on the Ultimate Strength of Cold-Formed Steel Bolted Connections

This paper presents experimental results and finite element analysis of the cold-formed steel bolted connection under shear loading. Experiments are conducted to study the ultimate behaviors, such as ultimate strength and failure mode of connections. The samples were fabricated into three different groups, single bolted, double bolted and quadruple bolted connection. Material properties were determined by tensile coupon testing. Bearing failure modes were detected in the bolted connection tests. The ultimate capacities were compared with the nominal strengths calculated using the AISI (2012). The comparisons show that the nominal strength parameters predicted by this specification is conservative. The finite element analysis shell elements were used to model the cold-formed steel plate while solid elements were used to model the bolted fastenings for the purpose of studying the structural behavior of bolted connections. Material nonlinearities, contact problem and geometry nonlinearities analysis are carried out in order to predict ultimate strength and failure mode of connections. The results show that the proposed model accurately represents the failure mode and ultimate strength of bolted connection, as determined from experimental investigation. The new factor for type of bearing connection has a good agreement with the tested bearing strength of bolt connection.

Parametric Study for Bearing Strength in Cold-Formed Steel Bolt Connections

The parametric study method was applied to study the strength of cold-formed steel bolt connection under in-plane loading. Finite element analysis with shell elements was used to model the cold-formed steel plate while solid elements were used to model the bolt fastener for the purpose of studying the structural behavior of bolt connections. Material nonlinearities, contact problems and geometric nonlinearity analysis were carried out to predict the ultimate strength and failure mode of the bolt connections. The finite element results showed that the proposed model accurately represents the failure mode and ultimate strength of a bolt connection, as determined from the experimental investigation. The bearing failure mode was detected in the finite element analysis and the experimental test. Utilizing the results of the parametric study, the outcome of the bolt diameter and the plate thickness on the bearing resistance of cold-formed steel connection was investigated and a new bearing factor parameter is proposed to improve the design standard equation.

An Analytical Method for Determining the Load Distribution of Single-Column Multibolt Connection

The purpose of this research was to investigate the effect of geometric variables on the bolt load distributions of a cold-formed steel bolt connection. The study was conducted using an experimental test, finite element analysis, and an analytical method. The experimental study was performed using single-lap shear testing of a concentrically loaded bolt connection fabricated from G550 cold-formed steel. Finite element analysis with shell elements was used to model the cold-formed steel plate while solid elements were used to model the bolt fastener for the purpose of studying the structural behavior of the bolt connections. Material nonlinearities, contact problems, and a geometric nonlinearity procedure were used to predict the failure behavior of the bolt connections. The analytical method was generated using the spring model. The bolt-plate interaction stiffness was newly proposed which was verified by the experiment and finite element model. It was applied to examine the effect of geometric variables on the single-column multibolt connection. The effects were studied of varying bolt diameter, plate thickness, and the plate thickness ratio (t2/t1) on the bolt load distribution. The results of the parametric study showed that thet2/t1ratio controlled the efficiency of the bolt load distribution more than the other parameters studied.

Finite Element Analysis on Tensile Stiffness of Cold-Formed Steel Bolted Connections

This paper presents a finite element analysis on the tensile stiffness of steel bolted connections which are fabricated from thin-walled cold-formed steel strips and their members. This type of bolted connection is usually used to assemble the diagonal bracing member in the light steel structure. Unlike the architectural steel structure, thin walled steel bolted connection cannot be simplified into a hinge joint due to the weak tensile stiffness of connection. The calculation of tensile stiffness of bolted connection is necessary to accurately evaluate the effectiveness of bracing system in the coldformed steel structure. Based on the existing test results and analysis results, finite element (FE) models with threedimensional solid elements were established to investigate the tensile stiffness of bolted connections between cold-formed steel plates under shear. The analysis with non-linear material and contact elements was carried out in order to predict the load-displacement relationships of bolted connections. Furthermore, a parametric study on single-bolted or two-bolted connections with different configurations was performed to study the relationship of connection tensile stiffness and structural parameters such as bolt diameter, plate thickness and steel yield strength. According to the stiffness results obtained from parametric study, six calculating equations for practical design of cold-formed steel bolted connection have been proposed. The calculation results of the stiffness equations are in a good correlation with those of FE analysis, and the proposed equations have been found to provide estimates of tensile stiffness of bolted connections with reasonable accuracy.

A probabilistic examination of the ultimate strength of cold-formed steel elements

The statistical characteristics (mean and variance) of the ultimate strength of cold-formed steel plates in uniform compression and pure bending are calculated and compared to deterministic approximations. Three quantities: plate thickness, longitudinal flexural residual stress magnitude and first mode imperfection magnitude, are treated as random variables. Based on existing experimental data, appropriate probability distributions are determined for the three random variables. The ultimate strength calculations are performed numerically using the finite element method (FEM). The statistical characteristics are calculated using two methods: Monte Carlo simulation and Taylor series approximation. The results are compared to the deterministic design approach of the American Iron and Steel Institute (AISI) Specification for the design of cold-formed structural members.

Local buckling of cold formed steel in composite structural elements at elevated temperatures

An inelastic semi-analytical finite strip method is used to analyse the local buckling behaviour of cold formed steel plates of composite steel-concrete structural elements at elevated temperatures. The decrease in yield stress and elastic modulus of the cold formed steel is represented at elevated temperatures by a series of nonlinear stress-strain relationships. The change in the material properties at elevated temperatures is shown to influence the local buckling behaviour of steel plate element in steel-concrete composite construction. Various boundary conditions are chosen in a parametric study, in which the influence of different variables is determined. Recommendations are given for the assignment of slenderness limits, and a simple method is presented to obtain the local buckling stresses at elevated temperatures. A design example of a profiled composite beam is used to illustrate the method presented.

Discussion: Effective width of stiffened cold-formed steel plates

Discussion: Effective width of stiffened cold-formed steel plates

Effective width of stiffened cold-formed steel plates

This paper reviews the experimental data available in the literature concerning the effective width concept. The formulae for effective width that are contained in the AISI-68 and the CSA S136-74 specifications are critically discussed in relationship to the experimental data. The effective width is shown to be clearly a function of the actual width, in contrast to the constant value implied by the CSA S136-74 specification. A formula of the type used in the AISI-68 specification is found to be very suitable. It provides for reduced strength due to interactive effects in plates of moderate width to thickness ratios and places a limiting value on the effective width of very thin plates.A new design rule, of the simple form Be = 2 − 1/B, is proposed as an appropriate guide for the design of stiffened cold-formed steel plates.