Mechanical Properties Of Cold-formed Steel Research Articles

Effect of cold-form and tensile strain rate on mechanical properties of Q345 steel at elevated temperatures

In recent years, cold-formed steel has been extensively used, and the mechanical properties of cold-formed steel at elevated temperatures have been received considerable attention. However, little research on mechanical properties of the corner parts at elevated temperatures has been published. Meanwhile, the tensile strain rates adapted in the previous research on cold-formed steel are different, and the effect of this factor on mechanical properties was rarely investigated. In order to get a deeper understanding of the mechanical properties of cold-formed Q345 steel at elevated temperatures, an experimental investigation on flat and corner parts in cold-formed Q345 sections with two nominal thickness of 1.5 mm and 2.5 mm under three different tensile rates, 0.06/min, 0.6/min and 1.2/min, was carried out at elevated temperatures ranging from 20 °C to 800 °C. The effects of tension strain rate, cold-forming and thickness on mechanical properties of Q345 steel were systematically studied. Then the test results were compared with the prediction results provided by the current design standards and the other researchers. Furthermore, prediction equations were proposed to determine the mechanical properties of cold-formed Q345 steel.

Simple Three-Coefficient Equation for Temperature-Dependent Mechanical Properties of Cold-Formed Steels

AbstractThe objective of this paper is to propose relationships for the reduction in mechanical properties of cold-formed steels at elevated temperature. Predicting the degradation of strength and ...

Experimental investigation of post-fire mechanical properties of Q235 cold-formed steel

Abstract Cold-formed steels are commonly used in construction applications. However, there is a lack of understanding on its post-fire mechanical properties. This paper presents an experimental investigation on post-fire mechanical properties of cold-formed steels. The test specimens were cut from flat portion and corners of cold-formed channel sections, which were exposed to temperatures ranging from ambient temperature to 800 °C, and then cooled with water and air. The specimens are of grade Q235, with section thicknesses of 1 mm and 2 mm. The stress-strain curves and mechanical properties of the specimens were obtained from tensile coupon tests. Test results of post-fire mechanical properties are presented. Moreover, evolution of microstructure and fracture morphology of specimens with different cooling methods were examined. Finally, predictive equations are proposed for evaluating the post-fire mechanical properties of Q235 cold-formed steel channel sections.

Experimental Investigation of Postfire Mechanical Properties of Q345 and G550 Cold-Formed Steel

AbstractThe postfire mechanical properties of cold-formed steel (CFS) are fundamental parameters for evaluating the residual performance of CFS structures after exposure to fire. In this paper, 230...

Pull-through capacities of cold-formed steel roof battens considering loading rate sensitivity

Static and fatigue pull-through failures of thin steel roof battens in the vicinity of batten to rafter screw connections are part of the major premature connection failures which lead to severe roof failures during high wind events. As wind speed and thereby wind uplift loading rate on a building roof varies over a wide range, the loading rate which should be used to conduct prototype roof tests is a moot point. Current wind loading standards and guidelines recommend a wider range of loading rates/frequencies in simulating static and cyclic wind loads. This could adversely affect the test results of loading/strain rate sensitive materials. Since cold-formed steels appear to be sensitive to loading rate, it is necessary to investigate the effect of loading rate on both static and fatigue pull-through capacities of cold-formed steel roof battens. Therefore, a series of static and cyclic pull-through tests was conducted at various loading rates on roof battens made of two grades (G300 and G550) and two thicknesses (0.75/0.80 and 0.95/1.00 mm). Test results showed that both static and fatigue pull-through capacities increase with increasing loading rate. To understand the loading rate sensitivity of roof battens, the effect of loading rate on the ultimate tensile strength of cold-formed steels was also investigated through a series of tensile coupon tests. Based on both pull-through and tensile coupon test results, suitable modifications and recommendations have been made to the current pull-through capacity equations and the current Low-High-Low (LHL) cyclic test loading frequency. A suitable material model is also proposed to determine the dynamic mechanical properties of cold-formed steels.

Residual capacity of fire exposed light gauge steel frame walls

Light gauge Steel Frame (LSF) walls made of cold-formed steel stud and track sections and lined with gypsum plasterboards are commonly used in buildings as load bearing members. During fire events, gypsum plasterboards act as a thermal barrier and delay the temperature rise in the steel studs. Fire usually occurs on one side of LSF walls during which a non-uniform temperature distribution is developed across the steel stud cross-section. This results in thermal bowing deformations and non-uniform distribution of strength and stiffness within the studs. In most situations, fires are extinguished well before excessive or permanent plastic deformations of studs and/or stud failures occur. Hence the LSF wall frames could be re-used provided their residual capacities after fire events are adequate. This paper presents a study aimed at determining the residual compression capacities of LSF wall studs following fire exposure. A full scale standard fire test of LSF wall panel was conducted first, followed by a series of short column tests of lipped channel studs obtained from the tested LSF wall panel. Finite element analyses of the tested studs were undertaken using the measured post-fire mechanical properties of cold-formed steels. The residual compression capacities of these fire exposed short columns were also predicted using the ambient temperature cold-formed steel design rules. A numerical parametric study was then undertaken for 3m long studs in LSF wall panels with varying wall configurations following an exposure to standard fire. This paper presents the details of these experimental and numerical studies of fire exposed LSF wall panels and the results. It demonstrates the potential of re-using LSF wall frames following fire exposures and provides appropriate limits for fire exposure time and stud hot flange temperature for three commonly used LSF wall configurations.

Experimental investigation of post-fire mechanical properties of cold-formed steels

Cold-formed steel members are widely used in residential, industrial and commercial buildings as primary load-bearing elements. During fire events, they will be exposed to elevated temperatures. If the general appearance of the structure is satisfactory after a fire event then the question that has to be answered is how the load bearing capacity of cold-formed steel members in these buildings has been affected. Hence after such fire events there is a need to evaluate the residual strength of these members. However, the post-fire behaviour of cold-formed steel members has not been investigated in the past. This means conservative decisions are likely to be made in relation to fire exposed cold-formed steel buildings. Therefore an experimental study was undertaken to investigate the post-fire mechanical properties of cold-formed steels. Tensile coupons taken from cold-formed steel sheets of three different steel grades and thicknesses were exposed to different elevated temperatures up to 800°C, and were then allowed to cool down to ambient temperature before they were tested to failure. Tensile coupon tests were conducted to obtain their post-fire stress–strain curves and associated mechanical properties (yield stress, Young׳s modulus, ultimate strength and ductility). It was found that the post-fire mechanical properties of cold-formed steels are reduced below the original ambient temperature mechanical properties if they had been exposed to temperatures exceeding 300°C. Hence a new set of equations is proposed to predict the post-fire mechanical properties of cold-formed steels. Such post-fire mechanical property assessments allow structural and fire engineers to make an accurate prediction of the safety of fire exposed cold-formed steel buildings. This paper presents the details of this experimental study and the results of post-fire mechanical properties of cold-formed steels. It also includes the results of a post-fire evaluation of cold-formed steel walls.

Determining elastic and shear moduli of cold-formed steel at elevated temperatures using a new sonic resonance method

An understanding of the mechanical properties of cold-formed steel (CFS) at elevated temperatures is critical for the design of CFS structures and analysis of these structures under fire; however, not much literature exists on mechanical properties at elevated temperatures. We report the measurements of elastic and shear moduli for CFS (ASTM-A1003) at elevated temperatures up to 350°C using a novel sonic resonance method. A Bode 100 network analyser was used to excite the CFS samples hanging inside a high-temperature furnace via a simple tweeter-type speaker, and for each the response signal was then detected by a Polytec OFV-5000 Laser Vibrometer Controller (Polytec Inc. Irvine, CA 92618). The resonance frequencies in both flexural and torsional modes are measured by the network analyser as a function of temperature, which allowed us to determine the elastic and the shear moduli. Both the elastic and the shear moduli decrease as the temperature increases. The results reported can be used in the CFS structure design and modelling at elevated temperatures. The new experimental methodology has been validated by a classical coupon test.

Mechanical properties of cold-formed steels at elevated temperatures

Mechanical properties have an important role in the fire safety design of cold-formed steel structures due to the rapid reduction in mechanical properties such as yield strength and elastic modulus under fire conditions and associated reduction to the load carrying capacities. Hence there is a need to fully understand the deterioration characteristics of yield strength and elastic modulus of cold-formed steels at elevated temperatures. Although past research has produced useful experimental data on the mechanical properties of cold-formed steels at elevated temperatures, such data do not yet cover different cold-formed steel grades and thicknesses. Therefore, an experimental study was undertaken to investigate the elevated temperature mechanical properties of two low and high strength steels with two thicknesses that are commonly used in Australia. Tensile coupon tests were undertaken using a steady state test method for temperatures in the range 20–700 °C. Test results were compared with the currently available reduction factors for yield strength and elastic modulus, and stress–strain curves, based on which further improvements were made. For this purpose, test results of many other cold-formed steels were also used based on other similar studies undertaken at the Queensland University of Technology. Improved equations were developed to predict the yield strength and elastic modulus reduction factors and stress–strain curves of a range of cold-formed steel grades and thicknesses used in Australia. This paper presents the results of this experimental study, comparisons with the results of past research and steel design standards, and the new predictive equations.