Description of stress-strain curves for cold-formed steels

The use of cold-formed steel (CFS) channel sections are becoming popular as the load-carrying members in building structures, and such channel sections often include web openings for the ease of installation of services. Traditional web openings are normally punched, and are unstiffened which can restrict the size and spacing of web openings. Recently, a new generation of CFS channel sections with edge-stiffened web openings has been developed, and is widely used in New Zealand. However, no experimental investigation has been reported in the literature for such channel sections under compression. In this paper, a total of 75 results comprising 26 axial compression tests and 49 finite element analysis results are reported on the compression resistance of CFS channel sections with both edge-stiffened and unstiffened web openings. For comparison, channel sections without web openings were also tested. For all specimens, initial imperfections were measured using a laser scanner. A nonlinear elasto-plastic finite element model was also developed, and the results showed good agreement with the test results. A parametric study was conducted using the validated finite element model to investigate the effect of opening spacing and column length on compression resistance of channel sections. It is shown that for the case of a channel section having seven edge-stiffened web openings, the compression resistance increased by as much as 22%, compared to a plain channel section. For comparison, the same section having unstiffened web openings had a 20% reduction in compression resistance, compared to a plain channel section.

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Effects of edge-stiffened web openings on the behaviour of cold-formed steel channel sections under compression

Exploration of the multidirectional stability and response of prefabricated volumetric modular steel structures

Q460 and Q690 are two most typical high strength steels applied extensively in industrial construction, mechanical engineering and other engineering structures due to their cost efﬁciency, high strength and toughness. Their residual mechanical performance after fire accidents is a crucial indicator for an appropriate post-fire safety evaluation. In addition, water has long been a universal agent for fire suppression, however it is typically ineffective on chemical or oil fires, and can be dangerous. Therefore, the post-fire mechanical properties of both Q460 and Q690 high strength steels cooled by fire-fighting foam from seven different high temperatures are investigated in this study. Test specimens are initially subjected to an elevated temperature ranging from 200 to 900 °C to simulate various fire conditions, and then these heated specimens are cooled to ambient temperature by fire-fighting foam. Subsequent tensile tests are performed on the fire-affected specimens to observe the failure mode, and obtain the stress-strain curve and other associated mechanical performance parameters. The visual appearances of Q460 and Q690 high strength steel tensile coupons are clearly changed after being heated and cooled by fire-fighting foam. In the case of fire-fighting foam cooling, the post-fire mechanical properties (except for the elastic modulus) of Q460 and Q690 high strength steels change drastically after exposure to temperatures above 600 °C (up to 900 °C). When exposed to the temperature of 900 °C, Q460 and Q690 high strength steels are able to regain 67% and 64% of their initial ultimate strength in the case of fire-fighting foam cooling, respectively. In contrast, the ductility of Q460 and Q690 high strength steels cooled from 900 °C by fire-fighting foam can gain 139% and 152% of their initial ductility, respectively. Meanwhile, the micro-fracture behavior is also observed to understand the effects of elevated temperatures and fire-fighting foam cooling on the post-fire mechanical properties. By comparing the results of previous studies on other two cooling methods, significant differences in the post-fire mechanical properties of Q460 and Q690 high strength steels cooled by different methods are discussed. At last, the predictive equations are developed to determine the post-fire mechanical properties of fire-affected Q460 and Q690 high strength steels when the fire-fighting foam cooling method is applied in fires.

Post-fire mechanical properties of Q460 and Q690 high strength steels after fire-fighting foam cooling

The problematic nature of steel hollow section joint fabrication, and a remedy using laser cutting technology: A review of research, applications, opportunities

This paper describes an experimental study to estimate the stub columns capacity of cold–formed square (SHS) and rectangular hollow sections (RHS) containing two opposite central circular perforations at column mid–height. The stub columns were extracted from commercially available Tata Structura–YSt 310 tubular sections, with minimum yield strength of 310 MPa, conforming to Indian Standard 4923. The influence of two opposite central circular perforations on the structural performance of tubular steel stub columns under concentric loading was investigated for perforation size to flat width ratios up to 0.9 The local geometric imperfections, load–end shortening curves, strain distributions at mid height of column and typical failure modes observed from the present test programme are documented in this paper. Further, the ultimate column capacities recorded from the test programme are compared with codified design predictions as well as design equations proposed by various researchers. Based on the comparison, it is observed that the predictions made by most of the currently available design equations are conservative and reliable but generally scattered for design of cold–formed tubular structural steel stub columns having central circular perforations.

Experimental investigation on performance of perforated cold–formed steel tubular stub columns

This paper describes experimental and numerical investigations conducted to characterize the basic material properties and design of YSt–310 cold–formed structural steel sections at Indian Institute of Technology, Guwahati. Square (SHS) and rectangular (RHS) hollow sections with minimum yield strength of 310 MPa manufactured by Tata Steel India, were considered in the study. Initially, results from elemental analysis via optical emission spectrometer (OES) investigation and metallographic examination using optical microscope are presented. Key stress–strain parameters viz., Young's modulus, proof stress, ultimate strength, percentage elongation, strain hardening exponent etc. were generated based on flat, corner and weld coupon tests data. Extent of corner strength enhancement due to cold – forming determined using Vickers's microhardness test are reported. Additionally, cross – section capacity of the stub columns were also investigated experimentally and numerically. The column capacities generated from test and finite element study are compared with the existing design code – EN 1993–1–1 (EN 1993-1-1, 2005) [1] and design rules – continuous strength method (CSM) (Zhao et al., 2017) [2] and direct strength method (DSM) (North American Specifification for the Design of Cold-Formed Steel Structural Members, 2016; Arrayago et al., 2017) [3,4]. Based on the comparison, modifications on the existing design code and rules are suggested to provide a more accurate and reliable compressive design prediction.

Tekcham Gishan Singh

Papers

Experimental investigation on performance of perforated cold–formed steel tubular stub columns

Structural performance of YSt–310 cold–formed tubular steel stub columns

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

Cold-formed steel square hollow members with circular perforations subjected to torsion

Post-fire mechanical properties of YSt-310 cold-formed steel tubular sections