Cold-formed Steel Tubular Sections Research Articles

Mechanical properties of low-alloyed YSt-355-FR (0.126%Mo) cold-formed steel tube at elevated temperatures

With the advancement in the steel-making process, micro-alloyed steels with small amounts of Nb and Mo, etc., have been developed, which can retain superior strength at higher temperatures. Towards this end, this study investigates a newly developed low-alloyed YSt-355-FR cold-formed steel having Mo content less than 0.15% through the evaluation of the mechanical properties of its hollow steel sections. The standard tension tests on 84 tensile coupons taken from every region (non-welded, welded, and corner) of hollow steel cross-section at steady-state were conducted at temperatures between 20 °C and 800 °C with 120 min holding time. The stress-strain curves were plotted at different temperature levels, and results were discussed in terms of reduction factors of key strength and stiffness properties. The test results show that the location of steel in the tube cross-section has a significant influence on its mechanical properties. The results obtained for the cold-formed YSt-355-FR structural steel suggest the necessary inclusion of proposed new strength reduction factors for the cold-formed steels and up-gradation in the strength reduction factors of hot-rolled steels in the relevant fire design standards. The use of yield strength at 2% strain (upto 500 °C) and at 1% strain (beyond 500 °C) yields optimum buckling strength of YSt-355-FR columns. The provisions mentioned in the EC3 safely predicted the buckling strength of the YSt-355-FR steel tube columns compared to that predicted by the finite element analysis. Important observations have been made in this study, which shall help designers and practitioners in designing steel structures using cold-formed steel tubular sections.

Tests of cold-formed normal and high strength steel tubes under tension

Abstract The construction field has a widespread usage of cold-formed steel tubular members in various types of structures. In recent decades, extensive research studies have been carried out on cold-formed steel hollow sections under various loading conditions. However, there is a lack of research study on the tensile performance of cold-formed steel tubular sections with the whole cross-section under tension. Therefore, the focus of this study is to investigate the structural behavior of cold-formed steel tubular sections with and without circular perforations under pure tension through experimental investigation. Eleven cross-section series made of cold-formed normal and high strength steel were considered. The nominal outer dimensions of hollow steel tubes ranged from 20 to 100 mm and the nominal wall thicknesses ranged from 1.5 to 8 mm. The mechanical properties were determined through tensile coupon tests. The measured 0.2% proof stresses ranged from 323 to 795 MPa. A total of 24 tensile tubular specimens, including twelve specimens with circular holes and the rest without hole, were tested with full cross-section under pure tension. Tensile test results of cold-formed steel tubular sections were discussed and compared with the tensile capacities predicted by the North American Specification, the Australian/New Zealand Standards and the European Code. The comparisons show that the existing design rules provide quite conservative and reliable tensile strength predictions for cold-formed steel tubular sections.

Mechanical properties and cross-sectional behavior of additively manufactured high strength steel tubular sections

Abstract Additive manufacturing, commonly known as 3D printing, is an evolutional technology in the manufacturing industry. This technology has already been embraced by different industries, such as aerospace and biomedical engineering, and the recent advance in this technology has generated a vast of societal excitement for its future. Despite the exciting prospect of its application in civil engineering, additive manufacturing technology is still at a perceived stage for construction industry. The benefits and potential in construction industry are rarely known in the field at this stage. This paper aims to investigate the mechanical properties and structural performance of additively manufactured high strength steel tubular sections at the cross-sectional level through experimental program. The specimens were additively manufactured from H13 steel powder by selective laser melting (SLM) with three different scanning patterns, where the typical yield strength (0.2% proof stress) of the conventionally manufactured H13 steel is around 1650 MPa. The test program comprised tensile coupon tests, compression coupon tests, hardness tests, microstructural characterization as well as geometric imperfection measurements and stub column tests. The anisotropy on mechanical properties was examined through tensile coupon tests in both longitudinal and transverse directions. Compression coupon tests were also conducted to investigate the differential strength of material in tension and compression. The influences of scanning patterns on mechanical properties and structural behavior of as-printed high strength steel tubular sections stub columns were also investigated. The test results were used to assess the applicability of existing design provisions in the American Specification, Australian and New Zealand Standard as well as European Code that originally developed for conventionally produced hot-rolled and cold-formed steel tubular sections to the additively manufactured high strength steel tubular non-slender sections in this study.

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

An experimental programme to study the residual mechanical strength of Tata Structura-YSt 310 cold-formed steel square and rectangular tubular sections (conforming to Indian Standard 4923) after being exposed to elevated temperature is described in this paper. First, the coupon specimens extracted from the flat regions are exposed to pre-determined elevated temperature in the range ~ 300–800 °C, and then the residual mechanical properties and hardness value were estimated at ambient temperature after natural air cooling. The results from the experimental programme are reported in this paper in the form of post-firestress-strain curves and associated basic material properties (e.g. elastic modulus, proof stresses, tensile strength, percentage elongation at fracture, Ramberg-Osgood material parameters etc.) as well as surface hardness values. The test results showed that most post-fire mechanical properties are appreciably different from ambient temperature material properties when exposed to a temperature higher than ~400 °C; whilst elastic modulus appears to remain unaffected even when the exposed temperature is up to ~800 °C. A near linear relationship of post-fire material strengths and hardness value was observed. Two sets empirical equations are proposed separately to predict the residual post-fire reduction factors based on the i)current experimental results of Tata Structura-YSt 310 cold-formed steel, and ii) cold-formed steel of various grades presently available in the literatures.

Mechanical properties of cold-formed steel tubular sections at elevated temperatures

Cold-formed steel tubular sections have been increasingly used as structural components in modern structures due to the many advantages they possess over conventional hot-rolled sections. Lack of knowledge on the structural fire performance of cold-formed steel tubular sections has raised concerns with respect to fire safety designs. Hence the knowledge of elevated temperature mechanical property deterioration characteristics of these sections is essential. Although design standards and past research studies provide empirical equations to predict these mechanical property deterioration characteristics, a detailed experimental investigation of cold-formed steel tubular sections to determine their elevated temperature mechanical properties is scarce. Therefore, an experimental investigation was carried out to determine the mechanical properties of cold-formed SHS, RHS and CHS at elevated temperatures. Tensile coupon tests were performed at temperatures ranging from 20°C to 800°C under steady state conditions to determine the reduced values of yield strength, stress at 2% strain, elastic modulus, and ultimate strength with increasing temperatures. Experimental results were then compared with those obtained from the current design standards and past research studies, which lead to a conclusion that the available reduction factors are either unsafe or more conservative. Therefore, suitable equations were proposed to determine the mechanical property reduction factors at elevated temperatures. This paper presents the details of this experimental investigation of cold-formed steel tubular columns and the results, which include the developed equations and a stress-strain model for elevated temperatures.