Stainless Steel Rectangular Hollow Sections Research Articles

Cross-section behaviour and capacity of cold-formed austenitic stainless steel flat-oval hollow sections under combined compression and bending

Flat-oval hollow section is composed of two semi-circular elements and two flat elements, with the semi-circular elements (exposed to wave and wind) offering a low level of hydrodynamic and aerodynamic drag and the flat elements facilitating connections with other members perpendicular to the wave and wind directions. This paper presents an experimental and numerical study of the cross-section behaviour and resistance of cold-formed austenitic stainless steel flat-oval hollow section stub columns under combined compression and bending. An experimental programme, including initial local geometric imperfection measurements and ten major-axis and minor-axis eccentric compression tests, was firstly carried out, with the test setups, procedures and results fully reported. Following the experimental programme, a numerical modelling programme was performed, with finite element models developed and validated against the eccentric compression test results and then used to conduct parametric studies to generate additional numerical data. Based on the test and numerical results, the relevant codified design interaction curves for cold-formed austenitic stainless steel rectangular hollow sections were evaluated for the applicability to their flat-oval hollow section counterparts. It was found from the evaluation results that the codified design interaction curves led to inaccurate resistance predictions, mainly due to the conservative end points (i.e. cross-section resistances under pure compression and pure bending) and inefficient shapes. Finally, a new design interaction curve was proposed through the use of more accurate end points and more efficient shape and offered more accurate and consistent resistance predictions for cold-formed austenitic stainless steel flat-oval hollow sections under combined loading than the codified design interaction curves.

Experimental and numerical investigations of austenitic stainless steel semi-oval hollow sections under combined compression and bending

Semi-oval hollow section is an innovative cross-section profile, including one semi-circular flange, one flat flange and two flat webs. While the semi-circular flange (exposed to fluid or wind) offers a low level of hydrodynamic or aerodynamic drag, the flat elements facilitate connections with other members. This paper presents experimental and numerical investigations into the local buckling behaviour and resistances of austenitic stainless steel semi-oval hollow sections under combined compression and bending. A testing programme was firstly conducted and included initial local geometric imperfection measurements and ten eccentric compression tests. In conjunction with the testing programme, a numerical modelling programme was performed, where finite element models were developed to validate against the test results and conduct parametric studies for expanding the test data pool over a wider range of cross-section dimensions and loading combinations. The obtained test and numerical data were used to evaluate the applicability of the relevant design interaction curves for austenitic stainless steel rectangular hollow sections, as prescribed in the European code and American specification, to austenitic stainless steel semi-oval hollow sections. On the basis of the evaluation results, the codified design interaction curves were found to provide conservative resistance predictions. Finally, an improved design interaction curve, with more accurate end points and suitable shape, was developed and led to more accurate and consistent resistance predictions for austenitic stainless steel semi-oval hollow sections under combined compression and bending.

Experimental programme on austenitic stainless steel RHS members subjected to monotonic and cyclic bending

Stainless steel is a corrosion resistant iron alloy with great potential in structural engineering due to its excellent mechanical features, durability and aesthetic properties. Since most of the existing research has concerned the behaviour of the material, the response of individual structural members, or the performance of simple structural systems under monotonic loading, one of the challenges that remains is the evaluation of the cyclic performance of members to promote its use in seismic design and exploit the excellent ductility and strain hardening properties of this material. For this reason, an experimental programme on austenitic stainless steel Rectangular Hollow Section (RHS) specimens was carried out at the Department of Civil Engineering of the Università degli Studi di Salerno in collaboration with the Universitat Politècnica de Catalunya. A total of eight RHS specimens were tested around the minor axis under both monotonic (three specimens) and cyclic (five specimens) loading, in an experimental set-up that followed a cantilever scheme. The main purpose of this study was to acquire information on the cyclic performance of austenitic steel structural members, focusing on the comparison between monotonic and cyclic behaviours. The outcomes of the tests included the load–displacement and the moment–rotation curves, the energy dissipation capacity, and the evaluation of the key rotation capacities of the members. The reported data are essential to enhance the still scarce research on the seismic behaviour of stainless steel structures.

Rotation capacity of cold-formed stainless steel RHS beams under cyclic loading

Stainless steel is a structural material with great potential in seismic design due to its ductile and strain hardening characteristics. However, no specific seismic design provisions exist for stainless steel, despite the remarkable differences with carbon steel. Moreover, research on the behaviour of stainless steel under cyclic conditions is scarce, not allowing designers to rely on accurate capacity models able to catch the actual member ductility under seismic excitation. Hence, the aim of this paper is to fill this lack and to provide simple provisions to estimate the total and stable part of the rotation capacity of stainless steel members with rectangular hollow section (RHS). A numerical study on 120 austenitic, ferritic and duplex beams under cyclic loading was performed following the ANSI/AISC 341 loading protocol. From the resulting skeleton curves, information on the ultimate strength and ductility (total and stable parts of the rotation capacity) were extracted. It was found that the ultimate bending moment resistance of RHS stainless steel beams under cyclic loading is accurately predicted by the Continuous Strength Method moment capacity, and that the rotation capacities can be related to the local slenderness by power functions calibrated from the numerical results. Finally, a tri-linear model that describes the full moment-rotation curves of stainless steel beams under cyclic loading is proposed using the calibrated equations, showing a good agreement with numerical moment-rotation curves, and which can be implemented in design software to define the behaviour of concentrated plasticity hinges.

Cold-formed stainless steel RHS members undergoing combined bending and web crippling: Testing, modelling and design

The behaviour and resistances of cold-formed stainless steel rectangular hollow section (RHS) members undergoing combined bending and web crippling were studied based upon experimental and numerical investigations. A test program consists of 4 pure bending tests, 7 pure web crippling tests and 23 web crippling-bending interaction tests was conducted. The RHS specimens were cold-rolled from lean-duplex and ferritic stainless steel sheets. Numerical models were built and validated against the test results. Upon validation, parametric studies comprised of 312 finite element analyses were undertaken. The obtained test and numerical results were compared with nominal resistances predicted from the American, Australian/New Zealand and European design standards for stainless steel structures. Moreover, the provisions in the North American Specification for cold-formed steel members were also evaluated. The comparison results indicate that the codified design provisions are generally safe to use for design of cold-formed stainless steel RHS members undergoing combined bending and web crippling, among which the European provision yields overly-conservative predictions. The codified web crippling-bending interaction curves can be applied for designing the stainless steel RHS members undergoing combined bending and web crippling, whilst improved predictions could be achieved by employing recently proposed bending and web crippling design rules.

Design of cold-rolled stainless steel rectangular hollow section columns

Considering the effects of cold-forming and strain hardening in the design of cold-formed stainless steel columns is an effective way to reduce construction costs. This approach has become a common trend in the revision of relevant design codes. A few studies were conducted in the past on two key aspects: (i) predicting the enhanced material properties in cold-formed stainless steel cross-sections and (ii) modifying the design methods to adapt to stainless steel material characteristics. However, in the existing literature, they had been separately studied, and integration of these two aspects to form a complete design method was rarely reported. In this study, a series of column tests were conducted on 19 stub and 32 long columns in rectangular hollow sections. The measured imperfections, material properties, load-displacement curves, and failure modes were reported. A new design method for columns was developed, which could clearly and accurately determine the column capacity over the space encompassed by member slenderness and cross-sectional slenderness values. The proposed design method and the method laid out in the Design Manual for Structural Stainless Steel were evaluated against the test data. It was demonstrated that the two design methods were both very conservative in predicting the column capacity when material properties in the annealed condition were used. However, their performances improved when the predicted enhanced material properties were used. Generally, the predictions of the proposed design method matched the test data better. Furthermore, a reliability analysis was conducted, and resistance factors were recommended for the corresponding design methods.

Effect of Uncertainty in Localized Imperfection on the Ultimate Compressive Strength of Cold-Formed Stainless Steel Hollow Sections

Stainless steel has excellent corrosion resistance properties, considerable long-term durability, and good mechanical strength. Hollow sections are a versatile and efficient form for construction applications. The use of cold-formed stainless steel rectangular hollow section (RHS) and square hollow section (SHS) in construction industry grasps the attention of designers conceiving long-term, cost-effective structures. For cold-formed RHS and SHS, localized imperfection (ω) resulting from rolling and fabrication process is inevitable. ω has inherent variability and has no definitive characterization. In this paper, statistical analysis of the maximum value of ω collected from available experimental data is conducted. A new approach utilizing Fourier series to generate the three-dimensional (3D) models of members with random ω is proposed. Probabilistic studies based on the proposed 3D models are then carried out to evaluate the effect of uncertainty in ω on the ultimate compressive strength of stainless steel columns with cold-formed RHS and SHS. A total of 21 columns that are prone to local buckling reduction are studied. The results show that uncertainty in ω has a considerable influence on the columns with relatively higher cross-sectional slenderness.

Plastic design of stainless steel continuous beams

In this paper an experimental study on eight simply-supported and four two-span continuous beams employing austenitic and duplex stainless steel rectangular hollow sections (RHS) is reported. In parallel with the tests, finite element models were developed. Upon validation against the experimental results, parametric studies were conducted to expand the available structural performance data over a range of cross-section slendernesses, structural systems and load configurations likely to occur in practice. The obtained experimental and numerical results along with collated test data were used to assess the accuracy of EN 1993-1-4 design provisions and to explore the possibility of plastic design for stainless steel indeterminate structures, simultaneously accounting for the effect of strain-hardening at cross-sectional level and moment redistribution exhibited by structures employing stocky cross-sections.

Experimental Investigation of Cold-Formed Stainless Steel Columns

An experimental investigation into the column strength of cold-formed stainless steel rectangular hollow sections is described in this paper. The columns tested displayed four cross-section sizes and were compressed between fixed ends. The tests were performed over a range of column lengths in order to obtain a column curve for each series of tests. The failure modes of the columns involved local buckling, overall flexural buckling, and combined local and overall buckling. The test strengths are compared with the design strengths predicted using the American, Australian/New Zealand, and European specifications for cold-formed stainless steel structures. The design strengths were calculated using the material properties obtained from both tensile coupon and stub column tests. It is concluded that the design strengths predicted by the three specifications are generally conservative. Reliability analysis of the design rules in the three specifications is performed. It is shown that the design strengths predicted by the Australian/New Zealand Standard are generally more reliable than the design strengths predicted by the American and European specifications.