Rectangular Hollow Sections Research Articles

Flexural behaviour of concrete-filled stainless steel SHS and RHS tubes strengthened by CFRP

This paper presents the experimental and numerical investigations on concrete-filled stainless steel square and rectangular hollow section (SHS and RHS) tubes subjected to in-plane bending. A total of 32 specimens were tested, in which one fourth of test specimens were unstrengthened for comparison. The ultimate strengths, failure modes, flexural stiffness, ductility and longitudinal strains of test specimens are reported. The corresponding finite element analysis (FEA) was also performed and calibrated against the test results. An extensive parametric study was carried out by using the verified finite element model to investigate the strengthening effect of CFRP on the flexural behaviour of concrete-filled stainless steel SHS and RHS tubes. It is shown from the comparison that the strengthening effect of CFRP was improved with the increase of the β value. Whereas, the ductility ratio was greatly deteriorated. Furthermore, the secant stiffness at 0.6Mu was recommended to be the flexural stiffness of concrete-filled stainless steel SHS and RHS tubes strengthened by CFRP in the practical applications. On the other hand, the flexural strength and flexural stiffness of concrete-filled stainless steel SHS and RHS tubes were increased with the increase of interface friction coefficient between stainless steel tube and concrete up to 0.6. The design formulae are also proposed for the flexural strengths and flexural stiffness of concrete-filled stainless steel SHS and RHS tubes strengthened by CFRP based on the current design rules for concrete-filled steel tubes by further considering the flexural strengths and flexural stiffness of the CFRP, which were verified to be accurate by the finite element analysis results.

Fatigue improvements of cracked rectangular hollow section steel beams strengthened with CFRP plates

Concerns over means to improve fatigue behavior of cracked rectangular hollow section (RHS) steel beams exist. This paper presents the details of strengthening schemes that was carried out using prestressed or high modulus carbon fiber reinforced polymer (CFRP) plates. A set of fatigue tests were conducted and results indicated that prestressed CFRP technique could increase fatigue crack propagation life 35.57 times longer than that of unrepaired one. The results also indicated that high modulus CFRP is effective at increasing fatigue life. Following crack propagation lives were calculated based on finite element models and close agreement with test results were observed. Thereafter, a parametric study was conducted considering the influence of various parameters such as the CFRP prestressing level, plate width and modulus on the fatigue life of the strengthened specimens. The findings of this paper can be employed to formulate design guidance for RHS beams under fatigue loading.

Experimental investigation and parametric analysis on overall buckling behavior of large-section aluminum alloy columns under axial compression

Experimental investigation was conducted on large-section extruded aluminum alloy columns of I-section and rectangular hollow section (RHS). Altogether seven columns with different slenderness ratios were comprised. The failure modes and stability resistance as well as load-displacement responses were identified. It was found that all tested specimens failed in flexural buckling. An extensive parametric analysis on 180 specimens was carried out with general FEA software ANSYS to evaluate the reliability level of the current design specifications including American aluminum design manual, Eurocode 9 and Chinese code GB 50429. The design stability resistance advised by Eurocode 9 and Chinese code GB 50429 is conservative, while that of American aluminum design manual slightly overestimates the practical stability resistance. Based on the parametric analysis results, a new design method was proposed to improve the design accuracy.

Behaviour and design of high-strength steel cross-sections under combined loading

The behaviour of hot-rolled high-strength steel (HSS) tubular sections under combined compression and uniaxial bending was investigated both experimentally and numerically. The experimental programme encompassed a series of material coupon tests, initial geometric imperfection measurements, residual stress measurements and 12 tests on stub columns subjected to uniaxial eccentric compression. Numerical models were developed and validated against the experimental results. An extensive parametric study was then performed with the aim of generating further structural performance data over a wider range of cross-section slendernesses, aspect ratios and applied eccentricities. The results were utilised for an assessment of the applicability of relevant Eurocode provisions to HSS cross-sections under combined loading. Conclusions regarding the applicability of Eurocode interaction curves to S460 and S690 square and rectangular hollow sections are presented.

RHS-to-RHS axially loaded X-connections near an open chord end

In all truss-type welded hollow structural section connection design procedures, the chord member is assumed continuous on both sides of the branch. New limits of applicability have recently been advocated, which specify minimum end distances from an open chord end to achieve the full connection strength. To investigate their suitability for rectangular hollow section (RHS) connections, an experimental program consisting of 12 RHS-to-RHS X-connections subject to branch axial compression was undertaken. For connections near a chord end, a modified yield line mechanism controlled. A proposed analytical model is derived, and by evaluating against the experimental results, is shown to accurately predict the yield loads. An EN 1993-1-8 amendment, transcribed from circular hollow section connections, is deemed excessively conservative, and a closed-form solution for the end distance, presented herein, is recommended for use with RHS connections. Alternatively, providing a cap plate is determined to be an effective stiffening method.

Compact cross-sections of mild and high-strength steel hollow-section beams

The Eurocode 3 rules for the high-strength steel (HSS: fy > 460 MPa) limit the analysis of beams to elastic global analysis and grades up to S700. In order to fully exploit the potential to design lightweight and sustainable steel structures, plastic analysis and the use of higher steel grades with fy > 700 MPa are desirable. The main concern is the low ultimate-to-yield strength ratio requirement for HSS, fu/fy > 1·05 according to BS EN 1993-1-12. Its influence on the resistance and rotation capacity of HSS square and rectangular hollow-section beams (SHS and RHS) is investigated in this study. The available results of four-point bending experiments on hollow-section beams are validated by finite-element analysis with special attention given to imperfections. Parametric study of steel grades S355–S960 indicates that the slenderness limits given in Eurocode 3 need to be reduced both for the mild steels and HSS.

Structural performance of YSt–310 cold–formed tubular steel 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 310MPa 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.

Behavior of Steel Rectangular Hollow Sections Subject to Blast Loading

AbstractLarge-scale far-field air-blast testing of cold-formed steel rectangular hollow sections (RHS) in flexure has been performed for the first time. These arena trials illustrated the excellent...

Experimental investigation of aluminum square and rectangular beams with circular perforations

Both three-point and four-point bending tests were conducted on aluminum square and rectangular beams with circular perforations. Test specimens consist of 9 perforated and 4 imperforated beams subjected to gradient and constant bending moment. The extrusion of 6061-T6 and 6063-T5 heat-treated aluminum alloys were used to manufacture square and rectangular hollow sections (SHS and RHS), respectively. The evaluation of the strength and behavior of aluminum square and rectangular beams focuses on the effects of the aspect ratio, the ratio of plate width, the ratio of plate slenderness, the ratio of perforation dimension and the number of perforations. Test results including the ultimate strengths, failure modes of local and flexural buckling failure, bending moment versus curvature curves and strain distributions along the circular perforations are all reported, which were employed to assess the suitability of the current design specifications. The comparison of test strengths with design strengths shows that the modified DSM for aluminum structural members is somewhat conservative with the lowest value of COV, whereas other design specifications for cold-formed steel and aluminum structural members are quite conservative with comparatively high value of COV. It is also demonstrated from the comparison that the perforated sections close to the mid-span of the beams are the critical section under gradient and constant bending moment. In addition, the comparison of test strengths with design strengths also reveals that the current design rules for perforated cold-formed steel and aluminum structural members are all conservative, in which North American Specifications (NAS) for perforated cold-formed steel structural members are generally appropriate with the lowest value of COV.

Design of cold-formed high strength steel tubular beams

A numerical investigation on cold-formed high strength steel (HSS) tubular beams is presented in this paper. The nominal 0.2% proof stresses of the HSS sections ranged from 700MPa to 1100MPa. In the complementary study [1], experimental investigation on the beam specimens have been performed. In the present study, numerical modelling methodology for beams was first validated and parametric study on the cold-formed HSS tubular beams was conducted. A total of 423 numerical data was obtained to investigate the structural performance of HSS tubular beams. The experimental and numerical results were then compared with the codified design guidelines from ANSI/AISC 360-10 [2], EN 1993-1-1 [3], AS 4100 [4] and AISI S100 [5] in addition to the predictions from Direct Strength Method (DSM) for square hollow sections (SHS), rectangular hollow sections (RHS) and circular hollow sections (CHS). The codified slenderness limits for sections subjected to bending were examined. Improvements on the design guidelines are proposed in this paper.

Design of stainless steel continuous beams with tubular cross-sections

This paper presents a comprehensive study on the application of global plastic design methods, not currently allowed in European specification provisions, to stainless steel rectangular and square hollow section continuous beams. The analysis of experimental and numerical continuous beam strengths highlighted that ultimate capacity predictions calculated based on global elastic analysis result in a considerable conservatism due to strain hardening and bending moment redistribution effects. Alternatively, the assessment and reliability analyses of the traditional plastic design methods demonstrated that the Class 1 cross-section limit provided in the European specification can be safely applied for the partial safety factor γM0 currently provided. However, the analysis evidenced that including bending moment redistribution in capacity predictions is not enough since strain hardening effects play an important role when stocky cross-sections are analysed. Thus, the Continuous Strength Method for indeterminate structures was also assessed and it was found to provide accurate capacity predictions for all analysed stainless steel grades. Finally, an alternative Direct Strength Method design approach is proposed for stainless steel continuous beams based on the Direct Strength Method bending capacity. The proposed method, statistically validated, accounts for strain hardening effects and moment redistribution and provides the best resistance predictions among the different design methods considered.

Simplified Models for the Material Characterization of Cold-Formed RHS.

It is well known that the cold-forming process used to manufacture tubes causes an increase in both the yielding stress and the ultimate strength of the corner material in rectangular steel hollow sections. This may have a significant effect on the resistance of any structure built with those profiles. However, the mentioned material hardening can be difficult to take into account in the calculations for member design or to evaluate the connection resistance through the design formulation or when using numerical simulation models. As an attempt to face the above-mentioned problem, the present paper presents a comparison among simplified approaches that consider homogeneous material properties for the whole section. It has been carried out by comparing the results obtained from the finite element modelling of stub column tests in which the material properties based on the flat faces were considered for the whole profile.

12.10: Structural response of high strength steel hollow sections under combined biaxial bending and compression

ABSTRACTThe benefits of high strength steel (HSS) as a structural material and its potential to lead to smaller sections and thus lighter structures has increased its use in the construction industry. Current design specifications for HSS are widely based on assumed analogies with normal strength steel, since they are based on a limited number of test data on HSS sections that were available when these specifications were published. Hence, their applicability to HSS requires assessment. Even though research towards this direction has grown, literature on the structural response of HSS under combined biaxial bending and compression is scarce. This paper presents a comprehensive numerical study on the cross‐sectional behaviour of S460 and S690 square and rectangular hollow sections under biaxial bending and compression. Finite element models are developed and validated against experimental results on 12 hot‐finished S460 and S690 stub columns under uniaxial eccentric compression. The numerically generated load‐deformation curves, the ultimate loads and the failure modes accurately replicate the experimental ones. Hence, the FE models are deemed able to predict the behaviour of stub columns subjected to combined compression and bending. Upon successful validation, extensive parametric studies aiming to generate additional structural performance data are executed. Two aspect ratios, eight cross‐sections with different thicknesses, and forty‐three combinations of initial loading eccentricities corresponding to different ratios of axial load to bending moments about both axes, are investigated for both steel grades. The results facilitate the determination of interaction failure surfaces and allow the assessment of relevant design specifications. It is concluded that the capacity of Class 1 and Class 2 cross‐sections is adequately predicted by European design provisions, with some conservative predictions occurring for S460 sections in the stocky slenderness range. For HSS semi‐compact cross‐sections under combined loading, the Eurocode provisions appear rather conservative, whilst the capacity of effective cross‐sections is overall well‐predicted.

12.20: Mechanical properties of cold‐formed stainless steel

ABSTRACTStainless steel is a material of many specific properties, which significantly differs from carbon steel ones. One of the main attributes of all stainless steel grades that haven't been satisfactorily investigated is the significant change of stress‐strain behaviour due to cold‐forming in fabrication process of structural elements. In the last decades some proposals for the most basic material properties have been developed. However they don't predict the whole stress strain diagram. In the paper presented research involves testing programme focused on virgin and cold‐worked elements of four stainless steel grades: austenitic (1.4404), ferritic (1.4003), duplex (1.4462) and lean duplex (1.4162). Selected grades represent the most used families of stainless steel specified for structural purposes and used for section fabricating via cold‐forming. Gathered data together with other available experimental results serve as a base for analytical part of the research. The main output was establishment of an analytical solution for a stress‐strain diagram of a whole structural cross‐section represented by square and rectangular hollow sections. Further objective was to establish relationships for mechanical properties such as ductility or ultimate strength as these issues have not been sufficiently investigated before. Conclusions contribute to the common design of stainless steel structures and help to precise finite element analyses using enhanced properties of cold‐worked stainless steel.

08.29: Experimental investigation of concrete‐filled double skin tubular stub columns with ferritic stainless steel outer tubes

ABSTRACTAn experimental investigation of concrete‐filled double skin tubular (CFDST) stub columns with ferritic stainless steel outer tubes and carbon steel inner tubes is presented in this paper. A total of 14 tests was carried out to study the axial compressive behaviour and strengths of CFDST specimens. The outer tubes were cold‐formed from ferritic stainless steel material (grade 1.4003) into rectangular hollow sections (RHS) with depth‐to‐thickness ratios ranging from 26.1 to 42.1, while the inner tubes were cold‐formed from carbon steel (grade S235) into square hollow sections (SHS) with width‐to‐thickness ratios ranging from 7.5 to 13.5. The gaps between the outer and inner tubes were filled by concrete with three different nominal cylinder strengths of 40, 80 and 120 MPa. The columns had different lengths so that the length‐to‐depth ratio remained at a constant value of 2.5. The CFDST specimens were subjected to uniform axial compression. The column strengths, load‐axial strain relationships and failure modes were evaluated in this paper. The test strengths were then compared with the strengths calculated from the existing design codes, where the guidance given in European Code, Australian Standard and two American Specifications for concrete‐filled columns were used. It is shown that current design rules provide conservative predictions for the resistance of CFDST stub columns with ferritic stainless steel outer tubes.

Tests on high-strength steel hollow sections: a review

Advances in technologies have allowed manufacturers to produce steel plates and sections with strengths of 690 MPa and higher. The use of high-strength steel has the potential for significantly reducing the material costs and the self-weight of structures. High-strength steel hollow sections can be either welded from steel plates or cold-formed from coils. Tests on different built-up high-strength steel hollow sections have been conducted around the globe, including Australia, China, Japan and the USA. The commonly used box-sections were tested; the slenderness limits and member capacities against compression were also studied. To investigate the performance of cold-formed high-strength steel hollow sections, the authors initiated a research programme in Hong Kong, which included both experimental and numerical investigations on cold-formed high-strength steel hollow sections. The sections include square, rectangular and circular hollow sections. Based on the results, recommendations on section slenderness limits and expressions for determining member capacity are proposed in these studies. This paper summarises recent research on high-strength steel hollow sections and also addresses the design recommendations and limits in codes for both built-up and cold-formed high-strength steel hollow sections.

01.04: Joints between open section beams and tubular columns: New configuration for semi‐rigid and moment resistant bolted joints

ABSTRACTThe appealing shape and the mechanical properties of the tubular members are the main responsible for their growing popularity amongst architects and engineers. However, their potential hasn't been properly explored due difficulties encountered in the joints conception and design, with special emphasis on the bolted joints if rigid and/or full strength behaviour is required for the joint.Currently, in the European regulation scenario, the guidance for the joints design is given in the EN 1993‐1‐8. The recommendations for joints with tubular members are given in its seventh chapter, where only welded solutions are considered. Bolted solutions aren't referred, and no guidance is given to predict the joints rotational stiffness and rotation capacity. However, a window is left open in the standard sixth chapter with the given method to predict the joints structural properties (component method). The method is applicable to joints in frames of any type, independently of its configuration and of the joined members’ sections. Once known the nonlinear response of each joint basic component, commonly represented by force‐displacement curves, the component method can be used to predict the joint structural properties.Regarding the current lack of information in this subject, the authors propose a new configuration for joints connecting open section beams to rectangular or square hollow section columns. The configuration was conceived with the double purpose of getting a joint with bending moment resistance capacity and with high initial rotational stiffness. Furthermore, looking on the current regulation scenario, it would be desirable that joints with the proposed configuration could be designed by the component method. Thus, the authors identified the joint active basic components, and are developing experimental work in the sense of establish the force‐displacement curves which represent the nonlinear response of the new basic components. The experimental work, already developed, on the basic components structural response is here summarily presented.

12.03: Buckling curves for stainless steel tubular columns

ABSTRACTTowards the development of more resilient and sustainable structures, interest in the use of high performance construction materials, such as stainless steels, has increased in recent years. Recent studies [1] have highlighted a number of deficiencies in the flexural buckling provisions given in Eurocode 3: Part 1.4 for the design of stainless steel compression members. Therefore, this study aims to investigate the effect of production route (cold‐formed and hot‐finished) and material grade (austenitic, duplex and ferritic) on the behaviour and design of stainless steel square and rectangular hollow section columns. Test data from the literature combined with numerical modelling data generated as part of this study are used to derive a series of buckling curves for the design of stainless steel columns. Reliability analysis in accordance with Annex D of EN 1990 has been carried out to show that the proposed buckling curves comply with the Eurocode reliability requirements.

10.11: Fire design of rectangular hollow section joints

ABSTRACTThe component method is a design approach for the characterization of the mechanical properties of structural joints and it is referred to in Eurocode 3 Part 1‐8. Eurocode design rules for open sections are already based on the component method. The design rules for joints between tubular hollow sections are still based on simple theoretical mechanical models validated against experimental test results. However, there are research activities in progress to extend the application of the component method also to hollow section joints in the next revision of Eurocode. The fire design of steel joints is carried out in accordance with Eurocode 3 Part 2. Eurocode gives only a guidance on how the temperature of the joint components can be assessed based on the local values of thermal resistance of the joint's fire protection. The method is not sufficient for the component method and Tampere University of Technology is currently carrying out experimental fire research to better understand the temperature distributions in the vicinity of the joint. The aim of the research is to develop experimental methods to determine steel temperatures at the actual joint component, spring, locations and to transfer this information into the joint design approach based on the component method. This paper introduces an experimental research demonstrating the actual temperature distributions within the joint area and highlights the differences between the failure modes and the design criteria at normal temperature design and fire design of a joint.

10.33: Flexural buckling behaviour of high strength steel columns under fire conditions

ABSTRACTIn this paper, a numerical modelling study using the finite element (FE) analysis package ABAQUS [1] has been carried out to study the flexural behaviour of square and rectangular hollow section columns made from high strength steel (HSS) grades S690QL and S700MC at temperatures up to 800°C. The FE model was validated using existing experimental data and then parametric studies were performed on columns with varying length and cross‐sectional properties. The results have been compared with recommendations given in Eurocode 3 Part 1–2 [2]. The analyses showed that the Eurocode is generally conservative with respect to the buckling coefficients derived and safely predicts the buckling behaviour resistance of columns made from S700MC and suggest a lower buckling curve may be needed for S690QL. It was also shown that the 0.2% proof stress rather than the stress at 2% total strain is a better parameter for deriving buckling curves in fire.