Rectangular Hollow Sections Research Articles

Cyclic axial loading tests on mortar-filled rectangular tube with various connection details

Although a mortar-filled rectangular hollow structural section (RHS) under monotonic loading has achieved large tensile capacity using various connection details and buckling capacity of RHS members, the structural capacity of the mortar-filled RHS tubes has not been investigated under cyclic loading. In this study, the seismic performances of newly developed mortar-filled RHS tubes with various connection details were evaluated under cyclic axial loading. The major test parameters included the end connection type, the thicknesses of the RHS tube, cap plate, and cleat plate, as well as the length of the RHS tube. The test results showed that the RHS tube in all specimens failed by tensile fracture before axial compression failure. The seismic performance of the embedded shear plate end connection with penetrating rebar was superior to that of a conventional welded T-end connection. The test results were compared with the current design code to evaluate the seismic capacity of the RHS tube according to the connection details. Design considerations for the connections of the mortar-filled rectangular tubes were also provided.

Hysteretic behavior of eccentric RHS beam-to-column joints under cyclic in-plane bending

This paper conducted experimental and numerical studies on the hysteretic behavior of eccentric rectangular hollow section (RHS) beam-to-column joints under cyclic in-plane bending. The study began with the design of both stiffened and unstiffened joints, followed by hysteresis tests that revealed failure modes like web weld tearing and stiffener fracture. The seismic performance of the joints was evaluated using hysteresis curves, skeleton curves, ductility coefficients, strength degradation coefficients, and energy dissipation coefficients. Compared to unstiffened joints, the stiffened joints exhibited a 30 % increase in peak load and a 18 % improvement in maximum energy dissipation coefficient. Subsequently, finite element (FE) analysis was performed, and the influence of key parameters on the hysteretic behavior was studied using validated FE models. The results indicated that the hysteretic behavior was positively correlated with the flange width ratio of beam to column, the ratio of beam section height to column flange width, and the thickness ratio of beam to column, while it was negatively correlated with the width-to-thickness ratio of the column. Finally, a mathematical model for the hysteretic behavior of both stiffened and unstiffened joints was developed and validated through experimental and FE comparison, offering practical applicability in engineering design.

Experimental testing and plastic strain analysis of high strength steel longitudinal plate to tubular X joints

Applying high strength steels to tubular joints can increase the propensity to fracture failure due to their lower ductility. However, to simulate the fracture behavior in the finite element (FE) analysis, sophisticated material damage model with rigorous fracture criteria should be incorporated. Recently, the latest draft of ISO 14346 has advocated the use of 5% strain limit in FE analysis of tubular joints. The strain limit concept has been further developed by the authors’ previous work, for its use as a practical alternative to the complicated material damage model. Specifically, a lowered limit of 2.5% was recommended for longitudinal plate to circular hollow section (CHS) joints subjected to in-plane bending. This study extends the strain limit investigation to longitudinal plate to tubular X joints subjected to tensile loads. An experimental program is first presented which included both CHS and rectangular hollow section (RHS) chord members fabricated from two high strength steels with nominal yield stresses of 460 MPa and 700 MPa. Based on test-validated supplemental numerical analyses, it is suggested that the joint load corresponding to 2.5% strain limit can be taken as the load-bearing capacity to suppress occurrence of a fracture failure for the tubular joint configurations considered in this study.

Stability of hot-finished and cold-formed steel hollow section columns: A comparative study

A comparative study into the buckling behaviour of hot-finished and cold-formed steel hollow section members subjected to axial compression is presented in this paper. The main differences between hot-finished and cold-formed hollow sections are initially discussed. An experimental programme conducted to investigate the local, global and local-global interactive buckling of hollow section columns is then described. Three S355 normalised hot-finished and three S355/S420 (dual certified) cold-formed profiles, covering circular, square and rectangular hollow sections (CHS, SHS and RHS respectively), were studied. The stress-strain characteristics of the examined materials were obtained through tensile coupon tests. 3D laser scanning was utilised to determine the distribution of geometric imperfections in selected SHS test specimens and a consistent approach to characterise different forms of geometric imperfections from the scan data is put forward. A stub column test was carried out on each cross-section to examine its local buckling behaviour, and a series of long column tests were performed on all test profiles. In total, 21 tensile coupon tests, six stub column tests and 40 long column tests were conducted in this programme. Finite element models were also developed, validated and used for parametric studies to generate supplementary numerical datasets. The obtained test and numerical data, along with the existing experimental results collected from the literature, were used to evaluate the accuracy and reliability of the Eurocode 3 (EC3) stability design provisions for hot-finished and cold-formed hollow section columns; aspects requiring improvements are highlighted to guide future studies.

Effect of web holes on web crippling capacity of rectangular hollow steel sections under two flange loadings

This paper presents experimental and numerical investigations on web crippling behavior of hot rolled rectangular hollow section (RHS) with web holes. A total of 20 rectangular hollow sections, subjected to interior-two-flange (ITF) and end-two-flange (ETF) loading conditions undergoing web crippling, were experimentally tested. The experimental program was designed to obtain web crippling of specimen having slenderness (h/t) value of 21.32, by varying size and offset distance of web holes under two flange loading conditions. Finite element models of experimentally tested beams were developed, and results of finite element analysis showed good agreement with experimental results. A parametric study was then conducted using finite element analysis on different cross section sizes, to demonstrate the effect of size and position of web holes on web crippling capacity of rectangular hollow sections. It was demonstrated that ratio of diameter of web hole to the depth of flat portion of web (a/h) and ratio of offset distance of web hole to the flat portion of web (x/h) are the primary parameters affecting the web crippling strength. Design recommendations in the form of reduction factors for both loading conditions are proposed, that are conservative to both experimental and finite element results. To assess the reliability level of design recommendations, reliability analyses were undertaken.

In-plane flexural behavior of eccentric rectangular hollow section (ERHS) X-joints: Experimental, numerical and analytical study

This paper investigates the in-plane flexural behavior of an eccentric rectangular hollow section (ERHS) X-joint, where the two braces are continuous at one side and the inner face is aligned with a chord sidewall. The presented X-joints are full lateral offset RHS joints. In this study, laboratory static testing is implemented on two ERHS X-joint specimens and one traditional RHS X-joint specimen under in-plane bending moment (IPBM), and the corresponding numerical simulation is conducted. The results show that the ultimate flexural strength and initial stiffness of the ERHS X-joints with a medium brace-to-chord width ratio (β) are larger than those of the RHS X-joints. The initial stiffness and strength of ERHS X-joints increase with the growth of β. Based on the load transferring mechanism, two analytical models and the relevant formulae are proposed to predict the strength of the ERHS X-joints with β ≤ 0.925 and β = 1.0, and the strength of joints with 0.925 <β < 1.0 can be determined by linear interpolation. The proposed analytical models are validated against experimental data and finite element results.

VALIDATION AND PARAMETRIC STUDY OF LEAN DUPLEX STAINLESS STEEL HOLLOW SECTION STUB COLUMNS BY FINITE ELEMENT ANALYSIS

In this research, a parametric study was conducted on square hollow sections (SHS) and rectangular hollow sections (RHS) columns made of a lean duplex stainless steel (LDSS) grade, namely EN 1.4162. The aim was to determine structural response data due to variations of different design parameters, which is vital in designing structural members. Finite element modeling was utilized for this and the validity of the models was confirmed by comparing them with existing experimental test data. Thickness, corner radius, load eccentricity and slenderness ratio were taken as the varying parameters to study. A total of 32 columns were modeled to study with five variations for each parameter, making a total of 160 variations. For each variation, the ultimate load and the corresponding end shortening were recorded. Each parameter has some effects on ultimate load or end shortening or both except corner radius, which has no significant effect. To visualize the effect of a parameter, a trend line equation was developed by plotting the average result of all column models for each variation of that particular parameter. A linear increase in ultimate load and end shortening can be observed with an increase in column thickness, while opposite trends were witnessed with load eccentricity. Though a linear rise in end shortening was caused by the slenderness ratio, no significant change was seen in the ultimate load of the columns. The mathematical equations presented can be employed to forecast the maximum load-bearing capacity and the associated amount of end shortening when designing structural hollow sections made of LDSS.

Localized loading behavior of cold-formed stainless steel RHS under interior-one-flange load case at elevated temperatures

The localized loading behavior of cold-formed stainless steel (CFSS) rectangular hollow section (RHS) members at elevated temperatures is investigated in this paper. Fifteen localized loading tests conducted at various temperatures up to 800 °C were reported. The tests were carried out under the Interior-One-Flange (IOF) load case as specified in American Specification for the design of cold-formed stainless steel structural members. Tensile coupon tests were performed to obtain the material properties of the CFSS RHS at various temperatures. Detailed information on dimensions, temperature histories, failure modes, load-deformation curves, localized loading capacities of specimens at various temperatures were presented. In addition, a numerical investigation was supplemented, where a total of 192 finite element (FE) analyses were undertaken after validation of developed FE model against the elevated-temperature test results. The influence of various parameters on the localized loading capacities of CFSS RHS at different temperatures under IOF load case was revealed. The obtained results were utilized to assess the applicability of the localized loading design provision for CFSS RHS under IOF load case codified in the American Specification to elevated temperature conditions. Moreover, the results were also compared with predictions based on existing design rules in literatures for cold-formed RHS at elevated temperatures. Furthermore, reliability analyses were carried out to assess the reliability levels of the assessed design methods. It is shown that the existing design rules can generally provide conservative and reliable predictions of the localized loading capacities for the CFSS RHS under IOF load case at elevated temperatures.

Stress concentration factors for RHS-to-RHS T-type moment-loaded end connections

The research presented in this paper is the continuation of a series of efforts to develop design formulae for rectangular hollow section (RHS)-to-RHS end connections and circular hollow section (CHS)-to-CHS end connections under fatigue loading. Normalized hot spot strains for the RHS-to-RHS T-type moment-loaded end connections (unreinforced and reinforced with a chord-end cap plate) are experimentally determined and compared to those in their regular connection counterparts (with sufficient chord continuity). Upon validation using the experimental data, a parametric finite-element study consisting of 448 models (including 336 stepped connections and 112 matched connections) is performed. The parametric study investigates the effects of chord end distance-to-width, branch-to-chord width, branch-to-chord thickness, and chord slenderness ratios, as well as the chord boundary condition (unreinforced or with a chord-end cap plate). Existing formulae in CIDECT Design Guide 8 for the calculation of the corresponding stress concentration factors (SCFs) are evaluated, and SCF correction factors are derived.

Optimization of cold-formed steel beam cross-sections for pallet rack storage systems

This paper aims to obtain optimized cold-formed beam cross-sections for industrial pallet rack storage systems. The optimal sections were obtained by applying fitness functions aimed at reducing cross-sectional area and/or displacement and solving them using the Genetic Algorithm. These functions imposed a behavioral constraint so that all optimized solutions had the same resistant bending moment. The calculation of the characteristic resistant bending moment was carried out according to the direct strength method, with load factors defined by the elastic stability analysis with CUFSM, in an analysis routine implemented on the MATLAB platform. Four parameterized sections were studied, verifying the optimum set of height, width and stiffening elements that met the objectives defined by functions, assuming reference values of a rectangular hollow section. Manufacturing constraints were also taken into account. The results show that it is possible to manufacture cold-formed beams that consume less material and/or have a better moment of inertia in relation to the reference section, without compromising the strength of the structural element.

Development of component stiffness equations for thread-fixed one-side bolt connections to an enclosed rectangular hollow section column under tension

Development of component stiffness equations for thread-fixed one-side bolt connections to an enclosed rectangular hollow section column under tension

Stiffness of Loaded Face of Steel Rectangular Hollow Section Columns with and without Concrete Infill in Beam-column Endplate Connections

This paper presents a new analytical approach for calculating the stiffness of the loaded face of a rectangular hollow section RHS column in beam-column connections with and without concrete infill, as well as with flush and extended endplates, to determine the behavior curve of these types of connections. The approach, based on Eurocode 03's component method, offers efficient analytical formulas for accurately determining the loaded face's stiffness. A comparison with existing methods demonstrates its remarkable simplicity and efficiency, allowing a simple beam model to represent the RHS column's behavior with all relevant parameters considered. Comparison of the new approach to existing ones from the literature demonstrates their reliability and efficiency. Furthermore, when compared to 32 experimental tests presenting nearly the entire range of probable connection configurations, as well as attachment techniques commonly used in construction practice, the margin of error does not exceed 12 percent on average and a maximum of less than 25 percent.

Fatigue enhancement of welded thin-walled tubular joints made of lean duplex steel

In the present work, the fatigue strength and enhancement techniques of welded thin-walled (wall thickness of t = 2 mm) square hollow section (SHS) joints made of lean duplex stainless steel (grade EN 1.4162) are experimentally and numerically studied. Experimental fatigue tests were carried out on gas metal arc-welded tubular X-joints subjected to fully reversed (applied stress ratio of R = −1) constant amplitude in-plane bending moment. Geometrical improvement techniques were investigated by applying fully penetrating fillet welds and using structural reinforcements. The applications of high-frequency mechanical impact (HFMI) treatment were examined in the context of further enhancing the fatigue strength of the geometrically improved joints. In addition to the experimental work carried out in this study, the fatigue test data of welded thin-walled SHS and rectangular hollow section (RHS) joints were extracted from literature. Structural stress concentration factors were numerically and analytically obtained to validate the fatigue assessment model for welded thin-walled tubular joints using the structural hot-spot stress method. In addition, the effective notch stress (ENS) concept with the reference radius of rref = 0.05 mm was implemented. Compared to the joints in the as-welded state, fatigue strength improvements of 1.53–2.7 were found in the geometrically improved joints. On the other hand, the HFMI treatment did not lead to an additional increase in the fatigue strength capacity of the studied AW joints. The CIDECT guidelines for the structural hot-spot stress method were found conservative for thin-walled joints (t < 3 mm) and could be recommended for fatigue design.

Instability of FGM rectangular hollow section (RHS) beam element under combined bending and compressive loads

Instability of FGM rectangular hollow section (RHS) beam element under combined bending and compressive loads

Monte Carlo simulation study on the reliability of concrete-filled HSS beam-column design provisions

Revisions were recently proposed to the way in which concrete-filled hollow structural section (HSS) members are handled in CSA S16. These revisions were based on previous research, comparisons to experiments, and a first-order reliability method analysis of existing provisions for compression and flexural members. In this paper, this topic is further expanded by using Monte Carlo Simulations (MCS) to determine the inherent reliability of the previous and new design rules for concrete-filled rectangular hollow section (RHS) and circular hollow section (CHS) beam-columns. A representative set of concrete-filled RHS and CHS members with variations in concrete strength, wall slenderness, effective length, and loading eccentricity are analyzed. Using MCS, the reliability index (β+) of each is determined over a range of live-to-dead load (L/D) ratios. Inherent β+ values are compared to the code-specified target (i.e., β+ = 3.0 per Annex B of CSA S16) and the CSA S16:19 and AISC 360-16 provisions.

Numerical and artificial intelligence based investigation on the development of design guidelines for pultruded GFRP RHS profiles subjected to web crippling

This article presents a numerical and artificial intelligence (AI) based investigation on the web crippling performance of pultruded glass fiber reinforced polymers’ (GFRP) rectangular hollow section (RHS) profiles subjected to interior-one-flange (IOF) loading conditions. To achieve the desired research objectives, a finite element based computational model was developed using one of the popular simulating software ABAQUS CAE. This model was then validated by utilizing the results reported in experimental investigation-based article of Chen and Wang. Once the finite element model was validated, an extensive parametric study was conducted to investigate the aforementioned phenomenon on the basis of which a comprehensive, universal, and coherent database was assembled. This database was then used to formulate the design guidelines for the web crippling design of pultruded GFRP RHS profiles by employing AI based gene expression programming (GEP). Based on the findings of numerical investigation, the web crippling capacity of abovementioned structural profiles subjected to IOF loading conditions was found to be directly related to that of section thickness and bearing length whereas inversely related to that of section width, section height, section’s corner radii, and profile length. On the basis of the findings of AI based investigation, the modified design rules proposed by this research were found to be accurately predicting the web crippling capacity of aforesaid structural profiles. This research is a significant contribution to the literature on the development of design guidelines for pultruded GFRP RHS profiles subjected to web crippling, however, there is still a lot to be done in this regard before getting to the ultimate conclusions.

Developing a lightweight hybrid profile concept with a steel shell and polymeric lattice core for optimal mechanical performance

The building industry needs new design approaches to minimize resource consumption and negative environmental impacts. This study proposes a lightweight hybrid profile that combines a thin steel shell and a polymeric lattice core. The core density and internal structure variation possibilities control the slender steel profile’s load-bearing capacity and optimize the hybrid structure’s weight because of a synergy of the composite section components. The test campaign employs a 3D printing technology for prototyping the lattice core because the manufacturing preciseness (including the internal stiffener structure) is vital for structural optimization and developing adequate numerical models. A straightforward example illustrates the proposed concept. Lateral compression tests on 100 mm long fragments of the slender rectangular hollow section (RHS) 200/100/4 mm (height/width/thickness) profile prove the mechanical efficiency of the proposed hybrid section concept. Reducing the RHS fragment length ensures the experimental identification of the stiffening mechanism in the polymeric insert using a digital image correlation (DIC) technique and simplifies the numerical model. The 3D-printed lattice polymeric core added only 28% to the weight of the hybrid RHS fragment and increased its mechanical resistance twice compared to the reference empty shell fragments. This effect is equivalent to raising the profile thickness from 4 mm to 6 mm, resulting in a 1.5-times increase in weight. Using recycled plastics, adhesive connecting the inserts, and optimizing the internal geometry of the core stiffeners, depending on the loading conditions, may further increase the economic benefits of the proposed hybrid profile concept.

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.

Component method and numerical investigation on the initial rotational stiffness of fillet welded rectangular hollow sections (RHS) T-joints

The initial rotational stiffness of the joint has a significant effect on the distribution of internal forces between the members. However, the original component method for calculating the initial rotational stiffness of fillet welded RHS T-joints does not consider the effect of fillet welds, which often results in an underestimation of the initial rotational stiffness. Therefore, in this paper, a modified component method based on the original component method is proposed to calculate the initial rotational stiffness of the joint, which focuses on the effect of the fillet weld size. The modified component method is compared with the original component method and tests to verify its reliability. Subsequently, parametric analyses were performed using the validated numerical model. The results show that (1) the mean value of the ratio of the initial stiffness of the joint calculated by the modified component method to the test value is 1.03, and the COV is 0.014. For the original component method, the mean value of the ratio is 0.72, and the COV is 0.018. (2) The initial rotational stiffness of the joint increases with the increase of the fillet weld throat thickness, chord thickness, and brace-to-chord width ratio (β), and the modified component method and the numerical simulation results are in good agreement. In conclusion, this paper's modified component method is more accurate and has better prediction performance than the original component method.

The Effects of Various Adhesives on Multiple Types of Quasi‐Static Mechanical Properties of Rectangular and Square Aluminum Hollow Sections Filled with Composite Metal Foam Cores

For composite metal foam structures to be used as load‐bearing and energy‐absorbing elements, comprehensive testing should be done. Therefore, an extensive characterization of foam‐filled structures by various load types, such as axial and lateral compression, as well as three‐point bending, is carried out, aiming to differentiate the behavior of various cross‐sectional geometry foam‐filled hollow sections and the application of a tough epoxy adhesive and a ductile polysiloxane adhesive. Applying the epoxy adhesive improves the overall energy absorption by 10% during axial compression compared to the sum of the foam and empty hollow section. The application of the polysiloxane adhesive over the epoxy one increases the deflection at failure during three‐point bending by an average of 58%. The deformation and strength during axial compression and three‐point bending are hollow section dominated, while the foam core dominates the deformation and the strength during lateral compression for both produce composite foam‐filled hollow sections with epoxy and polysiloxane adhesive bonding.