Rectangular Hollow Section Joints Research Articles

Weld size and resistance in rectangular hollow section T-joints

When chord face failure occurs, one of the factors, which influence the resistance of the square hollow sections joint is the brace-to-chord width ratio of the joint. This includes the size of the weld connecting the two members. The influence of weld type and weld size on the behaviour of rectangular and square hollow section joints was studied at the Czech Technical University in Prague.This paper describes an experimental and numerical investigation of square hollow section joints. The welded T-joints were loaded by axial compression. Three different types of welds were investigated - butt welds, fillet welds and a combination of these types. Experimental results for the T-joint together with material characteristics are provided. The paper presents a validation of the numerical model to experimental data. The research-oriented model with shell elements, prepared in RFEM finite element software, represents well the behaviour of square and rectangular hollow section joints. A parametric study with a broader range of sections was performed using the design-oriented shell elements model. Based on the results of the experimental and numerical investigations a modification of the analytical equations used in current prEN1993-1-8:2021 is proposed.

Performance and design of full-width RHS X and T joints under brace axial tension and brace bending

Within the research framework for updating the international design standard ISO 14346 for hollow section joints, this study examines brace failure and chord sidewall failure in full-width rectangular hollow section (RHS) X and T joints under brace axial tension, brace in-plane bending and brace out-of-plane bending. The codified design rules for full-width RHS joints are reviewed, with their limitations highlighted. Design resistance equations for brace failure, based on the modified effective width method, and also for chord sidewall failure, using the modified bearing–buckling method and the Lan–Kuhn method, are then proposed. Up-to-date experimental and numerical results are collated from the literature, which cover a wide range of geometrical parameters, steel grades ranging from S235 to S960, varying weld details, and loading cases of brace axial tension, brace in-plane bending and brace out-of-plane bending. The compiled results are adopted to evaluate the performance of full-width RHS joints and to assess suitability of the proposed design resistance equations. It is shown that weld details can significantly affect the deformation capacity and static strengths of full-width RHS joints. The proposed design resistance equations yield conservative and reliable strength predictions for full-width RHS joints. Welding guidance and user-friendly design rules, in which an extension to include Class 3 cross-sections is included, are suggested for full-width RHS X and T joints.

Analyzing of bolted joints for connecting rectangular hollow sections in reticulated shells

ABSTRACT This paper investigates a novel joint method for connecting rectangular hollow section (RHS) members in reticulated shells. It is proposed to overcome the problem of connecting rectangular tubes using the traditional joint (cast steel joint) under dead and snow load. A case study is a structure in the eastern region of Turkey that was built on August 20, 2019. This museum-style structure is 40 meters long and 20 meters wide, with an oval shape. In the middle of the building, five tree-shaped columns were used. ANSYS is used to create a refined 3D solid model of the RHS joint. The moment-rotation results show that the proposed RHS joint (plate steel joint) for connecting rectangular hollow section members can be considered a semi-rigid connection and preferred due to its lower cost and weight. Moreover, the dissipated energy capacity has been raised by approximately 3.22 times when the plate steel type model has been used instead of the cast steel type. The stress ratios indicate that the connection stress in the Cast steel type model is lower than the stress in the Plate steel type model. As a result, the Cast steel type model is determined to be incredibly safe and more rigid than plate steel. Furthermore, since the resulting stress rates are lower than those of S355 steel, both models (cast and plate steel type models) can be used for connecting RHS.

Optimized design of fillet welds in RHS joints for EN 1993‐1‐8

AbstractISO 14346 permits fillet welds in rectangular hollow section (RHS) joints to be designed either (i) to develop the capacity of the connected brace or (ii) to resist the actual load(s) in the brace (i.e. as “fit‐for‐purpose”). However, no methods for design according to approach (ii) are given in the ISO or any European standard. In this paper, data from 41 weld‐critical tests on RHS gapped K, T, Y and X joints under brace axial load(s) are analysed to determine a reliable method for the design of fillet welds as “fit‐for‐purpose”. “Weld effective length” formulae are evaluated in conjunction with EN 1993‐1‐8 (directional and simplified methods) according to the standard procedure of EN 1990. A reliable method, based on ISO 14346, is proposed for calculating the design resistance of all‐around fillet welds in RHS gapped K, T, Y and X joints. Updates to the minimum fillet weld throat thicknesses required to develop the capacity of a connected RHS brace are also discussed.

SIMULATION OF T-JOINTS BETWEEN RHS STEEL MEMBERS WITH OFFSET IN ABAQUS CAE

The current paper focuses on numerical simulation peculiarities of offset welded rectangular hollow section joints. Understanding the modelling techniques can result in easier and faster and above all correct outcomes from FEA for future use. The steel joints under discussion are composed from cold-formed regular rectangular hollow sections where RHS brace members are laterally shifted from chord axis. Joints work under monotonically increasing compression load applied to a brace top. Numerical models were developed in FE programme Abaqus. FE-models is composed of C3D8R 8-noded solid linear brick elements with an emphasis on mesh size effect and modelling of a weld seam. FE advanced model were compiled considering both material and geometric nonlinearities. For validation purposes, the full-scale laboratory tests were conducted. Proposed FE models reliably predict the structural behaviour of welded offset T-joints thanks to good agreement achieved on deformation limit 3 % b0 with the maximum deviation 10.3 %.

Design of chord sidewall failure in RHS joints using steel grades up to S960

It is well known that the current design rules adopted by international design codes such as ISO 14346 and design guides, e.g., the CIDECT design guide No. 3, for chord sidewall failure in mild steel rectangular hollow section (RHS) joints under brace axial compression are considerably conservative, if the RHS joints are adequately supported out-of-plane. This paper presents an investigation into chord sidewall failure in RHS joints using steel grades up to S960. Representative existing design methods for chord sidewall failure in RHS joints are reviewed, and two alternative design methods, i.e., the modified bearing–buckling method and the Lan–Kuhn​ method, are proposed. Up-to-date test and numerical results reported in the literature are compiled. A wide range of geometric parameters, steel grades up to S960 and loading cases of brace axial loading, brace in-plane bending and brace out-of-plane bending are covered. The existing and proposed design methods are assessed against the collated results. The effects of brace-to-chord height ratio, brace angle, steel grade and chord stress ratio are evaluated. It is shown that the proposed design methods can provide more consistent resistance predictions for chord sidewall failure in mild steel and high-strength steel RHS joints under brace axial compression. Corresponding user-friendly design rules are suggested. The design of chord sidewall failure in RHS joints under brace axial tension, brace in-plane bending and brace out-of-plane bending is discussed. Further required research on, in particular, high-strength steel RHS joints is highlighted.

Mechanical behaviour of welded high strength steel rectangular hollow section joints

The material reduction factor of rectangular hollow section (RHS) joints in a new version of Eurocode 3 part 1–8 is validate for steel with the nominal yield strength up to 700 MPa. In this paper, finite element simulations of gap K-joints are conducted to investigate effects of material properties, gap size of the joint, the brace to chord width ratio and welds type on the secondary bending stresses and the resistance. The governing failure mode considered for all the FE models is the chord face failure followed by brace sidewall failure. The ratio of axial stresses to the nominal stress was lower in the compressive brace made of higher strength steel grades compared to the mild strength grades. The maximum secondary bending stresses is 0.12–0.32 yield strength. The secondary bending stresses are increasing with the increase of the steel grade and the brace to chord width ratio and with reducing the gap size. The level of secondary bending stresses varied between 38% and 56% of the average normal axial stress. The secondary bending stresses of fillet-welded joints are larger than the butt-welded joints. The yield line model is used to predict the ultimate load and good agreement is obtained compared with FE results.

Stress concentration factor parametric formulae for concrete-filled rectangular hollow section K-joints with perfobond ribs

A new type of tubular joint made of rectangular hollow section (RHS) braces welded onto concrete-filled RHS (CFRHS) chords stiffened by longitudinally welding perfobond ribs to the inner faces has been studied earlier and demonstrated a better fatigue behaviour than a conventional empty RHS joint. In this paper, stress concentration factor (SCF) parametric design equations were developed for CFRHS K-joints with perfobond ribs through finite element (FE) analysis to fill a gap in current design guides for this type of K-joints. Three-dimensional FE models were developed using the ABAQUS software to simulate the hot spot stress distribution at the brace-chord intersection. FE results were successfully verified using experimental results of nine Y-joints from literature and one truss K-joint in this research. A comprehensive parametric study including 570 models was then carried out on CFRHS K-joints with perfobond ribs to examine the SCFs with five key dimensionless geometric parameters and three basic loading conditions involving axial loading in the chord and brace and bending in the chord. Consequently, a total of 36 SCF parametric equations were established using regression analysis. Subsequently, the number of formulae was reduced to six equations to predict the maximum SCFs for practical application.

Static resistance of laser-made, non-welded T RHS joints estimated using the component method

This study aims to develop a procedure for predicting the static resistances of non-welded, laser-made T rectangular hollow section (RHS) joints, and estimations are provided, using the well-known beam-column I section joints component method for the first time. The results of theoretical and experimental studies on 11 such joints, created as one- or two-sided joints, undertaken by the author and others are described. Comparison are drawn between the theoretical and experimental results, and remarks regarding similar types of one-sided welded T RHS joints are provided. Finally, to summarise this stage of the research, conclusions are presented. The stiffness of the studied joints was not considered.

Fatigue behaviour of non-integral Y-joint of concrete-filled rectangular hollow section continuous chord stiffened with perfobond ribs

This paper examines the fatigue behaviour of non-integral welded joint of rectangular hollow section (RHS) brace and a continuous concrete-filled RHS (CFRHS) chord stiffened by internal perfobond ribs. A total of eleven Y-joints, including two control specimens with hollow section chords, were tested under axial force in the brace. The effects of concrete infill and perfobond ribs on the stress concentration factors (SCFs) are examined. The crack-initiation fatigue life and loss-of-strength fatigue life were established. Comparisons of the measured fatigue life with existing experimental data of square hollow section (SHS) joints without concrete infill or perfobond ribs and with predictions made using design guides are also presented. The test results show that the same Sh-N curve based on the hot spot stress method can be adopted for RHS joints with and without concrete infill and perfobond ribs. However, a significant decrease of SCFs in CFRHS joints with perfobond ribs is observed compared to the RHS joints. In addition, for the full-width joints (β = 1), CIDECT and DNV design guides Sh-N curves overestimate the fatigue strength of CFRHS joint with perfobond ribs, while the API design guide underestimates its fatigue strength.

Design of concrete-filled high strength steel tubular joints subjected to compression

Design of concrete-filled high strength steel tubular joints subjected to compression is examined. A numerical investigation on concrete-filled high strength steel rectangular hollow section (RHS) joints is presented in this paper. The high strength steel RHS tubes had nominal yield stresses of 700 and 900 MPa. The concrete infills had nominal concrete cylinder strengths of 35 and 100 MPa. Finite element (FE) models were developed and verified against test results, showing the capability of replicating the experimental ultimate strengths, failure modes and load-deformation histories. Upon verification, a parametric study comprised 312 FE analyses was carried out. The ultimate strengths of the concrete-filled high strength steel RHS joints obtained from the parametric study together with available test results in the literature were compared with the nominal strengths calculated from existing design provisions. It is shown that the CIDECT predictions exhibited significant scatter and generally conservative for the concrete-filled high strength steel RHS joints. However, the CIDECT predictions overestimated the strengths of concrete-filled high strength steel RHS joints with chord sidewall slenderness ratio exceeded 50. Therefore, new design rules are proposed in this study for concrete-filled high strength steel RHS joints subjected to compression. Furthermore, reliability analysis was performed to assess the design rules.

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.

Fatigue crack growth of arbitrary planar cracks in welded components

Engineering components that are subjected to cyclic loads frequently contain imperfections which can rationally be assessed using linear elastic fracture mechanics. Fatigue crack growth models make use of the stress intensity factor (SIF) range and the maximum SIF or R-ratio to describe the driving force for crack propagation. Determining the stress intensity factor in welded components is difficult because the stress field is complex due to the structural geometry of the component, the local geometry of the weld and the residual stresses caused by the welding process. In many cases, the crack geometry will also be complex. Weight function (WF) solutions for numerous crack geometries have been published, e.g. for through cracks, edge cracks, surface cracks and corner cracks. However, the use of the WF for cracks of arbitrary shape is less developed. The point-load WF method for arbitrary planar cracks gives sufficiently accurate estimates of stress intensity factors for embedded cracks, but the results for the surface and edge cracks are less accurate. A new form of the general point-load WF more suitable for surface breaking cracks is proposed and is combined with a crack tip plasticity-based crack growth model. During numerical simulations, cracks are normally modelled using a discrete number of linear segments. A new method for shifting these segments as a crack advances is also proposed. The method is verified based on comparison with published experimental results for welded rectangular hollow section joint subjected to bending and torsion.

Robust Mesh Insensitive Structural Stress Method for Fatigue Analysis of Welded Structures

The design of welded structures and careful fatigue design evaluation is especially important in structural design since the stress concentrations at the welds have significant impact on the overall fatigue lives of the structures. Currently, the nominal stress or hot spot stress methods are widely used in the field for fatigue design evaluation. However, design based on these methods requires constructing separate S-N curves from the fatigue testing based on the joint geometry, loading, thickness, etc. It is also difficult to evaluate the fatigue performance using finite element analysis, where the calculated stress can vary according to element size, type, etc. To overcome these challenges, Battelle has developed a novel, mesh insensitive structural stress method (Verity ® ). The stresses are calculated using the balanced nodal forces and moments obtained at the weld toe location from the finite element solutions. Working with industry partners, Battelle has also developed a unified master S-N curve that combines the effects of joint geometry, loading modes and thicknesses. Battelle's structural stress procedure has been adopted as design weld fatigue codes by ASME Sec. VIII Div. 2 (ASME Boiler and Pressure Vessel Code) and API 579/ASME FFS-1 (Fitness-for-Service Evaluation). As a case study, the fatigue life prediction of a rectangular hollow section joint using a new structural stress method is presented in this paper.

Ultimate Capacity of the K-Type Overlapped Rectangular Hollow Section Joints

The intensity calculating of simple joints is one of the most important thing in the design of space truss with hollow sections. By using the finite element method and close reference to material and geometrical nonlinear properties, numerical simulation analysis of the ultimate strength of K-type overlapped Rectangular Hollow Section joints under the axial force and bending moment was studied. The influence of the overlapped ratios and other geometrical parameters on the ultimate bearing capacity was investigated and explained graphically. With the thickness ratio of the chord bar and web member increasing, the ultimate capacity increased. And with the overlapped ratio increasing, the node capacity reduced.

Round-Robin Study on Stress Analysis for the Effective Notch Stress Approach

The effective notch stress approach for the fatigue strength assessment of welded structures as included in the Fatigue Design Recommendations of the IIW requires the numerical analysis of the elastic notch stress in the weld toe and/or weld root which is fictitiously rounded with a radius of 1 mm. In order to establish guidelines for modelling the structure and evaluating the results, several numerical analyses have been performed in a round robin. This covers three welded details of different complexity where either the weld toe or the weld root is the potential crack location. The first example is a cruciform joint with non-load carrying fillet welds in one load case and load carrying in the other. The second is a complex T-joint of rectangular hollow section (RHS) members which was also subject of the so-called SAE-FDE weld challenge to predict fatigue life. The third is the fillet-welded end connection of a RHS joint being prone to fatigue failure at the weld root with non-fused root faces. The results are compared with each other and conclusions are drawn with regard to appropriate modelling and to the scatter of results to be expected.

Local strain energy approach applied to fatigue analysis of welded rectangular hollow section joints

This paper deals with fatigue life assessments of welded rectangular hollow sections made of steels and aluminium alloys, in a T-joint configuration, carried out by means of a local stress approach. The welded toe region is modelled like a sharp V-notch with an opening angle of 135 and the intensity of the asymptotic stress distributions is quantified by means of the Notch Stress Intensity Factors (NSIFs). In order to carefully evaluate the NSIFs of hollow sections welded in a T-joint configuration, some Three-Dimensional (3D) Finite Element (FE) analyses are firstly carried out. Afterwards, the NSIFs are used to evaluate the mean value of the strain energy density over a semicircular sector of radius RC at the welded toe. The radius RC is thought of as a material-dependent parameter. The experimental values of fatigue life are compared with those predicted by two previously scatter bands curves recently reported in the literature for welded joints made of structural steel and aluminium alloy. These curves were drawn by using mainly fatigue data obtained from cruciform and T-shaped welded joints. Although the analyses reported here represent only a first attempt to extend an energy-based approach to 3D hollow section joints, the comparison shows that a quite satisfactory assessment of the fatigue life can also be obtained for this type of welded joints. The agreement is good for welded joints made of structural steel, whereas the predictions are found to be in the safe direction for welded joints made of aluminium.

A consistent crack modelling and analysis of rectangular hollow section joints

This paper proposes a flexible approach to model one or several cracks under the weld toe of a rectangular hollow section (RHS) joint by mapping the two-dimensional crack's curvature onto the three-dimensional crack surface. Based on this model, an automatic mesh technique is developed to generate the entire finite element mesh of the damaged joint. This method can generate the mesh of cracks with any length, position, quantity, shape, and type (surface crack or through-thickness crack). Because of the steep stress gradient at the stress concentration region, the mesh around the crack front is refined using several mesh refinement steps to capture the stress distribution accurately. The generated model is then applied to study the plastic collapse load and crack opening displacement (COD) of some cracked RHS T-joints. Comparison between the numerical results and experimental test data shows that a good agreement is obtained for a typical RHS T-joint specimen subjected to brace end tension load. Thus, it confirms the efficiency and reliability of the proposed modelling approach for any cracked RHS T-joints.

Equilibrium-equivalent structural stress approach to fatigue analysis of a rectangular hollow section joint

The equilibrium-equivalent structural stress method has been recently developed through several joint industry projects as a robust method to analyze welded components using finite element methods. This method has been proven effective in correlating a large amount of published fatigue test results in the literature. The authors employed this equilibrium-equivalent structural stress method for a competition organized by the SAE Fatigue Design & Evaluation (FD&E) Committee to predict the fatigue life of a rectangular hollow section joint. Among all the methods used by many participants, the authors’ life prediction was selected as the best, based on the actual test results. This paper provides the details of the SAE FD&E fatigue challenge problem definition, test results, and our structural stress approach. The predicted mean life by the equilibrium-equivalent structural stress method utilizing the proposed ASME Div. II Structural Stress curve was in excellent agreement with the actual mean life of the experimental results. Other stress indexes (such as the maximum principal stress and the von Mises stress) had maximum stress at a location different from the actual crack location. Furthermore, the equilibrium-equivalent structural stress showed significant mesh tolerance with only a few percent difference in stresses when halving the mesh size.

Fatigue design of welded aluminum rectangular hollow section joints

Fatigue design methods for welded aluminum joints are reviewed, including various approaches to fatigue life estimation currently adopted in design codes across a range of industrial applications. The applicability of these established methodologies to the fatigue design of automotive space frame structures is critically assessed. The hot spot stress method is identified as the most promising in terms of providing a coherent and comprehensive approach to design. Particular problems related to implementation are considered such as failure sites and determination of appropriate stress concentration factors from physical models, finite element calculations or parametric equations. Preliminary results from finite element stress analyses and fatigue tests are also presented for rectangular hollow sections welded in a T-joint configuration. Recommendations are made for a design methodology for welded rectangular hollow-section joints in aluminum space frames, including use of a single hot spot S–N curve.