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The study aims to investigate the impact of uniform, grooving and non-uniform corrosion degradation on the hot-spot stresses of a T-shaped tubular joint using the finite element method. The through-thickness linearization method is employed to estimate the hot-spot stresses, allowing a more reasonable consideration of the effect of grooving corrosion and non-unform corrosion. The grooving corrosion degradation is modelled assuming that the corrosion rate of the weld metal is 1.4 times that of the base metal. The non-uniform corrosion is modelled by moving the nodes around the weld by a random distance along the direction perpendicular to the surface. The random distances are generated based on the surface roughness parameter Ra. The results indicate that the stress concentration factor (SCF) increases with the uniform corrosion depth. The grooving corroded tubular joint results in a higher SCF than those of the corresponding uniformly corroded tubular joint. The non-uniform corrosion can lead to SCF deviations from the SCF of the uniformly corroded tubular joint. The SCF deviation at the critical region follows the normal distribution, and its standard deviation increases with Ra. [ABSTRACT FROM AUTHOR]

T-joints are frequently subjected to various types of loading during service. This study aims to investigate the influence of loading modes on stress concentration in the brace/chord intersection zone. Different loading combinations with various directions have been applied to examine stress distribution along the weld toe and the location of hot spots under different loading cases. To achieve this, two approaches have been developed; one experimental and the other numerical. Numerical simulations using Abaqus, validated by experimental data, enabled us to predict the most critical combinations leading to plasticization damage in the studied T-joint. The results obtained can provide valuable recommendations for the design and safety assessment of tubular T-joints. [ABSTRACT FROM AUTHOR]

The design axial resistance for circular hollow section (CHS) XX joints is typically calculated as the product of the CHS X joint resistance and a multiplanar factor. A simple function has been used as the multiplanar factor, which is independent of the joint geometry parameters. In this study, it is first shown that the geometry-independent multiplanar factor does not properly reflect the true behavior of CHS XX joints, resulting in an overly conservative design for joints with large braces. Therefore, an analytical ring model is developed that more accurately captures the effect of the two important nondimensional geometric parameters, namely the brace-to-chord diameter ratio (β) and chord diameter-to-thickness ratio (2γ). Subsequently, extensive test-validated numerical parametric analyses are performed, including a wide range of geometric and loading parameters, to propose an improved design resistance based on the developed analytical ring model. The formulated design resistance showed a better accuracy compared to the current code design resistance. [ABSTRACT FROM AUTHOR]

Recently, fiber-reinforced polymers (FRP) have begun to be used for steel structure reinforcement, following decades of successful utilization for the reinforcement of concrete structures. However, rehabilitation of tubular joints with a crack at the interface of mating members using FRP has rarely been investigated. A tubular KT-joint having a semi-elliptical crack subjected to axial tensile load is explored in this study. The joint was simulated using the fracture tool of ANSYS Structural, and the effect of crack size, location, and FRP reinforcement on stress intensity factor (SIF) was evaluated. The numerical simulations show that FRP reinforcement reduces the SIF, decreases the likelihood of crack growth, and may increase the fatigue life. A 4–12% reduction per millimeter thickness of unidirectional FRP was recorded. [ABSTRACT FROM AUTHOR]

The study aims to investigate the impact of uniform, grooving and non-uniform corrosion degradation on the hot-spot stresses of a T-shaped tubular joint using the finite element method. The through-thickness linearization method is employed to estimate the hot-spot stresses, allowing a more reasonable consideration of the effect of grooving corrosion and non-unform corrosion. The grooving corrosion degradation is modelled assuming that the corrosion rate of the weld metal is 1.4 times that of the base metal. The non-uniform corrosion is modelled by moving the nodes around the weld by a random distance along the direction perpendicular to the surface. The random distances are generated based on the surface roughness parameter Ra. The results indicate that the stress concentration factor (SCF) increases with the uniform corrosion depth. The grooving corroded tubular joint results in a higher SCF than those of the corresponding uniformly corroded tubular joint. The non-uniform corrosion can lead to SCF deviations from the SCF of the uniformly corroded tubular joint. The SCF deviation at the critical region follows the normal distribution, and its standard deviation increases with Ra.

High fatigue load, which exists widely in steel building structures, likely leads to brittle failure at the joints, supports, and so on. This can lead to the partial or total damage of the structure and even to cause the collapse of the whole structure. This article aims to provide a method to simulate high-cycle crack propagation in tubular joints, which is one of the most common types occurring in steel structures. Firstly, sixteen T-shaped tubular joint models under different load conditions and initial crack dimensions were built through the coordinate mapping method. Secondly, based on the extended finite element method (XFEM), an algorithm was developed by combining the secondary development in Abaqus and a quasistatic simulation method to simulate high-cycle crack growth in tubular joints under a constant amplitude. The results of the simulations were compared with experimental data. The study found that the surface stress calculated from the tubular joint models using the coordinate mapping method was close to the experimental data. Through the comparison of the crack propagation rate and the crack growth process between the simulation and experiment results, the simulation method was validated. When a crack penetrated the tube wall, the difference in the load cycles between the simulations and the experiment was 9.5%. The initial crack dimension had an impact on the crack propagation, with the decrease in the a/c and KII generally becoming the dominant factor with respect to the crack growth, while the fatigue life of the joints tended to increase. [ABSTRACT FROM AUTHOR]

In recent years, simple design methods for high strength steel tubular joints have been proposed by several design standards. According to these standards, the design resistance of high strength steel joints is obtained from the same design equations used for mild steel joints, but the resistance should be reduced properly by applying the material factor and/or the design yield stress. The material factor is a direct reduction factor to design resistance which generally corresponds to 0.9 for 460-grade and 0.8 for 700-grade steels, while the design yield stress (or f u/ f y limit) is a measure to account for the low f u/ f y ratios of high strength steels. In this study, a recent experimental program on moment-loaded high strength steel tubular joints is reported, which covered both circular (CHS) and rectangular (RHS) hollow section joints and both in-plane bending (IPB) and out-of-plane bending (OPB) moments. Based on the test results and additional test data collected from available database, the design equations, material factor, and design yield stress recommended by the revised draft of EN 1993-1-8 (prEN 1993-1-8) are evaluated for moment-loaded tubular joints made of grade 700 steels. It is shown that the prEN 1993-1-8 equations, combined with the material factor and design yield stress, generally provide conservative moment resistances for 700-grade tubular X and T-joints. However, based on the experimental implication that nonuniform stress distribution may cause an early fracture in CHS joints, it is suggested that the effective width, which is usually considered only for RHS joints, be considered also for CHS joints subjected to OPB. [ABSTRACT FROM AUTHOR]

One of the main challenges in applying high strength steel to tubular structures is appropriate design of the welded joints between high strength steel tubular members, i.e., high strength steel tubular joints. Although certain design standards have provided design guidance for tubular joints with steel grades up to S460 or S700, it is generally agreed that current design provisions for high strength steel tubular joints recommended by the design standards need further validation based on experimental evidence. Results of a recent testing program on cold-formed high strength steel K joints are presented in this paper to augment the test database of high strength steel tubular joints and evaluate related design provisions in the revised draft of EN 1993-1-8 (prEN 1993-1-8) including the material factor and the yield ratio limit (fy≤0.8fu). The material factor 0.9 for grade 460 steel is found to be appropriate for the ductile chord failure (plastification) of circular hollow section (CHS) K gap joints. However, it is observed that brace fracture can also be involved in the failure of CHS K gap joints when high strength steel is used, although this kind of limit state is currently not covered by prEN 1993-1-8. For CHS K overlap joints and box section K gap joints fabricated from grade 460 steels, the prEN 1993-1-8 equations provide unconservative design resistances or design resistances with insufficient margin of safety. Particularly, it is pointed out that the widely accepted rules to determine the effective width properties may be unconservative for high strength steel joints. [ABSTRACT FROM AUTHOR]

In offshore jacket structures, the stress within the chord thickness of tubular joints arises from both membrane and bending stresses. The Degree of Bending (DoB)—the ratio of bending stress to the total stress—is key to evaluating these joints' fatigue resistance. This study delves into the DoB in tubular X-joints reinforced with fiber-reinforced polymer (FRP) subjected to in-plane bending moment. It begins by validating finite element (FE) analysis accuracy through comparison with existing theoretical and experimental evidence. Following this, the analysis of 166 joints was conducted to examine how variations in FRP characteristics (such as type, layer count, and layout) and the joints' dimensionless geometric factors influence the DoB and its ratio in reinforced joints compared to their unreinforced counterparts. Findings indicate that FRP layers enhance fatigue resistance by lowering hot spot stresses on the chord's inner and outer surfaces and elevating the DoB value by up to 26.16%. Consequently, the study introduces a parametric formula for calculating the DoB in FRP-reinforced tubular X-joints under an in-plane bending moment. This development is significant, as there was no existing parametric formula for determining DoB in FRP-reinforced joints. The proposed formula stands out for its high determination coefficient and minimal error, effectively addressing a notable gap in the field. • The Degree of Bending (DoB) evaluation in FRP-reinforced tubular X-joints under in-plane bending (IPB) is conducted. • 166 finite element models are analyzed for parametric investigation. • The influence of FRP characteristics and geometric factors on the DoB is investigated. • A parametric formula is introduced to calculate the DoB in FRP-reinforced tubular X-joints subjected to IPB moment. [ABSTRACT FROM AUTHOR]

Recently, fiber-reinforced polymers (FRP) have begun to be used for steel structure reinforcement, following decades of successful utilization for the reinforcement of concrete structures. However, rehabilitation of tubular joints with a crack at the interface of mating members using FRP has rarely been investigated. A tubular KT-joint having a semi-elliptical crack subjected to axial tensile load is explored in this study. The joint was simulated using the fracture tool of ANSYS Structural, and the effect of crack size, location, and FRP reinforcement on stress intensity factor (SIF) was evaluated. The numerical simulations show that FRP reinforcement reduces the SIF, decreases the likelihood of crack growth, and may increase the fatigue life. A 4–12% reduction per millimeter thickness of unidirectional FRP was recorded.

High fatigue load, which exists widely in steel building structures, likely leads to brittle failure at the joints, supports, and so on. This can lead to the partial or total damage of the structure and even to cause the collapse of the whole structure. This article aims to provide a method to simulate high-cycle crack propagation in tubular joints, which is one of the most common types occurring in steel structures. Firstly, sixteen T-shaped tubular joint models under different load conditions and initial crack dimensions were built through the coordinate mapping method. Secondly, based on the extended finite element method (XFEM), an algorithm was developed by combining the secondary development in Abaqus and a quasistatic simulation method to simulate high-cycle crack growth in tubular joints under a constant amplitude. The results of the simulations were compared with experimental data. The study found that the surface stress calculated from the tubular joint models using the coordinate mapping method was close to the experimental data. Through the comparison of the crack propagation rate and the crack growth process between the simulation and experiment results, the simulation method was validated. When a crack penetrated the tube wall, the difference in the load cycles between the simulations and the experiment was 9.5%. The initial crack dimension had an impact on the crack propagation, with the decrease in the a/c and KII generally becoming the dominant factor with respect to the crack growth, while the fatigue life of the joints tended to increase.

Studying the bearing mechanism of concrete-filled steel tubular (CFST) arch components and constructing the quantitative design method of the CFST arch is an important subject in underground support. In order to clarify the bending and compression properties of CFST arch joints, considering different structural parameters of the joint, bending and compression tests of square CFST components without joints, with tubular joints and with flange joints were carried out. The mechanical properties and failure modes of the bending and compression combinations of each component were analyzed, and the influence of structural parameters of joints on their bearing capacity was clarified. The results show that (1) the failure mode of the component without a joint and the component with a tubular joint present uniform curve deformation, and the flange joint presents typical brittle failure and broken line failure; (2) compared to the specimens without a joint and with a flange joint, the tubular joint has higher yielding strength and ultimate strength due to the strengthening effect of the tubular joint, while the bending bearing capacity is 623.639 KN; (3) the tubular length and flange thickness are the key structural parameters of the two types of joints, which have a significant influence on the bending capacity of the specimens; (4) the tubular joint has a simple structure and high bearing capacity, so it should be used as the preferred joint connection form of the concrete-filled steel tubular support arch in deep mine roadways with complex conditions. [ABSTRACT FROM AUTHOR]

This paper presents a novel procedure for robotic scanning of weld grooves in large tubular T-joints. The procedure is designed to record the discrete weld groove scans using a commercially available line laser scanner which is attached to the robot end-effector. The advantage of the proposed algorithm is that it does not require any prior knowledge of the joint interface geometry, while only two initial scanning positions have to be specified. The position and orientation of the following scan are calculated using the data from two previous weld groove scans, so once initiated, the scanning process is fully autonomous. The procedure is a two-step algorithm consisting of the prediction and correction substeps, where the position and orientation of the sensor for the following scan are predicted and corrected. Such a procedure does not require frequent weld groove scanning for navigation along the groove. The performance of the proposed procedure is studied experimentally using an industrial-size T-joint specimen. Several cases of scanning motion parameters have been tested, and a discussion on the results is given. [ABSTRACT FROM AUTHOR]

• In-plane-bending SCF of FRP-strengthened steel tubular welded T-joints is studied. • Test data showed up to 35 % reduction in hot spot stress due to CFRP-strengthening. • The hot-spot stresses predicted by numerical models well agreed with the test data. • A numeric paramedic study was performed on SCF of FRP-strengthened tubular joints. • Parametric formulas were proposed for IPB-SCFs of FRP-strengthened tubular joints. This study reports the first experimental study on the in-plane bending stress concentration factor (SCF) of steel tubular T-joints with fibre-reinforced-polymer (FRP) jacketing. Experimental results showed that the SCF of the FRP-strengthened specimens was reduced by up to 35 %, thereby significantly improving the fatigue strength of the joints. A numerical model, validated with experimental data, was used to further investigate the SCF of FRP-strengthened joints with different geometric/mechanical properties. Nonlinear regression analysis was also performed using experimental and numerical data, and parametric formulas were proposed for the in-plane bending SCF of FRP-strengthened tubular steel joints. [ABSTRACT FROM AUTHOR]

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 r ref = 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. • Experiments on the fatigue performance of thin-walled tubular LDX joints. • Various techniques to enhance the fatigue strength of tubular joints. • Analysis of thin-walled tubular joints using local approaches. • Validation of the CIDECT guidelines for the fatigue design of thin-walled joints. [ABSTRACT FROM AUTHOR]

This article deals with the fatigue behaviour of thick‐walled welded K‐joints made up of circular hollow sections (CHS). Two important aspects of the investigations were the extension of the application range to large CHS and the development of practice‐oriented recommendations for fabrication and quality assurance for weld shape and weld quality. For this purpose, fatigue tests were conducted on large CHS joints and on single K‐joints with specified weld irregularities. These studies were accompanied by systematic ultrasonic tests using the phased‐array technique, which were also used for the development of an inspection method for these complex weld geometries. Based on the results achieved by these experimental studies and additional numerical and statistical investigations, a proposal for a German design guideline (DASt‐Richtlinie 029) was finally elaborated to promote the practical implementation of trusses made up of CHS with thick‐walled chords and also to take a first step towards standardization. [ABSTRACT FROM AUTHOR]

An efficient crack propagation (CP) simulation system based on a shell-solid finite element (FE) modeling is newly established. Three-dimensional (3D) CP simulation for a curvilinearly propagating surface crack in a steel circular hollow section (CHS) T-joint is carried out. Entire model is generated by a shell FEs, and cracked welded part is generated by a solid FEs. They are connected with a rigid body element (RBE). Stress intensity factors (SIFs) are computed for analyzing CP rate and CP direction of the crack employing the virtual crack closure-integral method (VCCM) with quadratic tetrahedral FEs. When the crack extends, only solid model is regenerated. To examine the effectiveness of the modeling, fatigue testing and simplified CP simulation results are employed. Hot spot stress (HSS) and weld toe magnification factor (Mk factor) formulas are used for the simplified CP method. CP phenomena of the fatigue test are studied through the fatigue assessment methods. [ABSTRACT FROM AUTHOR]

In steel moment frames or vierendeel trusses comprised of hollow section members, T‐shaped joints are formed that are subjected to brace in‐plane bending moment (IPB). For mild steel, a large number of studies have been conducted on the behavior of tubular T‐joints subjected to IPB. However, the studies for high‐strength steel T‐joints are quite limited and mostly focused on axially loaded cases. In this paper, recent testing program conducted by the authors for high‐strength steel circular hollow section (CHS) T‐joints under IPB was presented. Supplemental numerical parametric study was conducted using the test‐validated nonlinear finite element (FE) analyses. In the FE analyses, various geometric shapes were considered such that the effect of key geometric factors and important failure modes could be identified. Based on the experimental and numerical results, a more rational deformation limit criterion under IPB loading was first proposed which can be applied to both mild and high‐strength steel joints. The chord plastification strength of high‐strength steel joints was evaluated using existing formulae and the required material factor for 700 MPa steel was suggested. [ABSTRACT FROM AUTHOR]

Welded tubular joints are integral components in various engineering structures, subject to cyclic loading conditions throughout their operational lifespan. This paper investigates the evolution of welding residual stresses within the CHS X-joint and CHS double K-joint under cyclic loading, shedding light on their intricate behavior and potential implications for structural integrity. The advanced XRD experimental technique enables the characterization and monitoring of residual stress variations over multiple loading cycles. Assisted by the non-destructive XRD measurements, this study validates the optimization-improved thermal-mechanical simulation method for predicting not only the as-welded residual stresses in the tubular joints but also the residual stress evolutions during the cyclic loading tests. The most pronounced relaxation of peak residual stresses in the tubular joints occurs within the first cycle and then maintains a relatively stable magnitude in subsequent cycles. The findings of this research contribute to the enhancement of structural reliability and serve as a foundation for mitigating the adverse effects of welding residual stresses in welded tubular joints under cyclic loading scenarios. • This paper reports the experimentally measured residual stress during cyclic loads. • The residual stresses in both X and DK CHS joints relax significantly within 1st cycle. • Numerical analyses predict closely the evolution of residual stresses under cyclic actions. [ABSTRACT FROM AUTHOR]

In this paper, a novel mathematical procedure is proposed which allows for determination of stresses in a defected adhesively bonded single lap tubular joint under torsion. It is assumed that the shear stress varies along the adhesive thickness and geometric dimensions of the tubes (adherends) as well as their mechanical properties may differ from each other. A quadratic displacement field is assumed for the adhesive layer along its thickness direction. Using linear elasticity, the formulation was set up in terms of mechanical properties of the adhesive and adherends to allow for investigation of their effects on final results. The semi-analytical results were verified by a finite element model. Excellent agreements were observed between the two methods. Results indicate that, any increase in the adhesive or adherend Young's modulus increases the peak values of interfacial shear stresses in the joint. The results also indicate that the presence of an imperfection such as a void or a debond in the overlap region will cause an increase in the value of interfacial shear stress in the regions close to the imperfection. This increase depends on the length and, especially, location of the defect. [ABSTRACT FROM AUTHOR]

This paper presents an elasticity solution of adhesive tubular joints in laminated composites, with axial symmetry. In this model, adherends are orthotropic shells and the stacking sequences can be either symmetric or asymmetric. Adhesive layer is homogenous and made of isotropic material. They are modelled as continuously distributed tension/compression and shear springs. Employing constitutive, kinematics and equilibrium equations, sets of differential equations for each inside and outside of overlap zones are obtained. By solving these equations, shear and peel stresses in adhesive layer(s), as well as deflections, stress resultants and moment resultants in the adherends are determined. It is seen that the magnitude of peel stresses due to transverse shear stress resultant is much greater than that obtained from axial stress resultant. The developed results are compared with those obtained by finite element analysis using ANSYS software. The comparisons demonstrate the accuracy and effectiveness of the aforementioned methods.

Copyright of Journal of Zhengzhou University: Engineering Science is the property of Editorial Office of Journal of Zhengzhou University: Engineering Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fatigue of welded tubular K‐joints made of circular hollow sections – standard‐compliant design and weld quality In steel and composite bridges, in industry structures, cranes or in the offshore industry trusses of circular hollow sections (CHS) with welded tubular K‐joints and thick‐walled chords are subject to high fatigue loading. However, normative regulations have been lacking so far for a fatigue verification of these joints. This paper summarises the results of the FOSTA research project P1163 dealing with this topic. Two important aspects of the investigations were the extension of the application range to large‐sized CHS (d > 500 mm) and the development of practice‐oriented recommendations for fabrication and quality assurance of weld geometries. For this purpose, fatigue tests were conducted on large‐sized CHS‐joints (chord dimensions 660 mm × 60 mm) and on K‐joints with specified weld root opening size and weld shape. These studies were accompanied by systematic ultrasonic tests with phased‐array which also were used for the development of an inspection method for these complex weld geometries. Based on the results, a proposal for a DASt‐Guideline was finally elaborated to promote the acceptance of trusses made of CHS with thick‐walled chords in practice and also to take a first step towards standardization. [ABSTRACT FROM AUTHOR]

The static bearing capacity and failure modes of damaged tubular T-joints retrofitted with collar plates under axial compression were investigated. Two-step loading was applied: First, the chord deformation was loaded to the pre-designed degree, followed by unloading and collar plate installation. Subsequently, the specimens were reloaded. The maximum capacity and corresponding displacement (Δ1,m) were determined, and the ratio of the chord deformation of the other joints to Δ1,m was utilized to define the damage degree. The maximum capacity of retrofitted tubular T-joints could be up to 13–77% in second step loading, compared with that of unreinforced T-joints; however, the capacity decreased by 2–10% compared to that of directly reinforced T-joints. Sixty-nine finite element models were generated. The effects of chord wall thickness, chord diameters and collar plate lengths on the bearing capacity under different damage degrees were analyzed. A satisfactory effect could be obtained by using a suitable size of expanded collar plates under a constant damage degree. Retrofitting with collar plates could mitigate the development of equivalent plastic strain in the joint intersection, even for considerably damaged tubular T-joints. A modified formula considering the damage degree was proposed for bearing capacity prediction of retrofitted tubular T-joints. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Offshore wind turbines (OWT) tripod substructures are widely used in China; their weakest components are three-planar circular hollow section (CHS) tubular Y-joints that can lead to their fatigue failure. In this study, finite element (FE) models are established to calculate the geometric stress distribution along the weld toe of these joints. The multi-planar interaction factor (MIF) is defined to quantify the multi-planar effect. According to the results of the FE models, the stress concentration factors (SCFs) and MIFs along the weld of three-planar tubular Y-joints under an axial load are obtained. After a geometric parameter investigation and numerous nonlinear regression analyses, a set of parametric equations for extreme values of the SCF and MIF is derived. The proposed equations satisfy the acceptance criteria of the UK Department of Energy. • MIF quantify the multi-planar interaction effect in the HSS calculation. • Space joints should be designed considering the multi-planar interaction effect. • The extreme values formulas of SCF and MIF for three-planar Y-joints are proposed. [ABSTRACT FROM AUTHOR]

The jacket offshore platform structures working in the environment are subjected to various external conditions, such as wave loads, wind loads and corrosion of sea water. Therefore, the research on reinforcement of tubular joints has great practical value for the safety of offshore platforms. In this article, the finite element (FE) models of T-type tubular joint (T-joint) and K-type tubular joint (K-joint) are established by ANSYS software. Triangular rib reinforcement and collar plate reinforcement are used to reinforce the tubular joints. The reinforcement effects are assessed through the ultimate bearing capacity, and the influences of parameters of the rib and the collar plate on the ultimate capacity are analyzed. Besides, the effects of the two reinforcement methods are compared under the combined loads, and the results show that the reinforcement of the ribbed plate is more effective in resisting the deformation caused by bending moment, while the reinforcement of the collar plate is more effective to avoid the plastic damage caused by the axial pressure. [ABSTRACT FROM AUTHOR]

Bonding with adhesives is increasingly being used in the design of mechanical structures, because of the significant advantages of this technique compared to traditional joints. Different joint configurations are available, depending on the desired bond strength to be achieved and geometry of the parent structures. Tubular joints find applications in the piping industry, vehicle frames or thin-walled tubes, for instance, but they are seldom studied in the literature. This work numerically compares the performance of three structural adhesives on the tensile strength of aluminium tubular joints, after validation of the numerical tool with experiments. The numerical analysis consisted of using the Finite Element (FE) method to analyse peel (σy) and shear stresses (τxy) in the adhesive layer and cohesive zone models (CZM) to predict the maximum load (Pm). Numerically, the effect of the overlap length (LO) and the thickness of the inner and outer tubes (tSI and tSE, respectively) is addressed. Additionally, outer and inner chamfering of the tubes was tested to reduce peak stresses and increase Pm. The CZM technique was positively validated for the strength analysis of tubular joints. It was also shown that the joints' geometry and type of adhesive highly influence the joints' behaviour. [ABSTRACT FROM AUTHOR]

Under the project of ' typical complex space joints of Beijing New Airport Terminal C type steel column'， space static loading tests were conducted on nine full-scale complex tubular joints to examine the effects of stiffening ribs, steel grades, and loading modes. The results show that the ultimate bearing capacity of the joints without stiffening ribs is insufficient ； Q345C steel joints with stiffening ribs experience earlier plasticity when subjected tD standard load condition ； Q460GJC steel joints with stiffening ribs can fully stay elastic under 1. 4 times the standard load level. Different loading modes affect more ort the joints without stiffening ribs, and have less influence on the remaining specimens. Based on the test results, the failure modes and ultimate bearing capacity of the joints were investigated and the arrangement of the stiffening ribs was optimized，with three stiffening ribs being the most suitable solution. [ABSTRACT FROM AUTHOR]

Highlights • Stress Concentration Factors (SCFs) are established for novel truss chord-brace welded joints. • Chord is a concrete-filled square hollow section stiffened with Perfobond Leister (PBL) ribs. • Joints with varying dimensions were first tested to measure hot spot stresses. • 3D FE models were developed and verified then used in comprehensive parametric study. • Design equations for SCF were developed based on multiple regression analysis of database. Abstract A novel tubular joint of concrete-filled square hollow section (CFSHS) chord welded to an SHS brace was studied experimentally and numerically to establish design equations for Stress Concentration Factors (SCFs) for fatigue design purposes. The chord was stiffened with internal perfobond ribs longitudinally welded to the inner faces. A series of joints with varying member sizes and wall thicknesses were first tested under axial force in the brace and the hot spot stresses were carefully measured. Three-dimensional finite element models were developed and validated with the experimental results. A comprehensive parametric study was then conducted on 90° T- and X-joints with perfobond ribs, to establish correlations between SCF and three key non-dimensional geometric parameters: brace width-to-chord width (β), width-to-wall thickness ratio of the chord (2 γ), and brace wall thickness-to-chord wall thickness ratio (τ). Four basic loading conditions were examined: axial tension and in-plane bending in the brace, and axial tension and in-plane bending in the chord. Finally, a series of SCF formulae and design charts were proposed based on multiple regression analysis. It was shown that under brace axial tension stress concentrations reduced by one third and two thirds in CFSHS chords without perfobond ribs and with perfobond ribs, respectively, compared to a SHS chord. Current design guides which are based on SHS sections, overestimate SCFs significantly for CFSHS sections with perfobond ribs. [ABSTRACT FROM AUTHOR]

Abstract Recently, CIDECT (International Committee for the Development and Study of Tubular Structures) has proposed the component method as a unified approach for the design of many types of connections, including welded tubular joints. Although CIDECT provides clear and simple equations for the resistance of welded tubular joints, the design of initial stiffness remains complicated and includes a number of uncertainties. This paper analyzes the theoretical approach for the initial axial stiffness of rectangular hollow section T joints. The validation against experimental data has shown that the component method considerably overestimates the stiffness of T joints. The paper develops new equations for the stiffness of the components "chord face in bending" and "chord side walls in compression". The equations are based on simplified mechanical models, employing finite element analyses to calculate the parameters for which analytical solutions are found extremely complicated. In addition, the article numerically investigates the effect of chord axial stresses on the axial stiffness of joints and proposes a corresponding chord stress function. Highlights • The paper analyses the initial axial stiffness of welded rectangular hollow section (RHS) T joints • Validation with experimental results showed that the CIDECT equations provides inaccurate prediction of initial stiffness • The paper developed and validated stiffnesses of the components "chord face in bending" and "chord side walls in compression" • Numerical simulations showed that chord axial stresses considerably affect the initial axial stiffness of RHS T joints • A chord stress function is proposed for initial axial stresses of RHS T joints [ABSTRACT FROM AUTHOR]

Fatigue is an important failure mode in offshore jacket platforms. To evaluate the fatigue damage, these platforms are periodically inspected during their lifetime. Regarding fatigue damage, the information from inspection consists of crack measurement. A Bayesian framework can be used to update the probability distribution of the crack size. The main purpose of this study is to develop a framework to update the probability distributions of all uncertain parameters involved in the fatigue crack growth analysis. This methodology maximizes the benefit of the inspection results by updating several uncertain parameters involved in the fracture mechanics approach. Two sets of cracks are used to obtain the updated distributions for uncertain parameters; prior cracks and simulated reality cracks. By comparing these cracks, the updated distributions for uncertain parameters are obtained. The updated crack size distribution can be used to update the estimation of the probability of failure. To demonstrate the developed framework, a tubular joint in a specific jacket platform is considered and the framework is applied for that joint. The results of the developed methodology indicate that the updated distributions of uncertain parameters shift towards the simulated reality distributions.

This paper presents an elasticity solution of adhesive tubular joints in laminated composites, with axial symmetry. In this model, adherends are orthotropic shells and the stacking sequences can be either symmetric or asymmetric. Adhesive layer is homogenous and made of isotropic material. They are modelled as continuously distributed tension/compression and shear springs. Employing constitutive, kinematics and equilibrium equations, sets of differential equations for each inside and outside of overlap zones are obtained. By solving these equations, shear and peel stresses in adhesive layer(s), as well as deflections, stress resultants and moment resultants in the adherends are determined. It is seen that the magnitude of peel stresses due to transverse shear stress resultant is much greater than that obtained from axial stress resultant. The developed results are compared with those obtained by finite element analysis using ANSYS software. The comparisons demonstrate the accuracy and effectiveness of the aforementioned methods. [ABSTRACT FROM AUTHOR]

Specimen testing of concrete-filled steel-tube (CFST) joints and the fatigue assessment approaches for such joints were investigated and summarized to understand comprehensively the fatigue behavior of CFST trusses. The main factors that influence the fatigue resistance of CFST joints were discussed. Nominal stress- and hot-spot stress (HSS)-based methods were compared based on available experimental results, and the current state and development direction of fatigue assessment of CFST joints were explored. Results showed that the fatigue failure mode, fatigue damage mechanism, anti-fatigue optimization design, and fatigue strengthening technology of CFST joints are more complex than those listed in fatigue design guidelines or specifications. Sufficient fatigue specimen testing and finite element analyses are necessary to predict the fatigue behavior of CFST joints via the HSS approach. Fracture mechanics approaches for the fatigue damage mechanism of welded tubular joints is a future research direction. [ABSTRACT FROM AUTHOR]

For the past few decades, a significant number of research efforts have been devoted to the studies of SCF values and parametric design formulae at certain positions in various uniplanar and multi-planar tubular joints. However, very few investigations on the multi-planar overlapped tubular joints have been reported. The main reason may lie in the complexity of combining effects between multi-planarity and overlapping. In this paper, a novel framework for deriving the unified SCFs is proposed by reducing joint modeling from multi-planar out-of-plane overlapping to equivalent uniplanar non-overlapping. By integrating the equivalent beam model with solid finite element modeling for the overlapped tubular KK -joint in offshore jack-ups, the procedures for computing the unified SCF values in the equivalent beam stick model are successfully developed. Verification of the proposed framework is obtained by comparing the unified SCFs based on basic load cases with those based on actual wave loading typically experienced by the jack-up. [ABSTRACT FROM AUTHOR]

An experimental investigation was conducted on empty and grouted stainless steel tubular X-joints with circular hollow section (CHS) chord member under axial compression. A total of 25 specimens including empty tubular joints, tubular joints with grouted brace members only, tubular joints with grouted chord member only and tubular joints with both grouted brace and chord members were tested. The joint strengths, failure modes, axial load-vertical displacement curves, axial load-chord deformation curves and strain distribution curves of all specimens were reported. The corresponding finite element analysis (FEA) was also performed and calibrated against the test results. Therefore, an extensive parametric study was carried out to evaluate the effects of main influential factors ( β , τ , grouting and grout strength) on the behaviour of grouted stainless steel tubular X-joints with CHS chord member under axial compression. It is shown from the comparison that the ultimate strengths of empty and grouted stainless steel tubular X-joints generally increased with the increase of the β and τ values. Furthermore, the ultimate strengths of stainless steel tubular X-joints with both grouted brace and chord members generally increased with the increase of the grout strength. Whereas, the grout strength has little influence on the ultimate strengths of stainless steel tubular X-joints with grouted chord member only. On the other hand, the joint strengths obtained from the tests and parametric study were compared with the design strengths calculated using the current design rules. It is shown from the comparison that the current design rules are generally unconservative for empty and grouted stainless steel tubular X-joints with CHS chord member under axial compression. Therefore, the new design equations were proposed in this study, which were verified to be more accurate. [ABSTRACT FROM AUTHOR]

The axial compression capacity of X-joints with and without external stiffeners was experimentally and numerically investigated. Two reinforced X-joints, with the brace-to-chord diameter ratio ( β ) equal to 0.51 and 0.73, were tested in this study and compared with the unreinforced ones from previous work. The failure modes and load-displacement curves of the unreinforced and reinforced X-joints were compared. The comparison showed that within the range of geometric studied, the external stiffener could increase the ultimate strength of the X-joints without reinforcement. The results of the finite element simulations on the X-joints with and without external stiffeners were verified against the experimental data. 256 X-joint FE models were generated and analysed to investigate the failure modes, the influence of the size of external stiffeners and joint geometry on the improvement of ultimate capacity of the joints under axial compression. Finally, a theoretic formulation, based on the modified yield line model, was developed and examined by the experimental and numerical results. [ABSTRACT FROM AUTHOR]

The paper studies numerically the behaviour of a beam-to-column joint between a hat-shaped steel beam (WQ-beam) and a concrete-filled composite column in a slim floor steel-concrete composite frame. 3D continuum elements are used in the discretization of the joint with contact surfaces between the components. Both material and geometrical nonlinearities are included. The computational results are verified by comparing them to experimental results. The verified model is applied to study the development of the load-transfer mechanisms in the joint. The load carrying capacity of the joint is categorized on the base of five parameters: the flange width, the web height, the wall thickness and the corners of the console, and the gap between the WQ-beam endplate and the column face. In addition, a criterion to evaluate the limit load of the joint is proposed. The design capacity of the joints from the proposed criterion is compared with the values calculated according to both other criteria and design code. It can be concluded that the proposed criterion is suitable for estimating the resistance of the studied joint. [ABSTRACT FROM AUTHOR]

Bonded joints are also widely used to join tubular components in the pipeline industry, in vehicle frames and in space structures. This work performs an experimental and numerical study of axially-loaded tubular joints between aluminium adherends and bonded with three different adhesives. The effect of the overlap length between inner and outer tubes (LO) was addressed in the experiments and numerical study. A Finite Element Method (FEM) analysis was undertaken to analyse peel (σ) and shear stresses (τ) in the adhesive layer. Cohesive zone models (CZM) were employed to predict the joint strength. The CZM technique was positively validated for the strength analysis of tubular joints. [ABSTRACT FROM AUTHOR]

The welded tubular joints can be used in several industrial fields including, metallic bridges, telecommunication tripods, oil platforms and pipelines. These structures can be damaged by concentrated stresses located in the toe weld vicinity. Semi-parametric formulas, currently available in the literature, can be used to predict the value of the stress concentration factor without given the hot spot location. In this work, a Finite Elements modeling was carried out for a T-joint, in order to have the concentrated stress value around the weld toe. This work was investigated for a series of combined loads.