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An experimental investigation was conducted on empty and grouted stainless steel square hollow section (SHS) tubular X- and T-joints subjected to axial compression. A total of 24 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 SHS tubular X- and T-joints subjected to axial compression. It is shown from the comparison that the ultimate strengths of empty and grouted stainless steel SHS tubular X- and T-joints generally increased with the increase of the β and τ values. The enhancement of joint strengths obtained from grouting both brace and chord members is much greater than that obtained from grouting chord member only. In addition, the ultimate strengths of stainless steel SHS tubular X- and T-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 SHS 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 conservative for the design of empty stainless steel SHS tubular X- and T-joints subjected to axial compression, but unconservative for the design of grouted stainless steel SHS tubular X- and T-joints subjected to axial compression. Therefore, the new design equations were proposed in this study, which were verified to be more accurate. [ABSTRACT FROM AUTHOR]

This paper presents two simplified procedures for the calculation of the Effective Notch Stress (ENS) on non-overlapping circular hollow section (CHS) K-joints. The proposed procedures aim to alleviate the modeling challenges associated with the traditional ENS calculation on joints with complex geometry, such as the CHS joints. The first procedure is an extension of the recently proposed extrapolation method, similar to the extrapolation in the widely-used Structural Hot-Spot Stress (SHSS) approach. The second procedure provides ENS estimations based on the parametric relationship between the ENS and SHSS. Through an extensive numerical study, this investigation develops parametric equations supporting each procedure, covering practical geometric range for CHS K-joints under balanced brace axial load. Both simplified procedures demonstrate close agreement with the traditional ENS calculation and provide reasonable fatigue life assessments with a substantial number of experimental data, based on the S-N framework. [ABSTRACT FROM AUTHOR]

This paper studies steel circular hollow section (CHS) X-joints by conducting experiments on the axial compressive strength of unreinforced and reinforced X-joints with external stiffening rings. Three pairs of unreinforced and reinforced X-joints were tested to compare their compressive load capacity. The diameter ratios (ß) between the brace and the chord ß were 0.25, 0.51 and 0.73 respectively. The experimental setup, parameters and results are presented. The failure modes and load-displacement curves of the unreinforced and reinforced X-joints were compared. It was shown that external stiffening rings greatly increased the axial compressive load capacity of the X-joints, by 86%, 75%, and 58% respectively. Finite element modelling accurately predicted the structural responses of the X-joints with and without external stiffening rings [ABSTRACT FROM AUTHOR]

Strain energy release rate (SERR) based damage analyses of functionally graded adhesively bonded tubular lap joints of laminated fiber reinforced plastic (FRP) composites under varied loadings have been studied using three-dimensional geometrically non-linear finite element (FE) analyses. FE simulations have been carried out when a tubular joint is subjected to axial and pressure loadings. SERR is utilized as the characterizing and governing parameter for assessing damages emanating from the critical location. Individual and total SERR over the damage front have been computed using modified crack closure integral (MCCI) based on the concept of linear elastic fracture mechanics. Results reveal that damage initiation locations in tubular joints subjected to axial and pressure loadings are entirely different. Furthermore, modes responsible for propagation of such damages in tubular joints under axial and pressure loadings are also different. Based on the FE simulations, tubular joints under pressure loading are found to be more vulnerable for damage initiation and its propagation. Furthermore, the damage propagation behavior of tubular joints with pre-embedded damages at the critical location has been compared between conventional mono-modulus adhesives and functionally graded adhesives with appropriate material gradation profile. Results indicate that material gradient profile of the adhesive layer offers excellent reduction in SERR for shorter interfacial failure lengths in tubular joints under axial loading which is desired to delay the damage growth. Improved crack growth resistance in the joint enhances the structural integrity and service life of the tubular joint structure. However, considerable reduction in SERR has not been noticed in the said joint when subjected to pressure loading. Hence, the use of functionally graded adhesive along the bond layer is recommended for the designer/technologist while designing tubular joint under general loading condition. [ABSTRACT FROM PUBLISHER]

Crack growth in a T-shaped tubular joint is studied using a newly developed system to simulate three-dimensional crack propagation and fatigue testing results. Tetrahedral finite element (FE) modeling is adopted to analyze a tubular structure with a curved surface crack. The virtual crack closure-integral method is used to evaluate the fracture mechanics parameters. The FE crack modeling with a remeshing procedure using an automated mesh generation system greatly simplifies the crack propagation simulation. The calculation results are compared with the experiments. [ABSTRACT FROM AUTHOR]

This paper presents an extrapolation method to determine the effective notch stress (ENS) on the weld toes of welded circular hollow section (CHS) X-joints in-line with the extrapolation method to determine the structural hot-spot stress in existing design guidelines. This investigation verifies and extends the recently proposed ENS extrapolation scheme to CHS X-joints, which elevates significantly the difficulty in generating a weld toe radius along the brace-to-chord intersection as required in existing guidelines. An extensive numerical study then investigates the ENS extrapolation for CHS X-joints under three loading conditions, namely, the brace axial load, the brace in-plane bending load, and the brace out-of-plane bending load. The numerical study derives a set of recommended extrapolation parameters that ensures accurate ENS estimation for each loading condition. This paper demonstrates that the proposed extrapolation method for the CHS X-joints yields good agreement with the standard ENS calculation procedure described in the International Institute of Welding (IIW) guideline. [ABSTRACT FROM AUTHOR]

Finite element analysis of a tubular T-joint subjected to various loading conditions including pure axial loading, pure in-plane bending (IPB) and different ratios of axial loading to in-plane bending loading has been carried out. This effort has been established to estimate magnitudes of the peak hot spot stresses (HSS) at the brace/chord intersection and to find the corresponding locations as well, since, in reality, offshore tubular structures are subjected to combined loading, and hence fatigue life of these structures is affected by combined loading. Therefore in this paper, at the first step, stress concentration factors (SCFs) for pure axial loading and in-plane bending loading are calculated using different parametric equations and finite element method (FEM). At the next step, the peak HSS distributions around the brace/chord intersection are presented and verified by the results obtained from the API RP2A Code procedure. Also the locations of the peak hot spot stresses which are the critical points in fatigue life assessment have been predicted.

This article presents the results of a numerical parametric study on the ultimate strength of internally crown- and saddle-stiffened circular hollow section tubular DT-, T-, and Y-joints subjected to brace axial compression or tension at elevated temperatures. Using well-validated finite element models, an extensive study of 640 ring-stiffened tubular joints consisting of 36 DT-joints, 36 T-joints, and 8 Y-joints at different temperatures ranging from 20°C to 800°C was conducted. The strength of the stiffened joints was obtained from finite element analysis. The joint strength reduction was compared with the reduction factors of steel yield stress and elastic modulus at elevated temperatures. The parametric study shows that the effects of joint geometric parameters and stiffening position on the strength reduction of the stiffened DT-, T-, and Y-joints at elevated temperatures fall in a narrow range. An equation for predicting the strength reduction of the stiffened DT-, T-, and Y-joints at elevated temperatures was proposed by introducing a temperature factor. The statistical analysis shows that the proposed equation could provide reasonably accurate joint strength predictions. [ABSTRACT FROM AUTHOR]

This study reports a deformation limit for the initiation of ductile fracture failure in fatigue-cracked circular hollow section (CHS) X- and K-joints subjected to brace axial tension. The proposed approach sets the deformation limit as the numerically computed crack driving force in a fatigue crack at the hot-spot location in the tubular joint reaches the material fracture toughness measured from standard fracture specimens. The calibration of the numerical procedure predicates on reported numerical computations on the crack driving force and previously published verification study against large-scale CHS X-joints with fatigue generated surface cracks. The development of the deformation limit includes a normalization procedure, which covers a wide range of the geometric parameters and material toughness levels. The lower-bound deformation limits thus developed follow a linear relationship with respect to the crack-depth ratio for both X- and K-joints. Comparison of the predicated deformation limit against experimental on cracked tubular X- and K-joints demonstrates the conservative nature of the proposed deformation limit. The proposed deformation limit, when extrapolated to a zero crack depth, provides an estimate on the deformation limits for intact X- and K-joints under brace axial loads. [ABSTRACT FROM AUTHOR]

This paper studies circular hollow section (CHS) T-joints by conducting experiments on the comparative axial compressive strength of unreinforced and reinforced T-joints. Three pairs of unreinforced and reinforced T-joints, a total of six specimens with the ratio of brace to chord diameter equal to 0.26, 0.51, and 0.74 respectively, were tested to determine their compressive load capacity. The specimen parameters, experimental setup, and test results are presented. The failure modes of the unreinforced and reinforced T-joints were compared. The unreinforced joints failed due to chord plastification, while the reinforced joints failed due to chord bending. The experiment indicated that the external stiffening ring significantly increased the axial compressive strength of the T-joints. Every reinforced joint behaved like a beam when loaded by concentrated force at the brace end; the strength of the reinforced joint can be predicted by calculating the plastic bending moment at the crown section. [ABSTRACT FROM AUTHOR]

In fatigue analysis, the structural detail of tubular joint has taken great attention among engineers. The DNV/GL-RP-0005 is covering this topic quite well for simple and clear joint cases. For complex joint and geometry, where joint classification is not available and there is limitation on validity range of non-dimensional geometric parameters, the challenges become a fact among engineers. The classification of joint is an important factor to consider in fatigue analysis. These joint configurations are identified by the connectivity and the load distribution of tubular joints. To overcome these problems to some extent, this paper compares the fatigue life of tubular joints in offshore jacket according to the stress concentration factors (SCF) in DNV/GL-RP-0005 and finite element method employed in Abaqus/CAE. The paper presents the geometric details, material properties and load history of the considered jacket structure. It then describes the global structural analysis and identification of critical tubular joints for fatigue life estimation. Hence, fatigue life is determined based on the guidelines provided in design codes. Fatigue analysis of tubular joints is conducted using the finite element employed in Abaqus/CAE as the next major step. Finally, predicted SCFs and fatigue lives are compared, and these observations tend to conclude that even though the fatigue life, which is calculated based on code given SCFs, provides more realistic prediction to the simple uniplanar joints, there is a doubt for complex joints and geometry, where joint classification is not available. Also, the study emphasized that it is very important to preciously investigate SCFs by considering accurate geometry of complex tubular joints for a good judgement of fatigue life. [ABSTRACT FROM AUTHOR]

In tubular joints of offshore platforms, joints may exhibit considerable flexibility since the materials in the chord members near the intersection zone of brace-chord behave as shell-like structures. The resulting flexibility may have significant effects on the local and overall behavior of offshore platforms. This study describes the derivation of a three-dimensional joint flexibility element which is based on physical interpretation of behavior of a tubular joint upon deformation. The element is developed on the basis of flexibility matrix and implemented in a finite element program to account for local joint flexibility effects in numerical models of jacket-type offshore platforms. Results are validated by more sophisticated multi-purpose software and compared against conventional rigid-joint models which are widely employed in practice. According to the results, the accuracy of response predictions is improved when the effects of joint flexibility are considered. This model can be used for predicting more accurate response of jacket-type offshore platforms. [ABSTRACT FROM AUTHOR]

This paper describes a numerical study of the stress distribution in a pin-loaded tube, loaded in tension, where more than one pin is used. The effect of changing the inter-pin distances, pin diameters and pin orientation (i.e. in-line or crossed) have been analysed and discussed. The study shows that there are significant through thickness effects as a result of out-of-plane deformations coupled with an unequal load distribution between each of the pins. Various configurations of pin positions are compared, and it is demonstrated that the joint design can be optimised by crossing, changing the diameter or moving particular pins. It is shown that constructing a joint employing three pins has advantages over a two pin arrangement and that the peak circumferential stress around a pin hole can be reduced by approximately 42% compared with using only a single pin: especially significant when fatigue loadings are considered. [ABSTRACT FROM AUTHOR]

Many shell structures used in modern technology consist of regular shell parts joined together along their common boundaries. We review different theoretical, numerical, and experimental approaches to modelling, analyses and design of the compound shell structures with junctions. Several alternative forms of boundary, continuity and jump conditions at the singular midsurface curves modelling the shell junction are reviewed. We also analyse the results obtained for special shell structures containing the cylinder–cylinder intersections, cone– , sphere– , and plate–cylinder junctions, tubular joints as well as other special types of junctions appearing in complex multi-shell structures. [ABSTRACT FROM AUTHOR]

This paper presents an approach to integrate a lower-bound material J – R curve into the load–deformation relationship for circular hollow section joints. The lower-bound J – R curve derives from a regression analysis of the experimental data for a wide range of structural steels reported in the literature and follows a linear relationship up to a maximum crack extension of 2.0 mm. The deterioration in the joint strength caused by ductile tearing adheres to a reduction factor based on the crack area. The J – R curve modified load–deformation responses compare closely with reported experimental results for both welded tubular joints and large-scale tubular frames. [ABSTRACT FROM AUTHOR]

This study reports a deformation limit for the initiation of ductile fracture failure in fatigue-cracked circular hollow section (CHS) X-joints subjected to brace in-plane bending. The proposed approach sets the deformation limit as the calculated crack driving force in a fatigue crack at the hot-spot location in the tubular joint reaches the material fracture toughness measured from standard fracture specimens. The calibration of the proposed approach and the numerical procedure utilizes two large-scale X-joint specimens with fatigue generated surface cracks. The subsequent numerical investigation covers X-joints with two different brace-to-chord intersection angles, a wide range of geometric parameters and a practical range of material parameters. The development of the deformation limit includes a non-dimensional material toughness, which covers both the geometric parameters and material properties. The lower-bound deformation limit thus developed exhibits a linear relationship with respect to the crack depth ratio and indicates consistent values among X-joints with different brace-to-chord intersection angles. [ABSTRACT FROM AUTHOR]

A theoretical investigation on cold-formed stainless steel tubular T- and X-joints fabricated from square and rectangular hollow section (SHS and RHS) brace and chord members was conducted in this study to develop analytical models. High strength stainless steel (duplex and high strength austenitic) and normal strength stainless steel (AISI 304) specimens were considered in the study. The yield line mechanism analysis which is based on the deformed shape of the axially loaded tubular joints observed from experimental and numerical investigations was performed to estimate the stainless steel tubular joint strengths subjected to chord face failure. The yield line models considered the weld size, the rounded corners of the chord member and the plastic hinges at the chord webs. In addition, the membrane force in the chord flange and the strain hardening of the material were also considered in the models. The effect of axial chord preload on the joint strength has been taken into account for the X-joints. Some existing theoretical models were also used to predict the structural behaviour of cold-formed stainless steel tubular joints subjected to chord side wall failure. The design rules for cold-formed stainless steel tubular joints failed by chord face and chord side wall were derived through a combination of theoretical and empirical analyses. Good agreements were achieved between the joint strengths predicted by the proposed design formulae and the results obtained from the experimental and numerical investigations. [ABSTRACT FROM AUTHOR]

This study reinforced circular hollow section (CHS) T-joints with external stiffeners and analyzed the axial strength of both the unreinforced and reinforced T-joints. The SHELL181 element in ANSYS was used to establish FE models of the T-joints. A comparison between the experimental results indicated that the numerical method could be used to compute the strength for the unreinforced and reinforced CHS T-joints. To further investigate the reinforcement effect of the external stiffeners, a numerical parametric study was conducted. The study then evaluated the variations in strength of differently sized stiffeners. It was found that the joint strength increased significantly as the size of the stiffener increased. The reinforcement effect is more dependent on the stiffener length than on the stiffener height, but it is reasonable to adopt stiffeners with equal lengths and heights since this shape is commonly-used in engineering projects. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the experimental findings on the fatigue performance and residual strength of the circular hollow section X-joints with a concrete-filled chord. The welding profile along the brace-to-chord intersection employs a recently proposed set of welding details, namely the full capacity tubular joint welds. The experimental investigation focuses on: 1) the stress concentration comparison corresponding to different stages of the specimen preparation, 2) the fatigue crack initiation life and propagation life; and 3) the comparison of the measured fatigue life with respect to the design S-N curves. The experimental measurement reveals that the fatigue crack propagation life contributes to a significant portion of the total fatigue life for both the hollow section tubular joints and the concrete-filled tubular joints. The total fatigue life of the test specimens complies with the life estimation based on the existing design S-N curves, originally developed for tubular joints fabricated using the complete joint penetration welds. The residual strength of the fatigue-cracked tubular joints follows approximately a linear relationship with respect to the percentage of the crack area along the brace-to-chord intersection. [Copyright &y& Elsevier]

Abstract: This paper describes experimental and numerical investigations on stress concentration factors (SCFs) of cold-formed stainless steel square and rectangular hollow section (SHS and RHS) tubular X-joints. Both high strength stainless steel (duplex and high strength austenitic) and normal strength stainless steel (AISI 304) specimens were investigated. The SCFs were experimentally determined under static loading by measuring the strains at typical hot spot locations using strip strain gauges. The corresponding finite element analysis was performed to simulate the non-uniform stress distribution along the brace and chord intersection region. Good agreement between the experimental and finite element analysis results was achieved. Therefore, an extensive parametric study was then carried out by using the verified finite element model to evaluate the effects of the SCFs of cold-formed stainless steel tubular X-joints. The SCFs at the hot spot locations obtained from the experimental investigation and parametric study were compared with those calculated using the design formulae given in the CIDECT for carbon steel tubular X-joints. It is shown from the comparison that the design rules for the SCFs specified in the CIDECT are generally quite unconservative for cold-formed stainless steel tubular X-joints. In this study, a unified design equation for the SCFs of cold-formed stainless steel tubular X-joints is proposed. The proposed design equation was based on the CIDECT design equation for carbon steel tubular X-joints. It is shown that the SCFs calculated from the proposed unified design equation are generally in agreement with the values predicted from finite element analysis. [Copyright &y& Elsevier]

Abstract: This paper reports a new incidence of brittle failure by lamellar splitting in a large-scale tubular X-joint and examines the possible causes of this failure. The X-joint, with multiple pre-existing fatigue cracks at the weld toe along the brace-to-chord intersection, experiences brittle failure during a monotonic in-plane bending test. Post-test sectioning of the material around the brace-to-chord intersection reveals lamellar splitting in the mid-thickness of the chord wall instead of rapid extensions of the fatigue cracks in the through-thickness direction. The lamellar splitting observed in this test differs from the conventional lamellar tearing both in its appearance and in its causes. The elongated nonmetallic inclusions concentrated at the mid-thickness, as revealed by the microscopic scanning, leads to delamination cracking near the mid-thickness and subsequently to the brittle failure of the joint. The material requirements in prevailing engineering codes do not suffice to prohibit the lamellar splitting failure observed in this study, which may cause catastrophic failures in engineering structures designed with insufficient redundancy. [Copyright &y& Elsevier]

Abstract: This paper proposes a new load–deformation formulation for circular hollow section (CHS) X- and K-joints to be implemented in the pushover analysis of steel frames. The proposed formulation describes the load–deformation relationship of the CHS X- and K-joint through a simple function with the coefficients dependent on the ultimate strength and the geometric parameters of the joint. The strength-dependent parameter follows the mean strength equations in the latest IIW recommendations, while the geometric-dependent parameters derive from the finite element results of the CHS X- and K-joints covering a practical geometric range. The proposed joint formulation predicts closely the load–deformation responses for planar CHS X- and K-joints measured in the experiments. The non-dimensional load–deformation formulation developed in the current study provides a calibrated basis in the phenomenological representation of the nonlinear joint behavior in push-over analyses of steel space frames. The experimental results from the large-scale 2-D and 3-D frame tests validate the accuracy of the proposed formulation, which is implemented in a nonlinear pushover analysis as joint-spring elements. [Copyright &y& Elsevier]

Abstract: This study examines the fatigue performance of tubular joints fabricated using a new type of enhanced partial joint penetration weld details under constant-amplitude brace in-plane bending actions. The experimental program includes four cyclic tests on two large-scale X-joints, each with a different surface treatment near the weld toe. The experimental results confirm the satisfactory fatigue performance of the tubular X-joints welded using enhanced partial joint penetration welds in comparison with the S-N curves developed for tubular joints with complete joint penetration welds, and demonstrate the significant improvement on the fatigue life rendered by the weld surface grinding and toe grinding. Root fatigue cracking occurs only in specimens with post-weld toe-grinding treatment which enhances the fatigue life for toe cracking. [Copyright &y& Elsevier]

Abstract: This paper summarizes the numerical investigation on the fatigue crack propagation in CHS X-joints under constant amplitude brace in-plane bending, in parallel with the experimental investigation reported in the companion paper. The finite element procedure examines the effects of the crack propagation angle, the crack-front profile and the interaction between adjacent fatigue cracks on the fatigue driving force, measured by the stress-intensity factors. The Paris type estimation provides a close prediction on the propagation life of weld toe cracks observed in the experiment. The initiation of the root crack, based on the Paris prediction, occurs much later than that of the toe crack. [Copyright &y& Elsevier]

Highlights: [•] This study proposes a new load–displacement formulation for fracture failure in tubular joints. [•] The load–deformation relationship during ductile tearing based on the measured J–R curve. [•] The unstable fracture failure occurs at J max determined from 1.5mm offset line in J–R curve. [•] The proposed approach predicts accurately the facture failure in tubular joints and frames. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes an energy-based η approach to estimate the elastic–plastic energy release rate for shallow surface cracks located at the weld toe at the chord crown point near the tension brace in the circular hollow section (CHS) K-joint. This approach evaluates the elastic–plastic energy release rate using the area under the load versus the load-line displacement curve for large-scale tubular K-joints, similar to the conventional η approach used to calculate the energy release rate for facture specimens described in material testing standards. The present work demonstrates that the value of ηpl equals 1 for the shallow cracks considered in tubular K-joints. The effective width (Beff ), via which the remaining ligament area (Alig ) is calculated, depends on the geometry of the K-joints. The plastic η approach with the proposed effective width Beff , coupled with a previous development on the nonlinear load–deformation formulation for K-joints, predicts closely the elastic–plastic energy release rate along the crack front for cracked tubular K-joints, compared to the conventional domain-integral method. [Copyright &y& Elsevier]

Abstract: This study reports an experimental investigation of a fatigue-cracked, pre-notched circular hollow section X-joints fabricated from high strength steels (with the yield strength higher than 800MPa) subjected to brace in-plane bending. The circular hollow section X-joint entails a prefabricated V-notch near the weld toe at the crown position. The experimental procedure applies a fatigue pre-cracking cyclic load followed by a monotonic brace in-plane bending, which leads to brittle through-thickness crack propagation after some amount of ductile tearing. The ductile tearing assessment, integrating the fracture resistance curve obtained from the small-scale fracture specimens and the crack extension in the large-scale tubular joint, predicts closely the load level at which unstable crack extension takes place. The generic level 2A curve outlined in the BS7910 provides an un-conservative estimate on the failure load of the X-joint specimen. The parametric numerical investigation reveals that the strength definition for the cracked joints imposes a significant effect on the shape of the failure assessment curve. [Copyright &y& Elsevier]

Abstract: This paper describes the numerical investigation of cold-formed stainless steel tubular T-joints, X-joints and X-joints with chord preload at elevated temperatures. A series of finite element analysis was performed on stainless steel tubular joints. The tubular T- and X-joints were welded from cold-formed square and rectangular hollow sections as brace and chord members. The material properties of high strength stainless steel (duplex and high strength austenitic) and normal strength stainless steel (AISI 304) at elevated temperatures were carefully incorporated in the finite element models. An extensive numerical study of 450 specimens consists of 20 T-joints, 10 X-joints and 20 X-joints with chord preload at different temperatures ranged from 22 to 870°C was conducted. The joint strengths, failure modes and load-deformation curves of stainless steel tubular joints at elevated temperatures were obtained from the finite element analysis. The numerical results were compared with the design strengths calculated from the existing design rules for stainless steel tubular joints at normal room temperature (ambient temperature) by using the material properties of stainless steel tubes at elevated temperatures. In the calculation of the joint strengths, the reduced material property of 0.2% proof stress was used due to the deterioration of material at elevated temperatures. Furthermore, design equations for cold-formed stainless steel tubular T- and X-joints at elevated temperatures are proposed by introducing a temperature factor (ξT ). A reliability analysis was performed to assess the existing and proposed design equations. [Copyright &y& Elsevier]

Abstract: The hot spot stress concentration factors (SCFs) for an as-welded tubular joint can be reduced by infilling the chord member with cementious grout, with associated improved fatigue strength for the grouted joint. However, inconsistent fatigue test results of grouted tubular joints are found in the published literature, which cannot be justified by hot spot stress approach. In order to obtain a better understanding for the fatigue performance of grouted tubular joints, a comprehensive fracture mechanics study is carried out for the reported fatigue test on as-welded tubular T-joint and another joint with grouted chord. The stress intensity factors (SIFs) of the two joints are determined by numerical method and then by empirical method. The SIF results are found to be consistent and in agreement of the fatigue test results. The presence of infilled grout in the chord is found to reduce the SCF, and lower the degree of bending (DOB). For tubular joints with weld toe fatigue cracking, the hot spot stress with lower DOB is associated with larger crack driving force and is more damaging than that with higher DOB. Hence, for fatigue assessment of grouted tubular joints it is essential to include the effect of DOB, which is ignored in hot spot stress S–N approach recommended in some current design codes. [Copyright &y& Elsevier]

Abstract: A new nonlinear two-dimensional tubular joint element is developed in this study on the basis of flexibility equations and the interaction between the axial force and the in-plane bending moment in the joint. Empirical equations are used to define the joint yielding in the axial direction and the in-plane rotation. An elastic–perfectly plastic yield function is adopted to include the combined effects of axial loads and bending moments on the yielding of the joint. The element formulation is straightforward, and it can readily be implemented in nonlinear finite element programs. Verification studies are carried out for the element to prove its suitability for the modeling of tubular joints of offshore jacket structures. It is concluded that the nonlinear joint model that has been developed produces accurate results, verified against experimental data as well as against sophisticated multi-axial finite element joint models. [Copyright &y& Elsevier]

This paper presents a finite element analysis (FEA), by using ANSYS 10.0 (SAS IP Inc 2005), to determine the stress concentration factor (SCF) of the dragline tubular joints. Different load cases, element types, weld sizes and shapes are considered in the analysis. The predicted SCF are compared with the experimental values based on full-size laboratory testing. Finite element (FE) model for the dragline tubular joint consists of the main chord and bracing members with all the attachments like, end plates, load cells, nuts and rods, with concave weld shape and equal weld leg length has been selected to determine SCF. Two layers of 10-node tetrahedral element (SOLID187) and 2 layers of 20-node hexahedral element (SOLID186) have been used in the FE model. The FEA results for all the laboratory test specimens are particularly good when loaded under load case 1 (LC1) and reasonable when loaded under load case 2 (LC2). [ABSTRACT FROM AUTHOR]

Stress Concentration Factor (SCF) is used as a reference to quantify the peak stress in welded tubular joints for fatigue assessment. At present, complex equations are available for calculating SCFs at selected locations of the brace-chord intersection curve of tubular joints for individual load cases. This paper presents an alternative approach to calculate SCF distribution along the intersection curve of tubular X-joints using neural networks. An SCF database based on the results of 300 finite element (FE) models was used to train and test the neural networks. Neural networks trained by these FE results were found to provide close predictions of the SCF distributions under each independent loading as well as combined loadings. Based on the parametric study it can be concluded that properly trained and well calibrated neural networks can be reliable alternatives to complicated SCF equations for predicting SCF at selected critical locations or along the brace-chord intersection curve of tubular joints. [ABSTRACT FROM AUTHOR]

Abstract: The paper describes laboratory tests of arc-welded T-joints between equal width rectangular hollow sections (called “matched box connections” in ANSI/AWS D1.1-2000 Structural Welding Code). The brace and chord members were cold-formed with a nominal yield stress of 350 MPa. The welds were laid using MMAW and GMAW processes without profiling the brace ends. The brace of each specimen was loaded in tension to failure with the chord supported continuously so as not to induce significant bending effects. The test results showed that the joint strength can be improved by using backing strips for the butt (or groove) welds, while backing rods (or filler rods) should not be used as they led to larger variation in joint strengths, and often, inferior strengths. The test strengths are compared with the design strengths obtained using the IIW Recommendations and Eurocode 3, Part 1.8. It is shown that for cold-formed tubes with a nominal yield stress of 350 MPa (or above), a design check on the strength of the butt (or groove) weld is required in addition to the checks on the strengths of the chord and brace members specified in the current design guidelines. An equation is proposed for calculating the strength of the weld. [Copyright &y& Elsevier]

Abstract: Composite pipes are becoming popular in the offshore oil and gas industry. These pipes are connected to one-another by various configurations of joints. The joints are usually the weakest link in the system. In this investigation we examine the response of various joint configurations subjected to torsion, one of the most common loading conditions in piping systems. Specifically, the theoretical analysis used to evaluate the stress field in the adhesive layers of tubular and socket type bonded sandwich lap joints is presented here. The two adherends of the joints may have different thickness and materials, and the adhesive layer may be flexible or brittle. The analysis is based on the general composite shell theory. The stress concentrations at and near the end of the joints as functions of various parameters, such as the overlap length, and thickness of the adhesive layer are studied. The effects of different adherend thickness ratios, adhesive thickness and overlap length are also studied. Results obtained from the proposed analytical solutions agree well with the results obtained from finite element analysis and those obtained by other workers. [Copyright &y& Elsevier]

It is common practice to calculate stress intensity factors for surface cracks in pipe–plate/tubular joints using stress intensity factor solutions developed for surface cracks in T-plate joints or flat plates with magnification factors. However, since these solutions cannot account for stress redistribution resulting from the reduction of member stiffness with crack growth, load shedding models have been introduced to modify these solutions. In the present work, a new method for the calculation of stress intensity factors for surface cracks in pipe–plate and tubular joints is developed. It is based on a model of T-plate weld joints with built-in ends and, therefore, accommodates load shedding effects directly. The method for the calculation of stress intensity factors for surface cracks in T-plate joints with built-in ends under arbitrary mode I loads using the weight function method is presented first. Then, applications of the T-plate joint with built-in ends model to calculate the stress intensity factors for surface cracks in pipe–plate and tubular T-joints are demonstrated. It is shown that the current model accounts for the load shedding effects directly and provides stress intensity factor solutions for surface cracks in pipe–plate and tubular joints accurately. [Copyright &y& Elsevier]

The existing fatigue design S–N curve for SHS-to-plate T-joints under in-plane bending is given in the Canadian Standard, CAN/CSA-S16.1-M89, in terms of the classification method. That S–N curve is however based on the class of longitudinally loaded plates with welded non-load carrying attachments, which are different from the SHS-to-plate T-joints. The increased use of welded thin-walled (t<4 mm) tubular joints in the road transport and agricultural industry for applications such as lighting poles, traffic sign supports, truck trailers, swing ploughs, haymakers and linkage graders, means that there is a need to develop fatigue design curves for tubular joints where the tube wall thickness is less than 4 mm. This paper aims to determine fatigue design curves for SHS-to-plate T-joints where the thin-walled tubes have a thickness of less than 4 mm. Tube-to-plate T-joints, made up by welding a square hollow section tube to a plate, are tested under fatigue loading. Constant stress-amplitude cyclic loading is applied to these connections as in-plane bending load. Stress concentration factors (SCFs) have been determined from strain distributions obtained using strain gauge measurements. Analysis of the fatigue test data using least squares method is carried out to determine the design curves of the tube-to-plate T-joints under in-plane bending, for both the classification method and the hot spot stress method. A class of 44 is recommended for the classification method. An Sr.hs–N curve is proposed, with a recommended SCF of 2.0 for the hot spot stress method. [Copyright &y& Elsevier]

Analysis of large-scale fatigue testing results has shown that the fatigue strength of offshore welded tubular joints is not dependent on the hot spot stress alone but is also significantly influenced by stress distributions around the intersection which are normally represented by several characteristic parameters. The through-thickness distribution for example is characterized by degree of bending. In order to represent the stress distribution along the intersection, the average stress concentration factor (SCF) concept was suggested and used in empirical stress intensity factor (SIF) models. However, this parameter alone is not enough to characterize the stress distribution along the intersection. Furthermore, there is no parametric equation available to predict this parameter. For this reason, a new concept, stress distribution concentration factor (SDCF), has been proposed in this study to describe the spread of stress distribution along the intersection. Systematic thin shell finite element analyses have been conducted for 330 different tubular Y, T and 330 X and DT joints, typical of those used in offshore structures, subjected to different modes of loading. On the basis of these results, a set of parametric equations has been derived for the average SCF and SDCF as a function of non-dimensional joint geometric ratios α, β, γ, τ and θ for each mode of loading and for both the chord and brace sides of the intersection of tubular welded Y, T, X and DT joints. [ABSTRACT FROM AUTHOR]

This paper describes a numerical study on stress concentration factors (SCFs) of stainless-steel hybrid tubular T-, Y- and X-joints with circular hollow sections (CHSs) and with square hollow sections (SHSs). The finite element models (FE models) were developed and validated against the corresponding test results available in the literature. The validated FE models were then utilized to perform an extensive parametric study containing 47 FE models for T-joints, 47 FE models for Y-joints and 47 FE models for X-joints. In total, 141 FE models were analyzed in the parametric study. The brace diameter to chord width ratio (β = d 1 ∕ b 0 ), brace to chord thickness ratio (τ = t 1 ∕ t 0 ) and chord width to thickness ratio (2 γ = b 0 ∕ t 0 ) were selected as the key geometric parameters in the parametric study. The SCFs at the hot spot locations obtained from the parametric study were compared against those calculated from the design formulae specified in the current design guidelines of the International Committee for the Development and Study of Tubular Structures (CIDECT). The comparison results show that the design formulae given in the CIDECT specification are not appropriate for predicting the SCFs of stainless-steel CHS-to-SHS hybrid tubular T-, Y- and X-joints. Therefore, new design equations were proposed in this study. It is shown that the values of SCFs calculated from the proposed design equations are generally in good agreement with the values obtained from the FEA. • FEA was performed on SCFs of stainless-steel CHS-to-SHS hybrid tubular joints. • The validated FEMs were used to conduct a parametric study comprising 141 FEMs. • Proposed design equations were appropriate for determining SCFs of such joints. [ABSTRACT FROM AUTHOR]

This paper describes an experimental and finite element investigation of the non-linear elastic--plastic force--displacement response of a simply supported tubular YT-joint under a range of ratios of the T- to Y-brace applied loads, in order to develop an understanding of the dependence of the joint response on loading path. The experiments consist of the static testing of simply supported tin--lead alloy models of tubular YT-joints under combined, proportionally applied T- and Y-brace-end axial forces. A number of different finite element approaches are presented and discussed via comparison with the test results. An improved version of the energy-based elastic--plastic prediction procedure of the present authors is presented; this is shown to represent a framework for the determination of the non-linear local joint T- and Y-brace force--displacement responses to arbitrary radial loading paths in the load space. The work is considered relevant to the simplification of tubular framework analysis methods for the calculation of accurate collapse loads, incorporating non-linear joint behaviour. [ABSTRACT FROM AUTHOR]