• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.1
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• pp.298-303
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• 2016

Owing to the advantages of reduced weight and wind effect, the space-framed towers that consist of vertical and horizontal members of circular hollow tubular sections have been adopted widely for various purposes. It is critical to guarantee the strengths of tubular joints where vertical and horizontal members are connected structurally to make the entire space-framed system behave as a single tower structure. In this study, a strength evaluation was conducted for T-type tubular joints subjected to the concurrent action of compression and bending. Three of the available design codes, i.e., AISC, Eurocode 3, ISO 19902 were investigated and a design equation was suggested for an ultimate strength interaction between the axial force and bending moment based on nonlinear finite element analyses by selecting the slenderness ratios at the joints as major parameters.

• Steel and Composite Structures
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• v.24 no.4
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• pp.425-439
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• 2017

As a thin-walled structure, local joint flexibility (LJF) in a tubular structure is prominent, and it may produce significant effect on the static performance for the overall structure. This study presents a simplified analytical model to analyze the static behavior for a steel tubular structure with LJF. The presented model simplifies a tubular structure into a frame model consisted of beam elements with considering the LJFs at the connections between any two elements. Theoretical equations of the simplified analytical model are deduced. Through comparison with 3-D finite element results of two typical planar tubular structures consisted of T- and Y-joints respectively, the presented method is proved to be accurate. Furthermore, the effect of LJF on the overall performance of the two tubular structures (including the deflection and the internal forces) is also investigated, and it is found from analyses of internal forces and deformation that a rigid connection assumption in a frame model by using beam elements in finite element analysis can provide unsafe and inaccurate estimation.

• Journal of Ocean Engineering and Technology
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• v.8 no.2
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• pp.141-150
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• 1994

In designing, the strength of tubular joint has been an important problem for integrity of steel structures in which many tubular members are used. This paper presents the results of FEM analysis on stress concentration and fatigue crack initiation life for two types of tubular joints. One is circular and rectangular T type joints which consist of circular brace and rectangular chord. Another is circular and circular T type joints which consist of circular brace and circular chord. FEM analyses were performed under the axial load and in-plane bending moment. The fatigue crack initiation life can be estimated by using $\varepsilon$-N curve and by applying the Palmgren-Miner linear damage rule. According to the results, the stress concentration factor(SCF) of circular and rectangular joints is higher than that of circular and circular joints. The fatigue crack initiation lives of circular-circular joints and circular-rectangular joints were calculated.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.145-150
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• 2002

Tubular joints having a large diameter in the offshore structure are reinforced using internal ring stiffener in order to increase the load carrying capacity. In this study, the static strengths of internally ring-stiffened tubular T-joints subjected to compressive brace loading are assessed. Nonlinear finite element analyses are used to compute the behavior of unstiffened and ring-stiffened T-joints. From the numerical results, internal ring stiffener is found to efficient in improving the ultimate capacity, and reinforcement effect are calculated. The influence of geometric parameters for members and ring is evaluated. Based on the FE results, regression analysis is performed considering practical sizes of ring stiffener, finally strength estimation formulae for ring-stiffened T-joints are proposed.

• Ocean Systems Engineering
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• v.13 no.1
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• pp.43-55
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• 2023

In this study, the SCFs in tubular T-joints stiffened with external ring under axial load are studied and discussed. After verification of the present numerical model with the results of several available experimental tests, 156 FE models were generated and analyzed to parametrically evaluate the effect of the joint geometry and the ring geometry on the SCFs. Results indicated that the SCF of the stiffened T-joints at crown point can be down to 24% of the SCF of the corresponding un-reinforced joint at the same point. Also, the effect of the ring on the SCF at saddle point is more remarkable than the effect of the ring on the SCF at crown point. Moreover, against un-reinforced joints under axial load, the SCF at saddle point of the stiffened joint is smaller than the SCF at crown point of that stiffened joint. The ring results in the redistribution of stresses in the ring and metal substrate. Also, the effect of the ring thickness on the decrease of the SCFs is slight and can be ignored. In final step, the geometric parameters affecting the SCFs of the stiffened T-joints are analyzed by multiple nonlinear regression analyses. An accurate formula is proposed for determining the SCFs.

• Steel and Composite Structures
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• v.3 no.2
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• pp.123-140
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• 2003

The importance of the research on moment-resistant properties of unstiffened tubular joints and the research background are introduced. The performed experimental research on the bending rigidity and capacity of the joints is reported. The emphasis is put on the discussion of the flexural behavior of the joints including sets of geometrical parameters of the joints and several loading combinations. Procedures and results of loading tests on four full size joints in planar KK and X configuration are described in details at first. Mechanical models are proposed to analyze the joint specimens. Three-dimensional nonlinear FE models are established and verified with the experimental results. By comparing the experimental data with the results of the analysis, it is reported reasonable to carry out the structural analysis under the assumption that the joint is fully rigidly connected, and their bending capacities can assure the strength of the members connected under certain limitation. Furthermore, a parametric formula for inplane bengding rigidity of T and Y type tubular joints is proposed on the basis of FE calculation and regression analysis. Compared with test results, it is shown that the parametric formula developed in this paper has good applicability.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.5 s.176
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• pp.1331-1342
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• 2000

In power generation systems a variety of structural components typically operate at high temperature and pressure. Therefore a life assessment methodology accounting for gradual creep fracture is increasingly needed for these components. The most critical defects in such structure are generally found in the form of semi-elliptical surface cracks in the welded tubular joints. Therefore the analysis of a semi-elliptical surface crack in a plate or a shell is an important problem in engineering fracture mechanics. On this background, via shell/line-spring finite element analyses of such surface cracks in the welded T and L joints under various loadings, we investigate J-integral along the crack front We first develop T and L joints auto mesh generation program providing ABAQUS input file composed of shell/line-spring finite elements. We then further develop a T and L joints life assessment program based on the experimental creep crack growth law and auto mesh generation program in a graphical user interface format Finally the remaining life of T and L joints for various analytical parameters are assessed using the developed life assessment program.

• Ocean Systems Engineering
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• v.8 no.4
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• pp.409-426
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• 2018

This paper presents the strengthening of tubular joint by wrapping Carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP). In this study, total number of layers, stacking sequence and length of wrapping are the different parameters involved when fiber reinforced polymers (FRP) composites are used for strengthening. For this, parameters where varied and results were compared with the reference joint. The best stacking sequence was identified which has the highest value in ultimate load with lesser deflections. For determining the best stacking sequence, numerical investigation was performed on CFRP composites; length of wrapping and number of layers were fixed. Later, the studies were focused on CFRP and GFRP strengthened joint by varying the total number of layers and length of wrapping. An attempt was done to propose a parametric equation from multiple regression analysis, which can be used for CFRP strengthened joints. Hashin failure criteria was used to check the failure of composites. Results revealed that FRP was having a greater influence in the load bearing capacity of joints, and in reducing the deflections and stresses of joint under axial compressive loads. It was also seen that, CFRP was far better than GFRP in reducing the stresses and deflection.

• Steel and Composite Structures
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• v.3 no.5
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• pp.321-331
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• 2003

The paper presents the results of an experimental investigation conducted on welded tubular joints, that are employed in offshore platforms, to study the behaviour and strength of these joints under axial brace compression loading. The geometrical configuration of the joints tested were T and Y. The nominal diameter of the chord and brace members of the joint were 324 and 219 mm respectively. The chord thickness was 12 mm and the brace 8 mm. The tested joints are approximately quarter size when compared to the largest joints in the platforms built in a shallow water depth of 80 m in the Bombay High field. Some of the joints were actually fabricated by a leading offshore agency which firm is directly involved in the fabrication of prototype structures. Strength of the internally ring-stiffened joints was found to be almost twice that of the unstiffened joints of the same configuration and dimensions. Bending of the chord as a whole was observed to be the predominant mode of deformation of the internally ring-stiffened joints in contrast to ovaling and punching shear of the unstiffened joints. It was observed in this investigation that unstiffened joint was stiffer in ovaling mode than in bending and that midspan deflection of unstiffened joint was insignificant when compared to that of the internally ring stiffened joint. The measured midspan deflection of the unstiffened joint in this investigation and its relation with the applied axial load compares very well with that predicted for the brace axial displacement by energy method published in the literature. A comparison of the measured deflection and ovaling of the unstiffened joint was made with that published by the author elsewhere in which numerical prediction of both quantities have been made using ANSYS software package. The agreement was found to be quite good.

• Steel and Composite Structures
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• v.4 no.2
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• pp.149-167
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• 2004

Offshore platforms have to serve in harsh environments and hence are likely to be damaged due to wave induced fatigue and environmental corrosion. Welded tubular joints in offshore platforms are most vulnerable to fatigue damage. Such damages endanger the integrity of the structure. Therefore it is all the more essential to assess the capacity of damaged structure from the point of view of its safety. Eight internally ring stiffened fatigue damaged tubular joints with nominal chord and brace diameter of 324 mm and 219 mm respectively and thickness 12 mm and 8 mm respectively were tested under axial brace compression loading to evaluate the reserve capacity of the joints. These joints had earlier been tested under fatigue loading under corrosive environments of synthetic sea water and hence they have been cracked. The extent of the damage varied from 35 to 50 per cent. One stiffened joint was also tested under axial brace tension loading. The residual strength of fatigue damaged stiffened joint tested under tension loading was observed to be less than one fourth of that tested under compression loading. It was observed in this experimental investigation that in the damaged condition, the joints possessed an in-built load-transfer mechanism. A bi-linear stress-strain model was developed in this investigation to predict the reserve capacity of the joint. This model considered the strain hardening effect. Close agreement was observed between the experimental and predicted results. The paper presents in detail the experimental investigation and the development of the analytical model to predict the reserve capacity of internally ring stiffened joints.