• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2001년도 가을 학술발표회 논문집
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• pp.269-276
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• 2001

Tubular structures are widely used for offshore platforms and truss type structures. In this paper, nonlinear finite element analysis is used to assess the static strength of stiffened tubular T-joints subjected to compressive brace loading. This joints was modelled with and without internal ring stiffener According to variation of ring geometries, the effect of ring stiffener for T-joints are investigated. Internal ring stiffener is found to be efficient improving ultimate strength of tubular joints. Relations of ring thickness and axial strength are observed considering geometric parameters of ring stiffeners.

• 한국해양공학회지
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• 제18권6호
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• pp.70-78
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• 2004

In order to increase the load carrying capacity of tubular structures, the joints of tubular members are usually reinforced with various reinforcement system. A stiffening method with internal ring stiffeners is effectively used for the steel tubular joint with a large diameter. In this study, the behavior of internally ring-stiffened tubular T-joints subjected to axial loading is assessed. For the parametric study, nonlinear finite element analyses are used to compute the static strength on non-stiffened and ring-stiffened T-joints. Based on the numerical results, an internal ring stiffener is found to be efficient in improving the static strength. The influence of geometric parameters has been determined, and the reinforcement effect are evaluated. Based on the FE results, regression analises are performed considering the practical size of ring stiffener. Finally strength estimation formulas for ring-stiffened tubular T-joints are proposed.

• Steel and Composite Structures
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• 제24권5호
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• pp.615-633
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• 2017

Fatigue crack initiated in welded tubular joints due to cyclic loading may produce harmful effect on the integrity of the tubular structures. To study such effect, both fatigue and static tests on nine circular tubular T-joint specimens made of carbon steel materials were carried out. The specimens were subjected to tensile loading in both fatigue and static tests. The load-displacement relation, the crack propagation and the failure mode of the specimens are all analyzed. The deterioration of the static strength of the cracked T-joints is also investigated and evaluated through an area reduction factor. Experimental results indicate that the static strength of a tubular T-joint with a surface crack seems to decrease slightly while a through crack has relatively remarkable effect on the reduction of the static strength. Additionally, experimental results also show that the toughness of the materials and the geometry of the specimens play an important role on the failure process of cracked tubular T-joints.

• Ocean Systems Engineering
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• 제4권2호
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• pp.151-167
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• 2014

It is common that analyses of offshore platforms being carried out with the assumption of rigid tubular joints. However, many researches have concluded that it is necessary that local joint flexibility (LJF) of tubular joints should be taken into account. Meanwhile, advanced analysis of old offshore platforms considering local joint flexibility leads to more accurate results. This paper presents an extensive finite-element (FE) based study on the flexibility of uni-planner multi-brace tubular Y-T and K-joints commonly found in offshore platforms. A wide range of geometric parameters of Y-T and K-joints in offshore practice is covered to generate reliable parametric equations for flexibility matrices. The formulas are obtained by non-linear regression analyses on the database. The proposed equations are verified against existing analytical and experimental formulations. The equations can be used reliably in global analyses of offshore structures to account for the LJF effects on overall behavior of the structure.

• Steel and Composite Structures
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• 제23권5호
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• pp.585-596
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• 2017

Tubular joints have been widely used in offshore platforms and space structures due to their merits such as easy fabrication, aesthetic appearance and better static strength. For existing tubular joints, a grouted sleeve reinforced method was proposed in this paper. Experimental tests on five tubular T-joints reinforced with the grouted sleeve and two conventional tubular T-joints were conducted to investigate their mechanical behaviour. A constant axial compressive force was applied to the chord end to simulate the compressive state of the chord member during the tests. Then an axial compressive force was applied to the top end of the brace member until the collapse of the joint specimens occurred. The parameters investigated herein were the grout thickness, the sleeve length coefficient and the sleeve construction method. The failure mode, ultimate load, initial stiffness and deformability of these joint specimens were discussed. It was found that: (1) The grouted sleeve could change the failure mode of tubular T-joints. (2) The grouted sleeve was observed to provide strength enhancement up to 154.3%~172.7% for the corresponding un-reinforced joint. (3) The initial stiffness and deformability were also greatly improved by the grouted sleeve. (4) The sleeve length coefficient was a key parameter for the improved effect of the grouted sleeve reinforced method.

• Steel and Composite Structures
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• 제32권3호
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• pp.361-372
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• 2019

Tubular joints are used in the construction of offshore structures and other land-based structures because of its ease of fabrication. These joints are subjected to different environmental loadings in their lifetime. At the time of fabrication or modification of an existing offshore platform, tubular joints are usually strengthened to withstand the environmental loads. Currently, various strengthening techniques such as ring stiffeners, gusset plates are employed to strengthen new and existing tubular joints. Due to some limitations with the present practices, some new techniques need to be addressed. Many researchers used Fibre Reinforced Polymer (FRP) to strengthen tubular joints. Some of the studies were focused on axial compression of Glass Fibre Reinforced Polymer (GFRP) strengthened tubular joints and found that it was an efficient technique. Earlier, the authors had performed studies on Carbon Fibre Reinforced Polymer (CFRP) strengthened tubular joint subjected to axial compression. The study steered to the conclusion that FRP composites is an alternative strengthening technique for tubular joints. In this work, the study was focused on axial compression of Y-joint and in plane and out of plane bending of T-joints. Experimental investigations were performed on these joints, fabricated from ASTM A106 Gr. B steel. Two sets of joints were fabricated for testing, one is a reference joint and the other is a joint strengthened with CFRP. After performing the set of experiments, test results were then compared with the numerical solution in ANSYS Parametric Design Language (APDL). It was observed that the joints strengthened with CFRP were having improved strength, lesser surface displacement and ovalization when compared to the reference joint.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 춘계학술대회 논문집
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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.

• 한국해양공학회지
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• 제8권2호
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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.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
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• pp.533-540
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• 2002

Tubular joints having a large diameter 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.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.315-320
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• 2007

An effective reinforcement method for steel tubular joints having a large chord diameter is the use of internal ring stiffeners. This paper presents the results of a numerical study on the static strength of internally ring-stiffened tubular X- and T-joints subjected to brace axial compression loading. Nonlinear finite element analyses are used to compute the joint strength. The influence of geometrical parameters has been studied and the maximum reinforcement effect of a ring stiffener has been evaluated. A strength ratio is defined. by the ratio of ring-stiffened joint strength to unstiffened joint strength, and an equation for this strength ratio is derived by regression analysis. Design optimization for ring stiffener of tubular joints is carried out using metropolis genetic algorithm.