Papers by Keyword: Tubular Joints

Abstract: Stress concentration factor (SCF) is an important parameter for the fatigue design of offshore joints. There are many empirical equations for quick estimation of SCF in tubular joints, based on experimental and numerical investigations. However, most of these equations apply at the crown and saddle points only, even though the maximum SCF may not always occur at these points, resulting in overestimated fatigue life. As the maximum SCF location varies due to multiplanar loads, damage, or reinforcement of joints, its location and magnitude are critical for a realistic fatigue life estimation. However, conventional statistical tools cannot approximate the complex behavior of SCF around the brace axis. On the other hand, artificial neural networks (ANN) can efficiently approximate complex phenomena. This study uses ANN to develop empirical models for determining SCF around the weld toe of KT-joints subjected to in-plane bending (IPB) loads. Eighteen hundred and fifty-eight (1858) designs were simulated using finite element analyses to generate data for training the ANN. Two IPB load conditions were focused on, and empirical equations were proposed for SCF around the chord side of the central brace-chord interface. These equations approximate maximum SCF with less than 5% error. This methodology applies to other joints and load configurations also.

Abstract: Welded tubular joints are widely used in long-span, space and offshore structures. In a welded tubular joint, the chord is generally subjected to loads in radius direction which are transmitted from the brace members in axial direction. As the strength of the chord in radius direction is generally much weaker than that of the brace in axial direction, failure occurs easily at the weld toe on the chord surface. To improve the bearing capacity of the joint structure, reinforcement is necessary. Several reinforcing methods were reported in the literature, such as doubler or collar plate reinforcement, internal stiffened ring reinforcement and bracket reinforcement etc. This paper presents the strengthening method by inner plate. From finite element analysis of many inner plated reinforced tubular joint models, the efficiency of reinforcement by inner plate is analyzed by comparing the static strength of reinforced models with that of unreinforced models. Based on a parametric study of the static strength of tubular joints reinforced by inner plate, the design considerations on inner plate strengthening tubular joints are also proposed.

Abstract: Welded rectangular steel tubular joints have been widely used in large span complicated steel structure engineering .With the type of the joints and structural measures complicated, there is no suitable joints theory formula in design specifications. In this paper, two different structural measures types of umbrella steel truss # 8 joints and 68 # joints in a Railway Station are static analysis ,which is by means of finite element software ANSYS and based on the principle of the joints member loading simultaneously. The analysis results show that: in the case of the joints member loading simultaneously, the carrying capacity variation of each member is not uniform coordination; With the different angle between the branch pipe of joints and main pipe, the changes of the degree of stress concentration in the four side surfaces of the member is different. The maximum difference is about 2-fold; compared 68 #joint with 8 # joint, its degree of stress concentration on the overall is small, which prove that structural measures of its domain joints is reasonable.

Abstract: Simple joint is a common connection type in tubular structures. In this joint, one or more tubes are welded directly on the surface of another tube. Local buckling occurs in panel zone when the joint load is heavy, and such local buckling will reduce the bearing capacity and stiffness of the joint. In order to improve bearing capacity of tubular joints, the joint needs to be strengthened. In this paper, the bending performance of the joint will be enhanced by welding two annular plates inside the surface of panel zone of chord member. By ANSYS finite element program, the bearing capacity of the joint with different inner annular plate was analyzed, including design bearing capacity and ultimate bearing capacity. The results showed that comparing to annular plate thickness variation, the width variation and interval variation have much more influence on the bearing capacity of the joint.

Abstract: For the further study on stress concentration and fatigue property of tubular joints of concrete-filled steel, we designed the fatigue test on tubular joints of concrete-filled steel.Associating with the calculation of finite element, we studied the stress concentration, cracking source of fatigue, and fatigue -related rules including cracking expansion. I did the equivalent calculating under variable amplitude loading. We proposed the criterion of fatigue failure when surface length of penetrated crack is about 3 times as the thickness of the wall. According to the experiment we verified that the tubular joints under the amplitude load this criterion is reasonable, secure and feasible.

Abstract: By research of simple tubular joints, thin-shell element analyses have been conducted for thousands of DTK joints frequently used in offshore structures in this paper. These joints are subjected to axial load, by use of nonlinear least squares fitter, the above results are derived a new set of parametric equations, in terms of several non-dimensional geometric ratios γ, ξ, β, τ and θ with the Origin software. Separate analyses have been conducted for the difference of SCFs in DTK joints and SCFs for TK joint from empirical formulas. The SCF results of these joints could act as a good reference for both further academic studies on SCF of other complex joints and engineering designing works.

Abstract: This paper presents methodologies for damage tolerance evaluation of tubular T- and Y-joints by using linear elastic fracture mechanics (LEFM) principles. The damage tolerance evaluation is in terms of crack growth analysis and remaining life prediction of tubular joints. Stress intensity factor (SIF) for T-butt plates which can be used for computation of SIF for tubular joints has been evaluated as per BS: 7910. It is observed from the literature that the expressions given in BS: 7910 for computation of SIF have not been used for remaining life prediction of tubular joints. In this paper, these expressions have been used for analytical prediction of remaining life of tubular T- and Y- joints subjected to constant amplitude loading (CAL) and variable amplitude loading (VAL). Wheeler residual stress model has been employed to represent the retardation effects due to tensile overloads. It is observed that remaining life predicted for T- and Y-joints under CAL are found to be in good agreement with those of experimental values reported in the literature. In the case of VAL, it is observed that crack growth retardation increases with increase of OLR resulting in higher predicted remaining life. It has also been observed that the predicted remaining life is influenced by the number of OLs and occurrence of OL. Early occurrence of OL causes the higher remaining life compared to later OLs.

Abstract: In the assessment of fatigue life of tubular joints in offshore engineering, hot spot stress range, in conventional method, is frequently used to predict the number of cycles that a tubular joint can sustain before failure from corresponding S-N curves. This method only considers the effect of the peak stress at the weld toe on the fatigue life of a tubular joint, but ignores that of the stress distribution along the weld toe. The effect of the stress distribution along the weld toe on the fatigue life of tubular joints can be evaluated indirectly by analyzing a fracture mechanics parameter, namely stress intensity factor. The stress intensity factor values of the surface cracks in the fatigue failure process for tubular joints subjected to different loading types, thus causing the difference of the stress distributions along the weld toe, are investigated from both numerical analysis and experimental measurement. The results show that the stress distribution along the weld toe has remarkable effect on the fatigue life of tubular joints.

Abstract: This paper reports a parametric stress analysis of various configurations of rack plate stiffened multi-planar welded KK joints using the finite element method. The KK joint finds application in the leg structure of offshore Oil & Gas jack-up platforms. The rack plate is a dual purpose element of the joint because it firstly functions as a stiffener which reduces the stress concentration at the brace/chord intersection. This could be an immense contribution to the increase in fatigue life of the joint but other hot spot sites are introduced to the joint. The rack is also used for raising and lowering of the jack-up hull which gives the jack-up platform its jacking capability. Over 120 models using a combination of shell and solid elements were built and analysed within ABAQUS. Non-dimensional joint geometric parameters; β, γ and . were employed in the study with . being defined as the ratio of rack thickness to chord diameter. Stress Concentration Factors (SCFs) were calculated under applied axial and OPB (out-of-plane-bending) loading. Three critical SCF locations were identified for each load case, with each location becoming the most critical based on the combination of the non-dimensional parameters selected for the joint. This is important as careful design can shift the critical SCF from an area inaccessible to NDT to one that can be easily inspected. The SCF values extracted from the models were used to derive six parametric equations through multiple regression analysis performed using MINITAB. The equations describe the SCF at the different locations as a function of the non-dimensional ratios. The equations not only allow the rapid optimisation of multi-planar joints but also can be used to quickly identify the location of maximum stress concentration and hence the likely position of fatigue cracks. This in itself is an invaluable tool for planning NDT procedures and schedules.

Abstract: In this paper three-dimensional welding simulations were carried out in FE software ANSYS in order to predict transient temperatures and the residual stresses in a three pass welded tubular joints. The thermal analysis and the moving heat source were verified with temperature measurements and the computed residual stresses were verified with hole drilling measurements. Then residual stress relaxation analyses were carried out on the tubular structure, with similar load cases as in earlier fatigue testing on the same tubular joint structures.