The Analysis of the Extrapolation Method Used in Typical Structures of Jacket Platforms

2015 ◽  
Author(s):  
Yifei Zhu ◽  
Shixiao Fu ◽  
Jianqiao Wu
Keyword(s):  
Numerical Calculation ◽  
Hot Spot ◽  
Shell Element ◽  
Welding Seam ◽  
Hot Spot Stress ◽  
Shell Elements ◽  
Tubular Joints ◽  
Element Simulation ◽  
Calculation Results ◽  
Fitting In

Acquiring the hot spot stress (HSS) in dangerous points of the structure (normally the welding seams of the structure) is the foundation of the offshore platform fatigue strength design. Because of the fact that it is very difficult and unpractical to install sensors in the welding seams, the most widely used method of acquiring the HSS currently is extrapolation, a method that obtains the HSS by extrapolating from stress of distant points. In order to figure out the feasibility of the method of extrapolation as well as the best ways to implement extrapolation in real practice, it is important to carry out numerical calculation of welded tubular joints in advance. To study the tubular joints, the finite element method (FEM) is the most widely adopted approach. In previous studies, shell elements are utilized to simulate tubular joints instead of solid elements concerning the difficulty. However, shell element simulation merely simulates the mid-surfaces of the tube walls so that shear stress in the direction of tube thicknesses are ignored, making the calculation of the stress concentration factor (SCF) inaccurate. In this study, the recommended ways of simulating the tubular Y- and T-joints are displayed and then the comparison of calculation results between different weld type, different mesh situations as well as different elements are given in order to bring up advice on numerical calculation for the study of extrapolation. The results of numerical calculation show that the extrapolation results are more accurate when we only consider the change of parameter α (chord length-to-chord radius ratio) and also, it is suggested to do the fitting in the area of 2t-4t away from the welding seam. These suggestions are verified by applying the method of extrapolation to a real jacket platform, which turns out that the fitting degree of extrapolation is very pleasant.

scholarly journals Fatigue Strength Curve for Tubular Joints of Offshore Structures under Dynamic Loading

Dynamics ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 125-133
Author(s):  
Sudath C. Siriwardane ◽  
Nirosha D. Adasooriya ◽  
Dimitrios Pavlou
Keyword(s):  
Fatigue Strength ◽  
Hot Spot ◽  
Offshore Structures ◽  
Hot Spot Stress ◽  
Tubular Joints ◽  
Jacket Structures ◽  
Strength Curve ◽  
Tubular Joint ◽  
Stress Concentration Factors

Offshore structures are subjected to dynamic environmental loads (wave and wind loads). A stress-life fatigue strength curve is proposed for tubular joints which are in the splash zone area of offshore jacket structures. The Det Norske Veritas (DNV) offshore structures standards given design T-curve in the air is modified with the environment-dependent parameters to obtain this fatigue strength curve. Validity of the curve is done by comparing fatigue lives given by the proposed curve with experimental fatigue lives of tubular joints tested in seawater under different loading conditions. The fatigue assessment of a case study tubular joint is performed using the proposed curve. Nominal stress ranges of the members, which are connected to the joint, are obtained by dynamic analysis of the jacket structure. Stress concentration factors are utilized with the nominal stresses to obtain the hot spot stress ranges. Fatigue lives are calculated and compared with the conventional approach. Hence the applicability and significance of the proposed fatigue strength curve are discussed.

Fatigue of Tubular Joints: Hot Spot Stress Method Revisited

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Pingsha Dong ◽  
Jeong K. Hong
Keyword(s):  
Hot Spot ◽  
Life Assessment ◽  
Structural Stress ◽  
T Joints ◽  
Hot Spot Stress ◽  
Tubular Joints ◽  
Fatigue Design ◽  
Fatigue Data ◽  
Section Viii ◽  
Remaining Life Assessment

A series of well-known tubular joints tested in UKSORP II have been re-evaluated using the mesh-insensitive structural stress method as a part of the on-going Battelle Structural Stress JIP efforts. In this report, the structural stress based analysis procedure is first presented for applications in tubular joints varying from simple T joints, double T Joints, YT joints with overlap, and K joints with various internal stiffening configurations. The structural stress based SCFs are then compared with those obtained using traditional surface extrapolation based hot spot stress methods. Their abilities in effectively correlating the fatigue data collected from these tubular joints are demonstrated. These tests are also compared with the T curve typically used for fatigue design of tubular joints as well as the structural stress based master S-N curve adopted by ASME Section VIII Div 2. Finally, some of the implications on fracture mechanics based remaining life assessment for tubular joints are discussed in light of the results obtained in this investigation.

scholarly journals A Numerical Evaluation of Structural Hot-Spot Stress Methods in Rib-To-Deck Joint of Orthotropic Steel Deck

2020 ◽  
Vol 10 (19) ◽  
pp. 6924
Author(s):  
Nouman Iqbal ◽  
Heng Fang ◽  
Ahsan Naseem ◽  
Muhammad Kashif ◽  
Hans De Backer
Keyword(s):  
Hot Spot ◽  
Evaluation Methods ◽  
Single Element ◽  
International Institute ◽  
Hot Spot Stress ◽  
Shell Elements ◽  
Orthotropic Steel Deck ◽  
Deck Plate ◽  
Stress States ◽  
Steel Deck

This study numerically investigates the limitations of structural hot-spot stress (SHSS) methods and proposes a guideline for the calculation of hot-spot stresses, which can be used for the better evaluation of fatigue-related problems. Four different SHSS evaluation methods have been applied to the rib-to-deck (RD) welded joint in orthotropic steel deck (OSD). These methods are used to calculate SHSS at this critical joint utilizing finite element analyses (FEA) based software Siemens NX.12. The limitations and the accuracy of these methods have been observed under different element types and meshing techniques. Moreover, the effect of the nodal-averaging feature is being studied. Two types of governing stresses are produced by the application of Eurocode fatigue load model-4. Essentially, the bending in deck-plate produces highly non-linear stress at the deck-toe, and the membrane effect in rib-plate generates linear stress at the rib-toe. Guidelines are proposed considering different parameters on these two stress states by applying SHSS evaluation methods. In comparison to other SHSS approaches, the International Institute of Welding (IIW) quadratic stress extrapolation (QSE) method shows better results for solid single-element, and the American Society of Mechanical Engineers (ASME) through thickness stress linearization (TTSL) method stands out in solid cubic-mesh technique. In general, shell elements have more consistent SHSS results as compared to solid elements for both stress states.

Automated Identification of Critical Tubular Joints of Offshore Jacket Structure by Deterministic Fatigue Analysis

2017 ◽  
Author(s):  
Shrikarpagam Dhandapani
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Offshore Structures ◽  
Fatigue Analysis ◽  
Optimized Design ◽  
Base Shear ◽  
Hot Spot Stress ◽  
Environmental Loads ◽  
Tubular Joints

Fatigue occurs in structures due to the stresses from cyclic environmental loads. Offshore environmental loads being highly cyclic and recurring in nature, fatigue analysis with high degree of accuracy is required for reliable and optimized design of offshore structures. The main aim of this paper is to automate the process of identification of fatigue critical tubular joints of an offshore jacket structure using deterministic fatigue analysis with emphasis on the Hot Spot Stress Range (HSSR), an important measure in estimating fatigue damage, calculated using three different approaches for each tubular joint. The first approach determines HSSR at the time of maximum base shear of the jacket, the second, by calculating the difference between maximum and minimum Hot Spot Stress (HSS) and the third, at all time-instants of the wave cycle. Thus fatigue damage and fatigue life of the tubular joints are estimated using the highest HSSR value and the joints with lower fatigue life are identified as fatigue sensitive joints. This ensures effective identification of critical tubular joints of the offshore jacket structure which needs detailed investigation or redesign for fatigue. The deterministic approach discussed in this paper is applicable to large jackets which contains more number of tubular joints where sophisticated fatigue assessment at the preliminary stage is computationally intensive and manual identification of fatigue critical joints is laborious.

Low Cycle Fatigue of T-Tubular Joints With In-Plane Bending Loading

2005 ◽  
Author(s):  
Jo̸rn Waalen ◽  
Stig Berge
Keyword(s):  
Low Cycle Fatigue ◽  
Hot Spot ◽  
Fatigue Loading ◽  
Hot Spot Stress ◽  
Tubular Joints ◽  
Fatigue Design ◽  
R Ratio ◽  
Plane Bending ◽  
Number Of Cycles ◽  
Bending Loading

Tubular T-joints were fatigue tested with in-plane bending loading. Six models were tested, three models with R-ratio of 0 and three with R = −1. Hot spot stress was measured for the brace and for the chord using the ECSC linear extrapolation procedure. Fatigue loading was applied in load control, to obtain through thickness cracking at a number of cycles in the range 3 000–64 000 cycles. The data were analysed and compared with the current fatigue design criteria for tubular joints.

Combined Hot-Spot Stress Procedures for Tubular Joints

1984 ◽  
Author(s):  
J. Buitrago ◽  
N. Zettlemoyer ◽  
J.L. Kahlich
Keyword(s):  
Hot Spot ◽  
Hot Spot Stress ◽  
Tubular Joints

scholarly journals SIZE EFFECT OF WELDED THIN-WALLED TUBULAR JOINTS

2007 ◽  
Vol 07 (01) ◽  
pp. 101-127 ◽  
Author(s):  
FIDELIS RUTENDO MASHIRI ◽  
XIAO-LING ZHAO ◽  
MANFRED A. HIRT ◽  
ALAIN NUSSBAUMER
Keyword(s):  
Size Effect ◽  
Wall Thickness ◽  
Hot Spot ◽  
Fatigue Behavior ◽  
T Joints ◽  
Hot Spot Stress ◽  
Tubular Joints ◽  
Thin Walled Tube ◽  
Simple Extrapolation ◽  
Thin Walled

This paper clarifies the terminologies used to describe the size effect on fatigue behavior of welded joints. It summarizes the existing research on size effect in the perspective of newly defined terminologies. It identifies knowledge gaps in designing tubular joints using the hot spot stress method, i.e. thin-walled tubular joints with wall thickness less than 4 mm and thick-walled tubular joints with wall thickness larger than 50 mm, or diameter to thickness ratio less than 24. It is the thin-walled tubular joints that are addressed in this paper. It is found that thin-walled tube-plate T-joints do not follow the conventional trend: the thinner the section is, the higher the fatigue life. It is also found that simple extrapolation of existing fatigue design curves may result in unsafe design of thin-walled tube–tube T-joints. The effect of chord stiffness on fatigue behavior of thin-walled tubular T-joints is also discussed.

Research on the Stress Fatigue Assessment about the Hot Spot Stress on the Bogie Frame

2011 ◽  
Vol 328-330 ◽  
pp. 1281-1286
Author(s):  
Bin Jie Wang ◽  
Qiang Li ◽  
Zhi Ming Liu
Keyword(s):  
Fatigue Strength ◽  
High Speed ◽  
Hot Spot ◽  
Nominal Stress ◽  
Bottom Flange ◽  
Bogie Frame ◽  
Hot Spot Stress ◽  
Shell Elements ◽  
Joint Section ◽  
Fatigue Evaluation

As the loading conditions for the railway vehicles are becoming more and more complex, nominal stress has been unable to fully satisfy the requirements for assessing fatigue strength for weld structures. Hot spots stress is much more closer to the actual stress of a weld structure, it can suit the demand of high speed trains’ fatigue evaluation better. In this paper, on the basis of UIC615-4 standard, the nominal stress of the welded bogie frame was calculated and its fatigue strength was assessed using FEA method. Also, set the joint section between drawbar seat and the transom bottom flange as the object of the study, succeeded in evaluating the hot spot stress of the welded bogie frame. Compared the hot spot stress calculation result with the nominal stress from shell elements, the result shows that hot spot stress is higher than the nominal stress. Using the hot spot stress to assess fatigue has the higher reliability

Study on the Hot Spot Stress Distribution at Multi-Planar Tubular KK Joints Under Axial Loads

2011 ◽  
Author(s):  
Jingxia Yue ◽  
Jin Gan ◽  
Weiguo Wu ◽  
Shihong Zhai ◽  
Yanhua Yang
Keyword(s):  
Finite Element ◽  
Hot Spot ◽  
Fe Analysis ◽  
Axial Loads ◽  
T Joints ◽  
Hot Spot Stress ◽  
Essential Information ◽  
Tubular Joints ◽  
Jack Up ◽  
Initial Prediction

The Hot Spot Stress (HSS) distribution around welded tubular joints in truss legs is essential information for the fatigue assessment of jack-up platforms. Both Finite Element (FE) analysis and model test were carried out on a multi-planar tubular KK joints under asymmetric axial loads in our research. The study shows that the HSS distribution around welded joints is different from common K or T joints, and the maximum HSS appears between crown and saddle on the chord surface at the chord-brace intersection. Moreover, some sensitive factors which influence the locations of the maximum HSS were investigated by FEA in this paper. The analysis results are useful for the optimal structure designing and crack initial prediction of the offshore jack-up platforms legs.

DESIGN S-N CURVES FOR T-, K-, AND X-CONCRETE-FILLED STEEL TUBULAR JOINTS

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
I. Musa ◽  
F. R. Mashiri ◽  
X. Zhu
Keyword(s):  
Least Squares Method ◽  
Hot Spot ◽  
High Stress ◽  
Steel Tubes ◽  
Hot Spot Stress ◽  
Welded Steel ◽  
High Stress Concentration ◽  
Tubular Joints ◽  
American Society ◽  
Concrete Filling

High stress concentration at the weld vicinity in welded steel tubular joints results in fatigue failure. Researchers have tried finding an effective method to reduce these stresses. Although concrete filling of the steel tubes has been used to reduce stresses at the joints in the recent two decades, the fatigue performance of concrete filled tubular joints is not yet fully understood. This paper summarizes research on the fatigue strength of concrete-filled steel tubular T-, K-, and X-joints. Based on available experimental results, the nominal stress and hot spot stress design S-N curves for concrete-filled steel tubular joints have been derived. The least squares method is used in the derivation of the design S-N curves according to the American Society for Testing and Materials (ASTM) specifications.

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