Influence of Pipeline Misalignment on the Local Buckling Response

2008 ◽  
Author(s):  
Aiman Al-Showaiter ◽  
Farid Taheri ◽  
Shawn Kenny
Keyword(s):  
Wall Thickness ◽  
Parametric Analysis ◽  
Local Buckling ◽  
Welding Process ◽  
Transportation Systems ◽  
Geometric Imperfections ◽  
Strain Capacity ◽  
Initial Imperfections ◽  
Initial Geometric Imperfections ◽  
Comparison Of The Results

Pipeline transportation systems are generally constructed by connecting individual linepipe segments through joint-to-joint end girth welds. The mechanical behavior of shell structures, such as a pipeline, can be sensitive to initial imperfections in geometry, material properties and loading. These initial imperfections can affect the pipeline load-deformation response and reduce the limit moment and strain capacity. Initial geometric imperfections may result from fabrication processes, as related to variations in the pipeline diameter and wall thickness. These geometric imperfections may have circumferential and longitudinal variation. During the construction process, the initial geometric imperfections may be the result of end misalignment due to longitudinal pipeline offset and ovality. This study examines the influence of initial geometric imperfections associated with joint-to-joint misalignment that may be present due to the girth welding process when connecting pipeline segments. A parametric analysis was conducted using finite element methods to assess the effects of diameter-to-wall thickness ratio, internal pressure, axial force, misalignment amplitude, and misalignment orientation, on the local buckling response of pipelines. Through this parametric analysis, the moment-curvature response, variation in section geometry with increasing curvature, limit moment and strain capacity were all examined. Comparison of the results with those obtained from the engineering codes and recommended practice is also presented. This study concludes that offset misalignment orientation, with respect to the bending axis, and the increasing misalignment imperfection amplitude both affect the pipeline peak moment and global strain capacity at the limit moment.

Comparison of Numerical Results With Experiments on the Ultimate Strength of Long Stiffened Panels

2011 ◽  
Author(s):  
Mingcai Xu ◽  
C. Guedes Soares
Keyword(s):  
Numerical Analysis ◽  
Test Results ◽  
Buckling Mode ◽  
Geometric Imperfections ◽  
Geometric Nonlinearities ◽  
Stiffened Panels ◽  
Initial Imperfections ◽  
Linear Buckling ◽  
Initial Geometric Imperfections ◽  
Collapse Behavior

The behavior of long stiffened panels are simulated numerically and compared with test results of axial compression until collapse, to investigate the influence of the stiffener’s geometry. The material and geometric nonlinearities are considered in the simulation. The initial geometric imperfections, which affect the collapse behavior of stiffened panels, are also analyzed. The initial imperfections are assumed to have the shape of the linear buckling mode. Four types of stiffeners are made of mild or high tensile steel for bar stiffeners and mild steel for ‘L’ and ‘U’ stiffeners. To produce adequate boundary conditions at the loaded edges, three bays stiffened panels were used in the tests and in the numerical analysis.

Effects of Initial Geometric Imperfections on the Stability of Steel-Concrete Composite Ribbed Shell

2011 ◽  
Vol 243-249 ◽  
pp. 7001-7004 ◽  
Author(s):  
Ling Ling Wang ◽  
Yu Zhen Chang
Keyword(s):  
Critical Load ◽  
Single Layer ◽  
Displacement Curve ◽  
Element Analysis ◽  
Geometric Imperfections ◽  
Initial Imperfections ◽  
Mode Method ◽  
Ribbed Shell ◽  
Instability Regions ◽  
Initial Geometric Imperfections

The paper proposed a new system of spatial structure: steel- concrete composite ribbed shell, and briefly compared the three analysis methods considering the initial imperfections of structures: the random imperfection mode method, the consistent imperfection mode method and the improved random imperfection mode method. By using of the consistent imperfection mode method and nonlinear finite element analysis software ANSYS, we analyzed a composite steel-concrete ribbed shell with the span of 40m and span ratio f/L=1/4, which is simply supported at its surrounding and is subjected to uniform loading along it’s whole span. The critical load and instability regions of this shell are presented. The results show that with the increasing of the initial imperfections, the value of critical load decreased from 27% to 36%; the trend of load-displacement curve and the location of structural instability regions remain unchanged, only the shape of instability regions will change. This indicted that the effect of the initial imperfections within composite ribbed shell is far less than its influence to the single-layer shell. The steel-concrete composed ribbed shell is not sensitive to the initial geometric imperfections and shows a strong post-buckling performance.

Thermal Buckling of Offshore Pipelines

1988 ◽  
Vol 110 (4) ◽  
pp. 355-364 ◽  
Author(s):  
G. T. Ju ◽  
S. Kyriakides
Keyword(s):  
Temperature Rise ◽  
Coulomb Friction ◽  
Thermal Buckling ◽  
Pipe Material ◽  
Rigid Foundation ◽  
Geometric Imperfections ◽  
Offshore Pipelines ◽  
Initial Imperfections ◽  
Initial Geometric Imperfections ◽  
Surrounding Soil

The vertical buckling of offshore pipelines caused by thermal loads is analyzed by modeling the pipeline as a long heavy beam resting on a rigid foundation. The axial restraint provided to the line by the surrounding soil is modeled as Coulomb friction. The study is concerned with the effect of localized, small initial geometric imperfections on the response and stability of the structure. In the presence of initial imperfections, the response is characterized by the temperature rise required to cause initial uplift and by a limit temperature rise beyond which the structure becomes unstable. Both of these critical values are shown to be sensitive to the form and magnitude of the imperfections as well as by the pipe material inelastic characteristics.

ELASTIC BUCKLING OF EXTERNALLY-PRESSURIZED IMPERFECT TOROIDAL SHELLS

2001 ◽  
Vol 01 (01) ◽  
pp. 31-45 ◽  
Author(s):  
GERARD D. GALLETLY
Keyword(s):  
Initial Imperfection ◽  
External Pressure ◽  
Elastic Buckling ◽  
Geometric Imperfections ◽  
Buckling Modes ◽  
Initial Imperfections ◽  
Numerical Studies ◽  
Initial Geometric Imperfections ◽  
Sinusoidal Buckling ◽  
Toroidal Shells

This paper summarizes the results of numerical studies into the effects of initial geometric imperfections on the elastic buckling behaviour of steel circular and elliptic toroidal shells subjected to follower-type external pressure. The types of initial imperfection studied are (a) axisymmetric localized ones and (b) sinusoidal buckling modes. The principal localized imperfections studied are (i) circular increased-radius "flat spots" and (ii) smooth dimples. The buckling pressures pcr of circular toroidal shells were not very sensitive to initial imperfections. With elliptic toroids, whether the shell was sensitive to initial imperfections or not depended on the ratio k(≡ a/b) of major to minor radii of the section. The shells on the ascending part of the pcr versus k curve behaved like circular toroidal shells, i.e. they were not sensitive to initial imperfections. However, the behaviour of elliptic toroids on the descending part of the versus k curve was very different. The numerical results quoted in the paper are for limited ranges of the geometric parameters. It would be useful to extend these ranges, to explore the effects of plasticity and to conduct model tests on imperfect steel models to verify the conclusions of the numerical studies.

scholarly journals Design Forces of Horizontal Braces Unlocated at Middle of Columns considering Random Initial Geometric Imperfections

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Jinyou Zhao ◽  
Junming Wei ◽  
Jun Wang
Keyword(s):  
Parametric Analysis ◽  
Column Height ◽  
Design Codes ◽  
The Finite Element Method ◽  
Geometric Imperfections ◽  
The Monte Carlo Method ◽  
Eurocode 3 ◽  
Out Of Plane ◽  
Current Design ◽  
Initial Geometric Imperfections

The horizontal bracing forces of column-bracing systems derived from past studies and current design codes were considered only located at middle of columns. Actually, the horizontal braces used to reduce the out-of-plane effective column lengths are frequently designed not to locate at middle of columns. In this paper, a large number of column-bracing systems with the horizontal braces unlocated at middle of columns were modelled and analyzed using the finite element method, in which the random initial geometric imperfections of both the columns and the horizontal braces unlocated at middle of columns were well considered by the Monte Carlo method. Based on the numerical calculations, parametric analysis, and probability statistics, the probability density function of the horizontal bracing forces was found, so that the corresponding design forces of horizontal braces unlocated at middle of columns were proposed which were compared with the design mid-height horizontal bracing forces in the previous study and the relevant codes. The results indicate that the design forces of the horizontal braces located at 0.6 column height are smaller than the mid-height horizontal bracing forces in the previous study while the design forces of horizontal braces located at 0.7 column height are larger than the mid-height horizontal bracing forces in the previous study. The proposed design forces of the horizontal braces located and unlocated at middle of columns are both smaller than the mid-height horizontal bracing forces stipulated in GB50017-2017, Eurocode 3-1992, and AS4100-1998. The above conclusions provide references for the engineering applications and further related code revisions.

Collapse of Deepwater Pipelines

1988 ◽  
Vol 110 (1) ◽  
pp. 1-11 ◽  
Author(s):  
M. K. Yeh ◽  
S. Kyriakides
Keyword(s):  
Wall Thickness ◽  
External Pressure ◽  
Full Scale ◽  
Stress Strain ◽  
Steel Tubes ◽  
Geometric Imperfections ◽  
Circular Shape ◽  
Geometric Deviations ◽  
Initial Geometric Imperfections ◽  
Grade Steel

The paper describes a series of full-scale collapse experiments using X-42 and X-65 grade steel tubes. The initial geometric imperfections of the tubes were measured using a specially designed scanning facility prior to collapsing them under external pressure. Geometric deviations from a circular shape were recorded at 90 points around the circumference. The wall thickness was also recorded at the same points. At least 31 circumferential scans were made over lengths of 9 diameters. The stress-strain characteristics in the axial and circumferential directions were measured for each tube. The measured parameters were used to calculate numerically the collapse pressures of the tubes. The biggest deviation between the experimental and calculated values was less than 8 percent. These are compared with the results obtained from the same analysis using various idealized imperfection measures.

scholarly journals Initial Geometric Imperfections: A Robust, Closed-Section Cold-Formed Box Profile Application Subject to Local Buckling

2021 ◽  
Vol 26 (1) ◽  
pp. 18-44
Author(s):  
N. Brambatti Junior ◽  
M. Walber ◽  
A.D. de Meira Junior
Keyword(s):  
Numerical Models ◽  
Experimental Testing ◽  
Local Buckling ◽  
Deformation Mode ◽  
Buckling Mode ◽  
Technical Literature ◽  
Geometric Imperfections ◽  
Open Section ◽  
Initial Geometric Imperfections ◽  
Object Of Study

AbstractInitial geometric imperfections are important for simulating local buckling in numerical models. References are found in the technical literature regarding open-section cold formed profiles. This work presents new procedures applied to a robust and closed-section cold formed profile subject to local buckling, and the use of procedures described in the technical literature already successfully used for open section profiles. The difference of this work in relation to the research already carried out is in the type of profile studied, in the mode of failure of the same and in the form of determination of the initial imperfections. The object of study of this work is a closed-section cold formed box profile with a short length when compared with its cross section and with local buckling failure mode. The strategies used in the present work to consider the initial geometric imperfections were to perform the linear stability analysis using the finite element method to obtain the local buckling mode that represents the deformed box profile geometry, to apply a multiplication factor in the displacements, replace the new geometry node coordinates for all profile nodes to induce the local buckling deformation mode, with model validation through experimental testing and the Effective Width Method (MLE) (ABNT NBR 14762 [1]). Finally, using the results of the collapse load of the experimental trial as a basis, it was possible to compare the results obtained by MLE and MEF. Thus, the presentation of this work used a methodology that describes the local buckling behavior and verified the precepts of the existing norms on the subject, combining theoretical and experimental methods, as they bring a better understanding of the structural problem in question.

Hybrid Randomness of Initial Imperfections and Axial Loading in Reliability of Cylindrical Shells

2010 ◽  
Vol 77 (3) ◽  
Author(s):  
Isaac Elishakoff ◽  
Lova Andriamasy ◽  
Maurice Lemaire
Keyword(s):  
Cylindrical Shells ◽  
Axial Loading ◽  
Combined Effect ◽  
Geometric Imperfections ◽  
Initial Imperfections ◽  
Applied Loading ◽  
Initial Geometric Imperfections

This study investigates the combined effect of randomness in initial geometric imperfections and the applied loading on the reliability of axially compressed cylindrical shells. In order to gain insight we consider simplest possible case when both the initial imperfections and the applied loads are uniformly distributed. It is shown that hybrid randomness may increase or decrease the reliability of the shell if the latter is treated, experiencing the sole randomness in initial imperfections.

scholarly journals Some aspects of consideration of initial imperfections in the calculations of stability of thin-walled elements of open profile

2021 ◽  
pp. 122-128
Author(s):  
Ivan Okhten ◽  
Olha Lukianchenko
Keyword(s):  
Middle Surface ◽  
Stability Loss ◽  
Critical Force ◽  
The Finite Element Method ◽  
Geometric Imperfections ◽  
Initial Imperfections ◽  
General Stability ◽  
Initial Geometric Imperfections ◽  
Linear And Nonlinear ◽  
The Stability

Performed analysis of the initial geometric imperfections influence on the stability of the open C-shaped bars. Test tasks were solved in MSC Nastran, which is based on the finite element method. Imperfections are given in different formulations: the general stability loss of an ideal bar, of wavy bulging of walls and shelves, of deplanation of a bar. To model imperfections, has been developed a program which for the formation of new coordinates of the nodes of the "deformed" model, the components of a vector similar to the form of stability loss are added to the corresponding coordinates of the middle surface of the bar. In this way, you can set initial imperfections in the forms of stability loss of the bar with different amplitude. Researches made with different values of the imperfection amplitude and eccentricity of applied efforts. All tasks are performed in linear and nonlinear staging. The conclusion is made regarding the influence of initial imperfections form and imperfection amplitude on the critical force in nonlinear calculations. It was found that the most affected are imperfections, which are given in the form of total loss of stability. It was revealed the influence of the imperfection amplitude on the magnitude of the critical force for such imperfections. The influence of imperfections amplitude given in the form of wavy bulging walls and in the form of deplanations is not affected on the value of the critical force.

Appraisal of Allowable Loads by Simplified Rules

1986 ◽  
Vol 108 (2) ◽  
pp. 131-137
Author(s):  
D. Moulin
Keyword(s):  
Experimental Investigation ◽  
Plastic Region ◽  
Thin Structures ◽  
Geometric Imperfections ◽  
Buckling Behavior ◽  
Simplified Method ◽  
Post Buckling ◽  
Initial Geometric Imperfections ◽  
Fast Breeder Reactors ◽  
Breeder Reactors

This paper presents a simplified method to analyze the buckling of thin structures like those of Liquid Metal Fast Breeder Reactors (LMFBR). The method is very similar to those used for the buckling of beams and columns with initial geometric imperfections, buckling in the plastic region. Special attention is paid to the strain hardening of material involved and to possible unstable post-buckling behavior. The analytical method uses elastic calculations and diagrams that account for various initial geometric defects. An application of the method is given. A comparison is made with an experimental investigation concerning a representative LMFBR component.

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