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.

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.

Evaluation of stiffened shell characteristics from imperfection measurements

1987 ◽  
Vol 22 (1) ◽  
pp. 17-23 ◽  
Author(s):  
H Abramovich ◽  
R Yaffe ◽  
J Singer
Keyword(s):  
Cylindrical Shells ◽  
Data Bank ◽  
Laboratory Scale ◽  
Experimental Results ◽  
Geometric Imperfections ◽  
Buckling Loads ◽  
Stiffened Shell ◽  
Initial Geometric Imperfections ◽  
Stiffened Cylindrical Shells

The measurement of initial geometric imperfections of stringer-stiffened cylindrical shells on a laboratory scale is reviewed and recent results are presented. Buckling loads are predicted by the multimode analysis and are compared with experimental results. The concept and purpose of an international imperfection data bank is outlined and the activity of the Technion branch is described. An evaluation of the characteristics of shells from their measured imperfection record is attempted.

Numerical Study about Combined Effect of Distributed Initial Imperfections and Dent on Ultimate Strength of Square Plates under Uni-Axial Compression

2015 ◽  
Vol 813-814 ◽  
pp. 1037-1041 ◽  
Author(s):  
Duraikannou Peroumal ◽  
E. Sidhuvilaji ◽  
B. Prabu ◽  
A.V. Raviprakash
Keyword(s):  
Ultimate Strength ◽  
Axial Compression ◽  
Thick Plate ◽  
Numerical Study ◽  
Combined Effect ◽  
Geometric Imperfections ◽  
Buckling Strength ◽  
Initial Imperfections ◽  
Numerical Result ◽  
Local Dent

Aim of this present work is to study the combined effect of distributed geometric global imperfection and a local dent on buckling strength of thin square plates subjected to uni-axial compression. Steady state non linear FE analysis including both material and geometrical non linearities is used to determine the ultimate strength of the dented plates. From the numerical result it is found that in case of low thickness plates global geometric imperfections effect is more dominant and in case of thick plate dent effect is found to be more dominant.

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.

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