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.

scholarly journals Effects of plies orientations and initial geometric imperfections on buckling strength of a composite stiffened panel

2018 ◽  
Vol 191 ◽  
pp. 00008
Author(s):  
Ikram Feddal ◽  
Abdellatif Khamlichi ◽  
Koutaiba Ameziane
Keyword(s):  
Stiffened Panel ◽  
Buckling Mode ◽  
Element Analysis ◽  
Geometric Imperfections ◽  
Stiffened Panels ◽  
Specific Strength ◽  
Euler Buckling ◽  
Buckling Behavior ◽  
Composite Stiffened Panel ◽  
Strength And Stiffness

The use of composite stiffened panels is common in several activities such as aerospace, marine and civil engineering. The biggest advantage of the composite materials is their high specific strength and stiffness ratios, coupled with weight reduction compared to conventional materials. However, any structural system may reach its limit and buckle under extreme circumstances by a progressive local failure of components. Moreover, stiffened panels are usually assembled from elementary parts. This affects the geometric as well as the material properties resulting in a considerable sensitivity to buckling phenomenon. In this work, the buckling behavior of a composite stiffened panel made from carbon Epoxy Prepregs is studied by using the finite element analysis under Abaqus software package. Different plies orientations sets were considered. The initial distributed geometric imperfections were modeled by means of the first Euler buckling mode. The nonlinear Riks method of analysis provided by Abaqus was applied. This method enables to predict more consistently unstable geometrically nonlinear induced collapse of a structure by detecting potential limit points during the loading history. It was found that plies orientations of the composite and the presence of geometric imperfections have huge influence on the strength resistance.

Elastic buckling of imperfect circular toroidal shells under external pressure

1998 ◽  
Vol 212 (3) ◽  
pp. 197-209 ◽  
Author(s):  
G D Galletly
Keyword(s):  
External Pressure ◽  
Mode Shapes ◽  
Buckling Mode ◽  
Geometric Imperfections ◽  
Buckling Modes ◽  
The North ◽  
Buckling Resistance ◽  
Maximum Decrease ◽  
Initial Geometric Imperfections ◽  
Toroidal Shells

When perfect, externally pressurized complete circular toroidal shells buckle, the minimum buckling pressure pcr usually occurs in the axisymmetric n = 0 mode, with pcr for n = 2 being only slightly larger. In the present paper, the effects of axisymmetric initial geometric imperfections on reducing pcr for the perfect shell are investigated. Various types of imperfection are studied, i.e. localized flat spots, smooth dimples, sinusoids and buckling mode shapes. The principal geometry investigated was R/b = 10, b/t = 100, although other geometries were also considered. The maximum decrease in buckling resistance, Δ pcr, was found to be about 16 per cent at δ 0/t = 1 and it occurred with smooth dimples at the north (φ = 180°) and south (φ=0°) poles. This value of Δ pcr is not large. Circular toroidal shells thus do not appear to be very sensitive to axisymmetric initial geometric imperfections. The reductions in the buckling pressure of the above shell, arising because of initial imperfections having the shape of the n = 0 and the n = 2 buckling modes, were 12 and 9 per cent respectively for wo/t = 1. These decreases in the buckling resistance are smaller than that for the ‘two smooth dimple’ case mentioned above.

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 Numerical analysis of stability of the stiffened plates subjected aliquant critical loads

2020 ◽  
Vol 16 (1) ◽  
pp. 54-61
Author(s):  
Gaik A. Manuylov ◽  
Sergey B. Kositsyn ◽  
Irina E. Grudtsyna
Keyword(s):  
Numerical Analysis ◽  
Critical Loads ◽  
Geometric Nonlinearity ◽  
Compressive Load ◽  
Stiffened Plates ◽  
Geometric Imperfections ◽  
Initial Geometric Imperfections ◽  
Analysis Of Stability ◽  
The Stability

The aim of the work is to research the precritical and postcritical equilibrium of the stiffened plates subjected aliquant critical loads. Methods. The finiteelement complex MSC PATRAN - NASTRAN was used in the paper. To simulate the plates, flat four-node elements were used. Calculations taking into account geometric nonlinearity were carried out. The material of the shells was considered absolutely elastic. Results. A technique has been developed to study the stability of reinforced longitudinally compressed plates; the critical forces of the stiffened plates of various thicknesses had been calculated. Graphs of deflections dependences on the value of the compressive load had been constructed. The influence of initial geometric imperfections on the value of the critical loads for stiffened plates has been investigated.

Behaviour of cold-formed steel built-up battened columns composed of four lipped angles: Tests and numerical validation

2019 ◽  
Vol 23 (1) ◽  
pp. 51-64 ◽  
Author(s):  
M Anbarasu
Keyword(s):  
Cross Section ◽  
Finite Element Models ◽  
Test Results ◽  
Design Standards ◽  
Geometric Imperfections ◽  
The North ◽  
Compression Behaviour ◽  
Cold Formed Steel ◽  
Initial Geometric Imperfections ◽  
Box Columns

This article mainly investigates the behaviour and strength of built-up battened box column composed of lipped angles under axial compression. Ten specimens were fabricated and tested under pinned with warping-restrained end condition including two different cross-section dimensions of columns with five different geometric lengths. Three material tensile coupon tests were conducted to obtain the material properties of the steel used for fabricating the test specimens. The overall initial geometric imperfections were measured. The plate slenderness, member slenderness, chord slenderness and slenderness of batten plates may affect the compression behaviour of cold-formed steel built-up battened box columns and were accordingly investigated. It was found that the chord slenderness significantly affects the compressive strength of the built-up columns. Test results, including the compression resistances, the load versus displacement responses and the deformed shapes were presented. The test strengths were compared with the design strengths predicted using the North American Specifications (AISI-S100:2016), EuroCode (EN1993-1-3:2006) and design equations proposed by EI Aghoury et al. The design strengths predictions by these two design standards were unconservative, with EI Aghoury et al.’s standard performing better. Finite-element models were developed and verified against the test results.

Buckling of shallow torispherical domes subjected to external pressure — a comparison of experiment, theory, and design codes

1987 ◽  
Vol 22 (3) ◽  
pp. 163-175 ◽  
Author(s):  
G D Galletly ◽  
J Kruzelecki ◽  
D G Moffat ◽  
B Warrington
Keyword(s):  
External Pressure ◽  
Test Results ◽  
Spherical Cap ◽  
Initial Shape ◽  
Geometric Imperfections ◽  
Shell Buckling ◽  
Theoretical Predictions ◽  
Design Values ◽  
Initial Geometric Imperfections ◽  
Thickness Measurements

The test results obtained on 24 externally-pressurised torispherical steel shells are given in this paper. The knuckle radius-to-diameter ratio of the domes varied from 0.06 to 0.18 and the spherical cap radius-to-thickness ratios were between 75 and 335. Initial shape and thickness measurements were carried out on all the torispheres and a summary of this information is given. The BOSOR 5 shell buckling program was employed to predict the buckling/collapse pressures of all the domes; both perfect domes and those with axisymmetric imperfections were considered. The correlation between the theoretical predictions and the experimental results was, in general, very good. The main conclusions of the present investigation are: (i) that some of the experimental buckling pressures were lower than those obtained by multiplying the BS 5500 design values by a safety factor of 1.5, and (ii) that those torispheres with sharp knuckle radii failed by plastic collapse in the knuckle region and the collapse pressures were not very sensitive to initial geometric imperfections. It thus appears that the BS 5500 rules relating to the strength of shallow torispheres subjected to external pressure need to be amended, and that the tolerances on geometric shape for cases which are likely to be imperfection-insensitive should be reconsidered.

scholarly journals Nonlinear dynamics of spherical shells buckling under step pressure

2019 ◽  
Vol 475 (2223) ◽  
pp. 20180884 ◽  
Author(s):  
Jan Sieber ◽  
John W. Hutchinson ◽  
J. Michael T. Thompson
Keyword(s):  
Nonlinear Dynamics ◽  
External Pressure ◽  
Dynamic Buckling ◽  
Spherically Symmetric ◽  
Imperfection Sensitivity ◽  
Spherical Shells ◽  
Buckling Mode ◽  
Geometric Imperfections ◽  
Pressure Threshold ◽  
Initial Geometric Imperfections

Dynamic buckling is addressed for complete elastic spherical shells subject to a rapidly applied step in external pressure. Insights from the perspective of nonlinear dynamics reveal essential mathematical features of the buckling phenomena. To capture the strong buckling imperfection-sensitivity, initial geometric imperfections in the form of an axisymmetric dimple at each pole are introduced. Dynamic buckling under the step pressure is related to the quasi-static buckling pressure. Both loadings produce catastrophic collapse of the shell for conditions in which the pressure is prescribed. Damping plays an important role in dynamic buckling because of the time-dependent nonlinear interaction among modes, particularly the interaction between the spherically symmetric ‘breathing’ mode and the buckling mode. In general, there is not a unique step pressure threshold separating responses associated with buckling from those that do not buckle. Instead, there exists a cascade of buckling thresholds, dependent on the damping and level of imperfection, separating pressures for which buckling occurs from those for which it does not occur. For shells with small and moderately small imperfections, the dynamic step buckling pressure can be substantially below the quasi-static buckling pressure.

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