Accurate Determination of Plastic Collapse Loads From Finite Element Analyses

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
C. Doerich ◽  
J. M. Rotter
Keyword(s):  
Finite Element ◽  
Accurate Determination ◽  
Shell Structures ◽  
Collapse Mechanism ◽  
Plastic Shell ◽  
Plastic Collapse ◽  
Collapse Load ◽  
Plastic Limit ◽  
Elastic Plastic ◽  
Collapse Strength

When computational modeling is used to evaluate the true strength of an imperfect elastic-plastic shell structure, the current European standard on shell structures requires that two reference strengths are always determined: the linear bifurcation load and the plastic limit (plastic collapse) load. These two loads are used in more than one way to characterize the strength of all imperfect elastic-plastic systems. Where parametric studies of a problem are being undertaken, it is particularly important that these two loads are accurately defined, since all other strengths will be related to them. For complex problems in shell structures, it is not possible to develop analytical solutions for the plastic collapse strength, and finite element analysis must be used. Unfortunately, because a collapse mechanism often requires the development of very extensive plasticity involving large local strains, and the collapse load is simply at the end of a slowly rising load-deflection curve, it is sometimes difficult for the analyst to accurately determine this plastic collapse strength. This paper describes two methods, based on modifications of the Southwell plot, of obtaining very accurate evaluations of the plastic limit load, irrespective of whether a fairly complete plastic strain field has developed or not. These two methods allow plastic collapse limit loads to be reported with great precision.

Effect of Bend Angle on Gross Plastic Deformation of Pipe Bends: A Finite Element Based Study

2015 ◽  
Author(s):  
Anindya Bhattacharya ◽  
Sachin Bapat ◽  
Hardik Patel ◽  
Shailan Patel
Keyword(s):  
Plastic Deformation ◽  
Finite Element ◽  
Failure Mechanisms ◽  
Bending Moment ◽  
Bend Angle ◽  
Piping System ◽  
Plastic Collapse ◽  
Collapse Load ◽  
Pipe Bend ◽  
Bend Angles

Bends are an integral part of a piping system. Because of the ability to ovalize and warp they offer more flexibility when compared to straight pipes. Piping Code ASME B31.3 [1] provides flexibility factors and stress intensification factors for the pipe bends. Like any other piping component, one of the failure mechanisms of a pipe bend is gross plastic deformation. In this paper, plastic collapse load of pipe bends have been analyzed for various bend parameters (bend parameter = tRbrm2) under internal pressure and in-plane bending moment for various bend angles using both small and large deformation theories. FE code ABAQUS version 6.9EF-1 has been used for the analyses.

Comparison of Plastic Collapse Load of Isolated Piping Part and Pipe Run

2016 ◽  
Author(s):  
Wolf Reinhardt
Keyword(s):  
Analysis Approach ◽  
Plastic Collapse ◽  
Loading Conditions ◽  
Collapse Load ◽  
Plastic Model ◽  
Elastic Plastic ◽  
Load Redistribution ◽  
Load Combination ◽  
Collapse Analysis ◽  
The Common

The analysis of plastic collapse may be used in the fitness-for-service analysis of piping parts. Typically, such an analysis is performed by first determining the loads on the part in question by piping analysis, and then applying the load or load combination to an isolated elastic-plastic model of the part to obtain the collapse load. Plastic load redistribution that would occur if a plastic collapse analysis of the entire pipe run was performed is not considered in the common analysis approach. This paper compares the results of pipe run and piping part plastic collapse analyses for a typical illustrative example under various loading conditions.

Constraint Solutions for Cracked Plates and Cylinders

2016 ◽  
Author(s):  
Caroline Meek ◽  
Marius Gintalas ◽  
Andrew H. Sherry ◽  
Robert A. Ainsworth
Keyword(s):  
Finite Element ◽  
Stress Field ◽  
Biaxial Loading ◽  
Analytical Determination ◽  
Plastic Collapse ◽  
Finite Element Analyses ◽  
Elastic Plastic ◽  
Cracked Plates ◽  
Computing Effort

There is little advice in fitness for service procedures for assessing constraint parameters T (elastic) and Q (elastic plastic) for biaxially loaded plates and cylinders. This paper presents the analytical determination of T stresses for biaxially loaded plates and the determination of Q for plates and cylinders using finite element analyses. It demonstrates the extent to which T can be used to conservatively predict Q and how, near collapse, Q can be estimated from the stress field corresponding to plastic collapse, enabling a significant reduction in computing effort. The effect of biaxial loading of plates and cylinders on these parameters is discussed as well as the differences found when comparing the values for plates and cylinders.

Evolutive and Kinematic Limit Analysis Algorithms for Large-Scale 3D Truss-Frame Structures: Comparison Application to Historic Iron Bridge Arch

2019 ◽  
Vol 17 (05) ◽  
pp. 1940020 ◽  
Author(s):  
Rosalba Ferrari ◽  
Giuseppe Cocchetti ◽  
Egidio Rizzi
Keyword(s):  
Limit Analysis ◽  
Large Scale ◽  
Computational Time ◽  
Frame Structures ◽  
Collapse Mechanism ◽  
Displacement Curve ◽  
Plastic Collapse ◽  
Collapse Load ◽  
Structural Element ◽  
Plastic Mechanism

Two new computational algorithms for the Limit Analysis (LA) of large-scale 3D truss-frame structures recently proposed by the authors are reconsidered and adapted for a comparison prediction of the elastoplastic response of a strategic beautiful historic infrastructure, namely the Paderno d’Adda bridge (or San Michele bridge), a riveted wrought iron railway viaduct that was built in northern Italy in 1889. The first LA algorithm traces a fully exact evolutive piece-wise linear elastoplastic response of the structure, up to plastic collapse, by reconstructing the true sequence of activation of made-available plastic joints (as a generalization of plastic hinges), in the true spirit of LA. The second LA algorithm develops an independent kinematic iterative approach apt to directly determine the plastic collapse state, in terms of collapse load multiplier and plastic mechanism, based on the upper-bound theorem of LA. Specifically, the marvelous doubly built-in parabolic arch of the bridge is analyzed, under a static loading configuration at try-out stage, and its elastoplastic response is investigated, in terms of evolutive load-displacement curve, collapse load multiplier and plastic collapse mechanism. The two LA algorithms are found to much effectively run and perform, despite the rather large size of the computational model, with a number of dofs in the order of four thousands, by achieving good corresponding matches in terms of the estimate of the load-bearing capacity and of the collapse characteristics of the arch substructure, showing this to constitute a well-set structural element. Moreover, the direct kinematic method displays a rather dramatic performance, in truly precipitating from above onto the collapse load multiplier and rapidly adjusting to the collapse mode, in very few iterations, by a considerable saving of computational time, with respect to the complete evolutive elastoplastic analysis. This shall open up the way for further adoption of such advanced LA tools, with LA regaining a new momentum within the modern optimization analysis of structural design and form-finding problems.

scholarly journals Plastic limit load of ellipsoidal pressure vessel head with nozzle under internal pressure loading

2013 ◽  
Vol 18 (4) ◽  
pp. 1263-1274 ◽  
Author(s):  
V.N. Skopinsky ◽  
N.A. Berkov ◽  
A.B. Smetankin
Keyword(s):  
Finite Element ◽  
Internal Pressure ◽  
Limit Load ◽  
Rate Of Change ◽  
Pressure Loading ◽  
Plastic Limit ◽  
Elastic Plastic ◽  
Limit Pressure ◽  
Plastic Limit Load ◽  
Plastic Limit Pressure

Abstract A new method and numerical procedure for determining the plastic limit load in an ellipsoid-cylinder intersection using the elastic-plastic finite element analysis are presented. The proposed method is based on the maximum criterion of the rate of change of the relative plastic work. For the elastic-plastic analysis of the nozzle connections the 2D finite element method and plasticity theory with strain hardening are used. The results of the comparison of the plastic limit pressure obtained on the basis of different known criteria and the proposed criterion are presented. A parametric study of ellipsoidal heads with a nozzle under internal pressure loading was performed. The effects of nondimensional geometric parameters of shell intersection on the plastic limit pressure are discussed.

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