Collapse Moment Research Articles

엘보우의 붕괴모멘트에 미치는 국부 감육결함의 영향

The purpose of this study is to investigate the effect of local wall thinning on the collapse of elbow subjected to internal pressure and bending moment. Thus, the nonlinear three-dimensional finite element analyses were performed to obtain the collapse moment of elbow containing various wall thinning defects located at intrados and extrados under two loading modes (closing and opening modes) with internal pressure. From the results of analysis, the effect of wall thinning defect on the global moment-rotation behavior of elbow was discussed, and the dependence of collapse moment of elbow on wall thinning depth, length, and circumferential angle was investigated under different loading mode and defect location.

Finite element modelling of plastic collapse of metallic single mitred pipe bends subject to in-plane bending moments

Theoretical analysis based on the finite element (FE) method for plastic collapse of metallic single mitred pipe bends of various geometries, subject to in-plane bending moment, were carried out using both ABAQUS and ANSYS structural FE programs covering both linear small displacement and non-linear large displacement analysis. Parametric surveys presented interesting features including an increase in plastic collapse in-plane bending moments after mitre angles of around 40°. Results obtained using either ANSYS or ABAQUS could not be compared against any available experimental data as they differ significantly in areas like strain hardening and other features of a real material that did not exist in the FE modelling. However, single case comparison with the only reported experimental work, known to the author, showed that large displacement FE analysis led to more realistic predictions. It is, therefore, concluded that despite complex behaviour of a real material as compared to material models available in FE analysis, effective plastic collapse moments can be predicted using the small displacement FE analysis.

718 T 継ぎ手配管の破壊強度に及ぼす局所減肉の影響

To investigate the fracture strength of Tee pipe with local wall thinning, for point bending tests were carried out using a Tee pipe with local wall thinning without internal pressure. Local wall thinning part is subjected either tensile or compressive stress. Three-dimensional elasto-plastic analyses were also carried out for the Tee pipe with local wall thinning by using Finite Element Method. It has been found that the fracture type is classified into ovalization or local buckling. However, the local wall thinning had no significant effect on the plastic collapse moment.

Parametric survey of upper and lower bound limit in-plane bending moments for single mitred pipe bends of various geometries

The problem of limit analysis for a cylinder–cylinder intersection forming a single mitred pipe bend subject to in-plane bending has been investigated. Lower bound analysis with new equations of force and moment equilibrium together with a higher number of parameters resulted in more stability as compared to a previous analysis of the same problem [PhD Thesis, The University of Manchester, 1991]. Concurrently, abaqus finite element plastic collapse moments were obtained as upper bounds to the problem. Two sets of results were compared, showing good agreement with each other. It could be finally concluded that the true limit moments are bounded in between.

Plastic Collapse Analysis of Slender Circular Tubes Subjected to Large Deformation Pure Bending

This paper presents a plastic mechanism analysis for thin-walled circular hollow section (CHS) tubes deforming in a multi-lobe or diamond collapse mode under large deformation pure bending. The fold formation process was such that the shell curvature flattened on the compression side transforming into a definite number of flat triangles attached to each other. The collapse proceeded progressively by folding about the base and sides of these triangular planes and over traveling hinge lines. The collapse mechanism was similar to the diamond crush mode. An existing kinematic model for an axially compressed thin-walled circular tube was modified to predict the collapse curve of a thin-walled tube under bending. Inextensional deformation and rigid plastic material behaviour were assumed in the derivation of the deformation energy. Ovalisation was observed during the test and its deformation energy was determined and found significant. An expression for the plastic collapse moment was obtained by equating the total energy absorbed in bending, rolling and ovalisation to the external work carried out during a given cycle of deformation. Comparisons of the predicted post-buckling moments and slopes of the collapse curves with those obtained from experiments carried out by the authors on cold-formed circular hollow sections show very good agreement.

Model of a viscous layer deformation by thermocapillary forces

Three-dimensional nonstationary flow of a viscous incompressible liquid is investigated in a layer, driven by a nonuniform distribution of temperature on its free boundaries. If the temperature given on the layer boundaries is quadratically dependent on horizontal coordinates, external mass forces are absent, and the motion starts from rest then the free boundary problem for the Navier–Stokes equations has an ‘exact’ solution in terms of two independent variables. Here the free boundaries of the layer remain parallel planes and the distance between them must be also determined. In present paper, we formulate conditions for both the unique solvability of the reduced problem globally in time and the collapse of the solution in finite time. We further study qualitative properties of the solution such as its behaviour for large time (in the case of global solvability of the problem), and the asymptotics of the solution near the collapse moment in the opposite case.

Fracture and general yield for carbon steel pipes with local wall thinning

Monotonic bending tests without internal pressure are conducted on 4 and 3.5 in. diameter full-scale carbon steel pipe specimens with local wall thinning in order to evaluate the structural integrity of power plant piping. The local wall thinning is simulated as erosion/corrosion metal loss. The eroded area of the wall thinning is subjected to tensile or compressive stress by applied bending moment. The maximum moments obtained from the tests are compared with the plastic collapse moments based on the net-section stress approach. The net-section stress approach based on flow stress σ f gives a conservative estimation, sometimes overly conservative. Although the net-section approach based on ultimate tensile strength σ u gives a slightly non-conservative estimation for some cases, the calculated values are close to the experimental data. Using the net-section stress approach based on σ u, the eroded depth and the angle at which a pipe undergoes general yielding were obtained.

The effect of internal pressure on in-plane collapse moment of elbows

Elastic–plastic finite element analysis has been carried out to evaluate collapse moments of six elbows with elbow factors varying from 0.24 to 0.6. Collapse moment is obtained by twice elastic slope method from the moment vs. end-rotation curve. The effect of internal pressure on in-plane closing/opening collapse moment is studied. For various elbow factors and level of internal pressure, total 60 and 54 cases are analysed for closing and opening mode of bending moment, respectively. Based on these results, two closed-form equations are proposed to evaluate the collapse moments of elbows under combined internal pressure and in-plane closing and opening bending moment.

Closed-Form Collapse Moment Equations of Elbows Under Combined Internal Pressure and In-Plane Bending Moment

Elastic-plastic finite element analysis has been carried out to evaluate collapse moments of six elbows with elbow factors varying from 0.24 to 0.6. The loading conditions of combined in-plane closing/opening bending moment and varying degree of internal pressure are considered in the analysis. For each case, collapse moment is obtained by twice elastic slope method from the moment versus end-rotation curve. Based on these results, two closed-form equations are proposed to evaluate the collapse moments of elbows under combined internal pressure and in-plane closing and opening bending moment. [S0094-9930(00)00103-7]

実大鉄骨梁の高温曲げ耐力に関する実験的研究

The load bearing capacities of steel simple beams in full-scale under elevated temperatures that are achieved by fire tests are discussed in this paper. The ISO standard and the other heating tests with loading were done for 17 specimens covered with some kind of thermal insulation. H-shape steelworks of the steelgrades of SS400 and SN400B which have several different section sizes specified in the JIS standard and the support spans of specimens are 6.951 or 5.1 meter. After the careful observation of tests results, authors concluded as followings: The collapse moments of the steel beams can be obtained from the test results of mean steel temperatures between 34℃ and 750℃ The deformation of the beam at a mid-span can be induced by load, steel temperature and some other parameters. Although the allowable temperature of a beam with the maximum service load of 16tonf/cm^2, is revealed to be less than 541℃ or so, the load capacities decreased with the temperature increase from 500℃ to 750℃

Bending Strength of Aluminum Rectangular Hollow Section T-joint.

Strength of welded T-joint of rectangular hollow section member of unequal width were studied under in plane and out of plane bending conditions. Rigid plastic model were used to get flange collapse moment. The solutions were checked by FEM, in various branch size, shape and thickness of chord tube web, and they were modified. The modified solutions were compared with the experiment of welded T-joint of 6063-T5 aluminum extrusions and good agreement were obtained.

Prediction of Mode Parameters and Moment-Rotation Curves for Crushed Thin-Walled Trapezoidal Tubes in Bending

In the context of kinematic models, a general procedure for the bending crush analysis of thin-walled members is proposed and applied to the trapezoidal and rectangular tubes in bending. The main emphasis of this study is given to the determination of collapse mode parameters and the prediction of post-collapse behaviors of the structural member. The mode shapes are determined by minimizing plastic energy rate of the members. Moment-rotation curves are obtained by differentiating the absorbed plastic energy with respect to the rotation angle. For small rotation angles the solution is modified by considering elastic buckling and plastic collapse moments. Through several examples a full range of post-collapse response of the thin-walled members is shown to be effectively calculated by the proposed method without making any recourse to experimental data.

Collapse of thick tubes under combined tension and bending

This paper presents FEM analyses of the collapse behaviour of thick tubes ( 10 < D 0 t < 40 ) under pure bending and combined tension and bending loads. Parameter studies of collapse moment and critical curvature for thick tubes under pure bending have been carried out to study the effects of diameter to thickness ratio D 0 t , yield parameter to Young's modulus ratio σ y E , strain-hardening parameter n and material anistropy parameter S. Formulae to predict collapse moment and curvature are derived based on the parameter studies. It has been confirmed that the model uncertainty of the derived equations is small. The responses of thick tubes under combined tension and bending have been studied. The effect of loading paths is presented. Criteria to determine ultimate collapse of tubes, e.g. limit load, extreme fibre strain and mean axial strain, are discussed. Parameric studies have been carried out on the effect of the collapse envelopes on diameter to thickness ratio D 0 t , material grade, strain-hardening parameter n and material anisotropy parameter S. Formulae for moment-tension, curvature-tension and curvature-axial strain envelopes are proposed based on the sensitivity study.

Fracture behaviour of stainless steel pipes containing circumferential cracks at room temperature and 280°C

The paper presents the experimental results of a research programme on fracture behaviour of austenitic stainless steel and TIG welds in pipes containing circumferential through-wall cracks at room temperature and 280°C. Pipes were loaded in pure bending using a four-point bend test method. The diameter of the pipes under investigation was 168 mm and 324 mm, with a thickness varying from 10 to 17 mm. As opposed to the behaviour of carbon steel pipes, it is found that the Net Section Collapse (NSC) criterion predicts the moment of instability. Crack mouth opening displacements (COD) and collapse moments calculated using the GE-EPRI engineering approach show a rather high scatter with respect to experimental results.

Elastic-plastic fracture analysis of carbon steel piping.

The elastic-plastic fracture of carbon steel piping having various pipe diameters and crack angles was analyzed using the latest CEGB R6 approach (R6 method) and ASME Screening Criteria (SC method). Results obtained are as follows: (1) It is necessary to apply the elastic-plastic fracture criterion instead of the plastic collapse criterion by increasing the pipe diameter and the crack angle, (2) For the standard pipes (from 6B to 26B), the plastic collapse criterion can stand within the crack angle of 24°. (3) The SC method gives a more conservative estimation than the R6 method. (4) A simplified elastic-plastic fracture analysis procedure based on the R6 method is proposed, where the unstable fracture moment can be calculated on the basis of the plastic collapse moment and the tabulated reduction factor.

Collapse Characteristics of a Thin-Walled Elbow: Validation of an Analytical Procedure

A nonlinear analysis procedure is validated in this paper to predict deformation response, up to collapse, of thin-walled Liquid Metal Reactor (LMR) piping elbows. Nonlinear shell analysis predictions are compared with experimental measurements of two full-scale large diameter (406 mm), thin-walled (D/t = 38), piping elbows tested at room temperature and at an elevated temperature in the Multi-Load Test Facility (MLTF) at Westinghouse. The overall and local deformation predictions agree very well with the measured deformation responses up to 60 percent of the measured plastic collapse moment, Mpce. The analytical-experimental correlation is reasonable up to 0.8 Mpce. At higher load levels the correlation is not as good; at collapse the analysis overpredicts measured deformations by as much as 30 percent.

The Local Buckling and Post Local Buckling Behaviour of Thin-Walled Beams

SummaryThis paper presents a theoretical analysis of the behaviour of thin-walled lipped channel beams subjected to end moments. In the analysis the beam section is assumed to be composed of a number of flat plates, joined at the edges. The mechanics of local instability of the walls of the beam are examined from a consideration of the strain energy stored in the component plates, and critical moments to cause local buckling are evaluated. The behaviour of the beam after local buckling is studied using a semi-energy method, whereby the stress and deflection systems throughout the section are linked by solving von Kármán’s compatibility equation for the component plates and the stress and deflection magnitudes are found from energy considerations. As collapse of the beam is approached, a simple plasticity analysis is incorporated in the theory in order to evaluate the collapse moment for the beam.The results of the analysis are compared with the findings of an extensive experimental investigation and it is shown that the theory is very accurate in its prescription of the experimental stresses and deflections. Comparison of the theoretical and experimental collapse moments also verifies the validity of the theoretical analysis.

Plastic Yielding of Single Notched Steel-Plates Due to Pure Bending

In the present paper, the problem of plastic yielding of notched steel plates subjected to pure bending is investigated experimentally. The test pieces examined are 0.34%C carbon steel plates which have a single wide notch with circular fillets. Six shapes of notches are examined. To clarify the effects due to the difference in the shape of notches, Lueders' bands and strain figures developed in the plates are observed in detail during the elastic-plastic stage of bending. The values of bending moment defined as the Limit or Collapse Moment are obtained for each notch. Constraint factor for each notch is given. They show the effects of the constraint of plastic deformation given by the neighbouring elastic regions.