1,721,003 research outputs found
A theoretical model for collapse of plate girders with perforated webs
No full textThe ultimate strength of plate girders with perforated webs under shearing and bending is investigated. The girders considered are transversely stiffened panels with aspect ratios (b/d) between 0.7 and 1.5. The holes in the webs are centrally located and they are of circular, rectangular and elongated shapes. The ultimate strength is determined using a theoretical model developed on the basis of stress fields and loading-carrying mechanism observed experimentally from test results and numerically from finite element calculations simplified to allow for the variation in panel and hole size. The predictions obtained from the theory are compared with experimental and numerical results available, and it is found that the theory provides reasonably accurate estimate
A parametric study of strength of tubular multiplanar KK-joints
No full textA parametric study of the static strength of circular hollow-section joints with the multiplanar KK configuration, commonly found in both onshore and offshore structures, is presented. The study, carried out using a well-calibrated and validated finite-element model, investigated the effects of the various geometric parameters on static strength. Particular attention was given to joints with low γ ratios, to where the amount of experimental data is scarce, to the effect of γ on strength, and to the influence of the two major failure modes. In all, a total of 50 joints were analyzed. The study has established a clear demarcation boundary between the two failure types as a function of the transverse gap between the braces. A strength database—compiled from the finite-element data generated and 37 existing test results—was used to formulate strength equations through multiple regression analyses. The equations were found to provide strength predictions to a very high degree of accuracy
Stress concentration factors in tubular K-joints under in-plane moment loading
No full textAn extensive parametric study is presented of the distributions of stress concentration factors in tubular K-joints commonly found in offshore platforms. The study covers a comprehensive range of geometric joint parameters for balanced in-plane moment loading. The results of the study were first used to assess two sets of widely used parametric equations, which predict the maximum stress concentration factors on the outer surfaces of the chord and the brace. The new database of finite-element results was then used to develop parametric equations for predicting stress concentration factors at key locations around the intersection on the outer as well as the inner surfaces of the chord. The reliability of the proposed and existing parametric equations was then assessed using an acrylic test joint database and some published test data measured from a steel model. Fracture mechanics fatigue calculations were also performed to demonstrate that the information provided from the proposed equations could be utilized to obtain accurate, and safe, fatigue life estimates
Prediction of weld toe magnification factors for semi-elliptical cracks in T-butt joints
No full textThis paper reports the background development of a set of equations for estimating weld toe magnification factors (Mk) for semi-elliptical cracks in T–butt joints. This set of equations has been included in the new British Standard BS 7910. The extensive finite element parametric study from which the database of Mk factors was generated is first reported. The parameters studied — crack depth and aspect ratios, attachment footprint, weld angle and weld toe radius — and the ranges covered are those likely to be found in real structures. The procedures for numerical modelling, analysis and stress intensity factor evaluation are described, and the effects of the various influencing parameters on the Mk factors are discussed. Estimation equations that were developed from multiple regression analyses of the database of Mk factors are detailed. The equations are shown, through statistical analyses, to be a very good fit to the database from which they were derived.<br/
Strength, stress and fracture analyses of offshore tubular joints using finite elements
No full textThe use of the finite element method for the analysis of offshore tubular joints is increasingly gaining popularity in both practical and research environments, as a result of the wide availability of powerful software and the rapidly falling computational costs. This paper reviews the modelling techniques used in the finite element analysis of tubular joints for obtained information on strength, stress fields and stress intensity factors. Guidance is given on model discretisation, choice of elements, material curve input, weld modelling, results interpretation and limitations of using numerical techniques. The information given will prove to be useful to both practitioners and researchers alike
Estimation of stress concentrations in single-sided welds in offshore tubular structures
No full textSingle sided welds commonly used for connecting braces to chords in tubular joints for offshore structures are known to have failed from cracks initiated at the root of the weld. There is currently no common industry standard to assess the fatigue performance of single-sided welds and hence guidelines on this issue are urgently needed. Fatigue assessment of single-sided welds requires knowledge of the stress concentrations in the weld root. The parametric study reported herein investigated the ratio of the maximum internal to maximum external weld SCF, the R ratio, in K-, Y-, X- and T-joints. The study, conducted using three-dimensional solid finite element models, generated a database of internal SCFs for the above joint types under axial, in-plane and out-of-plane bending loadings. Design equations for calculating R for each joint type for various loading modes, developed from multiple regression analyses, are proposed.<br/
Ultimate capacity of axially loaded multiplaner double k-Joints in circular hollow sections
No full textStress intensity factor solutions for semi-elliptical weld-toe cracks in T-butt geometries
No full textWeld toe magnification factors are widely used in the evaluation of stress intensity factors for cracks in welded structures. Traditionally, the weld magnification factor has been determined from 2-D plane strain models containing edge cracks. However, it has long been recognised that a semi-elliptical weld toe crack cannot be accurately represented by a 2-D approximation due to the 3-D nature of the geometry. As a consequence, some recent research has been carried out using 3-D numerical modelling, which highlights the limitations of the 2-D approach. Nevertheless, 3-D solutions are still scarce and are of limited validity due to the difficulties associated with creating the numerical models. This paper reports the most extensive 3-D numerical investigation of semi-elliptical cracks in T-butt geometries to date. Based on the numerical results, new and accurate equations for weld magnification factors were derived, which quantify the 3-D effects present and emphasise the importance of the attachment. The results obtained from these equations are then used in an assessment of existing solutions.<br/
Estimation of stress intensity factor solutions for weld toe cracks in offshore tubular joints
No full textThis paper proposes an engineering methodology for estimating stress intensity factor (K) Solutions for semi-elliptical weld toe cracks in tubular joints. The methodology uses the T-butt solutions proposed previously by the authors in conjunction with the joints. The estimated K factors are then compared stress concentration factors and the degrees of bending in the uncracked tubular with those obtained from a well-validated finite element procedure and the validity of the proposed methodology is demonstrated. A more refined way of calculating the uncracked stress field parameters which leads to more accurate predictions is also proposed. Fatigue crack growth calculations on experimental joints indicate that the proposed methodology is conservative
Parametric equations for distributions of stress concentration factors in tubular K-joints under out-of-plane moment loading
No full textAn extensive parametric study, using finite elements, of the stress concentration factors in tubular K-joints commonly found in offshore platforms is presented. This study covers a comprehensive range of geometric joint parameters for unbalanced out-of-plane moment loading. The results of the study were first used to assess the widely used parametric equations of Efthymiou (Proceedings of the Conference on Recent Developments in Tubular Joints Technology, Surrey, 1988, p. 2–1) and Lloyds Register (Proceedings of the 1st International Society of Offshore Polar Engineers Conference, 1991, Edinburgh), which provide predictions of stress concentration factors at the saddle on the outer surfaces of the chord and the brace as a function of the joint geometric ratios. The database of thin shell finite element results generated was then used to develop parametric equations for predicting stress concentration factors at key locations around the joint intersection on the outer, as well as the inner, surfaces of the chord. The reliability of the proposed and existing parametric equations was then assessed using the acrylic joint database published by the UK Department of Energy (Draft Background to New Fatigue Design Guidance for Steel Joints and Connections in Offshore Structures, 1995). The paper concludes with fracture mechanics fatigue calculations to demonstrate that the information provided from the proposed equations could be utilised to obtain accurate, and safe, fatigue life estimates
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