112 research outputs found
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
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
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/
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/
Numerical modelling of CHS joints with multiplaner double-K configuration
No full textA numerical study on the static strength of CHS (circular hollow section) joints with the multiplanar double-K configuration is presented. The aim of the work was to establish a valid and accurate finite element model for an extensive parametric study and to investigate the various factors which influence static strength. These factors included modelling the effect of the weld geometry, boundary conditions at chord and brace ends, mode of loading, chord length and material properties. The numerical results were rigorously calibrated against existing experimental data. The study has given an insight into the many aspects of elastic-plastic finite element analysis which is gradually replacing experimental testing as the main tool of research in tubular joint technology.<br/
Fatigue crack curvature under the weld toe in an offshore tubular joint
No full textExperimental tests on offshore tubular joints show that fatigue cracks, as well as curving around the brace/chord intersection, curve under the weld toe as they propagate through the chord wall. However, when producing stress intensity factor solutions for tubular joints, this curvature is usually ignored due to modelling difficulties. In this paper, detailed numerical models of surface cracks in tubular T-joints are used to simulate experimental observations of crack curvature reported in the literature. When compared with the experimental observations, the numerical results help to clarify the mechanism behind crack curvature. Based on the principal stress criterion, an approximate method for predicting crack curvature is proposed
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/
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