Fat classes of welded steel details derived from the master design curve of the peak stress method

In this paper, the peak stress method (PSM) is adopted to analyse the fatigue strength of steel welded joints. According to this method, a single design curve is expressed in terms of a properly defined equivalent peak stress and it is valid for fatigue design of arc-welded steel joints. Private companies often need simple finite element beam models for fatigue strength assessments, because of the large dimensions of the structures. However, beam elements provide nominal stresses (and not local stresses) that must be compared with appropriate fatigue strength values (the FAT classes) available in design standards. Due to the limited number of FAT classes available, finding the appropriate one is frequently troublesome, particularly when complex geometries are considered. The objective of this work is to define FAT classes in terms of nominal stress for a number of geometrically complex structural details, starting from the design curve of the PSM. FAT classes have also been determined using the hot spot stress approach. Then the results obtained with the two methods are compared. The structural details analysed in the present paper are typically adopted in amusement park structures and are not classified in common design standards

definition of nominal stress based fat classes of complex welded steel structures using the peak stress method

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Fatigue assessment of weld toe and weld root failures in steel welded joints according to the peak stress method

The peak stress method is an engineering, finite element (FE)-oriented application of the local approach based on the notch-stress intensity factors (NSIFs), which quantify the intensity of the local, linear elastic stress field at the potential crack initiation points (either the weld toe or the weld root). All effects due to plate thickness, joint shape and loading mode (axial or bending) are fully included in the NSIFs, such that a single design curve is sufficient to assess the fatigue strength of arc-welded joints in structural steels, tested in the as-welded conditions. The design stresses to analyse the fatigue strength are the peak stresses evaluated by FEM at the weld toe or the weld root, which are modelled as sharp notches with a tip radius equal to zero. The mean value of the FE size adopted to calculate the singular peak stresses can be chosen within a range of applicability, while the FE pattern of elements to use is the free mesh generated automatically by the Ansys\u2122 numerical code. Due to the rather coarse meshes required to apply the PSM and its suitability to be used directly with results of 3D FE analyses, the method is rather useful in everyday design practice

FATIGUE ASSESSMENT OF WELD TOE AND WELD ROOT FAILURES IN STEEL WELDED JOINTS ACCORDING TO THE PEAK STRESS METHOD

The Peak Stress Method is an engineering, FE-oriented application of the local approach based on the Notch-Stress Intensity Factors (N-SIFs), which quantify the intensity of the local, linear elastic stress field at the potential crack initiation points (either the weld toe or the weld root). All effects due to plate thickness, joint shape and loading mode (axial or bending) are fully included in the N-SIFs, such that a single design curve is sufficient to assess the fatigue strength of arc-welded joints in structural steels, tested in the as-welded conditions. The design stresses to analyse the fatigue strength are the peak stresses evaluated by FEM at the weld toe or the weld root, which are modelled as sharp notches with a tip radius equal to zero. The mean value of the FE size adopted to calculate the singular peak stresses can be chosen within a range of applicability, while the FE pattern of elements to use is the free mesh generated automatically by Ansys\uf0d4 numerical code. Due to the rather coarse meshes required to apply the PSM and its suitability to be used directly with results of three-dimensional FE analyses, it seems that the method is rather useful in the everyday design practise

Multiaxial fatigue assessment of welded steel details according to the peak stress method: Industrial case studies

In fatigue design of welded joints, the Peak Stress Method (PSM) is an engineering, rapid, finite element-based tool to apply the notch stress intensity factor (NSIF) approach. The PSM presents some advantages, such as: (i) coarse meshes can be adopted, the required FE size being some orders of magnitude larger than that necessary to evaluate the NSIFs from the local stress distributions; (ii) only a single stress value is sufficient to estimate the NSIFs; (iii) 2D as well as 3D FE models can be used and (iv) the design engineer is able to determine the crack initiation point when competition between weld root and weld toe failure exists. Therefore the PSM may be a convenient design tool to adopt in the industry. In the present paper, new fatigue results have been generated by testing plate-to-tube welded steel details taken from industrial case studies under in-phase bending-torsion fatigue loadings. In particular, full-penetration joints adopted in the structure of a roundabout-type carousel and fillet-welded joints for quarter-turn scotch-yoke valve actuators have been tested. Experimental fatigue results have been analysed using the PSM, which proved to identify correctly the fatigue crack initiation location. Finally, a fairly good agreement has been obtained between the experimental results and the relevant PSM-based design curves

Multiaxial fatigue assessment of welded steel details according to the peak stress method based on tetra elements

The Peak Stress Method (PSM) is an engineering, FE-oriented application of the notch stress intensity factor (NSIF) approach to fatigue design of welded joints, which takes advantage of the singular linear elastic peak stresses from FE analyses with coarse meshes. Originally, the PSM was calibrated by using 3D, eight-node brick elements, taking advantage of the submodeling technique. Recently, the PSM has been calibrated by using ten-node tetra elements, which are able to directly discretize complex 3D geometries without the need for submodels. The PSM was validated for pure axial or bending loadings as well as pure torsion loadings; recently it has been extended to multiaxial loadings by adopting a design stress, the so-called equivalent peak stress, in conjunction with a reference design fatigue curve. After having briefly recalled the calibration of the PSM with tetra elements, the paper presents some applications of the PSM relevant to steel plate-to-tube welded details of industrial interest under in-phase bending-torsion fatigue loadings. Experimental data have been re-analysed using the PSM based on tetra elements. Eventually a good agreement between experimental and theoretical results has been obtained in terms of fatigue crack initiation location as well as total fatigue life

Pasta Consumption and Connected Dietary Habits: Associations with Glucose Control, Adiposity Measures, and Cardiovascular Risk Factors in People with Type 2 Diabetes-TOSCA.IT Study

Pasta is a refined carbohydrate with a low glycemic index. Whether pasta shares the metabolic advantages of other low glycemic index foods has not really been investigated. The aim of this study is to document, in people with type-2 diabetes, the consumption of pasta, the connected dietary habits, and the association with glucose control, measures of adiposity, and major cardiovascular risk factors

Pasta Consumption and Connected Dietary Habits: Associations with Glucose Control, Adiposity Measures, and Cardiovascular Risk Factors in People with Type2 Diabetes-TOSCA.IT Study.

Background: Pasta is a refined carbohydrate with a low glycemic index. Whether pasta shares the metabolic advantages of other low glycemic index foods has not really been investigated. The aim of this study is to document, in people with type-2 diabetes, the consumption of pasta, the connected dietary habits, and the association with glucose control, measures of adiposity, and major cardiovascular risk factors. Methods: We studied 2562 participants. The dietary habits were assessed with the European Prospective Investigation into Cancer and Nutrition (EPIC) questionnaire. Sex-specific quartiles of pasta consumption were created in order to explore the study aims. Results: A higher pasta consumption was associated with a lower intake of proteins, total and saturated fat, cholesterol, added sugar, and fiber. Glucose control, body mass index, prevalence of obesity, and visceral obesity were not significantly different across the quartiles of pasta intake. No relation was found with LDL cholesterol and triglycerides, but there was an inverse relation with HDL-cholesterol. Systolic blood pressure increased with pasta consumption; but this relation was not confirmed after correction for confounders. Conclusions: In people with type-2 diabetes, the consumption of pasta, within the limits recommended for total carbohydrates intake, is not associated with worsening of glucose control, measures of adiposity, and major cardiovascular risk factors. Keywords: body mass index; cardiovascular risk factors; dietary habits; glucose control; pasta consumption; type 2 diabetes