Types Of Axial Loading Research Articles

Degree of bending (DoB) in jack-up unit tubular KK-joints under the axial, in-plane bending (IPB), and out-of-plane bending (OPB) loads

ABSTRACT The determination of degree of bending (DoB) is critical to improve the accuracy of estimating fatigue life using stress life (S-N) method. Based on the truss structure of jack-up unit, the numerical model of tubular KK-joints including rack plate (thickness is 180mm) is established. In the present research, the data extracted from 378 FE analyses on 108 tubular KK-joints models were used to study the effect of geometric parameters on DoB values of KK-joints under six different types of axial loading, IPB and OPB loadings. The geometric parameters affecting the DoB of tubular KK-joints are analyzed by multiple nonlinear regression analysis, and 21 parameter design formulas are obtained to calculate the DoB values of tubular KK-joints under axial loadings, IPB and OPB loadings. The established geometric parameter equation can effectively evaluate the fatigue characteristics of truss legs with rack plate of jackup unit.

Local joint flexibility of multi-planar tubular TT-joints: Study of geometrical effects and the formulation for offshore design practice

Results of a parametric investigation carried out on the local joint flexibility (LJF) of multi-planar tubular TT-joints, also called two-planar DT-joints, are presented and discussed in this paper. A set of finite element (FE) analyses were conducted on 81 FE models subjected to two types of axial loading in order to study the effects of geometrical properties of the DT-joint on the LJF factor (fLJF). Developed FE models were validated using available experimental data and parametric equations. Results indicated that the increase of the γ leads to the increase of the fLJF; while the increase of the β and/or the τ leads to the decrease of the fLJF. In joints with bigger values of the γ, the increase of the β results in more drastic decrease of the fLJF. The amount of the fLJF change due to the increase of the parameter τ is much smaller compared to the other geometrical parameters. The fLJF values in two-planar DT- and uniplanar T-joints were compared. Results showed that the multi-planarity effect on the LJF is considerable and consequently the application of the equations already available for uniplanar T-joints to calculate the fLJF in two-planar DT-joints may result in highly over- or under-predicting results. To tackle this problem, FE results were used to derive a new parametric equation for the prediction of the fLJF in axially loaded two-planar DT-joints and the developed formula was checked against the UK DoE acceptance criteria.

Effects of geometrical parameters on the local joint flexibility (LJF) of three-planar tubular T-joints in offshore structures

ABSTRACT In this paper, the results of a parametric study conducted on the local joint flexibility (LJF) of three-planar tubular T-joints are presented and discussed. A set of finite element (FE) analyses were carried out on 81 FE models subjected to two types of axial loading in order to study the effects of geometrical characteristics of three-planar T-joint on the LJF factor (f LJF). Generated FE models were verified against available experimental data and parametric equations. The f LJF values in three-planar and uniplanar T-joints were compared. Results showed that the multi-planarity effect on the LJF is considerable and consequently the application of the equations already available for uniplanar T-joints to calculate the f LJF in three-planar T-joints may result in highly over- or under-predicting results. To tackle this problem, FE results were used to develop a new parametric formula for the prediction of the f LJF in axially loaded three-planar T-joints.

Effects of geometrical parameters on the degree of bending (DoB) in multi-planar tubular XT-joints of offshore structures subjected to axial loading

The degree of bending (DoB) characterizes the member through-the-thickness stress distribution which has a profound effect on the fatigue behavior of tubular joints commonly found in steel offshore structures and the determination of DoB values is essential for improving the accuracy of fatigue life estimation. Multi-planar joints are an intrinsic feature of offshore tubular structures and the multi-planarity might have a considerable effect on the DoB values at the brace-to-chord intersection. Nevertheless, for multi-planar joints which cover the majority of practical applications, much fewer investigations have been reported on the DoB due to the complexity and high cost involved. In the present research, data extracted from the stress analysis of 81 finite element (FE) models, verified using available parametric equations, was used to study the effects of geometrical parameters on the DoB values in multi-planar tubular XT-joints subjected to two types of axial loading. Parametric FE study was followed by a set of the nonlinear regression analyses to develop four new DoB parametric equations for the fatigue analysis and design of axially loaded multi-planar XT-joints.

Degree of bending (DoB) in offshore tubular KT-joints under the axial, in-plane bending (IPB), and out-of-plane bending (OPB) loads

Through-the-thickness stress distribution characterized by the degree of bending (DoB) has a major effect on the fatigue behavior of tubular joints commonly found in steel offshore structures. The determination of DoB values is essential for improving the accuracy of fatigue life estimation using the stress-life (S–N) method and particularly for predicting the fatigue crack growth based on the fracture mechanics (FM) approach. In the present research, data extracted from 648 finite element (FE) analyses carried out on 81 tubular KT-joint models was used to study the effects of geometrical parameters on the DoB values in KT-joints subjected to eight different types of loading including two types of axial loading, three types of in-plane bending (IPB) moment loading, and three types of out-of-plane bending (OPB) moment loading. Generated FE models were validated using experimental data, previous FE results, and available parametric equations. Geometrically parametric investigation was followed by a set of nonlinear regression analyses to develop 21 parametric design formulas for the calculation of the DoB in tubular KT-joints under the axial, IPB, and OPB loadings.

Static behavior of offshore two-planar tubular KT-joints under axial loading at fire-induced elevated temperatures

A total of 540 nonlinear steady-state finite element analyses were performed to study the influence of temperature and dimensionless geometrical parameters (β, γ, θ, and τ) on the ultimate strength, failure modes, and initial stiffness of two-planar tubular KT-joints. The joints were analyzed under two types of axial loading and five different temperatures (20 °C, 200 °C, 400 °C, 550 °C, and 700 °C). So far, there has not been any equation available for calculating the ultimate strength of two-planar tubular KT-joints at elevated temperatures. Hence, after parametric study, a set of design formulas were developed through nonlinear regression analyses, to calculate the ultimate strength of two-planar tubular KT-joints subjected to axial loading at elevated temperatures.

Probabilistic analysis of the DoB in axially-loaded tubular KT-joints of offshore structures

The degree of bending (DoB) characterizing the through-the-thickness stress distribution has a profound effect on the fatigue behavior of tubular joints commonly found in steel offshore structures and the determination of DoB values is essential for improving the accuracy of fatigue life estimation. Probability density functions of the involved random variables are necessary for the fatigue reliability analysis of offshore structures. The objective of present research was the derivation of probability density function (PDF) for the DoB in tubular KT-joints commonly found in jacket-type offshore platforms. A total of 162 finite element (FE) analyses were carried out on 81 FE models of KT-joints subjected to two types of axial loading. Generated FE models were validated using experimental data, previous FE results, and available parametric equations. Based on the results of parametric FE study, a sample database was prepared for the DoB values and density histograms were generated for respective samples based on the Freedman-Diaconis rule. Thirteen theoretical PDFs were fitted to the developed histograms and the maximum likelihood (ML) method was applied to evaluate the parameters of fitted PDFs. In each case, the Kolmogorov-Smirnov test was used to evaluate the goodness of fit. Finally, the Generalized Extreme Value model was proposed as the governing probability distribution function for the DoB. After substituting the values of estimated parameters, six fully defined PDFs were presented for the DoB in tubular KT-joints subjected to two types of axial loading.

Effects of geometrical parameters on the degree of bending (DoB) in two-planar tubular DT-joints of offshore jacket structures subjected to axial and bending loads

The fatigue life of tubular joints commonly found in offshore structures is not only dependent on the value of hot-spot stress (HSS), but is also significantly influenced by the through-the-thickness stress distribution characterized by the degree of bending (DoB). In the present research, data extracted from the finite element (FE) analyses carried out on 81 two-planar tubular DT-joint models was used to study the effects of geometrical parameters on the DoB values in DT-joints subjected to six different types of loading including two types of axial loading, two types of in-plane bending (IPB) moment loading, and two types of out-of-plane bending (OPB) moment loading. Generated FE models were validated using available parametric equations. The determination of DoB values in a tubular joint is essential for improving the accuracy of fatigue life estimation using the stress-life (SN) method and particularly for predicting the fatigue crack growth based on the fracture mechanics (FM) approach. Geometrically parametric investigation was followed by a set of nonlinear regression analyses to develop three DoB parametric formulas for the fatigue analysis and design of two-planar DT-joints.

Static strength of axially loaded tubular KT-joints at elevated temperatures: Study of geometrical effects and parametric formulation

This paper aims to study the structural behavior of tubular KT-joints subjected to axial loading at fire induced elevated temperatures. At first, a finite element (FE) model was developed and validated against the data available from experimental tests. Then, a set of 810 FE analyses were performed to study the influence of temperature and dimensionless geometrical parameters (β, γ, θ, and τ) on the ultimate strength and initial stiffness. The joints were analyzed under two types of axial loading and five different temperatures (20 °C, 200 °C, 400 °C, 550 °C, and 700 °C). Up to now, there has not been any design formula available for determining the ultimate strength of KT-joints at elevated temperatures. Hence, after parametric study, a new equation was developed through nonlinear regression analyses, for calculating the ultimate strength of KT-joints subjected to axial loading at elevated temperatures.

Local joint flexibility of two-planar tubular DK-joints in OWTs subjected to axial loading: Parametric study of geometrical effects and design formulation

Tubular DK-joint is one of the most common joint types in jacket substructure of offshore wind turbines (OWTs). Results of a parametric investigation carried out on the local joint flexibility (LJF) of two-planar tubular DK-joints under axial loading are presented and discussed in this paper. A total of 162 finite element (FE) analyses were conducted on 81 FE models under two types of axial loading in order to study the effect of the geometrical properties of the DK-joint on the LJF factor (fLJF). Developed FE models were validated based on the available experimental data, FE results, and parametric equations. The weld profile effects were also studied. The fLJF in two-planar DK- and uniplanar K-joints were compared. Results showed that the multi-planarity effect on the LJF is considerable and consequently the application of the equations already available for uniplanar K-joints to calculate the fLJF in two-planar DK-joints can result in highly over-predicting results. To tackle this problem, FE results were used to derive a set of parametric formulas for the prediction of the fLJF in axially loaded two-planar DK-joints and the developed formulas were checked according to the UK DoE acceptance criteria.

On finite element analysis of sling wire rope subjected to axial loading

This paper explores some aspects of finite element modeling of 7×19 IWS (wire rope with Independent wire strand core), as mostly used sling wire rope. First, the 1×19 stainless steel wire strand core was investigated. The numerical analysis was carried out by the finite element method. In this analysis two different types of contacts were investigated: bonded and frictional contact. The strand core was subjected to two different types of axial loading. The obtained results were compared with the solutions calculated from the available literature. Finally, using the advanced modeling techniques, the parametric 3D model of 7×19 IWS was also analyzed by using the finite element method, in order to provide a better understanding and, hence, prediction, of the mechanical behavior of the sling wire ropes.

3D FINITE ELEMENT MODELING OF SLING WIRE ROPE IN LIFTING AND TRANSPORT PROCESSES

Paper explores some aspects of 3D modeling of ‘aircraft cable’ as mostly used sling wire rope. First, the 1×19 stainless steel core of ‘aircraft cable’ was investigated. The analysis was carried out by finite element method based computer program. The software used allowed two different types of contacts, including friction. The sling wire rope core was subjected to two different types of axial loading. The obtained results were compared with the solutions calculated from the literature (Costello 2012). Finally, using the advanced modeling techniques, the parametric 3D model of 7×19 ‘aircraft cable’ was analyzed using finite element method, in order to provide a better understanding and, hence, prediction, of the mechanical behavior of the sling wire ropes in lifting processes.

On dynamic buckling of elastic–plastic beams

A theoretical study of dynamic buckling of elastic–plastic beams under compressive axial forces is presented. It is assumed that the loading process is so slow that axial inertia effects may be neglected. Four types of axial loading are considered. It is supposed that the beam's material has linear strain hardening. Equations of motion are derived from Hamilton's principle. A numerical method of integrating these equations is presented. The main aim of the paper is to shed light on the problem how the deflection shapes develop in the post-critical stage. For this purpose six examples are presented.