In-plane Bending Load Research Articles

Modeling Stress Concentration Factors for Fatigue Design of KT-Joints Subjected to In-Plane Bending Loads Using Artificial Neural Networks

Stress concentration factor (SCF) is an important parameter for the fatigue design of offshore joints. There are many empirical equations for quick estimation of SCF in tubular joints, based on experimental and numerical investigations. However, most of these equations apply at the crown and saddle points only, even though the maximum SCF may not always occur at these points, resulting in overestimated fatigue life. As the maximum SCF location varies due to multiplanar loads, damage, or reinforcement of joints, its location and magnitude are critical for a realistic fatigue life estimation. However, conventional statistical tools cannot approximate the complex behavior of SCF around the brace axis. On the other hand, artificial neural networks (ANN) can efficiently approximate complex phenomena. This study uses ANN to develop empirical models for determining SCF around the weld toe of KT-joints subjected to in-plane bending (IPB) loads. Eighteen hundred and fifty-eight (1858) designs were simulated using finite element analyses to generate data for training the ANN. Two IPB load conditions were focused on, and empirical equations were proposed for SCF around the chord side of the central brace-chord interface. These equations approximate maximum SCF with less than 5% error. This methodology applies to other joints and load configurations also.

Identification of probability distributions of SCFs in three-planar KT-joints

KT-joints are crucial in jacket platforms, providing structural integrity by effectively transferring loads between the main chord and braces. Their robust design ensures stability and durability in harsh offshore environments, preventing structural failures and enhancing the platform's overall safety and performance. This study presents the findings of finite element (FE) analysis conducted on 324 tubular three-planar KT-joints subjected to in-plane bending (IPB) loadings. The purpose of the research was to generate a probability distribution (PD) for the stress concentration factors (SCFs) under bending moments. To the authors' knowledge, no previous research has analyzed the PD of the maximum SCFs in three-planar KT-joints. Consequently, data representing the maximum SCFs were collected from the three-planar KT connections. The maximum likelihood method was used to determine the distribution parameters. The goodness-of-fit of the Generalized Extreme Value distribution was assessed using the Kolmogorov-Smirnov (KS) and Chi-square (CS) tests. The results indicated that this distribution is the most suitable for modeling three-planar KT-joints under IPB loading. In the subsequent stage, well-defined theoretical probability density functions (PDFs) and cumulative distribution functions (CDFs) were developed. Furthermore, probability-probability diagrams demonstrated that the proposed PD closely aligns with the observed data.

Stability design of multi-celled corrugated-plate CFST walls under combined axial and in-plane bending loads

Multi-celled corrugated-plate concrete-filled steel tubular (MC-CFST) walls are innovative steel-concrete composite walls comprising horizontally arranged corrugated steel plates, interval flat steel plates, and infilled concrete. Due to the significantly improved out-of-plane stiffness, the corrugated steel plate provides a considerable confinement effect on the infilled concrete, which enhances the structural efficiency and cost-effectiveness of MC-CFST walls. In this study, the stability performance of MC-CFST walls under combined axial and in-plane bending loads was investigated through extensive numerical simulations. A refined finite element (FE) model was established and validated using existing test results. Moreover, a formula for calculating the bending capacity of MC-CFST walls was also derived and validated against FE results. Additionally, parametric analyses were conducted to evaluate the effects of various factors such as the wall width, wall height, concrete strength, steel strength, and width of individual corrugated cells on the global stability performance. It was found that the stability performance was predominantly affected by the overall width of the wall rather than the width of the individual corrugated cells, with an increase in wall dimensions generally diminishing the stability performance. Furthermore, increasing the concrete strength improved the stability performance, while increasing the steel strength had a negative effect. Finally, a design formula was proposed for evaluating the bearing capacity and stability performance of MC-CFST walls under combined axial and in-plane bending loads. The formula demonstrated good agreement with the FE results, and it could provide a valuable reference for practical designs of MC-CFST walls.

Study on hysteresis performance of corroded CHS T-joints under in-plane bending load

This research aims to examine the hysteresis behavior of corroded circular hollow section (CHS) T-joints when subjected to cyclic bending loading. Quasi-static tests including the coupling of brace axial load and in-plane cyclic moment were conducted on corroded CHS T-joint specimens to analyze the effects of corrosion damage on the hysteresis curve, failure mechanism, carrying capacity, and energy dissipation of the joints. Experimental results indicated the corrosion damage located at the different regions of joints had varying effects on the hysteresis behaviors of CHS T-joints. 1) The brace corrosion degree was more severe than the chord corrosion degree under the same exposure condition, however, the chord corrosion had a more significant influence on reducing the stiffness and ultimate carrying capacity of CHS T-joints. The ultimate capacity of CHS T-joints was found to decline by more than 20 % when the equivalent thickness loss of the chord was about 9.2 %. 2) Compared with chord corrosion, the brace corrosion would relieve the concave deformation and local plastic deformation of the chord so that more plastic cyclic damage concentrated around the intersection line. As a result, the through cracks prematurely occurred from the crown points on both sides, and the energy dissipation of CHS T-joints declined by more than 25 % when the equivalent thickness loss of the brace was about 13 %. The presence of axial loading on the brace not only affects the symmetry of hysteresis curves in CHS T-joints with non-uniform corrosion, but also exacerbates the concave deformation of the chord in chord corroded joints during the failure stage, thereby affecting the shape of hysteresis loops and fracture behavior of CHS T-joints when subjected to in-plane cyclic bending load.

Shear-bearing capacity prediction of concrete-infilled double steel corrugated-plate shear walls

The concrete-infilled double steel corrugated-plate shear wall (CDSCW), consisting of two corrugated plates, infilled concrete, and two boundary elements, is a highly efficient force-resistant structural component under axial compression, in-plane bending, and shear loading. Previous research has primarily focused on the structural performance of CDSCWs under axial compression and bending loads. However, there is still a lack of a sufficiently accurate design method for predicting the shear-carrying capacity of CDSCWs. This paper presents numerical investigations into the shear buckling behavior of corrugated plates and proposes the shear strength design method of CDSCWs. Firstly, the shear elastic bilateral buckling behavior of corrugated plates subjected to lateral constraints of high-strength bolts is explored, considering influences of the bolt arrangement, the bolt spacing, and the dimensions of the plates. The formulas involving various buckling modes are established as a foundation for the further elastoplastic buckling capacity prediction. Then, by applying the normalized slenderness ratio, this study suggests the shear-carrying capacity design of the corrugated plates considering the bolt constraints and unilateral concrete constraint on the plates. Moreover, the shear-carrying mechanism of the CDSCWs is revealed: when CDSCWs experiences shear failure, the corrugated plates are primarily subjected to the shear load, with the boundary elements acting as constraints on the corrugated plates. Finally, a design method is proposed for the CDSCWs’ shear-carrying capacity prediction, which shows good accuracy and offers foundations for the stability design of corrugated plates under shear loads.

Experimental and numerical investigations on stress concentration factors of concrete filled steel tube X-joints.

An SHS-CFSHS X-joint is fabricated by welding two square hollow section (SHS) braces to a concrete-filled square hollow section (CFSHS) chord. In this paper, the stress concentration factors (SCFs) of SHS-CFSHS X-joints are investigated through experimental tests and finite element analysis (FEA), with the hot spot stress method serving as the analytical approach. Eight specimens are designed and manufactured, with FE models built in software ANSYS. These FE models are validated against the test results. The specimens are tested under brace axial tension to determine the SCFs of the X-joints. It shows that the concrete filled in the chord effectively reduces the SCFs of the X-joints. To further explore various load conditions and the influence of the parameters, FEA is carried out and a total of 64 FE models are built. Based on the FEA results, multiple regression analysis is used to obtain the SCF formulae of SHS-CFSHS X-joints under axial tension load and in-plane bending load in the brace, respectively. Comparison and analysis of the SCF results obtained from experimental tests, the proposed formulae, and FE simulations reveal that the formulae presented in this study are both conservative and suitable for predicting SCFs.

Structural Behaviour of FRP-Reinforced Tubular T-Joint Subjected to Combined In-Plane Bending and Axial Load

In this study, 90 finite-element models are used to explore the behaviour of fibre-reinforced polymer (FRP) reinforced joints under combined in-plane bending (IPB) and axial load (AX). The effects of joint geometry, FRP layer count, and AX levels of the chord or brace are considered. Three typical failure modes are observed: chord plastic failure, brace plastic failure, and brace buckling failure. Increasing the number of FRP layers can ensure that failure is chord-related failure in a ductility manner rather than the unexpectedly brace-related brittle failure. Depending on the stress distribution of fibres, FRP reinforcement can restrict the deformation of joints subjected to complex loading patterns. Moreover, added FRP layers efficiently reduce the effect of brace AX on the IPB resistance. Finally, a modified strength equation is established, including the influence of FRP reinforcement, chord AX, and brace AX.

Bending load effects on stress concentration factor distribution of multi-planar DTKY tubular joints

The stress concentration factor (SCF) in tubular joints is an important parameter in calculating the fatigue life of offshore structures. In design practices, estimating the SCF is usually based on standard empirical formulas, providing the majority for uni-planar tubular joints, and could not be applied directly for multi-planar joint cases. Therefore, accurate SCF estimation became critical for specific multi-planar tubular joints commonly found as members of offshore platforms. More detailed analyses of complex designs are possible with the recent development of finite element analysis and supported by advanced digital computers. Thus, this research is intended to analyze the SCF of multi-planar DTKY tubular joints with finite element analysis. The local model of the tubular joint will be simulated for bending moment load cases. The results show stress distribution characteristic of the joint at both brace and chord sides. The results indicated that the SCF of the joint under the in-plane bending (IPB) loading is higher at the brace than the chord side, with values of 2.83 and 1.47, respectively. Meanwhile, under the out-of-plane bending (OPB) loading, the SCF is 2.43 at the chord saddle location and 3.54 at the brace saddle location.

Design of functionally graded material to reduce stress concentration around semicircular notches for Inplane tensile and bending loads

Design of functionally graded material to reduce stress concentration around semicircular notches for Inplane tensile and bending loads

Damage sensitivity studies of composite honeycomb sandwich structures under in-plane compression and 4-point bending: Experiments and numerical simulations

Honeycomb sandwich structures, especially those with carbon-fiber panels and Nomex-honeycomb cores, are widely employed in automobiles and aircraft due to their excellent mechanical properties. Here, in-plane compression and 4-point bending experiments, as well as FEM simulations, are performed for a composite honeycomb sandwich structure with face-core de-bonding defects or impact damage to evaluate the damage sensitivity. It is found that the structure exhibits a higher sensitivity to impact damage than to de-bonding defects. Impact damage caused by an energy of 3 J–5.5 J can alter the failure mode under both in-plane compression and 4-point bending loads, and reduce in-plane compression strength by more than 50 % and 4-point bending strength by 15 %. In comparison, de-bonding defects of the same size can change the failure mode and decrease the strength by only 10 % under in-plane compression. The developed FEM model predicts all failure modes and residual strengths obtained from experiments. The simulation results show that the structural characteristics of producing concaves in the facesheet and core are the dominant contributors to structural failure. Our model, covering all geometric and structural details of the honeycomb core, provides a useful tool for studying the mechanical behaviors of such structures.

Analysis of Stress Concentration Factors due to in-Plane Bending and out-of-Plane Bending Loads on Tubular TY-Joints of Offshore Structures

The aim of this work is to study the stress distributions and the location of hot spots stress in the vicinity of the intersection lines of the tubular elements of the tubular TY-joints. Using the finite element models, we analyze the effects of geometrical parameters on the stress concentration factor in the case of in-plane bending and out-of-plane bending loads, around the weld toe of the tubular joints. Our results reveal the location of the maximum stress concentration factor at the heel or toe in the case of in-plane bending loads and at the saddle point in the case of out-of-plane bending loads. Six parametric equations are established and used to calculate the stress concentration factor at critical locations using the non-linear regression method. The results obtained from the finite element analysis are close to the results of the parametric equations and the experimental data from the previous work.

Study of matrix modifications by nano-clay on the mechanical properties of AA3003 honeycomb sandwich panels

Face/core debonding is one of the crucial problems of composite sandwich panels which consist of AA3003 aluminium honeycomb and glass fiber reinforced polymer face sheets. The panel was prepared by a hand-lay process at different nano-clay weight addition of 0%, 2%, 4%, and 6% with the objective of improving face/core adhesion. Interface bonding between face sheets and honeycomb core composite sandwiches and their mechanical behavior were investigated under in-plane compression and bending load. The flexural property of sandwich panels due to the influence of variation in strain rate is further determined. The morphologies of fractured samples were investigated by scanning electron microscope (SEM). The results revealed a significant improvement in mechanical characteristics when nano-clay was loaded to the composites at a concentration from 2 to 4 wt%, and the in-plane compression and flexural failure load values increased by 45% and 81%, respectively, when compared to a pristine sample. It was observed that increasing strain rate led to the increase in failure load of the sandwich panel. SEM images of fractured surfaces showed residual aluminium honeycomb was present in the face sheet, which indicates better adhesion between aluminium honeycomb core and face sheets.

SCFs in tubular X-connections retrofitted with FRP under in-plane bending load

This paper investigates the stress concentration factors (SCFs) in tubular X-connections retrofitted with fiber reinforced polymer (FRP) under in-plane bending moment. For this aim, a finite element (FE) model was generated and validated using available 13 experimental tests. After that, 276 FE models were created to investigate the effect of the FRP (layer number, orientation, and material) and the connection geometry (β, γ, and τ) on the SCFs. In these models, the contact between the FRP sheets and the steel members (chord, weld, and braces) was modeled. Results indicated that the rise of the FRP sheet number causes a notable drop in the SCFs. Also, the increment of the elastic modulus of FRP along the fibers causes a decrement of the SCF ratios. Moreover, the SCF in an X-connection retrofitted with CFRP can be down to 37% of that of the un-retrofitted connection. Despite the notable efficacy of the FRP sheets on the drop of the SCFs in the X-connections, there is not any study or equation on the X-joints with FRP. Therefore, a precise equation was proposed for quantifying the SCFs in X-connections with FRP. Also, the proposed equation was checked according to the UK DoE acceptance standard.

Chord plastification strength of longitudinal plate-to-CHS joints with steel grade up to 460 MPa under combined axial compression and in-plane bending

Up-to-date design rules for tubular joints with welded branch plate(s) were recently formulated in prEN 1993-1-8. The design rules cover joints of high-strength steel tubular members whose yield stress is up to 460 MPa by incorporating the material factor (or joint strength reduction factor). However, the background data for the specified material factor need to be further augmented. In this study, the material factor for steel grade 460 was further investigated based on an extensive test-validated numerical analysis. Longitudinal X- and T-type plate-to-circular hollow section (CHS) joints were considered in the analysis, and their nondimensional geometric parameters were carefully chosen to induce a ductile chord plastification failure only. For the loading conditions, the combined axial compression and in-plane bending (IPB) were included in addition to the individual loading case. It was first shown that when IPB loading is involved, the use of a widely accepted 3% deformation limit criterion often yields a conservative joint strength rating. A more reasonable criterion is proposed considering both the 3% indentation limit and an additional limit in terms of the joint rotation angle. With the new deformation limit criterion, the code-specified material factor (0.90) for steel grade 460 was found to be appropriate for the X- and T-joints regardless of the loading type. Meanwhile, it was also noted that the current design standards or guides do not provide an interaction relationship for the design of joints under combined axial compression and IPB. Based on the analysis results of this study, the use of a linear interaction equation is recommended for both mild and high-strength steel joints.

Stress concentration factors of multi-planar tubular KT-joints subjected to in-plane bending moments

Numerical research on the stress concentration factors (SCFs) in uniplanar tubular joints is abundantly reported in literature. However, it has been shown that SCF equations for uniplanar joints can lead to both under- or overestimation of the SCFs in multi-planar joints. In this paper, a parametric finite element study of 81 different three-planar KT joints subjected to five different in-plane bending loading conditions is performed. The effects of different non-dimensional geometrical parameters on the SCF values at the crown locations of the central and outer braces are studied. Based on nonlinear regression analyses of the finite element results, a new set of SCF equations is developed and presented.

Stress concentration factors in tubular T/Y-connections reinforced with FRP under in-plane bending load

Stress concentration factors (SCFs) in steel tubular T/Y-connections strengthened with fiber reinforced polymer (FRP) are investigated. In the first step, a finite element (FE) model was developed and verified using data of several available experimental tests and empirical formulas. After that, 134 FE models of T/Y-joints with and without FRP were created and analyzed under in-plane bending (IPB) load. In the FE models, the contact between the FRP layers and the members (chord, brace, and weld) was defined. Results showed that the increase of the FRP layer number leads to the notable decrease of the SCFs. Also, the SCFs of a T/Y-joint reinforced with FRP can be down to 40% of the SCF of the corresponding unreinforced joint. Finally, FE results were used to propose two parametric formulas for determining the SCFs in the T/Y-joints strengthened with FRP subjected to IPB load. The proposed formulas were checked according to the UK Department of Energy acceptance criteria.

Geometrical effects on the LJF of tubular T/Y-joints with doubler plate in offshore wind turbines

ABSTRACT In this study, the Local Joint Flexibility (LJF) of tubular T/Y-joints with doubler plate under in-plane bending (IPB) load is investigated. In the first step, a finite element (FE) model was developed and verified using the available experimental results. In the next step, 252 FE models were generated to investigate the effect of the joint geometry on the LJF factor (f LJF). Results showed that the increase of the doubler plate size results in the considerable decrease of the f LJF. Also, the f LJF of a T/Y-joint reinforced with doubler plate can be down to 26% of the f LJF of the corresponding unreinforced joint. Despite the considerable effect of the doubler plate on the f LJF, there is not any study on the f LJF of the tubular joints with doubler plate. Hence, after a parametric study, FE results were used to propose a parametric formula for determining the f LJF.

Moments around elliptical hole in a symmetric laminated composite plate under hygrothermal environment

Abstract In the present paper, solution of moment distribution around elliptical hole in symmetric infinite laminated plate is obtained. The solution is based on Lekhnitskii and Savin formulation considering in-plane bending moment at infinity and hygrothermal effects. The present solution is in close agreement with the existing literature. The parametric study to learn the effect of parameters like in-plane bending loading, volume fraction of fiber, temperature, moisture content and hole parameter (a/b ratio) on moment distribution around elliptical hole is presented. The unidirectional lamina properties are obtained using a micromechanical approach. The study revealed, under hygrothermal environment these factors affects the moment concentration.

Stress concentration factors of RHS T-connections with galvanizing holes under in-plane bending

The hot spot stress method recommended by the CIDECT Design Guide 8 cannot be directly used in the fatigue design of galvanized tubular steel connections since: (1) the hot-dipping process can sometimes significantly change the residual stress magnitude and distribution at the welded joint; and (2) sufficiently large vent and drain holes must be specified at the welded joint location prior to galvanizing, and quite often at the locations recommended by the design guide for calculation of hot spot stresses. Hence, the existing formulae and charts for determination of Stress Concentration Factors (SCFs) may not be applicable. In this study, Finite Element (FE) modelling was performed to examine the existing SCF formulae for welded rectangular hollow section (RHS) T-connections under brace in-plane bending. The FE models were validated by comparison of the experimental results from six large-scale connection tests. A parametric study including 192 FE models with varied hole locations, brace-to-chord width ratios, chord wall slendernesses, and brace-to-chord thickness ratios, shows that the existing SCF formulae can lead to unsafe predictions. Critical hot spot stress locations are thus identified. The effects of both brace in-plane bending and chord loading were studied. New design formulae that take the vent and drain holes into account are proposed. These formulae are shown to provide more accurate predictions of SCFs in such connections.

Local joint flexibility of CHS T/Y-connections strengthened with collar plate under in-plane bending load: Parametric study of geometrical effects and design formulation

In this paper, the Local Joint Flexibility (LJF) of the tubular T/Y-connections strengthened with collar plate under in-plane bending (IPB) load was investigated and compared to the LJF of the corresponding un-strengthened connections. In the first step, a finite element (FE) model was developed and validated against the results of experimental tests conducted in the present author's previous study, experimental tests carried out by other researchers, and available parametric equations. Afterward, a total number of 168 3-D finite element (FE) models were generated to investigate the effect of the connection geometry (β, γ, and τ), the angle between brace and chord (θ), and the collar plate size (η, τc) on the LJF factor (fLJF). Results showed that the increment of the η, τc, β, τ, and the reduction of the θ and γ result in the decreases of the fLJF. Also, the fLJF of a collar plate strengthened T/Y-connection can be down to 29% of the fLJF of the corresponding un-strengthened connection. Finally, FE results were used to propose a parametric formula for determining the fLJF of T/Y-connections strengthened with collar plate subjected to IPB load. Also, the proposed formula was checked according to the UK DoE acceptance standard.