A Simplified Model for the Effect of Weld-Induced Residual Stresses on the Axial Ultimate Strength of Stiffened Plates

The present work investigates the compressive axial ultimate strength of fillet-welded steel-plated ship structures subjected to uniaxial compression,in which the residual stresses in the welded plates are calculated by a thermo-elasto-plastic finite element analysis that is used to fit an idealized model of residual stress distribution.The numerical results of ultimate strength based on the simplified model of residual stress show good agreement with those of various methods including the International Association of Classification Societies(IACS)Common Structural Rules(CSR),leading to the conclusion that the simplified model can be effectively used to represent the distribution of residual stresses in steel-plated structures in a wide range of engineering applications.It is concluded that the widths of the tension zones in the welded plates have a quasi-linear behavior with respect to the plate slenderness.The effect of residual stress on the axial strength of the stiffened plate is analyzed and discussed.

A Computational Investigation of the Group Effect of Pits on the Ultimate Strength of Steel Plates

In this work, we focus on assessing the group effect of localized corrosion on the ultimate strength of the marine structural plates and study the load-deformation behaviors of plates of various slenderness and uniaxial compression.Meanwhile, we investigate different corroded patterns from a single circular pit to 25 circular pits distributed over the plate and carry out hundreds of nonlinear finite element simulations by combining the number, depth, distribution of pits with imperfections and slenderness of plate. The distribution of multiple pits causes scattering of stress concentration on the plate, then the plastic section of plate changes with wider distribution of damage simultaneously. The ultimate strength arises when un-loading zone comprised of the yielding strips and holes extends across the plate. It can be concluded that the corroded condition defined as group effect of pits manipulates the deformation state and the loading capacity of plate at the ultimate strength mode that coincides with the proportion of effective loading area and section in the process of post-buckling. To validate the effect of pits group, we perform the numerical experiments of the post-buckling of steel plates containing pits in a row with different orientation.

Reliability of the Ultimate Strength of Ship Stiffened Panel Subjected to Random Corrosion Degradation

Attentions have been increasingly paid to the influence of the corrosion on the ultimate strength of ship structures. In consideration of the random characteristics of the corrosion of ship structures, the method for the ultimate strength analysis of the ship stiffened panel structure subjected to random corrosion degradation is presented. According to the measured corrosion data of the bulk carriers, the distribution characteristics of the corrosion data for the stiffened panel on the midship deck are analyzed, and a random corrosion model is established. The ultimate strength of the corroded stiffened panel is calculated by lhe nonlinear finite element analysis. The statistical descriptions of the ultimate strength of the corroded stiffened panel are defined through the Monte Carlo simulations. A formula is proposed on the ultimate strength reduction of the stiffened panel as a function of the corrosion volume. The reliability analysis of the ultimate strength of the corroded deck stiffened panel is performed. It shows that both the corrosion data of the deck stiffened panel and the ultimate strength of the random corroded deck stiffened panel follow the log-normal distribution. The ultimate stress ratio of the stiffened panel is inversely proportional to the corrosion volume ratio.

Restoration of Ultimate Strength of Dented Hemispheres Under External Hydrostatic Pressure

This study aimed to restore the ultimate strength of dented stainless-steel hemispheres with a radius of 90 mm and a thickness of 0.86 mm.All of the hemispheres were subjected to external hydrostatic pressure.Small stainless-steel stiffened caps were used to eliminate the effect of indention on the ultimate strength.These caps had a radius of 36 mm,a thickness of 0.76 mm,and a height of 10.44 mm.Six hemispherical samples,including two intact hemispheres,two dented hemispheres without stiffening,and two dented hemispheres with stiffening,were prepared.Each hemi-sphere was geometrically measured for shape and thickness,hydrostatically tested for destruction,and numerically evaluated for comparison.The experimental and numerical data agreed well with each other.As a result,a spherical cap can effectively restore the ultimate strength of dented hemispheres under external hydrostatic pressure.The proposed restoration approach can be used to strengthen underwater pressure hulls with large local geometric imperfections.

ULTIMATE STRENGTH OF POSTBUCKLING FORSIMPLY SUPPORTED RECTANGULAR COMPOSITE THIN PLATES UNDER COMPRESSION

It is proved that the ultimate strength of postbuckling for simply supported rectangular composite thin plates under compression is far higher than their buckling stress through the tests of 283 rectangular composite thin laminates in this paper. The ultimate strength of the composite thin plates is studied using large-deflection theory and small-deflection theory of thin plates. According to the failure criterion of the composites ultimate strength is found finally. It is in accordance with the experimental values for the plates having 45 degrees off-axial, and for longitudinal and latitudinal plates, when beta < 0.11, the theoretical values are higher. The coefficient C given in this paper may be referred to in product designing.

Ultimate Strength Analysis of Offshore Jacket Platform

The ultimate strength analysis of offshore jacket platforms is a research project which has been developed in recent years. With the rapid development of marine oil industry, the departments of design and IMR (Inspection, Maintenance and Repair) in the offshore engineering have attached great importance to this project. The research procedure applies to both the stress check of new design platforms and the whole safety assessment of existing platforms. In this paper, we combine the pseudo non-linear technique with the linear analysis program and successfully analyze the ultimate strength of the space frame structure subject to the concentrated load and a real jacket platform subject to the dead load and environmental load.

A Simple Empirical Formula for Predicting the Ultimate Strength of Ship Plates with Elastically Restrained Edges in Axial Compression

An investigation is conducted on the static ultimate limit state assessment of ship hull plates with elastically restrained edges subjected to axial compression.Both material and geometric non-linearities were considered in finite element(FE)analysis.The initial geometric imperfection of the plate was considered,while the residual stress introduced by welding was not considered.The ultimate strength of simply supported ship hull plates compared well with the existing empirical formula to validate the correctness of the applied boundary conditions,initial imperfection and mesh size.The extensive FE calculations on the ultimate strength of ship hull plates with elastically restrained edges are presented.Then a new simple empirical formula for plate ultimate strength is developed,which includes the effect of the rotational restraint stiffness,rotational restraint stiffness,and aspect ratios.By applying the new formula and FE method to ship hull plates in real ships,a good coincidence of the results between these two methods is obtained,which indicates that the new formula can accurately predict the ultimate strength of ship hull plates with elastically restrained edges.

A useful guide of effective mesh-size decision in predicting the ultimate strength of flat-and curved plates in compression

The present study aims to determine the appropriate size of mesh or the number of the element(NoE)for flat-and curved plates,which is suggested to assess its safety subjected to axial compression based on the ultimate limit state(ULS)design and analysis concept.The unstiffened panel(=plate)and stiff-ened panel,considered primary members of ships and ship-shaped offshore structures,are subjected to repeated axial compression and tension caused by continued vertical bending moments applied to the hull girder.Plates are attached with stiffeners by welding,and 6,8 or 10 elements are generally rec-ommended to allocate in flat-plate’s breadth direction in between stiffeners for finite-element(FE)mod-elling,which enables the presentation of the shape of initial deflection applied to the plate.In the case of the load-shorting curve for curved plate,it is reported that the nonlinear behaviour characteristics,i.e.,snap-through,snap-back,secondary buckling and others,appear in typical flank angle.To take this into account,we investigated the preferred number of elements(6,8 or 10)generally applied to the flat plate whether it is an appropriate or more fine-sized element(or mesh)that should be considered.A useful guide is documented based on obtained outcomes which may help structural engineers select optimised mesh-size to predict ultimate strength and understand its characteristic of the flat and curved plates.

Effect of Strain Rate on Ultimate Strength and Fractograph in Tungsten Alloy

The effect of strain rate on ultimate strength and fractograph was investigated for tungsten alloy with four different technologies. As the strain rate rises, the ultimate strength increases and morphology of fracture surface gradually transits from detachment of interface between W pellets and matrices to cleavage of W pellets. Meanwhile, low strength tungsten alloy has higher sensitivity to strain rate.

Ultimate Compressive Strength Prediction for Stiffened Panels by Counterpropagation Neural Networks(CPN)

Stiffened Panels are important strength members in ship and offshore structures. A new method based on counterpropagation neural networks (CPN) is proposed in this paper to predict the ultimate compressive strength of stiffened panels. Compared with two-parametric polynomial, this method can take more parameters into account and make more use of experimental data. Numerical study is carried out to verify the validation of this method. The new method may find wide application in practical design.

Compressive Strength of Tubular Members with Combined Pitting Corrosion and Crack Damage

Tubular members subject to combined pitting corrosion and crack damage were numerically studied to clarify the reduction of ultimate strength and failure behavior,based on numerical models validated against available experi-ments.The effects of length,location and inclined angle of a crack under combined damage were studied to disclose the mechanism of interaction between the crack and corrosion pits.The methods,named as linear superposition directly accumulating the effects of solo crack and solo pitting damage,as well as crack projection transferring an inclined crack to a transverse one,were discussed and verified in the view of assessing ultimate strength of tubular members with combined damage.It was shown that the former is practical but complex while the next always over-estimates the residual strength.Besides,the location and inclined angle of a crack have a subtle effect on the reduction of ultimate strength under combined damage,especially at higher level of pitting damage,due to the synergistic effect between corrosion pits and cracks.Such effect can lead to early occurrence of plasticity and local buckling by inducing stress interaction between crack tips and pits,and causing more significant strength reduction compared with a solo type of damage.A practical method was proposed to determine the loss ratio of cross-sectional area on the equivalent weakest section of a damaged member.Based on the loss ratio,a formula was presented to predict the ultimate strength of damaged members with combined damage,showing good applicability.

Use of Plant-Based Accelerator to Enhance Rate of Gain of Strength of Kenyan Blended Cement

Concrete is the most widely used construction material in the world. The situation in the country is not an exception as most of the infrastructures in Kenya such as buildings, bridges, concrete drainage among others, are constructed using concrete. Sadly, the failure of buildings and other concrete structures is very common in Kenya. Blended Portland cement type 32.5 N/mm2 is the most widely used concrete binder material and is found in all parts of the country. Despite blended cement CEM 32.5 being the most commonly used cement type in construction industry in Kenya and most developing countries as a result of its low price and availability locally, its strength gain has been proven to be lower compared to when other types of cement are used due to quantity of pozzolanic material added to the blend. This paper outlines findings of an experimental investigation on the use of cypress tree extract as an accelerator to enhance rate of gain of strength on Kenyan blended cements. Six different blended cement brands locally available were used during the study. Cement chemical analysis was done using X-ray diffraction method while for the cypress extract, Atomic Absorption Spectrometer machine was used. Physical and mechanical properties were checked based on the British standards. The generation of the concrete mix design was done using the British DOE method and concrete was tested for the compressive strength at 7, 14, 21, 28, 56 and 90 days. It was observed that 15% dosage of the extract expressed as a mass percentage of the cement content gives the most improved compressive strength of concrete, 10.4% at 7 days and 9.5% at 28 days hence the optimum. It was further noted that when Cypress tree extract is used as an accelerator in the mix, the blended cement concrete achieves the design strength at 27 days saving 10 days of the project duration compared to when no accelerator is used while the ultimate strength is achieved at 67 days. The study therefore recommends the use of the cypress tree bark extract at a dosage of 15%, by mass, of the cement content as an accelerator when the structure is to be loaded at 28 days and waiting up to 39 days before loading the structure if no accelerator is used for blended cement concrete.

Influence of La-Ce Mischmetal on Dendritical Arm Space and Ultimate Tensile Strength in ZL105 Alloys

The influence of pure La, pure Ce, (La+Ce) mischmetal on the dendritical arm space(LDAS) of ZL105 alloy in cylinderical casting was studied. The effects of adding amount of (La+ Ce) mischmetal on LDAs and ultimate tensile strength(b) were investigated, and the relationship between b and LDAS was founded. (La+Ce) mischmetal has stronger ability to refine LDAs than pure La or pure Ce. The proper adding amounts of it is 0.15% (mass fraction). LDAs has a remarkable effect on ah of casting, which can be predicted by the regression equation obtained in this work.

An Improved Formulation for the Ultimate Static Strength of Tubular Joints subjected to Combined Loads

-'The effect of interaction of loads on the ultimate static strength of tubular joints of offshore fixed platforms, is a practical problem. But there is still absence of rigorous theory to explain available experimental data and empirical criteria for the static strength of tubular joints. The idea of yield at hot spot of tubular joints is introduced in this paper. The interaction equations of plastic capacity for the tubular joints under combined loads (two and three different kinds) are derived. Thereafter the Yura's test data and empirical criteria of ultimate static strength for the tubular joints can be explained. The idea of classification of category of loads in accordance with experimental data and the present theory is suggested. Finally, the improved ultimate capacity equations for tubular joints are recommended. The physical significance of the coefficient of plastic reservation Qp is discussed.

裂纹加筋和缺口加筋对钢加筋板极限强度的影响

This paper numerically evaluates the effect of the crack position on the ultimate strength of stiffened panels.Imperfections such as notches and cracks in aged marine stiffened panels can reduce their ultimate strength.To investigate the effect of crack length and position,a series of nonlinear finite element analyses were carried out and two cases were considered,i.e.,case 1 with thin stiffeners and case 2 with thick stiffeners.In both cases,the stiffeners have the same cross-section area.To have a basis for comparison,the intact panels were modeled as well.The cracks and notches were in the longitudinal and transverse direction and were assumed to be in the middle part of the panel.The cracks and notches were assumed to be through the thickness and there is neither crack propagation nor contact between crack faces.Based on the numerical results,longitudinal cracks affect the behavior of the stiffened panels in the postbuckling region.When the stiffeners are thinner,they buckle first and provide no reserved strength after plate buckling.Thus,cracks in the stiffeners do not affect the ultimate strength in the case of the thinner stiffeners.Generally,when stiffeners are thicker,they affect the postbuckling behavior more.In that case,cracks in the stiffeners affect the buckling and failure modes of the stiffened panels.The effect of notch was also studied.In contrast to the longitudinal crack in stiffeners,a notch in the stiffeners reduces the ultimate strength of the stiffened panel for both slender and thick stiffeners.

用于抵抗扭转采取边缘弹性约束下的单轴压缩下板材极限强度:一种新的综合方法

The ultimate strength of platings under compression is one of the most important factors to be addressed in the ship design.Current Rules for ship structural design generally provide explicit strength check criteria against buckling for simply supported and clamped platings.Nevertheless,ship platings generally exhibit an intermediate behaviour between the simple support and the clamped conditions,which implies that the torsional stiffness of supporting members should be duly considered.Hence,the main aim of this study is the development of new design formulas for the ultimate strength of platings under uniaxial compression,with short and/or long edges elastically restrained against torsion.In this respect,two benchmark studies are performed.The former is devoted to the development of new equations for the elastic buckling coefficients of platings with edges elastically restrained against torsion,based on the results of the eigenvalue buckling analysis,performed by Ansys Mechanical APDL.The latter investigates the ultimate strength of platings with elastically restrained edges,by systematically varying the plate slenderness ratio and the torsional stiffness of supporting members.Finally,the effectiveness of the new formulation is checked against a wide number of finite element(FE)simulations,to cover the entire design space of ship platings.

Static Analysis of Collision Strength of Offshore Platform

In this paper a numerical analysis method combining FEM incemental technique with limit analysis concept is proposed for the study of the static strength of offshore platform in collision. Large deformation and plasticity are accounted for and the limit yield surface expressed by generalized stress for a tubular section is derived. The modified stiffness matrix of space beam element is formulated by Plastic Node Method. The buckling behavior of beam columns can also be taken into account. It can trace the generation of plastic hinges during loading and finally the ultimate strength of offshore platform against collision is obtained.

Ductility and Ultimate Capacity of Concrete-Filled Lattice Rectangular Steel Tube Columns

A kind of concrete-filled lattice rectangular steel tube(CFLRST)column was put forward.The numerical simulation was modeled to analyze the mechanical characteristic of CFLRST column.By comparing the load-deformation curves from the test results,the rationality and reliability of the finite element model has been confirmed,moreover,the change of the section stiffness and stress in the forcing process and the ultimate bearing capacity of the column were analyzed.Based on the model,the comparison of ultimate bearing capacity and ductility between CFLRST column and reinforced concrete(RC)column were also analyzed.The results of the finite element analysis show that the loading process of CFLRST column consists of elastic stage,yield stage and failure stage.The failure modes are mainly strength failure and failure of elastoplastic instability.CFLRST column has higher bearing capacities in comparison with reinforced concrete columns with the same steel ratio.In addition,the stiffness degeneration of CFLRST column is slower than RC column and CFLRST column has good ductility.

Mechanical and Electrical Properties of Some Sn-Zn Based Lead-Free Quinary Alloys

Although there are many lead-free soldering alloys on the market, none of them have ideal qualities. The researchers are combining binary alloys with a variety of additional materials to create the soldering alloys’ features. The eutectic Sn-9Zn alloy is among them. This paper investigated the mechanical and electrical properties of Sn-9Zn-x (Ag, Cu, Sb);{x = 0.2, 0.4, and 0.6} lead-free solder alloys. The mechanical properties such as elastic modulus, ultimate tensile strength (UTS), yield strength (YS), and ductility were examined at the strain rates in a range from 4.17 10−3 s−1 to 208.5 10−3 s−1 at room temperature. It is found that increasing the content of the alloying elements and strain rate increases the elastic modulus, ultimate tensile strength, and yield strength while the ductility decreases. The electrical conductivity of the alloys is found to be a little smaller than that of the Sn-9Zn eutectic alloy.

Assessment of Aged Offshore Jacket Type Platforms Considering Environmental Loads and Degradation Parameters

Offshore steel structures are a common investment in oil and gas industries operating in shallow to medium depth seas.These structures have become increasingly popular since the mid-19th century,with a typical design life of 30-50 years.Despite their popularity,the structural integrity of existing offshore structures remains a controversial topic.Environmental loads and material degradation have been identified as significant factors that can compromise the structural integrity of offshore structures.To address this issue,this study aims to investigate the reserved strength capacity of a selected offshore structure located in the Malaysian Seas.The study will explore the effect of oceanographic data,variations in vertical load,and corrosion on the structure’s main members.To determine the impact of each variable on the reserved strength ratio(RSR)of the structure,several pushover analyses were conducted with different variables.Previous literature has shown little or no relationship between seawater wave height,gravity loads,and corrosion allowance on submerged steel members and the RSR of offshore structures.However,this study aims tofill this gap in knowledge by examining these variables’effects on the RSR of offshore structures.The study’sfindings indicate that even a slight increase in wave height can significantly impact the structure’s RSR due to the increase in lateral loading,potentially leading to severe damage to structural components and the foundation model.Additionally,gravity loads had an adverse effect on the RSR of the structure when more than double the vertical load was added.Corrosion allowance was also found to impact the RSR,particularly when assuming significant wall thickness corrosion in primary members.Overall,thefindings of this study have important implications for the design and maintenance of offshore structures.The results suggest that engineers and operators should pay close attention to the potential impacts of environmental loads,such as wave height and gravity loads,and material degradation,such as corrosion allowance,on the structural integrity of offshore structures.This information can be used to optimize the design and maintenance of offshore structures,leading to safer and more efficient operations.