Search

PurposeReliable estimations of the extent of corrosion and time required to reach specific safety limits are crucial for assessing the reliability of aging reinforced concrete (RC) bridges. Engineers and decision-makers can use these figures to plan suitable inspection and maintenance operations.Design/methodology/approachAnalytical, empirical and numerical approaches for estimating the service life of corroded RC structures were presented and compared. The concrete cover cracking times, which were predicted by the previously proposed analytical models, were compared with the experimentally obtained cracking times to identify the model/s for RC bridges. The shortcomings and limitations of the existing models are discussed.FindingsThe empirical models typically depend on the rate of corrosion, diameter of steel reinforcement and concrete cover depth and based on basic mathematical formula. In contrast, the analytical and numerical models contain the strength and stiffness properties of concrete as well as type of corrosion products and incorporate more complex mechanical factors. Four existing analytical models were analyzed and their performance was evaluated against existing experimental data in literature. All the considered analytical models were assumed thick-walled cylinder models. The maximum difference between observed cracking time from different test data and calculated cracking time using the developed models is 36.5%. The cracking times extend with increase in concrete cover and decrease with corrosion current density. The development of service life prediction models that considers factors such as heterogeneity of concrete, non-uniform corrosion along rebar, rust production rate and a more accurate representation of the corrosion accommodating region are some of the areas for further research.Research limitations/implicationsOutcome of this paper partially bridge the gap between theory and practice, as it is the basis to estimate the serviceability of corrosion-affected RC structures and to propose maintenance and repair strategies for the structures. For structural design and evaluation, the crack-width criterion is the greatest practical importance, and structural engineers, operators and asset managers should pay close attention to it. Additionally, repair costs for corrosion-induced serviceability failures, particularly concrete cracking and spalling, are significantly higher than those for strength failures. Therefore, to optimize the maintenance cost of RC structures, it is essential to precisely forecast the serviceability of corrosion-affected concrete structures. The lifespan of RC structures may be extended by timely repairs. This helps stake holders to manage the resources.Practical implicationsIn order to improve modeling of corrosion-induced cracking, important areas for future research were identified. Heterogeneity properties of concrete, concept of porous zone (accommodation effect of pores should be quantified), actual corrosion morphology (non-uniform corrosion along the length of rebar), interaction between sustain load and corrosions were not considered in existing models. Therefore, this work suggested for further researches should consider them as input and develop models which have best prediction capacity.Social implicationsThis work has positive impact on society and will not affect the quality of life. Predicting service life of structures is necessary for maintenance and repair strategy plans. Optimizing maintenance strategy is used to extend asset life, reduce asset failures, minimize repair cost, and improve health and safety for society.Originality/valueThe degree of accuracy and applicability of the existing service life prediction models used for RC were assessed by comparing the predicted cracking times with the experimentally obtained times reported in the literature. The shortcomings of the models were identified and areas where further research is required are recommended.

This paper deals with state of the art in structural health monitoring (SHM) methods in offshore and marine structures. Most SHM methods have been developed for onshore infrastructures. Few studies are available to implement SHM technologies in offshore and marine structures. This paper aims to fill this gap and highlight the challenges in implementing SHM methods in offshore and marine structures. The present work categorises the available techniques for establishing SHM models in oil rigs, offshore wind turbine structures, subsea systems, vessels, pipelines and so on. Additionally, the capabilities of proposed ideas in recent publications are classified into three main categories: model-based methods, vibration-based methods and digital twin methods. Recently developed novel signal processing and machine learning algorithms are reviewed and their abilities are discussed. Developed methods in vision-based and population-based approaches are also presented and discussed. The aim of this paper is to provide guidelines for selecting and establishing SHM in offshore and marine structures.

PurposeSeveral experimental and numerical studies were performed in the past to estimate buckling capacity of corroded tubular members. However, the effect of initial imperfections has not been properly considered in most of these earlier proposed formulas. Therefore, the main objective of this paper is to propose an accurate analytical formula to determine the buckling capacity of patched corroded tubular members.Design/methodology/approachTubular members with initial geometrical imperfections can be regarded as beam-columns because of the combination of axial load and bending moment. The proposed formula is derived for a rectangular corrosion patch. The proposed formula is verified with results from finite element analysis of corroded tubular members and experimental results. The formula is also applied to an existing offshore jacket structure to highlight its significance and applicability. It is found that the buckling capacity of jacket members in splash zone reduces significantly with ageing. This reduction is around 29 and 14% for the selected brace and leg member respectively, during the design life. Finally, it is concluded that corrosion reduces the buckling capacity significantly and the proposed formula can be easily applied by practicing engineers to give an accurate and slightly conservative estimate the remaining buckling capacity.FindingsThe main finding is the new formula which accurately and conservatively estimate the buckling capacity of corroded tubular members. The proposed formula considers the secondary effect of both initial geometrical imperfections and shifting of centroid because of corrosion.Originality/valueThe proposed new formula is unique and original in that it considers both secondary effects from geometrical imperfections, reduction of cross-section from corrosion wastage and shifting of centroid because of corrosion. Finally, it is concluded that corrosion reduces the buckling capacity significantly and the proposed formula can be easily applied by practicing engineers to conservatively estimate the remaining buckling capacity and verify if further, more advanced estimations are needed.

PurposeBrinell, Vickers and low-force Vickers hardness measurements are herein adopted to investigate and quantify the fatigue damage evolution in specimens made of S355J2+AR ferritic pearlitic steel. Though nano and microhardness measurements have been well adopted, they require a strict preparation routine, whereas macroscopic hardness measurements are not as stringent.Design/methodology/approachThe feasibility of adopting macroscopic hardness measurements as a means of measuring fatigue damage is investigated through a combination of experimental tests and finite element analyses with both Brinell and Vickers hardness indenter.FindingsIt is found that the Brinell hardness measurements method seems more feasible, regarding finding a continuous and significant change during the fatigue life, in comparison to both Vickers and low-force Vickers. Thereafter, the question regarding the feasibility of the hardness measurements as a method of assessing accumulated fatigue damage in situ is discussed.Originality/valueMuch work has previously been performed towards correlation of the micro and nano hardness indentations, which generally has stringent preparation requirements before testing. Herein, the adoption of macroscopic hardness measurements as a means of assessing accumulated fatigue damage is considered both experimentally and theoretically.

Recently proposed damage models are presented and compared. In addition, adeterministic algorithm for nonlinear fatigue damage monitoring is presented and discussed.Furthermore, the commonly adopted functional forms for damage modelling is proposed andthe adequacy of their functional form is directly investigated by the help of experimental data.Thereafter, the accuracy and whether the presented models give conservative estimates incomparison to Miner’s rule are checked with experimental data. It is found that the proposedmodels generally perform better for various materials commonly subjected to fatigue. Finally,it is discussed how both the theory and deterministic algorithms now exist for both adoptingnonlinear functions in design if the expected loading sequence can be determined, whereas itcan always be adopted for fatigue based structural health monitoring.

Orthotropic Steel Decks have been used in long-span bridges for several decades because of their high capacity to weight ratio. However, many fatigue related issues have been reported. This paper provides an overview of the main existing fatigue prediction models and discusses their relevance for the fatigue life assessment of Orthotropic Steel Bridge Decks (OSBDs). Several case studies have proven the importance of considering the combined effect of wind and traffic loadings to estimate the fatigue life of long-span bridges. The importance of incorporating welding residual stresses is also well documented while it is often disregarded in design practices. Reliability-based fatigue assessment methods make it possible to quantify how the sources of uncertainty related to loading conditions, welding residual stresses or fabrication defects can affect the fatigue reliability of OSBDs. Monte Carlo simulations are often used to perform probabilistic analyses, but machine-learning algorithms are very promising and computationally efficient. The shortcomings of the Palmgren-Miner rule are discussed and the need for alternative damage accumulation indexes is clear. A number of conclusions are drawn from the analysis of fatigue tests conducted on OSBDs.

Offshore structures are subjected to dynamic environmental loads (wave and wind loads). A stress-life fatigue strength curve is proposed for tubular joints which are in the splash zone area of offshore jacket structures. The Det Norske Veritas (DNV) offshore structures standards given design T-curve in the air is modified with the environment-dependent parameters to obtain this fatigue strength curve. Validity of the curve is done by comparing fatigue lives given by the proposed curve with experimental fatigue lives of tubular joints tested in seawater under different loading conditions. The fatigue assessment of a case study tubular joint is performed using the proposed curve. Nominal stress ranges of the members, which are connected to the joint, are obtained by dynamic analysis of the jacket structure. Stress concentration factors are utilized with the nominal stresses to obtain the hot spot stress ranges. Fatigue lives are calculated and compared with the conventional approach. Hence the applicability and significance of the proposed fatigue strength curve are discussed.

A vast amount of research has been carried out towards the goal of quantifying changes related to the fatigue damaging process in materials throughout the fatigue life. However, no recommended practice has been developed for the experimental measurement of fatigue damage before a macroscopic crack has been initiated. Therefore, this paper reviews the existing fatigue damage detection and measurement techniques on the basis of both momentum within the research field and their being considered non-destructive. The techniques are separated into two categories, namely, fatigue crack monitoring and fatigue damage monitoring. The parameters of these techniques, which quantify the physical and mechanical changes of the materials during the fatigue life, were critically reviewed in regard to the mechanism behind the change, limitations, shortcomings, etc. The acoustic emission, hardness, ultrasonic, magnetic and potential drop methods are applicable for in-situ measurements while positron annihilation and X-ray diffraction are more suitable for laboratory assessments. Even though all the revived methods are applicable for metals, acoustic emissions, X-ray diffraction, ultrasonic, strain-based and thermometric methods are also suitable for composites. The reliability, advantages, weaknesses, case/material dependency and applicability of each method are compared and tabulated for making a framework for choosing suitable technique for fatigue crack or damage detection of material or components.

Thickness reduction due to uniform corrosion increases the tendency of lateral torsional buckling (LTB) of open cross-sections and it reduces the moment capacity of the beam. The effect of the various corrosion cases on the LTB moment capacity (M b,rd) of the I-beams are investigated in this paper. An analytical framework for patch corroded I-beams is introduced to provide a guideline for simulating the nonlinear lateral torsional buckling behaviour of patch corroded simple beams. Hence the effect of different corrosion scenarios to reduce the buckling reduction factor (η LT) is investigated by conducting a parametric study. Twelve different beam lengths were considered to obtain different non-dimensional slenderness ratios (λ LT) in this parametric study. The degraded buckling curves were obtained for each corrosion scenarios.

The structural integrity assessment of ageing structures for possible life extension has been identified as a growing challenge in the oil and gas industry worldwide. Although the available guidelines provide a general assessment process, it is necessary to have more detailed guidelines. This can be achieved by adding relevant theories and models which can capture time-dependent structural degradation more precisely. To address this, a new framework for possible life extension is proposed in this paper. The proposed framework provides more precise corrosion models, new damage theories and assessment guidelines to predict the remaining fatigue life and check the structural adequacy in all the limit states during the whole extended service life. Initially, the paper presents the proposed framework in detail. The framework approach is then applied to an ageing jacket as a case study and results are compared with conventional approach. The proposed approach results in a remaining life of ten years as compared to one year using the conventional approach. Thus, the jacket structure can be safely operated for an additional nine years using the proposed approach. Recommendations are also made on increasing the remaining fatigue life using life improvement techniques. Finally, the applicability, significance and validity of the proposed framework are discussed.

Several fatigue damage models have been proposed in the past to overcome the shortcomings of the commonly used Miner’s rule. However, application of these models requires either the determination of material parameters or modifications to the S-N curve of the material. To overcome these problems, a new fatigue damage model is proposed in this paper. The proposed model is based on the commonly available S-N curve parameters of the material and does not require any additional material parameter determination or S-N curve modification. The validity of the proposed fatigue damage model is confirmed by comparing the experimentally derived damage evolution curves for C 45 and 16 Mn steel. The proposed model gives a better agreement with these experimental results compared to previous models. A new damage transfer concept is also proposed for a more accurate estimation of fatigue life and is verified with experimental results for fatigue lives of six materials. The predicted fatigue lives are in better correlation with experimental results compared to Miner’s rule and other recently proposed models. Finally, the application of the proposed model is illustrated by a case of welded joints. The model is applied to butt and fillet welded joints and the predicted fatigue lives show better agreement with experimental results compared to earlier models. The maximum and average deviations from the experimental results are 20% and 9% respectively. It is concluded that the proposed model can be easily applied by practising engineers for an accurate prediction of fatigue life.

A new model to estimate multiaxial high cycle fatigue life is presented in this paper. The proposed model is used for finding fatigue life of multiaxial random proportional loading by considering mesoscopic scale failure mechanism. The predicted fatigue lives by new model which consists of a new damage indicator is better than that of existing fatigue models. The experimental fatigue lives of 14 tests and theoretically predicted lives were compared. The model was verified. The proposed model predicted multiaxial fatigue model was shown a good agreement when comparing with previous models for random loadings.

This paper proposes a conceptual framework for the essential maintenance of truss bridges based on an accurate remaining fatigue life estimation technique. The framework mainly consists of structural appraisal based critical members and connections identification, remaining fatigue lives estimation of critical connections and time dependent member replacement or strengthening scheme. In the stage of critical member identification, detailed structural appraisal has to be conducted giving priority to visual inspection for condition, FE analysis, and material testing, experimental static and dynamic load testing. Accurate fatigue life estimation techniques of both members and connections consist of measured stress histories and recently developed new fatigue models. A verification of the proposed framework is conducted by comparing the predicted replacement scheme with a sequence of experimental failure and fatigue life of selected test specimens. Finally, the proposed framework was applied to a case study railway bridge to obtain time dependent member replacement scheme and obtained results were compared with previous estimations. Hence, validity and merits of the proposed framework were confirmed.

Miner’s rule is commonly used in fatigue life estimations and is also recommended by design standards. Recently, a few models have been proposed, to capture loading sequence effects more precisely than Miner’s rule. However, practical applications of these models have not been found, due to the requirement for additional material parameters. The authors have recently proposed a nonlinear fatigue damage model, which does not require any additional material parameters, other than the S-N curve. It can be applied by practicing engineers, using partially known S-N curves given in design standards, including the corresponding detail categories. The model has been verified with several materials for both damage evolution curves and fatigue life estimations. Verification of this model for S355 (SAE 1020) structural steel used in offshore structures is desirable for the industry. Experimental techniques, based on characterizing fatigue damage using physical quantities, have also recently been developed by the authors and are used for this verification. Subsequently, damage evolution curves under load increase test and constant amplitude tests are developed by observing the changes in plastic strain amplitude, electrical resistance and temperature. The corresponding fatigue strength curve is developed. This curve is used, together with the proposed damage index, for further verification of the proposed model for S355 (SAE 1020) structural steel. Finally, application of the proposed model is shown for an existing offshore jacket structure, and the results are compared with those of the conventional approach. Hence, the importance and significance of the proposed model is further established.

Damage in offshore structures is mainly due to fatigue multiaxial stress state at structural joints, and fatigue strength assessment of such joints through the critical-plane criterion is well-accepted by the scientific community. A novel relationship to estimate the critical plane orientation is proposed in the present paper. Such a relationship is implemented in the stress-based critical-plane criterion by Carpinteri et al., which is applicable to any metallic material under multiaxial constant amplitude fatigue loading. Fatigue life of specimens made of different metallic materials is herein evaluated by using such a criterion. The experimental fatigue life of each specimen examined is compared with the analytical one. The relationship above seems to be a useful tool for estimations of fatigue life under multiaxial loading.

A simplified formula for deriving full range S–N curves of steels with ultimate tensile strength

(C) 2015 The Author. Published by Elsevier Ltd in Case Studies in Engineering Failure Analysis, vol. 4. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). The bridges experience increasing traffic volume and weight, deteriorating of components and large number of stress cycles. Therefore, assessment of the current condition of steel railway bridges becomes necessary. Most of the commonly available approaches for structural health monitoring are based on visual inspection and non-destructive testing methods. The visual inspection is unreliable as those depend on uncertainty behind inspectors and their experience. Also, the non-destructive testing methods are found to be expensive. Therefore, recent researches have noticed that dynamic modal parameters or vibration measurement-based structural health monitoring methods are economical and may also provide more realistic predictions to damage state of civil infrastructure. Therefore this paper proposes a simple technique to locate the damage region of railway truss bridges based on measured modal parameters. The technique is discussed with a case study. Initially paper describes the details of considered railway bridge. Then observations of visual inspection, material testing and in situ load testing are discussed under separate sections. Development of validated finite element model of the considered bridge is comprehensively discussed. Hence, variations of modal parameters versus position of the damage are plotted. These plots are considered as the main reference for locating the damage of the railway bridge in future periodical inspection by comparing the measured corresponding modal parameters. Finally the procedure of periodical vibration measure- ment and damage locating technique are clearly illustrated.

In fatigue analysis, the structural detail of tubular joint has taken great attention among engineers. The DNV/GL-RP-0005 is covering this topic quite well for simple and clear joint cases. For complex joint and geometry, where joint classification is not available and there is limitation on validity range of non-dimensional geometric parameters, the challenges become a fact among engineers. The classification of joint is an important factor to consider in fatigue analysis. These joint configurations are identified by the connectivity and the load distribution of tubular joints. To overcome these problems to some extent, this paper compares the fatigue life of tubular joints in offshore jacket according to the stress concentration factors (SCF) in DNV/GL-RP-0005 and finite element method employed in Abaqus/CAE. The paper presents the geometric details, material properties and load history of the considered jacket structure. It then describes the global structural analysis and identification of critical tubular joints for fatigue life estimation. Hence, fatigue life is determined based on the guidelines provided in design codes. Fatigue analysis of tubular joints is conducted using the finite element employed in Abaqus/CAE as the next major step. Finally, predicted SCFs and fatigue lives are compared, and these observations tend to conclude that even though the fatigue life, which is calculated based on code given SCFs, provides more realistic prediction to the simple uniplanar joints, there is a doubt for complex joints and geometry, where joint classification is not available. Also, the study emphasized that it is very important to preciously investigate SCFs by considering accurate geometry of complex tubular joints for a good judgement of fatigue life.

The need for material specific monotonic test based full range stress – life curves is discussed. Combining monotonic test based empirical fatigue formulae and a Wholer field mathematical model, a new formula for developing full range stress life curves for medium strength steels is proposed. The accuracy of the proposed formula is verified using experimental fatigue data of six steels. The cumulative fatigue damage and future life of a connection detail of a steel bridge is estimated using a full range S–N curve developed by employing the proposed formula. For this estimation, stress concentration factors of the connection detail are determined using a finite element model and, cumulative damage is evaluated using both miner rule and sequential law. The damage and future life so estimated are compared with those estimated using the code provided conventional method; the importance of employing material specific S–N curves with appropriate stress concentration factors for special connection details and correct damage accumulation methods is highlighted.

The remaining life estimation of ageing structures has been identified as a growing challenge in the oil and gas industry. Although the available guidelines provide a general fatigue assessment process, it is necessary to have more detailed guidelines by adding relevant theories and models which can capture the time-dependent structural degradation more precisely. To address this, a new framework is proposed in this paper. The proposed framework provides recommendations on various issues such as simulation of structural degradation, loading history, effect of localized corrosion, selection of a suitable fatigue strength curve and fatigue damage theories. Recently developed precise fatigue damage theory is also included in the proposed framework.

Very high cycle fatigue properties of various steels were studied using findings of previous research and laboratory fatigue testing. First, experimental data for more than 550 specimens covering 25 high and medium strength steels were used to investigate the relationships between the applied stress, number of failure cycles, size of defects or inclusions at fracture origins and stress intensity factors. Using the results of the investigation of these data, general conclusions were arrived at for steels as a whole. It was observed that the size of the failure origin can be predicted using strength properties of steels. Existing methods for estimating major parameters such as size of failure origins and stress intensity factors were reviewed, new methods were proposed and their accuracy was verified using experimental data. Also, the possibility of simplifying existing formulae with substitutions for the major parameters was reviewed. Employing these major parameters, new formulae for predicting fatigue strengths of both medium and high strength steels were proposed. Predictions of these proposed formulae were compared with existing well known formulae using experimental data and statistical methods highlighting the simplicity and importance of the proposed formulae. The ability of employing the proposed formulae for predicting, “fatigue strengths that are more close to the real values” as well as “fatigue strengths that are more safe and conservative” was reviewed. Secondly, fatigue properties and failure causes of medium strength – low carbon structural steels that are usually used in civil engineering structures were investigated. For this investigation, 35 smooth specimens of five steels were tested using a rotating bending fatigue tester. It was observed that fatigue failures occur up to around 10 7 cycles and that the failure originates from the surface. It was found that the formulae proposed are able to predict failures of these medium strengths steels. Slopes of stress life curves in the very high cycle fatigue regions were well predicted by these proposed formulae while the predictions were fairly aligned with values suggested in previous research. Finally, recommendations were given for employing suitable prediction methods considering safety and importance of components and structures.

This paper presents a method to estimate remaining fatigue lives of railway bridge members subjected to time-dependent corrosion. The method addresses effects of material loss due to general (uniform) corrosion and fatigue strength degradation of material due to corrosive environment. The method mainly consists of stress history, which is obtained by considering the effect of time-dependent loss of material, full-range S–N curve, which represents the corrosive environment, and sequential law, which takes the loading sequence effect more precisely in to account than Miner's rule. Initially, nonlinear behaviour of material loss over time (i.e. time-dependent growth of corrosion wastage) is discussed, and hence, necessary formulae to calculate time-dependent cross-sectional properties are comprehensively presented. Then finite element analysis-based procedure is clearly proposed to predict stress histories of corroded members. A technique is introduced to obtain the full-range S–N curve for the corroded structural detail. The concept of sequential law is summarized with the algorithm, and then the proposed method is applied to predict the remaining fatigue lives of the corroded members of a railway bridge. The predicted remaining lives were compared with the previous method-based estimations, and comparisons reveal the range of 16–47% reduction of fatigue lives of critical members when time-dependent corrosion is taken into account. Also, the results reveal that the corroded members of smaller cross-sectional area are most vulnerable for fatigue damage. Finally, significance of the proposed method is confirmed.

This paper presents a simple approach to predict the failure of steel structures under the interaction effect of fracture and fatigue which is termed as ultra-low cycle fatigue (ULCF) failure. The approach mainly consists of simple fracture criterion, which is obtained from further simplification of available cyclic void growth model (CVGM). As for alternative component of ULCF analysis, a simple non-linear hardening model is proposed to employ in elasto-plastic analysis for situations where parameters of available mix hardening models (combined isotropic and kinematic hardening models) are difficult to determine. Initially the simplified ULCF fracture criterion is clearly presented and associated ULCF fracture prediction methodology is also indicated. Then the elasto-plastic hardening model is proposed and model behavior is compared with experimental behavior of few materials. The procedure to determine hardening constants and finite element (FE) formulation are also clearly mentioned. The simplified approach is then employed to determine ULCF fracture of some structural models. Hence verification of the simplified approach is confirmed by comparing the results with previous approaches-based estimations. Finally, study tends to conclude that the simplified approach produces reasonable accurate prediction to ULCF fracture of steel structures where magnitude of triaxiality remains relatively constant. Further, it was able to prove that commonly available elasto-plastic FEM packages can be reasonably employed to estimate ULCF fracture of steel structure when simplified ULCF fracture criterion governs the failure.

A new model is proposed in this paper for the estimation of the life of bridges subject to damage caused by high cycle fatigue combined with low cycle fatigue taking account of the interaction of high and low amplitude loadings. High cycle fatigue is caused by normal routine traffic (low amplitude) loading while low cycle fatigue is caused by extreme (high amplitude) loading situations produced by such as earthquakes. The model mainly consists of a new damage indicator and a new strain-life fatigue curve. Total strain is treated as the damage variable. The proposed model predictions were verified by comparing with fatigue test results for four materials reported in the literature. The proposed model was then applied to estimate the fatigue life of a bridge member subject to combined high and low-cycle fatigue damage caused by normal traffic and by earthquake loadings. The results of the case study, confirm the importance and applicability of the proposed model.

This paper presents a new fatigue model to predict life of steel bridges considering the effect of high amplitude loading. It consists of a modified strain-life curve and a new strain based damage index. Modified strain-life curve consists of Coffin-Manson relation in low cycle fatigue region and a new strain-life curve in high cycle fatigue region. The damage variable is based on a modified von Mises equivalent strain to account for the effects of loading nonproportionality and strain path orientation in multiaxial stress state. The proposed model was verified with experimental test results of two materials available on the literature. Then, it was illustrated with an old riveted wrought iron railway bridge. The obtained results verify the effectiveness of the proposed model over commonly used Miner's rule based life prediction of steel bridges.

The current fatigue life estimation methods of railway bridges are generally based on combinations of measured strain histories, Miner’s rule, and railway code provided fatigue curve. Even though the past measured strain histories are available for major bridges, most of the old bridges do not have past strain measurements. Furthermore, in case of existing railway bridges where the detailed loading history is known, Miner’s rule might provide incorrect results because of its omission of load sequence effect. These reasons hinder the usage of current methods to estimate the realistic remaining fatigue life of most of the existing railway bridges. Therefore, a new method is presented in this article to estimate remaining fatigue life of riveted railway bridges. The method mainly consists of predicted stress histories, recently developed sequential law and fully known Wöhler curve. Here, it is essential to use the fully known Wöhler curve as the related fatigue curve. Hence, the technique, which utilizes transfer of the partially known Wöhler curve to fully known curve, is also discussed in this article. Further, this method describes a reasonably accurate procedure to obtain the past stress histories from present day measured strains. Initially, the article describes the proposed method for remaining fatigue life estimation. Then the sequential law and associated fully known S-N curve determination procedure are verified by comparing theoretical fatigue life, damage behavior with real fatigue life and damage behavior of few materials. Finally, the remaining fatigue life of an existing railway bridge is estimated. Hence, validity and merits of the proposed method is confirmed by comparing the results with previous method-based fatigue lives.

This paper proposes a new fatigue model to estimate multiaxial high cycle fatigue life for variable amplitude proportional loading conditions based on grain-scale plasticity (mesoscopic plasticity). The model mainly consists of a new damage indicator, which gives a better prediction to fatigue life in the case of variable amplitude loading. The model prediction is verified by comparing with fatigue test results. Finally, the proposed model is applied to estimate the fatigue life of a riveted connection and the associated procedure is clearly indicated.

Miner’s rule is generally accepted as the fatigue criteria for life estimation of railway bridges. Similarly, it has always been acknowledged as a simplification that is easy to use in design where detailed loading history is unknown. But in the case of existing railway bridges where the detailed loading history is known, Miner’s rule might provide incorrect results because of its omission of load sequence effect. Recently, a new damage indicator-based sequential law has been proposed to capture the load sequence effect more precisely. However, application of this sequential law to estimate the remaining fatigue lives of existing railway bridges has not been properly studied. Therefore, the major objective of this paper is to estimate the remaining fatigue life of a railway bridge using the sequential law and hence introduces a new approach to estimate remaining fatigue life of riveted railway bridges. This approach is specially based on combination of real stress histories, sequential law and fully known Wohler curve. The practice of sequential law to obtain the remaining fatigue lives due to both uniaxial and multiaxial stresses are described by estimating remaining life of a considered railway bridge. Further, the obtained fatigue lives are compared with Miner’s estimations. Hence it could be concluded that it is advisable to apply the sequential law for assessment of remaining fatigue lives of riveted railway bridges, where the detailed stress histories are known.

This paper first describes the importance of using location specific S-N curves for fatigue damage assessment of existing steel structures. It discusses the existing concepts and methods for developing S-N curves using empirical formulae and monotonic strength parameters, such as the ultimate tensile strength and hardness. It also discusses relationships among these monotonic parameters. Then it presents formulae for developing hardness-based full range S-N curves for medium strength steels. The formulae are verified using experimental data obtained from both monotonic and cyclic testing. Finally, it describes the advantages of these hardness-based formulae for developing location specific S-N curves as hardness testing is a non-destructive test which can be carried out on specific locations in structures.

The objective of this paper is to compare the predictions of deterministic and probabilistic fatigue assessment methods. The paper focuses on the nominal stress method in the stress-life approach. Three different assessment methods are presented and compared, the traditional deterministic method, the closed form method and the probabilistic method. The traditional method is the one described in Eurocode. The closed form method involves using a Weibull distribution to represent the stress spectrum. The probabilistic method involves the use of Monte Carlo simulations to obtain the probability of failure, Pf . An alternative fatigue load model is newly proposed in this paper. The associated procedures of the three assessment methods were verified and then used for fatigue analysis of a road bridge. Finally, the limitations, shortcomings and recommendation are concluded based on the research and the obtained results.

This paper presents optimized design geometries of wire sheaves that are used in offshore drilling operations. Seven different design geometries of wire sheaves are considered for this study. The criteria considered in this comparison are utilization ratios of yield and buckling capacities and fatigue life. The constrained used are the self-weight and rotational inertia. The obtained utilization ratios of yield capacity, buckling capacity, and fatigue life against the weight and rotational moment of inertia are finally compared. The comparisons reveal that currently used lightest sheave geometry has very good yield and buckling capacities than all other geometries. But it has high self-weight and rotational inertia. Finally, the web with decreasing thickness which has a lowest rotational inertia is proposed as the most suitable design geometry, if the expected design life is limited to 20 years. Different sheave geometries are also proposed depending on the required design service life.

Remaining fatigue life estimation of corroded members of a railway bridge is presented in this paper. The method used in this study addresses effects of material loss due to general (uniform) corrosion and fatigue strength degradation of material due to corrosive environment. Initially the information of the considered bridge is discussed. The inspection records, corrosion information and loads on the bridge are discussed in detail. Then a model is introduced to describe time-dependent growth of general corrosion wastage. Then finite element method employed time history dynamic analysis is performed to obtain stress histories of corroded members. A full range S-N curve is proposed for corroded structural detail. The sequential law, which takes the loading sequence effect more precisely in to account than Miner’s rule, is used to obtain remaining fatigue lives. Finally significance and validity of the method are confirmed by comparing the predicted fatigue lives with previous estimations.

Generally design load capacity of pad eyes used in offshore lifting operations is determined based on the guidelines given in lifting standards. In 2012, NORSOK issued a new standard, R-002 “Lifting equipment”, to ensure that adequate safety requirements are complied with in connection to lifting operations on the Norwegian continental shelf. To ensure the accuracy of the followed design procedure, this paper presents experimental verification of 3.25 tons pad eyes. Initially, paper reviews various factors that are important to consider in a lifting operations, and provides important theoretical basis. Then details related to execution, analysis and results of the experimental testing. Several pad eyes are produced by changing the weld types, weld sizes and different hole sizes. Quasi static loads are applied to the pad eyes by changing different directions. The experimentally obtained load capacities were compared with theoretically calculated design load capacities. Finally significance, accuracy and limitations of the new guidelines are confirmed.

The stress concentration factors of tubular joints have taken great attention among engineers. The DNV/GL-RP-0005 is covering this topic quite well for simple and clear joint cases. For complex joint and geometry, where joint classification isn’t available and limitation on validity range of non- dimensional geometric parameters, the challenges become a fact among engineers. The classification of joint is important for the fatigue analysis. These joint configurations are identified by the connectivity and the load distribution of tubular joints. To overcome these problems to some extent, this paper compares the SCFs which were obtained by parametric equations given in DNV/GL-RP-0005, finite element analysis and full scale experimental test results of four different types of tubular joints in offshore jackets. Finally, the validity and limitation of each method are discussed.

Researchers in the past have proposed several fatigue damage models to overcome the shortcomings of the commonly used Miner's rule. However, requirements of material parameters or S-N curve modifications restricts their practical applications. Also, application of most of these models under variable amplitude loading conditions have not been found. To overcome these restrictions, a new fatigue damage model is proposed in this paper. The proposed model can be applied by practicing engineers using only the S-N curve given in the standard codes of practice. The model is verified with experimentally derived damage evolution curves for C 45 and 16 Mn and gives better agreement compared to previous models. The model predicted fatigue lives are also in better correlation with experimental results compared to previous models as shown in earlier published work by the authors. The proposed model is applied to welded joints subjected to variable amplitude loadings in this paper. The model given around 8% shorter fatigue lives compared to Eurocode given Miner's rule. This shows the importance of applying accurate fatigue damage models for welded joints.

Offshore installations are subjected to harsh marine environment and often have damages from corrosion. Several experimental and numerical studies were performed in the past to estimate buckling capacity of corroded tubular members. However, these studies were either based on limited experimental tests or numerical analyses of few cases resulting in semi-empirical relations. Also, there are no guidelines and recommendations in the currently available design standards. To fulfil this research gap, a new formula is proposed to estimate the residual strength of tubular members considering corrosion and initial geometrical imperfections. The proposed formula is verified with results from finite element analyses performed on several members and for varying corrosion patch parameters. The members are selected to represent the most relevant Eurocode buckling curve for tubular members. It is concluded that corrosion reduces the buckling capacity significantly and the proposed formula can be easily applied by practicing engineers without performing detailed numerical analyses.

Structural integrity control (SIC) is an increasingly important element of offshore structures. Not only is it used in newly built and existing offshore structures (e.g. oil and gas (O&G) production & process facilities (P&PFs), wind turbine installations, etc.), but SIC is also essential for ageing offshore platforms which are subjected to an extension of their design service life. In these cases, SIC programs must be performed to assess the platforms. If any significant changes in structural integrity (SI) are discovered, then it is essential to implement an appropriate strengthening, modification and/or repair (SMR) plan. Currently, welded and grouted repairs are mostly used for SMR. Although a welded repair may typically restore a structure to its initial condition, if the damage is due to fatigue loading and welded repairs have been carried out, then historical evidence reveals that there is a high potential for the damage to reappear over time. On the other hand, mechanical connections are significantly heavier than grouted connections. Consequently, grouted repairs are widely used to provide additional strength, for instance, to handle situations such as preventing propagation of a dent or buckle, sleeved repairs, leg strengthening, clamped repair for load transfer, leak sealing and plugging, etc. This manuscript examines current developments in grouted connections and their comparative pros and cons in relation to welded or mechanical connections. It also provides recommendations for future research requirements to further develop SMR with grouted connections.

Objective: To develop a web-based educational resource for health professionals responsible for the management of spinal cord injury (SCI). The resource: www.elearnSCI.org is comprised of seven learning modules, each subdivided into various submodules. Six of the seven modules address the educational needs of all disciplines involved in comprehensive SCI management. The seventh module addresses prevention of SCI. Each submodule includes an overview, activities, self-assessment questions and references. Development of the resource: Three hundred and thirty-two experts from The International Spinal Cord Society (ISCoS) and various affiliated societies from 36 countries were involved in developing the resource through 28 subcommittees. The content of each submodule was reviewed and approved by the Education and Scientific Committees of ISCoS and finally by an Editorial Committee of 23 experts. Key features: The content of the learning modules is relevant to students and to new as well as experienced SCI healthcare professionals. The content is applicable globally, has received consumer input and is available at no cost. The material is presented on a website underpinned by a sophisticated content-management system, which allows easy maintenance and ready update of all the content. The resource conforms to key principles of e-learning, including appropriateness of curriculum, engagement of learners, innovative approaches, effective learning, ease of use, inclusion, assessment, coherence, consistency, transparency, cost effectiveness and feedback. Conclusion: www.elearnSCI.org provides a cost effective way of training healthcare professionals that goes beyond the textbook and traditional face-to-face teaching. Spinal Cord (2013) 51, 176-182; doi:10.1038/sc.2012.177

This paper presents a simple criterion to predict the fracture of offshore steel structures due to the interaction effect of ductile fracture and fatigue, which is termed as extremely-low cycle fatigue (ELCF) fracture. The criterion has been obtained from further simplification of available cyclic void growth model (CVGM). The main advantage behind this simplified criterion (i.e. simple criterion) is that it can be easily utilized with commonly available elasto-plastic finite element (FE) packages than the previous CVGM criterion. Initially the simplified ELCF fracture criterion is clearly presented. And the associated ELCF fracture prediction methodology is also indicated. The simplified criterion is then employed to determine ELCF fracture of some structural models. Hence verification of the simplified criterion is confirmed by comparing the results with previous criterion-based estimations. Then the simplified criterion is applied to predict the ELCF fracture of a reduced beam section specimen. Finally, study tends to conclude that the simplified criterion provides reasonable accurate prediction to ELCF fracture of offshore steel structures where magnitude of triaxiality remains relatively constant.Copyright © 2012 by ASME