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An offshore energy transition, even if only a gradual one, from carbon-emitting fossil fuel extraction to cleaner sources is recommended, if we are to slow the harmful impacts of climate change. The potential for sustainable reuse of decommissioned offshore jacket platforms to support wind turbines is being considered as an attractive proposition in such a transition. To maximize the benefits of such reuse of assets, what is needed is a rational optimization strategy that considers the remaining life of a repurposed platform, associated retrofit and construction costs, and a future period of gross renewable energy generation following installation of the wind turbine. We outline a study that employs a fatigue reliability-based framework, based on the global fatigue approach and Palmgren–Miner’s rule, to aid in such sustainable reuse planning and optimization. The framework proposed identifies an optimized reuse plan that incorporates metocean data analysis, structural analysis, life cycle evaluation, and revenue optimization. We employ a case study and sustainable reuse scenario for a site in the vicinity of Porto (Leixões), Portugal.

Dams are considered as the critical part of infrastructure of any country, and their construction requires considerable amounts of capital and labor. The optimal design of dams can lead to significant savings in time and cost. In this regard, the goal of this study is proposing an efficient framework for the probabilistic design of gravity dams using a new developed reliability-based design optimization (RBDO) approach. In this RBDO approach, the concreting volume of dam is considered as the objective function of the optimization problem under uncertainties, while the geometric parameters are considered as the decision variables. To solve the RBDO problem of the gravity dam design, a new surrogate model consists of a hybrid Support Vector Regression (SVR) based generalized normal distribution optimization (GNDO) is coupled to the Monte Carlo Simulation (MCS). The hybrid SVR-GNDO is utilized to predict the dam response in order to decrease the computational cost during the RBDO analysis. The use of GNDO-SVR instead of SVR increased the predicted R2 from 0.85 to 0.99. The proposed method was implemented on the Pine Flat dam in California (USA). The results showed that the performance of the RBDO approach in the optimal design of a concrete gravity dam has a better safety level than the deterministic approach. This is such that the presented new hybrid model was able to reduce the failure probability of the design under uncertainty from 71% to 0.000018% by increasing the volume of concrete used in the dam by 8%.

The focus of this research work was predicting the fatigue life of mechanical components used for industrial and transport systems. To understand how the phenomenon of fatigue occurs in a material, the fatigue crack growth is studied. The purpose of this work was to create a graphical user interface (GUI) under Matlab to allow researchers to conduct the parametric studies of fatigue crack propagation to predict fatigue life. In this work, three models for fatigue crack propagation were used: those of Paris, Walker and Forman in order to study the three parameters: the Paris exponent m, load ratio R and hardness K IC , respectively. In addition, a novel model FCG was developed to study the influence of the hardening parameters (K′, n′) on fatigue crack propagation. The comparison of the simulation results with those in the literature shows good agreement.

Spatial and temporal temperature variations in bridge structures due to changes in the surrounding climate cause bridge expansion which, if restrained, may induce secondary stresses in structures. Temperature effects have always been considered to be one of the most critical issues in the performance of traditional Prestressed Concrete (PC) bridges. In order to (1) develop an efficient temperature loading model for predicting bridge temperature-induced response; and (2) develop guidelines addressing the effects of temperature loading in reliability-based condition evaluation, numerical and analytical studies were conducted on a PC girder bridge in Oklahoma, USA. This paper focuses on the probabilistic modelling of temperature loading. Firstly, a heat transfer model was established using hourly input climate data to estimate the temperature distribution, and compared with monitoring counterparts for calibration. Secondly, the validated analytical model was employed to investigate the effects of thermal properties of concrete by a parametric analysis; Based on extreme environmental conditions from the 20-year climatic data and analytical results, probabilistic models of uniformly distributed temperature fields and temperature gradients were proposed, and the temperature loading value with a 75-year return period was determined and compared with recommended value in the AASHTO LRFD. The proposed temperature loading model can aid engineers in predicting the thermal behavior of PC bridges in Oklahoma, USA.

Spatial and temporal temperature variations in bridge structures due to changes in the surrounding climate produce movements which, if restrained, may induce stresses in the structure. Temperature effects have always been considered to be one of the critical issues that affect the performance of prestressed concrete (PC) bridges. In order to (1) develop an efficient temperature loading model for predicting bridge temperature-induced response; and (2) develop guidelines to incorporate the effects of temperature actions in reliability-based condition evaluation, numerical and analytical studies were conducted on a PC girder bridge in Oklahoma, USA. This paper focuses on the structural reliability analysis on the temperature loading action in accordance with AASHTO LRFD specification. A three-dimensional (3D) finite element method (FEM) model was established to estimate the movement and stress under temperature loading, and compared with monitoring counterparts. Then, the validated model was utilized for probabilistic analyses to assess the temperature load effects. Based on the probabilistic temperature loading model proposed in the first paper, loads and resistances statistics from published literature, reliability analyses of AASHTO LRFD limit states were performed by Monte Carlo simulation (MCS) and Rackwitz-Fiessler procedure to determine the safety level in terms of reliability index.

Fatigue assessment in the presence of intricate geometries is critical for ensuring structural integrity and reliability of engineering components. Based on the energy field intensity (EFI) approac...

Fatigue damage in marine structures is generally assessed by means of stress−number of cycles (S−N) curves. These curves are obtained from many experimental tests on structural components. Fracture mechanics (FM), using the crack propagation method is also a practical technique. In this approach, fatigue damage is estimated based on crack propagation from an initial crack size through the surface and depth of structural members. In this paper, S−N curves based on FM were compared with S−N curves obtained following two standards: DNVGL-RP-C203 and API-RP2A-WSD. The results showed that the curves did not agree well. Therefore, to obtain better fitting, calibration factors are needed. From S−N curves established for two stages, two calibration factors – α1 (for the first stage) and α2 (for the second stage) – are proposed for fitting S−N curves based on the FM approach with the DNV GL and the API S−N curves. The wall thickness, the initial crack depth and the critical crack depth were found to have a significant effect on determination of the calibration factors.

Although several old riveted bridges served more than 100–150 years in the world, some of them are still in the application, generally limited by the economic budget or cultural relic protection reason. Hence, the status of those bridges needed to be evaluated to support the bridge management and rehabilitation, especially with the increasing traffic flow along with their service life. Nowadays, fatigue detail class 71 in the EN 1993-1-9 is generally recommended to evaluate the fatigue behaviour of the riveted joints. But the predicted fatigue behaviour of riveted connection using the recommended S-N curves is excessive conservative because the differences of connection geometries and materials are not fully considered using the global nominal stress methods. Therefore, in this paper, a two-phase fatigue performance approach based on local strain and Paris law, respectively, fatigue crack initiation and propagation phases, combined with numerical simulation, is an effective surrogate method to predict the fatigue performance of riveted connections, considering the material and geometry effects. A good agreement is observed when compared to numerical simulation with experimental observations.

Structural components with different scales normally show different fatigue behaviors, which are virtually dominated by defects originated from multiple sources, including manufacturing processes. This paper reviews three types of size effects (statistical, geometrical, technological) as well as their recent advances in metal fatigue, aiming to provide a guide for fatigue strength assessment of engineering components containing defects, inclusions and material inhomogeneity. Firstly, the background of inherent defects and defect-based failure mechanism are briefly outlined, and fatigue failure analysis based on fracture mechanics as well as statistics theory are emphasized. Then, two approaches commonly applied in statistical size effect modeling, i.e. critical defect method and weakest link method, are elaborated. In addition, the highly stressed volume method is introduced for considering the geometrical size effects, and the technological (production and surface) size effect is briefly overviewed. Finally, further directions on size effect in metal fatigue under defects are explored.

To investigate the accuracy of commonly used algorithms for prediction of creep and shrinkage effects in concrete structures, a comparative study is carried out using the finite element (FE) models with various user-defined time-dependent material properties. Numerical results are compared with available benchmark tests to justify the FE models. Results show that the FE model following the concrete integral creep (CIC) algorithm is close to the test result. The secondarily developed subroutine on the universal commercial FE platform is able to represent the time-dependent behavior of the concrete cylinders. CIC shows higher accuracy once alternating load history is considered, though the rate of creep method (RCM) and age-adjusted effective modulus method (AEMM) show the same accuracy as CIC under constant load. CIC shows outstanding compatibility with the material model specified in contemporary design codes. It seems that the CIC model can be used for a detailed evaluation of concrete structures, while RCM and AEMM might be used for preliminary and rough analysis.

Wind, as a sustainable and affordable energy source, represents a strong alternative to traditional energy sources. However, wind power is only one of the options, together with other renewable energy sources. Consequently, the core concerns for wind turbine manufacturers and operators are to increase its reliability and decrease costs, therefore enhancing commercial competitiveness. Among typical failure modes of wind turbines, fatigue is a common and critical source. Given the significance of fatigue reliability in wind turbine structural integrity, reliable probabilistic fatigue theories are necessary for design scheme optimization. By reducing the expenses on manufacturing, operation, and maintenance in reliability- and cost-optimal ways, the cost of energy can be significantly reduced. This study systematically reviews the state-of-the-art technology for fatigue reliability of wind turbines, and elaborates on the evolution of methodology in wind load uncertainty modelling. In addition, fatigue reliability assessment techniques on four typical components are summarized. Finally, discussions and conclusions are presented, intending to provide direct insights into future theoretical development and methodological innovation in this field.

With the improvement of computational capability, finite element simulation is an increasingly practical method to accurately predict the ultimate capacity and ductile fracture behavior of high-strength bolts. However, the mesh size affects the results of FE simulations but related research on mesh size effects is relatively limited. In the present contribution, the mesoscale critical equivalent plastic strain (MCEPS) is used as a failure index for calibrating the parameters of ductile fracture locus of high-strength bolts with different mesh sizes. The identified fracture locus is compared with a large bulk of experimental data taken from the previously published literature. The results showed that mesh size can have high effects on the calibrated parameters of the plastic constitutive relationship after necking and ductile fracture locus of high-strength bolts.

PurposeThe purpose of this scientific work is to simulate the fatigue damage under random loading, taking into account the mean stress effect on fatigue lifetime and using the Rainflow counting technique to assess the fatigue damage by the Ansys software. The used material is aluminum alloy 6082-T6. A comparison with literature results has confirmed this investigation in this paper.Design/methodology/approachThe study of fatigue under random loading is based on the same concepts as constant loading with the addition of damage summation. The proportion of damage caused by a stress cycle depends not only on the alternating stress but also on the mean stress.FindingsAnalysis of the fatigue damage shows that the number of relative damage due to each cycle.Originality/valueThis paper aims to simulate the fatigue damage under random loading for aluminum alloys.

Offshore structures have a long service life and involve high cost. However, the working environment of offshore structures is harsh. When an accident occurs, it causes an adverse social impact and economic loss. Therefore, in the design process of offshore structures, in order to enhance their safety, this is an important problem that needs attention. Reliability-based design and optimisation (RBDO) using saddlepoint approximation (SA) is a powerful method to enhance the reliability of offshore structures. The SA utilises a cumulant generating function and saddlepoint to approximately express the probability density function and cumulative distribution function of a limit-state function. To further improve the accuracy of reliability evaluation in RBDO with SA, in this study, a mean-value second-order SA (MVSOSA) is introduced. A RBDO with MVSOSA strategy is proposed for the design problem of a wellhead platform. An engineering case study illustrates the application of the proposed method.

Multiaxial fatigue is frequently present on engineering structures and is the cause of many mechanical failures. However, multiaxial fatigue analysis is full of questions and different points of view. Thus, throughout this study, Susmel’s criterion, a recent multiaxial fatigue damage model also known as the Modified Wohler Curve Method, is presented, explained and assessed. Experimental data of axial, torsional and proportional (axial+torsional) fatigue tests conducted on S355 structural steel and under different stress ratios were analysed and evaluated according to this model. Mean fatigue design curves for each loading condition were obtained and plotted in the high cycle fatigue region. Finally, the ability of Susmel’s criterion to assess the multiaxial fatigue behaviour of S355 steel in the high cycle region was evaluated by determining the error index between the theoretically estimated and the experimental fatigue damage. Susmel’s model was found to be adequate to describe the fatigue behaviour of the steel under study in high cycle region.

Together with the development of numerical tools for stress-strain analysis, approaches to deal with fracture mechanics problems have been the object of continuous improvement. For linear-elastic fracture mechanics problems, the determination of Stress Intensity Factors (SIF) is available as a post-processing possibility in most commercial finite element software packages such as Ansys and Abaqus, allowing the users to perform straightforward assessments of cracked mechanical parts or structures. However, available techniques for SIF determination in post-processing of these commercial solutions are almost limited to the so-called displacement extrapolation and J-integral techniques. In the present work, the implementation of the J-integral technique is revised considering a new finite element software, labeled as Omicron. Furthermore, a more recent technique, the modified Virtual Crack Closure Technique (mVCCT) is also implemented and evaluated. For results assessment, finite element models were built in Omicron and SIFs were determined considering the J-integral and mVCCT approaches. From this study, it is concluded that the mVCCT implementation is simpler than the J-integral and it allows to determine accurately SIFs. Nevertheless, this technique is not straightly available in the current versions of the commercial packages for finite element modeling, which require separate post-processing for SIF determination.

In large companies, warehouse logistics usually include shuttle pallet carriers that are responsible for the transportation of various goods and products. These shuttles run along steel rails, which are usually produced from thin metal sheets that are cold roll-formed into the desired section. These shuttles also work 24 hours a day, 7 days a week, so the rails are very sensitive to fatigue phenomena, caused by the cyclic loading of the moving shuttles, moreover, cracks due to material fatigue have already been observed in these types of rails. In addition, the competitiveness of the European industrial sector is pushing the design of these profiles to lower thickness requirements, which further increases concerns about their fatigue performance. Within this background, the FASTCOLD European project has been carried out, whose research plan consists in developing fatigue design rules for the mentioned applications, which are not covered by existing Eurocode 3 rules, which only addresses thick hot-rolled sections. Experimental fatigue testing has been carried out backed by numerical simulations of these tests. A new fatigue setup has been developed to generate representative fatigue cracking to the shuttle cyclic loads. Numerical simulations of the cold roll-forming fabrication process are also being carried out to determine the importance of the residual stresses in the fatigue life of the rail. With the experimental data obtained from fatigue testing backed by numerical simulations, important contributions are made to the design codes (e.g. Eurocode 3) in dealing with the fatigue design of such critical details.

In this study, the simultaneous application of sacrificial piles and cable was experimentally examined as a pier scour countermeasure. The experiments were carried out for a single pier, a group of two and three piers using a clear-water regime. It is believed that applying the sacrificial piles and cable at the same time decreases the scour depth at a single pier and a group of two piers efficiently. In a group of three piers, the sacrificial piles with triangular configuration were able to decrease the scour depth considerably with a value of 69% reduction at the first pier. Nevertheless, the cable affects the scour depth reduction negatively at the group of three piers. This research highlights that the combination of cable and sacrificial piles is a suitable method to decrease the local scour at a single and a group of two piers, while sacrificial piles alone can be highly recommended for the group of three piers.

PurposeEngineered stone is a material which can be described as an artificial stone. The exemplary application area is sink production. There are very few research projects about this type of material. In fact, most of them are research conducted by the manufacturing company, which are limited to the basic properties of the material. However, knowledge about fracture mechanic of this material may be crucial in terms of usage. The paper aims to discuss this issue.Design/methodology/approachAnalysis of the inside structure was made using an optical microscope as well as SEM. In the paper, methods which can be used to obtain data about fracture behaviour of material are presented. Using eXtended Finite Element Method and experimental data from three-point bending of notched specimens stress intensity factors (SIFs) for I and II load modes were obtained. Finally, a comparison between the fracture initiation angle in the function of the ration of SIFs for I/II load modes and maximum tangential stress hypothesis prediction was presented.FindingsAnalysis of the inside structure proves that this type of material has an uneven distribution of particle size. This can follow to void and micronotches formation and, later, to the failure of the material. A method of obtaining stress intensity factors for the discussed type of material and specimens can be successfully applied to other similar material, as proposed in this work. Standard crack angle propagation criteria are not sufficient for this type of material.Originality/valueThere are very few research papers about this type of material. The subject of fracture mechanic is not properly discovered, despite the fact that IT is important in terms of the application area of these materials.

Modeling of the notch and size effects on fatigue behavior of materials is vital for ensuring structural integrity and reliability of engineering components. This study presents a methodology considering both effects of notch and size to analyze the fatigue life distribution of specimens with different geometries using the highly stressed volume approach. Specifically, a dynamic model coefficient considering the influence of different maximum local stresses is developed by modeling the size effect of highly stressed volumes with Weibull distribution. Experimental data of three aluminum and titanium alloys are utilized for model validation and comparison. Fatigue lives of three materials with different geometries are evaluated respectively, and predicted P-S-N curves indicate that proposed model predictions agree well with the probabilistic scatter band of experimental results.

Purpose The purpose of this paper is to evaluate the fatigue process through the dynamic analysis of the global structural model and local static sub-modelling in a critical detail using the hot-spot stress approach. The detail was studied in three different positions at the “Alcácer do Sal” access viaduct, and the methodologies from the IIW and Eurocode EN 1993-1-9 were compared. Design/methodology/approach In this study, the fatigue life process based on the hot-spot stress approach was evaluated using a global dynamic analysis and a local sub-modelling based on a static analysis of welded connections in the “Alcácer do Sal” railway structure, Portugal, taking into consideration the recommendations from IIW and Eurocode EN 1993-1-9. The hot-spot stresses were calculated through the static analysis of the sub-model of the welded connection for each vibration mode with the aim to obtain the temporal stresses using the modal coordinates and modal stresses of the extrapolation points. The Ansys® and Matlab® softwares were used for the numerical analysis and the hot-spot stress calculations, respectively. Findings The proposed methodology/approach to obtain fatigue assessment is based on the modal analysis of the global structural model and local static sub-modelling. The modal analysis was used to extract the boundary conditions to be used in the local model to determine the temporal stresses of the extrapolation points. Based on the modal superposition method, the stresses as function of time were obtained for fatigue life evaluation of a critical detail by the hot-spot stress approach. The detail was studied in three different positions. Originality/value In the present study, a global-local fatigue methodology based on dynamic analysis of the global structural model and local static sub-modelling of the critical detail using the hot-spot stress approach is proposed. Herein, the modal analysis of the global structural model supported by the modal superposition method was used to obtain the matrix of modal coordinates. The static analysis of the local sub-model for each mode from the modal analysis of global structural model was done to estimate the hot-spot stresses. The fatigue damage calculation was based on S-N curve of the critical detail and rainflow method. The IIW recommendation proved to be more conservative compared to the proposed rules in the Eurocode EN 1993-1-9. The global-local modelling based on dynamic analysis is an important and effective tool for fatigue evaluation in welded joints.

Long-term exposure to a harsh environment leads to irreversible degradation of mechanical properties of fiber-reinforced polymer (FRP) profiles. Understanding the aging effects on pultruded...

The reliable performance of composite tubes conveying nanofluid is an essential issue for robust design under dynamic loads. Further, the frequency failure mode of these structures is a considerable performance function to provide a balance between mass and stiffness of the structure. The ability of the first-order reliability method (FORM)-based finite-step adaptive length (FAL) is discussed for reliability analysis of composite tubes under frequency failure mode. The performances for efficiency and robustness to evaluate the failure probability FORM formulas are discussed. Therefore, the capability of FAL using the steepest descent sensitivity vector is compared with three FORM formulations that are extended by the steepest descent search direction for nanocomposite tubes conveying nanofluid. In this current work, the Navier scheme is employed for calculating the frequency failure mode. Furthermore, the robustness and efficiency related to the steepest descent FORM formulas of HL-RF, directional stability transformation method (DSTM), and finite-step length (FSL) are compared with FAL. Based on this discussion, FAL contains efficient formula in comparison with other FORM formulas. Moreover, it is found that FSL formulas as well as FAL formulas are more robust than HL-RF and DSTM. This structure's failure probability rises as the fluid velocity and pipe diameter increase.

Fatigue damage is treacherous and can lead to the failure of offshore structures. The purpose of this research is to evaluate and discuss the stress concentration factor (SCF) values for tw...