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The determination of the dynamic performance of a high-speed (HS) railway bridge is an ever-increasingly topical matter in public transportation networks owing to the broad establishment of ongoing HS railway transportation networks and the implementation of conventional networks for superior operational vehicle velocities. This paper examines the fatigue performance of a welded gusset plate connection of a composite steel I-girder railway bridge under trains moving within a certain range of velocities. The global three-dimensional finite element models (FEMs) are applied to examine the dynamic response of the I-girder composite steel-concrete railway bridge. The natural frequencies of the numerical model of bridge are verified using ambient vibration test results. A local three-dimensional FEM is generated in accordance with critical welded gusset plate connection using the ABAQUS platform. The local submodel is generated congruent with displacement field interpolation. The fatigue performance of a welded joint zone considering critical stress accumulation regions is determined by the hot-spot stress method under resonance conditions due to train passage with varying velocities. Stress cycles are extracted by taking real traffic spectra into account. Fatigue damage is calculated by using Palmgren-Miner's rule and the rain-flow counting method. The outcomes demonstrate that the bridge is not vulnerable to the forthcoming fatigue failure mode. [ABSTRACT FROM AUTHOR]

Wire and arc additively manufactured (WAAM) parts and structures often present internal defects, such as gas pores, and cause irregularities in the manufacturing process. In order to describe and assess the effect of internal defects in fatigue design, this research study investigates the fatigue strength of wire arc additive manufactured structures covering the influence of imperfections, particularly gas pores. Single pass WAAM structures are manufactured using titanium alloy Ti-6Al-4V and round fatigue, tensile specimen are extracted. Tensile tests and uniaxial fatigue tests with a load stress ratio of R = 0.1 were carried out, whereby fatigue test results are used for further assessments. An extensive fractographic and metallographic fracture surface analysis is utilized to characterize and measure crack-initiating defects. As surface pores as well as bulk pores are detected, a stress intensity equivalent ∆Keqv transformation approach is presented in this study. Thereby, the defect size of the surface pore is transformed to an increased defect size, which is equivalent to a bulk pore. Subsequently, the fatigue strength assessment method by Tiryakioğlu, commonly used for casting processes, is applied. For this method, a cumulative Gumbel extreme value distribution is utilized to statistically describe the defect size. The fitted distribution with modified data reveals a better agreement with the experimental data than unmodified. Additionally, the validation of the model shows that the usage of the ∆K modified data demonstrates better results, with a slight underestimation of up to about −7%, compared to unmodified data, with an overestimation of up to about 14%, comparing the number of load cycles until failure. Hence, the presented approach applying a stress intensity equivalent transformation of surface to bulk pores facilitates a sound fatigue strength assessment of WAAM Ti-6Al-4V structures.

Fatigue performance is often a key aspect when dealing with existing steel structures such as steel bridges or offshore constructions. This issue proves to be more critical as these structures are usually located in aggressive environments and are thus exposed to progressive degradation. Indeed, disruptive phenomena such as corrosion can severely worsen the fatigue performance of the steel components. Currently, the normative standards do not provide a codified procedure for the fatigue checks of steel structures subjected to ongoing corrosion. Within this framework, in this paper a simplified approach for the life-cycle assessment of corroded steel structures is proposed. For this purpose, the concept of “critical corrosion degree” is introduced, allowing the expression of corrosion fatigue checks in a more direct “demand vs. capacity” form with respect to the currently available methods. A first validation of such methodology is reported for the corrosion fatigue tests drawn from the literature. The predicted levels of critical corrosion are in good agreement with the values of artificially induced corrosion (i.e., 4, 8, and 12% of mass loss, respectively), with a maximum relative error of ≈9.3% for the most corroded specimen. Finally, parametrical analyses are performed, highlighting the influence of the model parameters on the corrosion fatigue performance of the steel elements.

Drilling is one of the costliest and risky activities in oil and gas industry due to complexity of interactions with downhole formation. Cyclic loads while drilling cause the initiation and growth of cracks in oil tubulars. This phenomenon, known as fatigue, results in permanent reduction of the failure-free service envelope of a certain tubular. Further, most of the drill string failures are triggered by fatigue, which results from repetitive cyclic bending loads and stresses in tensile or buckled drill strings. Fatigue is a cumulative and non-reversible condition induced by repetitive cyclic bending loads and tensile or buckled drill pipe stresses. Fatigue exists even though cyclic tension of the drill pipe material is much lower than static strength limit. Present work investigates fatigue capacity of the 4" WT38 drill pipe connection where cracks have been observed. In accordance with the geometry of connection, a hot spot stress from bending moment is calculated in the crack location in the first thread (upper) of the pin. The DNVGL-RP-C203 SN-curve B1 "in air" is used as relevant fatigue SN curve for the drill pipe thread location. Finite element method (FEM) is employed in modeling and analyzing of drill pipe on pin-box connections. With this method, various connections can be investigated relatively faster and cheaper compared with experimental tests. It is found that the fatigue failure may have been caused as a result of the cyclic load level and number of load cycles. A detailed discussion of the fatigue damage assessment concludes the paper. [ABSTRACT FROM AUTHOR]

The fatigue of structural details of ships is of great importance in the maritime industry as they can lead to cracks which can jeopardize structural integrity. The hopper knuckle is among the most vulnerable areas in a ship with respect to fatigue damage. Analysis of the hopper knuckle has become mandatory for tankers in the Class Ship Rules and in the International Association of Classification Societies Common Structural Rules. Along with the fatigue damage record of the vessels, the fatigue analysis of the hopper knuckles is essential to ensure that the vessels have sufficient fatigue strength. In the current work, fatigue calculations are performed of the upper and lower hopper knuckle connections within midship of the oil tanker using simplified fatigue calculations based on Det Norske Veritas (DNVGL) Classification Note No. 30.7. The fatigue analysis is based on 25 years of operation in worldwide wave environment. A cargo hold model (½ + 1 + ½) amidships and a local finite element model of the hopper knuckle are generated. The local model provides relevant hotspot stress for fatigue life calculations. The results from the hopper knuckle fatigue analysis show that the vessels may expect fatigue cracks at lower hopper knuckle before the vessel reaches its design life of 25 years. Based on the findings, it is recommended to fit soft brackets and close scallops at the lower hopper knuckle on selected common frames in all cargo holds. [ABSTRACT FROM AUTHOR]

Engineers and analysts primarily rely on the Energy Institute's (EI) Guidelines for the Avoidance of Vibration Induced Fatigue Failure in Process Pipework to determine the possibility of a piping system failing due to flow induced vibration. Whilst the EI Guidelines provides a quantitative measure for the likelihood of failure and gives possible remedial actions, certain key parameters such as the fatigue life cannot be obtained. In this work a procedure for incorporating the underlying wall pressure fluctuations in a finite element model for the purpose of determining the fatigue life of a piping system is provided. Numerical simulations are used to determine the fatigue life for a flowline transporting natural gas at three different flow velocities; 65 m/s, 130 m/s and 170 m/s. The study also experimentally investigates the wall pressure fluctuations associated with single phase flow in a geometrically complex manifold. Extensive wall pressure fluctuation measurements associated with water flowing at 1.6 m/s and air flowing at 3 m/s are presented. It has been shown that owing to the dramatic changes in geometry, the pressure fluctuations associated with a fully developed turbulent flow are significantly greater than that observed at an undisturbed position. Unlike the simple 90o elbow or mitre bend, the fluctuations within the manifold remain pronounced with no decay in amplitude. Specifically, for the case of water flowing at 1.6 m/s it is observed that the mean square pressure along the manifold falls within the range of 113 dB and 116 dB, whilst the undisturbed position had a mean square pressure of 104 dB. For the case of air flowing at 3 m/s, the mean square pressure ranged between 101 dB and 107 dB throughout the entire manifold. [ABSTRACT FROM AUTHOR]

To evaluate the improvement of the fatigue performance of orthotropic steel deck by different reinforcement schemes, the fatigue performance of the OSD(orthotropic steel deck) reinforced by steel-UHPC (ultra-high performance concrete) and ERE (epoxy bond chips layer, resin asphalt and epoxy bond chips layer) were compared. Based on the data of stress records for a continuous week, the maximum stress amplitude, the equivalent stress amplitude, and the residual fatigue life of each fatigue-prone detail were calculated by the linear cumulative rule. A finite element model was established to quantitatively compare the stiffness of the two strengthening schemes. The influence of traffic flow and temperature change on the fatigue life of fatigue-prone details was analyzed. The results show that the maximum stress amplitude and the equivalent stress amplitude of each fatigue-prone detail of the steel-UHPC composite bridge deck are smaller than those of the ERE pavement bridge deck. The fatigue life of each fatigue-prone detail of the steel-UHPC composite bridge deck is greater than that of the ERE pavement bridge deck except for fatigue-prone details with infinite fatigue life. The steel-UHPC composite bridge deck has greater bending stiffness, and the maximum deflection of the steel-UHPC deck is 67.29% of that of the ERE pavement bridge deck. The influences of the flow rate increase on the fatigue life of each fatigue-prone detail of the bridge deck reinforced by two reinforcement schemes are basically the same, and the steel-UHPC composite deck has better high temperature resistance. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method for physical fatigue assessment that can be applied in wearable systems, by utilizing a set of real-time measurable cardiovascular parameters. Daylength measurements, including a morning test set, physical exercise during the day, and an afternoon test set were conducted on 16 healthy subjects (8 female and 8 male). To analyze cardiovascular parameters for physical fatigue assessment, electrocardiography, pulse wave and blood pressure were measured during the test sets. The fatigue assessment questionnaire score, reaction time, countermovement jump height and hand grip strength were also measured and used as reference parameters. This study demonstrates that (i) the compiled test battery can selectively assess the rested vs. physically-fatigued states; (ii) the obtained linear support-vector machine, trained using the heart rate variability based parameter (F-score 0.842, accuracy 0.813) and pulse arrival time based parameter (F-score 0.875, accuracy 0.875) shows a promising ability to classify between the physically mildly fatigued and significantly fatigued states. Despite the somewhat limited study group size, the results of the study are unique and provide a significant advancement on the existing physical fatigue assessment methods towards a personalized and continuous real-time fatigue monitoring system with wearable sensors.

Vibration Therapy (VT) stimulate the muscle spindles, which in turn enhances its afferent activities. The present study was designed to investigate the effect of VT at 23 and 35 Hz on muscle performance. The EMG features (six time-domain (TD) and four frequency-domain (FD)) and a new formula for computing neuromuscular performance were used as dependent variables to evaluate the effect of VT. The EMG recording was performed at 50% MVC during grip endurance test before and after VT. The EMG features were extracted out of raw EMG signals acquired from four forearm muscles, viz., flexor digitorum superficialis (FDS); flexor carpi ulnaris (FCU); extensor carpi radialis brevis (ECRB); and extensor carpi ulnaris (ECU) in supine position. Fatigue assessments were evaluated based on the pattern of TD and FD features. Statistical analysis showed a significant difference in the effect of vibration exposure frequency on IEMG (p < 0.001), MAV (p = 0.041), SSI (p = 0.032), and WL (p < 0.001) of FCU muscle. In addition, the greatest increase in neuromuscular efficiency (NME) was observed in the performance of ECRB after 35 Hz of VT and ECU muscles after 23 Hz of VT. The features of EMG signals could be used for fatigue analysis. However, the slope based on the median frequency regression line may be the best feature for fatigue assessment. [ABSTRACT FROM AUTHOR]

Nowadays, the dynamical energy market in Europe requires fast response times and advanced grid control. As a result, Francis turbine runners are subject to complex hydrodynamic forces based on low-load flow phenomena. However, transient events and in particular the turbine startup is considered as the most damaging operating condition. Therefore, experimental and numerical methods are combined to investigate the behavior of a prototype Francis turbine runner during startup. In the experimental part of the study dynamical stress is obtained by strain gauges and used to predict the runner lifetime. Additional to the conventional startup, a second scheme aiming for a higher life expectancy by reducing the opening limit is tested. The experimental part reveal high stress amplitudes during the fast opening process of the guide vanes. The reason therefore is a counter rotating draft tube vortex formation which is discovers by the use of numerical simulation. These 3 up to 4 small vortices are inducing unsteady pressure pulsations at approximately 36 Hz. With the application of the second startup schema, a reduction of the stress amplitudes of around 17 % is archived. It is verified that the change of the startup schema can significantly impact the runner lifetime. • Experimental and numerical methods are combined to investigate the behavior of a Francis turbine during the startup process. • The experiments prove that a significant reduction of the runner stress is achieved by lowering the opening limit. • It is revealed that counter-rotating vortex structures in the draft tube are responsible for high dynamical runner stress. • It is validated that the new transient CFD method is useful for the fatigue assessment of prototype Francis turbine runners. [ABSTRACT FROM AUTHOR]

The use of high strength steel has the potential to reduce the amount of steel used in bridges and thereby, facilitate a more sustainable construction. A survey of existing bridges built using high strength steel is presented in this paper with emphasis on the Swedish bridge stock. The survey aimed at identifying the steel grades that were used and where in the cross-section they have been used. A case study on the influence of fatigue shows that today's regulations make it more difficult to use high strength steel in comparison to previous regulations. [ABSTRACT FROM AUTHOR]

Diaphragm cutouts are set to release redundant constraints and hence reduce weld fatigue at the connection of U-ribs to diaphragms in orthotropic steel decks. However, most fatigue cracks which originate from the edge of cutouts are in fact detected in the diaphragms. Therefore, a retrofit technology on cracked cutouts at the diaphragm is proposed and applied to the orthotropic steel box girder of a suspension bridge. Firstly, the stress concentration on the cutout is analyzed through refined finite element analyses. Furthermore, the fatigue cracked cutouts are retrofitted by changing their geometrical parameters. Thereafter, an optimized geometry and the size of diaphragm cutouts were confirmed and applied in the rehabilitation of a suspension bridge. On-site wheel load tests were carried out before and after retrofitting of the diaphragm cutout. The stress distributions along the edges of the cutouts and at the side of a diaphragm were measured under a moving vehicle. The stress spectra at two critical locations on the edge of a cutout was obtained under longitudinally and laterally moving vehicles. Finally, the fatigue life of the cutouts is assessed by the modified nominal stress method. The analytical and test results indicate that the wheel loads on the deck transmit stress to the diaphragms through the U-ribs, during the load transmission process, the stress flow is obstructed by diaphragm cutouts, resulting in local stress concentrations around the cutouts. In addition, the overall size of the cutouts should be small, but the radius of the transition arc should be large, thus the stress flow will not be obviously obstructed. After the retrofitting of the cutouts by improved geometry, the maximum stress decreases by 87.6 MPa, which is about 40% of the original stress. The equivalent constant amplitude stress is reduced by 55.2% when the lateral position of the wheel loads is taken into consideration. Based on the stresses obtained by finite element analysis (FEA) and experimental tests, the fatigue lives of the original cutouts are 1.7 and 4.9 years, respectively, which increase to 78.1 and 155.5 years, respectively, after the cutouts were retrofitted, which indicates that the improved geometry and retrofit technology can enhance the fatigue performance and extend the fatigue life of diaphragm cutouts with fatigue cracks. [ABSTRACT FROM AUTHOR]

Bridges have a significant role in society but are often massive structures requiring a high amount of materials, leading to high consumption of natural resources and high costs. In this respect, the use of high-strength steel (HSS) may represent a significant advantage as it enables to reduce the quantity of materials required for a structure to fulfil its function. Notwithstanding this potential benefit, the use of slender plates allowed by HSS makes I-girders more vulnerable to local bucking phenomena and fatigue issues. Hence, this article aims to discuss the potential advantages of HSS in bridge design, in terms of structural, environmental and economic performances. The discussion is based on a comparative analysis, in which a bridge made of steel grade S355 is compared with two alternative designs made of steel grade S690. The results of the analysis showed that although the use of HSS in bridges enables to save steel, thus providing some environmental advantages, in terms of costs the differences are negligible due to the higher requirements of HSS bridges. [ABSTRACT FROM AUTHOR]

Fatigue properties are of fundamental importance and extremely time consuming to be assessed. The aim of this research activity is to apply the Thermographic Method (TM) and the Static Thermographic Method (STM) during fatigue and tensile tests to correlate the temperature trend to the fatigue properties of an S355 steel. The material was retrieved from an in‐service port crane. Traditional fatigue tests were performed in order to evaluate the S‐N curve with a scatter band. Step load tests were carried out deriving the fatigue limit and the Energy Parameter of the material. Static tensile tests were performed to obtain the stress at which the temperature trend deviates from the thermoelastic behavior. The fatigue properties obtained by means of the energetic methods were compared to the traditional ones showing a good agreement. [ABSTRACT FROM AUTHOR]

Fatigue load models for road bridges given in the Eurocode EN1991-2 have been calibrated considering real traffic measurements that became available around 1990. Since then, traffic composition has evolved considerably, also considering the issuing of the 96/53/EC Directive, which legitimated member states, on an equal and not discriminatory basis, to allow the circulation of Long and Heavy Vehicles (LHVs). Thus, the appropriateness of fatigue load models to cover also the effects of these vehicles, which are longer, heavier and potentially more damaging than common Heavy Goods Vehicles (HGVs), became an issue. The aim of the study is to assess how the evolution of European traffic influences the fatigue assessment of bridges. To capture the essence of the problem, three different real traffic measurements are compared in terms of fatigue damage: the Auxerre (FR) traffic, adopted to define fatigue load models in EN1991-2; the Moerdijk (NL) traffic, characterized by a high percentage of LHVs; and the Igualada (ES) traffic. To assess the current relevance of fatigue load models LM2 and LM4 of EN1991-2, the aptitude of these models to adequately reproduce the effects caused by LHVs is discussed in detail. The results demonstrate that the Auxerre traffic is still the most onerous; that the Moerdijk traffic is generally more severe than the Igualada traffic, and that the fatigue load models of Eurocode do not require major updates. The study is further supplemented by investigating the suitability of the formulae provided in the Eurocodes for the damage equivalence factors λ 2 and λ 3 to express the influence of the total lorry volume on the fatigue damage. In that latter case, the conclusion is that the formulae proposed in the Eurocodes, based on the assumption of a linear fatigue strength S – N curve with constant conventional slope m , could lead to erroneous, even unsafe, estimates of the fatigue life, especially when details are characterized by constant amplitude fatigue limit Δ σ D , thus calling for further improvements of the formulae themselves. [ABSTRACT FROM AUTHOR]

The steel-UHPC composite deck is an effective solution to fatigue cracks of orthotropic steel decks (OSD) in steel bridges. However, limited research has been reported on the hot spot stress distribution of the steel-UHPC composite deck. This study investigates the hot spot stress distribution and residual fatigue life evaluation of the steel-UHPC deck in a long-span cable-stayed bridge. The two extrapolation points' strain at fatigue-prone details were continuously measured under in-service traffic flow. The hot spot stress time history at each detail of the conventional OSD deck and steel-UHPC deck were analyzed and compared. The residual fatigue life of each detail was calculated. A three-dimensional finite element (FE) model was established and validated through experimental results. The bridge deck's deflection, the asphalt pavement's tensile stress, and the stress distribution at the floor beam cutout were numerically studied using the validated FE model. The results showed that the UHPC layer significantly reduced the hot spot stress and extended the fatigue life at each fatigue detail. The UHPC layer reduced the bridge deck's deflection and the asphalt pavement's tensile stress. Compared with nominal stress method, the hot spot stress method can better describe the large stress gradient distribution induced by the stress concentration at fatigue detail. • Field strain monitoring was conducted on a long-span cable-stayed bridge under in-service traffic. • The hot spot stress were obtained through two points extrapolation method. • Hot spot stress distribution of the conventional deck and steel-UHPC deck was compared. • Fatigue performance of steel-UHPC deck were evaluated based on monitored data. • Numerical simulation of steel-UHPC deck was conducted by a validated FE model. [ABSTRACT FROM AUTHOR]

• A design procedure for the cladding of central measuring shroud based on elastoplastic model was proposed. • Considering actual operating situation, design of cladding against cyclic thermal shock loads was performed. • Compared to the elastic model, the design results of cladding thickness and gap distance is greatly reduced. • The increase of cladding thickness is beneficial for central measuring shroud, but harmful for cladding. The thermal shock caused by scram conditions greatly affects the service life of central measuring shroud. Cladding, as a protective layer, can be adopted to protect the central measuring shroud. In this study, a cladding design procedure based on elastoplastic model was proposed and verified by experiment. Then, the cladding thickness and gap distance were designed. And the temperature and strain distribution were analyzed and discussed. It was found that under thermal shock condition, the cladding thickness and gap distance should be at least 2 mm and 2.66 mm to guarantee safety. Compared to elastic model, the design results of elastoplastic model are reduced by 50 % for cladding thickness and 33.5 % for gap distance. The increase of cladding thickness is beneficial for central measuring shroud, but harmful for cladding. The alternating tensile and compressive strain caused by temperature changes is the main reason for total strain fluctuation. [ABSTRACT FROM AUTHOR]

This research focusses on the fatigue behaviour of welded components made of high strength duplex (EN 1.4162) and carbon steel. It starts by investigating the base material alongside welded cruciform joints submitted to cyclic loading through experiments and finite element models. The obtained results are then compared with existing research on high strength (carbon and stainless) steel equivalents. This collated database of >500 reference test results is then used to assess the applicability of the current Eurocode and IIW provisions to predict the fatigue life of higher strength steels and to propose new rules that include the benefit of their higher material strength. Proposals are made to upgrade certain fatigue classes (e.g., transverse stiffeners and butt welds) when high strength steel grades are employed. The reliability of these proposals is then supported by the use Weibull models, commonly used in survival analysis. • Fatigue behaviour of welded cruciform joints (duplex EN 1.4162 grade) is observed. • SN-curves of similar details made of high-strength steels (HSS) were reassessed. • Improvement to the fatigue design rules for these grades is proposed. • The reliability of these proposals is supported by the use Weibull models. [ABSTRACT FROM AUTHOR]

This work presented salient features of the steel behavior of seven metallic bridges close to, or over, 100 years old, among the Spanish conventional rail network as well as the results of a fatigue life expectancy study. A preliminary study of the properties of the constituent materials obtained from the bridges samples was carried out followed by dynamic fatigue tests under service representative loads. Due to the steelmaking techniques in the late 19th and early 20th centuries, disperse fatigue behavior results were obtained. However, the wide safety margins with which these bridges were designed, as well as the mechanical properties of the steel (relatively good mechanical resistance but with low ductility), seem to guarantee a long fatigue life. This estimate decreases sharply with increasing loads.

Fatigue strength dictates life and cost of welded structures and is often a direct result of initial manufacturing variations and defects. This paper addresses this coupling through proposing and applying the methodology of predictive life-cycle costing (PLCC) to evaluate a welded structure exhibiting manufacturing-induced variations in penetration depth. It is found that if a full-width crack is a fact, a 50% thicker design can result in life-cycle cost reductions of 60% due to reduced repair costs. The paper demonstrates the importance of incorporating manufacturing variations in an early design stage to ensure an overall minimized life-cycle cost.

Safety assessment with respect to seismic and vertical loads of existing and very old masonry structures is currently a central topic for the scientific engineering community. In particular, there are many ancient bridges still in service that are subjected to higher and more frequent cyclic loads. For these structures, it is important to determine the actual fatigue strength, rather than the ultimate carrying capacity. In this way the remaining service life, with possible traffic load limitations, may be estimated. This paper reports an updated review of the state-of-the art on recently published fatigue models that account for deterioration effects under cyclic loads. In addition, results related to fatigue performance of a bridge are shown and comments are provided. The numerical comparisons among existing fatigue models reveal that the application of the available fatigue models is particularly problematic for ancient masonry elements, where appropriate stress-life curves are required.

The main aim of the present work is to investigate the effects of different parameters on the fatigue strength of four different welded details through an energetic approach based on the Strain Energy Density failure criteria. The results of the finite element analyses have been compared with the fatigue strength predicted by the design guidance EN 1993-1-9:2005, also known as Eurocode 3, which establishes the rules for the fatigue design of steel welded joints. The results obtained in this work highlight an overestimation of the fatigue strength by the Eurocode 3 with regard to the details considered.

Fatigue failures are a concern for old riveted steel bridges since most of them were not originally designed taking into account fatigue. The usual fatigue assessment approach for riveted joints consists of using the fatigue class 71 S-N curve proposed in Eurocode 3, part 1–9. However, this approach may lead to excessive conservative predictions since it is applied indistinctly for different riveted connection geometries and materials. Riveted joints fatigue classification according to the proposal of Taras and Greiner produce more consistent description of the experimental data rather than the Class 71 S-N curve as proposed in the EC3. Local approaches are an alternative methodology to perform fatigue characterization of any type of joints, made of any material, providing that material fatigue properties are available as well as accurate numerical models of the joints. This paper presents an experimental campaign and a numerical analysis concerning down-scale riveted specimens. The fatigue behaviour of these riveted joints was also modelled using standard and extended finite element methods. The different models produced diverse predictions, depending on the failure modes considered. • An experimental campaign and a numerical analysis concerning down-scale riveted specimens were made. • Two finite element methods to assess the fatigue behaviour of the down-scale riveted joint, FEM and XFEM, were used. • Fatigue life predictions were assessed including both fatigue crack initiation and crack propagation phases. • The number of cycles to initiate a fatigue crack was computed using local notch strain approaches. • The number of cycles in crack propagation phase was computed based on the CIM using 3D XFEM, as well as the VCCT. [ABSTRACT FROM AUTHOR]

Previously to the renovation of a long steel highway bridge, built in 1969, the remaining fatigue life of the orthotropic bridge deck should be analysed. The bridge structure is a very slender box‐girder bridge with three spans (L = 120 + 210 + 82 = 412 m). The heavy traffic is very high, with approximately 1,2 million trucks per year in the busiest lane. This paper gives a summary of the comprehensive numerical analyses, combined with extensive measurements (traffic data, stress spectra at relevant details) and also fatigue tests on full scale test specimen. Fortunately, in front of the bridge an automatic lorry counting device was installed and therefore the numbers and types of lorries in each lane, on each day, within the last decade were well‐known. In addition, simplified models for the numerical simulation of the heavy traffic on the orthotropic bridge deck are shown, with comparison to field measurements of stress spectra under service conditions. These measurements were done to overcome the uncertainties in the simulation, e.g. overloads, specific lorry types, different positions within the lane and dynamic effects. Fatigue tests were done for the detail of the joint between the longitudinal ribs and the cross girder, with a non‐typical only one sided welded connection. For this detail also a very effective strengthening solution was developed and tested. [ABSTRACT FROM AUTHOR]

• The stress amplification factor considering the initial deformation effect of thin plates is derived. • Nonlinear finite element calculation and fatigue test results are used to verify the feasibility of the modified formula. • The modified formula can accurately reflect the stress concentration effect of thin plates butt joints. In addition to dislocation and welding angle deformation during the processing of welded joints of thin plates, additional curvature deformation will occur in the thin plates, which is defined as the initial deformation of the plates. Due to the existence of dislocation and angular deformation, additional secondary bending moment effect will appear in the welded structure, which will affect the stress concentration at the weld toe. Therefore, DNV and IIW specifications recommend the stress amplification factor formula caused by welding imperfections. However, the current evaluation formula is mostly applicable to the stress concentration correction of thick plate welded structures, which does not consider the additional initial deformation effect caused by thin plate welding. Therefore, on the basis of the revised formula for thick plates, the stress amplification factor considering the initial deformation effect of thin plates is derived in this paper, and the calculation results are compared with those in traditional codes. Nonlinear finite element calculation results and fatigue test results are used to verify the feasibility and validity of the formula. The results show that, when considering the initial deformation of welding plates, the traditional code formula has a large error, and the revised calculation results are in good agreement with the finite element calculation results, which can accurately reflect the stress concentration effect at the welding toe of the thin plates butt joints. [ABSTRACT FROM AUTHOR]

This paper deals with the experimental and numerical investigations of the structural behaviour of a rolling stock's seats system under static and fatigue loading conditions, aimed to assess the reliability of some multiaxial fatigue failure criteria implemented in the FE model. According to the NF F31–119 standard, a specific full-scale multiaxial testing machine has been used for the fatigue test. During the test, a visual inspection approach with a detection interval of 3·105 cycles has been adopted. After 1.2·106 cycles the test has been stopped and a Liquid Penetrant Inspection (LPI) has been carried out in order to detect accurately cracks nucleation and propagation. Moreover, numerical analyses, based on the Finite Elements (FE) Method, have been performed on the EN-AW 6060 T5 aluminium alloy structure of a rolling stock's seats to predict the most affected zones where the cracks nucleation may occur under multiaxial fatigue loads. Since the in-service applied loads belong to Multiaxial High-Cycle Fatigue (MHCF) load class, Sines, Crossland and Dang Van criteria have been used to post-process the predicted results achieved by the FE analyses. For validation purpose, numerical and experimental results have been compared. According to the numerical-experimental results comparison, Dang Van criterion provided the best level of accuracy. • Static and fatigue behaviour of a rolling of an aluminium structure of rolling stock's seats was evaluated. • FE analyses have been carried out in order to predict the areas of the structure where cracks can nucleate. • Sines, Crossland and Dang Van criteria have been implemented in the developed FE model. • Dang Van one provides the most effective and reliable results for this application. • The numerical results have generally shown a good correlation with the experimental ones. • The investigated criteria can detect the areas where the cracks can nucleate, but they cannot predict their propagation. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of 09Mn2Si steel used for the transmission natural gas pipeline "Mastakh-Berge-Yakutsk" have been investigated comprehensively after 37 years of operation. The results obtained for the specimens cut from the pipe were compared to those obtained using the preserved (reference) specimens. It is demonstrated that long-term operation in harsh climate does change the pearlitic microstructure appreciably. The strain aging however can be noticed through precipitation of finely dispersed carbides in the grain interior. The latter causes some embrittlement of the steel measured under impact loading. Revealed microstructural changes are not practically important for "quasi-static" tension or hardness properties. Nonetheless, under cyclic testing the microstructure degradation, which occurred during long-term operation, results in a considerable reduction of fatigue life, which is particularly pronounced during the crack initiation stage. The microstructure degradation is most clearly seen in sharply reduced impact toughness which dropped by a factor of two at temperatures below zero Centigrade. Reasons and mechanisms of the observed phenomena are discussed. Unlabelled Image • Long-term service of the steel caused no significant changes in the cementite phase, however hydrogen charging can occur. • The revealed microstructure degradation exerts only little effect under static tension and by hardness measurements. • After long-term service, the fatigue life decreased by ~16 %. • The impact fracture toughness of the used steel is maximum decreased by a factor of ~2.2 at T = –70 °C. • The degradation of properties is attributed to accumulation of defects in the material during operation. [ABSTRACT FROM AUTHOR]

Highlights • A fatigue analysis of a type of fillet welded joint is presented. • Four welded joint series for evaluating the fatigue performance were produced. • The fatigue behaviour combines an experimental campaign and numerical analysis. • In this fatigue analysis two main numerical tools – FEM and XFEM – were used. • Fatigue predictions based on crack initiation and propagation phases were made. Abstract This paper presents a fatigue analysis of a type of fillet welded joint representative of one main joint of the steel box girder of the Alcácer do Sal railway bridge. From previous studies, it was found that the welded joint between the box girder diagonal and the central hanger gusset is one of the most stressed details of the bridge. This welded joint was not fully manufactured according to current construction procedures, as regards the fillet weld end configuration. In order to assess the fatigue behaviour of such welded joint, the present study combines an experimental campaign and numerical analysis. A total of four welded joint series were produced in order to allow the comparison of the fatigue performance of similar type of welded joint of the Alcácer do Sal bridge with welded joints produced according to existing recommendations, such as EC3. Since scale-down specimens were considered, two different thicknesses were included in this study for each joint configuration, to allow the verification of any thickness effect. Concerning the numerical analyses, two main numerical tools were used: the standard Finite Element Method (FEM) with ANSYS and the eXtended Finite Element Method (XFEM) with ABAQUS. Fatigue life predictions were performed including both fatigue crack initiation and fatigue crack propagation phases. The number of cycles to initiate a fatigue crack was computed using local notch strain-life approaches, and the number of cycles for fatigue crack propagation was computed by integrating the Paris fatigue crack growth law with stress intensity factors computed with ANSYS (virtual crack closure technique) and ABAQUS (contour integral method, 3D XFEM model). Experimental tests demonstrated little influence of fillet weld end geometry on fatigue behaviour of welded joints and plate thickness effects were also reduced as also confirmed by the similar fatigue crack propagation rates. Both numerical simulations provided very accurate predictions of the experimental S-N curves, however the XFEM modelling opens new possibilities for mix-mode fatigue crack propagation simulations. [ABSTRACT FROM AUTHOR]

Featured Application: The results of this work can be used in the evaluation of existing prestressed concrete slab-between-girder bridges for fatigue. In the Netherlands, the assessment of existing prestressed concrete slab-between-girder bridges has revealed that the thin, transversely prestressed slabs may be critical for static and fatigue punching when evaluated using the recently introduced Eurocodes. On the other hand, compressive membrane action increases the capacity of these slabs, and it changes the failure mode from bending to punching shear. To improve the assessment of the existing prestressed slab-between-girder bridges in the Netherlands, two 1:2 scale models of an existing bridge, i.e., the Van Brienenoord Bridge, were built in the laboratory and tested monotonically, as well as under cycles of loading. The result of these experiments revealed: (1) the static strength of the decks, which showed that compressive membrane action significantly enhanced the punching capacity, and (2) the Wöhler curve of the decks, showed that the compressive membrane action remains under fatigue loading. The experimental results could then be used in the assessment of the most critical existing slab-between-girder bridges. The outcome was that the bridge had sufficient punching capacity for static and fatigue loads and, therefore, the existing slab-between-girder bridges in the Netherlands fulfilled the code requirements for static and fatigue punching. [ABSTRACT FROM AUTHOR]

Highlights • A novel spectral fatigue method is proposed for Gaussian bimodal processes. • Factor ξ is introduced to reflect coupling between low & high frequency modes. • The method is not only efficient but more accurate than other spectral methods. Abstract Fatigue damage assessment of narrow-banded (NB) Gaussian processes in frequency domain has been a classical problem since the 1960s, in that the frequency-domain approach is more efficient than the time-domain approach such as the Monte-Carlo simulation based rainflow counting. However, when the random process of stress is wide-banded (WB) and particularly contains two or more peaks well apart in the spectrum, it is still difficult to accurately assess the fatigue damage by spectral methods, even if the process is Gaussian. On the basis of the single-moment method and the spectral discretization idea, this paper presents an efficient and accurate method for the bimodal Gaussian fatigue assessment. In this method, the mutual influence between the narrow-banded low-frequency (LF) stress and the high-frequency (HF) stress is reflected by a coefficient ξ dependent on the high-low frequency ratio γ , the energy ratio β and the slope parameter k of material's S-N curve. Time-domain rainflow counting is used as the reference to judge the accuracy of this new method against several popular spectral methods, i.e., Jiao-Moan (JM) method, single moment (SM) method, Low's bimodal method (LOW) and Tovo-Benasciutti (TB) method. For wide ranges of γ , β , k and all bimodal patterns (NB-LF with NB-HF, WB-LF with NB-HF, NB-LF with WB-HF and WB-LF with WB-HF), the proposed method is most accurate among all methods, demonstrating its great potential in engineering practice. [ABSTRACT FROM AUTHOR]

Axial low-cycle fatigue tests are conducted on transverse butt joint specimens and cruciform joint specimens made of carbon structural steel GB Q235B. The effect of slip between the specimens and the grips of the test machine is considered by the proposal of a linear slip model. The cyclic softening properties are studied by observing the variation of stress amplitude with cycles. The cyclic stress–strain curve and the strain–life curve for both kinds of specimens are obtained based on the fatigue test data, and the corresponding coefficients are fitted. In order to verify the fatigue test results, finite element models of specimens are established and the corresponding fatigue life assessment is conducted using the local stress–strain approach and the equivalent structural stress approach, respectively. The results show that the effect of slip is unneglectable and the established linear slip model is reasonable. The two kinds of specimens both show a strain softening property, but cruciform joint specimens experience sudden falls of stress amplitude during the test due to the damage of welded lines; cruciform joint specimens show an either one-side failure mode or two-side failure mode while butt joint specimens only show a one-side failure mode; the two-side failure mode tends to lead to shorter fatigue life, so in the design of cruciform joint, such failure mode should be avoided. [ABSTRACT FROM AUTHOR]

Highlights • A novel spectral moments equivalence based lumping block method is developed. • A correction factor is introduced to improve the performance of the proposed method. • The effectiveness of the method is validated with numerical and experimental results. • The new method outperforms the conventional methods both in accuracy and robustness. Abstract This paper provides a novel lumping block equivalence method, termed as spectral moments equivalenc e (SME) based method, to improve the efficiency of fatigue assessment in preliminary design stage. In the newly SME method, an equivalent equation of representative sea state's spectral wave energy and original sea state's spectral wave energy is set up in the fatigue equivalence viewpoint. The relations of wave parameters and wave spectral moments are introduced into the SME method to determine the equivalent significant wave height and up-crossing wave period of the representative sea state. A key feature of the SME method is that the effect of S-N curve's slope and quantity of sea state in lumping block is incorporated into the equivalent formulae to make the method applicable to different lumping block partitions and fatigue curves. In addition, the SME method also has advantage of preserving the stochastic characteristics of sea states. Cumulative fatigue damage of fixed and floating offshore platforms are generated to verify the validity and applicability of the SME method. Numerical results indicate that the SME method not only yields the most accurate fatigue assessment but also has robustness to block partitions and offshore structures. [ABSTRACT FROM AUTHOR]

The main aim of the present work is to investigate the effects of different parameters on the fatigue strength of four different welded details through an energetic approach based on the Strain Energy Density failure criteria. The results of the finite element analyses have been compared with the fatigue strength predicted by the design guidance EN 1993-1-9:2005, also known as Eurocode 3, which establishes the rules for the fatigue design of steel welded joints. The results obtained in this work highlight an overestimation of the fatigue strength by the Eurocode 3 with regard to the details considered. [ABSTRACT FROM AUTHOR]

Abstract In the context of fatigue evaluation of riveted railway bridges, cross-girder to main beam connections are frequently critical details. Secondary effects, such as out-of-plane bending and dynamic amplifications due to the proximity to loading paths which in the case of old bridges were not taken into account in the original design, may lead to severe increase of fatigue damage. The fatigue assessment of old riveted railway bridges has been addressed in the last years by developing local models of critical riveted joints that are linked to global models. This local-global modelling approach aims at evaluating local secondary stresses. Former fatigue probabilistic analyses of riveted joints have been focused on resistance variability rather than on loading/stresses (actions) variability. In this paper a probabilistic procedure to include the variability of loading in the fatigue analysis of complex riveted joints of railway bridges is proposed assuming loading as a random variable. Local finite element models were developed and later coupled with the global model in order to obtain the real stresses associated to real trains crossing the bridge. To reduce computational time, the results obtained from these local models were inputted in a Linear Fracture Mechanics model, supported by Paris fatigue crack propagation law. Monte Carlo simulation technique was applied to calculate the fatigue reliability of an old riveted railway bridge, considering traffic records from previous studies on the bridge. Highlights • Proposed probabilistic procedure to include loading variability in fatigue analysis of riveted joints of railway bridges. • Local FEM coupled with global model in order to obtain the real stresses associated to real trains crossing the bridge. • Results from the local FEM inputted in a Linear Fracture Mechanics model, supported by Paris fatigue crack propagation law. • The shape functions from local finite element model for extreme trains were calculated. • Monte Carlo simulation technique implemented for fatigue reliability of an old riveted railway bridge. [ABSTRACT FROM AUTHOR]

Highlights • The accurate geometry models are analyzed for complex welded joints under multiaxial loading. • Multiaxial fatigue assessments are systematically carried out using the notch stress approach. • The statistical analysis and probability of non-conservative prediction are determined for six multiaxial fatigue criteria. Abstract The notch stress method is often recommended for fatigue assessment of complex welded joints as it can consider the influence of weld toe geometric parameters on local stress. However, the application of the notch stress method is still in the exploratory stage in multiaxial fatigue compared with the traditional nominal stress method and structural stress method. Considering the geometric effect at the weld toe, the notch stress method describes the local stress with an accurate geometry model and the complex stress states at the damage point under multiaxial loading are determined in the local coordinate system. Using the notch stress method, six classical multiaxial fatigue criteria are re-evaluated for a series of typical welded joints in the literatures under both proportional and non-proportional loads. In order to evaluate the different criteria quantitatively, a statistical analysis is performed and the probability of non-conservative prediction is determined for each multiaxial fatigue criterion. The results show that the S-N curve for notch stress under multiaxial loading has a lower inclination and higher fatigue class compared with the uniaxial curve recommended by IIW. [ABSTRACT FROM AUTHOR]

Highlights • A fatigue life assessment procedure for the float collar under random waves is proposed. • The probability density function for estimating the floating system fatigue life is investigated. • The fatigue lifetime of the float collar based on short- and long-term stress distribution are analyzed. Abstract Fish farms have moved into the open sea in recent years and the failure risk of fish cages has increased in the harsher environmental conditions. Fatigue failure is an important limit state for the floating system of the fish cage under the long-term action of waves. A fatigue analysis of the high-density polyethylene (HDPE) floating system in random waves is presented to investigate the applicable probability density function for estimating the floating system fatigue life in this study. The stress response of the floating collars is firstly analyzed based on the finite element analysis combined with a hydrodynamic model. The stress histories of floating collars under each sea state are counted using the rainflow method as a benchmark for frequency domain fatigue analysis. The short- and long-term distributions of the stress ranges were fitted by various probability density functions including Rayleigh, Weibull, Gamma and generalized extreme value (GEV) distributions. Comparisons of the estimated fatigue life using different short- and long-term distributions were performed. Results indicate fatigue estimations based on the GEV and Gamma distributions of the short-term stress range by removing the negligible low stress range give much more accurate fatigue damage results than the traditional Rayleigh distribution. Weibull distribution overestimates the fatigue lifetime of the floating collar. The fatigue lifetime based on the long-term distribution was evaluated and was compared with the rainflow statistic and deterministic method results. The results show the long-term distribution is much more conservative for estimating the fatigue lifetime of the floating system. [ABSTRACT FROM AUTHOR]

• Strain estimation using data-driven Singular Value Decomposition (SVD). • Reliability-based probabilistic fatigue assessment using reliability Kernel Density Estimation (KDE). • Investigation of estimated strain response for fatigue evaluation in bridges. Performing bridge fatigue evaluation using field measurements can be difficult given the amount of data needed for effective assessment, access needed to effectively monitor all fatigue prone locations, and associated power requirements and cost. Several studies have been conducted that estimate strain response at unmeasured locations using indirect measurements and subsequently investigate the quality of the estimation using certain metrics [1]. There is little to no research focusing on pragmatically extending these estimation techniques to probabilistic fatigue assessment. This may be because strain estimation has primarily been successful when applied to numerical and laboratory specimens and perceived potential for difficulties associated with applying developed techniques at scale. This study investigates using data-driven, Singular Value Decomposition (SVD), estimated strains at unmeasured locations for probabilistic fatigue assessment of an in-service, railway, bridge. Before performing strain estimations, SVD Proper Orthogonal Modes (POM) variability was reduced using two classification approaches: k-means clustering and root mean square (RMS); and self-organizing maps (SOMs) and POMs. After estimated strains were obtained, reliability analyses using Kernel Density Estimation (KDE) were utilized to perform probabilistic fatigue assessments. Resulting reliability indices computed using estimated strains were compared against reliability indices obtained using measured strains at the same locations. Results showed that reliability indices computed using estimated strains matched closely with indices obtained using measured strains. [ABSTRACT FROM AUTHOR]

A long-term fatigue assessment method based on EWP concept is proposed. 'Equivalent wave probability (EWP)' is the fictitious (H S , T m)'s joint probability distribution function (JPDF), for which the frequency distribution of the stress variance R 2, f(R 2), calculated by spectral fatigue assessment agrees with the observed one. By choosing probability function p(R 2) to fit f(R 2), the R 2's statistical model (R2SM) which represents the relation between the EWP parameters and R 2's population parameters is developed, and the Bayesian inference, which can estimate the EWP parameters from the measured R 2 data is developed. The EWP at the reference position (RP) can be determined by Bayesian inference from the measured R 2 through the R2SM at RP. To accurately estimate the measured f(R 2) at the target position (TP) from the EWP at RP, an R2SM correction factor at TP, denoted by α TP , is introduced in the process of assimilating R2SM. The resulting R2SM, which has been assimilated by Bayesian inference using measured data, is referred to as data-assimilated R2SM (DAR2SM). The fatigue assessment using EWP at RP as the input of DAR2SM at TP is called Bayes-EWP-DAR2SM analysis. The validity of Bayes-EWP-DAR2SM analysis is verified by using the long-term (about four years) multi(12)-position hull monitoring (HM) data of an 8,600TEU container ship. The fatigue damages estimated by Bayes-EWP-DAR2SM based solely on the stress history of a single sensor are in agreement with measurements with sufficient accuracy, independent of the chosen data assimilation period. This demonstrates that the multi-position fatigue assessment solely through HM at one RP based on EWP concept is realized. • 8600 TEU container ship's onboard hull monitoring (HM) at 12 positions over 4 years. • Statistical model between parameters of wave probability and stress statistics. • Equivalent wave probability (EWP) parameters are determined by Bayesian inference. • Multi-position fatigue assessment solely through HM at one sensor based on EWP. • EWP concept has sufficient accuracy regardless of the data assimilation period. [ABSTRACT FROM AUTHOR]