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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.

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.

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.

PurposeIn the last decades, the demand and use of renewable energies have been increasing. The increase in renewable energies, particularly wind energy, leads to the development and innovation of powerful wind energy converters as well as increased production requirements. Hence, a higher supporting structure is required to achieve higher wind speed with less turbulence. To date, the onshore wind towers with tubular connections are the most used. The maximum diameter of this type of tower is limited by transportation logistics. The purpose of this paper is to propose an alternative wind turbine lattice structure based on half-pipe steel connections.Design/methodology/approachIn this study, a new concept of steel hybrid tower has been proposed. The focus of this work is the development of a lattice structure. Therefore, the geometry of the lattice part of the tower is assessed to decrease the number of joints and bolts. The sections used in the lattice structure are constructed in a polygonal shape. The elements are obtained by cold forming and bolted along the length. The members are connected by gusset plates and preloaded bolts. A numerical investigation of joints is carried out using the finite element (FE) software ABAQUS.FindingsBased on the proposed study, the six “legs” solution with K braces under 45° angle and height/spread ratio of 4/1 and 5/1 provides the most suitable balance between the weight of the supporting structure, number of bolts in joints and reaction forces in the foundations, when compared with four “legs” solution.Originality/valueIn this investigation, the failure modes of elements and joints of an alternative wind turbine lattice structures, as well as the rotation stiffness of the joints, are determined. The FE results show good agreement with the analytical calculation proposed by EC3-1-8 standard.

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.

A new formulation of a Logistic deterministic S-N curve is applied to fatigue data of metallic materials from ancient Portuguese riveted steel bridges. This formulation is based on a modified logistic relation that uses three parameters to fit the low-cycle- (LCF), finite-life- and high-cycle-fatigue (HCF) regions. This model is compared to the Kohout-Vechet fatigue model, which has a refined adjustment from very low-cycle fatigue (VLCF) to very high-cycle fatigue (VHCF). These models are also compared with other models, such as, power law and fatigue-life curve from the ASTM E739 standard. The modelling performance of the S-N curves was made using the fatigue data considering the stress fatigue damage parameter for the materials from the Eiffel, Luiz I, F�o and Trez�i riveted steel bridges. Using a qualitative methodology of graphical adjustment analysis and another quantitative using the mean square error, it was possible to evaluate the performance of the mean S-N curve formulation. The results showed that the formulation of the S-N curve using the Logistic equation applied to the metallic materials from the old bridges resulted in a superior performance when compared with others models under consideration, both in the estimation of fatigue behaviour in the low-cycle fatigue (LCF) region and in the lowest mean square error.

In this paper, the failure probability of corroded pipelines made by X60 steel grade is evaluated. For this complex real engineering failure problem, the burst corroded performance function is developed using an M5Tree model based on calibration with real burst test database. In addition statistical analysis of ILI-report data is conducted for best modeling of corrosion defects geometries (i.e. defects length and depth) based on Anderson-Darling statistic where different PDFs (i.e. Normal, Lognormal, Frechet, Gumbel, Weibull) were tested. Moreover, the effect of defects geometries on the failure probability of the case-studies were investigated for various operating regimes. Then the influence of distributions on the reliability analysis were also illustrated. Results indicated that increases in defects depth are strongly reduced the safety levels of this problem, where miss-selection of defects distributions could lead to conservatives results.

Engineering structures, such as bridges, pressure vessels, machines, etc., are subject to variable load cycles during their lifetime that can cause fatigue damage. Fatigue design of steel structures is based on double S-N curves and the estimation of fatigue damage caused by load cycles. This estimation is calculated by cycle counting methods combined with the Palmgren-Miner rule. The presented software, Fatigue Damage Tool (FDT), is based on the design assumptions of the Eurocode 3 EN1993-1-9 standard. The cycle counting method implemented in FDT is the rainflow counting algorithm according to the ASTM E1049-85 standard, and it uses the Palmgren-Miner rule to calculate de fatigue damage for a critical detail. In this paper, the software is applied to estimate the fatigue damage accumulation for a critical detail at the mid-span of the Varzeas railway bridge. Additionally, FDT can also be applied to several other types of engineering structures.

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.

This book chapter intends to provide a fatigue database for some representative materials of old Portuguese metallic bridges (Eiffel, Luiz I, Fao, Pinhao and Trezoi). Puddle irons and structural steels are covered, depending of construction year of the bridge. Besides the base materials, also S–N fatigue data of riveted joints made of original rivets or new rivets are presented, but in any case using original plates. As regards the materials characterization, S–N fatigue data obtained using smooth specimens is presented; also, fatigue crack propagation data obtained using CT specimens is presented. The monotonic tensile properties are also characterized as well as the microstructures. S–N fatigue data for riveted joints was also presented and compared with existing literature data, including existing design curves. This comparison shows some data falling below the design S–N curves that corroborates the presence of cracks originated by the prior operation of the bridge or material degradation. Regarding the strain-life behaviour of the materials investigated, the number of transition reversals decreases with increasing age of the materials. Only the material from the Trezoi bridge shows a transition life typical of low carbon steels. The fatigue crack propagation tests showed that Paris law gives a good description of the fatigue crack growth data with an exponent always greater than 3. The C coefficient was in same range of that recommended in literature for modern construction steels.

Wire arc additive manufacturing (WAAM) has increasingly attracted attention in the construction sector because of its ability to produce large metallic structural parts in short times. In this paper, Coffin-Manson and Morrow (CMM) equation is employed to compare the fatigue life of WAAM stainless steel with the structural steels S355 and S690. The results showed that the fatigue performance of structural steel is better than the WAAM stainless steel, the fatigue performance vertical to printing direction (WAAM-900) is better than it along the printing direction (WAAM-00). In addition, the fatigue cycle of the transition reversals of structural steel is much less than it of WAAM stainless. With the increasing the fatigue cycle, the maximum density of the strain amplitude ratio is gradually increased to 1.0. The probabilistic parameters of CMM equation were obtained by a stochastic analysis using Latin hypercube sampling strategies. The probabilistic strain-fatigue life behaviour obtained from the constant exponent sampling strategy is higher when compared with the varied exponent sampling strategy for both WAAM stainless and structural steels.

The paper deals with the subject of diagnostics and the quick repairs of long-term operated metallic materials. Special attention was paid to historical materials, where the structure (e.g., puddle iron) is different from modern structural steels. In such materials, the processes of microstructural degradation occur as a result of several decades of exposure, which could overpass 100 years. In some cases, their intensity can be potentially catastrophic. For this reason, the search for minimally invasive diagnostic methods is ongoing. In this paper, corrosion and fracture toughness tests were conducted, and the results of these studies were presented for two material states: post-operated and normalized (as a state &ldquo, restoring&rdquo, virgin state). Moreover, through the use of modern numerical methods, composite crack-resistant patches have been designed to reduce the stress intensity factors under cyclic loads. As a result, fatigue lifetime was extended (propagation phase) by more than 300%.

Racking systems applied in logistics warehouses are built with thin steel sections that are joined by bolted connections. In fully automatic systems, these structures are loaded 7/7 days and 24/24 hours raising fatigue issues due to the cyclic nature of the resulting stresses. According to the current industrial practice, those bolted joints are tight with no torque control, leading to the concept of snug tight bolts, which behaves similarly to non-preloaded bolted joints. Eurocode 3 has no reference about fatigue rules of bolted connections between thin-walled cold formed steels. This paper aims at analyzing the fatigue behaviour of bolted (snug tight vs. preloaded) joints in order to provide fatigue design rules for possible update of Eurocode 3 existing rules. A significant fatigue testing program was performed to investigate the influence of different bolts arrangements, stress R-Ratios and bolt preloads, including snug tight, on fatigue life. The obtained results were analyzed under ASTM E739 procedure in order to obtain S-N curves. This work revealed an average fatigue strength of 114 MPa at 2E6 cycles for the snug tight bolted joints. Preloaded bolt joints presented an average fatigue strength of 108 MPa at 2E6 cycles. Discrepancies between S-N curves suggested by Eurocode 3 and fatigue data obtained experimentally were verified.&nbsp

Aero engine components like compressor discs normally operate under harsh conditions like complex multiaxial stress states. Notch effect is often critical for structural integrity assessment in virtue of complex structure and discontinuities. According to the notch effect under cyclic loadings, a computational framework for multiaxial fatigue analysis of compressor discs is established by coupling finite element (FE) simulation of stress gradient with Fatemi-Socie (FS) criterion. Specifically, a notch support extension method accounting for stress gradient effect is elaborated through elasto-plastic FE analysis, which can be determined for fatigue life prediction of arbitrary shaped components. Experimental fatigue data for smooth and notched specimens of TC4 and GH4169 alloys demonstrated the appropriateness of the proposed computational approach. The applicability and performance of the prediction model to a compressor blade-disc attachment subjected to field spectra is presented. Results show that testing effect can be significantly reduced by using this framework with acceptable prediction accuracy.

The fatigue damage assessment of large bridges is highly conditioned by the required computational high demands. Generally, in order to overcome the multi-scale problem, global and local models are needed to properly account for both global structural behaviour and the local nature of the fatigue damage. The analysis of such structural problems using direct time-integration algorithms is impracticable in most of the cases, which leads to the necessity of developing alternative methodologies in order to increase the computational efficiency and the accuracy of fatigue cracking assessments. In this respect, effective computational algorithms based on the modal superposition technique have been proposed and implemented in previous works. Overall, such workflow considers the interaction between the global and local models combined with the application of the modal stress intensity factor concept. Aiming at performing an efficient and accurate assessment of the fatigue damage, firstly, combining the Fracture Mechanics principles and crack propagation laws, the crack propagation phase in a complex bridge detail is analysed. In this regard, the present paper aims at proposing relevant improvements to the above-mentioned methodology, namely: i) the refinement of the implemented submodelling techniques in order to increase the accuracy of stress and strain fields computation and allow to account for smaller initial crack lengths; ii) the analysis and limitation of the considered number of vibration modes to the relevant ones for the local dynamic response; and iii) the implementation of a parallel computing approach for the calculation of the modal stress intensity factors related to the vibration modes defined in ii). The fatigue assessment procedures were applied to an assumed cracked welded detail of a recent railway composite bowstring bridge located in Portugal. Also, since the assumption of a pre-existing crack may lead to very conservative predictions, the modal superposition technique is further extended to evaluate the fatigue crack initiation phase, demonstrating the safety of the analysed case study in the absence of existing defects.

Steel and composite steel-concrete bridges are subjected to random traffic loads along their life cycle which generate significant dynamic impacts. The road-roughness of asphalt pavements is one of the most important aspects that contributes to the significant increase of the stress amplitudes and hence to serious load-induced fatigue concerns. In this context, welded joints are well known as the weakest points in bridges, since they are prone to stress concentrations leading to initiation of fatigue cracks being in current design codes evaluated using primarily the nominal stress method (NSM). However, a more accurate stress definition, which considers the complexity of the stress field at the welds, becomes necessary mainly in old roadway steel bridges that are often subjected to out-of-plane stresses. In this paper, the hot-spot stress method (HSM) is used to evaluate the fatigue life of a welded joint subjected to distortion induced-fatigue, considering the vehicle speeds and a progressive deterioration model for the road pavement. The welded joint was modelled by solid elements and was integrated with a 3D dynamic bridge model using the sub modelling technique. Besides the importance of considering the bridge-vehicle dynamic interactions with the pavement road-roughness, the dynamic amplification effects on local stresses and the relatively high scatter found in the fatigue lives considering global and local approaches show that a detailed local stress definition is fundamental to evaluate the fatigue performance of existing roadway bridges. The effects of the annual traffic increase rate on the fatigue life are also discussed.

PurposeThe purpose of this paper is to investigate the fatigue performance of a welded detail from a composite steel-concrete railway twin girder bridge caused by a passenger train circulating at varying speeds, by identifying the dynamic amplification scenarios induced by resonance. For this purpose, the hotspot stress method is used, instead of the traditional nominal stress methods.Design/methodology/approachThis paper assesses the fatigue behavior of a welded connection considering critical stress concentration locations (hotspot). Finite element analysis (FEA) is applied, utilizing both a global and a local submodel, made compatible by displacements field interpolation. The dynamic response is obtained through the modal superposition method. Stress cycles are extracted with the rainflow counting method and the fatigue damage is calculated with Palmgren-Miner’s rule. The feasibility of five submodels with different mesh densities, i.e. 1, 2, 4, 8 and 20 mm is verified.FindingsAn increase in the fatigue damage due to the resonance effect was found for the train traveling at a speed of 225 km/h. A good agreement between the computed fatigue damage for the submodels is achieved. However, a non-monotonic hotspot stress/fatigue damage vs mesh density convergence was observed with a peak observed for the 4 mm model, which endorses the mesh sensitivity that could occur when using the surface stress extrapolation detailed rules specified in the standards for the hotspot stress method.Originality/valueAdvanced dynamic analyses are proposed to obtain local stresses in order to apply a local method for the fatigue assessment of a bridge’s structure subjected to high-speed railway traffic on the basis of the mode superposition technique resulting in much less computing times.

Purpose Recent studies have proposed the application of local fatigue approaches based on fracture mechanics or on strain-life material relations for the fatigue analysis of metallic structures. However, only few studies in the literature apply local approaches in the riveted bridges analysis; although these approaches can be applied to any type of connections, requiring a detailed stress analysis of joints and, consequently, considerable computational resources costs. The approach based on S-N curves, formulated in nominal or net stresses, is more usual in the fatigue analysis of riveted bridges. Due to economic factors, riveted bridges have had their operating life extended, while changes in the transport system over the years have subjected such structures to overloads different from those originally planned. These bridges, most of them centenary, were not originally designed accounting for fatigue damage; they represent an important group of structures that are very likely subjected to significant fatigue damage indexes. These factors make necessary detailed residual fatigue life studies to substantiate the decisions of extend (or not) the operational period of these bridges. The paper aims to discuss these issues. Design/methodology/approach The present paper presents a methodology aiming at applying the local approaches in the fatigue analysis of riveted joints of metallic bridges, through the use of sub-modeling techniques and procedures automation. The use of such techniques made such an application viable by keeping the computational costs involved at a moderate level. The proposed procedures were demonstrated using the Trezói Railway Bridge, located on the Beira Alta line, Portugal, built shortly after the Second World War. The proposed set of procedures allowed, through finite elements analysis, to obtain the relevant stresses to perform local fatigue damage analysis. A global structural model was constructed, using beam elements, and local models of a critical node were built with solid finite elements. The structure is analyzed under the passage of regulatory trains. The details of the modeling performed and the computation of the principal stresses in the vicinity of a node and the tangential/circumferential stresses at the holes of two critical riveted connections of that node are analyzed and a fatigue damage analysis is carried out. Findings In the proposed submodelling approach, disassembling the complex riveted nodes into riveted subassemblies allowed the evaluation of the local stresses at riveted holes at an affordable computational cost. Originality/value A methodology is proposed to allow the application of local fatigue analysis in real complex riveted joints, mitigating the computational costs that would result from a full model of the node with all rivets.

Purpose The purpose of this paper is twofold: first, to observe an influence of different Composite Fibre-Reinforced Polymer (CFRP) patches, whose application to metals is very easy, in suppling and significantly elongating the service time; and second, the numerical calculation of the reduced stress intensity factor (SIF) range for strengthened cracked steel specimens. Design/methodology/approach One of the successful strengthening methods is the CFRP patching along the fatigue crack paths. The presented approach has been studied and discussed in this paper on the background of the numerical and experimental data. As it was expected, the proposed strengthening method is efficient and promising in case of the “immediate” repairs of critical members with cracks. The manufacturing process of specimens and test methodology as well as numerical approach to calculate SIFs for various reinforcements of steel specimens are presented. For this purpose, the Extended Finite Element Method was involved and described. Findings The main mechanism of fatigue crack growth retardation is associated with local ΔK reduction due to CFRP patches; any type of reinforcement results in an increase in af and a significant decrease in SIF values. The beach-marking method is described as a good, reliable and comprehensive method to capture the crack propagation in structures consisting of various materials and could be applied successfully for mixed mode testing. Originality/value A detailed experimental-numerical approach for fatigue crack growth in long-term operated structures made of steel is presented. The strengthening methodology is presented with consideration of the various CFRP patches configurations.

This work presents global and local fatigue approaches for snug-tight (common in rack structures) and preloaded bolted joints using thin hot-dip galvanized steel plates, where the zinc coating results in a low friction coefficient. Moreover, S-N data supporting the current revision of Eurocode 3 (EN 1993-1-9) is generated by considering remote and net stresses computed directly or by numerical analysis. Additionally, a master S-N curve based on elastic peak stresses is obtained encompassing the effects of the various tested conditions. Finally, a local fatigue life prediction based on the modified Morrow model combined with elastoplastic numerical analysis returns satisfactory results.

Purpose Adhesively bonded joints are gaining importance in the structural joining processes competing against welding and bolting processes. However, long-term behaviour of adhesively bonded joints is still an open question. Due to the increasing interest in adhesively bonded joints, mainly in the transports industry, there is a need to deep the knowledge about the fatigue behaviour of adhesive joints with metallic substrates allowing the development of reliable joints to resist cyclic loadings. The paper aims to discuss these issues. Design/methodology/approach An experimental research aiming at characterizing the fatigue behaviour of adhesively bonded aluminium substrates is presented in this paper, covering both fatigue crack propagation and global S-N behaviours. Double cantilever beam (DCB), end notch flexure (ENF) and double lap joints (DLJ) specimens built using the AA6061T651 substrate and epoxy adhesive were used to evaluate the pure modes I and II fatigue crack propagation rates and the S-N fatigue behaviours. Findings DCB and ENF specimens allowed the formulation of pure modes I and II fatigue crack propagation laws including the propagation thresholds. DLJs showed higher static shear strength than recommended by the manufacturer for aluminium substrates, but fatigue resistance of the DLJs was lower than suggested by the manufacturer. The fatigue damage process in the DLJs was dominated by a fatigue crack initiation process. Originality/value A consistent fatigue research on adhesively bonded aluminium substrates is presented covering in the same study aspects of fatigue crack propagation and fatigue crack initiation. Data reduction schemes involving both numerical and analytical procedures were followed. Proposed work constitutes a rigorous basis for future fatigue prediction models developments.

Surface damages caused by the impact of flying objects are important factors responsible for fatigue performance degradation of high-speed railway axles, both qualitative and quantitative assessment of these damages are necessary for the maintenance of these axles. In this paper, cubical projectiles were used to reproduce actual damages on S38C axle specimens by a compressed-gas gun at varying velocities. Morphologies of simulated impact damages were characterized, and fatigue strengths of specimens under different impact damages were determined by the step-loading method. Results show that fatigue strength of impacted specimens reduces with the increase of damage depth; besides, other factors, including damage orientation, damage shape, and microstructural damage also exert their contributions. Finally, evaluation on fatigue strength reduction has been performed based on the damage tolerance philosophy.

Local fatigue approaches, such as, the stress-life, strain-life or energetic approaches defines a framework to estimate the fatigue crack initiation from notches of structural details. Various engineering structures, such as, bridges, wind towers, among others, are subjected to cyclic dynamic loadings which may substantially reduce the strength of these structures. Nowadays, the structural systems tend to be more complex being necessary to find computationally efficient solutions to perform their fatigue analysis, accounting for dynamic actions corresponding to long complex loading events (e.g. diversity of trains crossing a bridge), mainly if local approaches are envisaged. Thus, this paper aims at presenting and validating a generalization of a methodology based on modal superposition technique, for fatigue damage parameters evaluation, which can be applied in fatigue analysis using local approaches. This technique was applied recently in the context of fatigue crack propagation based on fracture mechanics, although it can be extended to compute the history of local notch stresses and strains at notches. A very important conclusion is that the technique can be explored for the case of local confined plasticity at notches whenever the global elastic behaviour of the component prevails. Local submodelling can be explored with this technique to avoid the necessity of large computational models. Local models are only needed to be run under linear elastic conditions for the selected modal shapes of the structure, being the local time history of fatigue damage variable computed by modal superposition for each loading event. That time history may be further post-processed for elastoplastic conditions using Neuber or Glinka’s analyses. Comparisons with direct integration elastoplastic dynamic analysis confirmed the feasibility of the proposed approach.

The full-scale static testing of wind turbine blades is an effective means to verify the accuracy and rationality of the blade design, and it is an indispensable part in the blade certification process. In the full-scale static experiments, the strain of the wind turbine blade is related to the applied loads, loading positions, stiffness, deflection, and other factors. At present, researches focus on the analysis of blade failure causes, blade load-bearing capacity, and parameter measurement methods in addition to the correlation analysis between the strain and the applied loads primarily. However, they neglect the loading positions and blade displacements. The correlation among the strain and applied loads, loading positions, displacements, etc. is nonlinear, besides that, the number of design variables is numerous, and thus the calculation and prediction of the blade strain are quite complicated and difficult using traditional numerical methods. Moreover, in full-scale static testing, the number of measuring points and strain gauges are limited, so the test data have insufficient significance to the calibration of the blade design. This paper has performed a study on the new strain prediction method by introducing intelligent algorithms. Back propagation neural network (BPNN) improved by Particle Swarm Optimization (PSO) has significant advantages in dealing with non-linear fitting and multi-input parameters. Models based on BPNN improved by PSO (PSO-BPNN) have better robustness and accuracy. Based on the advantages of the neural network in dealing with complex problems, a strain-predictive PSO-BPNN model for full-scale static experiment of a certain wind turbine blade was established. In addition, the strain values for the unmeasured points were predicted. The accuracy of the PSO-BPNN prediction model was verified by comparing with the BPNN model and the simulation test. Both the applicability and usability of strain-predictive neural network models were verified by comparing the prediction results with simulation outcomes. The comparison results show that PSO-BPNN can be utilized to predict the strain of unmeasured points of wind turbine blades during static testing, and this provides more data for characteristic structural parameters calculation.

This paper proposes a strain prediction method for wind turbine blades using genetic algorithm back propagation neural networks (GA-BPNNs) with applied loads, loading positions, and displacement as inputs, and the study can be used to provide more data for the wind turbine blades’ health assessment and life prediction. Among all parameters to be tested in full-scale static testing of wind turbine blades, strain is very important. The correlation between the blade strain and the applied loads, loading position, displacement, etc., is non-linear, and the number of input variables is too much, thus the calculation and prediction of the blade strain are very complex and difficult. Moreover, the number of measuring points on the blade is limited, so the full-scale blade static test cannot usually provide enough data and information for the improvement of the blade design. As a result of these concerns, this paper studies strain prediction methods for full-scale blade static testing by introducing GA-BPNN. The accuracy and usability of the GA-BPNN prediction model was verified by the comparison with BPNN model and the FEA results. The results show that BPNN can be effectively used to predict the strain of unmeasured points of wind turbine blades.

The maintenance and safety of ancient bridges is a major concern of governmental authorities. In particular, the safety of old riveted bridges fabricated and placed into service at the end of the 19th century deserves particular attention. These structures are susceptible to exhibit high fatigue damage levels due to their long operational period with increasing traffic intensity associated to an original design not covering the fatigue phenomenon. This paper reviews recent fatigue behaviour investigations on single and double shear riveted joints performed by Universities of Porto (Portugal), Tras-os-Montes e Alto Douro (Portugal), and Wroclaw (Poland), in particular concerning the fatigue characterization of riveted joints extracted from representative Portuguese riveted bridges, namely the Eiffel, Luiz I, Fao, Pinhao and Trezoi bridges. In order to overcome the influence of scatter and establish a reliable assessment for the obtained experimental data, two statistical approaches were used: implement linearized boundaries following the recommendation in ASTM E739 standard and defining probabilistic S N fields using the Castillo & Fernandez-Canteli model. This statistical analysis allows to propose design S N curves for single and double riveted joints and evaluate the applicability (safety) of using the design curves suggested in Eurocode 3 as well as design curves proposed by Taras and Greiner.

The paper summarises an experimental study on the fatigue crack propagation and cracks paths in ancient steel&mdash, 19th-century puddle iron from the Eiffel bridge. The tests were performed with the load R-ratio equal to 0.05 and 0.5. All tests were performed under different notch inclinations (mode I + II). The fatigue crack growth rate in the tested material is significantly higher than its &ldquo, modern&rdquo, equivalent&mdash, low carbon mild steel. The crack closure phenomenon occurs in specimens during the process of crack growth. Understanding this aspect is crucial for the examination of a stress R-ratio influence on kinetic fatigue fracture diagram (KFFD) description. Both the experimental and numerical approach, using the HP VEE environment, has been applied to the crack closure as well as the crack opening forces&rsquo, estimation. These analyses are based on the deformation of the hysteresis loop. The algorithm that was implemented in the numerical environment is promising when it comes to describing the kinetics of fatigue crack growth (taking into consideration the crack closure effect) in old metallic materials.

There are many old riveted bridges constructed 100–150 years ago around the world. In Portugal, it is counted that about 100 riveted bridges, which were built based on traffic intensity and vehicle weight, are no longer suitable nowadays. However, mainly due to economic reasons, those riveted bridges are still in service. Thus, the remaining performance is suggested to be accurately evaluated to determine possible repairs. However, the fatigue performance investigation of such riveted joints in old bridges is relatively limited. Then, fatigue assessment concerning the riveted joint is not contemplated in the current standard as EC3. This paper presents an experimental campaign of riveted joints. Three types of riveted connections are conducted to obtain the fatigue behaviour. Then experimental results, and its design curves obtained based on the ASTM E739 standard, are compared to S-N design curves, suggested for riveted connection. The fatigue strength predicted from class 71 in EC3 is lower than it obtained from test results.

In this paper, the normalized variable V=(log N-B)(log Ao-C), as derived from the probabilistic S-N field of Castillo and Canteli, is taken as a reference for calculation of damage accumulation and probability of failure using the Miner number in scenarios of variable amplitude loading. Alternative damage measures, such as the classical Miner and logarithmic Miner, are also considered for comparison between theoretical lifetime prediction and experimental data. The suitability of this approach is confirmed for it provides safe lifetime prediction when applied to fatigue data obtained for riveted joints made of a puddle iron original from the Fao bridge, as well as for data from experimental programs published elsewhere carried out for different materials (aluminium and concrete specimens) under distinct variable loading histories.

This paper presents a study aiming at characterizing the fatigue crack growth behaviour of the 6082-T6 aluminium alloy using standard CT specimens. The fatigue crack growth threshold is also characterized according to the ASTM E 647 standard. Besides the standard CT specimens with sharp notches, specimens with initial circular notches were also fatigue tested. The threshold stress intensity factor ranges, ΔK th , are compared for the distinct notches under study. The fatigue crack propagation rate in the regime II are obtained using the Paris law. A comparison is made between the CT specimens geometries with distinct notches under consideration. The ΔK th values for the geometry of standard CT specimens present lower values when compared with the geometry of the CT specimens with blunted notches.

The objective of this paper is to propose an accurate and computationally efficient method for the fatigue assessment of bridge details, using Fracture Mechanics and crack propagation laws. The proposed workflow benefits from the combination of finite element submodeling techniques and modal superposition method with the new concept of modal stress intensity factors. The new methodology was applied to the fatigue analysis of a complex bridge under real traffic conditions. The simulation of fatigue crack propagation in a critical detail of the structure was achieved with minimal computer resources and within a short time frame.

Cumulative fatigue damage is a continuous and irreversible process that refers to the degradation of the component mechanical properties under cyclic loadings. In this work, using the concept of isodamage curves, a new non-linear fatigue damage accumulation model is proposed to account for fatigue damage evolution under multiple load levels. In particular, a computational process is established in which the isodamage curves converge into one point due to the exhaustion of static toughness. Experimental data of five materials are used for model validation and comparison. Results indicate that the proposed model provides better life predictions than the other four models.

The mean stress effect plays an important role in the fatigue life predictions, its influence significantly changes high-cycle fatigue behaviour, directly decreasing the fatigue limit with the increase of the mean stress. Fatigue design of structural details and mechanical components must account for mean stress effects in order to guarantee the performance and safety criteria during their foreseen operational life. The purpose of this research work is to develop a new methodology to generate a constant life diagram (CLD) for metallic materials, based on assumptions of Haigh diagram and artificial neural networks, using the probabilistic Stussi fatigue S-N fields. This proposed methodology can estimate the safety region for high-cycle fatigue regimes as a function of the mean stress and stress amplitude in regions where tensile loading is predominance, using fatigue S-N curves only for two stress R-ratios. In this approach, the experimental fatigue data of the P355NL1 pressure vessel steel available for three stress R-ratios (−1, −0.5, 0), are used. A multilayer perceptron network has been trained with the back-propagation algorithm; its architecture consists of two input neurons ( σ m , N ) and one output neuron ( σ a ). The suggested CLD based on trained artificial neural network algorithm and probabilistic Stussi fatigue fields applied to dog-bone shaped specimens made of P355NL1 steel showed a good agreement with the high-cycle fatigue experimental data, only using the stress R-ratios equal to 0 and −0.5. Furthermore, a procedure for estimating the fatigue resistance reduction factor, K f , for the fatigue life prediction of structural details (stress R-ratios equal to 0, 0.15 and 0.3) in extrapolation regions is suggested and used to generate the K f results for stress R-ratios from −1 to 0.3, based on machine learning artificial neural network algorithm.

FBG sensors are often packaged within composites before they are pasted on the blade surface, and many studies have shown that the materials, fatigue properties, geometric parameters, etc. of intermediate layer have influences on the measuring accuracy of the FBG sensors. Thus, this paper established an reliability calculation model based on strain transfer efficiency for the measuring accuracy of FBG sensors packaged by composites, analyzed the influences of material properties and geometric parameters of the adhesive layer on the performance of FBG sensors based on finite element analysis (FEA) method, and then compared the differences of strain transfer efficiency and reliability of the FBG sensors under different load conditions. The results show that the bond length and the bond thickness of the adhesive layer have greater influences on the performance of the FBG sensors compared with other parameters, both the strain transfer efficiency and the reliability of the FBG sensors will reduce over time under suddenly applied load and increase with increasing frequency of the alternating load.

One of the major concerns in offshore structures are the welded connections where fatigue failures are highly relevant. In many cases of offshore welded connections, the fatigue cracks initiated may grow from the weld to the base material, but also from the root of the weld. In this study, the evaluation of design S-N curves for a double-side welded connection made of S355J2 steel used in offshore applications is proposed. The characteristic fatigue curve of the double-side welded connection is obtained using statistical analyses based either in the ASTM E739 standard as well as the probabilistic fatigue model proposed by Castillo & Fernández-Canteli. This study concludes with a comparison between the experimental fatigue curves obtained and the design S-N curves proposed in design codes for offshore structures. Existing code recommendations are very conservative when comparing the design S-N curves with the proposed new characteristic S-N curves. For the joint under investigation the hot spot and nominal stress approaches yield very similar S-N results.

This chapter presents results of numerical simulations of cyclic large-scale tests described in Chap. 5, using various constitutive models including some described in Chap. 6 and material properties identified with material (small-scale) test data obtained in Chaps. 2 and 3.

This chapter presents the results of numerical simulations of monotonic large-scale tests described in Chap. 4, using constitutive models described in Chap. 6 and material properties identified with material (small-scale) test data obtained in Chap. 2.

This chapter presents results of small-scale cyclic tests performed with smooth and notched specimens made of various pipeline steels. Both LCF and ULCF behaviours will be investigated. The generated experimental data is used latter in plasticity/damage models calibration/validation which will be later used in finite element simulation of large-scale piping components made of similar materials.

This paper presents experimental and numerical results from embedment tests carried out accordingly the EN383 standard. The experimental program included series of compressive embedment tests, along the parallel and perpendicular-to-grain directions. The specimens were manufactured with maritime pine wood and were loaded using a steel dowel. The load-displacement curves resulted from experimental tests allowed to estimate the embedding strength and the foundation modulus. Concerning the numerical simulations, a plasticity model, based on Hill's criterion, was used to simulate the mechanical behaviour observed in the embedment tests. The wood was modelled as an orthotropic material following an elasto-plastic behaviour. The steel dowel was considered isotropic material and modelled with elastic behaviour. Besides, the interaction between both materials was modelled using contact finite elements. A parametric study to evaluate the influence of dowel/wood clearance and different friction coefficients was performed. The proposed 3D finite element model showed the capability to simulate the non-linear behaviour observed in the experimental embedment tests. An experimental/numerical procedure for the identification of constitutive models aiming the simulation of ductile behaviour of wood was presented. This is particularly important to simulate the mechanical behaviour of doweled joints.

The maintenance of old riveted bridges has become a major concern for railroad managers across Europe. These metallic structures, built on their majority on the second half of the 19th century, are indeed submitted to ever increasing traffic loads (augmentation in weight and speed of rolling stock). To assess the remaining life of these metallic bridges, some critical structural details have been identified and associated to S-N curves to be used in damage estimation (using Palmgren-Miner's rule for cumulative damage, for example). These constructional details are often described in construction standards, such as the EN 1993-1-9, the BS 5400 and the AASHTO standards. The particularity of older hot-riveted bridges is that their numerous geometric configurations are often under-represented, thus, limiting the accuracy of damage estimation. To compensate the absence of hot riveted assemblies in the standards, numerous research groups have performed extensive experimental campaigns. However, the heterogeneity and rarity of the material (no longer produced nowadays), as well as the very diverse geometrical configurations used at the time of the construction of the bridges (given the novelty proposed by the introduction of metal as a new material in monumental construction), makes difficult the comparison of experimental data. In order to facilitate interpretation and differentiation of fatigue data of a particular type of constructional detail, experimental data from double shear assemblies manufactured from three different metallic ancient bridges is considered (French and Portuguese puddled iron bridges). Then, through statistical analysis (linearized boundaries and the Fernandez-Canteli model), the S-N curves corresponding to their structural configuration are identified. Comparisons to the EN 1993-1-9, the BS 5400 and the AASHTO standards are also proposed. The combination of the S-N curves and Fracture Mechanics approaches can be used to evaluate the residual life of the old riveted metallic bridges. Thus, a statistical analysis and discussion of experimental fatigue crack propagation data available for materials from the ancient riveted metallic bridges are made. This analysis is important for the application of the Fracture Mechanics approaches to predict the residual life of structural details.

Different strategies can be used to perform reparations and reinforcements of ancient bolted and riveted metallic bridges. As the riveting process is not currently a common practice, it requires proper equipment and skilled workers. Another solution is the use of welding. However, the weldability of old steels is poor. Bolts are very attractive alternative solutions, and are most commonly used to repair old metallic bridges. Fitted bolts are expensive solutions; the alternative is the use of resin-injected bolts. The behavior of bolted joints with preloaded resin-injected bolts has been studied using quasi-static and creep tests; however, few studies on the slip and fatigue behavior of these joints can be found in the literature. This paper presents an overview of a few experimental programs that were carried out by several authors aiming at evaluating the fatigue behavior of single and double shear resin-injected bolted connections. A comparison between the experimental data of joints with preloaded standard bolts and preloaded resin-injected bolts shows a fatigue strength reduction in the latter. Since Eurocode 3 (EC3) suggests the same fatigue strength curve for joints made of resin-injected bolts and standard bolts, this may raise some concerns. Furthermore, research on the feasibility of using both bonded and bolted connections is shown. This last study was performed with high-strength low-alloy structural steel plates and an acrylic structural adhesive for metal bonding. For both case studies, a statistical analysis is performed on fatigue experimental data using linearized boundaries and the Castillo and Fernández-Canteli model. Fatigue design curves are proposed and compared with the design suggestions of several European and North American standards. Keywords: Fatigue, Connections, Structural reinforcements, Structural adhesives, S-N curves, Resin-injected bolts

Fatigue damage is a concern for riveted metallic bridges due to the long operational period they have been subjected along with increasing traffic intensity. The usual fatigue assessment approach for riveted joints consists on using the global S–N curves with nominal or net stresses. Existing practice is based on the adoption of a unique S–N curve (e.g. the Eurocode 3, Class 71 S–N curve). However, this approach may lead to excessive conservative predictions since it is applied indistinctly of the riveted detail geometries (e.g. does not recognize the need for detail categorization) and materials (e.g. not specifically developed for puddle irons). Alternatively, local approaches to fatigue may be applied to 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 a numerical study concerning the fatigue modelling of riveted and bolted joints made of puddle iron from the centenary Portuguese Fao Bridge. Fatigue is assumed a process of crack initiation and propagation, both processes modelled using respectively the local strain and the Fracture Mechanics based fatigue approaches. A finite element model of the joints is proposed using solid and contact finite elements. The effects of the clamping stresses as well as the friction are taking into account with the proposed model. Numerical S–N curves are predicted and compared with the experimental data available for the investigated joints, a good agreement being observed.

This paper presents an experimental investigation of the development of adhesively bonded reinforcing techniques for dowel-type wood connections. One of the proposed techniques is based on the application of carbon fiber reinforced plastic (CFRP) laminates (glued with epoxy adhesives) in the areas surrounding the holes of the wood members. The other technique is based on a novel reinforcing procedure involving the application of steel inserts that are glued to the holes of the timber members. For this latter technique, two distinct commercial epoxy adhesives were investigated. Both techniques were demonstrated for maritime pine wood. The experimental program comprised embedding tests, carried out according to the procedures of the EN 383 standard, with and without reinforcements, and included both parallel- and perpendicular-to-grain quasi-static loading. The embedding strength and foundation modulus were determined and compared between the non-reinforced and reinforced solutions. Furthermore, three series of single dowel T-connections were tested, one without reinforcement and two series reinforced with metallic inserts and CFRP laminates, respectively. The analysis of the experimental results showed the improved performance of the strengthening solutions. Additionally, it is important to emphasize that the reinforcement based on CFRP laminates was more effective in eliminating brittle failure modes in the wood members.

Traditionally, fatigue crack initiation has been modelled based on strain-life relations whereas fatigue crack propagation has been modelled using fracture mechanics concepts. Recently, new fatigue crack growth models, based on elastic–plastic stress–strain histories at the crack tip region, along with strain-life damage models have been proposed, which constitutes a class of local fatigue crack propagation models. Therefore, a unified local approach is feasible to model both crack initiation and crack propagation. An application of such a unified local approach to fatigue is presented in this paper. In particular, a notched rectangular plate, made of P355NL1 steel is modelled in order to generate S – N curves for distinct stress R -ratios. The predictions are compared with available experimental data. The required strain-life data of the P355NL1 steel is also presented in the paper, in a probabilistic form, using adequate fatigue damage parameters. Finally, the probabilistic S – N field is proposed for the notched detail and a good correlation of the available experimental data is observed.

The use of higher strength steels allows the design of lighter, slenderer and simpler structures. Nevertheless, the increase of the yield strength of the steels does not correspond to a proportional increase of fatigue resistance, which makes the application of high strength steels on structures prone to fatigue, a major concern of the design. This paper presents a comparison of the fatigue behavior between the S355 mild steel and the S690 high strength steel grades, supported by an experimental program of fatigue tests of smooth specimens, performed under strain control, and fatigue crack propagation tests. Besides the cyclic elastoplastic characterization, the fatigue tests of smooth small size specimens allow the assessment of the fatigue crack initiation behavior of the materials. Results show that the S690 steel grade presents a higher resistance to fatigue crack initiation than the S355 steel. However, the resistance to fatigue crack propagation is lower for the S690 steel grade, which justifies an inverse dependence between static strength and fatigue life, for applications where fatigue crack propagation is the governing phenomenon. Consequently, the design of structural details with the S690 steel should avoid sharp notches that significantly reduce the fatigue crack initiation process.

Miner’s rule for fatigue damage accumulation does not address conveniently the sequential effects of the fatigue loading due to underloads or overloads though such effects need to be taken into account for specific applications using a convenient model. Non-conservative (unsafe) or over-conservative (non-economic) fatigue predictions may result from such a linear damage analysis. To overcome these limitations, non-linear damage approaches are being proposed in the literature, as for instance, the double linear damage rule (DLDR). Further, advanced probabilistic models, as an alternative to deterministic ones, are being currently applied to fatigue damage assessment under variable (random) amplitude loading, though without including, up to present, sequential effects on the damage accumulation. In this paper, the synergetic effect of applying a non-linear fatigue damage model based on the DLDR in conjunction with a probabilistic approach based on the p-S-N field is pursued allowing the above mentioned sequential effects to be incorporated into a probabilistic damage prediction. The proposed approach was tested with existing fatigue block loading data available for the P355NL1 pressure vessel steel.

Ultra or extreme low-cycle fatigue of steels has been deserving increasing interest by the researchers since it corresponds to a fatigue domain not fully understood nor explored. It has been recognized that fatigue damage under extreme loading conditions is representative of several practical applications (e.g. seismic actions, accidental loads) and pipelines are a type of components that could undergo such extreme loading conditions. In addition, concerning the pipelines, reeling could also contribute to significant plastic cycles. ULCF damage corresponds to a transition damage behavior between the LCF and monotonic ductile damage. Therefore studies on ULCF usually needs to cover those bounding damage processes. ULCF testing exploring large-scale specimens is rare. The aim of this paper is to investigate the ultra-low-cycle fatigue of large-scale straight pipes subjected to cyclic pure bending tests which were performed under the framework of the ULCF European/RFCS project. In detail, two steel grades used on pipelines manufacturing were investigated, namely the X60 and X65 piping steels, respectively with the following nominal diameters of 16” (w.t. 9.5 mm) and 8 5/8” (w.t. 5.59 mm). A specifically developed testing setup was used to perform the cyclic bending of the straight pipes, combined with internal pressure, until the pipes collapse. The failure was preceded by local plastic instability (buckling), motivating the concentration of cyclic plastic deformation leading to macroscopic crack initiation and propagation. In addition to the full-scale tests, the plain material was investigated under monotonic and ULCF conditions using both smooth and notched specimens. In order to assess the stress/strain fields in the straight pipes, finite element models of the straight pipes were developed and simulations were performed under the experimental displacement histories. Nonlinear plasticity models with kinematic hardening, inputted on finite element simulations, were calibrated by means of small-scale data. Moreover, the test data of small-scale tests was used on the identification of damage models constants (e.g. Coffin-Manson), which in turn were applied to simulate the failure cycles of the tested straight pipes. The ASME B&PVC VIII Div.2 procedures were also used to compute the failure cycles for the straight pipes to allow an assessment of these existing procedures.