Fatigue Capacity Research Articles

Low-Cycle Fatigue Properties of Bimetallic Steel Bar with Buckling: Energy-Based Numerical and Experimental Investigations.

A bimetallic steel bar (BSB) consisting of stainless-steel cladding and carbon steel substrate exhibits excellent corrosion resistance and good mechanical properties. The bimetallic structure of BSBs may affect their low-cycle fatigue performance, and current investigations on the above issue are limited. In this study, the low-cycle fatigue properties of bimetallic steel bars (BSBs) with inelastic buckling were investigated. Experiments and numerical studies were conducted to investigate the low-cycle fatigue capacity for BSBs, considering buckling. The buckling mode of BSBs is discussed. The hysteretic loops and energy properties of BSBs with various slenderness ratios (L/D) and fatigue strain amplitudes (εa) are investigated. With increases in the L/D and εa, the original symmetry for hysteresis loops disappears gradually, which is caused by the buckling. A predictive equation revealing the relation between the εa and fatigue life is suggested, which considers the effects of the L/D. A numerical modelling method is suggested to predict the hysteretic curves of BSBs. The effect of buckling on the stress and energy properties of BSBs is discussed through the numerical analysis of 44 models including the effects of the L/D, εa, and cladding ratios. The numerical analysis results illustrate that the hysteresis loops of BSBs with various εa values exhibit similar shapes. The increase in the cladding ratio reduces the peak stress and the dissipated energy properties of BSBs. The hysteresis loop energy density decreases by about 3% with an increase of 0.1 in the cladding ratio. It is recommended that the proportion of stainless steel inBSBs should be minimized once the corrosion resistance requirements are met.

Structural performance of fibre reinforced recycled aggregate concrete road kerb sections under monotonic and cyclic loading

In recent years, there has been a notable emphasis on waste reduction and the adoption of recycled materials within the construction industry to reduce the industry’s overall carbon footprint. This study investigates the structural performances of concrete kerb sections prepared with five different concrete mixes containing recycled concrete aggregate, recycled tyre-derived aggregates and recycled polypropylene fibres. Kerb sections were cast at a road site in a suburb of Adelaide, Australia. After the concrete hardened, sections were cut and brought to the laboratory. A large number of monotonic and cyclic load tests were conducted on the kerb sections. The load-carrying capacity, bending moment capacity, cyclic fatigue capacity, durability properties along with deformation tolerance were evaluated. Kerb sections made with concrete containing recycled aggregate and polypropylene fibre could sustain nearly 2000 cycles of loading. Kerb sections prepared with natural aggregate concrete performed comparatively better. The addition of polypropylene fibre significantly improved the post-cracking behaviour of kerb sections and can delay crack propagation and other distress when subjected to cyclic loadings such as excessive soil movement, e.g., in areas with expansive soils or prone to tree root migration. Long-term observation may be required to confirm the mechanical and durability performance improvement in real field conditions.

Fatigue and monotonically-loaded reinforced concrete specimens subjected to partial area loading

The degradation of concrete structures is often due to the continuous application of compressive fatigue loads. Understanding of concrete behaviour in different environmental conditions and under especial fatigue loading arrangements, particularly in cases where the loaded area is smaller than loaded element, herein referred to as partially loaded area, is of utmost importance to make a realistic prediction of the concrete fatigue life for a reliable design of civil engineering infrastructure. This paper focuses on investigating the fatigue performance of reinforced concrete specimens subjected to partially loaded areas, considering the influences of steel fibres, reinforcement arrangement, and the environmental factor of water submergence. A typical example of a partially loaded concrete component subjected to fatigue loading is circular spread footings used as concrete foundations for typical wind turbines. In these types of elements, the compressive strength of the concrete can be enhanced due to the confinement provided by way of lateral restraint stemming from surrounding concrete and reinforcement. However, design codes primarily address static loading and lack specific criteria for fatigue loading in these partially loaded regions. To address this research gap, results from a comprehensive experimental study, which in total included 111 concrete specimens subjected to monotonic loading and 25 specimens tested under cyclic loading, were used to study this problem. The investigation aimed to evaluate the effects of steel fibres and reinforcement arrangement on both static and fatigue capacity. Additionally, the impact of submerging concrete structures in water on their fatigue performance was examined, revealing a decrease in their fatigue life. The experimental results demonstrated that the presence of steel fibres and splitting reinforcement significantly increased both static and fatigue capacity. Most current design codes neglect the environmental factor of water submergence, leading to reduced fatigue capacity in concrete structures. Consequently, the validity of the design codes DNV-OS-C502 and fib Model Code 2010 was evaluated, and a new environmental factor for partially loaded areas subjected to cyclic loading is proposed. To evaluate the experimental results and understand the mechanical response, nonlinear finite element analyses were conducted using a smeared-crack continuum modelling procedure coupled with high cycle fatigue material models to assess its applicability for estimating fatigue performance of partially loaded reinforced concrete elements. It was found that a plane stress modelling procedure was capable of estimating fatigue capacity for dry concrete components, however, overestimated the fatigue capacity of wet concrete components.

Fatigue design of stress relief grooves to prevent weld root fatigue in butt-welded cast steel to ultra-high-strength steel joints

In the welded joints, fatigue failures typically originate from defects or notch-like geometries under cyclic loading. This study investigates the impact of stress relief grooves (SRG) on the fatigue performance of butt-welded cast steel to ultra-high-strength steel components using experimental fatigue tests and finite element method. The experiments examined the fatigue properties of hybrid joints between G26CrMo4 cast steel (t = 20 mm) and S960 steel plate (t = 6 mm) with and without SRG. Gas metal arc welding process was used to weld the butt joints that had a permanent root backing machined on the cast steel part, causing a crack-like defect to the weld root. Additionally, the top surfaces of the welded parts were aligned, resulting in a significant axial misalignment in the butt joint. The SRG, positioned close to the weld root, was found to have a beneficial influence on the joint’s fatigue performance by a factor of 1.2 when using the nominal stress criterion. However, the fatigue capacity was still roughly 35% lower compared to the symmetrical equivalent due to the secondary bending stress, caused by axial misalignment. The finite element analyses indicated that the SRG reduces the amount of secondary stresses at the weld root leading to lower total structural stress. The study recommends using the FAT80 (m = 3) design curve in the structural stress method, for similar butt-welds having a crack-like defect, parallel to the loading direction, at the weld root. However, for welded joints with crack-like defects, it is advisable to use linear elastic fracture mechanics rather than relying solely on stress-based local approaches.

Fatigue Analysis of a Jacket-Supported Offshore Wind Turbine at Block Island Wind Farm.

Offshore wind-turbine (OWT) support structures are subjected to cyclic dynamic loads with variations in loadings from wind and waves as well as the rotation of blades throughout their lifetime. The magnitude and extent of the cyclic loading can create a fatigue limit state controlling the design of support structures. In this paper, the remaining fatigue life of the support structure for a GE Haliade 6 MW fixed-bottom jacket offshore wind turbine within the Block Island Wind Farm (BIWF) is assessed. The fatigue damage to the tower and the jacket support structure using stress time histories at instrumented and non-instrumented locations are processed. Two validated finite-element models are utilized for assessing the stress cycles. The modal expansion method and a simplified approach using static calculations of the responses are employed to estimate the stress at the non-instrumented locations-known as virtual sensors. It is found that the hotspots at the base of the tower have longer service lives than the jacket. The fatigue damage to the jacket leg joints is less than 20% and 40% of its fatigue capacity during the 25-year design lifetime of the BIWF OWT, using the modal expansion method and the simplified static approach, respectively.

Probabilistic inspection planning for fatigue cracks in floating production, storage, and offloading units

Probabilistic inspection planning for fatigue cracks in floating production, storage, and offloading units

Code-conforming fatigue life assessment of riveted lap shear joints

Recent studies highlighted the importance of an accurate assessment of the remaining life of historical steel riveted bridges to plan and design their maintenance. Such structures are usually prone to fatigue damage due to the high number of cumulated cyclic stresses over their service life. Currently, limited guidelines are available for evaluating the fatigue strength of riveted connections. According to the JRC-ECCS document Assessment of Existing Steel Structures: Recommendations for Estimation of Remaining Fatigue Life, the fatigue capacity of riveted connections should be evaluated through the fatigue class 71, whose prediction may be excessively conservative. Therefore, this paper summarizes the results of a theoretical study and an experimental campaign aimed at characterizing the high-cycle fatigue of riveted shear splices. Experimental fatigue results have been collected from the literature, and a database has been built, including material property, loading condition, riveting process, and geometry information. The collected data and those obtained from the performed tests have been statistically elaborated to investigate the influence of such parameters on their fatigue strength. Finally, comparisons with the recommended fatigue classes are provided to discuss their suitability in predicting the fatigue strength of the investigated riveted connections.

Experimental Study on Seismic Fatigue Capacity of High- and Mild-Strength Structural Steels with and without Corrosion

The test results on hourglass specimens of steel under repetitive sine loads provide graphs that indicate the stress range in terms of the number of cycles to failure and are known as S-N curves. Using this curve, it is determined that if the applied stress is less than a certain level, failure will not occur as the number of load cycles increases. The S-N curve can be affected by several factors such as yield stress, temperature, surface properties, and corrosion. In this research, the S-N curve has been investigated for two types of high-strength steels, S690 and S460, as well as two types of mild-strength steels, S235 and S355, at 25°C, and S355 with corrosion. The numbers of samples used for S235 and S460 steels were 45 each while S355 and S690 steels were 36 each and for S355 with corrosion was 15 with the high cycle fatigue curve obtained for them. To investigate the effect of plate thickness on the high cycle fatigue of the samples, four sets of 24-piece S235 steel samples, being 96 samples in total, were made of plates with different thicknesses of 8, 12, 15, and 20 mm and tested. Finally, a four-story three-span steel moment frame was designed, and under the Northridge earthquake record, the high cycle fatigue was investigated. It was observed that the high cycle fatigue was not effective for the mentioned structure under the Northridge earthquake record, but in the corroded structure, damage from high cycle fatigue occurs under this record.

Seismic performance evaluation of high‐post‐yield stiffness concentrically braced steel frames under mainshock‐consistent‐aftershock sequences

AbstractStructures may be subjected to earthquake sequences after major mainshock (MS) events in seismically active sites within a short time. As a result, they may be susceptible to damage accumulation, which may hinder their performance under consecutive seismic loading. This study evaluates the effects of earthquake sequences on the seismic performance of seismic‐resistant concentrically braced steel frames designed to Eurocode‐8. The frames under investigation have concentric chevron‐type braces with replaceable hourglass‐shaped pins made of duplex stainless steel. The seismic energy is dissipated through inelastic deformations concentrated in the pins while keeping the other members elastic. The stainless‐steel pins provide the frame with high‐post‐yield stiffness to reduce the residual drifts after a seismic event. The seismic behaviour of the frame is assessed using site hazard‐specific mainshock‐consistent‐aftershock (MS‐AS) sequences selected for a site in Terni, Central Italy. Nonlinear back‐to‐back dynamic analyses are performed at multiple intensity levels while adopting detailed numerical nonlinear models created in OpenSees. We show that the implemented behaviour factor satisfies the life safety assurance objective while keeping the maximum residual inter‐storey drifts below 1/300 to permit an easy substitution of the damaged pins after the design‐level earthquake without being curtailed by the potential following events. We then develop prediction models for the damage accumulation in the pins, considering different energy‐based intensity measures and we show that the cumulative absolute velocity‐based model is the most efficient predictor in this particular case. Finally, the damage accumulation in the pins is evaluated, confirming their superior low‐cycle fatigue capacity under earthquake sequences.

Fatigue behavior of unidirectional fiber‐reinforced pultruded composites with high volume fiber fraction

AbstractPultrusion is a high‐volume manufacturing process for fiber‐reinforced polymer (FRP) composites ensuring high strength and quality products. However, research studies are very limited on the fatigue behavior of these products, especially with unidirectional fiber alignment. This study investigates the fatigue behavior of the unidirectional pultruded glass FRP (GFRP) composites with high fiber volume fraction ( ). Tension–tension fatigue loading was applied with different levels of applied stress, frequency, and gripping condition until failure. Results showed that the high composites have significantly low fatigue life cycle. Moreover, increasing the frequency showed better fatigue resistance, while the tabs geometry has insignificant effect on the fatigue behavior of the dog‐bone shaped specimens. Comparison with available literature showed that GFRP composites with high have lower fatigue performance than those with low . A fatigue capacity reduction factor is also proposed for unidirectional GFRP composites as a function of the .

Study on the Rheological Properties of Formic Acid Lignin Modified Asphalt

Lignin is a major waste product of biofuel and paper industries that can be used as a modifier to improve the relevant properties of asphalt. To investigate the effect of lignin and formic acid lignin wood incorporations into asphalt and the effect on asphalt binder that was unaged and aged for 85 min, 5 h, and 10 h, a series of tests were conducted, including high- and low-temperature rheological tests by a dynamic shear rheometer (DSR), followed by Fourier transform infrared spectroscopy (FTIR) tests, and finally by gel permeation chromatography (GPC). The test results show that the additions of lignin and formic acid lignin could improve the high-temperature performance and fatigue capacity of asphalt. In addition, at the glass-transition temperature, it was observed that the additions of lignin and formic acid lignin into asphalt can effectively improve cracking at low temperatures; however, the quantity of lignin and formic acid lignin should be controlled. Fourier transform infrared spectroscopy tests showed that the purity of lignin treated with formic acid decreased, and degradation and formylation of the same formic acid-treated lignin occurred, indicating that the lignin underwent chemical changes following acid treatment. The analysis of the results by gel permeation chromatography (GPC) showed that, with aging, the average molecular weight (Mw) of lignin-modified asphalt decreased. The reason was that lignin and formic acid lignin were cracked during aging, which reduced their molecular weights.

Parametric Study of the Numerical Model of a Bolted Connection of Steel Structure for Photovoltaic Panels.

In the face of the reality that unexpectedly mobilized the governments of most central European countries (including Poland), the development of renewable energy sources (RES) seems to be an important direction. Therefore, both wind parks and solar farms will be constructed at double speed for energetic independence. This urgency makes the market of producers of structures for mounting solar panels also need to adapt quickly to the new situation. New constructions adapted to quick assembly with the use of nutless screw connections seem to be one of the best solutions. These structures must not only be easy and quick to install but also durable, which makes the connections resistant to cyclical loads. The speed of assembly of the substructure can be achieved precisely with the help of nutless connections, but their durability should be carefully analyzed. This article presents parametric analyses of the numerical model of this type of connection. The selection of appropriate numerical models for simulation is of key importance in the fatigue strength analysis of bolted connections. This article investigates two different models used in numerical fatigue analyses performed in the Abaqus FEA and FE-Safe program, namely, traditional bolt with nut and innovative self-tapping nutless bolt. Extended parametric analyses of both numerical models were carried out, which ultimately allowed optimization of the fatigue capacity of the connection.

Fatigue design sensitivities of large monopile offshore wind turbines

AbstractThe input for fatigue analyses of offshore wind turbines is typically chosen based on design values provided by design standards. While this provides a straightforward design methodology, the contribution of different input parameters to the uncertainty in the fatigue damage estimates is usually unknown. This knowledge is important to have when improving current designs and methodologies, and the parameters governing the uncertainty is typically found through a sensitivity analysis. Several sensitivity studies have been performed for monopile‐based offshore wind turbines, typically focusing on specific turbines and engineering disciplines. This paper performs a sensitivity study for three monopile‐based offshore wind turbines (5 MW, 10 MW, 15 MW) using parameters from several engineering disciplines. The results show that the fatigue utilization is primarily governed by the uncertainty in the SN curves and fatigue capacity. Following this, the uncertainty in the environmental conditions is the dominating uncertainty, with wind loads becoming increasingly important as turbine size increases. Additionally, the effect of modelling uncertainties is investigated. The wind‐related model uncertainties dominate in the tower top, while uncertainties in the wave and soil models dominate in the tower base and monopile. Designers wanting to reduce the uncertainty in a design are recommended to focus on the environmental conditions, and using as accurate models as possible. All modelling uncertainties are significant, but research should particularly be focused on wave directionality and soil models.

Influence of Corrosion Damage on Fatigue Limit Capacities of Offshore Wind Turbine Substructure

The decrease in structural capacities under the limit states caused by structural corrosion is a potential hazard for the safety of offshore structures. Considering the influence of corrosion factors, a fatigue analysis of the typical tubular joints of an offshore wind turbine (OWT) substructure under operation and wave loads during the service period was performed. The structural corrosion was equivalent to a two-parameter Weibull distribution in the analysis. According to the Miner linear fatigue accumulation criterion, the accumulated fatigue damage of three different typical tubular joints in the initial stage and at operation periods of 10, 20, and 30 years was calculated. The most critical tubular joint of the studied OWT substructure is located at the connection between the pile foundations and braces. Owing to the increase in structural corrosion during the operation period, a remarkable decrease in the tubular joint fatigue capacities under the operation and wave loads was observed.

Machine-learning-based prediction of vortex-induced vibration in long-span bridges using limited information

Long-span bridges are susceptible to wind-induced vibration due to their high flexibility, low-frequency dominance, and light damping capacity. Vortex-induced vibrations (VIVs), which usually occur under in-service conditions, can result in discomfort to users and detrimental effects on the fatigue capacity of structural elements; therefore, accurate VIV assessments are essential in ensuring the vibrational serviceability of bridges. Despite the research efforts of data-driven VIV prediction, the robustness and general applicability of the proposed methods remains challenging, in that each method requires different conditions for the datasets in order to develop machine-learning (ML) models. Furthermore, collecting sufficient VIV datasets (anomaly state) from various operational conditions is impractical, time-consuming, and even impossible in some situations compared with non-VIV datasets (normal state). This imbalance in the dataset could degrade the model performance. To address this issue, this paper focuses on developing a general framework for introducing ML algorithms to predict VIVs with a limited amount of information. To properly replicate the practical cases, two different scenarios are assumed along with the amount of VIV data: (1) no VIV data are available, or (2) only a small number of VIV data can be obtained. A variety of ML-assisted methods are introduced for each scenario to predict VIVs in order to demonstrate the versatility of the proposed framework. The effectiveness and applicability of the proposed framework are demonstrated using actual monitoring data. Different methods are prepared to provide further insight into the ML algorithms used for VIV prediction. The proposed framework in this paper is expected to advance our knowledge and understanding of the application of ML algorithms to bridge systems, which are essential in enhancing resilience against wind hazards.

Initial parameters to estimate the fatigue strength of welded structures using a fracture mechanical model

Producing S-N curves using experimental testing is a costly and time-consuming practice. An alternative to experimental testing is to estimate the fatigue strength of welded steel structures by using a linear elastic fracture mechanical (LEFM) approach. However, to get reasonable estimations of the fatigue strength, a suitable choice of initial parameters has to be made. The objective of this paper is to produce recommendations for initial parameters based on a selection of fatigue experiments. The recommendations were verified against a fatigue experiment covering a corrugated web plate girder and provided a realistic estimation of the fatigue capacity.

Optimal life-cycle mitigation of fatigue failure risk for structural systems

Fatigue failure risk can be mitigated both by increasing the design fatigue capacity of the structural components and by conducting more frequent inspection and maintenance actions. The optimal combination of these two types of safety measure is structure dependent. It depends, among others, on the relative cost of the safety measures, the consequences of failure, the level of redundancy, the number of deteriorating components and the statistical dependence among components. In this article, a generic system representation is used to parametrise deteriorating structures according to these system characteristics. Based on this system representation, we investigate patterns of optimal life-cycle fatigue mitigation and provide recommendations for fatigue design. Results show that it can be cost-efficient to achieve system-level safety requirements with high component reliabilities at design and less frequent inspections. Furthermore, we show that the minimum requirements for fatigue design that are typically prescribed in design standards to avoid the need for inspections are not enough unless sufficient redundancy is ensured.

Probabilistic fatigue model for design and life extension of mooring chains, including mean load and corrosion effects

A probabilistic model for mooring chain fatigue damage is developed based on the S–N approach. The effects of mean load and corrosion condition on the fatigue capacity of the chains are included by adopting a parameterized S–N curve intercept parameter, and the model allows for the uncertainties and time dependencies of these to be addressed. Uncertainties in fatigue loads are also accounted for, including the annual variability which may be of importance in certain cases. Furthermore, the resulting model distinguishes between damage due to prior known loads and future unknown loads, to allow for reduced uncertainties in case that the load history is available from measurements or calculations. Measures are taken to ensure that the correlation between mean and cyclic loads is handled implicitly. A case study based on extensive hindcast-based simulations for a realistic mooring system is performed, and the respective effects of uncertainties in fatigue capacity, corrosion development and fatigue loads are presented and discussed.

Reconsidering the strength of concrete pavements

ABSTRACT Concrete pavements develop cracks with the accumulation of fatigue damage caused by the combined effect of vehicular and environmental loadings. In Mechanistic-Empirical (ME) design, the ratio of stresses to some measure of strength is used to evaluate incremental damage, which is then related to cracking. Typically, this measure is the Modulus of Rupture (MOR) of a beam made of the same material. The flexural strength is also known to vary with the thickness of the beam. However, the variation of flexural strength due the presence of eigenstresses from temperature or moisture distributions has not received sufficient attention. A non-linear fracture mechanics model demonstrated that the thickness-adjusted flexural strength can also be used for characterising the maximum elastic stress under a linear temperature distribution. However, under a non-linear temperature distribution, the material may sustain a higher or lower maximum elastic stress than the flexural strength. To model this, a practical analytical expression for the apparent flexural strength was derived and showed excellent agreement with numerical simulations as well as with a model based on equivalent elastic deformation energy. The model was used to show that the fatigue capacity under a typical axle load varies with various non-linear temperature distributions.

Iron-Based shape memory alloy for strengthening of 113-Year bridge

This study focuses on the large-scale application of a Fe-Mn-Si shape memory alloy (Fe-SMA) for strengthening a historic roadway bridge in Petrov nad Desnou (113-years), Czech Republic. To the best of the authors’ knowledge, this is the first application of an iron-based SMA (Fe-SMA) for prestressed strengthening of a bridge. In this study, the shape memory effect (SME) of the Fe-SMA was used for the prestressed strengthening of bridge girders. A mechanical anchorage system was developed to apply multiple Fe-SMA strips to the steel girders of the bridge subjected to daily passengers and heavy trucks. The SME of the Fe-SMA was activated by heating to approximately 260 °C using ceramic heating pads. The test results showed that the recovery stress of the Fe-SMA strips resulted in a compressive stress of approximately –33 MPa in the lower flange of the bridge girder. This compressive stress significantly increased the yield and fatigue capacity of the strengthened girder. Before and after the strengthening, the bridge was loaded with a 45-ton crane to assess the efficiency and performance of the system. Laboratory experiments were performed to optimize the mechanical anchors and examine the feasibility of the proposed strengthening method prior to application to the bridge. Finally, long-term monitoring of the prestressed Fe-SMA plates after installation on the bridge was conducted. The results showed that the main loss of the prestressing force caused by relaxation occurred within the first 30 days after activation and was approximately 20% of the original prestress.