Offshore wind has been identified as one of the emerging sustainable energy sources in the United Kingdom. Offshore wind turbine support structures are mainly fabricated of welded tubular members, similar to structures used for oil and gas applications, and are exposed to highly dynamic, harsh marine environments. However, their structural details and design requirements are significantly different due to the magnitude and frequency of operational and environmental loadings acting on the support structures. These conditions would significantly affect their structural dynamic response characteristics due to the magnitude of the applied load. This may therefore have some significant effects on the crack growth behaviour and the extent to which corrosion can be associated with damage to the support structures. However, the magnitude of the applied load might depend on turbine size, water depth, soil conditions and type of support structures. It is therefore essential to design wind turbine support structures against prescribed limit states to ensure economical and safe operation. This paper presents a review of corrosion fatigue in offshore structures as regards the effects of seawater, environment and mechanical loading. Existing literature which documents results from previous campaigns is presented, including works referring to oil and gas structures, highlighting the significant difference in the aspects of loading and use of modern fabrication processes, with a view to illustrating the requirements for an update to the existing corrosion fatigue database that will suit offshore wind structures׳ design requirements.

Review of corrosion fatigue in offshore structures: Present status and challenges in the offshore wind sector

Structures made using high-strength steel (HSS) offer numerous benefits in terms of mechanical performance, economy and sustainability. With such structures increasingly being used in practice, aca...

A review of research on high-strength steel structures

Retardation of fatigue crack growth in high strength steel S690 using a modified stop-hole technique

Three-dimensional fatigue crack propagation simulation using extended finite element methods for steel grades S355 and S690 considering mean stress effects

https://northumbria-test.eprints-hosting.org/id/document/266529

Real-time monitoring, prognosis, and resilient control for wind turbine systems

A comparison of the fatigue behavior between S355 and S690 steel grades

This paper describes the development, calibration and preliminary results of the structural monitoring system in-stalled in a 80 meters high steel wind tower supporting a 2.1MW turbine Wind Class III IEC2a erected in the central part of Portugal. The monitoring period corresponds to about fifteen months of measurements. Results presented refer to stress distribution on shell and in bolts at different heights, stress fatigue spectra, section forces along height evaluated from the stress measurements and comparison with design forces, dynamic response in terms of accelerations, stresses, deflections and rotations.

Structural monitoring of a wind turbine steel tower

A year-long monitoring of preloaded free-maintenance bolts – Estimation of preload loss on BobTail bolts

This paper presents results from the structural monitoring of a steel wind tower characterized and presented in Part I of the paper. Monitoring period corresponds to about fifteen months of measurements. Results presented refer to stress distribution on shell and in bolts at different heights, stress fatigue spectra, section forces along height evaluated from the stress measurements and comparison with design forces, dynamic response in terms of accelerations, stresses, deflections and rotations.

Structural monitoring of a wind turbine steel tower – Part II: monitoring results

Micropiles, which are small-diameter deep foundation solutions with diameters that can measure up to 300 mm, are often used to reinforce new and existing foundations. Their use in the foundations of structures with high eccentricity, such as wind towers when subjected to wind loads, may lead to more efficient and economical solutions. As the new generation of wind towers will reach more than 150 m tall, very large and uneconomical gravity foundations are required. In regions of high seismicity this problem is aggravated. To evaluate the behavior of micropiles under variable loading and predict the improvement of the reinforced solution, load tests were performed on steel micropiles under controlled laboratory conditions. A total of 36 tests were conducted on 3-m-long pipe micropiles, both while isolated and in 2 by 2 groups, with three different spacings. The micropiles were installed in a cylindrical container filled with calibrated sand and tested under monotonic and cyclic loading, first without grout, then when low-pressure grouted and retested, with the aim to evaluate the improvement caused by the grout injection, the micropile spacing, and application of cyclic loading both in terms of resistance and stiffness. An improvement both in stiffness and resistance due to the grouting was obtained and, for the applied cyclic loading, there was no clear reduction in micropile cyclic stiffness. The presented results provide a tool for the calibration of numerical models to estimate the behavior of real-scale micropiles installed in higher density sand.

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R. Matos

Papers

A comparison of the fatigue behavior between S355 and S690 steel grades

Structural monitoring of a wind turbine steel tower

A year-long monitoring of preloaded free-maintenance bolts – Estimation of preload loss on BobTail bolts

Structural monitoring of a wind turbine steel tower – Part II: monitoring results

Axial monotonic and cyclic testing of micropiles in loose sand