Cracks in wind turbine foundations pose a direct risk to Structural Integrity reliability of wind farms, requiring careful failure investigation to identify their actual causes. In this context, the combination of field inspections, non-destructive testing, and structural analysis is essential to differentiate between cracks of structural, rheological, or mechanical origin, as well as to define corrective actions compatible with regulatory requirements. Continue reading to learn more about the methodology applied and the results obtained in this case study.

Introduction

The energy industry is essential to the country's economic development, as it powers various sectors of the economy. In this sense, to meet the constant increase in energy demand, a large infrastructure is needed that includes various types of energy sources, such as hydroelectric, thermal, nuclear power plants, wind farms, among others, as well as transmission and distribution systems infrastructure. Thus, given its economic importance, it is essential that the structures that make up the numerous segments of the energy industry be designed, executed, and evaluated by qualified professionals. In addition, proper care and maintenance of these assets is indispensable.

Succes story

A client identified cracks in the reinforced concrete foundations of wind turbines at a wind farm. In this type of situation, the main challenge is to identify the causes of the cracks. In general, cracks in reinforced concrete elements can be caused by various factors, some of which are internal and others external, and may be the result of stresses not anticipated in the design, for example.

For this reason, Kot Engenharia hired to investigate the cause of the cracks in the foundations and determine the actions required for structural recovery, so that the structure operates in accordance with regulatory structural performance requirements. The results obtained through 3D scanning of one of these bases can be seen below in Video 1.

Video 1: Crack in wind turbine base - SOURCE: Kot Collection.

Services provided

The investigation of cracks in the foundations involved field inspection and engineering calculations, in order to determine the executive and design aspects that could lead to cracks in the reinforced concrete pieces.

Figure 1: Services provided - SOURCE: Kot Collection.

Several influencing factors have been established for the occurrence of cracks in concrete, which can be divided into two groups:

• • Factors that favor the occurrence of shrinkage cracks;

• • Factors that favor the occurrence of mechanical cracks.

Figure 2: Aggravating factors of cracking - SOURCE: Kot Collection.

Field tests

At this stage, non-destructive testing made it possible to verify factors related to the quality of the foundations' execution that had an impact on the occurrence of cracks. Vale that this stage is of great importance for failure investigations, as it allows the identification of aspects that cannot be evaluated by structural analysis of the parts according to the design.

In addition, Kot Engenharia ultrasonic tomography testing to identify possible discontinuities in the concrete, as well as to verify the dimensions of the reinforcing bars (rebars). Complementarily, pacometry testing was performed to determine the position of the reinforcements and subsequently compare them with the tomography image results.

Figure 3: Ultrasonic tomography on concrete - SOURCE: Kot Collection.

Structural analysis of the foundation

Next, the foundations were verified using analytical and numerical models, with the aim of evaluating the design and dimensioning of the structure in relation to existing demands and, thereby, identifying any design non-conformities, if they existed.

Figure 4: Analysis models - SOURCE: Kot Collection.

A three-dimensional model based on the Finite Element Method (FEM) was used to analyze the anchoring region of the wind turbine structure with the reinforced concrete base (figure 5).

Figure 5: Finite element computer model of a wind turbine foundation - SOURCE: Kot Collection.

As a result, analytical and numerical models made it possible to identify the stresses acting on reinforced concrete, thus determining the risk of component failure.

Final considerations

In summary, by applying the available field and numerical techniques, it was possible to determine the causes for the appearance of cracks, which have two distinct origins: cracks resulting from concrete shrinkage and cracks of mechanical origin. In addition, non-destructive testing on concrete foundations was essential for verifying compliance with the design, as well as allowing the identification of construction-related discontinuities in the parts.

Mechanical cracks are characterized by larger openings and are associated with compromised concrete structure resistance, which may be related, among other factors, to structural design. Thus, based on the results of the analysis models, it was possible to identify mechanical cracks, which are compatible with the stresses acting on the wind turbine foundation elements.

The assessment of unconventional reinforced concrete structures, such as wind turbine foundations, requires a team of professionals with experience in inspection, modeling and structural analysis. Kot has a team of professionals qualified in unconventional analysis, ready to provide reliable solutions on demand. Contact our team for more information!

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