Introduction

The energy industry is essential to the country's economic development, as it powers the various sectors of the economy. To meet the constant increase in energy demand, a large infrastructure is needed that includes various types of energy generating sources, such as: hydroelectric, thermal, nuclear power plants, wind farms, among others, as well as the infrastructure of transmission and distribution systems. Given their economic importance, it is essential that the structures that make up the many segments of the energy industry are designed, executed and assessed by qualified professionals. In addition, proper care and maintenance of these assets is essential.

Succes story

A client identified cracks in the reinforced concrete foundations of wind turbines at a wind farm. The main challenge in this type of situation is to identify the causes of the cracks. Cracks in reinforced concrete elements can originate from various factors, some of which are autogenous and others of which are external, which can be the result of unforeseen design stresses, for example.

Kot Engenharia was 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 compliance with the normative requirements for structural performance. Video 1 shows the results obtained from a 3D scan of one of these foundations.

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

The non-destructive tests made it possible to verify factors relating to the quality of the foundations that had an impact on the occurrence of cracks. This stage is of great importance for failure investigations, as it allows aspects to be identified that cannot be assessed by structural analysis of the parts according to the design.

Kot Engenharia carried out ultrasonic tomography in order to identify possible discontinuities in the concrete, as well as checking the dimensions of the reinforcement bars(rebars). In addition, a pacometry test was carried out to determine the position of the reinforcements and then compare them with the tomography image results.

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

Structural analysis of the foundation

The foundations were checked using analytical and numerical models, with the aim of evaluating the design and dimensioning of the structure in relation to the existing stresses, and thereby identifying any design non-conformities.

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.

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

Final considerations

By applying the available field and numerical techniques, it was possible to determine the causes of the cracks, which have two distinct origins: cracks caused by concrete shrinkage and cracks of mechanical origin. The non-destructive tests on the concrete foundations were fundamental in verifying adherence to the design, as well as allowing the identification of discontinuities of constructive origin in the pieces.

Cracks of mechanical origin are characterized by larger openings and are associated with impairment of the resistant capacity of the concrete structure, which may be related, among other factors, to structural design. Based on the results of the analysis models, it was possible to identify cracks of mechanical origin, which are compatible with the forces 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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