Verification of Anchoring in Foundations of Wind Turbine Towers

Abstract

Tubular steel towers are the most common supporting structure of wind converters. The towers' foundation covers an important part of the initial cost and its configuration depends heavily on the type of subsoil. Onshore structures are founded on spread footing foundations or pile foundations with the first being the commonest. In these spread footing foundations, the tower is either embedded in the concrete foundation slab or the tower bottom flange is anchored to the concrete by means of pretensioned bolts. This anchoring of the steel tower on the concrete foundation is very rarely analyzed separately and recent failures due to inadequate design have alerted the wind industry towards the solution of the problem. For the purposes of the analytical and numerical approaches, two alternative types of foundation dimensioning are investigated. The tower properties of the two configurations are the same, providing the same loading and material data. The analytical study of the foundation anchoring is performed with the use of the equivalent ring method and the numerical verification of the two foundation solutions is performed with the use of a detailed micro model. The same micro model is used for the calculation of the fatigue life of the tower bottom joint following the damage accumulation method. In both foundation solutions, the total cross sectional area of the anchor bolts is proved to be the decisive factor for the selection of bolt size and number. The size of the tower bottom diameter plays also an important role on the maximum number and size of bolts used. Both analytical and numerical results are in good agreement and valuable outcomes are emerging from the comparative study on the foundation dimensioning of contemporary structures.

Research on the Effect of Aerodynamic Imbalance on Fatigue Performance of a Wind Turbine Foundation with Embedded Steel Ring

“…McAlorum et al [2] monitored cracks on the surface of the WT foundation with FBG-based long-gauge strain sensors, and in this paper, the cracks on the surface of the WT's foundation are divided into three types: reactive, permanent, and behavioral, and are described in detail. At the same time, large tensile and compressive forces are transferred to the foundation by the ESR, and the concrete in the anchorage zone of the ESR is subjected to high-cycle fatigue loading, causing concrete in foundations to operate at higher stress [3][4][5][6]. If things continue this way, the concrete in the compressive zone of the WT foundation may experience high cycling, resulting in fatigue accumulation.…”

Research on Anchorage Performance of the Foundation Ring for Wind Turbines

“…Fujiyama [10] analyzed the stability of wind turbine support structures by defining their vibration characteristics using field-monitoring data. Examining the fatigue characteristics of wind turbine foundations, Stavridou [11] found that the diameter of the tower bottom significantly affected fatigue life. He [6] observed the internal stresses in a wind turbine foundation and found that the primary external load was borne by the base flange of the foundation ring.…”

Performance Analysis of an Improved Gravity Anchor Bolt Expanded Foundation

“…Most onshore wind turbines are built on extended foundations, which are divided into gravity foundations and anchor pile foundations. As shown in Figure 3, there are two ways to connect the tower and the foundation in the extended foundation: one is to embed the tower directly into the concrete foundation slab ('foundation ring'); the other is to fix the bottom flange of the tower on the concrete by using prestressed bolts ('anchor cage ring') [26]. The foundation ring is widely used because of its simple structure, large production, convenient quality control, and convenient installation [28,29].…”