Effects of Concrete Compressive Strength and Thickness on the Natural Frequency of a Prestressed Concrete Wind Tower

Abstract

In wind tower design, the natural frequency must remain within a safe working range to avoid resonance. This study investigates the effects of concrete thickness and compressive strength on the first natural frequency of a 100 m prestressed concrete tower supporting a 5 MW turbine. Sixty-four models were analyzed using finite element modal analysis. The tower was modeled using 4 m Class 1 3D Bernoulli beam segments, each subdivided into ten elements, and the turbine was represented by a concentrated mass at the top. Two studies were conducted for concrete classes C30, C40, C50, and C60: one varying both base and top thickness (study 1), and another varying only the base thickness (study 2). For a given concrete class, increasing thickness resulted in a higher natural frequency, but with decreasing impact as thickness grew, indicating a tendency toward stabilization. Likewise, higher concrete strength increased the natural frequency, although the effect diminished at higher strength levels. For all geometries, the natural frequencies relative to C50 were 85.6% for C30, 93.3% for C40, and 103.9% for C60.