Experimental and numerical investigation of steel-grout-steel sandwich shells for wind turbine towers

Abstract

Aiming at enhancing a wind turbine tower's performance while keeping its external diameter below transportability-imposed limits, a steel-grout-steel sandwich base segment comprising a high diameter-to-thickness ratio is investigated herein, as an alternative to plain steel towers. An experimental campaign was firstly carried out, involving downscaled tower specimens which comprise the above said cross-section under bending loads, followed by the development of an elaborate finite-element (FE) model which can accurately capture the experimental behavior in terms of strength, stiffness and failure mechanism. A full-scale version of the validated model, representing the bottom segment of a wind turbine tower under design loads, was finally employed for the conduction of a parametric analysis, as regards the structure's geometry and material properties, and the investigation of the sandwich concept's possible advantages over a conventional steel structure. Owing to the synergy between the steel tubes and the grout core, the composite specimens almost reached their plastic moment capacity, premature buckling was prevented, and ductility was preserved, despite the significantly high diameter-to-thickness ratio of the steel tubes and the thin grout core. Although performance deteriorates as the diameter-to-thickness ratio of the two steel tubes increases, the relative advantage of the sandwich tower over a plain steel one becomes more prominent, especially when high-strength grout is used. It is thus demonstrated that a sandwich-type shell comprising a thin layer of grout may improve a wind turbine tower's load capacity, stiffness and stability without increasing the total amount of steel, nor extending its base diameter beyond transportability-related restrictions.