Strengthening Mechanism of Studs for Embedded-Ring Foundation of Wind Turbine Tower

Abstract

The embedded-ring wind turbine foundations were widely applied in the early development stage of wind power industries because of its properties such as easy installation and adjustment. However, different damages occurred on some embedded-ring wind turbine foundations in recent years. Based on the common damage phenomena of embedded-ring wind turbine foundations, the structural defects and damage mechanisms of embedded-ring wind turbine foundations are analyzed in a gradual way. Cheese head studs are proposed to be welded on the lateral wall of the steel ring to strengthen the connection between the steel ring and the foundation concrete. The foundation pier is elevated 1 m to increase the embedded depth of the steel ring. The circumferential confining pressure is applied on the lateral side of the foundation pier to lead it into a state of pressure. One simplified method is proposed to calculate the contribution of welding studs in this strengthening method. Taking an embedded-ring wind turbine foundation as an example, the numerical analyses for the original foundation and the reinforced one are carried out to compare the stress and strain distribution changes. Based on the numerical results corresponding to the peak and valley value loads, the fatigue life of the concrete and studs are evaluated according to the relevant design codes. The numerical results show that this strengthening method can coordinate the deformation of the embedded steel ring and the foundation concrete by circumferential prestressing and welding studs. The maximum principal stresses of the foundation pier and the fatigue stress range of the concrete around the bottom of the steel ring have been greatly reduced after strengthening. The gaps between the embedded steel ring and the foundation pier are also obviously decreased because of these strengthening measures. The stress concentration phenomena of the concrete around the T-shaped flange have been remarkably improved. The fatigue life can meet the requirements of relevant design codes after strengthening. Therefore, it can be concluded that the safety performance and service life of the embedded-ring foundation can be guaranteed.