Securing Wind Turbines: The Anchor Bolt Cage Explained
The anchor bolt cage in a wind turbine foundation plays a vital role in securing the turbine tower to its base. This circular assembly of anchor bolts, embedded in the foundation pedestal and slab, is engineered to withstand the intense forces at the tower base generated by wind, turbine operation, and other environmental loads. In the video above, we explain the unique features and components of this advanced system that is critical to the stability and durability of wind turbines! However, if you prefer silent reading, we present this same material below.
What’s an Anchor Bolt Cage?
An anchor bolt cage for a wind turbine foundation is a crucial component that secures the wind turbine tower to the foundation. It consists of a circular arrangement of anchor bolts embedded in concrete, providing stability and strength to the turbine's tower by resisting the various forces it experiences, such as wind loads, torque, and vibrations.
Tower-to-Foundation Connection
The tower wall refers to the cylindrical structure of the wind turbine that extends upward from the foundation to support the nacelle and blades. The tower is usually made of steel and is designed to withstand the loads and stresses imposed by the turbine's operation. The base of the tower wall is the tower base flange and is connected to the foundation using anchor bolts. Bolt nuts are the nuts that fasten the wind turbine’s tower to the foundation. These nuts are threaded onto the anchor bolts that protrude from the concrete foundation, securing the tower in place. Typically, there are multiple layers of nuts and washers, which help to distribute the load and ensure a firm connection.
Anchor Bolts & Sleeves
Anchor bolts are long, sleeved rods embedded into the concrete foundation. These bolts extend upward, passing through the base of the wind turbine tower, and are secured with anchor bolt nuts. The primary purpose of anchor bolts is to hold the turbine tower in place, transferring loads from the tower to the foundation. The anchor bolts are post-tensioned to keep the concrete in compression during turbine operation.
Anchor bolt sleeves are hollow cylindrical components that surround the anchor bolts within the concrete foundation. These sleeves prevent direct contact between the anchor bolts and the concrete, which allows for post-tensioning and ensuring that the concrete in and surrounding the anchor bolt cage remains in a state of compression during turbine operation.
Grout Layer
The grout layer between the base of the wind turbine tower and the top of the concrete foundation helps to ensure an even distribution of contact pressure from the tower to the foundation.
Embedment Ring
The embedment ring is a metal ring embedded in the concrete foundation at the bottom end of the anchor bolt cage. It helps to distribute the load from the anchor bolts into the concrete foundation, ensuring a secure connection between the tower and the foundation. The embedment ring also serves to align the anchor bolts and maintain their spacing during the construction process.
Bolt Cage Supports
The cage supports rest on the base of the foundation pit. They support the weight of the anchor bolt cage during the construction process, ensuring that the cage remains in the correct position while the concrete is poured and cured.
