Tower and Foundation: An Example

The load dynamic design of materials and structure used in ENERCON towers provide the best conditions for transport, installation and use. Over and above the binding national and international norms (e.g.: DIN and Eurocode) ENERCON sets its own standards which surpass quality and safety norms.

Virtual 3D models of the tower designs are produced during the development phase using the finite element method (FEM). All possible stress on the wind turbine is then simulated on the model. This means that accurate predictions concerning tower stability and service life are not left to chance before building a prototype. ENERCON continuously evaluates additional measurements on existing turbines providing further verification of the calculated data. ENERCON’s calculations are confirmed by results produced by specially commissioned certification bodies, research institutes and engineering firms.

The aesthetic aspect is also a decisive factor during tower development, which is obvious in the finished product. The streamlined gradually tapered design offers a visibly sophisticated concept which has next to nothing in common with the huge and bulky conventional cylindrical structures.

Tubular steel tower

ENERCON tubular steel towers are manufactured in several individual tower sections connected using stress reducing L-flanges. Unlike conventional flange connections (such as those used in steel chimney construction), the welding seam of the L-flange is outside the stress zone.

Due to their relatively small circumference, shorter ENERCON tubular steel towers are mounted on the foundations using a so-called foundation basket, which consists of a double rowed circular array of threaded steel bolts. A retainer ring, fitted to the tower flange dimensions, is used to hold the individual bolts in position. When the foundation is completed, the lower tower section is placed on the bolts protruding out of the concrete surface and then bolted with nuts and washers.

A specially developed foundation connection system is used for taller ENERCON steel towers. A cylindrical structural element is set on the blinding layer and precisely aligned with adjusting bolts Once the foundation is completed, the tower is flanged together with the foundation section.

Manufacturing of Towers by Enercon - © Enercon

Precast concrete tower

ENERCON precast concrete towers are made using specially developed prestressed steel reinforcement. The individual tower sections and foundation are fastened together to form an inseparable unit with stay cables running through jacket tubes in the core of the concrete tower wall. The tower sections themselves are manufactured entirely in the precasting plant. Specially constructed steel moulds assure manufacturing precision for each individual concrete section. This manufacturing process minimises dimensional tolerances which assures a high degree of fitting accuracy. Here again, ENERCON’s Quality Assurance Department carries out strict inspections. Detailed procedural and work instructions are available for each manufacturing sector. This ensures that each individual manufacturing stage as well as the materials used can be completely retraced.

Foundation construction

The foundation transmits the wind turbine’s dead load and wind load into the ground. ENERCON foundations are always circular.

Foundation of a Enercon E-33 - © Enercon

Advantages of ENERCON round foundations

Foundation section of a Enercon E-70 - © Enercon

Depending on the site, the ground can only absorb a certain amount of compressive strain so the foundation surfaces are adapted accordingly. ENERCON’s circular foundations are designed based on this elementary realisation and as a rule are installed as shallow foundations. If necessary, (in soft soil for example) a special deep foundation distributes the load down to deeper load-bearing soil strata. The piles, symmetrically arranged, are slightly inclined so that the imagined extended pile centre lines meet at a point above the centre of the foundation. This provides maximum force/load distribution over the entire surface.

Text and Photos: ENERCON, Germany.