Part B - Certificates and approval requirements 
17 
• Special aspects for certifying steel structures: 
The stability certificate for circular cylindrical shells is allowed to be obtained in accordance with 
section 10.1.3 of the „Richtlinie für Windenergieanlagen - Einwirkungen und Standsicherheitsnach 
weise für Turm und Gründung“ (edition March 2004) f181 by the Deutsches Institut für Bautechnik 
Certification of the fatigue limit status for driven piles (also for monopiles) shall take account of 
the damage proportion from the pile driving itself. 
Certification of grouted joint connections shall be obtained in accordance with the recommen 
dations of GL or DNV using the finite element method (FEM) and, if necessary, confirmed by 
laboratory tests conducted in an accredited test institute. 
3.2.3.4 Structural design 
• Specialties of steel fabrications: 
The special corrosion risks shall be taken into account when using high-grade steel compo 
nents. 
The wind turbine (e.g. steel tower) and equipment (secondary steel such as boat landing, plat 
forms and ladders) shall be connected to the lightning protection and earthing system. 
Driven monopiles shall have a minimum ratio of diameter to wall thickness D/t = 100 if at all 
possible. 
• Specialties of solid constructions: 
Care shall be taken to route lightning protection and earth cables through the concrete struc 
tures for dissipation into the soil (e.g. connection to existing reinforcement). 
The special corrosion risks shall be taken into account when using high-grade steel compo 
nents. 
The structural design of reinforced concrete and prestressed concrete reinforcement shall take 
account of the aspects of minimum and crack reinforcement, rod and edge spacings, concrete 
covering, bending radii, anchoring and encroachment lengths, anchoring points for the trans 
verse force reinforcement as well as corrosion protection measures in prestressing elements. 
3.2.4 Foundation elements 
3.2.4.1 Preliminary remarks 
Offshore wind turbines are structures with a high degree of difficulty, their foundations are to be classi 
fied in geotechnical category 3 (earth and foundation structures as well as geotechnical measures with a 
high geotechnical risk) in accordance with DIN 1054-2005.01 f191. They require their foundation design 
to be conducted by an engineer with numerous safety certificates (stability against collapse and service 
ability) on the basis of an individual soil investigation and assessment involving an expert in geotechnol 
ogy with thorough knowledge and experience in this area. 
Quite apart from the uncertainties of the local soil situation, it is also necessary to consider the limited 
possibilities of deterministic calculation models in geotechnology when drafting the foundation elements 
of offshore wind turbines. 
The achievable „accuracy“ of numerical model calculations including the soil is significantly lower than 
that of design components due to the implementation of what are, by necessity, highly simplified stress 
deformation relationships and contact surface conditions. As a rule, therefore, variations of the signifi 
cant influencing parameters shall be undertaken by means of which their influence on the draft target is 
limited and which indicate how the overall structure will „behave“ within these limits to a sufficient degree 
of probability.