Standards and Practices - Structural Integrity of Offshore Wind Turbines - page 44

as blade-wind-tower interaction and presence or absence of yaw con-
trol. Similarly, IEC 61400-3 lacks some of the detailed provisions given
by API RP 2A with respect to certain offshore engineering practices.
It is important for the industry to develop a full understanding of the
differences in the requirements and overall performance levels inherent in
these codes. This comparison should seek to clarify the relative levels of
structural reliability inherent within each code when applied to a wind tur-
bine project at a specific location and to evaluate the similarities and dif-
ferences in the consequences of failure (either loss of function or collapse
of the structure) for the types of facilities.
One final issue is that floating platforms for wind turbines are explicitly
not covered by IEC 61400-3. Research will be necessary to define all issues
that may affect the design of such a structure. Such issues are likely to
include hydrostatic and hydrodynamic stability, coupled aerodynamic
loading from the rotor and wave loading, station keeping, and electrical
distribution system connections for a highly compliant support structure.
ISO STANDARDS
As described previously, the ISO 19900 series of standards addresses off-
shore platforms for the oil and gas industries. These standards were based
on existing API standards for fixed steel and floating structures and on a
Norwegian standard, the leading offshore concrete standard. The over-
sight groups (work groups under ISO TC 67/SC 7) for these ISO standards
are establishing an ongoing updating and maintenance process now that
the first version of the standards has been published. To meet industry
needs while the European Union standards requirements were developed,
the load and resistance factor design (LRFD) version of API RP 2A was
adopted as an interim ISO standard. An international committee structure
with considerable U.S. and API leadership and engagement developed the
second version of the Fixed Steel Platform standard (ISO 19902), as well
as a suite of accompanying general offshore standards: ISO 19903 (Fixed
Concrete Structures), ISO 19904 (Floating Systems), ISO 19905 (Jackups),
and ISO 19908 (Arctic Structures). A full description of the ISO and API
work programs is given by Wisch et al. (2010). This ISO series harmonizes
international practices into a single, integrated suite of standards. The ISO