Wind Energy

58
High-cycle Fatigue of “Ultra-High Performance
Concrete” and “Grouted Joints” for Offshore
Wind Energy Turbines
L. Lohaus and S. Anders
58.1 Introduction
“Grouted Joints” are well known for offshore platforms in the oil and petroleum
industry. Besides, they have already been used in Monopile-foundations and
are being considered for Tripod-foundations in deeper water for offshore wind
energy converters. In offshore wind energy applications, only ultra-high performance
concrete (UHPC) has been used up to now. UHPC itself is known
for its outstanding mechanical characteristics in static tests, but only little
is known about the dynamic behaviour in terms of fatigue strength, damage
development or the performance in “Grouted Joints.”
58.2 Ultra-High Performance Concrete
UHPC is known for its distinct brittle failure and its outstanding compressive
strength, but only little is known about its fatigue performance [3, 4].
Experiments on different UHPC mixes [3], with compressive strengths
ranging from 135 to 225 MPa, have indicated, that attention has to be paid
to the fatigue strength, which seems to be lower for high-cycle fatigue compared
to normal-strength concrete using normalized stresses, as illustrated in
Fig. 58.1.
In contrast to the UHPC mix tested in Aalborg, heat treatment with
different temperatures was used in Hannover and Kassel. In addition, the
UHPC mix tested in Kassel contained 2.5 vol.% of 9 mm long steel fibres. The
tests performed by the University of Kassel are displayed as a dashed line,
because the number of tests was limited.
Deformation measurements and the development of Young’s modulus during
fatigue tests have indicated, that the distinct brittleness of UHPC can
also be observed in fatigue loading. These results are in good agreement with
deformation measurements on UHPC reported in [3].