Fatigue Performance of Adhesive Joints in Timber Wind Turbine Towers - A study to evaluate the fatigue performance of adhesive joints in timber connections
Typ
Examensarbete för masterexamen
Program
Publicerad
2020
Författare
Karlsson, Erik
Lindvall, Simon
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Fatigue is a process which weakens a material over time under variable load. For some materials, the fatigue process is known and studied and thus the damage
accumulation can be predicted and taken well into consideration when designing
construction elements. For materials like steel, these properties are well known and
checked whenever a steel construction is designed. For timber however, it is a rather
unexplored subject and one which this thesis focuses on.
The reason that the fatigue process has not been researched for timber is that it
is rarely the deciding factor for the capacity of timber structures with bridges as
an exception. However, for wind turbine towers, the amount of load cycles is extensive.
During their lifetime, they will experience a high number of load cycles
with low stress levels. This is called high cycle fatigue. This raises the question of
the fatigue properties which will have a high demand regarding these load conditions.
This thesis is focused on the application of glued in rod connection, which also have a
lacking design regulation, even for static loading. For this connection, some research
has been concluded, where some reliable design regimes have been put forward along
with some information about the connections. The information available was gathered
and put forward in order to present a reliable design recommendation. The
available design regimes were tested using general coding software and then compared
with other available lab tests done previously by others. In conjunction to
this, an finite element model made in Abaqus was produced in order to provide further
understanding and general knowledge into these connection types under cyclic
as well as static loading.
The conclusion was finally made that an adhesive layer of 2mm would be optimal for
this type of connection, if fatigue as well as a static performance is to be retained.
The adhesive itself should be restricted to either polyurethane or epoxy of the 2-
components type. These two adhesives gave similar performance properties with
small differences that could be neglected. The recommended edge and rod distance
should be kept to no less than 2.5d as well as 4d respectively. The use of a laminated
veneer lumber would simplify the connection with regard to load angles toward
grains but glulam is a viable option, especially glulam made out of spruce or other
coniferous lumber. The pullout strength was generally improved when increasing
the anchorage length of the rod. Anyhow, the fatigue performance did not benefit
of this to the same extent.
Beskrivning
Ämne/nyckelord
Fatigue , Adhesive connections , Timber structures , Wind turbine towers