Stress concentration at the door opening of steel towers for
wind turbines
Abstract: The increasing interest in wind energy leads to higher demands of wind
turbines. Higher production rates caused by the demand make it essential to
develop tower for wind turbines in a way that cost savings in the whole
production and assembly are achieved.
An optimization of the tower and tower details which lead to material or
assembly time reductions is the main objective of a European research
project, HISTWIN.
The project is focusing on competitiveness of steel towers for wind turbines.
Steel towers for multi megawatt turbines usually consist of several conical
steel segments which are welded together to sections. These sections are
connected by bolted flange connections or by the innovative friction
connection developed within the project.
This report investigates the lower tower section which includes the door
opening. The door is used for service and maintenance to come into the tower.
Around the door opening there is a stiffener. Design of the door opening and
the stiffener is govern by a stress distribution. These stresses were
analyzed using the FEM software Abaqus v.6.7. The tower’s shell thickness and
the thickness of the stiffener around the door opening were investigated in
the parametric study done by the Abaqus. The aim was to investigate the
influence of thickness and material changes around the door opening and its
influence on the stress level.
Another criterion of thin walled structures is the resistance against
buckling. The tower’s structure was also investigated concerning the
possibility to reduce resistance due to buckling. The reduction of the
bearing resistance of the lower segment of the tower varies with the
amplitude of imperfections.
The state of the art tower uses steel S355 with yield strength of 355MPa. A
change of the material to steel with higher strength was studied.
It is concluded that savings of the amount of steel used are possible.
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