Engineering Structures 98 (2015) 151–162
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Engineering Structures
journal homepage: www.elsevier.com/locate/engstruct
Friction connection vs. ring flange connection in steel towers for wind
converters
Marko Pavlović a,d, Christine Heistermann a,⇑, Milan Veljković a, Daniel Pak b, Markus Feldmann b,
Carlos Rebelo c, Luis Simões da Silva c
a
Steel Structures, Luleå University of Technology, 97187 Luleå, Sweden
Institute for Steel Construction, RWTH Aachen University, Mies-van-der-Rohe-Straße 1, 52074 Aachen, Germany
ISISE, Department of Civil Engineering, University of Coimbra, Rua Luís Reis Santos, Pólo 2, 3030-788 Coimbra, Portugal
d
University of Belgrade, Faculty of Civil Engineering, Serbia1
b
c
a r t i c l e
i n f o
Article history:
Received 19 August 2014
Revised 13 April 2015
Accepted 15 April 2015
Keywords:
Towers for wind converters
Friction connection
Long open slotted holes
High strength steel
Overall bending moment resistance
Local buckling
FEA
a b s t r a c t
Tubular steel towers are the most commonly used structures to support wind converters. Towers are
fabricated in welded segments, complying with the traffic requirements for transportation, and in-situ
assembled. Ring flange connections are used to connect two segments. Fatigue endurance of the ring
flange to the shell weld, class 71, is often the design criterion and imposes a limit on the shell thickness.
Recently studied friction connections with long opened slotted holes, in HISTWIN and HISTWIN2
projects, provides a remedy for this limitation. The main purpose of this paper is to compare performance
of the ring flange connection and the novel friction considering connection of a real tubular tower
segment 3.37 m in diameter and 24 mm shell thickness. This cross-section is designed for the ultimate
load MEd = 45.8 MNm and the steel grade S355. Finite Element Method is used to investigate possible
failure modes of the connection. Advanced FEA comprise the realistic geometry of the connection, ductile
damage material model and element removal using explicit dynamic solver. This allows sophisticated
analysis of the behaviour and direct comparison of the results for both connection alternatives. The
FEA is validated by down-scaled experiments performed previously within the HISTWIN project. The
friction connection is thoroughly examined: geometry of the connection, influence of the shell imperfection in the vicinity of the connection and possible use of higher resistance steel grades. By focusing on key
issues of the friction connection recommendations for the design are provided together with a numerical
example.
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
Steel tubular towers for wind converters are fabricated from
steel plates, rolled into short cylinders and welded to a segment
suitable for transportation, usually 20–30 m long. On site, the segments are lifted on top of each other and assembled most often by
the ring flange connection. Diameters of towers with common hub
height of 80–100 m are rather large e.g. 3–4 m and shell thicknesses can be up to 40–50 mm, depending on the site condition,
wind turbine class, and the steel grade used. The fabrication process of the traditional ring flange connection is laborious and
⇑ Corresponding author. Tel.: +46 920 491632.
E-mail addresses: [email protected], [email protected] (M. Pavlović),
[email protected] (C. Heistermann), [email protected] (M. Veljković),
[email protected] (D. Pak), [email protected] (M. Feldmann),
[email protected] (C. Rebelo), [email protected] (L. Simões da Silva).
1
Permanent position.
http://dx.doi.org/10.1016/j.engstruct.2015.04.026
0141-0296/Ó 2015 Elsevier Ltd. All rights reserved.
costly. The fatigue resistance is low due to welding i.e. fatigue class
between 36 and 71, which leads to thicker shells. A breakthrough
in design and fabrication of towers is achieved using an innovative
solution of assembling joints using a single overlapping friction
connection with long opened slotted holes (henceforth called the
friction connection), shown in Fig. 1.
Feasibility tests on 2 m diameter tower segments within
HISTWIN [1] and HISTWIN2 [2] projects demonstrated easy fabrication and assembling of the tower segments using the friction
connection. Cost benefits indicating that the friction connection
is about 80% less expensive than the flange connection is shown
in [1]. Scaled-down experiments on tower segments in bending
with the ring flange connection and the friction connection have
been conducted but still no tests or field measurements are
available on real tower dimensions.
Experiments and FEA of a single overlapping joint and scaleddown friction connection have been conducted previously by