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An alternative connection in steel towers for wind turbines
2008 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The increasing prices of fossil fuels during the last decades have sparked increasing interest and investments in wind power plants to expand their share of electricity production and improve windmill technology with new and more economical inventions and sustainable solutions. A RFCS (research fund for coal and steel) research project called HISTWIN has the aim to improve the competitiveness of the windmill towers made of steel. The towers for high power wind generators often consist of several cylindrical slightly tapered steel segments connected by bolted flanges. This is a traditional and well established solution. One part of the project is to examine if a friction connection can be used instead of the traditional flange connection, because the friction connection will introduce two mprovements: it is expected to have higher fatigue class, leading to less steel consumption and the tower will be faster to assemble. The proposed friction connection is a lap connection bolted with tension control bolts, TC-bolts. One plate of the connection has normal sized holes while the other plate has long open slots. This solution is expected to reduce the total cost of the tower with at least 10%. The main objective of this report is to establish structural characteristics of static behavior and the ks factor for this type of connection according to Eurocode and to investigate the performance of TC-bolts in the connection. The ks factor is a factor that reduces the slip resistance for friction connections in EN 1993 - Part 1-8 regarding size of holes used in the connection. There are no specific rules for long open slots in EN 1993 - Part 1-8 which are used in the proposed connection. Another aim of this report is to evaluate different ways to control the preload. The objective is to evaluate properties of TC-bolts and its competitiveness. The ks factor is evaluated from four groups of specimens. The tested specimens have two types of surfaces and have three different configurations of bolt placement in the specimens. Design of the tower connections are done with the experimentally obtained ks factor for a lap connection and comparison is made with an ordinary flange connection. The results in this report shows that the use of TC-bolts is a very competitive method to control the preload with respect to speed of installation, and that the bolts perform well under various conditions and treatments. The experiments done in this report shows that the proposed connection has a ks factor equal to 0,75 as the connections are prevented from in-plane rotation, this can be compared with the ks factor for long slotted holes which is equal to 0,63. Economical calculations show that if a lap connection with long open slots is used instead of an ordinary flange connection, the cost will be reduced by more than 85 % per connection in a wind tower. These calculations are done with respect to price of flanges and bolts provided by HISTWIN partners.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Lap joint, Friction connection, Slip resistance, Long slotted, holes, Steel tower, Pretensioned bolts, Long open slots, TC-, bolts
Keyword [sv]
URN: urn:nbn:se:ltu:diva-59037ISRN: LTU-EX--08/199--SELocal ID: f93ff151-c6ea-4e49-b6e6-3e6f74daee70OAI: diva2:1032425
Subject / course
Student thesis, at least 30 credits
Educational program
Civil Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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