7.1.2 History

The use of headed studs in fastening systems dates back to the early 1970s. The first headed studs used in building nuclear power plants were PECO concrete anchors. In 1971, Peco Bolzenschweifitechnik GmbH was acquired by Nelson StudWelding Co. and had its name changed to Nelson Bolzenschweiss-Technik GmbH. After a long time as part of the TRW-group, Nelson Bolzenschweiss-Technik moved to the Fabri-Steel Group in Michigan, USA, in 2000, and has belonged to Doncasters Group Ltd, UK, since 2009. However, the company label, Nelson, remains unchanged to date.

The headed studs found in older nuclear power plants under the names ‘Peco’, ‘Nelson’ and ‘TRW-Nelson’ are all the same product. Following extensive tests and expert opinions by Professors Roik and Bode, the DIBt granted the first general approval for headed studs (anchoring steel plates using welded-on Nelson headed studs, approval no. Z-21.5-82) in 1983.

Not long after that, the DIBt issued further headed stud licences for the Koster & Co. of Ennepetal (Z-21.5-280) and Riss AG of Dallikon, Switzerland (Z-21.5-296).

Headed stud anchors were still designed based on permissible tension and lateral loads at the time. Existing edge and plane factors were allowed for via reduction factors (kappa method). When the licence was amended in 1995, an extended calculation method (CC method) was introduced and the semi-probabilistic safety concept was used instead.

The DIBt issued the first European Technical Approval for fastenings in November 2003. The two licence notices ETA-03/0039 (KOCO headed studs) and ETA-03/0041 (Nelson headed studs) were extended in 2008, and are the current state-of-the-art rules.

The particular safety requirements involved that mean using headed studs in nuclear power plants must be approved by the licensing authorities in each case.