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CROSS Safety Report

Blind bolt fixings

Report ID: 86 Published: 1 October 2007 Region: CROSS-UK

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Overview

A reporter shares their experience on the use of blind bolts.

Key Learning Outcomes

For civil and structural design engineers:

  • Connections can often be the weak link in structures and attention to detail is required to ensure what is designed can be fabricated

  • Careful consideration is required for connections, particularly at interfaces between different materials. The role of tolerances should not be overlooked.

  • The Steel Construction Institute has published a document AD 276 entitled 'The use of Toggle Bolts' which provides advice on these type of fixings

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Further to the item on blind bolts, also known as toggle bolts, in Newsletter No 6, another reporter has written with experience of such fasteners. They say that a few years ago their firm had a joint fail because of blind bolts which almost caused a collapse. This led the firm to investigate the stated design values of the product that was used.

The findings resulted in a complete company ban on the product and the Steel Construction Institute subsequently produced an advisory note on the subject. The reporter considers that failure is due to the wasted shank area being in the shear plane which results in the capacity being about a 1/3 of the stated design values.

The supporting wall thickness needs to be so great that in practice the bolts will seldom reach the test values. In the opinion of the reporter such fixings may be very dangerous in certain circumstances.

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