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High tensile bolts (June 3, 2010)
High tensile bolts,high-tension bolt,bolt connection failing,joints,bolt, nut,hardened washer,high strength materials,Bolts and nuts
High tensile bolt is a bolt that is adjusted to a carefully controlled tension by means of a calibrated torsion wrench; used in place of a rivet. Also known as high-tension bolt. The HSE is making this information available to the construction industry as supplementary guidance to that contained in BS 7121 Part 2:2003 ¡°Code of practice for safe use of cranes ¨C Inspection, testing and examination¡±, and comes as a result of ongoing work with the tower crane industry. This information is issued without prejudice to any ongoing investigation. The HSE is issuing this technical alert to remind those who own, operate and hire tower cranes that they should ensure that high tensile bolt connections, including those on masts, jibs and slew rings of their tower cranes, are correctly installed and pre-loaded (tensioned). Failure to do so could lead to the bolt connection failing, with catastrophic consequences. High tensile bolt connections are used on tower crane joints, including those on mast, jib and slew rings bearings. They consist of a bolt, nut, and hardened washer, and on occasions a spacing sleeve. All of the components should be manufactured from high strength materials. Bolts and nuts are typically manufactured to BS EN ISO 898-1 and BS EN 20898-2, and are marked with a manufacturer¡¯s logo or name, strength grade and a batch number. Only components of the same strength grade should be used together. For example a Bolt of Grade 10.9 should only be used with nut of Grade 10. High tensile bolt connections are subject to repeated cyclic loading as the crane lifts and lowers loads and slews. When correctly installed and pre-loaded high tensile bolt connections can transmit very large loads. Since summer 2006, HSE has been undertaking a programme of visits to tower crane companies incorporating site and head office visits to discuss health and safety management of the supply, erection, operation and dismantling of tower cranes. During these visits the HSE will be discussing procedures to ensure that high tensile bolt connections on masts, jibs and slew rings of their tower cranes are correctly installed and pre-loaded. This technical alert provides supplementary information, and should be acted upon in conjunction, to that recently issued by HSE to the construction industry on the importance of the safe erection, operation, maintenance and dismantling of tower cranes.
