Advisory Desk: AD 302: Tightening of Ordinary Bolts

0607NSCJul06

Advisory Desk Holorib AD 302 Tightening of Ordinary Bolts. The advisory service regularly receives requests for a set of torque values in connection with the installation of ordinary bolts. This usually arises because a criterion is required for the project QA procedures in order to ensure that ordinary bolts are ‘correctly tightened’. Section 6.1 in the National Specification for Structural Steelwork for Building Construction 4th edition (NSSS) deals with the installation of ordinary bolted assemblies and clause 6.1.8 states that ‘Bolts may be assembled using power tools or shall be fully tightened by hand using appropriate spanners in accordance with BS 2583’. It should be noted that BS 2583 is a spanner standard and does not deal with tightening procedures or torque values. Traditional British practice has been to hand tighten ordinary bolts using podger spanners. That is, when an average erector fully tightens an ordinary bolt using a podger spanner the bolt is correctly tightened. There is no specified minimum torque values required and this is all that is necessary to ensure that the nut does not come loose in steelwork used in building construction. The commentary on the NSSS 4th edition states ‘The intention of 6.1.8. on bolt tightening of ordinary bolts is that the bolts are at least ‘spanner tight’ whether they be assembled using impact tools or hand spanners to BS 2583’. The following table appears in the Commentary to the NSSS 4th edition as well as in two of the green book series on Joints in Steel Construction; Simple Connections P 212 and Moment Connections P 207. The torque values given in the table are simply an equivalent to hand tightening using a podger spanner. The original Podger Spanner There has never been a better floor decking profile than Holorib. For over 30 years, it’s set standards that many B aspire to. The UK’s most widely specified floor decking profile, it’s consistently been a top performer on a wide L range of projects. •Speed, simplicity and economic advantages Bolt Size B L Torque (Nm) •Particularly suited to intricate shapes and irregular layoutsApproximate M16 60 460 90 * * Values are indicative of torque •Always available ex stock (UK only) M20 70 550 110 * achieved when hand tightened •Supplied in both S280 and S350 structural galvanised steel M24 85 640 130 * using a force of 250N. M30 100 730 160 * Holorib also has all the support you’d expect from the UK’s number one in The SCI recommends that generally, torque on ordinary bolts need steel decking. not be checked. If torque values are required, then the values shown in the above table may be used. Verification should take place after For more details on Holorib and all our products and services, visit rlsd.com the installation of all the bolts in a joint at the steel erection stage. It is acceptable to retighten bolts which become loose due to the subsequent tightening of the other bolts in the joint. However, it is not necessary to retighten or verify the bolts in a joint following the erection of other members, or tightening of the bolts in other joints in the structure. Likewise, it is not required to check the Richard Lees Steel Decking Ltd bolts in joints following subsequent erection operations; pouring of Moor Farm Road West, The Airfield, concrete or erection of cladding for example. These torque values Ashbourne, Derbyshire DE6 1HD, UK. are irrespective of the bolt grade used and in no way imply that Tel: +44 (0) 1335 300 999 Fax: +44 (0) 1335 300 888 installation by power tools is to be preferred to hand tightening using Email: rlsd.decks@skanska.co.uk a podger spanner. Ordinary bolts particularly those specified to BS 4190, should not www.rlsd.com be torqued to the values used for preloaded (HSFG) bolts because they have thinner nuts than preloaded bolts. The risk of thread stripping exists if these higher torque values are applied. Contact: Thomas Cosgrove Email: t.cosgrove@steel-sci.com Tel: 01344 623345 NSC July/August 2006 39


0607NSCJul06
To see the actual publication please follow the link above