Flexibility of mechanical fastenings of very thin-walled steel structures

Normal calculations of flexibility as a deformation characteristic of fastenings disregard the plastic response of screwed fastenings of very thin-walled steel structures. Preliminary tests have, however, shown that, unlike bolted fastenings in thick-walled steel structures, in screwed fastenings of very thin-walled steel structures the occurence of considerable plastic deformations can be observed from the beginning of loading. These should not be generally neglected in establishing the design characteristics of fastenings, i.e. design strength and design flexibility. This paper deals with cases in which an approximate value of ‘elastic flexibility’ can be used with sufficient accuracy, and how the analysis may be made more accurate by taking into account ‘elasto-plastic flexibility’.Extensive experimental research into the behaviour of screwed fastenings of very thin-walled steel structures subjected to non-repeated loading, repeated fluctuating and reversed loading, and multi-level loading simulating wind loading has been carried out, and ‘elastic flexibilities’ of selected fastenings have been established. At the same time, conditions for their application taking into account the elasto-plastic behaviour of fastenings subjected to repeated loading have been determined.