Dynamic behaviour of axially pre-loaded tubular steel members of offshore structures subjected to impact damage

The behaviour of an axially pre-loaded cylindrical member of an offshore st ructure, hit by a supply ship, has been investigated. The effects of axial pre-loading on the dynamic properties of members, the extent of damage and propagation of dynamic instability in the tubular members have also been in vestigated. Numerical models have been validated using available experiment al data from the literature although these are mostly static with no pre-lo ading. Axial preloading was found to change the dynamic characteristics of some cylindrical members quite dramatically while it had no significant eff ect on others. The study examined whether there was any change in the behav iour between local and global modes when the loading was dynamic rather tha n static. The effect of damping on the dynamic instability of axially prelo aded tubes under lateral dynamic loads was also studied. It was observed th at for some geometries the quasi-static response can be used to define the boundary between bounded and unbounded dynamic responses. The main contribu tion of this study, compared with previous investigations reported in the l iterature, is that both pre-loading and dynamic effects have been included. (C) 1999 Elsevier Science Ltd. All rights reserved.