Axially pre-loaded steel tubes subjected to lateral impacts: an experimental study

Steel tubes are widely encountered in industrial applications and are commonly exposed to accidental loads. Collision between supply ships and the legs and bracing members of offshore oil rigs, impact of heavy dropped objects on these members, mishandling during the launching and installation of marine structures, explosions and collision of moving ice sheets with offshore structures are examples of such accidents. Prior to an accident, tubular structural members will be carrying their normal operational loads. It is very important that this service load (pre-loading) is considered when the effect of impact damage is going to be estimated. This paper describes the experimental studies in which axially pre-loaded tubes were examined under lateral dynamic impact loads. The tubes were impacted by a dropped object with a velocity of about 7 m/s at their mid-span. The experimental investigation was aimed at gaining an insight and understanding of the dynamic failure and behaviour of the impacted tubes and to provide bench-marking data on the response of axially loaded steel tubes subjected to lateral impact. The main advantage of the current investigation, compared with those carried out previously and reported in the literature, is that both pre-loading and dynamic effects are included in the study. From the results of the experimental work, it can be concluded that pre-loading had a marked effect on the lateral collapse capacity of the cylinders.