Hyperloop is an avant-garde idea for high-speed transportation of passengers and freight in a pod or capsule-like vehicle travelling through an hermetically sealed tube with reduced internal pressure. Its maximum envisaged speed is around 1200 km/h, which would be directly comparable to airplane travel and much faster than road and railway transportation. Because the unconventional, ad hoc civil infrastructure required for Hyperloop is still under a conceptual design phase, one of the most important steps to undertake at this stage is to develop analytical models and tools to simulate the mechanical behaviour, so that any potential issue can be anticipated. This article is a novel comprehensive study of the relevant phenomena that influence the design of Hyperloop infrastructure from the structural engineering viewpoint. The aim is to obtain, for the first time, representative values of the main internal forces and stresses leading to a preliminary design of the vacuum tube and, simultaneously, to provide relevant insight into the main phenomena involved. Depending on the longitudinal restrictions implemented at the piers, two basic configurations based on steel tubes are proposed. The strength and stability of the tube have been analysed thoroughly by taking into account the self and dead weight, internal low pressure, wind, thermal and traversing vehicle dynamic effects. Fatigue has also been assessed at potential critical locations. The relevance of each external action has been suitably highlighted, with particular emphasis on the predominant thermal and buckling effects. Estimates of the required tube thickness are provided, and resonance phenomena at some particular speeds are pointed out. Since the Hyperloop concept comprises both vehicle design and structure standardization that strongly relate to each other, their definition must be advanced in parallel. This work represents a starting point for future detailed studies, as the HL technology evolves through subsequent stages when relevant details of vehicle design will be available.
