PSI - Issue 44

Andrea Santangelo et al. / Procedia Structural Integrity 44 (2023) 626–632 Andrea Santangelo/ Structural Integrity Procedia 00 (2022) 000–000

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complement to linear induction motor propulsion, the hyperloop concept considers the use of regenerative braking. Another system used by hyperloop commercial venture is it instead based on axial compressors that generates thrust compressing the air in front of the vehicle and force it out of the back at higher energy. 3. Hyperloop infrastructure design The vacuum structure design is primarily dependent on the tube geometry and choice of the material. The choice of the right geometry and shape is a complex trade-off between vehicle size, speed, power consumption, and cost, whereas the tube material used is a trade-off between stiffness (i.e., structural strength), leakage, environmental impact, and cost. 3.1. Vacuum structures The above ground vacuum infrastructure could be easily considered as a continuous multi-span bridge with a high profile of deck but considerably lighter than would have been if it was a typical bridge structure – and the vehicle loads are significantly lighter as well. The early design of the perfectly circular shaped tubes with uniform thickness it is now considered not the most favourable for many reasons, spanning from engineering complexity design to bending instability both in plane and out-of-plane. The design of a polygonal shaped tubes, besides allowing a better engineering of the whole system, solves many of the stability problems related to the unbalanced forces caused by the light stiffness compared to conventional bridge decks. The most common material of choice referenced has been steel, followed by concrete with unique mechanical properties (UHPC – Ultra High-Performance Concrete) to more conventional pre-stressed or post-tensioned concrete. While both materials are recognized as preferred construction material by developers, further testing and understanding are needed to assess their application for different environments. The use of an internal sealing lining is also sometimes proposed to enhance the sealing properties of the concrete. Developers have identified other materials such as fiberglass and certain plastic composites that could support a low-pressure environment. However, development costs, the limited availability of infrastructure capable of producing the quantities required and the less desirable overall construction challenges has, to date, constrained research into these alternatives. 3.2. Support bearings Coupling connections and bearing supports have been widely used in the modern high-speed rail and Maglev design. Accurate identification of their mechanical properties is mandatory for the hyperloop vacuum structures design to minimize the dynamic effects of resonance and displacement amplifications. Structural Bearings to be used for hyperloop may be fixed (displacement-restrained) or movable (free expansion) as required for the standard multi-span bridge design. Movable bearings may include guides to control the direction of translation. Fixed and guided bearings shall be designed to resist all appropriate loads and restrain unwanted translation. Besides the typical requirements needed for any bridge infrastructure, some of the specific requirements must include: • Movements in restrained and unrestrained directions should be limited to maintain the structural integrity of the vacuum infrastructure. The bearing design shall also be coordinated with the design of other elements such that total relative deflections at the joints conform to displacement limit requirements. • Bearings should be designed for potentially significant lateral loads and corresponding deformations, e.g., due to seismic and unbalanced pressure loads. • Bearings and their interface with pier and girders need to be adjustable to meet the high level of precision needed during the construction of hyperloop infrastructures. • Bearing should be often able to carry tension loads, due to the lightness of the vacuum infrastructure and the unbalanced forces.