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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4.2. Thermal loads The operating conditions of an hyperloop system is deformation-sensitive along its length and therefore temperature effects on the structural system should be carefully evaluated. The thermal loads could create large deflections (free expansion structural scheme) or axial stress (displacement restraint structural scheme) in areas where large temperature fluctuations are typical. The time-varying and non-uniform temperature gradient along the tube perimeter (due to daily sun exposure) induce also a continuous variable bending stress (and lateral displacements) to be offset by the lateral capacity of the support bearings. Together with the thermal loads derived from solar radiation, the dynamic friction between the capsule and the inner surface of the tube could drastically increase the thermal stress of the vacuum structure and must be also carefully evaluated during the preliminary design of the hyperloop infrastructure; the ratio between the area of the tube and the vehicle (also called blockage ratio) is one of the main factors that govern all the hyperloop basic design hypotheses. The choice of the more suited construction material should consider the thermal behaviour; of all trade-off materials, steel and concrete have comparable heat expansion, whilst other alloys and plastic composites have significantly higher heat expansion. 4.3. Dynamic amplification The dynamic behaviour of the hyperloop system is quite complex and it involves at least five levels of interaction between the various subsystem: • Vehicle Dynamics • Vehicle Suspension and Guidance • Surface Roughness • Infrastructure dynamics (Tubes+ pylons + bearing supports) • Soil dynamics (SSI) One of the preliminary studies to be addressed while evaluating the dynamic load amplification of the hyperloop infrastructure is the vehicle-track-structure interaction in cases where the first vertical bending mode of the tube structure has a frequency close to the frequencies of the vertical modes of the vehicle. The main parameter to be evaluated is the critical vehicle velocity. Critical vehicle velocity The repetitive loading induced by a passing vehicle can give rise to resonant effects that may amplify the dynamic response of both the vehicles and the structure considerably. At a certain critical train velocity, the main cyclic load effect can often be related to the flexural modal frequency of the structure; however, higher order modes may also contribute to the resonant response although the fundamental mode is typically dominating. Naturally, many combinations of characteristic lengths and natural frequencies may give rise to resonances at different critical speeds, but the combination of the vehicle length (or a cluster of a vehicles magnetically connected) and the fundamental natural frequency typically cause the largest amplification of the response. At resonance, the vertical oscillations of the vehicle will be in phase with the oscillation of the vacuum tube itself. The dynamic evaluation of the bearing system flexibility decreases the natural frequency and thus the critical velocity for resonance phenomenon; it could reach up to 20-30 percent and it becomes larger for shorter spans. It is also obvious that elastic supports will increase both dynamic and nondynamic amplitudes and deflections. 4.4. Seismic hazard The development of magnetic floating vehicles with electric propulsion system (Maglev) has reached quite high-speed operative and safety levels with the adoption of the Japanese SC-Maglev (Super Conductive Maglev Shinkansen ), that could reach up to 600 km/h even in high seismic hazard areas of the world such as Japan. Based on their extensive research on this technology, the hyperloop system could approach (and hopefully solve) the event of earthquake shakes 4.3.1