PSI - Issue 44

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

629

4

3.3. Expansion joints The expansion joint is a device required between each span at the column locations to provide continuity for the low pressure environment within the tube during thermal expansion (or contraction). Moreover, they should provide enough capacity to ensure the continuity also for wind and seismic actions, long term creep and shrinkage. Since the hyperloop superstructure tubes could be considered as a multi-span supported bridge, the expansion joints are one of the most susceptible locations of overstress due to potential excessive nonlinear deformation that could lead to pounding and buckling stress. Lastly, the expansion joints are subjected to more load cycles than other superstructure elements and thus, fatigue. One of the most viable solutions is a flexible rubber omega seal and steel bellow. This solution has been detailed as the preferred choice for many factors, primarily including design life, resistance to UV exposure and ability to calculate its performance based on known scientific approaches. This steel bellow could be installed in-situ through a welded fit up to steel flanges embedded into the concrete tube. 3.4. Pylons The pylons’ primary function is to support the vacuum structures along the length of the route. They are commonly considered to be casted with standard or prestressed concrete and they are often considered equipped with deep foundation systems. The forces acting on the pylons are primarily compression, even it might turn in tension in some cases due to the lightness of the tubes. The spacing of the pylons is largely determined by the geographic constraints along the specific route and the stiffness of the above vacuum structures. It is usually assumed to range between 20 to 40 meters. In addition, the pylon to tube connection nominal position must be adjustable vertically and sideways to guarantee proper alignment despite possible ground settling. The pylons must withstand vibrations and accelerations caused by earthquakes and stresses from continuous thermal expansion and contraction of the tubular vacuum structures. 4. Hyperloop infrastructure loads The vacuum superstructure design involves the evaluation of the forces acting on the whole system, whilst they are originated from the own weights of the infrastructure, the operating loads, and the operational loads of the hyperloop. Leaving aside the basic load analysis usually computed for a typical multispan bridge (“dead loads”), there are some loads that should require a particular focus while designing an hyperloop infrastructure. 4.1. Vacuum loads All vacuum structures shall be designed for external atmospheric pressures up to 101,325 Pa (1.0 atm) while the operating pressure is around 100 Pa. For underground or underwater structures, the vacuum load shall be superimposed with earth/rock pressure and water pressure loads. This operative load condition is often considered as “unbalanced” and it could be found in some structural parts of the system such as: • Curved tube structure and its supporting components • Entry and exit switch structure • Gate valve • Airlocks • Transition segments between main line to local lines • Structures with doors or end caps These infrastructure structural parts, together with their supports, should be designed for the deformation and force effects of the unbalanced vacuum loads.