Light, microreinforced UHPC shell structures optimised to deformations using the example of parabolic trough collectors in concentrating solar power plants

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Shell structures made from UHPC and micro-reinforcement or GRP meshes acc. to the guiding principle "form follows forces", have been confirmed to be extremely slender, deflection-resistant and producible with striking surface accuracy during the first period. Focus has purposely been laid on parabolic shell-troughs of solar power plants concentrating insolation to gain green energy. These structures are predestinated for fundamental and detailed research due to its very complex demands for deflection-restrained sun tracking, environmental exposure in deserts and quality assured serial production. The approach taken is interactive, interdisciplinary and multileveled, including conceptual and component design as well as detailing provisions. Scientific analyses accompanied by experimental verifications and iterative optimizations are performed involving a bunch of engineering disciplines, e.g. concrete design, structural mechanics and dynamics, wind as well as solar and materials engineering. In the currently running period boundary conditions are explored, specific impact conditions investigated, precision demands assessed and numerical models developed. Algorithms for multi-criteria optimization have been adapted and tested as well as checks on the rigidity and vibration safety features of the structure have been performed. In experiments adequate concrete mixtures have been designed and a geometric surveying procedure - able to approve the shell's shape-accuracy - has been established. Finally, the interactive research activities merged into an innovative full-scale prototype of a parabolic trough collector made from UHPC. With respect to recent developments of parabolic troughs aside, that enable notably increased lengths and widths, here the essential innovations of a second period aim at the realisation of hollow instead of single-walled shells introducing pre-stressing. This way structural weight should be significantly decreased while its stiffness against deformation can be maintained or even amplified. Furthermore, the performance ratio of UHPC in compression can be efficiently improved. Stochastic uncertainties in geometry, material and wind loads and also due to structural degradation during service shall be captured by simulation based optimisation techniques on response surfaces to ensure structural robustness. Wind tunnel tests will deliver quasi-static but also multi-criteria, transient wind pressure data for fully transient modal analyses. The experimental part comprises the general but specific nodal design required by a hollow shell structure in accordance to formwork, manufacturing process and reinforcing techniques. Finally, a full-size prototype collector with photogrammetric proven surface accuracy and conform to all theoretical design requirements laid out above is envisaged.