Analysis of Prestressed Sandwich Panels with Ultra-High Performance Concrete Facings

Sandwich-structured composites represent an efficient method to establish building envelopes which concurrently satisfy several demands. Besides low self-weight with high load-bearing capacity, sandwich panels provide sufficient physical properties, such as heat and sound insulation. In general, sandwich panels for applications in building industry are made of flat or thin profiled metal sheets or thick concrete facings. However, standard elements without additional bearing structures are limited to short spans. In contrast, spatially shaped concrete structures with folded plate or curved geometry provide high stiffness and load-carrying capacity even for thin elements.The application of folded plate and curved concrete structures to sandwich panels combines the advantages of both construction methods enabling light elements with long spans and high load-carrying capacities. To realise thin facings in various shapes, high performance cementitious composites are advantageous. Ultra-high performance fibre reinforced concrete (UHPFRC) provides high compressive and tensile strengths with ductile material behaviour. The application of non-corrosive reinforcement, e.g. carbon fibre reinforced polymer (CFRP), allows for filigree concrete elements with a thin concrete cover to only fulfil bond requirements. For sandwich panels with folded plate or curved facings, new production methods are necessary to account for cross-sections in various shapes as well as high bond strengths between UHPFRC facings and core material.This thesis introduces the stepwise development of innovative sandwich panels. Materials and interactions of different components are investigated by experimental testing and numerical modelling. Theoretical considerations are conducted to determine the tensile strength of UHPFRC from flexural testing. Additionally, approaches to calculate moment-curvature relationships of UHPFRC sections with CFRP reinforcement are derived and applied to further theoretical investigations. Subsequently, input parameters for non-linear numerical simulations are deduced. To determine bond strengths, transfer lengths and minimum dimensions of thin UHPFRC elements, investigations on the bond behaviour of prestressed elements with CFRP reinforcement are conducted. Thus, dimensions of folded plate and doubly curved UHPFRC elements are identified. Investigations on small-scale sandwich sections under tensile and shear loading are performed to specify stiffness and strength of the core material and shear connectors. This serves as a basis for further theoretical approaches and numerical modelling. Based on the previous findings, the flexural behaviour of folded plate and doubly curved sandwich panels is investigated. Finally, an analytical model for sandwich panels is proposed which accounts for cracking of prestressed UHPRC facings with CFRP tendons