Folded-plate and curved sandwich panels made of high performance materials for long-span roof elements

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Sandwich constructions with concrete layers made of non-corrosive high performance materials, facilitate light, sustainable and integral building structures according to form follows force. Shell structures built in the early 20th century belong to the group of mono-functional construction members. Nevertheless a high potential regarding load carrying capacity and slenderness is obvious. The combination of shells and sandwich constructions leads to structural members, which exhibit coexisting features, namely small consumption of resources, high energy efficiency and modularity as well as sound insulation and fire protection.In the first and second funding period the basic principles for the establishment of pre-tensioned folded plate and doubly-curved sandwich structures have been investigated. Besides the development of a reusable anchorage for CFRP (carbon fibre reinforced polymer), the bond behaviour of pre-tensioned CFRP in high performance concrete was characterised and a minimum thickness for a crack-free transmission zone was determined. In component tests under tension and shear loading, a high potential of core layers, which were foamed in pack could be shown. Flexural testing under short-time loading on folded-plate and doubly-curved pre-tensioned single shell beams and sandwich shell beams already showed a high capability of this design.The goals of the requested project are the development of practice-oriented production techniques and to establish the basis of long-span sandwich elements with facings made of thin-walled sawtooth roof beams and doubly-curved shell beams in cooperation with industrial partners. For this purpose, designs of medium-span (c. 15 m) and long-span (c. 25 m) structures are worked out. In the second step a clamping technology for CFRP reinforcement for the application in precast-plants is developed. For thin-walled folded-plate and doubly-curved concrete facings CFRP reinforcement grids are designed and special formwork needs to be developed. The joining process of large-sized elements by foaming in pack of polyurethane is developed. To ensure high sandwich action, the application of pin and continuous shear connectors is tested, which additionally are appropriate to carry loads induced due to the foaming process. In numerical simulations as well as component and large-scale experimental testing geometries and material combinations (UHPC, TRC, PU, connecting devices, pre-tensioned CFRP) are varied to achieve a load transfer according to form follows force. After the characterisation of single load transfer mechanisms, an engineering model for folded-plate and doubly-curved sandwich beams is derived, which accounts for short-term and long-term loading.