Weitspannende Sandwichelemente mit vorgespannten Deckschichten aus Carbonbeton

Sandwichelemente mit Betondeckschichten besitzen gute bauphysikalische Eigenschaften, einen hohen Vorfertigungsgrad, geringe Montagezeiten und eine gute architektonische Gestaltbarkeit. Werden die Deckschichten mit einer Betonstahlbewehrung ausgeführt, ergibt sich ihre Dicke aufgrund der in EC 2 [1] geforderten Mindestbetondeckung zum Korrosionsschutz der Bewehrung zu etwa 80 mm [2]. Weiterhin wird bei der Bemessung von Stahlbetonsandwichelementen die Verbundtragwirkungen zwischen den einzelnen Schichten nicht angesetzt, sodass das volle Potenzial der Sandwichbauweise bei Stahlbetonsandwichelementen nicht ausgeschöpft wird. Das Forschungsvorhaben beschäftigte sich daher, aufbauend auf den Ergebnissen aus den Projekten HE 2637/16-1 und HE 2637/16-2 [3], s. S.356 ff ., mit der praxisnahen Umsetzung von weitspannenden Sandwichelementen mit dünnen Deckschichten unter Ausnutzung der Sandwichtragwirkung. Ein analytisches Berechnungsmodell, das im Zuge des Vorhabens entwickelt wurde, berücksichtigt die Verbundtragwirkung zwischen den einzelnen Schichten und kann das Trag- und Verformungsverhalten zutreffend abbilden.Sandwich elements with concrete facings have excellent physical properties, a high level of prefabrication, short assembly times and various architectural design options. The facings are usually produced with steel reinforcement, which leads to a thickness of about 80 mm due to the minimum concrete cover required in EC 2 [1] for corrosion protection of the reinforcement [2]. Furthermore, the bond between the single layers are not taken into account in the design of sandwich elements, so that the full potential of sandwich constructions with reinforced concrete facings is not completely exhausted. Based on the projects HE 2637/16-1 and HE 2637/16-2 [3], see page 356 et seq., the focus of the transfer project was set on wide-span sandwich elements with thin facings made of carbon reinforced concrete and their practical production. An analytical model, which was developed during the project term, takes into account the bond between the single layers and can accurately represent the load-bearing and deformation behaviour of the novel sandwich elements

Zum Tragverhalten von Sandwichelementen aus Textilbeton mit schlaffer und vorgespannter Bewehrung

The combination of high-strength concrete with non-corrosive reinforcement made of carbon fibre reinforced plastic (CFRP) or alkali-resistant (AR) glass creates a high-performance composite material which is characterised by high load-bearing capacity and durability. The use of this composite material in sandwich construction enables the manufacturing of lightweight and slender precast elements for building envelopes with excellent physical properties. The characteristics of the insulation core and its bond properties with the two facings made of textile-reinforced concrete are decisive for the performance of such sandwich elements. In this thesis, the development of two sandwich elements is described, which are designed for use as wall and roof elements, respectively. For the long-span roof elements, a two-component polyurethane (PU) is used as stiff core with high bond strength. To reduce cracking and deflection of the roof elements, the facings are prestressed with CFRP tendons. Due to limited dimensions and thus lower stresses, a soft insulation material and a non-corrosive reinforcement without prestressing are used for the wall elements. In order to analyse the load-bearing and deformation behaviour of the two element types, small-sized test specimens are initially examined. In the next step, the bond properties of the reinforcement materials are determined with pull-out tests and tests on transfer length, while the load-bearing behaviour of the composite material is characterised by tensile tests and four-point bending tests. Tests on small-sized sandwich elements under tensile, compression and shear loads provide information on the sandwich effect and the decisive failure mechanisms. Generally, the sandwich core consists either of a textile connecting device, a foamed PU insulation or a combination of both components. Based on the results, models for describing the load-bearing and deformation behaviour of the small-sized sandwich elements are developed, serving as input values for the calculation approach of the large-sized elements. Finally, large-sized bending tests are conducted to determine the performance of the developed sandwich elements. Based on the sandwich theory of STAMM and WITTE, an analytical model is developed to calculate the load-bearing and deformation behaviour of the large-sized specimens. Spring models with graded spring characteristics are used to implement the textile connecting devices and the foamed PU core as well as their successive failure in the calculation approach. The calculated ultimate loads, deformations and failure mechanisms are in good agreement with the test results of the large-sized sandwich elements