Pre-tensioned concrete with different types of reinforcement made of carbon fibre reinforced polymers

• Applicant: Professor Dr.-Ing. Alexander Stark
• Subject Area: Structural Engineering, Building Informatics and Construction Operation
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 530620462

Structurally high performing and at the same time slender precast concrete elements can be achieved by pre-tensioned concrete, since the prestressing force is transferred by bond alone. With reinforcements made of corrosion-resistant carbon fibre reinforced polymers (CFRP), minimum concrete covers are only dependent on bond requirements, and not related to durability considerations. In addition to prestressing reinforcement, rebars or meshes are arranged to increase ductility, efficiency and serviceability. Especially, corrosion-resistant CFRP reinforcements allow for tensile stresses or cracking in the prestressed tension zone under service loads. In addition to geometric influences, CFRP reinforcements also show manufacturer-dependent surface properties. As a result of different bond properties for different reinforcements, cracking of concrete may lead to unpredictable stress redistributions. Due to the lack of plasticity, different types of CFRP reinforcements in one structural member must be investigated in detail not only at service loads but also at maximum capacity in order to exclude premature failure and proper utilise individual reinforcement positions due to redistributed stresses. Therefore, the aim of this research project is the systematic analysis of the bond behavior of different CFRP reinforcements with and without prestressing in concrete with different strengths (normal strength, high strength and ultra-high performance concrete). With numerical and mechanically-based calculation models as well as small-scale and large-scale test setups for validation, material combinations and geometric boundary conditions are varied in such a way that the essential bond mechanisms and structural performance of cross-sections prestressed and additionally reinforced with CFRP reinforcements can be isolated. The theoretical and experimental investigations are geared and iteratively conducted at meso and macro level. First, the isolated bond behavior of different CFRP reinforcements with and without prestressing is analyzed. Based on this, stress redistributions and utilization rates of different reinforcements (rebars, meshes and prestressing tendons) with different bond properties are investigated under static, permanent and cyclic loads. For this purpose, investigations under pure tensile loading are carried out on idealized sections of a flexural tensile zone. To verify this idealization, the redistributions are analyzed in beam cross-sections under flexural loading including investigations on the anchorage behavior of CFRP reinforcements. Subsequently, engineering models are to be derived on the basis of developed mechanically-based calculation models. These are supposed to still take into account all information for determining the bond and stress redistribution behavior under flexural loading of different pre-tensioned and non-pre-tensioned CFRP reinforcement types.

• DFG Programme: Research Grants