Torsional load-bearing capacity of concrete components with rod-shaped reinforcement made of fiber-reinforced plastic

Due to their very high strength and corrosion resistance, reinforcing elements made of fiber-reinforced plastics (hereinafter: FRP) are in many cases a cost-effective alternative to conventional steel reinforcement, particularly in corrosive environments. However, the design models developed for reinforced concrete cannot simply be applied to FRP reinforcement; rather, their applicability must be carefully examined, taking into account the different material properties.

With regard to shear capacity, extensive test series have already been conducted on components with FRP reinforcement under shear loading, from which corresponding design models have been derived. In contrast, however, there is a lack of comprehensive findings from tests under torsional loading, and it is unclear to what extent conclusions regarding torsional capacity can be drawn from the load-bearing behavior under shear. For this reason, there is currently no experimentally validated design concept for concrete members with FRP reinforcement under torsional loading; consequently, the draft of the DAfStb guideline “Concrete Members with Nonmetallic Reinforcement,” which is currently being developed by the German Committee for Reinforced Concrete (DAfStb), does not contain any provisions for torsional design.

Therefore, as part of this research project, a comprehensive literature review of component tests involving bar-shaped non-metallic reinforcement under torsional stress will be conducted, and all available torsional tests will be compiled into a database and evaluated in comparison to tests with reinforcing steel .

To expand the database and investigate various effects on torsional behavior, supplementary tests will be conducted and evaluated on FRP-reinforced components under torsional loading. By integrating strain gauges into the reinforcement, the primary objective is to investigate the allowable strain of the stirrup reinforcement.

Based on these investigations, an initial pragmatic and experimentally validated design approach will be formulated, which is based on the fundamental design concept of the DAfStb guideline “Concrete Members with Non-metallic Reinforcement.”