PSI - Issue 64

Szymon Grzesiak et al. / Procedia Structural Integrity 64 (2024) 269–276 S. Grzesiak, C. de Sousa, M. Pahn / Structural Integrity Procedia 00 (2019) 000 – 000

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Nomenclature a f

distance of the FRP - strip from the end support in mm

h k

height of concrete cross section

scaling factor

concrete cross section FRP cross section steel cross section

V Ed design value for the acting shear force V Rd,c design value for the shear resistance for members not requiring shear reinforcement V Rd,c,fe design value for the shear resistance to prevent concrete cover separation t f width of FRP strip γ c concrete partial factor ρ s1 longitudinal steel reinforcement ratio

A c A f

A s1

width of concrete cross section

b c b f

width of FRP strip

distance from top of cross section to steel reinforcement concrete compressive strength loading force from hydraulic jack

d s1

f c F

By taking X-ray scans from different sides of concrete elements, 3D data can be created, which makes it possible to visualize and measure internal cracks, pores and defects (Giese and Herbers et al. (2023)). This can enable a detailed analysis of the structural reinforcement elements that are embedded in the concrete matrix. Potential risks to its integrity, such as corrosion, can thereby be thoroughly investigated. The use of NDT in defects detection is especially relevant in the renovation of existing buildings and infrastructure, where the continuous assessment of their structural health is of great importance. For example, by checking the condition of strengthened structures, CT could be very useful for accessing invisible areas ( Dybeł and Kucharska (2021)). These inaccessible areas are e.g. cracks under FRP strips in FRP strengthened structures. The reason to consider this is, that nowadays the strengthening systems with FRP strips increasingly gain in importance due to their supporting effect in the field of structural engineering (Nizic (2011)). Also, during new constructions, modifications and expansions for the absorption of increased loads are often needed and the sustainability of the adopted reinforcement measures are often put in question. Similarly, the fatigue stress of important infrastructures such as bridges is not to be underestimated. By increasing demands on the use of bridges, caused by permanent and cyclical loads due to more intensive traffic, installed fatigue stresses can accelerate so that a time restriction on its usage or the strengthening of certain bridge parts have to be implemented (Günes (2004)). At the moment, predominantly carbon fiber reinforced polymer strips (CFRP) are used for strengthening purposes (Czaderski and Martinelli et al. (2012); Michels and Sena-Cruz et al. (2013); Grzesiak, Pahn and Schultz-Cornelius (2022)). The CFRP delivers the benefit of small weight in connection with high strength but also disadvantages such as high costs as it requires an energy-intensive production process Grzesiak, Pahn and Schultz-Cornelius (2022). An alternative, cheaper and environmentally friendly material is basalt (Grzesiak and Pahn et al. (2022)). The application possibilities of basalt fiber reinforced polymer strips (BFRP) taking into account its decisive bending capacity are compared with those of established CFRP strips in Grzesiak, Schultz-Cornelius and Pahn (2023). Aim of this paper is to present the potential of a non-destructive testing approach using CT in the context of damage analysis for concrete structures. An example will be shown on a small laboratory concrete sample, focusing on how to methodically approach the scan and process the resulting data. Finally, the results will be discussed, and some further research possibilities will be presented. 2. Methodology 2.1. Experimental program To demonstrate the potential of NDT using CT in the context of damage analysis of concrete structures, reinforced concrete samples containing cracks were analyzed. The analyzed specimens consist of two reinforced concrete beams with externally glued BFRP strips and subjected to three-point bending tests. The experiments were performed in