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In the study some results of numerical analyses performed on FRP-to-concrete bonded joints for direct-shear tests are presented. These results will support better preparation for experiments planned on real-scale elements.
Externally bonded fiber-reinforced polymer (FRP) materials have been for years widely used as an alternative method to traditional techniques of strengthening of concrete elements. One of failure type of such elements is the intermediate crack (IC) debonding of FRP strips initiated at the tip of flexural or flexural/shear cracks in concrete substrate. The IC debonding leads to the FRP debonding failure [1,2]. The proper modelling of that complex behaviour requires definition of traction-separation law for the FRP-concrete interface [3,4]. In the paper a fracture mechanics approach is used for defining this law.
In the research the FRP strip debonding from concrete surface is modelled using the eXtended Finite Element Method (XFEM) employed in Abaqus code [2,5]. The failure mechanism definition includes damage initiation as well as damage evolution which are based on the traction-separation law. For damage initiation the quadratic stress criterion was used and for damage evolution the power law fracture energy criterion based on components GI (Mode I) for concrete and GII (Mode II) for the interfacial FRP-concrete joint. The interfacial fracture energy represents the total external energy required to create, propagate and fully open crack along FRP–concrete interface. It has been proved, among other things, that the bond strength depends strongly on the interfacial energy GII. Finding the right interfacial fracture energy of analysed joint is still an open issue because of large amount of parameters which govern the local bond–slip behaviour as well as the bond strength of FRP-concrete joints. This will be the subject of further investigation.
References:
[1] Jankowiak I., Analysis of RC beams strengthened by CFRP strips – Experimental and FEA study, Archives of Civil and Mechanical Engineering, 2012, 12, pp.376-388
[2] Jankowiak I., XFEM analysis of intermediate crack debonding of FRP strengthened RC beams, Advances in Mechanics: Theoretical, Computational and Interdisciplinary Issues: proceedings of the 21st International Conference CMM, Poland, 2016, pp.235-239
[3] X.Z. Lu, J.G. Teng, L.P.Ye, J.J. Jiang, Bond–slip models for FRP sheets/plates bonded to concrete, Engineering Structures, 2005, 27, pp.920–937
[4] Al-Saawani, M.A. et al., Finite element modeling of debonding failures in FRP-strengthened concrete beams using cohesive zone model, Polymers 2022, 14, 1889
[5] Abaqus User's Guide, Dassault Systemes, USA, 2024
