Control of CFRP strengthening applied to civil structures by IR thermography

摘要

NdT methods are highly promoted by an increasing demand of checking the effectiveness of strengthening and repair intervention on structural components, both in buildings and bridges. IR thermography exhibits excellent performances, particularly when innovative materials as CFRP (Carbon Fiber Reinforced Polymer) are used. Non destructive control by the use of thermographic analysis is used to detect adhesion defects or imperfections, which can lead the component to become brittle and collapsing unexpectedly. This paper shows as the geometrical evaluation of delaminated areas is carried out. Laboratory tests both on reduced or full scale are illustrated in order to set up and validate the proposed procedure. An experimental study on samples bonded with FRP and containing defects appropriately applied at the interface, will be presented. A series of beams (10 m long) have been tested under bending loads and strengthened conditions, by placing a pre-impregnated thin carbon (CFRP) laminate at the intrados. Different reinforcement configurations have been adopted in the beams (ordinary steel reinforcement and with addition of pre-stressed strands), using mechanical devices for the anchorage of the supplementary pre-tension of the strips. At local level, the simulation of possible lack of bonding during loading or intrinsic defects and imperfections has been contextually analysed on specifically dimensioned specimens. Different algorithms have been applied at the evaluation stage in order to estimate the defect size and location. Particularly, the extension of the delamination is estimate with a simple and robust algorithm. In facts, standards set the limit for acceptable defects, both in terms of number and size. The most significant results of the mathematical simulation and tests obtained through the application of thermographic inspection on preliminary samples and full-scale beams are discussed in the paper.