GPR investigation of the strengthening system of a historic masonry tower

In this paper the condition assessment of the strengthening system of a masonry tower was carried out by the GPR method. The study provided unique experimental data acquired during measurements of the reinforced concrete frame embedded in masonry walls. Conducted numerical and experimental investigations were focused on the phenomenon of the diffraction–refraction scattering of the electromagnetic energy. A hyperbola resulting from the diffraction of the electromagnetic wave by a steel rod revealed a clear refraction point at the boundary between concrete and the brick wall. A novel procedure for determining the boundary between two media, where one of them contains a circular inclusion, was developed. A system of equations describing the refracted hyperbolic diffraction curve was derived. The study demonstrated that the identification of the actual width of the reinforced concrete strengthening was possible analysing refracted waves previously diffracted on bars, where the point of refraction indicated the boundary between media. Numerical simulations of electromagnetic wave propagation were carried out to enhance the interpretation of results of GPR surveys in the complex masonry structure strengthened by reinforced concrete. The particular interest was paid on characteristics of wave patterns at the boundary between media having different electrical properties. The obtained numerical and experimental results revealed the high usefulness of the GPR method in the diagnosis of wall structures made with different materials. [Display omitted] •The strengthening system of the historic masonry structure is evaluated by the GPR method.•The hyperbola caused by a steel rod is refracted at the boundary between masonry and concrete.•The equations describing a hyperbola refracted at the boundary of two media are derived.•The identification of the refraction point enables the evaluation of the width of a concrete part of the strengthening system.•Simulations of GPR field become a significant support in the interpretation of GPR surveys in complex structures.