Evaluation of the GPR (1.2 GHz) technique in the characterization of masonry shells of the Theatro Municipal do Rio de Janeiro

Abstract

The geometric characterization and evaluation of structural integrity are challenges for the preservation of historical buildings. The challenges are associated to the lack of constructive records, material diversity, access and contact restrictions, and sample extraction. Non-destructive tests are indicated in these cases. The objective of this paper is to evaluate the Ground Penetrating Radar (GPR) technique with 1.2 GHz antenna in the study of the determination of material thickness and discontinuities in the masonry shells of the Theatro Municipal do Rio de Janeiro, a heritage built in early 20th century, with high historical and cultural value. With paintings by renowned artists on their intrados, the domes and vault of brick masonry were at risk of collapse in the 1970s due to differential settlements in the supports and moisture, compromising their paintings. A strengthening intervention was carried out in 1976. Considering the masonry of bricks the main component, the electromagnetic wave propagation velocity was determined as 0,15 m/ns in one of the support walls, allowing to estimate the thicknesses of the elements ranging between 20 and 31 cm. Materials incorporated into the structure were identified: reinforcement, metal inserts and bricks. However, the frequency of the antenna did not allow the detection of damages. The application of the GPR to the characterization of materials and investigation of the integrity of the domes of the Theatro Municipal highlights the potential of this technology to study heritage and other constructions.

Methodologies for assessing the structural integrity of historic masonry domes and vaults

“…Measurements made with the mushroom plunger were on average 27% smaller than those obtained with the conventional plunger at nearby locations. Due to the infeasibility of removing cores from the structure, the results of this test could not be correlated with mechanical properties [60]. The ultrasonic wave velocity speed test with indirect transmission method was applied to evaluate the quality of the materials in the vault, concrete beam, and brick masonry walls to estimate their mechanical properties (Figure 9b) [65].…”

“…The ultrasonic wave velocity speed test with indirect transmission method was applied to evaluate the quality of the materials in the vault, concrete beam, and brick masonry walls to estimate their mechanical properties (Figure 9b) [65]. The distance of the transducers was controlled and the detection time of the P and R waves was measured from graphs of relative amplitude of the pulse as a function of the time it takes to travel from the transmitting transducer to the receiver [60]. The latter showed the lowest speed values (Figure 10), probably due to the greater porosity of the material and the presence of mortar joints.…”

“…The GPR tests were carried out with 1.2 GHz frequency antennas and were useful to estimate the thickness of the domes and vault, the dimensions of the bricks, validate the construction characteristics, and detect hidden materials in the structure (Figure 9c) [60], [66]. 3D surveys were also carried out in each of the studied elements, but the radargrams were not considered satisfactory for analysis due to the high reflection of the steel net and consequent signal attenuation in the entire area below the net.…”

“…Two monotonic double flat jack tests were carried out in brick masonry walls (Test I and Test II) to estimate the modulus of elasticity of the material, assuming that the tested walls are representative of the structure of the TMRJ (Figure 9d) [60]. After equipment calibration in the laboratory (Figure 12a) [67], a stress vs. strain diagram was obtained from the measurement of the displacements resulting from the application of axial load (Figure 12b) [68].…”