Giovanna Concu

Acoustic Tomography for Non Destructive Testing of Stone Masonry

Acoustic methods seem to be very suitable for evaluating a building condition because they give information with immediacy, rapidity and relatively low cost. They are based on measurements of the velocity of acoustic waves propagating through the material. Those methods are often carried out applying the Through Transmission Technique, in which the wave is transmitted by a transducer through the test object and received by a second transducer on the opposite side. In this paper, the sonic tomography imaging based on this technique has been used for non destructive testing of a stone masonry. The tomography implies that a ill-posed linear equations system has to be solved, in order to determine the velocities distribution inside the tested structure, thus highlighting the presence of anomalies. Different inversion algorithms, chosen between the most commonly used, have been implemented for determining the distribution of waves velocity in selected sections of the tested masonry.

Prediction of Building Limestone Physical and Mechanical Properties by Means of Ultrasonic P-Wave Velocity

The aim of this study was to evaluate ultrasonic P-wave velocity as a feature for predicting some physical and mechanical properties that describe the behavior of local building limestone. To this end, both ultrasonic testing and compressive tests were carried out on several limestone specimens and statistical correlation between ultrasonic velocity and density, compressive strength, and modulus of elasticity was studied. The effectiveness of ultrasonic velocity was evaluated by regression, with the aim of observing the coefficient of determination r 2 between ultrasonic velocity and the aforementioned parameters, and the mathematical expressions of the correlations were found and discussed. The strong relations that were established between ultrasonic velocity and limestone properties indicate that these parameters can be reasonably estimated by means of this nondestructive parameter. This may be of great value in a preliminary phase of the diagnosis and inspection of stone masonry conditions, especially when the possibility of sampling material cores is reduced.

Measurement system for non-destructive testing using ultrasonic tomography spectral attenuation

This paper presents a measuring system and the automated measuring procedure for non-destructive diagnosis of stone masonry structures. The diagnosis is based on algorithms using the propagation times and the frequency centroid downshift of ultrasonic signals.

Prediction of Concrete Compressive Strength by Means of Combined Non-Destructive Testing

The problem of estimating mechanical properties of buildings materials is a major issue in civil engineering, especially when dealing with existing structures. In such occasion a valuable help is given by Non Destructive Testings, which allow materials characteristics to be evaluated in a non-invasive way. This paper analyses the efficacy of the SonReb method - a non destructive technique which statistically combines the results of Ultrasonic and Rebound Hammer Testing in predicting concrete compressive strength. The SonReb method has been applied on concrete specimens later on exposed to compressive strength test. The effectiveness of several empirical formulas expressing SonReb results is illustrated and discussed.

Acoustic NDT on Building Materials Using Features Extraction Techniques

Ultrasonic materials analysis is based on the principle that the propagation of any wave is affected by the medium through which it travels. Thus, changes in measurable parameters associated with the passage of a wave through a material can be correlated with changes in physical properties of the material. In this paper, an ultrasonic technique has been experimented for non destructive testing of building structures. In particular, several parameters associated with acoustic waves propagating through a trachite masonry and a concrete pillar have been analyzed and discussed making reference to a Finite Element model of the structures.

FRP Strengthening of Masonry Columns: Experimental Tests and Theoretical Analysis

Structural rehabilitation involving upgrading of existing structures and buildings conservation has becoming increasingly important. In this paper an experimental campaign on natural stone masonry columns axially confined by fiber reinforced polymers (FRP) is presented and discussed. Two different FRP wrapping system have been used: CFRP (carbon-fiber-reinforced polymer) embedded in epoxy resin, and FRMC (fiber-reinforced-cementitious matrix) embedded in two layers of a special mortar acting as bonding agent. A comparison between the two systems has been carried out. Results show that the ultimate load, stiffness and ductility significantly increase compared with unreinforced columns. Pre-damaged columns strengthened with CFRP and FRCM recover their load bearing capacity and improve their ductility. In addition, experimental results have been compared to theoretical strength previsions provided by literature analytical models, and findings have been analyzed and discussed.

Finite Element Modelling of Acoustic Waves Propagation in Stone Masonry

Abstract. The paper deals with the finite element modelling of acoustic waves propagation through a stone masonry specimen. In the last decades major efforts have been devoted to improve Sonic and Ultrasonic analysis of structural members and provide suitable correlations between acoustic wave features and the material parameters. This paper concerns the ultrasonic analysis and tomography of a masonry specimen made of trachyte blocks and cement mortar, including an inner void as an anomaly supposed to be detected by the analysis. The tests were performed with several equipments accordingly to the Direct Transmission Technique, transmitting an ultrasound signal by a piezoelectric transducer and detecting and analysing the signal received on the opposite side by another transducer. Basically the transmission time of the signal through an ideal path from the emitting and receiving transducers and the resulting wave speed are regarded as the main phenomenological measurements for non-homogeneity and anomalies detection.

Strength Class Prediction of Sardinia Grown Timber by Means of Non Destructive Parameters

In Italy timber and wood products are becoming increasingly used for building constructions due to their excellent physics and mechanical properties. International Codes require the use of wood previously graded according to the current regulation. This paper reports the preliminary results of an experimental campaign aimed at verifying the reliability of the use of Sardinian timber as structural material. For this purpose Maritime Pine boards from two different Sardinian areas have been analyzed and visual strength graded. Physical and morphological properties (density, knots, clusters knot, resin pockets, deviation of the grain, annual ring width position of board respect to the pith, humidity, etc.) along with mechanical and non destructive properties (elastic modulus, tensile strength, ultrasonic pulse velocity) have been checked. Timber properties have been statistically evaluated in order to identify the performance of the base material. Regression analyses have been carried out by studying the correlation between non destructive parameters and mechanical properties in order to define a criterion for predicting the strength class of the base material.

Non Invasive Acoustic Measurements for Faults Detecting in Building Materials and Structures

Over the past years both large and small restoration and conservation works on monuments, civil and industrial buildings have become of great interest. As indicators of the historical period in which they were built, all construction works have both their architectural style and the material used in their construction. Indeed, for thousands of years humans built using the same materials (wood, stone, brick, mortar and gypsum) up to the introduction of concrete at the beginning of the 19th century. Although concrete has replaced the old materials used in historical buildings, there still remains the problem of forestalling their deterioration and restoring them, also in the light of the importance of such works from the historical, cultural and economic viewpoints. Problems connected with the restoration of buildings, whether in reinforced concrete, masonry or wood, are quite complex and are essentially linked to the reuse, and thus the redesign, of the existing heritage of buildings. Indeed, cultural, social and economic reasons foster to the desire to lengthen the life of this heritage beyond normal physiological limits and thus its fruition far beyond its useful life. The problems to be addressed vary widely since there are noteworthy differences from one job to another; it is sufficient to consider just the social value of a building of great historical value, which is usually protected by severe restrictions aimed at conserving its artistic and cultural features, or an industrial building the use of which must be completely changed while at the same time maintaining its structural characteristics. It is evident that there is not one single answer to such widely differing situations: each job must be addressed from the cultural, technological and technical standpoints as a special case. The proper management of the rehabilitation of a building implies a knowledge of its real static conditions to be restored, the mechanical, physical and chemical characteristics of the materials of which it is built and the presence and characteristics of defects, anomalies and so on. Of fundamental importance is the diagnosis of materials and structures and many researchers, as well as companies that produce restoration materials, have carried out studies in this field. Methods for structural diagnosis and faults detecting are beginning to appear, albeit in an extremely divergent way, in tenders, rules, guidelines and so on. To exemplify, non-invasive diagnostic techniques are often used to determine whether or not materials compatible with the original structure have been used in restoration works: if not,

Non-destructive methods as a tool in the assessment of monumental buildings condition

Results of a diagnostic campaign carried out on ancient Santa Maria Church in Oristano (Italy), with the purpose of evaluating the structural condition before starting a restoration program, are reported. The beautiful building showed signs of damage such as cracks, gathered especially on the facade’s masonry and on the accessing arches of the lateral chapels contiguous to the facade. With the aim at non-invasively getting the higher number of reliable data about the real static condition of the church’s facade and its out-buildings, several non-destructive investigations have been carried out. As a first step a global visual inspection has been run. Then, sonic tests, endoscopy and flat jacks have been carried out on the facade’s masonry, and a dynamic test has been run on the tie rods that link the facade to the lateral chapel’s masonries. Finally, the development of the cracks in the arches has been monitored for a period of fourteen months.