Monica Valdes

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.

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.

Grading of Low-Quality Wood for Use in Structural Elements

Timber is a sustainable resource, environmentally friendly and aesthetically pleasing. Using locally grown timber as building material leads to economic, social and environmental benefits. Being an organic material, timber is not homogeneous; hence, it is crucial to predict the base material quality. International codes require the use of wood previously graded according to the current regulations in order to verify its reliability when used as structural material. An exhaustive analysis of the state of art of different methodologies and code requirements for structural timber grading is presented herein. Structural timber grading methods and their applicability to low-strength timber is analysed and discussed with reference to Maritime Pine locally grown in Sardinia (Italy). Several physical and morphological parameters such as density, the presence of knots, clusters of knots, grain deviation, warping, annual ring width and moisture content had to be measured. Moreover, mechanical parameters (tensile strength and modulus of elasticity in tension) were measured and analysed in order to identify the strength class of Sardinian Maritime Pine. The operational issues related to the application of the different methodologies and code requirements for structural grading of low-quality wood are also discussed and analysed.

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.

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.

DYNAMIC DETERMINATION OF THE MODULUS OF ELASTICITY OF MARITIME PINE CROSS-LAMINATED PANELS USING VIBRATION METHODS

This paper describes the preliminary results of an ongoing research activity involving Maritime Pine Cross-Laminated Timber (CLT) panels, aimed to exploit the potentialities of this native species of Sardinia. The modulus of elasticity (MOE) is a key parameter for grading wooden products and evaluating the overall mechanical properties of panels. Free Vibration tests can be an effective method to assess the dynamic MOE of wooden products; the method is based on the direct measurement of the first vibration mode frequency of the specimens and the indirect determination of the elastic parameters. The present work shows a straightforward approach to evaluate the dynamic MOE of cross-laminated panels by choosing suitable boundary conditions depending on the specimen sizes. For this purpose, various experimental tests were conducted on different configurations aiming to evaluate the dynamic MOE for the considered cases. Furthermore, the relationship between global vibrational behaviour of panels and original boards MOE has been investigated. The dynamic MOE obtained by vibration testing method has been compared with the static MOE evaluated by bending tests in order to find a correlation. A linear relationship between dynamic and static MOE was found, with the dynamic MOE being slightly higher than the static MOE, as expected. The dependence of the correlation upon the applied methodology was determined and regression equations were derived and are provided in the paper.