Correlations between destructive and four NDT techniques tests on historic timber elements

The paper presents results from the wide experimental campaign of NDTs on ancient timber roof structure of Palace Malvezzi (Bologna) dated before 20th Century in situ and in laboratory, using several different techniques (visual inspection, 4-point bending test, ultrasound test, moisture content test, drilling penetration resistance, spectral analyser, ground penetrating radar test together with comparative laboratory destructive and NDTs on the ancient timber beams. Moisture content of ancient timber beams has been varied to check its influence on mechanical properties. Modulus of elasticity was obtained on 4 full-scale beams by 4-point bending test but also by ultrasound testing and by spectral analyser. Compression strength. Local weak points (decay, knots, splits, joints) were determined on site and in the laboratory by visual inspection and by testing via penetration drilling resistance and ground penetration radar. Samples were tested parallel and perpendicular to grain. On site testing was carried out first by visual inspection, afterwards by measuring modulus of elasticity by four point on site bending test, ultrasonic device, measuring moisture content and drilling penetration resistance. A correlation between NDTs parameter and results from destructive tests of compression, tensile and bending strength is presented in order to propose a methodology for obtaining accurate mechanical properties of the material, residual bearing capacity and stiffness of timber elements. Influence of the moisture and stress lavel in element are examined and correlation between NDT parameters, static MOE and strengths obtained by destructive testings are determined. Experimental campaign has been designed, developed and financed inside the EU FP7 project SMooHS (Smart Monitoring of Historic Structures) (2008-2011) by partners from University of Zagreb and University of Bologna