Correlating Visual Grading with NTD Methods for Assessing Timber Condition in Historic Buildings

Abstract

This study aimed to develop, apply and assess a visual grading system that could evaluate the preservation state of historic buildings structural timbers and correlate it with three NDT methods that are widely used during diagnostic surveys. Assessing timber condition is crucial not only for the structural analysis of buildings, but also for reinsuring that well preserved original material of Cultural Heritage will not be lost. However, assessment based only on NDT results may be biased as it depends on many parameters such as i) the natural variability of wood ii) the type and degree of deterioration iii) the experimental conditions e.t.c. Furthermore, results obtained are not always coinciding and they are often unrelated to the macrosopic condition of timbers. Therefore, this work investigates comparatively a grading system developed based on European with results obtained from ultrasounds application, resistograph profiling and X-ray radiation. The three NDT techniques were tested on samples coming from a post Byzantine mansion in Athens, which presented various types and degrees of decay. For comparison reasons techniques were applied on sound wood of the same species also. Prior to NTD implementation, samples were conditioned in two different RH in order to examine the role of wood moisture on NTD results.