Grippa, Maria Rosaria (2009) Structural identification of ancient timber constructions by non-destructive techniques. [Tesi di dottorato] (Unpublished)

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The refurbishment and enhancement of the existing building heritage held a very important rule in all the Europe Countries, where the belief that historical constructions should be preserved and restored, confirming their initial static function by means of appropriate interventions in harmony with the pre-existent structural configuration, is deeply rooted. In many ancient buildings located in historical centres of Italy and more widely of the Mediterranean area, the horizontal load-bearing structures, such as roof and floor, are made of timber, which is one of the oldest structural material, together with masonry and stone. In particular, most ancient complex systems are composed by two main superimposed units, such as beam floor and vaulted ceiling or light vault, often connected each other, which are an evidence of the past applications and technologies and, at the same time, the ancestors of the modern framed systems. Actually, the analysis of ancient structures, made of timber, is very cumbersome for all the inherent difficulties to be faced at both material and structural behaviour characterization. In particular, due to its nature, wood presents natural defects and structural anomalies, moreover it suffers a biological deterioration, closely connected to the environmental conditions. Therefore, the static behaviour of the whole structures and of each component, together with the state of conservation of single members and their complete characterization should be identified after an accurate in situ evaluation of the condition of the standing structures. In this context, non-destructive evaluation (NDE) methods are excellent to achieve a good level of knowledge in the structural analysis, diagnosis and restoration. The visual inspection is the most simple and oldest non-destructive method, which is traditionally used to grade wood in end-use categories. Recently, instrumental non-destructive techniques have evolved as a means for evaluating physical and mechanical properties of wood and detecting internal defects and decay. Generally, NDT methods present several advantages such as their practical utilization, transport and efficiency, however up to now, although they allow to gather a lot of useful information about the state of conservation of the timber members, these are only qualitative and do not lead to the determination of the mechanical properties, necessary to estimate the strength and stiffness capabilities of the structural systems. The general aim of this thesis is the structural identification of ancient timber constructions, including several aspects and applications, summarized in three main topics, as follow: - Analysis of historical timber structures. The attentions is focused on studies case which are the complex roofing structures of the Royal Palace of Naples. - Study of an innovative system for r.c.-timber floor. The new connector between the timber beam and the concrete slab consists of a steel collar, composed by two or more parts, bolted together at appropriate folded wings. Monotonic push-out tests and bending test on a full-scale composite floor are presented. - Mechanical characterization of timber by means of NDT-DT correlations. A research activity has been developed by means of an extensive experimental campaign, including non-destructive investigations (NDT) and destructive tests (DT) on structural elements and defect-free specimens, made of old chestnut wood. Experimental results are discussed and statistically analyzed in order to calibrate novel correlations between NDT and DT parameters, based on linear regression model.

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