APPLICATION OF A WAVELET BASED METHODOLOGY FOR STRUCTURAL DYNAMIC IDENTIFICATION IN HISTORICAL MASONRY STRUCTURES

This thesis deals with the problem of dynamic tests in historical masonry structures via a multidisciplinary approach: the basic classical background of structural engineering meets and supplements itself via classical and advanced signal processing tools, typical of other branches of engineering. In particular in this work together with the classical fast Fourier transform (FFT) based algorithm for modal parameters'extraction, a newer, more advanced and quite well established as well tool based on wavelet transform is experienced. Reecting its interdisciplinary nature this thesis is made up of two main parts: the former more analytical and numerical in which some theoretical and practical aspects related with the application of wavelet transform for modal parameter extraction are faced out and the latter, purely experimental, in which the methodology is used for studying two historical masonry structures, a bell tower built in XIII century and a multispans arch bridge built at the end of XIX century. Both these structures, even if at different scales, can be considered as belonging to the cultural heritage of their area. This thesis is organized as pointed out in the following: Chapter 1 sketches out the aims and objectives of the present work; Chapter 2 sketches some basics of integral transformations and introduces some basic denitions and terminology common in wavelet analysis. The analytical properties of a particular wavelet function, Gabor wavelet, are illustrated in detail, being this function used for the analysis of the data collected during the dynamic tests; Chapter 3 details some specicities of wavelet based analysis applied to structural dynamic identification. In particular the inuence of edge-eects in the damping coecient determination is introduced and studied; Chapter 4 introduces the rst case study, the Bell tower of St. Niccola'Church in Pisa. Due to the extensive study carried out on this structure this case study is split in two distinct chapters, this being the former. This chapter focuses on the geometrical surveys and on the historical research on materials used in the construction. Both these information were essential for the preliminary numerical model; Chapter 5 describes the way dynamic tests were carried out on the Bell tower of St. Niccola and details the main results achieved. Then it illustrates results of static analysis performed on the calibrated numerical model for evaluating reliable stresses on the materials and on the ground; Chapter 6 describes the second case study, the main Vara bridge and the wide dynamic tests campaign that was performed on it. Interesting results regarding the time variability of equivalent viscous damping coecients and eigenfrequencies are highlighted; Chapter 7 summarizes the main results achieved in the present work. The thesis is completed by two Appendixes labeled A and B that deepens the properties of sensor used in both dynamic tests and the story of the Private Marble Railway of Carrara, the Company leader in the past in marble blocks extraction that at the end of XIX decided to build lots of infrastructures for marble transportation modernization; among them the main Vara bridge.