Seismic Retrofitting and Restoration of Historical Buildings Using Innovative Materials: the Case of Carmine’s Bell Tower in Naples

Abstract

A general multidisciplinary procedure to approach the study of heritage building is synthesized in this PhD thesis considering the main features necessary to identify the structural behaviour of such type of buildings (historical inquires, geometric survey, material identification, in situ inquires) according to qualitative and quantitative methodologies. An in-depth survey has been carried out on the masonry of the Bell Tower of the “Santa Maria del Carmine” Church in the city of Naples, Italy. The analyses followed a multidisciplinary approach to identify its architectural and structural features, to identify the materials used and the state of damage and interventions made in various periods, to assess the stress state in the masonry under gravity loads, and to define its dynamic behavior. The information gathered represents the starting point for designing a seismic upgrade to meet the standards applied to historic monuments. A detailed historical, architectonical and structural inquires have been developed on the Bell Tower of “Santa Maria del Carmine” sited in Naples. These inquires have been preliminary to the study of the Tower by a finite element model for static and dynamic loads. The Bell Tower of “Santa Maria del Carmine” is an ancient (XVII century) historical masonry building located in city of Naples (Italy). The Tower is 68m high and is made by faced yellow tuff masonry along the initial 41 meters of height and by clay bricks along the upper levels. Internal and external walls are covered by decorative dark stone along the first nine meters. Geometrical and material surveys were performed to evaluate the actual damage state, the sequence of changes in the structures. Detailed experimental in situ investigations have been performed to define the geometry, to find the composing materials, to characterize their mechanical properties, to analyze damage condition and to identify the dynamic behaviour of the structure. The experimental results have been successively used to develop a numerical 3-D FE model. This model has been used to perform a linear static analysis under gravity loads to calibrate the mechanical parameters given by experimental results (i.e. the density of materials) and to check the safety condition for the vertical loads usually acting on the structure. Then, a linear dynamic analysis has been also accomplished to assess the values of Young’s modulus of materials and the constraint conditions offered by the surrounding buildings, based on parametric comparisons with the experimental results (natural frequencies and corresponding modal shapes obtained by dynamic in situ tests). This last study has been useful to understand the behaviour of the Tower under horizontal actions like an earthquake, considering that the structure is located in a medium risk seismic area. Therefore with the assumption of a ‘global behaviour’ of the Tower, a non linear static analysis (Push - over) was carried out based on the results of the previous inquiries, pointing out a low risk condition for the expected seismic actions (peak ground acceleration of 0.168g). Considering that previous numerical analysis evidenced that the Tower satisfied global checks for the expected seismic actions, in this paper attention is focussed on the study of local out-of-plane mechanisms activated by those actions. To prevent the activation of local mechanisms an innovative and low invasive intervention with FRP materials has been designed in the areas where local checks were not satisfying.