Assessment of structural reliability: a dynamic monitoring approach

The subject of this thesis is framed in the field of vibration based monitoring. In particular the work is focused on: implementing techniques of extraction of features, the use of collected data to recognize damages and the combined application of knowledge coming from monitoring systems with the classical structural safety formulations to a real case stud

Dynamic response of PC bridge beams under different damages

The present paper describes the dynamic test campaign on prestressed concrete bridge beams taken from a dismantled viaduct in Turin, Italy after a service life of 50 years in the framework of BRIDGE|50 research project. Dynamic measurements were previously performed on the decks from which the 29 beams were taken to characterize the behaviour of the viaduct in service condition. Successively the single beams are tested to analyse and evaluate the effects of the different damage levels on the dynamic properties. The vibration data have been collected before the application of static load, after the first cracking condition and after the maximum load applied on the beam to extract the principal modal components. The results highlight the correlation among the evolution of the damage and the dynamic response of the beam and then the effectiveness of vibration tests to identify the occurrence of damages and follow their evolution. The experimental findings could be used in future works to explore the effects of damages of the single beams on the global response of this bridge typology. This work presents the results of the experimental tests on the first eight beams tested

Condition Assessment of an Early Thin Reinforced Concrete Vaulted System

For the analysis and conservation of architectural heritage a multi-disciplinary approach is required. In the specific case of early concrete buildings, survey and experimental investigations constitute a fundamental source of information for verifying the actual structural behavior and the residual safety levels. This paper reports the direct experience acquired from an extensive experimental campaign conducted on the Paraboloide in Casale Monferrato. The study aims to be an example of how condition assessment of the structural heritage of the early 1900s, with an apparently simple geometric shape and composition, can actually contribute in understanding hidden structural complexity. Moreover, this work may provide useful information to researchers and practitioners who are approaching this specific structural typology (e.g., the industrial heritage represented by parabolic concrete silos). In more details, results are presented regarding the in-situ investigations, and the laboratory tests carried out to analyze the mechanical performance inherent to both (i) local aspects of the structure, such as the quality of the materials and connections, and (ii) global aspects, such as the modal response of the structure. Furthermore, considerations are made on the results of the experimental campaign, also through the corroboration of numerical models

Dynamic investigation on the Mirandola bell tower in post-earthquake scenarios

After the seismic events of the 20th and 29th of May 2012 in Emilia (Italy), most of the monumental and historic buildings of the area were severely damaged. In a few structures, partial collapse mechanisms were observed (e.g. façade tilting, out-of-plane overturning of panels…). This paper presents the case-study of the bell tower of the Santa Maria Maggiore cathedral, located in Mirandola (Italy). The dynamic response of the structure was evaluated through operational modal analysis using ambient vibrations, a consolidated non-destructive procedure that estimates the dynamic parameters of the bell-tower. The dynamic tests were carried out in pre-intervention and post-intervention conditions in order to understand the sensitivity of dynamic measurements to safety interventions. Furthermore, a comparative study is made with similar cases of undamaged masonry towers up to the 6th mode. Finally, an investigation on the state of connections and of the building itself is carried out via FE model updating

Innovative technique for the base isolation of existing buildings

An innovative base isolation system has been recently proposed for the retrofitting of existing buildings, in which the isolation layer is inserted under the building foundations so that the building, along with its foundations, is isolated from the surrounding soil. The isolation layer resides in closely-spaced micro-tunnels, constructed under the entire width of the building. These micro-tunnels, along with the trenches around the building, isolate the structure from the surrounding soil. The execution of these micro-tunnels is the most critical construction stage, because it may result in settlements which can damage the structure. In this paper, the behaviour of an existing structure, consisting of a masonry wall subjected to tunnelling-induced ground subsidence, is analysed. A parametric study is conducted using 2-D nonlinear finite element analyses to understand the role of key factors such as strength and stiffness of soil and masonry, roughness of soil-structure interface, excavation sequence of tunnels, wall dimensions and openings configuration. The study identifies the design variables which influence the most the risk of structural damage and suggests the most effective damage symptoms to be monitored during constructio

Identificazione dinamica sperimentale di edifici strategici sotto sisma

Edifici pubblici quali ospedali, scuole, chiese e municipi costituiscono un patrimonio di importanza strategica per la vita di una comunità. La loro gestione richiede un periodico monitoraggio delle condizioni di sicurezza sia a breve che a lungo termine che può oggi essere condotto in modo efficace ed oggettivo mediante sistemi automatici e permanenti di misura delle vibrazioni strutturali. All'occorrenza di un evento sismico, tali sistemi hanno il merito di cogliere l'effettivo comportamento dinamico della struttura, permettendo la calibrazione sperimentale di modelli numerici, utili per una accurata valutazione del livello di sicurezza sismico e per la progettazione di interventi migliorativi. In quest'ottica assume particolare rilievo la rete di monitoraggio dinamico permanente di edifici strategici realizzata dal Dipartimento di Protezione Civile. Quattro di questi edifici sono stati scelti come casi studio allo scopo di analizzarne la risposta acquisita durante il recente evento sismico del Gennaio 2012 in Lunigiana/Garfagnana. Il presente articolo riporta i risultati della caratterizzazione dinamica condotta su uno di essi: il municipio di San Romano in Garfagnana (LU

Innovative technique for the base isolation of existing buildings

An innovative base isolation system has been recently proposed for the retrofitting of existing buildings, in which the isolation layer is inserted under the building foundations so that the building, along with its foundations, is isolated from the surrounding soil. The isolation layer resides in closely-spaced micro-tunnels, constructed under the entire width of the building. These micro-tunnels, along with the trenches around the building, isolate the structure from the surrounding soil. The execution of these micro-tunnels is the most critical construction stage, because it may result in settlements which can damage the structure. In this paper, the behaviour of an existing structure, consisting of a masonry wall subjected to tunnelling-induced ground subsidence, is analysed. A parametric study is conducted using 2-D nonlinear finite element analyses to understand the role of key factors such as strength and stiffness of soil and masonry, roughness of soil-structure interface, excavation sequence of tunnels, wall dimensions and openings configuration. The study identifies the design variables which influence the most the risk of structural damage and suggests the most effective damage symptoms to be monitored during constructio

Load tests on dismantled 50-year-old prestressed concrete bridge deck beams

This paper presents the results of three large scale experimental tests within the survey conducted on 50-year-old prestressed concrete (PC) girders for the BRIDGE|50 research project (www.bridge50.org). The girders were retrieved from a viaduct before dismantling operations once located in the urban area of Turin, Italy. Together with other structural members they represent one of the most prominent project of this type worldwide. The PC elements have 19.2 m span length and I-shaped cross section with 14 cm cast-in situ slab with variable damage due to deterioration caused by both service and lifting operations during dismantling phase. For each specimen, static tests have carried out applying monotonic or cyclic loading up to the ultimate load, measuring deflections, loads and strains in several positions for two I beams and one box beam. The results of the tests in terms of load-deflection responses and strains are reported for each beam investigated and compared considering previous tests from the same project already reported in literature. The experimental findings highlight the specific structural response and residual capacity of the tested members in presence of damage, cyclic loading and different tested section. The outcomes of the project will provide a valuable database of reference for the assessment of the residual structural performance of existing bridges

Large-scale experimental testing of 50-year-old prestressed concrete bridge girder

This paper reports on large-scale loading tests survey carried out on 50-year-oldprestressed concrete girders as part of the BRIDGE|50 research project (www.bridge50.org).The girders were retrieved from an existing viaduct in Turin, Italy. The prestressed concreteelements were 19.2 m long and had an I-shaped cross-section with a cast-in-situ slab. Variabledamages were found, due to in-service deterioration and/or subsequent lifting operations duringthe demolition phase. Each specimen was subjected to static tests using monotonic or cyclicloading up to the ultimate load. This paper reports the results of tests on the second group offour girders, comparing their load-deflection responses and strains with those of the first groupsubjected to a different static scheme. The experimental findings highlight the global structuralresponse from bending to bending/shear failure; the outcomes will define a valuable referencedatabase for assessing the residual structural performance of existing girder bridges