Structural and seismic monitoring of historical and contemporary buildings: general principles and applications

Structural Health Monitoring (SHM) indicates the continuous or periodic assessment of the conditions of a structure or a set of structures using information from sensor systems, integrated or autonomous, and from any further operation that is aimed at preserving structural integrity. SHM is a broad and multidisciplinary field, both for the spectrum of sciences and technologies involved and for the variety of applications. The technological developments that have made the advancement of this discipline possible come from many fields, including physics, chemistry, materials science, biology, but above all aerospace, civil, electronic and mechanical engineering. The first applications, at the turn of the sixties and seventies, concerned the integrity control of remote structural elements, such as foundation piles and submerged parts of off-shore platforms, but nowadays this type of monitoring is practiced on airplanes, vehicles spacecraft, ships, helicopters, automobiles, bridges, buildings, civil infrastructure, power plants, pipelines, electronic systems, manufacturing and processing facilities, and biological systems. This paper carries out an extensive examination of the theoretical and applicative foundations of structural and seismic monitoring, focusing in particular on methods that exploit natural vibrations and their use both in the diagnosis and in the prediction of the seismic response of civil structures, infrastructure networks, and traditional and modern architectural heritage

Instantaneous identification of Bouc-Wen-type hysteretic systems from seismic response data

This paper presents a technique for identification of non-linear hysteretic systems subjected to non-stationary loading. In the numerical simulations, a Bouc-Wen model was chosen for its ability to represent the properties of a wide class of real hysteretic systems. The parameters of the model are computed instantaneously by approximating the internal restoring force surface through an "ad hoc" polynomial basis. Instantaneous estimates result from time-varying spectra of the response signals. A numerical application of interest to earthquake engineering is finally reported

Geometric and structural information for the analysis of historical domes: the case of SS. Trinità church in Torino

Investigation into the geometric configuration of historical masonry domes is fundamental when studying the structural behaviour of these architectural elements, above all if they have historical and artistic relevance. Indeed, accurate geometric information is essential also for the construction of reliable mechanical models, to monitor the condition state of the building and to plan strengthening and conservation interventions. To this aim, a multidisciplinary approach is required to collate the highest possible amount of data useful for the numerical modelling, including historical and archival research. The "SS. Trinità" church is a 16th century building of great historical, architectural and structural significance in the historic centre of Turin. It owes its fame primarily to the architect who built it, Ascanio Vitozzi, and to its large dome, built after the architect’s death. The availability of a recently undertaken laser scanner survey of the intrados of the dome made it possible to detect several depressions of the masonry cap. These findings can be either due to construction defects, or to structural problems that developed over centuries, or to the severe fire which struck the dome in 1942. In this multidisciplinary research, different numerical models of the masonry dome of SS.Trinità church were built. As a first step, a geometric study was based on the point cloud from the laser scanning. Then, structural analyses were conducted on the two different models of the dome-tambour system of the building, in order to try to explain the observed deformation behaviou

Understanding the structures of Pier Luigi Nervi: a multidisciplinary approach

[EN] The paper describes the strategies adopted to carry out the knowledge campaign on Hall C built by Pier Luigi Nervi at Torino Esposizioni, between 1949 and 1950, and belonging to the architectural heritage of the 20th century. The structure was built by combining reinforced concrete and ferrocement elements, thus implementing what for Nervi would later become the distinctive construction system of his artwork, which combined the use of precast in situ and cast-in-place elements.  The extensive review of the historical documentation allowed the identification of the distinctive features and material differences of all structural elements in order to formulate the least invasive testing campaign possible, combining sample extraction with non-destructive testing. The paper aims to illustrate the problems and challenges associated with the creation of interpretive models of the built heritage through the relationship between historical critical investigations and structural diagnosis and is intended to serve as an example for an appropriate phase of investigation aimed at developing guidelines for the conservation of a complex and iconic work.The present work is supported by the Keeping it Modern grant awarded by The Getty Foundation of Los Angeles (USA).Lenticchia, E.; Ceravolo, R.; Faccio, P. (2023). Understanding the structures of Pier Luigi Nervi: a multidisciplinary approach. VITRUVIO - International Journal of Architectural Technology and Sustainability. 8:66-75. https://doi.org/10.4995/vitruvio-ijats.2023.188626675

Sensor Placement Strategies for the Seismic Monitoring of Complex Vaulted Structures of the Modern Architectural Heritage

Effective diagnostic and monitoring systems are highly needed in the building and infrastructure sector, to provide a comprehensive assessment of the structural health state and improve the maintenance and restoration planning. Vibration-based techniques, and especially ambient vibration testing, have proved to be particularly suitable for both periodic and continuous monitoring of existing structures. As a general requirement, permanent systems must include a sensing network able to run a continuous surveillance and provide reliable analyses based on different information sources. The variability in the environmental and operating conditions needs to be accounted for in designing such a sensor network, but it is mainly the structural typology that governs the optimal sensor placement strategy. Architectural heritage consists of a great variety of buildings and monuments that significantly differ from each other in terms of typology, historic period, construction techniques, and materials. In this paper, the main issues regarding seismic protection and analysis of the modern architectural heritage are introduced and applied to one of the vaulted structures built by Pier Luigi Nervi in the Turin Exhibition Centre. The importance of attaining an adequate level of knowledge in historic structures is also highlighted. After an overview of the Turin Exhibition Centre and its construction innovations, this paper focuses on Hall B, describing the structural design conceived by Pier Luigi Nervi. A seismic assessment of the structures of Hall B is then presented, considering the potential seismic damage to nonstructural elements. Subsequently, the application of an optimal sensor placement strategy is described with reference to two different scenarios: the first one corresponding to the undamaged structure and the second one that considers a possible damage to the infill walls. Finally, a novel damage-scenario-driven sensor placement strategy based on a combination of the two above mentioned is proposed and discussed. One of the major conclusions drawn from the analyses performed is that nonstructural elements undergoing seismic damage or degradation may significantly affect the global dynamic response and consequently the optimal sensing configurations

Effect of noise in the time-frequency estimate of the peridynamic bond elastic constant parameter

The Peridynamic (PD) theory is a modern nonlocal (nonlinear, elastic /inelastic, with-out/with memory) theory able to deal with long-range forces and discontinuity in materials. For this reason the theory is suitable for the monitoring of masonry structures. Starting from a special case of PD formulation, named Bond-Based Peridynamic (BBPD), a feature ob-tained by the idealization of real systems with BBPD is used for SHM purposes: the bond elastic constant parameter. To characterize the damage (i.e. permanent deterioration of ma-terial and/or geometric properties of the systems) occurring in systems idealized with PD models, a joint time-frequency direct estimate of the parameter values is performed using a Short Time Fourier Transform (STFF) of the systems response and the input acceleration at the base of the systems. The method is applied numerically and the effect of noise in the time-frequency evaluation of the parameter values is analyzed. The study concludes that PD can provides simply and strong information on the health of simulated systems, allowing at the same time an easy and scalable parametrization of civil, especially masonry, structures, while the bond elastic constant parameter can be used for the damage characterization, i.e. to detect, quantify and localize the damage in a generic system

Bayesian Calibration of Hysteretic Parameters with Consideration of the Model Discrepancy for Use in Seismic Structural Health Monitoring

Bayesian model calibration techniques are commonly employed in the characterization of nonlinear dynamic systems, as they provide a conceptual and effective framework to deal with model uncertainties, experimental errors and procedure assumptions. This understanding has resulted in the need to introduce a model discrepancy term to account for the differences between model-based predictions and real observations. Indeed, the goal of this work is to investigate model-driven seismic structural health monitoring procedures based on a Bayesian uncertainty quantification framework, and thus make relevant considerations for its use in the seismic structural health monitoring, focusing on masonry structures. Specifically, the Bayesian inference has been applied to the calibration of nonlinear hysteretic systems to both provide: (i) most probable values (MPV) of the parameters following the calibration; and (ii) estimates of the model discrepancy posterior distribution. The effect of the model discrepancy in the calibration is first illustrated recurring to a single degree of freedom using a Bouc–Wen type oscillator as a numerical benchmark. The model discrepancy is then introduced for calibrating a reference nonlinear Bouc–Wen model derived from real data acquired on a monitored masonry building. The main novelty of this study is the application of the framework of uncertainty quantification on models representing data measured directly on masonry structures during seismic events

Exploring Problems and Prospective of Satellite Interferometric Data for the Seismic Structural Health Monitoring of Existing Buildings and Architectural Heritage

Satellite interferometric data represent a promising source of information for the Structural Health Monitoring (SHM) of the existing built environment. This is especially true because they show differential temporal-spatial displacements of remotely monitored points, which can be easily interpreted with a visual inspection of their time-histories for different locations defined a priori. However, the interferometric information is commonly referred to extended territories (at the scale of city or region), thus several problems arise in the implementation of automatic SHM techniques for the damage detection, localization, and assessment of the built environment at a point level (scale of the building or lower). Despite a long list of challenges, interferometric data have also the potential to become a useful source to assess the health of a structure, especially for helping in define structural early warning methodologies. For this reason, in the paper, the authors summarize the main challenges in the use of satellite interferometric data for civil SHM, and rather than proposing remedial actions, try to critically analyze the challenges and perspectives for future applications

Non-destructive testing on aramid fibres for the long-term assessment of interventions on heritage structures

High strength fibre reinforced polymers (FRPs) are composite materials made of fibres such as carbon, aramid and/or glass, and a resin matrix. FRPs are commonly used for structural repair and strengthening interventions and exhibit high potential for applications to existing constructions, including heritage buildings. In regard to aramid fibres, uncertainties about the long-term behaviour of these materials have often made the designers reluctant to use them in structural engineering. The present study describes simple and non-destructive nonlinearity tests for assessing damage or degradation of structural properties in Kevlar fibres. This was obtained by using high precision measurements to detect small deviations in the dynamic response measured on fibres and ropes. The change in dynamic properties was then related to a damage produced by exposure of the sample to UV rays for a defined time period, which simulated long-term sun exposure. In order to investigate the sensitivity of such an approach to damage detection, non-linearity characterisation tests were conducted on aramid fibres in both damaged and undamaged states. With the purpose of carrying out dynamic tests on small fibre specimens, a dedicated instrumentation was designed and built in cooperation with the Metrology Laboratory of the Department of Electronics at the Politecnico di Torino

AE propagation velocity calculation for stiffness estimation in Pier Luigi Nervi’s concrete structures

Abstract In the present paper, the acoustic emission (AE) device is used with an innovative approach, based on the calculation of P-wave propagation velocity (vp ), to detect the stiffness characteristics and the diffused damage of in-service old concrete structures. The paper presents the result of a recent testing campaign carried out on the slant pillars composing the vertical bearing structures designed by Pier Luigi Nervi in one of his most iconic buildings: the Hall B of Torino Esposizioni. In order to investigate the properties of these inclined pillars, localizations of artificial sources (hammer impacts), by the triangulation procedure, were performed on three different inclined elements characterized by stiffness discrepancies due to different causes: the casting procedures, executed in different stages, and the enlargement of the hall happened a few years later the beginning of the construction. In the present work, the relationship between the velocity of AE signals and the elastic characteristics (principally elastic modulus, E) is evaluated in order to discriminate the stiffness level of the slanted pillars. The procedure presented made it possible to develop an innovative investigation method able to estimate, by means of AE, the state of conservation and the elastic properties and the damage level of the monitored concrete and reinforced concrete structures