In the last years an increasing interest has been devoted to all the topics related to the security and safety of people. Particular attention has been paid to health monitoring of large civil structures hosting many people, such as high-rise buildings and stadiums. Some extraordinary events, such as the Millennium Bridge oscillations in London, excited by pedestrians, or the Bruce Springsteen concert at the Ullevi Stadium in which coordinated jumps from the crowd caused serious damage to the structure, and drew attention toward a deeper and more careful study of all those problems related to the dynamic behavior of civil structures and their interaction with crowds. Research on these topics is also aimed, among others, at developing techniques allowing for a continuous monitoring of the structure, starting from a set of measurements that can be performed continuously, 24 h a day, without the need to stop the structure's functionality. The vast scientific literature confirms the possibility of relating st...

Health assessment of historical buildings by means of monitoring systems is for sure a fundamental step to preserve architectural heritage, especially for countries as Italy, rich in ancient monuments. Events such as earthquakes or severe weather phenomena constitute a major risk for these buildings because of their age and the related weakness to sustain exceptional excitations. The availability of a continuous, real-time, and automatic structural health monitoring system is considered a useful tool for early detection of a potentially dangerous situation for the structure and its occupants. The choice of the best measurement strategy provided by the monitoring system is crucial: a compromise must be found between the need of information, complexity of the measuring system and the related costs. Due to the difficulty in modelling most historical structures, it is a hard task to fix proper and safe limits relying on model-generated predictions only. The availability of long-term records of the structural response can help get this goal, not just relying on models, but also detecting changes in some parameters obtained from time records. This article presents a challenging example: the structural health monitoring of the Duomo di Milano main spire during and after restoration.

Transmissibility functions have been widely applied into the field of structural health monitoring, especially for damage detection. However, due to the existence of few analytical research works to conceive the significance of damage onset, the inherent mechanism of damage identification based on transmissibility function has not yet been clearly and deeply evaluated. In this article, an analytical approach has been investigated to demonstrate how to localize damage components caused by mass and stiffness change in terms of multiple-degree-of-freedom mass–spring–damper system, based on the inherent analysis between the transmissibility functions for any two consecutive masses. This study also points out the importance of the system input: various input location may lead to different recognized damage regions. Related simulation case studies and laboratory activities are carried out, proving the effectiveness and accuracy of the proposed approach.

Embedding optical fibers with fiber Bragg grating (FBG) sensors in 3D-printed samples can effectively facilitate the systematic use of smart materials in many fields such as civil, bio-medical and soft robotics applications. The aim of the study is to analyze different combinations of filament materials and FBG coatings, and to assess their metrological characteristics. Eighteen samples are fabricated and tested under different mechanical and thermal conditions. The repeated tests allow to perform an evaluation of the measurement repeatability for each sample, along with an analysis of the samples sensitivity. The filaments employed are acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and thermoplastic polyurethane (TPU). The fiber coatings are acrylate, Ormocer® and polyimide. The fiber coating has no significative influence on the performance of the sensors. The tests for temperature sensitivity highlight a good performance of ABS (116 pm/°C) and TPU samples (32 pm/°C) up to 60 °C, whereas the fabricated PLA samples (139 pm/°C for polyimide, 55 pm/°C for acrylate, 14 pm/°C for Ormocer®) cannot be used above 40 °C. The tests for strain sensitivity in axial elongation show an average sensitivity of 3.049 nm/mm for ABS, 1.991 nm/mm for PLA, 3.726 nm/mm for TPU. The bending tests show that all specimens materials have different sensitivity to elongation (2.994 nm/mm for ABS, 0.668 nm/mm for PLA, 0.149 nm/mm for TPU). Only for acrylate in PLA samples an effective difference for bending sensitivity resulted (1.241 nm/mm for the acrylate coating vs 2.366 nm/mm for the other coatings).