This paper reports on a pilot project for long-term structural health monitoring of historical city gates. This structural typology is what today remains of the defensive structures that ...characterised the medieval centres of many European cities. Even though in the last years the scientific community has paid great attention to the structural analysis and on the structural health monitoring of masonry towers, which are apparently similar to the typology of city gates, only a few studies explicitly approach such heritage buildings. In most cases, the surviving gates are immersed in the daily vehicular-traffic flows and hence continuously subjected to traffic-induced vibration. Consequently, a key point both for their conservation is the assessment of the optimal sensors position to be used for reliable structural health monitoring procedures. These issues are here discussed with reference to a specific case: the San Niccolò gate in Florence (Italy). First, an expeditious experimental campaign performed with a reduced number of accelerometers is reported. This test is aimed to identify a numerical model that is subsequently employed to design the optimal sensor position of long-term structural monitoring. This optimal sensor grid must be assessed to ensure a low-cost and sustainable dynamic monitoring system but, at the same time, to maximize the information contents.
The recent developments of micro-electro-mechanical systems and wireless sensor networks allow today the use of low-cost and small-size sensors for continuous monitoring of civil structures. Both ...these features are very important for the low impact of the sensor grid in heritage structures, ensuring a low-cost and sustainable dynamic monitoring system. Over the last 20 years the use of sensor networks for continuous monitoring has received a growing interest. Anyway, still numerous questions remain opened about the sensitivity of measurement devices, the optimization of number and positioning of sensors, the energy efficiency of the network, and the development of algorithms for real-time data analysis. This paper, based on the aforementioned motivations, discusses about a monitoring system made of micro-electro-mechanical sensors connected through a wireless network. The architecture of the wireless sensor network and the automatized procedure proposed for the continuous processing of the recorded signals are discussed and described with reference to an explicative masonry tower case study. It is believed that the proposed technologies can provide an economical and relatively non-invasive tool for real-time structural monitoring and that, moreover, the availability of large amounts of data from actual measurements can give effective information on the structural behaviour of historic constructions.
A comprehensive understanding of the dynamic behavior of a tree can play a key role in the tree stability analysis. Indeed, through an engineering approach, the living tree can be modeled as a ...mechanical system and monitored observing its dynamic properties. In the current work, procedures of dynamic identification used in civil engineering are applied to the case study of a black locust (Robinia pseudoacacia L.). The tree was instrumented with 13 seismic, high-sensitivity accelerometers. Time histories of the tree response under ambient vibration were recorded. Three representative sections of the trunk (the collar, the diameter at breast height, and the tree fork) were equipped with three accelerometers, in order to obtain lateral and torsional vibrations. Moreover, two pairs of accelerometers were fixed on the two main branches. The results show that it is possible to identify the natural frequencies of a tree under ambient vibrations, thanks also to the support of a preliminary finite element model. Even though the optimal position is under the tree fork, the sensors fixed at the diameter at breast height allow a clear identification of the main peaks in the frequency domain.
•A new automated procedure for the Operational Modal Analysis.•Introduction of a setup procedure to reduce the modelling errors.•Introduction of a Modal Quality Index.•Application and discussion of ...the results on two historic masonry towers.
Many efforts have been made in the last decade to define Automated Operational Modal Analysis (AOMA) procedures able to process large datasets from long-term monitoring systems. However, some issues are still open and further studies on this topic are needed; in particular following points should be better investigated: i) controlling the tuning parameters to minimize the modelling errors, ii) defining suitable automatization method for processing large datasets and iii) validating the extracted modal parameters. These points are investigated in this paper with the aim of enhancing the current AOMA procedures based on the Stochastic Subspace Identification (SSI) techniques, and the following novelties are introduced: i) a minimization approach for the tuning of the initial parameters in the SSI algorithm, ii) a statistical method to automatically define the cut-off threshold in the hierarchical clustering phase, and iii) a Modal Quality Index (MQI) – ranging from 0 to 1 – to validate the identified modes. The above novelties represent key aspects that allow a real-time check of the modal parameters provided by a monitoring system within a Continuous Structural Health monitoring (CSHM) framework.
Summary
Traffic‐induced vibration is one of the main causes of small (often only cosmetic) damages for Heritage buildings. The heavy public road‐transport, often very close to these structures, may ...lead to fatigue phenomena due to induced continuous vibrations and consequently damages. Even if all the International Standards agree to define the velocity—expressed in terms of Peak Particle Velocity (PPV) or Peak Particle Component Velocity (PCPV)—as reference damage indicator, a standard procedure for calculating those values starting from accelerometers data is indeed absent (or needs to be better specified). This paper—taking into account that in most cases velocities cannot be directly measured—first compares the efficiency of two of the most common employed methods: the trapezoidal rule and the long Discrete Fourier Transform. This comparison is performed discussing the experimental activity performed on the SS. Annunziata's lodge in Florence (Italy) which is particularly exposed to traffic‐induced vibrations. Subsequently, a systematic analysis of the traffic‐induced vibration phenomenon was performed based on (i) dynamic identification by means of accelerometers data; (ii) calculation of the velocities (PPV and PCPV); (iii) analysis of the traffic component effects; and (iv) analysis of the Structure‐Soil Interaction (SSI) by using results obtained by means of Falling Weight Tests (FWT). Eventually, a comparison with the results of a previous dynamic test campaign performed in 1994 is reported, underlining a consistent increase of the traffic‐induced vibrations on the lodge possibly caused by the increase of the road unevenness.
•Numerical study on the seismic behaviour of masonry towers.•Critical insight into the results obtained.•Comparison between seismic risk of confined and unconfined structure.
This study analyses the ...seismic risk of a confined historic masonry tower located in Italy (San Gimignano) critically discussing the multilevel assessment path proposed by the Italian “Guidelines for the assessment and mitigation of the seismic risk of the cultural heritage”. Specifically, these guidelines identify a methodological path which aims to coordinate the phases of investigation and drive the grade of resolution of the structural assessment, depending on different possible objectives. The paper compares the results obtained with the three different levels of evaluation employed to estimate the seismic risk of the tower: level LV1 (analysis at territorial scale), level LV2 (local analysis) and level LV3 (global analysis). The main variables considered are the mechanical properties of the masonry walls and the degree of constraint generated by the buildings surrounding the tower with specific attention to the latter variable. Numerical insights on the seismic behaviour of the tower are presented and discussed through a comparative approach. The obtained results show significant differences between the numerical models of the confined and the isolated tower in terms of both capacity curves and damage pattern and point out the needs of additional studies regarding the numerical assessment of the effects of the interaction between a tower and its adjacent lower buildings.
•Estimation of damping ratios on a short-span RC bridge with half-joints beam through AVTs in in-service conditions.•Minimum signal length to minimize the bias in the damping estimation.•Analysis of ...the damping with a fixed-length moving window over the entire vibration signatures.•Correlation between signals properties and estimated damping parameters.
Experimental tests for dynamic identification of reinforced concrete (RC) bridges by means of Operational Modal Analysis (OMA) are increasingly used in common engineering practice. Nevertheless, especially when measurements are carried out under in-service conditions (i.e. under traffic induced vibrations), some drawbacks should be carefully considered, especially in the damping-ratio quantification. As a matter of fact, the estimation is affected by several factors: i) the length of the signals, ii) the non-stationarity of the input process, and iii) the dependence on the vibration amplitude. Even if the damping ratio is a key parameter in the bridge dynamics, a major part of these aspects has not been yet fully investigated to estimate reliable values.
Starting from a dynamic test program on a short-span RC bridge with half-joints in Italy, this paper investigates the issues mentioned above for the damping ratio estimation of the first two modes focusing on: i) the influence of the signal length, ii) the effects of the signals properties, and iii) their correlation with the vibration amplitude. Both the Stochastic Subspace Identification technique fed with the signal covariance (SSI-cov) and the Random Decrement technique (RD) have been used to compute the damping ratios from the collected signals. This paper shows how a convergence of the results cannot be attained by simply increasing the sample size, suggesting that the nature of the vibration itself influences the damping values. A negative, although weak, correlation between the damping ratio and the power of the signals indicates that several factors play a crucial role in the damping estimation in the short span RC bridges with half-joints.
Additive Manufacturing (AM) has emerged as an economical and feasible technology for creating industrial components. This paper evaluates the use of AM for inductive Wireless Power Transfer (WPT) ...systems. In particular, the innovative use of metal 3D printing is proposed as a manufacturing process for the coils. For this reason, the recent improvement of metal AM is proposed as a suitable solution to increase design opportunities, reduce costs and production time while improving transmission efficiency. In fact, the WPT coil current distribution can be preliminarily studied through Finite Element Analysis (FEA) to optimize its cross-section and geometry. In this work, a general design procedure for WPT coils using metal AM is presented and this technology is compared with traditional solutions (i.e. hollow and litz wire) through extensive experimental measurements. The analysis shows that AM allows to reduce the parasitic resistance, costs and weight while increasing the transmission efficiency. Thus, the obtained results confirm the potential of AM for producing WPT coils, nominating this technology as a flexible, sustainable, and rapid solution for custom WPT coils production.
Purpose
To evaluate safety and efficacy of the novel percutaneous interspinous device (PID) for the treatment of symptomatic degenerative lumbar spinal stenosis (DLSS) in 3 different centers.
Methods
...From November 2016 to March 2020, 255 patients (male 125, mean age 71.2 years old range 49–91 years old) with neurogenic claudication, confirmed by electromyography, related to mono or bi-segmental lumbar central canal and/or foraminal stenosis were enrolled in the study. Magnetic resonance (MR) and/or computer tomography (CT), physical exam, and Visual Analogue Scale (VAS) and Zurich Claudication Questionnaire (ZCQ) were performed before and 6 months after the procedure. All treatments were performed under fluoroscopic guidance with local anesthesia and mild sedation. Technical success was defined as correct placement of the Lobster® (Demetrios Medical, Firenze, Italy) PID as demonstrated by computer tomography (CT) performed immediately after treatment; spinoplasty was performed in selected patients.
Results
PID placement was accomplished with a 99.6% success rate (257/258). The one device that was not implanted was due to a spinous process fracture. In 28 patients, more than 1 device was implanted in the same session (max 3 PIDs); 6 patients required a second implant in different session. A total of 172 prophylactic spinoplasties were performed (59.3%). No major complications occurred; 3 device misplacements were successfully treated with percutaneous retrieval and new device deployment. 99.6% of patients experienced clinical improvement.
Conclusion
Lobster PID is an effective and safe minimally invasive decompression method for central canal and neural foraminal stenosis when patients are correctly selected.
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