ABSTRACT: The general topic investigated in this thesis is “structural health monitoring”, with s... more ABSTRACT: The general topic investigated in this thesis is “structural health monitoring”, with special care being devoted to damage detection and localization. The study is focused on methods which work in the space of the observed variables, where the global information measures can be used to detect the damage. In this context damage detection is demanded to global measures such as entropy or Lyapunov exponents. The comparison of these measures computed in subspaces of the observed variables or in their expansions, allows one to perform a sort of sensitivity analysis on the role of the variables involved in the problem.
Such global measures are able to detect but not to directly localize damage. For this purpose, a new approach to detect and localize the damage is formulated and implemented. It exploits response surface techniques to approximate the relationship among the observed variables. Comparing the resulting models in different damaged and undamaged situations identifies the response differences and their causes.
The response surface procedure is described from its basic theoretical aspects up to the features of its numerical implementation. Additionally, the global measures introduced above drive the analyst in establishing whether or not the problem is well posed, i.e., whether or not the set of measured quantities are able to detect the specific damage to be localized.
The validation of the proposed methodology is first numerically pursued by applying it to the benchmark case set up by the Structural Health Monitoring Panel of the American Society of Civil Engineering (ASCE). The procedure is then tested on two different experimental situations. While the first study of a three-dimensional steel frame reproduces the features of the benchmark problem, the second investigation covers a monumental structure situation, where damage is represented by more or less extended cracks in the masonry. The potential expressed by the procedure also in this second application seems to promise interesting exploitation possibilities.
the Sustainable Places 2017 (SP2017) Conference, 2017
Built to Specifications (B2S) is a Horizon 2020 EU-funded project involving 20 European partners ... more Built to Specifications (B2S) is a Horizon 2020 EU-funded project involving 20 European partners that seeks to reduce the gap between a building designed and as-built energy performance. To do this, the project will put a new set of breakthrough technological advances for self-inspection checks and quality assurance measures into the hands of construction professionals. This collection of smart tools will help building stakeholders at all levels in meeting EU energy efficiency targets.
EACS 2016 Paper No. 141<br>Infrastructures for helicopter landing, the so called heliports,... more EACS 2016 Paper No. 141<br>Infrastructures for helicopter landing, the so called heliports, are becoming more and more common. From a safety point of view, this means a clustering of helicopter trajectories with an increase of accident occurrence at the site. The surrounding buildings are subjected to a spread of vibration waves. The goal of this contribution is to investigate policies for driving these waves far from where they could cause economical losses.
In the space of design variables, a cost function is defined whose value must either be constant ... more In the space of design variables, a cost function is defined whose value must either be constant or fall within an assigned range. Also a set of scenarios against which robustness should be assessed is introduced. The result will be a robustness index dependent on both the given range of design costs and the given aggression scenarios. By adopting a Differential Evolution (DE) genetic algorithm, the zero-one (survival-failure) domains are identified in the space of the design variables. Each feasible solution, i.e., any structural design of acceptable cost satisfying the safety requirement, will then be associated with a robustness index. A numerical example is discussed in order to explain the computational details of the proposed method
A model of the human-induced actions, where the consequences of humans unpredictability, together... more A model of the human-induced actions, where the consequences of humans unpredictability, together with their response to social and psychological stimuli, are regarded as stochasticity, is developed. After defining a moving grid of nodes in the direction of the crossing, an average action per node is assigned. This value is modified by the following two contributions. A fluctuation, which involves two spatial variables and the time variable, is introduced by stochastic simulation, with a cross-spectral density function which accounts for the spatial dispersion of the single trajectories. A geometric shape function is formulated to account for a non-homogeneous spatial distribution of the pedestrians across the bridge deck. The procedure of assessing the vibrations serviceability of new footbridges requires to be thoroughly revised in light of the increased slenderness and spans achieved by using innovative construction materials of high strength (Zivanovic et al., 2005; van Nimmen e...
In this paper the data acquired on a pedestrian timber bridge under different Omovingi loads conf... more In this paper the data acquired on a pedestrian timber bridge under different Omovingi loads configurations are reported and analysed by applying a time-frequency decomposition technique. This approach allows the authors to better identify the dynamic behavior of the bridge under the above loads. A first in situ experimental campaign was carried out on November 7, 2013, with the aim of recording the accelerations induced by people walking and running along the bridge (the so called human induced vibration Ð HIV). For this purpose, the footbridge was equipped by accelerometers. The pedestrian bridge under investigation is located not far from the town of Belluno, Italy, and connects the two sides of the outlet channel of the OSanta Crocei Lake. To better fit the structure to the surrounding naturalistic area, eco-friendly construction materials with low environmental impact were adopted during the design stage. In particular glued laminated timber (GLT) and steel elements are used, l...
International Journal of Sustainable Materials and Structural Systems, 2020
This work presents an overview of some of the most promising technologies for the structural heal... more This work presents an overview of some of the most promising technologies for the structural health monitoring (SHM) of in-service tunnels. The common goal of damage or unusual behaviour detection is best pursued by an integrated approach based on the concurrent deployment of multiple technologies. Typically, traditional SHM systems are installed in problematic or special areas of the tunnels, giving information on conditions and helping manage maintenance. However, these methodologies often have the drawbacks of forcing the interruption of traffic for SHM system installation and monitoring only selected portions. Alternative solutions that would make it possible to keep the tunnel in normal operation and/or to analyse the entire infrastructure development through successive and continuous scanning stages, would be beneficial. In this paper, the authors will briefly review some traditional monitoring technologies for tunnels. Furthermore, the work is aimed at identifying alternative solutions, limiting or avoiding traffic interruptions.
Sensing devices are the main support for any experimental activity. The user expects that they ar... more Sensing devices are the main support for any experimental activity. The user expects that they are transparent, i.e., any measurement provides an assessment of a physical variable. Recent microelectronics developments caused significant modifications in the products offered by the market. Data fusion is the source of a recent jump in that technology, but the transparency of the result is no longer evident. In this paper, the authors consider the data fusion of displacement and acceleration measurements via a Kalman filter. The assemblage of two sensors is produced from scratch, and the critical aspects of the consequent data fusion are emphasized.
Long-time storage effects on shape memory alloy wires This paper is dedicated to the memory of Fr... more Long-time storage effects on shape memory alloy wires This paper is dedicated to the memory of Franz Ziegler
Recent studies were dedicated to the realization of measurements on stay-cable samples of differe... more Recent studies were dedicated to the realization of measurements on stay-cable samples of different geometry and static conditions as available at several facilities. The elaboration of the acquired data showed a a satisfactory efficacy of the dampers made of NiTi wires in smoothing the cable oscillations. A further attempt to investigate the applicability of the achieved results beyond the specific case-studies represented by the tested cable-stayed samples is herein pursued. Comparative studies are carried out by varying the diameter of the NiTi wire so that similar measurements can be taken also from laboratory steel cables of reduced size. Details of the preparation of the Ni-Ti wires are discussed with particular attention being paid to the suppression of the creep phenomenon. The resulting shape of the hysteretic cycle differs according to the wire diameter, which affects the order of the fitting polynomial to be used when trying to retrieve the experimental results by numerical analyses. For a NiTi wire of given diameter, an estimate of the amount of dissipated energy per cycle is given at low levels of maximum strain, which correspond to a fatigue fracture life of the order of millions of cycles. The dissipative capability is affected by both the temperature and the cycling frequency at which the tests are performed. Such effects are quantified and an ageing process is proposed in order to extend the working temperature range of the damper to cold weathers typical of the winter season in Northern Europe and Canada. A procedure for the simulation of the shape memory alloy behavior in lengthy cables by finite element analysis is eventually outlined.
Proceedings of the Second International Conference on Performance-based and Life-cycle Structural Engineering (PLSE 2015), 2015
A benchmark problem on an existing cable-stayed bridge was recently proposed. Recorded signals ar... more A benchmark problem on an existing cable-stayed bridge was recently proposed. Recorded signals are available for standard working conditions and for special events (typhoons!). In this contribution, the authors report their attempt to detect significant variations in the cable tension during these extreme events.
ABSTRACT A deeper understanding of the effectiveness of adopting devices mounting shape memory al... more ABSTRACT A deeper understanding of the effectiveness of adopting devices mounting shape memory alloy (SMA) elements in applications targeted to the mitigation of vibrations is pursued via an experimental approach. During a seismic event, less than 1000 loading-unloading cycles of the alloy are required to mitigate the earthquake effects. However, the aging effects during the time of inactivity prior to the oscillations (several decades characterized by the yearly summer-winter temperature wave) should be considered in order to avoid and/or minimize them. In this paper, the results obtained by carrying out, in different laboratories, fatigue tests on SMA specimens are compared and discussed. Furthermore, the effects of seismic events on a steel structure, with and without SMA dampers, are numerically simulated using ANSYS. Under an earthquake excitation, the SMA devices halve the oscillation amplitudes and show re-centering properties. To confirm this result, an experimental campaign is conducted by actually installing the proposed devices on a physical model of the structure and by evaluating their performance under different excitations induced by an actuator.
The EU funded SPARTACUS project pursues the implementation of a small size, low-power consumption... more The EU funded SPARTACUS project pursues the implementation of a small size, low-power consumption, tracking-unit integrating satellite receiver and antenna with terrestrial inertial sensors, enabling a dead reckoning functionality. In case of a good GNSS signal coverage, precise positioning and timing capabilities of the system are double-checked, while the positioning accuracy for dead reckoning has to be validated. In this paper, the results of field tests simulations are presented in order to validate the positioning performance in the absence of the GNSS signal. Two goals are pursued to secure tracking and functionalities customized for: (i) critical transport assets, and (ii) flow of relief support goods from the sending side to the receiving place.
The use of Shape Memory Alloys in dampers devices able to reduce the wind, rain or traffic induce... more The use of Shape Memory Alloys in dampers devices able to reduce the wind, rain or traffic induced oscillations in stayed cables is well represented in the literature. An analysis realized on standard cables at existing facilities shows the reliable efficiency of the SMA wire in damping oscillations. Such studies also provide tools to build the SMA dampers and to account for the effects of the external temperature in the SMA. The particular study reported in this paper focuses on a critical discussion on the relation between the wire diameter and macroscopic behavior and external temperature effects. The damping requires the absorption of the mechanical energy and its conversion to heat via the action of hysteresis cycles. The study was realized on wires of different diameters. In particular, the study centers on wires of diameter 0.2, 0.5 and 2.46 mm. The flat cycles showed by the thin wires (i.e., diameter 0.2 and 0.5 mm) and the non-classical S-shaped cycles of wires of diameter ...
ABSTRACT: The general topic investigated in this thesis is “structural health monitoring”, with s... more ABSTRACT: The general topic investigated in this thesis is “structural health monitoring”, with special care being devoted to damage detection and localization. The study is focused on methods which work in the space of the observed variables, where the global information measures can be used to detect the damage. In this context damage detection is demanded to global measures such as entropy or Lyapunov exponents. The comparison of these measures computed in subspaces of the observed variables or in their expansions, allows one to perform a sort of sensitivity analysis on the role of the variables involved in the problem.
Such global measures are able to detect but not to directly localize damage. For this purpose, a new approach to detect and localize the damage is formulated and implemented. It exploits response surface techniques to approximate the relationship among the observed variables. Comparing the resulting models in different damaged and undamaged situations identifies the response differences and their causes.
The response surface procedure is described from its basic theoretical aspects up to the features of its numerical implementation. Additionally, the global measures introduced above drive the analyst in establishing whether or not the problem is well posed, i.e., whether or not the set of measured quantities are able to detect the specific damage to be localized.
The validation of the proposed methodology is first numerically pursued by applying it to the benchmark case set up by the Structural Health Monitoring Panel of the American Society of Civil Engineering (ASCE). The procedure is then tested on two different experimental situations. While the first study of a three-dimensional steel frame reproduces the features of the benchmark problem, the second investigation covers a monumental structure situation, where damage is represented by more or less extended cracks in the masonry. The potential expressed by the procedure also in this second application seems to promise interesting exploitation possibilities.
the Sustainable Places 2017 (SP2017) Conference, 2017
Built to Specifications (B2S) is a Horizon 2020 EU-funded project involving 20 European partners ... more Built to Specifications (B2S) is a Horizon 2020 EU-funded project involving 20 European partners that seeks to reduce the gap between a building designed and as-built energy performance. To do this, the project will put a new set of breakthrough technological advances for self-inspection checks and quality assurance measures into the hands of construction professionals. This collection of smart tools will help building stakeholders at all levels in meeting EU energy efficiency targets.
EACS 2016 Paper No. 141<br>Infrastructures for helicopter landing, the so called heliports,... more EACS 2016 Paper No. 141<br>Infrastructures for helicopter landing, the so called heliports, are becoming more and more common. From a safety point of view, this means a clustering of helicopter trajectories with an increase of accident occurrence at the site. The surrounding buildings are subjected to a spread of vibration waves. The goal of this contribution is to investigate policies for driving these waves far from where they could cause economical losses.
In the space of design variables, a cost function is defined whose value must either be constant ... more In the space of design variables, a cost function is defined whose value must either be constant or fall within an assigned range. Also a set of scenarios against which robustness should be assessed is introduced. The result will be a robustness index dependent on both the given range of design costs and the given aggression scenarios. By adopting a Differential Evolution (DE) genetic algorithm, the zero-one (survival-failure) domains are identified in the space of the design variables. Each feasible solution, i.e., any structural design of acceptable cost satisfying the safety requirement, will then be associated with a robustness index. A numerical example is discussed in order to explain the computational details of the proposed method
A model of the human-induced actions, where the consequences of humans unpredictability, together... more A model of the human-induced actions, where the consequences of humans unpredictability, together with their response to social and psychological stimuli, are regarded as stochasticity, is developed. After defining a moving grid of nodes in the direction of the crossing, an average action per node is assigned. This value is modified by the following two contributions. A fluctuation, which involves two spatial variables and the time variable, is introduced by stochastic simulation, with a cross-spectral density function which accounts for the spatial dispersion of the single trajectories. A geometric shape function is formulated to account for a non-homogeneous spatial distribution of the pedestrians across the bridge deck. The procedure of assessing the vibrations serviceability of new footbridges requires to be thoroughly revised in light of the increased slenderness and spans achieved by using innovative construction materials of high strength (Zivanovic et al., 2005; van Nimmen e...
In this paper the data acquired on a pedestrian timber bridge under different Omovingi loads conf... more In this paper the data acquired on a pedestrian timber bridge under different Omovingi loads configurations are reported and analysed by applying a time-frequency decomposition technique. This approach allows the authors to better identify the dynamic behavior of the bridge under the above loads. A first in situ experimental campaign was carried out on November 7, 2013, with the aim of recording the accelerations induced by people walking and running along the bridge (the so called human induced vibration Ð HIV). For this purpose, the footbridge was equipped by accelerometers. The pedestrian bridge under investigation is located not far from the town of Belluno, Italy, and connects the two sides of the outlet channel of the OSanta Crocei Lake. To better fit the structure to the surrounding naturalistic area, eco-friendly construction materials with low environmental impact were adopted during the design stage. In particular glued laminated timber (GLT) and steel elements are used, l...
International Journal of Sustainable Materials and Structural Systems, 2020
This work presents an overview of some of the most promising technologies for the structural heal... more This work presents an overview of some of the most promising technologies for the structural health monitoring (SHM) of in-service tunnels. The common goal of damage or unusual behaviour detection is best pursued by an integrated approach based on the concurrent deployment of multiple technologies. Typically, traditional SHM systems are installed in problematic or special areas of the tunnels, giving information on conditions and helping manage maintenance. However, these methodologies often have the drawbacks of forcing the interruption of traffic for SHM system installation and monitoring only selected portions. Alternative solutions that would make it possible to keep the tunnel in normal operation and/or to analyse the entire infrastructure development through successive and continuous scanning stages, would be beneficial. In this paper, the authors will briefly review some traditional monitoring technologies for tunnels. Furthermore, the work is aimed at identifying alternative solutions, limiting or avoiding traffic interruptions.
Sensing devices are the main support for any experimental activity. The user expects that they ar... more Sensing devices are the main support for any experimental activity. The user expects that they are transparent, i.e., any measurement provides an assessment of a physical variable. Recent microelectronics developments caused significant modifications in the products offered by the market. Data fusion is the source of a recent jump in that technology, but the transparency of the result is no longer evident. In this paper, the authors consider the data fusion of displacement and acceleration measurements via a Kalman filter. The assemblage of two sensors is produced from scratch, and the critical aspects of the consequent data fusion are emphasized.
Long-time storage effects on shape memory alloy wires This paper is dedicated to the memory of Fr... more Long-time storage effects on shape memory alloy wires This paper is dedicated to the memory of Franz Ziegler
Recent studies were dedicated to the realization of measurements on stay-cable samples of differe... more Recent studies were dedicated to the realization of measurements on stay-cable samples of different geometry and static conditions as available at several facilities. The elaboration of the acquired data showed a a satisfactory efficacy of the dampers made of NiTi wires in smoothing the cable oscillations. A further attempt to investigate the applicability of the achieved results beyond the specific case-studies represented by the tested cable-stayed samples is herein pursued. Comparative studies are carried out by varying the diameter of the NiTi wire so that similar measurements can be taken also from laboratory steel cables of reduced size. Details of the preparation of the Ni-Ti wires are discussed with particular attention being paid to the suppression of the creep phenomenon. The resulting shape of the hysteretic cycle differs according to the wire diameter, which affects the order of the fitting polynomial to be used when trying to retrieve the experimental results by numerical analyses. For a NiTi wire of given diameter, an estimate of the amount of dissipated energy per cycle is given at low levels of maximum strain, which correspond to a fatigue fracture life of the order of millions of cycles. The dissipative capability is affected by both the temperature and the cycling frequency at which the tests are performed. Such effects are quantified and an ageing process is proposed in order to extend the working temperature range of the damper to cold weathers typical of the winter season in Northern Europe and Canada. A procedure for the simulation of the shape memory alloy behavior in lengthy cables by finite element analysis is eventually outlined.
Proceedings of the Second International Conference on Performance-based and Life-cycle Structural Engineering (PLSE 2015), 2015
A benchmark problem on an existing cable-stayed bridge was recently proposed. Recorded signals ar... more A benchmark problem on an existing cable-stayed bridge was recently proposed. Recorded signals are available for standard working conditions and for special events (typhoons!). In this contribution, the authors report their attempt to detect significant variations in the cable tension during these extreme events.
ABSTRACT A deeper understanding of the effectiveness of adopting devices mounting shape memory al... more ABSTRACT A deeper understanding of the effectiveness of adopting devices mounting shape memory alloy (SMA) elements in applications targeted to the mitigation of vibrations is pursued via an experimental approach. During a seismic event, less than 1000 loading-unloading cycles of the alloy are required to mitigate the earthquake effects. However, the aging effects during the time of inactivity prior to the oscillations (several decades characterized by the yearly summer-winter temperature wave) should be considered in order to avoid and/or minimize them. In this paper, the results obtained by carrying out, in different laboratories, fatigue tests on SMA specimens are compared and discussed. Furthermore, the effects of seismic events on a steel structure, with and without SMA dampers, are numerically simulated using ANSYS. Under an earthquake excitation, the SMA devices halve the oscillation amplitudes and show re-centering properties. To confirm this result, an experimental campaign is conducted by actually installing the proposed devices on a physical model of the structure and by evaluating their performance under different excitations induced by an actuator.
The EU funded SPARTACUS project pursues the implementation of a small size, low-power consumption... more The EU funded SPARTACUS project pursues the implementation of a small size, low-power consumption, tracking-unit integrating satellite receiver and antenna with terrestrial inertial sensors, enabling a dead reckoning functionality. In case of a good GNSS signal coverage, precise positioning and timing capabilities of the system are double-checked, while the positioning accuracy for dead reckoning has to be validated. In this paper, the results of field tests simulations are presented in order to validate the positioning performance in the absence of the GNSS signal. Two goals are pursued to secure tracking and functionalities customized for: (i) critical transport assets, and (ii) flow of relief support goods from the sending side to the receiving place.
The use of Shape Memory Alloys in dampers devices able to reduce the wind, rain or traffic induce... more The use of Shape Memory Alloys in dampers devices able to reduce the wind, rain or traffic induced oscillations in stayed cables is well represented in the literature. An analysis realized on standard cables at existing facilities shows the reliable efficiency of the SMA wire in damping oscillations. Such studies also provide tools to build the SMA dampers and to account for the effects of the external temperature in the SMA. The particular study reported in this paper focuses on a critical discussion on the relation between the wire diameter and macroscopic behavior and external temperature effects. The damping requires the absorption of the mechanical energy and its conversion to heat via the action of hysteresis cycles. The study was realized on wires of different diameters. In particular, the study centers on wires of diameter 0.2, 0.5 and 2.46 mm. The flat cycles showed by the thin wires (i.e., diameter 0.2 and 0.5 mm) and the non-classical S-shaped cycles of wires of diameter ...
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Books by Sara Casciati
Such global measures are able to detect but not to directly localize damage. For this purpose, a new approach to detect and localize the damage is formulated and implemented. It exploits response surface techniques to approximate the relationship among the observed variables. Comparing the resulting models in different damaged and undamaged situations identifies the response differences and their causes.
The response surface procedure is described from its basic theoretical aspects up to the features of its numerical implementation. Additionally, the global measures introduced above drive the analyst in establishing whether or not the problem is well posed, i.e., whether or not the set of measured quantities are able to detect the specific damage to be localized.
The validation of the proposed methodology is first numerically pursued by applying it to the benchmark case set up by the Structural Health Monitoring Panel of the American Society of Civil Engineering (ASCE). The procedure is then tested on two different experimental situations. While the first study of a three-dimensional steel frame reproduces the features of the benchmark problem, the second investigation covers a monumental structure situation, where damage is represented by more or less extended cracks in the masonry. The potential expressed by the procedure also in this second application seems to promise interesting exploitation possibilities.
Papers by Sara Casciati
Such global measures are able to detect but not to directly localize damage. For this purpose, a new approach to detect and localize the damage is formulated and implemented. It exploits response surface techniques to approximate the relationship among the observed variables. Comparing the resulting models in different damaged and undamaged situations identifies the response differences and their causes.
The response surface procedure is described from its basic theoretical aspects up to the features of its numerical implementation. Additionally, the global measures introduced above drive the analyst in establishing whether or not the problem is well posed, i.e., whether or not the set of measured quantities are able to detect the specific damage to be localized.
The validation of the proposed methodology is first numerically pursued by applying it to the benchmark case set up by the Structural Health Monitoring Panel of the American Society of Civil Engineering (ASCE). The procedure is then tested on two different experimental situations. While the first study of a three-dimensional steel frame reproduces the features of the benchmark problem, the second investigation covers a monumental structure situation, where damage is represented by more or less extended cracks in the masonry. The potential expressed by the procedure also in this second application seems to promise interesting exploitation possibilities.