- Risk and Vulnerability, Smart Materials, Mechanics of Materials, Solid Mechanics, System Identification, Shape Memory Alloys, and 34 moreStructural Reliability, Fatigue, Nonlinear dynamics, Optimization techniques, Structural Dynamics, Reliability-Based Optimization, Structural Health Monitoring, Vibration Control, Smart Structure, Damage detection, Dynamical Systems, Civil Engineering, Mechanical Behavior Of Materials, Vibrations, Materials Characterisation, Structural Analysis, Applied Mathematics, Evolutionary algorithms, Earthquake Engineering, Active Vibration Control, Engineering Mechanics, Continuum Mechanics, Soil-Structure Interaction, Finite Element Methods, Fracture Mechanics, Mechanics of Fracture, Fatigue and Damage, Structural Control, Computational Mechanics, Applied Mechanics, Structural Engineering, Finite Element Analysis (Engineering), Monument Preservation, Conservation and protection of monuments, and Wireless Sensor Networksedit
- (Born 2 September 1977,Pavia, Italyedit
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... 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.
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.
Research Interests: Civil Engineering, Mechanics, Numerical Simulations, Statistics, Engineering Mechanics, and 48 moreStructural Engineering, Multivariate Statistics, Sensors and Sensing, System Identification, Signal Processing, Wireless Communications, Computational Mechanics, Traffic Simulation, Vibrations, Vibrational dynamics, Applied Statistics, Structural Dynamics, Time Series, Sensor, Nonlinear dynamics, Nonlinear Time Series, Wireless Sensor Networks, Response Surface Methodology, Experimental Mechanics, Solid Mechanics, System Dynamics, Numerical Analysis, Bridge Engineering, Structural Health Monitoring, Damage detection, Applied Mechanics, Spatial Statistics, Experimental Physics, Regression Models, Steel Structure, Numerical Modelling, Wireless networks, Vibration, Benchmarking, Time series analysis, Applied Numerical Methods in Engineering, Cracked Media, Crack detection, Steel Structures, Braces, Masonry, Frame Analysis, Bifurcation, vibration based methods for Structural Health Monitoring (SHM), Retrofitting and Strengthening of Structures, Time Series Data, Multiple Linear Regression, and Stability and Chaos
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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... 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.
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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... 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
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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... 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...
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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... 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...
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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... 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.
Research Interests: Engineering, Materials Science, Thermodynamics, Structural Engineering, Computational Mechanics, and 12 moreVibrations, Numerical Analysis, Vibration Control, Materials Science and Engineering, Thermomechanical Analysis, Experimental Analysis of Behavior, Shape Memory Alloys, Cable-Stayed Bridges, Energy Dissipation, Nickel Titanium, Wire And Cable Materials, and Damper
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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,... 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.
Research Interests: Engineering, Materials Engineering, Civil Engineering, Materials Science, Dynamical Systems, and 15 moreEarthquake Engineering, Advanced materials in architecture, Experimental Mechanics, Materials, Materials Characterisation, Applied Mechanics, Mechanical Behavior Of Materials, Fatigue, Materials Science and Engineering, Dissipative Systems, Dampers, Laboratory experiment, Hysteretic energy dissipation capacity, Earthquake Resistance, and Damper
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... 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.
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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... 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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The design of a control law requires two preliminary actions: to introduce a numerical model of the system to be controlled, together with its reduced‐order approximation, and to fix the number and positions of the actuators, together... more
The design of a control law requires two preliminary actions: to introduce a numerical model of the system to be controlled, together with its reduced‐order approximation, and to fix the number and positions of the actuators, together with those of the sensors providing the feedback. The link between measured acceleration quantities and model variables was successfully demanded to the Kalman filter in seismic applications. When moving to wind excitation, the standard approach is no longer viable, and one meets several options, which are discussed in the paper. A timber footbridge is studied to provide a numerical example. Copyright © 2015 John Wiley & Sons, Ltd.
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Research Interests: Engineering, Civil Engineering, Earthquake Engineering, Vibration Control, Structural Health Monitoring, and 15 moreStructural Control, Seismic Retrofit, Adaptivity, Decentralized Control, Control Management, Seismic Isolation, Piezoelectricity, Multidisciplinary Approach, Hybrid Control, Shape Control, Pedestrian Bridges, Damper, Building envelopes, Magnetorheological Damper, and Shake table tests
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Research Interests: Engineering, Civil Engineering, Computational Physics, Engineering Mechanics, Computational Mechanics, and 15 moreComputational Materials Science, Construction Materials, Computational Modeling, Concrete, Applied Statistics, Computational Statistics, Computational Modelling, A Priori Knowledge, Finite Element, Crack propagation, Cross Correlation, Correlation, Discontinuity, Carrying Capacity, and Bending Test
The problem of cleaning structural monitoring data from thermal effects has been studied since the pioneering developments in this area. The first attempts approached the problem in a statistical way, in terms of time history... more
The problem of cleaning structural monitoring data from thermal effects has been studied since the pioneering developments in this area. The first attempts approached the problem in a statistical way, in terms of time history correlations. The availability of powerful numerical tools able to solve the thermo-mechanical stress-strain analysis suggests pursuing a dynamic modeling approach. However, defining boundary conditions and assigning the initial conditions can be problematic. Some aspects of such an analysis are discussed in this paper and a proposed procedure is exemplified with reference to an existing railway bridge.
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EACS 2016 Paper No. 140<br>Elaborations from an experimental campaign on a footbridge are re-elaborated. After the parameters of a consistent numerical model have been calibrated, recorded signals and numerical analyses are... more
EACS 2016 Paper No. 140<br>Elaborations from an experimental campaign on a footbridge are re-elaborated. After the parameters of a consistent numerical model have been calibrated, recorded signals and numerical analyses are exploited in view of improving the structural monitoring features adopted up to now. The transient character of human crossing is demanded to a further suitable numerical model. As an ultimate target of the investigation, the potential of simple structural control schemes on the cable tension is discussed.
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A dynamic laboratory test was carried out on a single-storey frame model placed on a shaking table. Measures were collected by a traditional scheme based on accelerometers installed on the storey and the basis of the frame structure, and... more
A dynamic laboratory test was carried out on a single-storey frame model placed on a shaking table. Measures were collected by a traditional scheme based on accelerometers installed on the storey and the basis of the frame structure, and by an innovative device, the SOFO dynamic system, which is based on long-gauge fiber-optic sensors installed in two different locations along one of the columns of the frame structure. The use of long-gauge strain sensors allows the detection of local damage that is visible in the global frequency response of the structure. In particular the fiber-optic sensors show a very high sensitivity and extend the frequency range (1mHz-1KHz). The peculiar contribution of this paper is to conduct an elaboration of the measured data through the damage detection scheme recently proposed by the first author. It is based on the idea of using a response surface model of the measure correlation for damage detection and localization.
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ABSTRACT 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... more
ABSTRACT 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
ABSTRACT When compared to wired sensor technology, wireless sensor technology often suffers long data collection delay, big noise floor and data loss. Addressing these challenges, a wireless data acquisition system was designed and... more
ABSTRACT When compared to wired sensor technology, wireless sensor technology often suffers long data collection delay, big noise floor and data loss. Addressing these challenges, a wireless data acquisition system was designed and implemented by the authors. It can provide a performance comparable to the one of a wired data acquisition system. In this paper, the system is validated by its application in the monitoring of a timber pedestrian bridge in Italy. The system features flexible sensor interfaces, high power efficiency, low noise data acquisition, real-time and lossless wireless data transmission, and a convenient graphical user interface. Two field experiments were conducted. In the first experiment, the wireless data acquisition unit was designed to use an unreliable communication mode, resulting in an underestimated data loss problem. In the second experiment, the system is improved. The ACK-RETRIES reliable communication mode and a data packet sequence number checking mechanism are adopted, so that the data loss was avoided. For a comparison, a wired portable data acquisition system VSS-3000 was also used to acquire data from one accelerometer. The results show that the wireless data acquisition system is able to acquire high quality data from low noise sensors in real time without data loss. Compared to the VSS-3000, the data acquired by the wireless sensor platform have a comparable and even better quality.
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ABSTRACT The availability of a suitable data acquisition sensor network is a key implementation issue to link models with real world structures. Non-contact displacement sensors should be preferred since they do not change the system... more
ABSTRACT The availability of a suitable data acquisition sensor network is a key implementation issue to link models with real world structures. Non-contact displacement sensors should be preferred since they do not change the system properties. A two-dimensional vision-based displacement measurement sensor is the focus of this contribution. In particular, the perspective distortion introduced by the angle between the optic axis of the camera and the normal to the plane in which the structural system deforms is considered. A two-dimensional affine transformation is utilized to eliminate the distortion from the recorded to the distortion-free image. The results of a laboratory experiment show the potential of the proposed approach.
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ABSTRACT The identification of those differences between the current behavior and the initial state of a structure which are indicative of the presence of damage is one of the aims of structural health monitoring. Since the last decades,... more
ABSTRACT The identification of those differences between the current behavior and the initial state of a structure which are indicative of the presence of damage is one of the aims of structural health monitoring. Since the last decades, considerable research advances have been conducted in the optimization field. In this paper, an objective function that minimizes the discrepancies between the analytical and the experimental modal features obtained from the measurements of the actual dynamic response of a structure is formulated. Once the stiffness parameters are set as design variables, the firefly algorithm is applied to carry out the iterations toward the global minima. Partial solutions are analyzed along different steps of the procedure and identified as local optima by calculating the new stiffness matrices and estimating the corresponding values of the objective function. Eventually, the damage detection and localization are pursued by the comparison between the stiffness matrix identified once the optimization process is finished and the starting one. This procedure is applied to a numerical example, which is representative of a generic structure meshed into finite elements where damage is introduced as a local stiffness reduction.
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ABSTRACT Several solutions have been proposed to mitigate the vibrations of stay cables in bridges, which are subjected to wind, rain and traffic loads. One possible solution relates to the use of semi-active devices, such as the ones... more
ABSTRACT Several solutions have been proposed to mitigate the vibrations of stay cables in bridges, which are subjected to wind, rain and traffic loads. One possible solution relates to the use of semi-active devices, such as the ones based on magneto-rheologic fluids. These devices need guaranteed electrical power, together with computational effort and technical attention. In contrast, shape memory alloy (SMA) wires were studied for application as passive elements. In the present work, the properties of SMA that are required to realize dampers provided with an appropriate reliability are discussed. In particular, the fatigue/fracture life of the SMA wires and the thermal effects induced by both external temperature and the self-heating process are studied. The SMA dampers were applied to stayed cables of realistic size and tested in &quot;facilities.&quot; Namely, the cables No 1 of 45 m length available at the ELSA-JRC in Ispra, Italy, and the 50 m cable of IFSTTAR near Nantes, in France, were considered. The experimental results establish a reduction of the vibration amplitude to one half or less than the one observed in the un-damped case. Furthermore, the installation of the SMA dampers causes an increase of the cable frequency. Performing a Windowed Fourier Transform or a Wavelet Transform analysis the evolution of frequency with the signal amplitude was studied. The change of amplitude produces a change of stiffness in the SMA. The adoption of an appropriate phenomenological model of the hysteresis cycle permits to perform numerical simulations using standard Finite Elements Analysis tools such as, for instance, the ANSYS software.
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ABSTRACT The application of Shape Memory Alloy (SMA) devices to practical uses need well established performance. The reliable application in some areas, as dampers in engineering, needs a known, relatively long fatigue life (some million... more
ABSTRACT The application of Shape Memory Alloy (SMA) devices to practical uses need well established performance. The reliable application in some areas, as dampers in engineering, needs a known, relatively long fatigue life (some million oscillations). The thermomechanical properties of SMA, based on their martensitic transformation, made them attractive to use for damping, taking advantage of the pseudoelastic window and hysteresis on transforming-retransforming. Due to size effects and to the fact that fatigue failure in metallic NiTi usually comes from a defect inducing crack growth, fatigue has to be studied for concrete applications, with the correct samples. The present work points out the possibility to apply NiTi to dampers and actuators. Testing machine experiments indicate that the main parameter controlling fatigue life is the effective stress on the NiTi wire. Long wire life (in the million cycle regime) can be achieved under limited stresses (around or under 200 MPa). Also, experiments have been done on thermal actuation of NiTi wire under traction at constant load. The results demonstrate that long actuator life (larger than 300000 cycles) can be achieved at low stresses (around 100 MPa), coherently with the mechanical cycling. From our results, NiTi is useful to effectively damp vibrations even at relatively low stresses and strains. The experimental results from facilities (cable No. 1 in ELSA-JRC, Ispra, Italy, and IFSTTAR test cable, near Nantes, France) confirm that NiTi wire is able to damp stayed cables.
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ABSTRACT The authors have access to an existing laboratory facility which has been used to validate different control schemes. The three-storey steel frame is mounted on a single-axis shaking table simulating the ground excitation. Four... more
ABSTRACT The authors have access to an existing laboratory facility which has been used to validate different control schemes. The three-storey steel frame is mounted on a single-axis shaking table simulating the ground excitation. Four single-axis wired accelerometers were mounted on each level (ground and floors of the frame). A mass cart driven by a DC motor, a DC motor position analog controller, and a controller board complete the early bed-test realization. Recently wireless sensor links and a digital position controller were introduced to update the AMD performance. In this paper the frame specimen is simulated by a numerical model allowing the authors to design and test the control laws without any risk of damaging the physical model.
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ABSTRACT The authors have access to an existing laboratory facility which has been used to validate different control schemes. The three-storey steel frame is mounted on a single-axis shaking table simulating the ground excitation. Four... more
ABSTRACT The authors have access to an existing laboratory facility which has been used to validate different control schemes. The three-storey steel frame is mounted on a single-axis shaking table simulating the ground excitation. Four single-axis wired accelerometers were mounted on each level (ground and floors of the frame). A mass cart driven by a DC motor, a DC motor position analog controller, and a controller board complete the early bed-test realization. Recently wireless sensor links and a digital position controller were introduced to update the AMD performance. In this paper the frame specimen is simulated by a numerical model allowing the authors to design and test the control laws without any risk of damaging the physical model.