Symposium FO
Embodying Intelligence in Structures and Integrated Systems


FO-1:IL01  Nonlinear Dynamics, Stabilization and Control of Nano- and Micro- Electromechanical Systems
O. Gottlieb, Mechanical Engineering Nonlinear and Chaotic Dynamical Systems Group, Technion - Israel Institute of Technology, Haifa, Israel

Nonlinear nano- and micro- electromechanical systems (NEMS/MEMS) have been studied extensively in recent years due to their promising potential for non-intrusive sensing, quantum computing and optical tweezing. Examples include micro-cantilever sensors for atomic force microscopy and nano-optomechanical resonators for light-structure interaction. While the former consist of externally modulated dynamical systems that exhibit orbital instabilities arising from both sensing and scanning, the latter are self-excited systems which exhibit non-stationary limit-cycle oscillations. To-date, these systems have been primarily modeled by single and two degree-of-freedom oscillators which cannot be used for response prediction or robust design beyond the range of their parameter estimation. Thus, in order to resolve the spatio-temporal complexity of NEMS/MEMS with multi-mode interactions we will describe a comprehensive continuum-based modeling process and its combined analytical and numerical investigation that enables construction of a robust nonlinear bifurcation structure for severe environmental conditions that are beyond the current limits of linear and weakly nonlinear phenomenological models.

FO-1:IL02  Modelling and Simulation of Electro-active Materials
A. Humer, A. Pechstein, M. Krommer, Institute of Technical Mechanics, JKU Linz, Linz, Austria

This paper is concerned with nonlinear modeling and efficient numerical simulation of electroactive materials with emphasis on field-activated electro-active polymers. Geometrical and physical nonlinearities are considered and modeling accounts for electromechanical coupling phenomena ranging from piezoelectricity and electrostriction to ferroelectricity and ponderomotive forces.
The present approach is based on multiple multiplicative decompositions of the deformation gradient tensor into a purely elastic part as well as electrical parts. The latter account for reversible electro-elasticity observed in piezoelectricity and electrostriction, but also for irreversible constitutive processes in ferroelectric materials to capture ferroelectric and buttery hysteresis. The approach is developed for finite strains, such that ponderomotive forces come into the play in addition to the coupling effects. Efficient numerical simulation is enabled through the development of novel three-dimensional mixed and discontinuous Finite Elements, by means of which complex structures with nonlinear and irreversible constitutive processes can be efficiently simulated.

FO-1:L03  Large Deformation and Hysteresis in Non-linear Electro-mechanics
A. Humer, A. Pechstein, M. KROMMER, Institute of Technical Mechanics, Johannes Kepler University, Linz, Austria

The electromechanical coupling in ferroelectric materials provides the basis for their usage as sensors and actuators. For the design of smart materials in novel engineering applications, accurate models for the evolution of the remanent polarization are required. The state of polarization changes irreversibly under sufficiently strong electric fields, but also mechanical loads may induce domain switching. Today’s composite piezoelectric transducers already allow comparatively large deformations beyond the geometrically linear range. Polymeric materials as PVDF may even require large strains to enable poling in the first place. For this reason, we transfer phenomenological models for domain switching in ferroelectric materials to the geometrically non-linear regime. In our approach, we follow the concept of a multiplicative decomposition of the deformation gradient, which is well-established, e.g., in finite strain plasticity. We introduce an additional deformation path that describes the evolution of the poled state from the unpoled reference configuration. The constitutive response is derived within a thermodynamical framework and from the principle of maximum dissipation, in which dissipative driving forces that govern changes of the remanent polarization are introduced.

FO-1:IL05  Experimental Characterization of a Smart Material via DIC
S. Casciati, D. Bortoluzzi, SIART srl, Pavia, Italy

When no extensometer is available in a generic tensile-compression test carried out by a universal testing machine (for instance a BIONIX from Material Testing Systems (MTS)), the test results only provide the relative displacement between the machine grips. The test does not provide any information on the local behavior of the material. In this contribution, the potential of an application of Digital Image Correlation (DIC) is presented, toward the reconstruction of the behavior along the specimen. In particular a Shape Memory Alloys (SMA) specimen is tested with emphasis on the coupling of the two measurement techniques.

FO-2:IL01  On the Use of Gyroscope and Accelerometer Sensors for Direct Displacement Measurements
Yizheng Liao, A.S. Kiremidjian, K. Balafas, R. Rajagopal, Stanford University, Stanford, CA, USA; H.-C. Loh, University of California San Diego, USA

In the past three decades we have seen significant hardware and software advances in new sensors, sensor networks, wireless communication, diagnostic algorithms and decision support platforms. While the field has reached certain maturity, actual deployment of advanced structural health monitoring (SHM) systems has been limited considering the multitude of structures in need of monitoring and evaluation. In addition to long-term deterioration, earthquakes, hurricanes and other natural and anthropogenic disasters pose the challenge of near real time assessment and alerts of critical infrastructure. This paper will present the design of a new wireless sensing system that combines accelerometers and gyroscopes to estimate the direct displacements due to excessive vibrations leading to impending collapse. An algorithm that combines the measurements from the accelerometers and the gyroscopes will be presented that demonstrates the estimation of the absolute maximum displacement and the residual displacement. The algorithm is tested with data obtained from tests conducted at the National Taiwan University on a three-story steel structure. Based on the measurements from the tests it is shown that excellent agreement is reached between the estimated and measured displacements.

FO-2:IL02  The Smart Potential of Vision-based Technology
L. Faravelli, Zhejiang University, Hangzhou, China; D. BORTOLUZZI, SIART srl, Pavia, Italy

The authors investigate the feasibility of applying a vision-based displacement-measurement technique in the characterization of smart materials. The reference sample is made by a Ni-Ti shape memory alloy (SMA) adopted for building a damper recently proposed in the literature. The experimental campaign tests are carried out on a universal testing machine (BIONIX from Material Testing Systems (MTS)) able to put in tension the SMA specimens. A commercial smartphone is used to collect images for analysis with Digital Image Correlation (DIC). The image acquisition rate is 10 frames per second. A system of LED markers is glued on the MTS machine grips, as well as along the SMA specimen. The MTS machine supplies information about forces at the end of the specimen and the relative displacement. The DIC process gives the relative displacements between the grips and the center of the specimen. The different phases of the test are discussed, to obtain as much information as possible on the behavior of the smart material.

FO-2:IL05  Simulation of Bending of a Plate Consisting of Shape Memory and Elastic-plastic Layers under Thermocycling after Preliminary Bending or Stretching
A.E. VOLKOV, N.A. VOLKOVA, E.A. VUKOLOV, Saint-Petersburg State University, Saint-Petersburg, Russia

A two-layer beam consisting of an elastic-plastic (or pseudoelastic) layer and a functional layer made of shape memory alloy (SMA) TiNi is considered. Constitutive relations for SMA are set by a microstructural model capable to calculate strain increment produced by arbitrary increments of stress and temperature. This model exploits the approximation of the small strains. Equations to calculate the variations of the strain and the internal variables are based on the experimentally registered kinetics of the martensitic transformations with an account of the crystallographic features of the transformation and the laws of equilibrium thermodynamics. Stress and phase distributions over the beam thickness were calculated by steps, by solving on each step the boundary-value problem for given increments of the bending moment (or curvature) and the tensile force (or relative elongation). Simplifying Bernoulli’s hypotheses were applied. The temperature was considered homogeneous over the thickness of the plate. The first stage of the numerical experiment was the simulation of preliminary deformation of the plate by bending or tension at a temperature corresponding to the martensitic state of the SMA layer. On the second stage, there was thermocyling across the temperature interval of the martensitic transformation producing the variation of the curvature. Simulations show that the range of curvature variation depends both on the total thickness of the beam and on the ratio of the layers thicknesses. The parameters of the composite beam under consideration securing the largest deflection variation are determined.

FO-3:L01  Efficient Method for Optimal Sensor Placement in Large-scale Structures
M. Ostrowski, B. Blachowski, A. Swiercz, P. Tauzowski, Institute of Fundamental Technological Research, Polish Academy of Sciences, Warsaw, Poland; P. Olaszek, Road and Bridge Research Institute, Warsaw, Poland; L. Jankowski, Institute of Fundamental Technological Research, Polish Academy of Sciences, Poland

In practice, the broadly used finite element (FE) models can have very large number of degrees of freedom (DOFs). A small subset of DOFs representing sensor locations that provides an extremum of a selected objective function corresponding to a metric of the expected measurement accuracy is sought. Thus, optimal sensor placement is characterized by its complex combinatorial nature and tremendous computational effort required. With the aid of convex relaxation, the proposed approach allows one to transform the original combinatorial problem into its continuous counterpart, which requires smaller computational effort – by a few orders of magnitude than famous Effective Independence method. The effectiveness of the method has been demonstrated using an example of a FE model of an existing railway bridge. First, the FE model has been calibrated with measured responses of the bridge under the moving load of a passing train. Then, sensor layout has been obtained in such a way that it optimises the estimate of modal coordinates of the mode shapes participating most significantly in the measured structural response.
The authors acknowledge the support of the National Science Centre, Poland (grant agreement 2018/31/B/ST8/03152).

FO-3:L02  Semi-active Decentralized Vibration Damping Strategy in Two-dimensional Frame Structures
B. Poplawski, G. Mikułowski, Ł. Jankowski, Institute of Fundamental Technological Research, Polish Academy of Sciences, Warsaw, Poland

Vibration damping is a very important aspect of engineering practice. The basic strategy of coping with vibrations is to properly design the structure, which will either eliminate or at least limit this phenomenon. When structural changes are not sufficient, a vibration damping system shall be introduced. We have developed a semi-active vibration damping system for 2D frame structures which proved to be efficient in various load conditions. Mitigation of vibration amplitudes, with very satisfying results, can be achieved both in free, as well as in forced vibrations which can have harmonic or purely random characteristics. In all cases numerical findings were confirmed with experimental investigations conducted on a similar structure, which authenticates the quality of the proposed control algorithm. Decentralization of the control system contributes to improving the safety and efficiency of the control. It also simplifies its implementation in the real structure, which is an additional advantage over the centralized control systems.
The authors acknowledge the support of the National Science Centre, Poland (grant agreement 2020/39/B/ST8/02615).

FO-3:L03  Structural Glass Panels: an Integrated System
G. Bidini, L. Barelli, C. Buratti, G. Castori, E. Belloni, E. Speranzini, University of Perugia, Department of Engineering, Perugia, Italy

In building envelope, transparent components play an important role. The structural glazing systems are the weak element of the casing in terms of mechanical resistance, thermal and acoustic insulation. In the present work, new structural glass panels with granular aerogel in interspace are investigated from different points of view. In particular, the mechanical characterization was carried out in order to assess the resistance to bending of the single glazing pane. To this end, a special instrument system was built to define an alternative configuration of the coaxial double ring test, able to predict the fracture strength of glass large samples (400x400 mm) without overpressure. The thermal and lighting performance of an innovative double glazing façade with granular aerogel was evaluated. An experimental campaign at pilot scale was developed: it is composed of two boxes of about 1.60 m x 2 m x 2 m high and of an external weather station. The rooms, identical in terms of size, construction materials, and orientation, are equipped with a two-wing window in the south wall surface: the first one has a standard glazing solution (double glazing with air in interspace), the second room is equipped with the innovative double glazing system with aerogel. The indoor mean air temperature and the surface temperature of the glass panes were monitored together with the illuminances for the lighting characterization. Finally, a brief energy characterization of the performance of the material was carried out by means of dynamic simulation models.

FO-3:IL04  Adaptive Stiffness Structural Systems: State of the Art and Practice
S. Nagarajaiah, Rice University, Houston, TX, USA

This seminar focuses on the state of art and practice of adaptive stiffness structural systems around the world. The talk will include details of recent developments and applications of seismic isolation, adaptive passive stiffness and damping systems, and uplift systems, and smart tuned mass dampers. Base isolation is widely accepted technology, which has protected critical structures around the world. Nonlinear dynamic analysis techniques developed to analyze large base isolated structures and its impact is presented. The successful performance of seismic isolated structures in recent earthquakes is presented in detail—made possible by system identification and structural monitoring systems in place to monitor their performance in large earthquakes. Recent developments and applications of large scale tuned mass dampers for earthquake/wind protection is presented. Recent advances in development of adaptive passive stiffness systems for seismic protection is presented. Analytical and experimental results of adaptive stiffness systems in structures are presented to show the effectiveness of the new and innovative concept of adaptive negative-positive tangential stiffness, which provides significant earthquake/wind protection, while keeping the primary system essentially elastic or mildly inelastic in strong earthquakes/winds—thus preventing significant damage experienced in traditional structures.

FO-4:IL01  Provisions for Passive Control Devices in the New Eurocode 8
C.Z. Chrysostomou, Cyprus University of Technology, Limassol, Cyprus

Structural Eurocodes are undergoing revision for the last few years. This revision is at its fourth and final phase, and it is expected that by 2025 the new versions of all Eurocodes will be made available to practicing engineers. Eurocode 8 (EN1998), which is the code for the Design of Structures for Earthquake Resistance, is also undergoing revision. One significant change in this revision is the parts for the design of passive control devices, which include provisions for base isolation and energy dissipation systems. In this paper the new structure of Eurocode 8 is presented concentrating on the provisions for base isolation and energy dissipation of new buildings in EN1998 Part1-1: General rules and seismic action, and in EN1998 Part 1-2: Rules for new buildings.
Reference will be also made to the provisions for such devices in other EN1998 parts.

FO-4:IL02  Some Aspects in Managing Smart Cities
R. DE LOTTO, University of Pavia, Department of Civil Engineering and Architecture, Pavia, Italy

Starting from the most recent debate regarding “smart” and “clever” cities, in the intervention author focuses on the practical and effective instruments and policies that surely will have a wide application in the future of worldwide urban context. The first deepening is purely theorical and regards the relation between the classical smartness definition in relation with the Agenda 2030 objective of Sustainability. Even if the complex relation (and sometimes the conflicts) among all these element may conduce very far from practical and realistic urban actions, it is extremely relevant to define the temporal framework in which these objectives and aims are inserted: for sure, smartness is based on a very “fast” idea of transformation, while sustainability is a long lasting group of objectives and targets. From another point of view, “smart city” is a synonymous of “technological city”; the most widespread idea is the application of advanced technological devices in everyday life. This is only a superficial way to look at the real smartness (or cleverness) of the urban settlements. It is true that some metropolis, such as Singapore and Taipei, are running to be considered the smartest cities in the world, and the use of big data assumed an extremely relevant role in the last years. One of the basic questions that should be put in the debate is: are these technological elements able to rise up the quality of life in the city?  There is a very interesting OECD database, the “Better life index”, that demonstrates how much some principles or aspects that city planners and architects consider relevant are, in peoples’ perception, not so important. Apart from the well-known separation between real data and perception, is it obvious that many opportunities (given by technological devices) may help well-structured behaviors to be more incisive but rarely they change the everyday life, but in long time (i.e. Google Navigator for traffic management, social media for personal information about relevant spaces of the city, etc.). Moreover, the idea of the city as spatial pattern is changing in its functions (dimension and density), in its relation between open and built spaces, in synthesis its basic structure because of the pandemic Covid-19. In conclusion, they will be defined possible scenarios of development of new technologies, that can delineate a city as “smart”, that will be more and more useful in the very next future.

FO-4:L03  Monitoring the Building Response during Borehole Excavation

The European project GEOFIT (Deployment of novel GEO-thermal systems, technologies and tools for energy efficient building retrofitting) is gathering more than 20 partners from all across Europe. The building structural monitoring is a quite important aspect within advanced geothermal based retrofitting methods. This paper presents a survey of the results achievable by standard accelerometric measurements as compared with those obtained by a Geo-radar system. This contribution focuses on the structural monitoring of a reinforced concrete building during the drilling phase necessary for borehole excavation.

FO-4:IL05  Rail Bolt Joint Looseness Monitoring Using PZT Sensing Network
Lu Zhou1,2, Yi-Qing Ni1,2, 1Hong Kong Branch of National Transit Electrification and Automation Engineering Technology Research Center, The Hong Kong Polytechnic University, Hong Kong, China; 2Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China

The degradation of wheel tread may result in serious hazards in the railway operation system. Therefore, timely wheel defect diagnosis of in-service trains to avoid tragic events is of particular importance. The focus of this study is to develop a novel wheel defect detection approach based on the relevance vector machine (RVM) which enables online detection of potentially defective wheels with trackside monitoring data acquired under different running speed conditions. With the dynamic strain responses collected by a trackside monitoring system, the cumulative Fourier amplitudes (CFA) values characterizing the effect of individual wheels are extracted to formulate multiple probabilistic regression models (MPRMs) in terms of multi-kernel RVM, which integrate two variables of vibration frequency and running speed. Compared with the general single-kernel RVM-based model, the proposed multi-kernel MPRM approach bears better local and global representation ability, generalization performance, and model simplicity in regard to the problem addressed. After the formulation of MPRMs, we adopt a Bayesian null hypothesis indicator for wheel defect identification and quantification, and the proposed method is demonstrated by utilizing the real-world monitoring data acquired by an FBG-based trackside monitoring system deployed on a high-speed trial railway. The results testify the validity of the proposed method in wheel defect detection under various running speed conditions.


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