This paper describes several interferometric techniques and their applications in structural damage identification. With that objective in mind, damaged aluminum beams with clamped-free and free-free boundary conditions are analyzed. Different damages cases are inflicted by creating small cuts perpendicular to the beams longitudinal axis, being the damage, therefore, characterized by the dimensions of these cuts. The out-of-plane displacement field of modal response is measured with an electronic speckle pattern interferometric system. The static and dynamic rotation fields, defined as the spatial derivative of the displacement field, are measured with two different speckle shearography systems. Second and third order spatial derivatives of the displacement field, which are related to the bending moment and shear force, are computed by differentiation techniques. The cuts locations are determined by looking for maximum values and/or perturbations of damage indicators based on bending moments and shear forces. This method is validated by comparing its results with numerical ones, from which the most suitable interferometric technique is chosen.

H. Lopes

J. Ribeiro

J.V. Ara&#xfa;jo dos Santos

Interferometric Techniques in Structural Damage Identification

A highly efficient seismic protection of bridges have been demonstrated by the passive control systems with mechanical links with selective viscoelastic energy dissipation through viscous friction and dry friction. These systems are able to take over the deformations and movements caused by temperature variations, those due to seismic activities and from road traffic. A number of natural factors such as atmospheric and anthropogenic parameters, such as shock and vibration from road traffic, lead to the degradation of the viscoelastic bonds of passive control systems based on rubber molding. The presence of the elastic and dissipative nonlinear forces in the functioning of antiseismic systems inevitably leads to quantitative and qualitative changes of the structural responses of bridges and viaducts both in time and spectral domains. The implications of these changes on the integrity and stability of the bridge or viaduct sections may be from the simplest to the most severe depending on the type of seismic excitation to which they are subjected. For these reasons, it is imperative that we should identify and quantify the degree of nonlinearity of antiseismic systems embedded in the structure of bridges and viaducts in order to prevent accidents with severe socioeconomic implications. In this way can determine the dependence of the nonlinear behavior of the bearing system and the degree of degradation of their viscoelastic links. From a theoretical point of view the following parameters of the vibration of the system will be comparatively analyzed: the displacement and acceleration of the bridge deck in time and frequency domains, the hysteretic loop, the representation in the plane of phases, the power spectral density and the spectrograms of the acceleration signals. From an experimental point of view there will be identified and plotted the parameters able to provide information regarding the abnormal operation of the bearings from the elastomer: system acceleration, representations in time and frequency and its spectrogram.

A. Leopa

S. Nastac

C. Debeleac

Numerical and Experimental Testing of Normality in the Functioning of the Bearings System

A piezoelectric cantilever type sensor for locating the precise weak-impact or touch position on a plate is presented in this paper. Since the importance of human-computer interface such as a touch panel system has been rapidly increasing recently, this study could suggest an appropriate sensor for the detection of a weak-impact point effectively and accurately for such a system. This sensor detects the out-of-plane vibration of a panel when a touch with a finger or pen is applied on it. The sensor is made with a steel beam and a single crystal PMN-PT patch is bonded on the beam, which is designed to detect the base vibration of the panel. The sensor was designed, manufactured to verify the detect ability of a weak-impact and attached on two different plates of a glass of 400 &#xd7; 400 &#xd7; 4 mm and a wooden MDF of 600 &#xd7; 600 &#xd7; 9 mm. The experiment result of the sensor was compared with that of an accelerometer which can also be used for the same purpose and shows clear weak-impact responses with a narrow-band property at its resonant frequency. It is expected that the cantilever type sensor in this study could be applied to make a simple flat plate into a touch panel when the time difference of arrivals method is used to locate the weak-impact point.

Young-Sup Lee

Sang-Kwon Lee

Kihong Shin

Piezoceramic Cantilever Sensor Design for Weak-Impact Detection on Plates

The vibration and damping characteristics of an assembled structure made of steel are investigated by an experimental modal analysis and compared with the results of a finite element modal analysis. A generic experiment is carried out to evaluate the stiffness and the damping properties of the structure's join patches. Using these results, an appropriate finite element model of the structure is developed where the join patches are represented by thin-layer elements containing material properties which are derived from the generic experiment's results. The joint's stiffness is modeled by orthotropic material behavior whereas the damping properties are represented by the model of constant hysteresis, leading to a complex-valued stiffness matrix. A comparison between the experimental and the numerical modal analysis shows good agreement. A more detailed damping model in conjunction with an optimization procedure for the joint's parameters results in an improved correlation between the experimental and the numerical modal quantities and reveals that the results of the generic experiment are sound.

A. Schmidt

S. Bograd

L. Gaul

Measurement of Join Patch Properties and Their Integration into Finite-Element Calculations of Assembled Structures

Design of Satellite Attitude Control System (ACS) that involves plant uncertainties and large angle manoeuvres following a stringent pointing control, may require new non-linear control techniques in order to have adequate stability, good performance and robustness. In that context, experimental validation of new non-linear control techniques through prototypes is the way to increase confidence in the controller designed. The Space Mechanics and Control Division (DMC) of INPE is constructing a 3-D simulator to supply the conditions for implementing and testing satellite ACS hardware and software. The 3-D simulator can accommodate various satellites components; like sensors, actuators, computers and its respective interface and electronic. Depending on the manoeuvre the 3-D simulator plant can be highly non-linear and if the simulator inertia parameters are not well determined the plant also can present some kind of uncertainty. As a result, controller designed by linear control technique can have its performance and robustness degraded, therefore controllers designed by new non-linear approach must be considered. This paper presents the application of the State-Dependent Riccati Equation (SDRE) method in conjunction with Kalman filter technique to design a controller for the DMC 3-D satellite simulator. The SDRE can be considered as the non-linear counterpart of Linear Quadratic Regulator (LQR) control technique. Initially, a simple comparison between the LQR and SDRE controller is performed. After that, practical applications are presented to address problems like presence of noise in process and measurements and incomplete state information. Kalman filter is considered as state observer to address these issues. The effects of the plant non-linearities and noises (uncertainties) are considered in the performance and robustness of the controller designed by the SDRE and Kalman filter. The 3-D simulator simulink-based model has been developed to perform the simulations examples to investigate the SDRE controller performance using the states estimated by the Kalman filter. Simulations have demonstrated the validity of the proposed approach, once the SDRE controller has presented good stability margin, great performance and robustness.

L.C.G. Souza

R.G. Gonz&#xe1;les

Application of the State-Dependent Riccati Equation and Kalman Filter Techniques to the Design of a Satellite Control System

Acoustic Emission (AE) techniques are used for the structural health monitoring of civil, aeronautic and aerospace structures. Recently, these structures are made of composite materials due to their advantages over traditional materials, but this increases the interpretation complexity of the failure modes present. Therefore, in order to make AE a trustworthy technique, reliable source location and damage mechanism characterization must be accomplished. On that account, this work proposes a novel approach based on a chirplet atomic decomposition, time-frequency energy distribution and dispersion analysis, where the failure-emitted signals are separated from extraneous noise and the detected modes are analyzed according to their dispersive behaviour and angular dependence characteristics. Dispersion relations are obtained by the use of a higher order plate theory on a non-absorbing anisotropic plate model, and then used in conjunction with the previous methodologies for mode identification and localization. The proposed methodology and model are validated, and the capability of the method to overcome practical issues encountered in AE testing is demonstrated experimentally.

M.A. Torres-Arredondo

C.-P. Fritzen

Characterization and Classification of Modes in Acoustic Emission Based on Dispersion Features and Energy Distribution Analysis

A wavelet based approach is proposed in this paper for analysis and optimization of the dynamical response of a multilayered medium subject to a moving load with respect to the material properties and thickness of supporting half-space. The investigated model consists of a load moving along a beam resting on a surface of a multilayered medium with infinite thickness and layers with different physical properties. The theoretical model is described by the Euler-Bernoulli equation for the beam and the Navier's elastodynamic equation of motion for a viscoelastic half-space. The moving load is modelled by a finite series of distributed harmonic loads. A special method based on a wavelet expansion of functions in the transform domain is adopted for calculation of displacements in the physical domain. The interaction between the beam and the multilayered medium is analyzed in order to obtain the vibration response at the surface and the critical velocities associated. The choice of the specific values of the design parameters for each layer, which minimize the vibration response of the multilayered medium, can be seen as a structural optimization problem. A first approach for using optimization techniques to explore the potential of the wavelet model is presented and briefly discussed. Results from the analysis of the vibration response are presented to illustrate the dynamic characterization obtained by using this method. Numerical examples reflecting the results of numerical optimizations with respect to a multilayered medium parameters are also presented.

Piotr Koziol

M.M. Neves

Multilayered Infinite Medium Subject to a Moving Load: Dynamic Response and Optimization Using Coiflet Expansion

The Attitude Control System (ACS) for Flexible Space Structures (FSS) like rigid-flexible satellite and solar sails demands great reliability, autonomy and robustness. The association of flexible motion and large angle maneuver imply that the FSS dynamics is only captured by complex non-linear mathematical model. As a result, FSS controller performance designed by linear control technique under the hypothesis of rigid dynamic can be degraded. Although vibrations can be suppressed rapidly, the flexibility effect can introduce a tracking error resulting in a minimum attitude acquisition time. On the other hand, faster manoeuvres can excite flexible modes in such a way to make the FSS lose the required pointing accuracy. In the present work, it is shown that a new multi-objective optimization algorithm, called M-GEOreal (Multi-objective Generalized Extremal Optimization with real codification), is a good tool to be used in such kind of problems. The M-GEOreal is a real coded version of the M-GEO evolutionary algorithm. Its performance on finding the gains of a non linear control law is evaluated through its application to the problem of controlling a large angle attitude manoeuvre of a rigid-flexible satellite.. The satellite non-linear model consists of a rigid central hub with a clamped free flexible beam. The multi-objective approach allows optimizing conflicting objective functions like time and energy. As a result, one can find a trade-off solution (non-dominated solutions). These solutions become available to the designer for posterior choice of an individual solution to be implemented. The non-dominated solutions are represented in the design space (Pareto set) and in the objective functions space (Pareto front). Having in mind the complexity of implementing a control algorithm in onboard satellite computer, this preliminary investigation has shown that the non-linear controller based on the M-GEOreal algorithm is a promising technique, since it has satisfied all the ACS requirements. A great advantage of the M-GEOreal procedure is its capacity to deal with non-linear system and designing non-linear controller with constant gains facilitating the on board computer implementation.

I. Mainenti-Lopes

F.L. De Sousa

Design of a Nonlinear Controller for a Rigid-Flexible Satellite Using Multi-Objective Generalized Extremal Optimization with Real Codification

Corrosion is a long-term process resulting in the deterioration of the reinforced concrete (RC) structures. Most of the structural problems observed under the impact of either earthquakes or service loads might occur due to corrosion. Therefore, prediction of the remaining service life of a corroding RC structure plays an important role to prevent serious premature damage. In this study, a corroded, 25-year-old high school building which has been demolished at an earlier time was analyzed as a function of corrosion rate. Bond-slip relationships were taken into account in nonlinear analyses as a function of corrosion rate for different time periods (i.e., non-corroded (t: 0), existing (t: 25) and 50 years after construction); and they were used to ensure the effect of time-dependent slip rotation on the global structural behaviour by modifying the target post-yield stiffness of each structural member. Nonlinear push-over analyses were performed by defining the time-dependent plastic hinge properties as a consequence of corrosion effects. In order to define the performance levels of three different time periods, nonlinear incremental dynamic analyses (IDA) were performed for 20 earthquake ground motion records as a function of corrosion rate. Results showed that bond-slip relationship between concrete and steel is very important in evaluating the non-linear behaviour of corroded RC structures.

Hakan Yalciner

Serhan Sensoy

Ozgur Eren

Effect of Corrosion Damage on the Performance Level of a 25-Year-Old Reinforced Concrete Building

Before establishing the priority settings for the reduction of seismic risk of water supply infrastructures, it is necessary to understand the dynamic behavior of elevated water tanks, which are components of those infrastructures. Among other information, the main frequencies of vibration of these structures must be estimated and the analytical models used in their analysis and design should reproduce the frequency values obtained by in-situ dynamic tests. This work focuses exclusively on reinforced concrete (RC) elevated water tanks (200&#x2013;750 m^3 of water at heights of 30&#x2013;40 m), which are very common structures in the water supply systems in Portugal since the mid XXth century. This type of structures can also be seen in many regions around the world. First, a nationwide survey was conducted to determine the most common typologies in the country in terms of structural layout. Second, an in-situ campaign using ambient vibration as input was performed for a group of selected structures to determine the main frequencies of vibration and to identify modal shapes and damping values. Third, a finite element model of several different typologies was developed using the water simply as a concentrated mass at the top; the elastic properties of the model of the structure including the foundation were calibrated, so that the frequencies of various mode shapes obtained by the analytical model would match the frequencies of the real structure. Finally, an expression was derived to estimate the fundamental frequency of a group of elevated water tank typologies based on the total mass at the top of the supporting structure, which include the water, the global lateral stiffness, and the height of the tank. This study, providing important information on the frequencies of vibration of RC-elevated water tanks, contributes in a definite way to the analysis and design of such water tanks.

H.M. Lopes

C.S. Oliveira

Use of In-Situ Dynamic Measurements to Calibrate Analytical Models of RC-Elevated Water Tanks

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Shock and Vibration publishes papers on all aspects of shock and vibration, especially in relation to civil, mechanical and aerospace engineering applications, as well as transport, materials and geoscience.&nbsp;

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Chief Editor&nbsp;Dr Tai Thai&nbsp;is based at the University of Melbourne and his current research focuses on high strength materials for sustainable construction of buildings, bridges and other infrastructure.

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