Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / A experiência dos engenheiros estruturais e os conhecimentos adquiridos pelo uso de materiais e novas tecnologias, têm ocasionado estruturas de aço e mistas (aço-concreto) de passarelas cada vez mais ousadas. Este fato tem gerado estruturas de passarelas esbeltas, e consequentemente, alterando os seus estados de limite de serviço e último associados ao seu projeto. Uma consequência direta desta tendência de projeto é o aumento considerável das vibrações das estruturas. Portanto, a presente investigação foi realizada com base em um modelo de carregamento mais realista, desenvolvido para incorporar os efeitos dinâmicos induzidos pela caminhada de pessoas. O modelo de carregamento considera a subida e a descida da massa efetiva do corpo em cada passo. A posição da carga dinâmica também foi alterada de acordo com a posição do pedestre sobre a estrutura e a função do tempo gerada, possui uma variação espacial e temporal. O efeito do calcanhar do pedestre também foi incorporado na análise. O modelo estrutural investigado baseia-se em uma passarela tubular (aço-concreto), medindo 82,5m. A estrutura é composta por três vãos (32,5 m, 20,0 m e 17,5 m, respectivamente) e dois balanços (7,5 m e 5,0 m, respectivamente). O sistema estrutural é constituído por perfis de aço tubular e uma laje de concreto, e é atualmente utilizada para travessia de pedestres. Esta investigação é realizada com base em resultados experimentais, relacionando a resposta dinâmica da passarela com as obtidas via modelos de elementos finitos. O modelo computacional proposto adota as técnicas de refinamento de malha, usualmente presente em simulações pelo método de elementos finitos. O modelo de elementos finitos foi desenvolvido e validado com resultados experimentais. Este modelo de passarela tubular permitiu uma avaliação dinâmica completa, investigando especialmente ao conforto humano e seus limites de utilização associados à vibração. A resposta dinâmica do sistema, em termos de acelerações de pico, foi obtida e comparada com os valores limites propostos por diversos autores e padrões de projeto. As acelerações de pico encontradas na presente análise indicou que a passarela tubular investigada apresentou problemas relacionados com o conforto humano. Por isso, foi detectado que este tipo de estrutura pode atingir níveis de vibrações excessivas que podem comprometer o conforto do usuário na passarela e especialmente a sua segurança. / The structural engineers experience and knowledge allied by the use newly developed materials and technologies have produced steel and composite (steel-concrete) footbridges with daring structures. This fact have generated very slender structural footbridges and consequently changed the serviceability and ultimate limit states associated to their design. A direct consequence of this design trend is a considerable increase of structural vibrations. Therefore, the present investigation was carried out based on a more realistic load model developed to incorporate the dynamic effects induced by people walking. The load model considered the ascent and descending movement of the human body effective mass at each step. The position of the dynamic load was also changed according to the individual position and the generated time function, having a space and time description. The effect of the human heel was also incorporated in the analysis. The investigated structural model was based on a tubular composite (steel-concrete) footbridge, spanning 82.5 m. The structure is composed by three spans (32.5 m, 17.5 m and 20.0 m, respectively) and two overhangs (7.5 m and 5.0 m, respectively). The structural system is constituted by tubular steel sections and a concrete slab and is currently used for pedestrian crossing. This investigation is carried out based on correlations between the experimental results related to the footbridge dynamic response and those obtained with finite element models. The proposed computational model adopted the usual mesh refinement techniques present in finite element method simulations. The finite element model has been developed and validated with the experimental results. This model enabled a complete dynamic evaluation of the investigated tubular footbridge especially in terms of human comfort and its associated vibration serviceability limit states. The system dynamic response, in terms of peak accelerations, was obtained and compared to the limiting values proposed by several authors and design standards. The peak accelerations found in the present analysis indicated that the investigated tubular footbridge presented problems related with human comfort. Hence it was detected that this type of structure can reach high vibration levels that can compromise the footbridge users comfort and especially its safety.

No description available.

To simplify the measurement of energy-based structural metrics, a general registration process for the scanning laser doppler vibrometer (SLDV) has been developed. Existing registration techniques, also known as pose estimation or position registration, suffer from mathematical complexity, instrument specificity, and the need for correct optimization initialization. These difficulties have been addressed through development of a general linear laser model and hybrid registration algorithm. These are applicable to any SLDV and allow the registration problem to be solved using straightforward mathematics. Additionally, the hybrid registration algorithm eliminates the need for correct optimization initialization by separating the optimization process from solution selection. The effectiveness of this approach is demonstrated through simulated application and by validation measurements performed on a specially prepared pipe. To increase understanding of the relationships between structural energy metrics and the acoustic response, the use of structural energy density (SED) in active structural acoustic control (ASAC) has also been studied. A genetic algorithm and other simulations were used to determine achievable reduction in acoustic radiation, characterize control system design, and compare SED-based control with the simpler velocity-based control. Using optimized sensor and actuator placements at optimally excited modal frequencies, attenuation of net acoustic intensity was proportional to attenuation of SED. At modal and non-modal frequencies, optimal SED-based ASAC system design is guided by establishing general symmetry between the structural disturbing force and the SED sensor and control actuator. Using fixed sensor and actuator placement, SED-based control has been found to provide superior performance to single point velocity control and very comparable performance to two-point velocity control. Its greatest strength is that it rarely causes unwanted amplifications of large amplitude when properly designed. Genetic algorithm simulations of SED-based ASAC indicated that optimal control effectiveness is obtained when sensors and actuators function in more than one role. For example, an actuator can be placed to simultaneously reduce structural vibration amplitude and reshape the response such that it radiates less efficiently. These principles can be applied to the design of any type of ASAC system.

As Civil Engineering structures, e.g., tall buildings, long span bridges, deep water offshore platforms, nuclear power plants, etc., have become more costly, complex and serve more critical functions, the consequences of their failure are catastrophic. Therefore, the protection of these structures against damage induced by large environmental loads, e.g., earthquakes, strong wind gusts and waves, etc., is without doubt, a worldwide priority. However, structures cannot be designed to withstand all possible external loads and some extraordinary loading episodes do occur, leading to damage or even failure of the structure. Protection of a structure against hazards can be achieved by various means such as modifying structural rigidities, increasing structural damping, and by attaching external devices, known as control devices. Control devices can be deployed either to isolate the structure from external excitation or to absorb input seismic energy to the structure (absorber) so as to mitigate vibration in the primary structure. Seismic base isolation is one such mechanism which isolates a structure from harmful ground excitations. Seismic base isolation is a widely accepted and implemented structural control mechanism due to its robustness and ease in deployment. Following the Northridge earthquake (1994), and Kobe earthquake (1995), the interest of structural engineers in understanding near-source ground motions has enhanced. Documents published after these earthquakes emphasized the issue of large base displacements because of the use of none or little isolation damping (of viscous type only) prior to these events. More recent studies have investigated analytically and experimentally, the efficiency of various dissipative mechanisms to protect seismic isolated structures from recorded near-source long period, pulse-type, high velocity ground motions. Consequently, hybrid isolation systems, seismic base isolation supplemented with damping mechanisms, have become the focus of current research trend in structural vibration control. Hybrid base isolation system incorporating passive supplemental damping devices like, viscous fluid dampers, etc., performs satisfactorily in minimizing isolator displacement but at the same time increases superstructure acceleration response. Furthermore, the passive system can be tuned to a particular frequency range and its performance decreases for frequencies of excitation outside the tunning bandwidth. In such a scenario, active control devices in addition to base isolation mechanism provide better performance in reducing base displacement and superstructure acceleration for a broad range of excitation frequencies. Tremendous power requirement and the possibility of power failure during seismic hazards restrict the usage of active systems as a supplemental device. Semi-active devices provide the robustness of passive devices and adaptive nature of active devices. These characteristics make them better suited for structural control applications. The recent focus is on the development of magnetorheological (MR) dampers as semi-active device for structural vibration control applications. MR dampers provide hysteretic damping and can operate with battery power. The thrust of this thesis is on developing a hybrid base isolation mechanism using MR dampers as a supplemental damping device. The use of MR damper as a semi-active device involves two steps; development of a model to describe the MR damper hysteretic behaviour; development of a proper nonlinear control algorithm to monitor MR damper current / voltage supply. Existing parametric models of MR damper hysteretic behaviour, e.g., Bouc-Wen model, fail to consider the effect of amplitude and frequency of excitation on the device. Recently reported literature has demonstrated the necessity of incorporating amplitude and frequency dependence of MR damper models. The current/voltage supply as the input variable to the MR damper restricts the direct use of any control algorithms developed for active control of structures. The force predicted by the available control algorithms should be mapped to equivalent current/voltage and then to be fed into the damper. Available semi-active algorithms in the literature used ‘on-off’ or ‘bang-bang’ strategy for MR applications due to nonlinear current/voltage-force relation of MR damper. The ‘on-off’ nature of these algorithms neither provides smooth change in MR damper current/voltage input nor considers all possible current/ voltage values within its minimum to maximum range. Secondly, these algorithms fail to consider the effect of the MR damper applied and commanded current/voltage dynamics. The thrust of this dissertation is to develop semi-active control algorithms to monitor MR damper supply current/voltage. The study develops a Bouc-Wen based model to characterize the MR damper hysteretic phenomenon. Experimental results and modeling details have been documented. A fuzzy based intelligent control and two model-based nonlinear control algorithms based on optimal dynamic inversion and integral backstepping have been developed. Performance of the fuzzy logic based intelligent control has been explored using experimental investigation on a three storey base isolated building. Further the application of the proposed controllers on a benchmark building; a benchmark highway bridge and a stay cable vibration reduction have been discussed. Experimental study has revealed that the performance of optimal FLC is better than manually designed FLC in terms of reducing base displacement and storey accelerations. The performance of both the FLCs (simple FLC and genetic algorithm based optimal FLC) is better than ‘passive-off’ (zero ampere current supply) and ‘passive-on’ (one ampere current supply) condition of MR damper applications. The ‘passive-off’ results have shown higher base displacements with lower storey accelerations, whereas, the ‘passive-on’ results have reduced base displacement to the least but at the same time increased the storey acceleration too much. The FLC monitored MR damper show a compromise between the two passive conditions. Analytical results confirm these observations. Numerical simulations of the base isolated building with the two model based MR damper control algorithms developed have shown a better performance over FLC and widely used clipped optimal algorithms. The applications of the proposed semi-active control algorithms (FLC, dynamic inversion and integral backstepping) have shown better performance in comparison to that of control algorithms provided with the benchmark studies.

Στην παρούσα διατριβή διερευνήθηκε για πρώτη φορά η δυνατότητα επέκτασης του ορίου εφαρμογής της γεωδαιτικής μεθόδου μέτρησης μετακινήσεων σε πλέον άκαμπτες (υψίσυχνες) κατασκευές με τη χρήση οργάνων GPS δειγματοληψίας 100Hz. Τα όργανα αυτά αποτελούν πρόκληση για διάφορους τομείς καθώς έχουν δυνατότητα δειγματοληψίας σχεδόν ίδιας τάξης μεγέθους με όργανα που χρησιμοποιούνται παραδοσιακά για την καταγραφή δυναμικών κινήσεων όπως επιταχυνσιογράφοι, σεισμόμετρα κτλ. Στην παρούσα διατριβή μελετήθηκαν τα χαρακτηριστικά του θορύβου των οργάνων GPS-100Hz μέσα από συστηματικά πειράματα “supervised learning”, όπου στατικοί δέκτες ή δέκτες κινούμενοι σε γνωστές οριζόντιες και κατακόρυφες τροχιές, επέτρεπαν να καταγραφεί και να αναλυθεί ο στατικός και δυναμικός θόρυβος διαφόρων τύπων. Η περαιτέρω μελέτη του θορύβου έδειξε ότι οι συσχετίσεις και το εύρος του επηρεάζονται σημαντικά από το εύρος συχνοτήτων του βρόχου PLL (Phase-Locked Loop bandwidth) του δέκτη GPS. Η χρήση βρόχου PLL με εύρος συχνοτήτων (bandwidth) 100Hz εξασφαλίζει ασυσχέτιστες μετρήσεις αλλά αυξάνει σημαντικά το εύρος του θορύβου (τυπική απόκλιση περίπου 3mm στους οριζόντιους άξονες και περίπου 6-7mm στον κατακόρυφο). Το φάσμα συχνοτήτων του θορύβου των χρονοσειρών συντεταγμένων GPS-100Hz χαρακτηρίζεται από μη τυχαίο (χρωματισμένο) θόρυβο στις χαμηλές συχνότητες (μέχρι περίπου 0.5Hz) και πρακτικά τυχαίο θόρυβο για τις υψηλές συχνότητες. Επιπλέον λόγω της δυνατότητας υψηλού ρυθμού δειγματοληψίας των οργάνων GPS-100Hz, έγινε δυνατό να διερευνηθεί για πρώτη φορά το φαινόμενο της δυναμικής πολυανάκλασης του δορυφορικού σήματος από κινούμενες ανακλαστικές επιφάνειες (dynamic multipath) και η επίδρασή του στις χρονοσειρές στιγμιαίων συντεταγμένων GPS. Με βάση τα συμπεράσματα της ανάλυσης των πειραματικών δεδομένων αναπτύχθηκε μεθοδολογία απομείωσης του θορύβου των χρονοσειρών στιγμιαίων μετατοπίσεων κατασκευών ενδιαφέροντος Πολιτικού Μηχανικού με βάση ψηφιακά φίλτρα ζώνης. Η μεθοδολογία αυτή επιτρέπει να εκτιμηθούν οριζόντιες και κατακόρυφες μετακινήσεις της τάξης των λίγων χιλιοστών. Η παραπάνω μεθοδολογία εφαρμόστηκε στις καταγραφές των ταλαντώσεων μίας ξύλινης πεζογέφυρας στην περιοχή της Πάτρας. Από αφιλτράριστες μετρήσεις GPS-100Hz εκτιμήθηκε εύρος εγκάρσιας ταλάντωσης της τάξης των 60-70mm και συχνότητα ταλάντωσης 0.92Hz. Στον κατακόρυφο άξονα εκτιμήθηκε συχνότητα ταλάντωσης 6.5Hz ενώ μετά την απομάκρυνση του θορύβου των μετρήσεων εκτιμήθηκε εύρος κατακόρυφης ταλάντωσης της τάξης των 3mm. Η πειραματική και αναλυτική διερεύνηση δείχνουν ότι η υψηλή δειγματοληψία που παρέχουν τα νέα όργανα GPS-100Hz προσφέρει δυνατότητα καλύτερης εκτίμησης των χαρακτηριστικών ταλάντωσης (συχνότητα/εύρος) σχετικά εύκαμπτων κατασκευών αλλά και επέκτασης των ορίων εφαρμογής του GPS σε μέτρηση δυναμικών μετακινήσεων δύσκαμπτων κατασκευών (ιδιοσυχνότητα μεγαλύτερη των 5Hz) με εύρος μέχρι λίγα χιλιοστά. / The possibility of the newly introduced GNSS receivers, with sampling rate up to 100Hz, for broadening the limits of application of GPS technology toward measuring the displacements of stiff (high-frequency) Civil Engineering Structures was studied in the present thesis. The new generation GPS receivers present a great challenge for various applications since they offer a sampling rate similar to the sampling rate of traditional instruments used in vibration measurement/monitoring like accelerometers and seismometers. The noise characteristics of the 100Hz GPS measurements were studied on the basis of systematic “supervised learning” experiments where instantaneous coordinate time-series from stationary receivers or receivers performing motions with known characteristics permitted to study static and dynamic noise of several types including noise due to dynamic multipath. The last phenomenon has been identified during the measurements of the response of bridges due to excitation by passing vehicles. The study of noise characteristics indicated that the correlations and noise amplitude is highly dependent on the PLL (Phase-Locked Loop) bandwidth used by the GPS receiver. The use of a 100Hz PLL bandwidth ensures uncorrelated instantaneous coordinates but at the cost of high amplitude noise (standard deviation approximately 3mm and 6-7mm along the horizontal and vertical axes respectively). The noise spectrum is characterized by a power-law with colored noise affecting low frequencies up to approximately 0.5Hz and white noise affecting higher frequencies. A methodology for the reduction of noise of the instantaneous coordinate time-series using band-pass filtering has been designed on the basis of the results of the experimental data. Application of the methodology permits the identification of millimeter level dynamic displacements similar to the ones developed during structural vibrations. The methodology was applied on the measurements of the oscillations of a timber bridge in Patras, Greece. Oscillation amplitudes around 60-70mm and a fundamental natural frequency of 0.92Hz were identified along the lateral axis of the bridge on the basis of unfiltered GPS coordinates. The first natural frequency along the vertical axis was estimated at 6.5Hz. After the de-noising of the GPS coordinates vertical oscillation amplitudes of around 3mm were successfully identified. The main result from the experimental and analytical investigation carried out in the present thesis is that the newly introduced GPS receivers with sampling rate up to 100Hz provide the opportunity of more detailed measurement of the oscillations and extraction of the dynamic characteristics of relatively flexible structures as well as the broadening of the limits of applications of GPS toward the measurement of dynamic displacements of stiff (natural frequencies >5Hz) structures.

Vibration testing of structures constitutes a crucial step in design and commissioning of engineering structures. The focus here is on simulating field conditions in a laboratory so that detailed investigations of the structural behavior under various future load scenarios can be carried out. A major enabling technology in recent years in this field of study, especially, in the context of earthquake engineering, and automotive testing, has been the development of servo-hydraulic actuation systems, which form the principal component of test facilities, such as, multi-axes shake tables for testing building structures under earthquake loads, multi-post testrigs for testing vehicles subjected to road loads, and reaction-wall based test systems for simulating horizontal effects of earthquake loads on building structures. These systems have enabled the conduct of systematic studies on simulation of nonlinear structures under transient loads, simulation of multi-component and spatially varying random loads, and combining numerical and experimental methods with a view to avoid scaling while testing small scale critical components of large built-up structures. The investigations reported in this thesis are in this area of research and are primarily aimed at exploring the potential of servo-hydraulic test systems to address a few intricate issues related to performance assessment of engineering vibrating systems. A broad-based overview of goals of experimental approaches in vibration engineering, including dynamic system characterization and performance assessment, is presented in Chapter 1. Also discussed are the brief details of vibration testing methods developed in the context of earthquake engineering (including quasi-static test, effective force test, shake table test, combined effective force and shake table test, various versions of pseudo-dynamic test, and real-time substructuring) and automotive vehicle testing (including input excitation based methods and response based methods). The discussion notes the remarkable success witnessed in combining mathematical methods and experimental techniques especially in problems of characterization of dynamic system properties. Similar success, however, is observed to be not wide-spread in the context of development of test methods aimed at performance assessment of vibrating systems. The review culminates with the identification of the following three problems to be tackled in the present thesis: (a) development of efficient experimental procedures to estimate time varying reliability of structures under multi-component earthquake loads and similar analysis of vehicle structures under spatially varying random road loads; the focus here is on achieving sampling variance reduction in estimating the reliability; (b) development of experimental procedures to determine optimal cross-power spectral density models of partially specified multi-component random loads so as to produce the highest and lowest response variance in a specified response variable; the focus here is on seismic tests of asymmetric structures under partially specified multi-component earthquake loads, and on characterizing optimal correlations between two parallel tracks which maximize or minimize the vehicle response; and (c) development of a modified pseudo-dynamic test procedure, to incorporate additional components in numerical and experimental modeling in terms of an augmented linearized variational equation, so as to assess and contain propagation of numerical and experimental errors. The subsequent three chapters of the thesis tackle these questions and in doing so the thesis makes the following contributions: (A) Inspired by the Girsanov transformation based Monte Carlo simulation method for estimating time-variant component reliability of vibrating systems, an experimental test procedure, which incorporates the Girsanov transformation step into its folds, has been developed to estimate the time-variant system reliability of engineering systems. The two main ingredients of application of this strategy consists of determination of a control vector, which is artificially introduced to facilitate reduction in sampling variance, and the formulation of the Radon-Nikodym derivative, which serves as the correction to be introduced in order to compensate for the addition of the artificial control. (B) In problems of response analysis of structures subjected to random earthquake loads and vibration of vehicles running on rough roads, it may not be always feasible to completely specify the external actions on the structures. In such situations, it is of interest to determine the most favorable and the least favorable responses, along with the models for missing information in the inputs which produce the extreme responses. The present study, again inspired by existing analytical solutions to this problem, develops an experimental procedure to characterize the optimal excitation models and associated responses. (C) In the context of PsD testing of nonlinear structure to earthquake loads, a refinement in the test procedure involving the treatment of a linearized variational equation is proposed. This has led to the estimation of the evolution of global error norm as test proceeds with time. The estimates of error thus obtained have been used to decide upon altering the time step of integration.

<p> Tuned Liquid Dampers (TLDs) are increasingly being used to suppress the dynamic vibration of tall buildings. An equivalent mechanical model is essential for rapid analysis and design of a TLD. The most common TLD tank geometries are circular, annular and rectangular. Rectangular tanks are utilized for 1-D and 2-D TLDs, whereas circular and annular are usually applied to axisymmetric structures. The amount of fluid that participates in the sloshing motion is directly influenced by the tank geometry. Although not commonly used, a TLD having a curved-bottom tank is expected to perform more effectively due to its relatively large value of effective mass. The main objective of this study is to develop mechanical models for seven TLDs with different tank geometries including the curved-bottom case, and to theoretically investigate the performance of rectangular, vertical-cylindrical and horizontal-cylindrical TLDs.</p> <p> Potential flow theory, linear long wave theory, Lagrange's equations and virtual work method are employed to develop the equivalent mechanical model parameters of TLDs with rectangular, vertical-cylindrical, horizontal-cylindrical, hyperboloid, triangular, sloped-bottom, and parabolic tank geometries. A rectangular, vertical-cylindrical and horizontal-cylindrical TLD are selected for further study using a single-degree-of-freedom (SDOF) model and a two degree of freedom structure-TLD system model applying the derived equivalent mechanical parameters.</p> <p> The dynamic characteristics of the TLDs as a SDOF system are investigated. The mechanical model is verified by comparing calculated values with experimental results for a rectangular TLD. The free surface motion, sloshing force and energy dissipation are found to be dependent upon the excitation amplitude. Analytical results also indicate that the horizontal-cylindrical TLD possesses the greatest normalized sloshing force and energy dissipation among the TLDs considered.</p> <p> The performances of various TLDs installed in a structure are studied in terms of effective damping, efficiency and robustness. Tuning ratio, structural response amplitude, mass ratio and liquid depth are adjusted to investigate their affect on the performance of the studied TLDs. Performance charts are developed and subsequently used to present the results. It is found that small liquid depth ratio and large mass ratio can lead to a robust structure-TLD system with small relative motion ratio between the structure and the vibration absorber. Comparisons of performance between the three TLDs are made and it can be concluded that the horizontal-cylindrical TLD is the most robust and effective device with the smallest relative motion ratio.</p> / Thesis / Master of Applied Science (MASc)

This study evaluates the effectiveness of actively controlled piezoceramics with positive position feedback (PPF) for reducing structural vibrations. A comparison is made between active control with PPF and a parallel resistor-inductor (RLC) shunt technique. The primary objectives of this study are to: 1. Explore the feasibility of using smart materials and fiber optics for simultaneous health monitoring and active damping of a representative aircraft panel. 2. Determine how optical fiber sensors may be used to detect vibration modes of an aircraft panel by investigating their use on a representative test article. 3. Determine how piezoelectric patches may be used to detect and counteract fundamental resonances of a representative test article. 4. Determine a control algorithm and hardware system to increase substantially the damping in the fundamental mode of the representative test article over a wide temperature range. 5. Develop a health-monitoring algorithm based on fiber optic sensors to detect impedance changes in a representative test article. 6. Make a comparison between active control with PPF and an RLC shunt technique. To achieve the objectives of this study, a special test rig was used to evaluate the performance of piezoelectric materials (PZTs) for vibration suppression. The test rig was used to rigidly clamp a flat 20-guage steel plate, and then excite the plate in various frequency ranges with an electromagnetic shaker. For each test, a data acquisition system was used to acquire the data to evaluate the performance of each PPF controller. Once the data was obtained, a comparison was made between active damping with PPF and passive damping with the RLC shunt technique. The active damping technique used for this study combined piezoelectric actuators with fiber optic sensors to achieve simultaneous active control and health monitoring of a test plate. The results of the active damping tests show that piezoelectric materials can provide substantial narrowband and broadband frequency reductions, while at the same time detecting damage on the test plate. More specifically, the test results indicate that smart damping materials can decrease the fundamental mode of vibration of the test plate by 23 dB and detect damage such as a loose bolt in the clamping frame, with the addition of only 0.04 lb of PZT on the test plate. The active damping technique reduced the plate vibrations at each mode within the frequency range of interest, with only one-third the amount of piezoelectric material needed for an RLC shunt circuit technique. / Master of Science

Ce travail de thèse présente la formalisation du problème de couplage d'une plaque en vibration de flexion avec le sol. La notion d'impédance intermodale de rayonnement vibratoire est définie de façon analogue à son équivalent acoustique. A partir de cette définition, la notion de masse, raideur et amortissement modal ajoutée sur la structure par le sol est introduite. L'effet sur le niveau vibratoire de la structure est présenté, notamment l'effet très amortissant du sol sur la structure. Une comparaison avec le modèle équivalent acoustique est présentée avec une attention particulière portée sur les différences entre les impédances intermodales. L'influence de la stratification sur le niveau vibratoire de la structure fait apparaitre des phénomènes nouveaux sur la partie imaginaire de l'impédance intermodale. Une comparaison théorie-expérience a été effectuée dans le cas d'une dalle de tramway couplée au sol. On présente également une comparaison avec un code numérique, MEFISSTO développé par P. Jean au sein du CSTB. On présente également une extension du modèle d'une plaque couplée au sol au cas de couplage de deux plaques avec le sol. On montre notamment que l'écriture du problème reste très similaire au problème d'une plaque couplée au sol. Les impédances intermodales peuvent encore être définies avec la prise en compte du couplage des modes d'une plaque sur les modes de l'autre plaque. On présentera trois applications de ce modèle. La première concerne l'utilisation d'une Barrière Vibratoire Horizontale à la surface du sol pour atténuer les vibrations issues d'une première plaque modélisant la dalle de tramway. Finalement une ouverture du problème de couplage d'une plaque avec le sol par l'utilisation de ce modèle dans des problématiques inverses est présentée. On montre qu'il est possible par un problème inverse de remonter aux efforts injectés sur une dalle de tramway au passage de celui-ci. / This thesis is concerned with the coupling between a fexural vibrating plate and a stratifed ground. A semi-analytical solution is introduced similar to the equivalent acoustical problem. The ground cross modal impedance is defined in a similar way as the equivalent acoustical impedance. From this definition, the ground added mass, stiffness and damping to the plate are presented. Similarities and discrepancies between the acoustical and the ground cross modal impedance are introduced. Influence of the ground stratification on the plate vibration shows new phenomena especially on the imaginary part of the ground cross modal impedance. A comparison between the model developed in this thesis and an experiment made on a tramway slab has been done as well as a comparison with a numerical model, MEFISSTO developed by P. jean at CSTB. One introduces an extension of the modeling developed and is concerned with modeling two flexural plates to the ground. It can be pointed out that problem formulation is still close to the problem formulation of one plate coupled to the ground. Three different fields of application of such modeling is presented. The first field of application is concerned with ground mitigation due to the passing tramway on. The first plate is the excited plate by the tramway and the second plate, called Horizontal Wave Barrier, is acting at the top surface as a ground attenuator. The second field of application is concerned with the modeling of building foundation. It is shown that the vibration received by the foundation of a building can be an input data for modeling an entire building vibration. The third field of application is concerned with different cases of tramway slab for reduction of ground vibration. Finally one presents an introduction of the use of this ground structure modeling in the case of inverse problem. It is shown that it is possible to identify injected force to the plate by the tramway. Furthermore the ground allows a regularization of the problem in the inversion which is not the case in the acoustical case.

No description available.