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It is desirable for any structural health monitoring (SHM) system to achieve maximum sensitivity with minimum sensor density. This may be accomplished using guided waves. The structural health monitoring system described herein is based on the excitation and reception of guided waves using piezoelectric elements as sensors. One of the main challenges faced is that in all but the most simple structures the wave interactions become too complex for the time domain signals to be interpreted directly.

It has become commonplace for discrete passive or active elements to be added to Structures to mitigate against vibration. More recently, semi-active damping has been a focus of research. Semi- active systems are attractive due to their performance, low cost, power consumption and control stability. In this thesis we consider how passive and semi-active damping systems may he designed to mitigate against. vibration in base-excited structures. initially we consider the base isolation of a single degree-of-freedom system. The optimality of the common sky-hook switching controller is assessed and its control form is generalised. Numerical and theoretical studies identify the optimal form of switching control and a linear switching surface controller is proposed which is found to achieve performance close to optimal. We propose the new design methodology of quasi-active damping . The motivation for this method is to approach the levels of performance obtainable using fully active systems whilst retaining the desirable attribute of semi- active systems, A quasiactive suspension design is proposed and validated in simulation. It is found that this system call produce a quasi-active region in the frequency response of very low displacement transmissibility. This study is then extended to consider how quasi-active systems should be designed specifically for use with magnetorheological dampers. The influence of external passive damping on 2:1 internal resonance in stay cables is examined. An efficient, low-order damped nonlinear cable model is derived and used to numerically generate stability boundaries. These are used to assess how damping should be designed to mitigate against this excitation mechanism. We then study the optimality of dipped-optimal LQR control in the semi-active clamping of cables. We propose the addition of all extra term to the cost function to encourage the control output. To satisfy the semi-active constraint. Finally we study the feasibility of real-time dynamic substructuring as a technique for the experimental testing of damped stay cables.

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There have been increasing economic and societal demands to ensure the safety of structures against both long-term and short-term damage, and adequate performance during the life span of structures. In this work, a statistical FE model updating using the modal flexibility residual error, which is defined as the difference between the measured modal flexibility and the theoretical one from the FE model, is proposed for the probabilistic damage assessment. On the basis that the structural parameters in the FE model and the measured modal parameters exhibit uncertainties, it is of considerable importance to analyze the influences from both the FE model and the measured modal parameters on the damage identification results. Therefore, the proposed method are formulated on the basis of integrating the conventional FE model updating method with the perturbation statistical framework, and thus employ the probability algorithms, aiming at evaluating the effect of uncertainties in the damage identification results. The idea is that by expanding each term in the conventional FE model updating equations with second-order Taylor series expansion, two recursive systems of equations are derived for estimating the first two moments (mean and covariance) of random structural parameters. The derived means and covariance of random structural parameters are second-order accuracy, as approximating the non linear function between the structural parameters and the modal flexibility. The numerical studies of a cantilever beam are presented to illustrate the proposed method from not only detecting damages but also assessing damages in terms of probability under different level of uncertainties in the FE model and the measured modal flexibility. The results are verified by the Monte Carlo Simulation (MCS) method, and the distribution of structural parameters of the FE model is accepted as normal distribution with a confidence level of 95%. After simulations, it is found that the proposed method is more vulnerable to the random errors in the measured modal flexibility than in structural parameters of the FE model. The effects of modally and spatially incomplete information of modal parameters, and multiple and different level of damage are. also investigated. Numerical simulations of a four-storey building are employed to compare the proposed method with another probabilistic damage assessment method, namely Bayesian probabilistic method. The results showed that the accuracy and robustness of the damage assessment using the proposed method are slightly lower than Bayesian probabilistic method, when there exist huge damages at multiple locations. However, when there exist small damages in the structure, accuracy and robustness of the damage detection using the proposed method are slightly higher than Bayesian probabilistic method. Lastly, experimental applications using the adhesively bonded GFRP beams are conducted in order to verify the proposed method. For comparison, three Non-FE model based damage assessment methods are also employed. The results showed that when the damage is severe, i.e. three GFRP plates are removed, both the proposed method and the considered three Non-Model based methods are able to identify the location and severity of the damage. However, when the damage is mild or insignificant the considered Non- model based methods are not clearly identify the location and severity of the damage, but the proposed method approximately assess the location and severity of the damage

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No description available.