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vvThere has been much work published in recent years on the use of vibration characteristicsto detect damage in bridges. Almost all of this work has been based on theassumption that the vibration is linear, i.e. the natural frequencies are not dependent onthe amplitude of oscillation. The aim of the work presented here was to investigate thepossibility of using changes in the non-linear vibration characteristics to detect damagein reinforced concrete bridges.These changes in the non-linear vibration characteristics were studied by conductingimpact excitation vibration tests on reinforced concrete beams. The non-linearitieswere detected by examining the changes in fundamental frequency over time (and henceover amplitude of vibration). Several time-frequency distribution estimation tools arediscussed including the discrete Fourier transform moving window, the auto-regressivemodel moving window, harmonic wavelets and examples of the Cohen class of bilineartime-frequency distributions. A detailed investigation into these various distributionpredictors was conducted to assess which is most suitable for analysing the vibrationsignals to detect changes in frequency with time.To understand the non-linearities in the vibration characteristics, a time-steppingmodel was described. The model is capable of including damage in the form of a momentrotationrelationship over the cracked region. It was validated for linear vibrationsagainst theoretical values and the representation of a non-linear mechanism using themodel was compared with experimental data.Static load tests were also conducted on the beams at various damage levels. Theyinvolved the use of vibrating wire strain gauges to investigate the moment-rotation behaviourover the cracked region. Several possible non-linear crack mechanisms are discussedand two of them are assessed using the vibration and the static load tests. Futureexperimental work is proposed to study the possible non-linear mechanisms further.The beam tests demonstrated that there is a change in non-linear vibration behaviourwith damage. The change is greatest at low levels of damage and after the beam hasbeen loaded to 30% of the failure load in three-point loading there is a reversal in thetrend and a slight reduction in non-linearity with further damage

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سمینار کارشناسی ارشد مهندسی صنایع، رویکردها و چالش های پیاده سازی مدیریت دانش در سازمان های دانش بنیان پروژه محورکتاب جامع آموزش اتوکد به زبان بسیار ساده در621 صفحهمدیریت استراتژیککلیات تحقیق در باب واژه خیر ✅فایل های دیگر✅

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