- Aied, Hussein

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# Aied, Hussein

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Aied, Hussein

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Aied, Hussein

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- PublicationResponse of a Simply Supported Beam with a Strain Rate Dependent Elasticity Modulus when Subjected to a Moving Load(2012-09)
; The structural response of a material to a load that is applied rapidly (dynamically) or applied very slowly (statically) can be considerably different. A vehicle moving across a concrete bridge represents an example of a dynamic load that is applied to a structure within a limited period of time that will depend on the velocity of the load. This paper explores the variation in the response of a beam when using a typical constant value or a time-variant value that depends on the strain experienced by the structure. Previous research has demonstrated that the static modulus of elasticity is smaller than the dynamic modulus. Some of this research is based on compression and tensile tests using samples where deformation is measured at one single location for different strain and stress rates, and they have led to formulas that allow characterizing the dynamic modulus as a function of strain rate. The latter is used in this investigation to quantify the effect of considering a time-varying modulus of elasticity in a structure traversed by a moving load. The simulation of a moving load across a simply supported beam is implemented in MATLAB for two different scenarios: (i) using a constant modulus of elasticity as it is common practice in vehicle-bridge interaction literature, and (ii) using a time-varying dynamic modulus of elasticity. A sensitivity study is carried out to evaluate the percentage of increase in the elasticity modulus with respect to its static value as a function of the load velocity and magnitude. Finally, a graph of dynamic amplification factor versus speed is provided for both the constant modulus and the time-varying modulus scenarios for comparison purposes. Results show that the influence of a time-varying modulus becomes significant for high load magnitudes travelling at high speeds.597 - PublicationEstimation of transitory changes in bending stiffness using the Hilbert-Huang transformA finite element model of a bridge can be calibrated based on field measurements, and then updated periodically using a structural health monitoring system. The value of a structural parameter such as bending stiffness can be adjusted to measurements using well-known modal updating techniques and monitored in conjunction with external effects such as temperature to assess the condition of the structure. A value of the parameter that is predominant during the period under investigation will be captured, however, in the case of bending stiffness, brief and transitory values could take place as a result of a section exceeding the yield point due to a moving traffic load. Given that the latter is probably the prelude of more severe damage, this paper proposes a novel two-stage method based on the Hilbert-Huang transform combined with a statistical optimization approach to characterize the stiffness changes associated with a non-linear response.
230 - PublicationIdentification of sudden stiffness changes in the acceleration response of a bridge to moving loads using ensemble empirical mode decompositionThe growth of heavy traffic together with aggressive environmental loads poses a threat to the safety of an aging bridge stock. Often, damage is only detected via visual inspection at a point when repairing costs can be quite significant. Ideally, bridge managers would want to identify a stiffness change as soon as possible, i.e., as it is occurring, to plan for prompt measures before reaching a prohibitive cost. Recent developments in signal processing techniques such as wavelet analysis and empirical mode decomposition (EMD) have aimed to address this need by identifying a stiffness change from a localised feature in the structural response to traffic. However, the effectiveness of these techniques is limited by the roughness of the road profile, the vehicle speed and the noise level. In this paper, ensemble empirical mode decomposition (EEMD) is applied by the first time to the acceleration response of a bridge model to a moving load with the purpose of capturing sudden stiffness changes. EEMD is more adaptive and appears to be better suited to non-linear signals than wavelets, and it reduces the mode mixing problem present in EMD. EEMD is tested in a variety of theoretical 3D vehicleâ€“bridge interaction scenarios. Stiffness changes are successfully identified, even for small affected regions, relatively poor profiles, high vehicle speeds and significant noise. The latter is due to the ability of EEMD to separate high frequency components associated to sudden stiffness changes from other frequency components associated to the vehicleâ€“bridge interaction system.
599ScopusÂ© Citations 61 - PublicationCharacterization of non-linear bearings using the Hilbert-Huang transformChanges in the performance of bearings can significantly vary the distribution of internal forces and moments in a structure as a result of environmental or operational loads. The response of a bearing has been traditionally idealized using a linear model but a non-linear representation produces a more accurate picture at the expense of modelling complexity and computational time. In this article, a lead rubber bearing is idealized using the hysteretic Boucâ€“Wen model. The Hilbertâ€“Huang transform is then employed to characterize the features of the non-linear system from the instantaneous frequencies of the bearing response to a time-varying force. Instantaneous frequencies are also shown to be a useful tool in detecting sudden damage to the bearings simulated by a reduction in the effective stiffness of the force-deformation loop.
830ScopusÂ© Citations 6 - PublicationTheoretical Response of a Simply Supported Beam with a Strain Rate Dependant Modulus to a Moving LoadMoving load problems typically consider a structural material with properties that do not vary while the load traverses the structure. However, there is evidence that for some materials the structure will respond with a higher modulus of elasticity than that corresponding to a static test for sufficiently high strain rates. This paper investigates the variation in strain rate of a simply supported beam made of a viscoelastic material traversed by a moving load and its effect on the modulus of elasticity. The influence of speed and magnitude of the moving load on the displacement and strain responses of the beam is discussed.
537ScopusÂ© Citations 11 - PublicationStructural Analysis of Bridges with Time-Variant Modulus of Elasticity under Moving LoadsA simply supported bridge model is used to investigate the effect of a strain rate dependent modulus of elasticity on the dynamic response of the structure to a moving load. The bridge is modelled as a one-dimensional discretized finite element beam and the moving load is represented by a point force. A constant modulus of elasticity is traditionally employed when simulating the dynamic response of structures under moving loads. In this paper, a time-variant modulus is used to calculate strains and displacements and compare them to the traditional approach for different speeds and bridge spans. The time-variant modulus is obtained from the strain rate of the structure which is used in turn to update the strain at each point in time. The results show significant changes in the modulus and in the resulting load effect as load magnitude and speed increase.
341 - PublicationApplication of the Hilbert-Huang Transform for Identification of Changes in Boundary Conditions of a Bridge Using Vibration Data due to TrafficThe translational restraints associated to pin and rocker bearings are typically idealized in the form of fixed and free conditions. However, elastomeric bearings need to be represented with springs to reasonably predict the time- and frequency-domain response of bridges under traffic-induced vibrations. Therefore, changes in the response of these bearings are common as a result of aging, deterioration, variation in loading levels and/or environmental changes. The latter makes difficult to discern if changes in the frequency content of the structural response to ambient vibration are due to changes in temperature, changes in normal operational loads or the occurrence of damage. In this paper, the bridge is idealized by a beam model supported on a hysteretic translational sprung support. The purpose is twofold: (a) to gather a better understanding of the variations of the bridge response with bearing performance; and (b) to be able to quickly identify an anomaly in the bearing. Empirical Mode Decomposition and the Hilbert-Huang Transform are employed to capture changes in the bearing stiffness from the bridge response.
455 - PublicationApplication of the Hilbert-Huang Transform to identification of changes in boundary conditions of a bridge using vibration data due to traffic(2013-07-10)
; The translational restraints associated to pin and rocker bearings are typically idealized in the form of fixed and free conditions. However, elastomeric bearings need to be represented with springs to reasonably predict the time- and frequency-domain response of bridges under traffic induced vibrations. Therefore, changes in the response of these bearings are common as a result of aging, deterioration, variation in loading levels and/or environmental changes. The latter makes difficult to discern if changes in the frequency content of the structural response to ambient vibration are due to changes in temperature, changes in normal operational loads or the occurrence of damage. In this paper, the bridge is idealized by a beam model supported on a hysteretic translational sprung support. The purpose is twofold: (a) to gather a better understanding of the variations of the bridge response with bearing performance; and (b) to be able to quickly identify an anomaly in the bearing. Empirical Mode Decomposition and the Hilbert-Huang Transform are employed to capture changes in the bearing stiffness from the bridge response.361