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Mohammed, Omar
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Mohammed, Omar
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Mohammed, Omar
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Now showing 1 - 7 of 7
- PublicationDamage detection in bridges based on patterns of dynamic amplificationThe pattern of Dynamic Amplification Factor (DAF) of the bridge strain response to a moving vehicle versus vehicle velocity is used to develop a level I damage technique. The challenge is to detect damage that causes only a small and difficult to detect frequency change with respect to the healthy condition. For this purpose, a damage index is defined based on subtracting the DAF-velocity pattern for the bridge in a prior healthy state from the DAF-velocity pattern corresponding to the damaged bridge. Simulations from a 3D vehicle-bridge interaction model are employed to show how the index increases with damage. The influence of the location of the strain sensors, the location, and severity of the damage, the road roughness, the corruption of measurements by noise, and the velocity range on the robustness of the technique are analysed. The relative changes in the proposed index as a result of damage are shown to clearly outperform the associated relative changes in frequencies, even for measurement locations far apart from the damage.
408Scopus© Citations 10 - PublicationDynamic amplification factor of continuous versus simply supported bridges due to the action of a moving vehicleResearch to date on Dynamic Amplification Factors (DAFs) caused by traffic loading, mostly focused on simply supported bridges, is extended here to multiple-span continuous bridges. Emphasis is placed upon assessing the DAF of hogging bending moments, which has not been sufficiently addressed in the literature. Vehicle-bridge interaction simulations are employed to analyze the response of a finite element discretized beam subjected to the crossing of two vehicle types: a 2-axle-truck and a 5-axle truck-trailer. Road irregularities are randomly generated for two ISO roughness classes. Noticeable differences appear between DAF of mid-span moment in a simply supported beam, and DAFs of the mid-span sagging moment and of the hogging moment over the internal support in a continuous multiple-span beam. Although the critical location of the maximum static moment over the internal support may indicate that DAF of hogging moment would have to be relatively small, this paper provides evidence that this is not always the case, and that DAFs of hogging moments can be as significant as DAF of sagging moments.
302Scopus© Citations 7 - PublicationFootprint caused by a vehicle configuration on the dynamic amplification of the bridge responseThe passage of a vehicle over a bridge leaves a unique footprint in the form of measured strains (or displacements) across the structure. This paper proposes a new level I damage detection method for short-span bridges using footprints of Dynamic Amplification Factor (DAF) versus vehicle speed. The total response of a bridge to a moving load is time- varying, and it can be assumed to be made of two components: 'static' and 'dynamic'. Here, DAF is defined as the ratio of the maximum total response to the maximum 'static' component. For a given bridge, DAF patterns will vary with vehicle configuration. However, for a vehicle configuration (or a number of them), the mean DAF pattern measured on the bridge will remain unaltered unless the conditions of the bridge changed. The latter is the subject of investigation in this paper. In order to test the feasibility of using these patterns for monitoring purposes, damage is simulated within a bridge model as stiffness losses of 10% and 30% at mid-span. Changes in stiffness are identified by differences between DAF patterns corresponding to the healthy and damaged bridges. Results show to be more sensitive to damage than a traditional level I damage detection method based on variation of natural frequencies.
Scopus© Citations 3 280 - PublicationDynamic impact of heavy long vehicles with equally spaced axles on short-span highway bridges(Vilnius Gediminas Technical University, 2018-03-27)
; ; Extremely large trucks with a weight exceeding the standard require a permit before they are allowed to cross the bridges of a specific route. For the purpose of safety, an escort is often employed to maintain a distance between vehicles and to ensure that the bridge load remain below the allowed maximum. Given that the speed of these large vehicles is quite slow and that the amplitude of vibrations normally declines when the vehicle mass is large, a minor dynamic amplification of the bridge response is expected. However, some of these large trucks have a unique feature characterized by “multiple equally-spaced axles”, something that is uncommon in normal vehicle. The application of axle forces at equal intervals can dynamically excite bridges to a considerable extent, even at low speeds. These “critical” low speeds are estimated a priori from the axle spacing of the truck and the main frequency of vibration of the bridge. This paper demonstrates that when the “critical” speed is unavoidable, a relatively high dynamic allowance must be added to static calculations before granting a permit to a long heavy vehicle.Scopus© Citations 10 349 - PublicationFootprint caused by a vehicle configuration on the dynamic amplification of the bridge response(2015-08)
; The passage of a vehicle over a bridge leaves a unique footprint in the form of measured strains (or displacements) across the structure. This paper proposes a new level I damage detection method for short-span bridges using footprints of Dynamic Amplification Factor (DAF) versus vehicle speed. The total response of a bridge to a moving load is timevarying, and it can be assumed to be made of two components: 'static' and 'dynamic'. Here, DAF is defined as the ratio of the maximum total response to the maximum 'static' component. For a given bridge, DAF patterns will vary with vehicle configuration. However, for a vehicle configuration (or a number of them), the mean DAF pattern measured on the bridge will remain unaltered unless the conditions of the bridge changed. The latter is the subject of investigation in this paper. In order to test the feasibility of using these patterns for monitoring purposes, damage is simulated within a bridge model as stiffness losses of 10% and 30% at mid-span. Changes in stiffness are identified by differences between DAF patterns corresponding to the healthy and damaged bridges. Results show to be more sensitive to damage than a traditional level I damage detection method based on variation of natural frequencies.360 - PublicationStatic and dynamic moments for any plane within a straight solid slab bridge caused by the crossing of a truckA lot of research has been carried out to explain the manner in which longitudinal moments of a bridge respond to traffic. The total longitudinal bending moment is made of 'static' and 'dynamic' components, which vary with time as a result of the inertial forces of the bridge and changes in value and point of application of the forces of the vehicle. However, there is limited evidence about how bending moments at planes other than longitudinal, or twisting moments, act in response to a moving vehicle. For the first time in the literature, this paper analyses the total resultant moments ('static' + 'dynamic') for any plane orientation (from 0 to 360°) at any location of a solid slab deck due to the crossing of a vehicle. The bridge is modelled as a simply supported straight orthotropic plate and the vehicle is modelled as a three-dimensional 5-axle articulated system composed of interconnected sprung and unsprung masses. Simulations are performed for three vehicle transverse paths and three speeds. Using Wood and Armer equations, the resultant moment at any plane orientation can be obtained from equilibrium of bending and twisting moments acting on longitudinal and transverse planes. Maximum twisting moments develop in planes at 45° with longitudinal and transverse planes. Bending moments reach maximum and minimum values at longitudinal and transverse planes. Nevertheless, the moments acting on other plane orientations cannot be ignored in order to accurately assess whether the moment capacity of the bridge provides adequate safety. Therefore, the amount of slab reinforcement will be sufficient provided that the moment capacity exceeds the applied moment for any location and plane. Critical locations with highest values of sagging, hogging and twisting are identified in the bridge, and the dynamic amplification associated to the applied moments is evaluated. Bridge codes such as the Eurocode employ a unique built-in dynamic amplification factor for moment that depends only on the bridge length and the number of lanes. This paper shows how to perform an improved assessment allowing for changes in dynamic behaviour with location and plane orientation, which may prevent needless expense in bridge rehabilitation.
303Scopus© Citations 10 - PublicationDynamic Amplification Factor of Continuous versus Simply Supported Bridges Due to the Action of a Moving Load(2014-08-29)
; ; ; This paper extends the research on dynamic amplification factors (DAFs) caused by traffic loading from simply supported to continuous (highway and railway) bridges. DAF is defined here as the ratio of maximum total load effect to maximum static load effect at a given section (mid-span). Another dynamic amplification factor FDAF can be defined as the ratio of the maximum total load effect throughout the entire bridge length to the maximum static load effect at a given section (mid-span). For continuous beam DAF/FDAF can be determined for both sagging and hogging bending moments. Noticeable differences appear among DAF/FDAF of mid-span bending moment in a simply supported beam, DAF/FDAF of the mid-span bending moment in a continuous beam and the DAF/FDAF of the bending moment over the internal support in a continuous beam. Three span lengths are tested in the simply supported beam models as well as three continuous beams made of two equal spans. Each model is subjected to a moving constant point load that travels at different velocities. The location of the maximum total moment varies depending on the speed. FDAF and DAF are plotted versus frequency ratio. The results showed that FDAF is often greater than DAF in simply supported and continuous beams. Also, FDAF of sagging bending moment in continuous beam is about 12 % greater than that the simply supported case. Moreover, the results showed that FDAF of hogging bending moments is about 3 % greater than those of sagging bending moments in continuous beam. Consequently, all values were larger than those of simply supported case.480