Recent energy harvesting research has developed dielectric elastomer (DE) energy harvesting devices for use in low
frequency applications including waves, wind and human motion. The use of dielectric elastomers for energy harvesting
is a growing field, which has great potential from an energy density viewpoint. While DE has shown promise for energy
harvesting applications such as walking where the mechanical behavior could affect the user, there has been little
investigation into the damping effects induced by DE energy harvesting. As devices capable of harvesting larger
amounts of energy are developed harvesting-induced changes in the mechanical behavior of the dielectric must be
investigated. This paper investigates the structural damping effects of DE energy harvesting in order to develop a more
in-depth understanding of the changes in system response due to increased energy harvesting. Results relating energy
harvesting strain and bias voltage to damping provide a framework for developing energy harvesting techniques which
improve the overall performance of the system.
In recent years, wireless sensors technologies are attracted many researchers in the field of structural health monitoring
(SHM) of civil, mechanical and aerospace systems. Another potential application of wireless sensors is in the Vehicle-Infrastructure Integration (VII) which is an initiative by the U.S. Department of Transportation to improve road safety
and reduce congestion, through as part of its Intelligent Transportation System program. However, fundamental issues
remain unresolved before a broad application of the wireless SHM or VII sensor network concept is the question of
sustainable power source for each independent sensor mounted on infrastructures. With a vast number of sensors
nodes/networks in the infrastructure, connecting them to the grid power source is simply uneconomical in the era of
wireless technology. The other option, which is providing power to each sensor from battery sources, has its own
setbacks, as batteries can only provide power for a limited period, have to be replaced periodically (often difficult and
costly), and their disposal creates environmental hazard. This study addresses the feasibility of energy harvesting from
the ambient vibration of transportation infrastructures to power wireless sensors. Based on the vibration responses from
simulation and field tests, vehicle induced vibrations on bridge and pavement were obtained and the theoretical power
output from such vibration sources were computed. The expected results from this study will be demonstrated by
avoiding complex wiring to the sensors by which the associated cost of wiring and batteries will be significantly reduced,
and at the same time the technology can easily be deployed, meaning it is one step forward in improving the SHM and
VII applications.
KEYWORDS: Bridges, Video, Sensors, Structural health monitoring, Image processing, Video surveillance, System identification, Stochastic processes, Video processing, Data modeling
Structural condition assessment of highway bridges is traditionally performed by visual inspections or nondestructive
evaluation techniques, which are either slow, unreliable or detects only local flaws. Instrumentation of bridges with
accelerometers and other sensors, however, can provide real-time data useful for monitoring the global structural
conditions of the bridges due to ambient and forced excitations. Traditionally, videos are used for surveillance purposes
and environmental monitoring of civil structures. In this paper the potential for the utilization of videos in an integrated
structural health monitoring of highway bridges beyond the mentioned traditional applications are reported. Results
obtained from the field tests, which were carried out on a short-span instrumented bridge, are presented. Videos of
vehicles passing by, together with signals from laser beam sensors placed on the side of the bridge, were captured, and
synchronized with data recordings from the accelerometers. For short-span highway bridges, vibration is predominantly
due to traffic excitation. A stochastic model of traffic excitation on bridges is developed assuming that vehicles
traversing a bridge (modeled as an elastic beam) form a sequence of Poisson process moving forces and that the contact
force of a vehicle on the bridge deck can be converted to equivalent dynamic loads at the nodes of the beam elements.
Basic information of vehicle types, arrival times and speeds are extracted from the video images to develop a physics-based
simulation model of the traffic excitation. This modeling approach aims at circumventing a difficulty in the
system identification of bridge structural parameters. Current practice of system identification of bridge parameters is
often based on the measured response (or system output) only, and knowledge of the input (traffic excitation) is either
unknown or assumed, making it difficult to obtain an accurate assessment of the state of the bridge structures. The
effectiveness and viability of this video-assisted approach are demonstrated by the field results. Finally, a technique on
how to integrate the weights of vehicles in the image processing algorithm is proposed.
Structural condition assessment of highway bridges is traditionally performed by visual inspections or nondestructive evaluation techniques, which are either slow, unreliable or detects only local flaws. Instrumentation of bridges with accelerometers and other sensors, however, can provide real-time data useful for monitoring the global structural conditions of the bridges due to ambient and forced excitations. This paper reports a video-assisted approach for structural health monitoring of highway bridges, with results from field tests and subsequent offline parameter identification. The field tests were performed on a short-span instrumented bridge. Videos of vehicles passing by were captured, synchronized with data recordings from the accelerometers. For short-span highway bridges, vibration is predominantly due to traffic excitation. A stochastic model of traffic excitation on bridges is developed assuming that vehicles traversing a bridge (modeled as an elastic beam) form a sequence of Poisson process moving loads and that the contact force of a vehicle on the bridge deck can be converted to equivalent dynamic loads at the nodes of the beam elements. Basic information of vehicle types, arrival times and speeds are extracted from video images to develop a physics-based simulation model of the traffic excitation. This modeling approach aims at circumventing a difficulty in the system identification of bridge structural parameters. Current practice of system identification of bridge parameters is often based on the measured response (or system output) only, and knowledge of the input (traffic excitation) is either unknown or assumed, making it difficult to obtain an accurate assessment of the state of the bridge structures. Our model reveals that traffic excitation on bridges is spatially correlated, an important feature that is usually incorrectly ignored in most output-only methods. A recursive Bayesian filtering is formulated to monitor the evolution of the state of the bridge. The effectiveness and viability of this video-assisted approach are demonstrated by the field results.
Structural condition assessment of highway bridges has long been relying on visual inspection, which, however, involves subjective judgment of the inspector and detects only local flaws. Local flaws might not affect the global performance of the bridge. By instrumenting bridges with accelerometers and other sensors, one is able to monitor ambient or forced vibration of the bridge and assess its global structural condition. Ambient vibration measurement outwits forced vibration measurement in that it requires no special test arrangement, such as traffic control or a heavy shaker. As a result, it can be continuously executed while the bridge is under its normal serving condition. For short-to mid-span highway bridges, ambient vibration is predominantly due to traffic excitation, inducing the bridge to vibrate mainly in vertical direction. Based on its physical nature, traffic excitation is modeled as moving loads from the passing vehicles whose arrivals and speeds are extracted from digital video. Traffic-induced vibration provides valuable information for assessing the health of super-structure, but is less sensitive to possible seismic damage in the sub-structure. During earthquakes, bridges are excited in all directions by short-duration un-stationary ground motion, and are expected to better reveal their sub-structure integrity. Therefore, traffic-induced and ground-motion-induced ambient vibration data are treated separately in this paper for different assessment objectives, because of the different characteristics and measurability of the excitation. By continuously monitoring the ambient vibration of the instrumented bridge, its global structural conditions of both super- and sub-structures can be evaluated with possible damage locations identified, which will aid local non-destructive evaluation or visual inspection to further localize and access the damage.
For long-term bridge health monitoring, structural dynamic properties are usually obtained by system identification based only on the system output (bridge vibration responses), because the system input (traffic excitation) is difficult to measure. To facilitate such identification the excitation is commonly assumed as spatially uncorrelated white noise. However, when physically modeling it as a stationary stream of moving forces traversing the bridge, whose arrivals at the bridge are in accordance with a Poisson process, the traffic excitation is found to be spatially correlated. In this paper a procedure for formulating the traffic excitation model based on its physics is proposed, which involves first converting the moving forces into equivalent nodal excitation time-histories by the dynamic nodal loading approach, and then applying the Campbell’s theorem for the filtered Poisson processes. By this procedure, a non-diagonal frequency-variant excitation spectrum density matrix (SDM) is obtained. This does not conform to the conventional white noise excitation model. One of the output-only identification techniques based on the conventional excitation model, the frequency domain decomposition technique is implemented to demonstrate that direct application of the technique to traffic-induced vibrations can lead to misleading results. The proposed procedure for formulating the traffic excitation SDM provides a way to describe primary knowledge of the traffic excitation in frequency domain even for complicated bridges, which will potentially enable improvement in output-only identification techniques with unknown but spatially correlated excitation.
Assessment of vehicle tire forces is important in problems related to the structural health monitoring of highway bridges, damage to road pavements, design of suspensions, and road safety issues. In this paper, the effects of using semi-active control strategies, such as MR dampers, in vehicle suspensions on the dynamic tire forces are examined for the development of smart suspension systems for pavement- and bridge-friendly vehicles. The vehicle dynamics is described by a general linear MDOF model with multiple contacts (i.e., a multiple-axle vehicle) with the road. It is assumed that the tires are always in contact with the road surface. In particular, we are interested in the evaluation of the tire forces due to a harmonic excitation. A technique is developed to analytically assess the magnitude of the resulting tire force in the case of a passive suspension. Although the technique discussed cannot directly be applied to the calculation of tire forces in vehicles with controlled suspensions, it can efficiently be used for design purposes, which is demonstrated by an example of a semi-active suspension based on the sky-hook control. The discussion is amply illustrated by numerical examples.
In this paper, the effects of using semi-active control strategy (such as MR dampers) in vehicle suspensions on the coupled vibrations of a vehicle traversing a bridge are examined in order to develop various designs of smart suspension systems for bridge-friendly vehicles. The bridge-vehicle coupled system is modeled as a simply supported beam traversed by a two-degree-of-freedom quarter-car model. The surface unevenness on the bridge deck is modeled as a deterministic profile of a sinusoidal wave. As the vehicle travels along the bridge, the system is excited as a result of the surface unevenness and this excitation is characterized by a frequency defined by the speed of travel and the wavelength of the profile. The dynamic interactions between the bridge and the vehicle due to surface deck irregularities are obtained by solving the coupled equations of motion. Numerical results of a passive control strategy show that, when the lower natural frequency of the vehicle matches with a natural frequency (usually the first frequency) of the bridge and the excitation frequency, the maximum response of the bridge is large while the response of the vehicle is relatively smaller, meaning that the bridge behaves like a vibration absorber. This is undesirable from a bridge design viewpoint. Comparative studies of passive and semi-active controls for the vehicle suspension are performed. It is demonstrated that skyhook control can significantly mitigate the response of the bridge, while ground-hook control reduces the tire force impacted onto the bridge.
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