Now showing 1 - 10 of 19
- PublicationModal analysis of a bridge using short-duration accelerationsThe application of unmanned aerial vehicle technology to bridge structural health monitoring has become a hot research topic due to its low cost, safety and high energy efficiency. However, flight duration and battery life are substantial technical limitations. Is a short data burst sufficient for damage detection? This paper intends to answer this question by developing a novel approach based on frequency domain decomposition to obtain the mode shapes from a short data burst. Then, the modal assurance criterion is used as an indicator of the differences between the estimated mode shapes from the short data burst and the exact eigenvectors from finite element analysis. Here, the short data burst is obtained from the simulated acceleration response of a bridge beam model due to the crossing of two quarter-cars. A new damage indicator based on the modal assurance criterion profile along the beam is proposed to locate and quantify damage.
- PublicationExtraction of dynamic features from short acceleration data bursts: a reviewIt is well known that structural damage can lead to changes in dynamic features such as frequencies, mode shapes, damping, vibration intensity, etc. Signal processing tools available to extract these features include Wavelet analysis, Fourier and Hilbert-Huang transforms. Acceleration data is typically used as input to these tools, given that it is a type of response with a relatively high dynamic component (i.e., oscillations in the response due to inertial forces of the structure) in relation to the static component (i.e., derived from time-varying static deflections as a result of time/spatial-varying loads). Almost all traditional signal processing approaches require access to long-time data sets. For instance, long periods of acceleration and multiple measurement points allow engineers to accurately define the mode shapes of a structure. In this paper, a scenario is envisioned where drones are used to charge sensors placed on bridges as well as to acquire the data recorded by the sensors for processing. The novelty is the challenge of monitoring structural condition in the context of acquiring limited quantities of data. The latter requires being able to deal with a very significant impact of edge effects and the loss of resolution due to the short duration of the signal. This paper reviews attempts to obtain bridge dynamic features overcoming these limitations, i.e., via multi-stage measurements as in the case of the Short Time Frequency Domain Decomposition method.
- PublicationEstimation of structural parameters using static loading testsStatic damage detection techniques make use of the observed change in the structure's static response (i.e., displacement, strain) to identify, locate and quantify damage. For a given load, the static response is related to the boundary conditions and distribution of structural stiffness throughout the structure. As damage can be characterised as a local reduction in structural stiffness, analysis of the structure's static response has been used extensively to locate and quantify damage. In recent years many new static damage detection techniques have been proposed, with most of the research being focused on the development of finite element based algorithms to estimate the stiffness of the structure. This paper reviews these techniques and discusses their potential when using modern surveying techniques.
- PublicationImpact of Superimposed and Truck Live Load on Modal Characteristics of Short-Span BridgesModal analysis characterizes the dynamic behaviour of structures, by means of their natural frequencies and mode shapes. Since these parameters are related to the flexural stiffness, many damage detection methods are based on measuring the vibration response of a structure. In particular, operational/ambient modal identification deals with cases where vibration is measured under operating conditions. In these circumstances, the exact nature and magnitude of the excitation forces is unknown and the frequencies measured on the structure may differ from those extracted in free vibration. In this paper, the vibrational response of a single short-span bridge deck, consisting on a simply supported slab, is simulated for different distributions of mass throughout the structure and the action of two typical 5-axle European trucks to address how modes and frequencies are affected by superimposed dead and live traffic loads. While the analysis focuses in the change of bridge frequencies, vehicle frequencies are also briefly discussed.
- PublicationNumerical analysis of techniques to extract bridge dynamic features from short records of accelerationThe use of drones in Structural Health Monitoring (SHM) to charge sensors mounted on a bridge and download their data has gathered interest over the last years. This approach presents the advantage of avoiding the need for long cables running over the bridge or for permanent access to electric power on site. Nonetheless, limitations exist regarding the amount of data that can be transmitted through this method. In contrast to traditional approaches to SHM relying on long records to assess the condition of a structure, the scenario envisioned here deals with short amounts of data. In this paper, specific methodologies for extraction of dynamic features from short data bursts of acceleration signal are tested through numerical simulations. The bridge is modelled as a simply supported finite element beam model that is excited by a series of moving concentrated forces, which represent a random traffic load. Initial conditions are varied allowing for scenarios in which the acceleration record may start once the vehicle is already on the bridge, finish before its exit or combine periods of free and forced vibration. The theoretical acceleration response is obtained for healthy and damage conditions of the bridge, and then corrupted with noise. Focus is placed on how effective these techniques are in overcoming the shortcuts derived from noise and from the short duration of the signal. Therefore, techniques to mitigate common problems such as mode-mixing and edge effects are investigated.
- PublicationEvaluation of the True Behaviour of the End Supports in the Carbajal de La Legua Old BridgeBridges are prone to bearing deterioration due to environmental causes or traffic overloading. For example, a bridge originally designed as simply supported may be behaving differently due to bearing aging and deterioration. The latter can lead to damage, not only to the bearings, but also to the rest of the structure. In this paper, load testing is used to evaluate the true behavior of the boundary conditions of an existing bridge and how they affect the overall structural response. For this purpose, a 16 m span concrete bridge is subjected to the forces applied by a truck loaded with quarry aggregate. Static measurements are obtained for several positions of the vehicle while dynamic ones are also obtained as the truck crosses the bridge at speed. These data is used to tune a 3D finite element model until achieving an accurate resemblance with the measurements. Boundary conditions are idealized with linear springs, which allow to consider all possible scenarios at both ends. Finally, spring constants that best fit the measurements are used to measure the impact of the boundary conditions on the distribution of internal forces in the structure.
- PublicationImpact of short-duration acceleration records on the ability of signal processing techniques to derive accurate bridge frequenciesThis paper envisions a scenario in which unmanned aerial vehicles gather data from low-cost and flexible wireless sensor networks, i.e., accelerometers. However, flight duration, coupled with limited sensor battery time, is a substantial technical limitation. In order to assess the impact of these constraints on bridge monitoring, this paper analyses the extraction of bridge dynamic features from short-duration acceleration records. The short acceleration record is simulated using the theoretical response of a simply supported beam subjected to a moving load. Estimated frequencies are obtained in free vibration and compared with the natural frequencies calculated from formula. Given that short records limit the resolution in the frequency domain, the error in the prediction of frequencies will typically decrease as the duration of the signal increases. Signal processing techniques for extracting dynamic features include the Fast Fourier Transform, Frequency Domain Decomposition, Continuous Wavelet Transform and Hilbert-Huang Transform. This paper carries out an assessment of the accuracy of these signal processing techniques in extracting frequencies as a function of the duration of the measurements. Edge effects and loss of resolution are shown to remain key issues to be addressed when the duration of the signal is too short.
- PublicationExperimental testing of a cross-entropy algorithm to detect damageCross-entropy optimization has recently been applied to the damage detection in structures subject to static loading. The optimization procedure minimizes the error between the measured deflection data and theoretical deflection data obtained from artificially generated finite element models based on assumed statistical distributions of stiffness for each discretized element. Following a number of iterations, the finite element model with stiffness properties producing deflections closer to reality is established as the mathematical model closest to the true structure. However, while previous testing of the algorithm has been relatively successful, it has been limited to theoretical simulations. Therefore, this paper conducts lab experiments on a beam loaded statically to test the accuracy of the algorithm. Deflections are measured for beam scenarios under different loading levels. The accuracy of the results is discussed and recommendations are made to improve the performance of the algorithm when implemented in practice.
- PublicationExperimental Testing of a Cross-Entropy Algorithm to Detect DamageCross-entropy optimization has recently been applied to the damage detection in structures subject to static loading. The optimization procedure minimizes the error between the measured deflection data and theoretical deflection data obtained from artificially generated finite element models based on assumed statistical distributions of stiffness for each discretized element. Following a number of iterations, the finite element model with stiffness properties producing deflections closer to reality is established as the mathematical model closest to the true structure. However, while previous testing of the algorithm has been relatively successful, it has been limited to theoretical simulations. Therefore, this paper conducts lab experiments on a beam loaded statically to test the accuracy of the algorithm. Deflections are measured for beam scenarios under different loading levels. The accuracy of the results is discussed and recommendations are made to improve the performance of the algorithm when implemented in practice.
Scopus© Citations 7 381
- PublicationSensitivity to Damage of the Forced Frequencies of a Simply Supported Beam Subjected to a Moving Quarter-CarThe vibration of bridges under operational conditions can be measured via accelerometers to extract their dynamic features. These features can then be monitored in time, although only a reduced number of cause-effect scenarios can be verified on the field. Therefore, theoretical models of the bridge are often employed for covering a wider range of scenarios. For instance, a variety of damage conditions can be introduced in a calibrated bridge model to obtain the associated frequencies, which can be subsequently compared to frequencies measured on-site for assessing the bridge condition. It must be noted that these frequencies may be influenced by factors other than damage, i.e., environmental effects due to temperature changes and operational effects due to traffic. During the forced vibration of a bridge caused by a moving vehicle, the frequencies governing the bridge response depend on the mass and stiffness ratios of the vehicle to the bridge. Therefore, records in free vibration are usually preferred or alternatively, the influence of operational loads is removed from forced vibration records before assessing whether damage has occurred or not. This paper shows that forced vibration stores relevant information about damage beyond the frequency changes derived from free vibration. Eigenvalue analysis is employed to investigate how forced frequencies change with the positions of a crossing vehicle and damage. The vehicle is modelled using a quarter-car and the bridge as a simply supported finite element beam, where damage is introduced via localized stiffness losses.
313Scopus© Citations 5