Now showing 1 - 10 of 11
  • Publication
    Accuracy of instantaneous frequencies predicted by the Hilbert-Huang transform for a bridge subjected to a moving vehicle
    This paper investigates the accuracy of the Hilbert-Huang transform (HHT) in capturing the time-varying frequencies of a short-span bridge traversed by a vehicle travelling at a constant speed. The bridge and vehicle are modelled as a simply supported beam and a quarter-car, respectively. The HHT uses empirical mode decomposition to divide the original signal into mono-component signals, called intrinsic mode functions (IMFs), where the Hilbert transform can extract instantaneous frequencies (IFs). Each IMF is associated with a dominant frequency band, although mode mixing is possible. In order to improve the predicted frequencies, several filters are applied before and after performing the HHT with a threefold purpose: (i) to remove the static component, (ii) to isolate the first mode of vibration, and (iii) to obtain meaningful and denoised IFs. The influences of a localized stiffness loss in the bridge, different vehicle speeds, and three signal-to-noise ratios on the results are discussed.
  • Publication
    Finite Element Updating using Cross-Entropy Combined with Random-Field Theory
    (Civil-Comp Press, 2014-09) ; ;
    In this paper, the possibility of introducing random field theory into the cross-entropy algorithm is studied. Cross-entropy algorithm is an optimization process that Walsh and González (2009) use to estimate the stiffness distribution of a structure given a set of displacements. Although this method has been successfully tested, many lines of improvement are still opened. Random field theory is incorporated into the algorithm in an attempt to account for spatial variability of stiffness throughout the structure. For this purpose, a correlation function, variable in space, is defined and, as a result, a modification of the algorithm is proposed. The modified algorithm is then tested using numerical simulations in a scenario consisting of a simply supported beam.
  • Publication
    Determination of Bridge Natural Frequencies Using a Moving Vehicle Instrumented with Accelerometers and GPS
    (Civil-Comp Press, 2008-09) ; ;
    An instrumented vehicle fitted with accelerometers and GPS allows recording frequencies with position. This information can be used to determine the main frequencies of a bridge as the vehicle traverses it. The accelerations, that contain the dynamic excitation result of the interaction between vehicle and bridge, can be processed using spectrum analysis. Numerical simulations are used to define the accuracy of the predicted frequency for a number of scenarios. Accuracy typically gets better as the bridge span increases, the vehicle speed decreases and the road gets smoother. Experimental data is also employed to test this measuring technique.
  • Publication
    Evaluation of the True Behaviour of the End Supports in the Carbajal de La Legua Old Bridge
    Bridges 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.
  • Publication
    Experimental testing of a cross-entropy algorithm to detect damage
    (Trans Tech Publications, 2013-07) ; ; ;
    Cross-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.
  • Publication
    Impact of Superimposed and Truck Live Load on Modal Characteristics of Short-Span Bridges
    Modal 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.
  • Publication
    Estimation of structural parameters using static loading tests
    Static 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.
  • Publication
    Verifying the suitability of uncoupled numerical methods for solving vehicle-bridge interaction problems
    The response of a structure subjected to a moving load can be obtained using coupled or uncoupled methods. The uncoupled method is often preferred since modal superposition is applicable, which implies computational efficiency and ease of implementation. However, the uncoupled method ignores the changes in the dynamic features of the combined structural system due to the time-varying location of the load. This paper analyses the extent to which the accuracy of the uncoupled method is affected by these changes. First, a parametric study is conducted on two discretized beam models traversed by a sprung mass at a constant speed. The error associated with the uncoupled method is calculated using the coupled solution as a reference. The influence of the load to structure mass and frequency ratios and the speed of the vehicle on the error is quantified. Heavier loads travelling at higher speeds are found to increase the inaccuracy of the uncoupled method. Then, the analysis is extended to a half-car travelling on a rough profile. Although errors from the uncoupled simulation remain low for the range of parameters under investigation, they may not be acceptable in some applications, i.e., the training of an algorithm for early damage detection.
      100Scopus© Citations 9
  • Publication
    Regularization Methods Applied to Noisy Response from Beams under Static Loading
    (American Society of Civil Engineers (ASCE), 2020-06) ; ;
    The estimation of flexural stiffness from static loading test data is the basis of many methods assessing the condition of structural elements. These methods are usually developed under the assumption of having sufficiently accurate data available. Hence, their performance deteriorates as the differences between the measured and true values of the response, often denoted as noise, increase. The proposed methodology is specifically designed to mitigate errors derived from noisy static data when estimating flexural stiffness. It relies on the linearization of the equations relating displacements to stiffness through the unit-force theorem, combined with regularization tools such as L-Curve and generalized cross-validation. The methodology is tested using theoretical simulations of the static response of a simply supported beam subjected to a 4-point flexural test for several levels of noise, two types of responses (deflections and rotations) and different levels of discretization. Recommendations for selecting the optimal regularization tool and parameter are provided. The use of rotations as inputs for predicting stiffness is shown to outperform deflections. Finally, the methodology is extended to a statically indeterminate beam.
      292Scopus© Citations 10
  • Publication
    Enhancing Student Performance through a Competitive Team Tournament
    In some engineering subjects, the nature of the material requires a maturation time in the student’s mind before being fully understood and the time constraints of modularization can become an impediment to the successful achievement of their learning outcomes. This paper presents a novel and efficient way of helping students to timely meet their learning outcomes by means of a Team Game Tournament. The principle behind a Team Game Tournament is that the success of a team lies on the success of the individuals composing the team. Therefore, team mates help each other and study more than individually because they care for them and for the team. A variation of Team Game Tournament inspired by the UEFA ‘Champions League’ is used here to address learning outcomes for two different age groups, four modules, four engineering degrees and two countries during the 2013/14 and 2014/15 academic seasons. It is noticed that the more games between the teams, the more effective the team work and learning has become. Confidential questionnaires and end-of-semester exams confirm the success of the competition in enhancing student satisfaction and learning.