Optimal design of energy harvesting from vibration subject to stochastic colored Gaussian process

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Some advances in extensive bridge monitoring using low cost dynamic characterization

Dynamic measurements will become a standard for bridge monitoring in the near future. This fact will produce an important cost reduction for maintenance. US Administration has a long term intensive research program in order to diminish the estimated current maintenance cost of US$7 billion per year over 20 years. An optimal intervention maintenance program demands a historical dynamical record, as well as an updated mathematical model of the structure to be monitored. In case that a model of the structure is not actually available it is possible to produce it, however this possibility does not exist for missing measurement records from the past. Current acquisition systems to monitor structures can be made more efficient by introducing the following improvements, under development in the Spanish research Project “Low cost bridge health monitoring by ambient vibration tests using wireless sensors”: (a) a complete wireless system to acquire sensor data, (b) a wireless system that permits the localization and the hardware identification of the whole sensor system. The applied localization system has been object of a recent patent, and (c) automatization of the modal identification process, aimed to diminish human intervention. This system is assembled with cheap components and allows the simultaneous use of a large number of sensors at a low placement cost. The engineer’s intervention is limited to the selection of sensor positions, probably based on a preliminary FE analysis. In case of multiple setups, also the position of a number of fixed reference sensors has to be decided. The wireless localization system will obtain the exact coordinates of all these sensors positions. When the selection of optimal positions is difficult, for example because of the lack of a proper FE model, this can be compensated by using a higher number of measuring (also reference) points. The described low cost acquisition system allows the responsible bridge administration to obtain historical dynamic identification records at reasonable costs that will be used in future maintenance programs. Therefore, due to the importance of the baseline monitoring record of a new bridge, a monitoring test just after its construction should be highly recommended, if not compulsory

Novel Generalized-a Methods for Interfield Parallel Integration of Heterogeneous Structural Dynamic Systems

A novel partitioned algorithm able to solve ODEs arising from transient structural dynamics is presented. The spatial domain is partitioned into a set of disconnected subdomains owing to computational or physical considerations, and continuity conditions of velocity at the interface are modelled using a dual Schur formulation, where Lagrange multipliers represent reaction forces. Interface equations along with subdomain equations lead to a system of DAEs for which an interfield parallel procedure is developed. The algorithm solves interface Lagrange multipliers, which are subsequently used to advance the solution in subdomains. The proposed coupling algorithm that enables arbitrary Generalized-a schemes to be coupled with different time steps in each subdomain is an extension of a method originally proposed by Pegon and Magonette. Thus, subcycling permitting to deal also with stiff and nonstiff subsystems is allowed. In detail, the paper presents the convergence analysis of the novel interfield parallel scheme for linear singleand two-degrees-of-freedom systems because a multi-degrees-of-freedom system is too difficult for a mathematical treatment. However, the insight gained from the analysis of these coupled problems and the consequent conclusions are confirmed by means of numerical experiments on a four-degrees-of-freedom system.JRC.G.5-European laboratory for structural assessmen

Finite element model updating of a footbridge based on static and dynamic measurements

The Palmas Altas footbridge is a recently built bridge in Sevilla (Spain) designed by architect Richard Rogers. It is a 78.6m long steel-concrete box girder. The bridge has three spans, with two pairs of intermediate oblique piers. The cross section of the box girder and the piers are variable along the bridge length. The footbridge has a cylindrical roof with a complex structural geometry, made of elliptical crossing bars and a cylindrical shell. Before being taken in use, the structural response of the footbridge was experimentally identified by an operational modal analysis. Mode shapes and frequencies have been clearly identified. In addition, the static response of the structure was obtained from a static load test. A detailed finite element model has been built for analyzing both the static as well as dynamic behavior of the bridge. A model updating process has been performed to improve static and dynamic response predictions. The present analysis is mainly focused on the in plane behavior of the bridge, for which both static and dynamic experimental information is available. Special attention is paid to the role of the bearings and foundations in the structural response. It is shown that the measured static response provides useful information about the response of the bridge and its foundation, which is not available from a dynamic analysis only.Ministerio de Economía y Competitividad BIA2010-1484

Analysis of dynamic coupling between spans of two multi-span bridges using ambient vibration measurements

Dynamic coupling in weakly coupled multi-span bridges usually is not considered in their design, since the coupling effects normally leave the structure on the safe side by reducing the peak-peak deflection of each span under moving vehicles and trains. Nonetheless in the framework of vibration monitoring, these coupling effects require further investigation, since some well known non-destructive damage identification technique relies on the fact that occurrence of damage leads to changes in structural dynamic properties, which are very often also influenced by the coupling effects. In this study, ambient vibration measurements were performed for two representative cases in order to investigate the dynamic coupling effects of these bridges. One is a three-span prestressed concrete highway bridge. And the other one is a five-span steel-plate-girder railway bridge. The experimental results verify the influence of dynamic coupling between adjacent spans for these two bridges. From the first bridge, it is also found that global modes of this weakly coupled multi-span bridge are very sensitive to the relative stiffness changes of an individual span, e.g., caused by localized damage.status: publishe

Effects of initial conditions in operational modal analysis

SUMMARY In this study, the effects of high-amplitude initial conditions on the accuracy of modal parameters, identified from output-only vibration data, are investigated. The influence on the sample output correlation function, which is the basis of most time-domain operational modal analysis techniques, is analyzed first. Then, a numerical simulation is performed to quantify the effect of nonzero initial conditions on the relative accuracy of natural frequencies, damping ratios, and mode shapes. It is shown that, when all identification assumptions are satisfied, high-amplitude initial conditions can significantly reduce the estimation errors, especially for short data records. Finally, a full-scale application is presented where the modal parameters of a six-span high-speed railway bridge are determined from output-only data. The results obtained with two different data sets are compared: The first one consists of the bridge's response to ambient data only, whereas the second one also contains the free vibration recorded immediately after a train passage. Although for most modes the results are similar, it is possible to identify some additional bending and torsion modes from the free vibration data with good accuracy. Copyright © 2013 John Wiley & Sons, Ltd. Copyright © 2013 John Wiley & Sons, Ltd.status: publishe

Dynamic behaviour of the Curved Cable-Stayed Bridge in Venice under different design choices

The paper presents and discusses the dynamic response of a curved cable-stayed bridge in Venice (Italy). Three distinct experimental campaigns in 2006, 2010 and 2011 led to identifying the bridge response in operational conditions. The dynamic identification included the characterization of both the deck and cables response. The authors developed a highly refined finite element (FE) model of the bridge, mirroring up to thirteen experimental modes. Two updating methods drove the estimate of the optimum parameters associated with the lowest discrepancy with the experimental modal parameters. The calibrated model was the base of a parametric analysis on the effects of the deck curvature, cables arrangement and tower cross-section inertia on the bridge dynamics. Specifically, the authors developed fourteen FE models of the bridge distinguished by the lack and different arrangement of the stay cables, the increasing value of the deck curvature and the tower inertia. The analysis intends to quantify the impact of the design choices of cable-stayed bridges on the modal parameters

An efficient approach to model updating for a multispan railway bridge using orthogonal diagonalization combined with improved particle swarm optimization

In this paper, a novel approach to model updating for a large-scale railway bridge using orthogonal diagonalization (OD) coupled with an improved particle swarm optimization (IPSO) is proposed. Particle swarm optimization (PSO) is a well-known and widely applied evolutionary algorithm. However, as other evolutionary algorithms (EAs), PSO has two main drawbacks that may reduce its capability to tackle optimization issues. A fundamental shortcoming of PSO is premature convergence. On the other hand, since PSO employs all populations to seek the best solution through iterations, it is very time-consuming. This makes PSO as well as EAs difficult to apply for optimization problems of large-scale structural models. In order to overcome those drawbacks, we propose coupling OD with IPSO (ODIPSO). OD is applied to arrange the position of particles and to select only particles with the best solution for next iterations, which helps to reduce the computational cost dramatically. There are several significant features of ODIPSO: (1) IPSO is employed to tackle the problem of premature convergence of PSO; (2) only one guide is used to update the velocity of particles instead of utilizing both guides, consisting of the local best and the global best; and (3) in each iteration, only the velocity and the position of the best particles are updated. In order to assess the effectiveness of the proposed approach, a large-scale railway bridge calibrated on the field is employed. This paper also introduces the use of wireless triaxial sensors (replacing classical wired systems) to obtain structural dynamic characteristics. The appearance of wireless triaxial transducers increases significantly the freedom in designing an ambient vibration test. The results show that ODIPSO not only outperforms PSO, IPSO and OD combined with PSO (ODPSO) in terms of accuracy, but also dramatically reduces the computational time compared to PSO and IPSO