The Experts below are selected from a list of 5157 Experts worldwide ranked by ideXlab platform
Zh Chen - One of the best experts on this subject based on the ideXlab platform.
-
enhanced damping for Bridge Cables using a self sensing mr damper
Smart Materials and Structures, 2016Co-Authors: Zh Chen, Kwok Ho LamAbstract:This paper investigates enhanced damping for protecting Bridge stay Cables from excessive vibration using a newly developed self-sensing magnetorheological (MR) damper. The semi-active control strategy for effectively operating the self-sensing MR damper is formulated based on the linear-quadratic-Gaussian (LQG) control by further considering a collocated control configuration, limited measurements and nonlinear damper dynamics. Due to its attractive feature of sensing-while-damping, the self-sensing MR damper facilitates the collocated control. On the other hand, only the sensor measurements from the self-sensing device are employed in the feedback control. The nonlinear dynamics of the self-sensing MR damper, represented by a validated Bayesian NARX network technique, are further accommodated in the control formulation to compensate for its nonlinearities. Numerical and experimental investigations are conducted on stay Cables equipped with the self-sensing MR damper operated in passive and semi-active control modes. The results verify that the collocated self-sensing MR damper facilitates smart damping for inclined Cables employing energy-dissipative LQG control with only force and displacement measurements at the damper. It is also demonstrated that the synthesis of nonlinear damper dynamics in the LQG control enhances damping force tracking efficiently, explores the features of the self-sensing MR damper, and achieves better control performance over the passive MR damping control and the Heaviside step function-based LQG control that ignores the damper dynamics.
-
Enhanced damping for Bridge Cables using a self-sensing MR damper
Institute of Physics Publishing, 2016Co-Authors: Zh Chen, Kh LamAbstract:This paper investigates enhanced damping for protecting Bridge stay Cables from excessive vibration using a newly developed self-sensing magnetorheological (MR) damper. The semi-active control strategy for effectively operating the self-sensing MR damper is formulated based on the linear-quadratic-Gaussian (LQG) control by further considering a collocated control configuration, limited measurements and nonlinear damper dynamics. Due to its attractive feature of sensing-while-damping, the self-sensing MR damper facilitates the collocated control. On the other hand, only the sensor measurements from the self-sensing device are employed in the feedback control. The nonlinear dynamics of the self-sensing MR damper, represented by a validated Bayesian NARX network technique, are further accommodated in the control formulation to compensate for its nonlinearities. Numerical and experimental investigations are conducted on stay Cables equipped with the self-sensing MR damper operated in passive and semi-active control modes. The results verify that the collocated self-sensing MR damper facilitates smart damping for inclined Cables employing energy-dissipative LQG control with only force and displacement measurements at the damper. It is also demonstrated that the synthesis of nonlinear damper dynamics in the LQG control enhances damping force tracking efficiently, explores the features of the self-sensing MR damper, and achieves better control performance over the passive MR damping control and the Heaviside step function-based LQG control that ignores the damper dynamics.Department of Civil and Environmental Engineerin
Christos T. Georgakis - One of the best experts on this subject based on the ideXlab platform.
-
statistical modeling of time series for ice accretion detection on Bridge Cables
Journal of Cold Regions Engineering, 2018Co-Authors: Julia Andre, Anne S Kiremidjian, Christos T. GeorgakisAbstract:AbstractIn the northern regions, ice accretion on Bridge Cables poses serious risks to the structure as well as to vehicular traffic when ice falls from the Cables onto the road. The detection and ...
-
structural health monitoring approach for detecting ice accretion on Bridge cable using the haar wavelet transform
Proceedings of SPIE, 2016Co-Authors: Julia Andre, Christos T. Georgakis, Anne S Kiremidjian, Yizheng Liao, Ram RajagopalAbstract:Ice accretion on Cables of Bridge structures poses serious risk to the structure as well as to vehicular traffic when the ice falls onto the road. Detection of ice formation, quantification of the amount of ice accumulated, and prediction of icefalls will increase the safety and serviceability of the structure. In this paper, an ice accretion detection algorithm is presented based on the Continuous Wavelet Transform (CWT). In the proposed algorithm, the acceleration signals obtained from Bridge Cables are transformed using wavelet method. The damage sensitive features (DSFs) are defined as a function of the wavelet energy at specific wavelet scales. It is found that as ice accretes on the Cables, the mass of cable increases, thus changing the wavelet energies. Hence, the DSFs can be used to track the change of Cables mass. To validate the proposed algorithm, we use the data collected from a laboratory experiment conducted at the Technical University of Denmark (DTU). In this experiment, a cable was placed in a wind tunnel as ice volume grew progressively. Several accelerometers were installed at various locations along the testing cable to collect vibration signals.
-
Effects of ice accretion on the aerodynamics of Bridge Cables
Journal of Wind Engineering and Industrial Aerodynamics, 2015Co-Authors: Cristoforo Demartino, Holger Koss, Christos T. Georgakis, Francesco RicciardelliAbstract:Abstract Undesirable wind induced vibrations of Bridge Cables can occur when atmospheric conditions are such to generate ice accretion. This paper contains the results of an extensive investigation of the effects of ice accretion due to in-cloud icing, on the aerodynamic characteristics of Bridge hangers and stay Cables. The aim of this paper is twofold; first, it was investigated the ice accretion process and the final shape of the ice accreted; then the aerodynamics of the ice accreted Bridge Cables was characterized, and related to the ice shape. Different climatic conditions, i.e. combinations of temperature, wind speed and yaw angle of accretion, were reproduced in a climatic wind tunnel, giving rise to different types of accretion. These were chosen such to generate the most common natural ice formations expected to produce Bridge cable vibrations. A description of the geometric characteristics of the ice accretions is given in the paper. Only for the Bridge hanger case, a short description of the evolution of the ice accretions is given. The aerodynamic force coefficients were then measured with varying yaw angle, angle of attack and wind speed, and are presented and discussed in the paper; these are found to be significantly affected by the characteristics of the ice accretion.
-
effects of surface roughness and cross sectional distortion on the wind induced response of Bridge Cables in dry conditions
Journal of Wind Engineering and Industrial Aerodynamics, 2015Co-Authors: Giulia Matteoni, Christos T. GeorgakisAbstract:Abstract Theoretical and experimental investigations to date have assumed that Bridge stay Cables can be modelled as ideal circular cylinders and that their aerodynamic coefficients are invariant with wind angle-of-attack. On the other hand it has been demonstrated that Bridge Cables are characterised by local alterations of their inherent surface roughness and shape. Small deviations from ideal circularity result in significant changes in the static drag and lift coefficients with Reynolds number. The present study focuses on the wind-induced response of a full-scale yawed Bridge cable section model, for varying Reynolds numbers and wind angles-of-attack. Using passive-dynamic wind tunnel tests, it is shown that the in-plane aerodynamic damping of a Bridge cable section, and the overall dynamic response, is strongly affected by changes in the wind angle-of-attack. Using the drag and lift coefficients, determined in static conditions for an identical cable model as the one used for passive-dynamic tests, the in-plane aerodynamic damping is evaluated by employing a one-degree-of-freedom (1 DOF) quasi-steady analytical model. Similarly, it is shown that regions of instability associated with the occurrence of negative aerodynamic damping are strongly dependent on the wind angle-of-attack.
-
preliminary probabilistic prediction of ice snow accretion on stay Cables based on meteorological variables
11th international conference on Structural Safety & Reliability Conference, 2013Co-Authors: Joan Hee Roldsgaard, Christos T. Georgakis, Anne S Kiremidjian, Michael Havbro FaberAbstract:The scope of the present paper is to present a framework for assessment of the probability of occurrence of ice/snow accretion on Bridge Cables. The framework utilizes Bayesian Probabilistic Networks and the methodology is illustrated with an example of the cable-stayed Oresund Bridge. The case study focuses on the ice/snow accretion due to the in-cloud icing or precipitation icing mechanisms and includes probabilistic assessments of the meteorological variables influencing the ice/snow accretion on the stay Cables. Different probability distribution functions are utilized for the representation of the meteorological variables and evaluated both by goodness-of-fit test and qualitatively. Conditional probability curves are developed to predict the amount of ice accretion given a set of meteorological conditions using the Gaussian Kernel Smoothing method. The fitted probability distribution functions for the meteorological variables and the conditional ice accretion curves are implemented in a Bayesian Probabilistic Network and the annual average number of ice/snow accretion occurrences is estimated. models for the relevant meteorological variables and the probability of occurrence of ice/snow accretion on the stay Cables is assessed using the proposed framework. 1.1 Outline of basic conditions for ice/snow accretion In order to estimate the occurrence probability of the ice or snow accretion the basic conditions for the ice/snow accretion process is reviewed. Typically ice/snow accretion on Cables occurs either by precipitation icing, in-cloud icing or hoar frost. Hoar frost is often neglected in the transmission line design, since the accretion is relatively lightweight. However it is believed that the ice accretion due to hoar frost can induce galloping vibrations of Bridge Cables and that even small ice lumps can be a hazard for the Bridge users, consequently hoar frost should be taken into account in this type of analysis. Precipitation icing can result in glaze, wet snow or dry snow, whereas in-cloud icing can result in soft or hard rime. Precipitation icing occurs at any location where precipitation is present at the same time as freezing temperatures. The type of precipitation icing depends on the vertical temperature layers (Therialut et al. 2006). The density of the ice that is likely to accrete on the Cables can be estimated from values of the temperature and wind velocity through Figure 1. The characteristics of the different icing types can be obtained from Table 1. Figure 1. The definition of the different icing types (IEC 60826, 2003). Table 1. Characteristics of different icing types. _______________________________________________ Density [kg/m] Temperature [°C] _______________________________________________ Precipitation icing _______________ Wet snow 300-800 -5 < T < 0 Glaze 700-900 -10 < T < 0 _______________ In-cloud icing _______________ Hard rime 600-800 -10 < T < 1 Soft rime 200-600 -20 < T 0 _______________ Hoar frost < 300 _______________ _______________________________________________ 2 MODEL OVERVIEW 2.1 Bayesian Probabilistic Network Figure 2 presents the BPN for assessment of the annual probability of occurrence of ice/snow accretion. The BPN represents the causal relationships between the most important variables affecting the two icing mechanisms considered in this analysis; in-cloud icing and precipitation icing. In the model, the states of the variables are represented discretely. Thus in the modeling, it is necessary to discretize all variables with continuous states. 2.2 Discretization, detailing and implementation Figure 2. The Bayesian Probabilistic Network: Assessment of annual probability of occurrence of ice/snow accretion on Bridge Cables. The assignment of a probability structure to the possible states of each variable in the BPN can be carried out by discretization of the probability distribution, if such a function is defined for the variable considered. Measurements are already discrete and their sampling frequency may be utilized to determine the lower bound and upper bounds in the discretization. Depending on whether the variables in the BPN have only outgoing edges (parent variables) or also ingoing edges (child variables) the discrete states of the variables are assigned unconditional or conditional probability tables, respectively (Faber et al. 2002). 2.3 Probabilistic Model Constituents The meteorological variables are often given as time series (stochastic processes) or in some situations as probability distribution functions (pdfs). The pdfs can directly be discretized and used in the BPN whereas some characteristics about the time series must be identified before a pdf can be used to characterize the variable. Here the investigation of the autocorrelation and cross-correlation functions can be an essential part of the analysis, since it can reveal if the stochastic processes are stationary and correlated with other variables (Madsen 2008). If a stochastic process is stationary and not crosscorrelated with any of the other variables, an appropriate marginal pdf can be identified by model estimation and testing – using a mixture of physical considerations with data assessment. In the case where the stochastic process is stationary but crosscorrelated to one or more of the variables, however, conditional pdfs must be identified. The dependency structure between two variables should also be apparent from the BPN. In the case the pdfs are not given a priory, different types of probability density functions should be tested in order to find the best estimate. The identified pdfs can be evaluated based on the Quantile-Quantile plot (Q-Q plot), estimated cumulative distribution function (CDF), pdf-plots and of goodness-of-fit tests such as the Kolmogorov–Smirnov test (K-S test). For different variables, the upper or lower tail of their distributions may be of greater importance than the overall distribution. This should be reviewed for each individual variable. To estimate the probability of annual occurrence of ice/snow accretion, a mathematical or experimental accretion models, monitoring data or different criterion can be used. The described framework for estimating the annual probability of occurrence of ice/snow accretion (icing) on Bridge Cables is illustrated through a case study of the stay Cables of the Oresund Bridge. 3 ANALYSIS OF THE METEOROLOGICAL DATA FOR THE ORESUND Bridge SITE The Oresund Bridge is a cable stayed Bridge connecting Denmark and Sweden with a main span of 490 m. Figure 3 shows the location of the Oresund Bridge and Copenhagen Airport. The Bridge is oriented in the N-W to S-E direction and the stay Cables are arranged in a harp configuration and are inclined with an angle of 30 degrees to the horizon. Figure 3. Map of the Oresund link and Kastrup Airport (Denmark) (http://www.worldgreatestsites.com/). The Danish Meteorological Institute (DMI) has a network of 65 observation stations covering Denmark. In the present paper measurements obtained from station 6180 are treated. This station is located at Copenhagen Airport, which is in flat terrain and close to the ocean. It was chosen to use data from the Copenhagen Airport station, since it is situated only about 10 km from the Oresund Bridge. This station has 10-min-mean values of the meteorological variables available for every 10 min since the 25th of June 2003. The data are obtained from that date until the 31st of December 2011 at 23:50. This gives a total of 447079 data points for the variables: wind velocity, wind direction, relative humidity and temperature. The precipitation is measured every third hour as the accumulated precipitation since the last measurement. Less than 0.5% of the data points of one of the variables are missing or reported as non-available. If one data point of one of the variables is missing, the equivalent data points of the other variables are also withdrawn.
Kwok Ho Lam - One of the best experts on this subject based on the ideXlab platform.
-
enhanced damping for Bridge Cables using a self sensing mr damper
Smart Materials and Structures, 2016Co-Authors: Zh Chen, Kwok Ho LamAbstract:This paper investigates enhanced damping for protecting Bridge stay Cables from excessive vibration using a newly developed self-sensing magnetorheological (MR) damper. The semi-active control strategy for effectively operating the self-sensing MR damper is formulated based on the linear-quadratic-Gaussian (LQG) control by further considering a collocated control configuration, limited measurements and nonlinear damper dynamics. Due to its attractive feature of sensing-while-damping, the self-sensing MR damper facilitates the collocated control. On the other hand, only the sensor measurements from the self-sensing device are employed in the feedback control. The nonlinear dynamics of the self-sensing MR damper, represented by a validated Bayesian NARX network technique, are further accommodated in the control formulation to compensate for its nonlinearities. Numerical and experimental investigations are conducted on stay Cables equipped with the self-sensing MR damper operated in passive and semi-active control modes. The results verify that the collocated self-sensing MR damper facilitates smart damping for inclined Cables employing energy-dissipative LQG control with only force and displacement measurements at the damper. It is also demonstrated that the synthesis of nonlinear damper dynamics in the LQG control enhances damping force tracking efficiently, explores the features of the self-sensing MR damper, and achieves better control performance over the passive MR damping control and the Heaviside step function-based LQG control that ignores the damper dynamics.
Raimondo Betti - One of the best experts on this subject based on the ideXlab platform.
-
a stochastic finite element approach to determine the safety of suspension Bridge Cables
2013 ASCE International Workshop on Computing in Civil Engineering IWCCE 2013, 2013Co-Authors: Arturo Montoya, Raimondo Betti, George Deodatis, Haim WaismanAbstract:A new methodology to determine the safety of suspension Bridge main Cables is proposed and illustrated on a corrosion-deteriorated cable composed of 9061 wires. The approach is the first one incorporating a finite element (FE) model to predict the cable’s failure load, accounting for load recovery due to friction in broken wires and simulating the reduced cable's strength as a three dimensional random field. In order to obtain the breaking load of a cable, the load is increased gradually (quasi-static loading) in a cable’s FE model, having wires break a few at a time according to their residual strength. Because of the load transfer to surrounding wires, the breakage of an individual wire affects the stress state inside the surrounding wires. This local damage eventually causes a global reduction in the load carrying capacity of the cable, up to a complete failure. The safety of the cable is determined through a Monte Carlo simulation, in which the reduced strength of the cable is generated for every realization through the Spectral Representation Method (SRM) and is input as a material parameter in the FE model. The statistics of the load that will drive a suspension Bridge cable to failure under a hypothetical deterioration state are obtained at the end of the simulation. INTRODUCTION The structural function of the main Cables in suspension Bridges is to transfer the tension load, derived by supporting the roadway, to the towers. The main Cables are composed of thousands of high strength parallel steel wires with a diameter of approximately 5 mm bundled together in strands either built in situ or prefabricated. These strands are then compacted and tightened together and eventually the cross section of the cable becomes semi-circular. The wires in pristine conditions have a strength ranging from 1570 MPa to 1800 MPa. However with aging, fatigue loading, and harsh environmental conditions, the wires strength reduces significantly (Shi et al., 2007). Field observations of aging suspension Bridges indicate serious distress of
-
load transfer and recovery length in parallel wires of suspension Bridge Cables
Journal of Engineering Mechanics-asce, 2011Co-Authors: Haim Waisman, Raimondo Betti, Arturo Montoya, I C NoyanAbstract:A new simplified contact model aimed at capturing the load transfer and recovery length in parallel steel wires, commonly used in main Cables of suspension Bridges, is presented. The approach is based on placing elastic–perfectly plastic spring elements at the contact region between the objects. These springs have varying stiffness (Model I) or yielding (Model II) depending on their proximity to the clamping loads. Their stiffness or yielding is highest when they are closer to this force, and it decays when they are farther away from the clamp. This decayed behavior is assigned according to Boussinesq’s well-known solution to a point load (applied on a half space). Both models converge quickly compared with a full contact model and recover Coulomb friction law on a two-dimensional (2D) benchmark problem. Moreover, when the same properties are chosen for all springs (disregarding Boussinesq solutions), the models reduce to the classical shear-lag model, which for high clamping (point) loads gives inaccurat...
-
random field based approach for strength evaluation of suspension Bridge Cables
Journal of Structural Engineering-asce, 2007Co-Authors: Yuwei Shi, George Deodatis, Raimondo BettiAbstract:A methodology is introduced to estimate the strength of suspension Bridge Cables using results of tensile strength tests performed on wire samples extracted from the Bridge’s main Cables. The innovation of the proposed methodology is to consider the spatial correlation of the wire strength over the wire’s length, a real and experimentally measured property of ductile steel wires that is disregarded in the current standard approach. The wire strength is modeled as a nonGaussian random field along its length. The number of parallel wires in the cable’s cross section is then considered to estimate the strength of the entire cable. The capabilities of the proposed methodology are demonstrated through an application involving an experimental data set of wire segments extracted from the Williamsburg Bridge. Results of the proposed methodology are compared to corresponding results of the current standard approach. It is explained why the former results are relatively more accurate than the latter. A procedure fo...
-
corrosion and embrittlement in high strength wires of suspension Bridge Cables
Journal of Bridge Engineering, 2005Co-Authors: Raimondo Betti, Alan C West, G Vermaas, Y CaoAbstract:An in-depth analysis of the deterioration mechanisms in high-strength wires of suspension Bridge Cables is presented. Accelerated cyclic corrosion tests were conducted to assess the relative effect of corrosion on galvanized and ungalvanized wires. Samples were corroded under various levels of sustained loads in a cabinet that cyclically applied an acidic salt spray, dry conditions, and 100% relative humidity at elevated temperature, and mass loss, hydrogen concentration, ultimate load, and elongation at failure were measured. Elongation measurements indicated a significant embrittlement of the wires that could not be explained solely by the presence of absorbed hydrogen (hydrogen embrittlement). The main cause of reduction of wire elongation was found to be the surface irregularities induced by the corrosion process. The experimental results were validated through a numerical analysis using a finite-element method model of the corroded steel wire and through a series of scanning electron microscope analyses of the fracture surfaces.
-
conditions of suspension Bridge Cables new york city case study
Transportation Research Record, 1999Co-Authors: Raimondo Betti, Bojidar YanevAbstract:From the opening of the Brooklyn Bridge in 1883 to the opening of the Verrazano Narrows Bridge in 1964 the New York City Metropolitan Area was the center of the most intensive construction of record-breaking suspension Bridges worldwide. Of the 10 suspension Bridges in the area, 5 established span-length records at their completion. As the twentieth century draws to a close the current records are held elsewhere and these Bridges hold a record for the average age and total traffic they have jointly accumulated over the last 115 years. An understanding of suspension Bridge behavior can be gained nowhere better than in the examination of the New York examples. In an unprecedented joint effort partly including the New York City Department of Transportation, the New York State Bridge Authority, and the Port Authority of New York and New Jersey, all available information and present common recommendations and guidelines for inspection and rehabilitation of the cable systems were pooled. Some conclusions about the resulting comprehensive study on the condition of cable systems in suspension Bridges located in the New York Metropolitan Area are presented.
Francesco Ricciardelli - One of the best experts on this subject based on the ideXlab platform.
-
Effects of ice accretion on the aerodynamics of Bridge Cables
Journal of Wind Engineering and Industrial Aerodynamics, 2015Co-Authors: Cristoforo Demartino, Holger Koss, Christos T. Georgakis, Francesco RicciardelliAbstract:Abstract Undesirable wind induced vibrations of Bridge Cables can occur when atmospheric conditions are such to generate ice accretion. This paper contains the results of an extensive investigation of the effects of ice accretion due to in-cloud icing, on the aerodynamic characteristics of Bridge hangers and stay Cables. The aim of this paper is twofold; first, it was investigated the ice accretion process and the final shape of the ice accreted; then the aerodynamics of the ice accreted Bridge Cables was characterized, and related to the ice shape. Different climatic conditions, i.e. combinations of temperature, wind speed and yaw angle of accretion, were reproduced in a climatic wind tunnel, giving rise to different types of accretion. These were chosen such to generate the most common natural ice formations expected to produce Bridge cable vibrations. A description of the geometric characteristics of the ice accretions is given in the paper. Only for the Bridge hanger case, a short description of the evolution of the ice accretions is given. The aerodynamic force coefficients were then measured with varying yaw angle, angle of attack and wind speed, and are presented and discussed in the paper; these are found to be significantly affected by the characteristics of the ice accretion.
-
aerodynamic stability of ice accreted Bridge Cables
Journal of Fluids and Structures, 2015Co-Authors: Cristoforo Demartino, Francesco RicciardelliAbstract:Abstract The prediction of galloping instability is usually based on a quasi-steady approach, in which instantaneous wind forces are derived from the aerodynamic force coefficients obtained in static wind tunnel tests. Several galloping models exist, that differ for the degrees of freedom and for the geometric and aerodynamic characteristics considered. The aim of this paper is twofold: first, it compares the background hypotheses of the different galloping models, and the results they produce. This is done though an application to ice-accreted Bridge Cables, the analysis of the stability of which is the second aim of the paper. Wind tunnel data obtained by the authors for Bridge hangers and stay Cables are used in the calculations. As to the comparison among the different models, not existing a benchmark, the research is not aimed at judging the quality of each of them, but rather at pointing out the differences they bring and at discussing their most appropriate application.