Bridge Hangers Research Articles

Service life prediction for steel wires in hangers of a newly built suspension bridge considering corrosion fatigue and traffic growth

As the critical load-carrying components, hangers of long-span suspension bridges are exposed to the combined actions of corrosive environment and cyclic stresses. Service life evaluation of hangers is an important issue for bridge maintenance and safety. In this study, a service life prediction framework is presented by establishing a direct link between site-specific traffic loads and corrosion fatigue processes of hangers' steel wires. The cyclic stress responses of hangers are firstly obtained by inputting the weigh-in-motion (WIM)-based reconstructed vehicular loads to the refined finite element model. The fatigue loading effects, that is, equivalent stress ranges and corresponding number of cycles extracted from cyclic stresses, are explicitly expressed as functions of the bridge-site traffic loads. Then, the service lives of steel wires can be predicted based on the corrosion fatigue analysis with traffic growth. The proposed framework is applied to a newly built suspension bridge in China. Ninety-day bridge-site WIM data are utilized. It is indicated that the growing traffic density would greatly shorten the pitting corrosion time and accelerate the fatigue crack propagation of the steel wires, resulting in a dramatic decrease of the service lives of the hangers' steel wires.

Performance of suspension bridge hangers exposed to hazardous material fires considering wind effects

Traffic accidents involving vehicles transporting hazardous materials (HazMat) can cause serious fire hazards, threatening the safety of bridge infrastructure as well as nearby traffic. For critical bridges such as long-span cable-stayed and suspension bridges, fire hazards can not only cause severe structural damage, but also serious traffic disruption, congestion, and accidents. Unlike short-span bridges, long-span cable-supported bridges often experience considerable wind effects at the height of the bridge deck which can significantly influence fire hazards. As the critical components of cable-supported bridges, the failure of cables or hangers due to fire may trigger progressive failure of the bridge structure. Existing studies on fire simulation of long-span bridges, however, are very limited. Typical fire hazard scenarios from vehicles transporting hazardous material (HazMat) are simulated with fire dynamics simulation (FDS) software on a suspension bridge with a focus on the threats to hangers. To more realistically consider the potential fire hazards to bridge hangers of long-span bridges, appropriate fuel size, transverse offset distance, and wind effects are considered. The study of a baseline scenario is carried out first and followed by parametric studies to investigate the effects of wind speeds, longitudinal offsets, hazardous material types and spill sizes on the fire simulation results.

The Study on the Influence of Hanger’s Different Axial Deflection Based on Weibull Distribution

Based on the finite element analysis and tests on the strength of 7-wires steel strands under deflection, the bearing capacity of hangers of arch bridges considering deflection is studied. According to the results of finite element analysis and tests on steel strands that make of hangers, it is found that the decrease of bearing capacity of hangers is caused by the decrease of ultimate tensile strength of steel strands under the deflection. The ultimate tensile strength of steel stands will be weakened with the increase of extent of deflection and obeys Weibull distribution. Thus, the relationship between the ultimate tensile strength of steel strands and deflection angles are obtained in this paper by finite element analysis and tests. Furtherly, the ultimate tensile strength of steel strands obeying Weibull distribution under the deflection is used the to further research the bearing capacity of hangers.

Predicting fatigue damage of highway suspension bridge hangers using weigh-in-motion data and machine learning

Continuous and real-time tension force monitoring is a key point in fatigue damage evaluation for bridge suspenders or hangers. Usually, effective sensors are not equipped in suspenders or hangers of in-service bridges to obtain tension force responses. Bridge-site-specified traffic loading information collected by Weigh-in-motion (WIM) system offers an opportunity to address this issue. The daily fatigue damage of hangers can be estimated by combination of the traffic loading data with finite element analysis. Support vector machine (SVM) is adopted to establish the regression models between daily fatigue damage and collected traffic loading parameters. Consequently, the future fatigue damage of cables or hangers can be predicted by feeding the subsequent WIM data into the regression models. This proposed method is validated in the fatigue life prediction of hangers on a suspension bridge. The SVM model configuration and generalisation ability are investigated in this study. This study presents a novel way to estimate the fatigue damage of the hanger without direct stress sensing equipment and provides new thoughts in interpreting the monitoring data to provide useful information for engineering decision makers.

Numerical simulation of unsteady galloping of two-dimensional iced transmission line with comparison to conventional quasi-steady analysis

Most of the previous works on numerical analysis of galloping of transmission lines are generally based on the quasi-steady theory. However, some wind tunnel tests of the rectangular section or hangers of suspension bridges have shown that the galloping phenomenon has a strong unsteady characteristic and the test results are quite different from the quasi-steady calculation results. Therefore, it is necessary to check the applicability of the quasi-static theory in galloping analysis of the ice-covered transmission line. Although some limited unsteady simulation researches have been conducted on the variation of parameters such as aerodynamic damping, aerodynamic coefficients with wind speed or wind attack angle, there is a need to investigate the numerical simulation of unsteady galloping of two-dimensional iced transmission line with comparison to wind tunnel test results. In this paper, it is proposed to conduct a two dimensional (2-D) unsteady numerical analysis of ice-covered transmission line galloping. First, wind tunnel tests of a typical crescent-shapes iced conductor are conducted firstly to check the subsequent quasi-steady and unsteady numerical analysis results. Then, a numerical simulation model consistent with the aeroelastic model in the wind tunnel test is established. The weak coupling methodology is used to consider the fluid-structure interaction in investigating a two-dimension numerical simulation of unsteady galloping of the iced conductor. First, the flow field is simulated to obtain the pressure and velocity distribution of the flow field. The fluid action on the iced conduct at the coupling interface is treated as an external load to the conductor. Then, the movement of the conduct is analyzed separately. The software ANSYS FLUENT is employed and redeveloped to numerically analyze the model responses based on fluid-structure interaction theory. The numerical simulation results of unsteady galloping of the iced conduct are compared with the measured responses of wind tunnel tests and the numerical results by the conventional quasi-steady theory, respectively.

Experimental investigation on aerodynamic interference of two kinds of suspension bridge hangers

In order to study the aerodynamic interference between cables of suspension bridge hangers, two types of cable test models with smooth and rough surfaces, which respectively correspond to parallel wire strand (PWS) and wire rope (WR) hangers, were manufactured. The comparisons between the features of wake-induced vibration of the PWS and WR hangers were carefully investigated by means of wind tunnel tests. First, a series of force measurement tests for the two types of hangers were carried out to measure the mean aerodynamic coefficients of the downstream cable within spatial region of 3 ≤X≤11 and -4≤Y≤4 with an interval of ΔX =ΔY=0.25. The results of the force measurement tests show that obvious differences between the force coefficients of the downstream PWS and WR hangers are found. It seems that the variation amplitude of the force coefficient of the PWS hanger is significantly larger than that of the WR hanger. Moreover, the mean drag and lift coefficients of the downstream PWS hanger for U=15m∕s are obviously different from those for U=10m∕s, which indicates that the wake-induced vibration of the hanger might be strongly related to wind velocity (i.e., Reynolds Number). Second, a series of vibration measurement wind tunnel tests for the PWS and WR hangers were carried out to measure the responses of the downstream cables within the spatial region of 2.5≤X≤11 and 0≤Y≤4 with an interval of ΔX=ΔY=0.25. The results show that obvious wake-induced vibrations are both observed for the PWS and WR hangers. However, it appears that the unstable region of the WR hanger is significantly less than that of the PWS hanger, which indicates that the WR cable seems to be more suitable than the PWS cable to be used as the hanger of suspension bridge. Parametric studies show that the wake-induced vibration of the PWS hanger is not divergent because the amplitude of the downstream cable stop increasing with the increase of the wind velocity, whereas the oscillation amplitude of the WR hanger keeps increasing with the increase of the wind velocity (up to 18 m/s in the wind tunnel). Moreover, it seems that the structural damping ratio have no significant influence on the critical wind velocity of the wake-induced vibration of the hanger of the suspension bridge.

Probabilistic versus Deterministic Assessment of the Minimum Structural Damping Required to Prevent Galloping of Dry Bridge Hangers

AbstractThe risk of large-amplitude vibrations of bridge hangers due to galloping instabilities has posed a challenge to the engineering and research communities. Galloping vibrations can lead to s...

Aerodynamic interference between the cables of the suspension bridge hanger

The hangers of long-span suspension bridges are significantly prone to wind-induced vibrations due to their light mass, low frequency, and small structural damping. However, the underlying mechanism of the hanger vibration is not clearly clarified yet. To study the aerodynamic interference between the cables of the hanger, which is a possible mechanism for the hanger vibration, a series of wind tunnel tests were carried out to measure the mean aerodynamic drag and lift coefficients of a leeward cylinder. Then, the motion equations governing the vibration of leeward cable were derived based on the quasi-steady assumption. The numerical results show that large-amplitude vibrations of the leeward cable will occur in the region of 1 ≤ | Y| ≤ 3, where Y is a non-dimensional vertical coordinate normalized with the diameter of the cylinder. It appears that the stable trajectory of the leeward cable is ellipse, and trajectory is clockwise above the center line of the wake, whereas anti-clockwise below the center line of the wake. An important finding is that the frequency of the stable vibration of the leeward cable is slightly smaller than its natural frequency, which implies that a negative aerodynamic stiffness might arise. The time histories of the aerodynamic stiffness and damping forces on the leeward cable were identified from the numerical results. It seems that there is always a positive work done within a period by the aerodynamic stiffness force, whereas a negative work by the aerodynamic damping force. The response characteristics of the leeward cable of the hanger of suspension bridge obtained in this study are identical with those of the wake-induced flutter widely discussed for the power transmission line. This implies that wake-induced flutter theory could well illustrate the underlying mechanism of the aerodynamic interference effects on the hangers of a suspension bridge.

Wake-induced vibration of the hanger of a suspension bridge: Field measurements and theoretical modeling

The underlying mechanism of the wind-induced vibration of the hangers of the suspension bridges is still not fully understood at present and hence is comprehensively examined in this study. More specifically, a series of field measurements on the No. 2 hanger of the Xihoumen Bridge was first carefully conducted. Large amplitude vibrations of the hanger were found and the oscillation amplitude of the leeward cable was obviously larger than that of the windward cables. Furthermore, the trajectory of the leeward cable was close to an ellipse, which agreed well with the major characteristics of wake-induced vibration. Then, a theoretical model for the wake-induced vibration based on a 3-D continuous cable was established. To obtain the responses of the leeward cable, the finite difference method (FDM) was adopted to numerically solve the established motion equation. Finally, numerical simulations by using the structural parameters of the No. 2 hanger of the Xihoumen Bridge were carried out within the spatial range of 4 4<=X<=10 and 0<=Y<=4 with a uniform interval of delta X= delta Y=0.25. The results obtained from numerical simulations agreed well with the main features obtained from the field observations on the Xihoumen Bridge. This observation indicates that the wake-induced vibration might be one of the reasons for the hanger oscillation of the suspension bridge. In addition, the effects of damping ratio and windward cable movement on the wake-induced vibration of the leeward cable were numerically investigated.

Modal flexibility based damage detection for suspension bridge hangers: A numerical and experimental investigation

This paper addresses the problem of damage detection in suspension bridge hangers, with an emphasis on the modal flexibility method. It aims at evaluating the capability and the accuracy of the modal flexibility method to detect and locate single and multiple damages in suspension bridge hangers, with different level of severity and various locations. The study is conducted numerically and experimentally on a laboratory suspension bridge mock-up. First, the covariance-driven stochastic subspace identification is used to extract the modal parameters of the bridge from experimental data, using only output measurements data from ambient vibration. Then, the method is demonstrated for several damage scenarios and compared against other classical methods, such as: Coordinate Modal Assurance Criterion (COMAC), Enhanced Coordinate Modal Assurance Criterion (ECOMAC), Mode Shape Curvature (MSC) and Modal Strain Energy (MSE). The paper demonstrates the relative merits and shortcomings of these methods which play a significant role in the damage detection of suspension bridges.

Effects of aerodynamic interference on the iced straddling hangers of suspension bridges by wind tunnel tests

The wind-induced vibration of suspension bridge hangers may be ascribed to hanger icing. The aerodynamic characteristics of the iced straddling hangers of suspension bridges under various working conditions are analyzed in this paper via wind tunnel experiments. The analysis results show that the aerodynamic characteristics of leeward hangers are greatly influenced by the varying thicknesses of B- and D-shaped ice and suggest that lift force must be considered in the static analysis of suspension bridges. The hanger spacing of A × B = 8D × 4D, where the aerodynamic characteristics of leeward hangers with both B- and D-shaped ice are stable, can be used as reference for designers. The change in the aerodynamic coefficients of leeward hangers must also be considered when analyzing the stability of the straddling hangers of suspension bridges because iced hangers have different relative positions and the Strouhal number of leeward hangers rapidly fluctuate when the relative angle (β) is 4°. The shielding effect of windward hangers on leeward hangers with B- and D-shaped ice is most visible at a wind attack angle of −24°, and the drag coefficients of D-shaped iced hangers are obviously less than those of B-shaped iced hangers. The results of static analysis of suspension bridges are produce on non-conservative side results when hanger icing is disregarded. The findings of this study work can be used as references in the structural design and wind-resistance designs of suspension bridges with straddling hangers.

Unsteady Theoretical Analysis on the Wake-Induced Vibration of Suspension Bridge Hangers

Unsteady Theoretical Analysis on the Wake-Induced Vibration of Suspension Bridge Hangers

Damage Detection in Active Suspension Bridges: An Experimental Investigation.

This paper considers a Hilbert marginal spectrum-based approach to health monitoring of active suspension bridge hangers. The paper proposes to takes advantage of the presence of active cables and use them as an excitation mean of the bridge, while they are used for active damping. The Hilbert–Huang transform is used to calculate the Hilbert marginal spectrum and establish a damage index for each hanger of the suspension bridge. The paper aims to investigate the method experimentally, through a series of damage scenarios, on a laboratory suspension bridge mock-up equipped with four active cables; each active cable is made of a displacement actuator collocated with a force sensor. Different locations and levels of damage severity are implemented. For the first time, the investigation demonstrates experimentally the effectiveness of the technique, as well as its limitations, to detect and locate the damage in hangers of a suspension bridge.

Fatigue performance investigation for hangers of suspension bridges based on site-specific vehicle loads

Hangers or suspenders of a suspension bridge are the primary load-carrying members and are vital to the structural integrity and service life of the bridge. Site-specific vehicle loads monitored by the weigh-in-motion system can assist to obtain the operational cyclic stresses of hangers. Differing from most existing studies, herein, a framework for fatigue performance investigation for hangers of suspension bridges is proposed utilizing the full information of the weigh-in-motion data. This framework includes four steps: (1) generate influence surfaces for hangers, (2) reconstruct vehicular loading flows based on the weigh-in-motion data, (3) calculate time histories of hanger tension forces, and (4) evaluate fatigue damages and predict fatigue lives. Critical issues, such as the loading configuration of trucks, the threshold of the gross vehicle weight, and the time step for stress calculation, have been studied and discussed in detail. Based on 8-month weigh-in-motion data of a prototype suspension bridge, it is shown that the fatigue damage of hangers can be evaluated day by day, and subsequently the fatigue lives can be predicted. The correlation between the fatigue damages and vehicular loads is also investigated in this study.

Wake-flow-induced vibrations of vertical hangers behind the tower of a long-span suspension bridge

Violent vibrations have been reported in the vertical hangers of long-span suspension bridges, especially for those located in the vicinity of the towers. In the present study, an experimental investigation is performed to characterize the wake-flow-induced vibrations of vertical hangers behind the tower of a suspension bridge. The tower column and vertical cable models are determined by using a long-span suspension bridge with a geometrical scale ratio of 1:10. Regular vortex shedding from the tower column model is detected in the near wake with a Strouhal number (St) of 0.20, and the turbulence intensity of the wake flow behind the tower column model is found to be quite high. Arranged at different stations behind the tower column model, the vertical cables experience violent vibrations. The vibration frequencies of the vertical cables are synchronized with the vortex shedding from the upstream tower model within a certain velocity range, during which severe cable vibrations take place. When the incoming wind speed becomes high, the cable vibrations exhibit multimode characteristics. It is also found that the vertical cables arranged at the rear are subject to the combined interferences of the tower column model and the front cables. As a result, the vibration responses of the rear cables are more violent than those of the front cables.

Fast Warning Method for Rigid Hangers in a High-Speed Railway Arch Bridge Using Long-Term Monitoring Data

AbstractExcessive vibration of arch bridge hangers is a potential threat to the driving safety of high-speed trains; therefore, it is important to study the vibration characteristics and fast warni...

Indirect monitoring of vortex-induced vibration of suspension bridge hangers

Wind loading of large suspension bridges produces a variety of structural responses, including the vortex-induced vibrations of the hangers. Because it is impractical to monitor each hanger, this study explores the possibility of assessing the presence of these vibrations indirectly by analyzing the responses elsewhere on the structure. To account for the time-varying nature of the wind velocity, it is necessary to use appropriate time–frequency analysis tools. The continuous wavelet transform and the short-term Fourier transform are used here to obtain clear correlations between the vortex shedding frequency and the energy content of the Hardanger Bridge responses. The analysis of recorded signals from a permanent monitoring system installed on the deck and a temporary system installed on some of the hangers shows that it is possible to indirectly detect hanger-related vortex-induced vibrations from the deck response. Furthermore, this study elaborates on the detection of the two types of vortex-induced vibrations (cross-flow and in-line), the spatial variability of the results, and a possibility to automate the detection process. The ideas reported can be implemented readily in existing structural health monitoring systems for large cable-supported structures not only to identify vortex-induced vibrations but also to gain a better understanding of their structural response.

Aerodynamic performance analysis of wind-sand flow on riding-type hangers of suspension bridges

With global climate and environment deterioration, the desertification is getting worse and the phenomenon of wind-sand flow frequently occurs in many areas. Hangers of suspension bridges may suffer the impact from wind-sand flow and be damaged. In this study, the riding-type hangers with four strands which are the commonly used hanger of long-span suspension bridges are taken as an example to investigate the influence of wind-sand flow on the hangers. The aerodynamic interference effect can occur among the four strands under the action of wind-sand flow. In order to explore the influence of wind-sand flow on the hangers, the wind-sand flow field around the riding-type hangers of a long-span suspension bridge is simulated within the FLUENT software on the basis of the numerical simulation of computational fluid dynamics. The pressure and velocity contour, aerostatic coefficients and forces produced by the wind-sand flow under different wind attack angle and volume fractions of sand phase are analyzed from the simulation. Results indicate that the forces exerted by the wind-sand flow on riding-type hangers are greater than the forces exerted only by wind. In the wind and wind-sand flow field, the drag and lift coefficients of the front two strands of hangers exhibit minor changes with increasing wind attack angle, whereas those of the back two strands increase first and then decrease to a small value. The volume fraction of the sand phase has an insignificant effect on the drag and lift coefficients, but has a significant effect on the force exerted on the hanger, and the force exerted on the hangers multiplies when the volume fraction of the sand phase multiplies. The results lay a theoretical foundation for the corrosion fatigue analysis of riding-type hangers for large-span suspension bridges under the action of wind-sand flow.

Bayesian estimation of tension in bridge hangers using modal frequency measurements

The tension of an arch bridge hanger is estimated using a number of experimentally identified modal frequencies. The hanger is connected through metallic plates to the bridge deck and arch. Two different categories of model classes are considered to simulate the vibrations of the hanger: an analytical model based on the Euler-Bernoulli beam theory, and a high-fidelity finite element (FE) model. A Bayesian parameter estimation and model selection method is used to discriminate between models, select the best model, and estimate the hanger tension and its uncertainty. It is demonstrated that the end plate connections and boundary conditions of the hanger due to the flexibility of the deck/arch significantly affect the estimate of the axial load and its uncertainty. A fixed-end high fidelity FE model of the hanger underestimates the hanger tension by more than 20 compared to a baseline FE model with flexible supports. Simplified beam models can give fairly accurate results, close to the ones obtained from the high fidelity FE model with flexible support conditions, provided that the concept of equivalent length is introduced and/or end rotational springs are included to simulate the flexibility of the hanger ends. The effect of the number of experimentally identified modal frequencies on the estimates of the hanger tension and its uncertainty is investigated.

Degradation Model and Security Analysis of Hangers of Suspension Bridges

Degradation Model and Security Analysis of Hangers of Suspension Bridges