Main Cables Of Suspension Bridges Research Articles

A Novel Methodology for Inspection and Strength Evaluation of Suspension Bridge Main Cables

A novel methodology is proposed to evaluate the ultimate strength of the main cables of suspension bridges using information obtained from site inspections and from tensile strength tests on selected wire samples extracted from the bridge’s main cables. A new model is proposed accounting for the spatial variation of individual wires’ strength along their length, an important physical attribute of corroded wires considered here for the first time. This model includes (1) mapping the corrosion stage variation along one-panel-long wires that are visible during an inspection; (2) establishing probability distribution functions for the ultimate tensile strength of 0.46 m (18 in.)–long wire segments in each corrosion stage group; (3) generating random realizations of the ultimate strength of all the wires in the cable’s cross section, accounting for their strength variation along the entire panel length; and (4) accounting for the effect of broken wires in the evaluation panel as well as in adjacent panels. A Monte Carlo simulation approach is finally proposed to generate random realizations of the ultimate overall strength of the cable, using an incremental loading procedure. The final outcome is the probability distribution of the ultimate strength of the entire cable. The methodology is demonstrated through the cable strength evaluation of the Franklin Delano Roosevelt Mid-Hudson Bridge using results of a 2009 inspection, and compared with corresponding results obtained using current guidelines. The proposed methodology provides estimates of higher accuracy and reliability for the cable’s ultimate strength, without essentially increasing the cost of inspections.

Numerical Simulation of Airflow in the Main Cable of Suspension Bridge with FPM Model

The main cable of suspension bridges is subject to corrosion and requires advanced anti-corrosion technology. Consequently, the internal airflow of the main cable has become a significant research focus. This study employs image processing and machine learning to analyze the cross-sectional images of the main cable and reveals the distribution characteristics of pores and fractures within the main cable cross-section. The numerical simulation model of the main cable is divided into inner and outer parts based on porosity, with porosity levels of 18.16% and 32.11%, respectively. Fractures randomly occurred in the inner part, with a probability of 31.37%. A simulation model based on fractured porous media (FPM) is developed, which innovatively incorporates the fracture flow model into the numerical simulation of the internal airflow of the main cable. The numerical simulation clearly explores the intricate details of the internal flow field of the main cable, revealing that the existence of fractures has a great impact on the internal flow field of the main cable. Additionally, the relative deviation of specific frictional head loss between the field experiment and numerical simulation is about 6.83%, indicating that the numerical simulation results are relatively reliable.

Parameter Selection for the Dehumidification System of the Main Cable of Suspension Bridge Based on Ventilation Experiments

Moisture in the main cable is the main cause of steel wire corrosion. Modern suspension bridges utilize main cable dehumidification systems to prevent corrosion. The main cable ventilation experiment can help the selection of the system parameters. This research is based on the ventilation experiment of the main cable of Xihoumen Bridge to obtain the design parameters of the dehumidification system. According to the experiment, the suitable dehumidification distance is 150–180 m; the pressure loss of the main cable with a length of 150 m is 200–300 Pa, so the inlet pressure should be higher than 300 Pa; increasing the outlet clamp can increase the dehumidification efficiency; Under single inlet and double outlet situation, every 100% increase in air volume increases the dehumidification capacity is about 35%. The water content of the main cable of Xihoumen Bridge is 5.74 kg/m3, and 1 m3 of dry air can remove 5.5 g of water under experimental conditions, and the minimum air volume is 30 m3/h. The main factors affecting the dehumidification time are air volume and leakage rate. Input these parameters into the dehumidification system for the dehumidification experiment, and the water content of the outlet clamp will drop by about 37.5% within ten days.

Reliability-assisted determination of partial factors for the design of main cables considering secondary stress effect

The main cables of suspension bridges typically serve as the primary load-carrying components. Determination of reasonable main cable sizes is crucial for the bridge safety and functionality. The limit state design method with the combination of partial factors has been widely used in multiple countries as a substitute for the factor of safety design method. Determination of reasonable partial factors that can properly satisfy a target reliability index has received much attention. However, most of the existing research neglects the secondary stress effect, which can be of a significant magnitude, for the main cable. To address the gap, this paper proposes a reliability-assisted framework for the determination of the partial factors considering both first and secondary stresses for the main cable design. Three suspension bridges with main span lengths ranging from 850 m to 2300 m are used as the engineering background. Results show that the recommended design factors can be used in the preliminary design stage to facilitate a reasonable cable design that yields the target reliability index, therefore validating the feasibility of the proposed framework.

Galloping analysis of the main cable in construction: An advanced nonlinear scheme

The main cables of suspension bridges in construction are non-circular sections and thus prone to galloping vibrations. The traditional galloping analysis is a linear scheme and cannot address the nonlinearities and coupling effects among the multidirectional vibrations. To provide an approach for the nonlinear galloping, this paper proposes an advanced continuum model based on Hamilton's principle and variational calculus, which can systemically consider the translational and rotational vibrations and the nonlinearities from the geometric, damping and wind effects. On this basis, the computational approach for the continuum model in COMSOL Multiphysics is investigated, and the result comparisons between the proposed approach and finite element method indicate that the continuum model together with the computational approach can accurately determine the dynamic responses of the main cable. When the quasi-steady based wind forces are included, the nonlinear model can be easily used for galloping analysis, and the limit cycle oscillations (LCOs) in the post-instability of the adopted example are obtained, which are the typical nonlinear aeroelastic phenomena for bluff bodies. Also, the obtained frequency evolution of the LCOs is discussed.

Dynamic contact behaviors of saddle materials for suspension bridge

In order to prevent skid accidents of main cable of suspension bridge, dynamic contact behaviors between saddle materials and steel wires were explored in the present study. Dynamic contact tests of saddle materials were conducted employing the self-made dynamic contact test rig. Dynamic contact behaviors of the saddle material (transverse slip, longitudinal deformation, contact state, wear mechanism) in a friction cycle were investigated. Effects of transverse and longitudinal locations, friction cycles and saddle materials on the dynamic contact behaviors were presented. The results show that dynamic contact states between saddle specimen and steel wireexhibits the adhesion-gross slip-adhesion-gross slip state in a friction cycle. The transverse slip and longitudinal deformation of saddle specimen both decrease with increasing distance to the contact interface, decrease along the transverse sliding direction, and increase with increasing friction cycles. The ZG270-480 saddle material exhibits the largest average transverse slip and longitudinal deformation, while ZG275-485 saddle material shows the smaller values.

Study of Anticorrosion System and Anticorrosion Mechanism for the Main Cable of Suspension Bridge

Abstract There are many problems in the commonly used anticorrosion technologies of the main cable, which has been difficult to meet the anticorrosion requirements of the main cable. In order to so...

Tie Rod-Equivalent Non-Linear Constitutive Law for Uniformly Loaded Cables.

Cables are typically used in engineering applications as tensile members. Relevant examples are the main cables of suspension bridges, the stays of cable-stayed bridges, the load-bearing and stabilizing cables of tensile structures, the anchor cables of floating mooring structures, the guy-ropes for ship masts, towers, and wind turbines, the copper cables of electrical power lines. Since cables are characterized by non-linear behavior, analysis of cable structures often requires advanced techniques, like non-linear FEM, able to consider geometric non-linearity. Nevertheless, a traditional simplified approach consists in replacing the cable with an equivalent tie rod, characterized by a suitable non-linear constitutive law. Currently used equivalent constitutive laws have been derived by Dischinger, Ernst and Irvine. Since the equivalence is restricted to taut cables, characterized by small sag to chord ratios, these traditional formulae are not appropriate for uniformly loaded sagging cables: the main cables of suspension bridges are a particularly emblematic case. Despite some recent attempts to find more refined solutions, the problem is still open, since closed form solutions of general validity are not available. In the paper, general analytical formulae of the non-linear constitutive law of the equivalent tie rod are proposed, distinguishing two relevant cases, according as the length of the cable can vary or not. The expressions, derived by applying the general form of the theorem of virtual work, can be applied independently on the material, on the sag to chord ratio, on the load intensity and on the stress level, so allowing the replacement of the whole cable with a single equivalent tie rod. The expressions are critically discussed referring to a wide parametric study also in comparison with the existing formulae, stressing the influence of the most relevant parameters.

New dehumidification system design and dehumidification test for the main cable of suspension bridge

New dehumidification system design and dehumidification test for the main cable of suspension bridge

On the modeling of the annual corrosion rate in main cables of suspension bridges using combined soft computing model and a novel nature-inspired algorithm

On the modeling of the annual corrosion rate in main cables of suspension bridges using combined soft computing model and a novel nature-inspired algorithm

A Novel Shape Finding Method for the Main Cable of Suspension Bridge Using Nonlinear Finite Element Approach

The determination of the final cable shape under the self-weight of the suspension bridge enables its safe construction and operation. Most existing studies solve the cable shape segment-by-segment in the Lagrangian coordinate system. This paper develops a novel shape finding method for the main cable of suspension bridge using nonlinear finite element approach with Eulerian description. The governing differential equations for a three-dimensional spatial main cable is developed before a one-dimensional linear shape function is introduced to solve the cable shape utilizing the Newton iteration method. The proposed method can be readily reduced to solve the two-dimensional parallel cable shape. Two iteration layers are required for the proposed method. The shape finding process has no need for the information of the cable material or cross section using the present technique. The commonly used segmental catenary method is compared with the present method using three cases study, i.e., a 1666-m-main-span earth-anchored suspension bridge with 2D parallel and 3D spatial main cables as well as a 300-m-main-span self-anchored suspension bridge with 3D spatial main cables. Numerical studies and iteration results show that the proposed shape finding technique is sufficiently accurate and operationally convenient to achieve the target configuration of the main cable.

Research on Dynamic Contact and Slip Mechanisms of Parallel Steel Wires in the Main Cable of Suspension Bridge

Research on Dynamic Contact and Slip Mechanisms of Parallel Steel Wires in the Main Cable of Suspension Bridge

Post-critical behavior of galloping for main cables of suspension bridges in construction phases

The main cables of suspension bridges show various cross-sectional shapes with the evolution of construction phases, and they may suffer from severe galloping at certain conditions. The aim of this work is to provide a convenient tool for predicting the critical condition and galloping amplitude of main cables, and to explore the in-depth driving mechanism of nonlinear galloping. Firstly, a numerical scheme of fluid–structure interaction (FSI) was developed to predict the galloping performance of main cables, and the numerical results of both critical conditions and vibration amplitude of galloping were compared to those of wind tunnel tests. The validated computational scheme was then used to investigate the driving mechanism of nonlinear galloping from the perspectives of nonlinear aerodynamic damping and work of aerodynamic lift. Moreover, the amplitude dependencies of unsteady and nonlinear aerodynamic lift were studied. It is found that the hysteresis of the flow with respect to the motion of the main cable is an important reason responsible for the nonnegligible unsteadiness in aerodynamic lift. Remarkable multiple-frequency components of aerodynamic lift emerged at large vibration amplitude, which were caused by the variation of instantaneous relative wind incidence angle for main cable in oscillation. Low-order harmonic components of aerodynamic lift at small vibration amplitude were the trigger of galloping, while the high-order components which contribute negative work at large vibration amplitude were responsible for the nonlinear aerodynamic damping and limited cycle oscillation. Unsteady characteristics of aerodynamic lift were the main cause for the variation of work proportions between different order harmonic components.

Experimental investigation of wind-induced vibrations of main cables for suspension bridges in construction phases

The main cables of suspension bridges show a changing cross-sectional shape with the evolution of construction phases, and they may suffer from severe wind-induced vibrations at certain conditions. The primary objective of this research was to examine the aerodynamic performance of the main cable in construction phases and to develop appropriate countermeasures to eliminate the potential wind-induced vibrations. Two cross-sections with different shapes of a main cable were chosen, and a series of wind tunnel tests were performed in a reduced wind velocity range of 32–366 using elastically mounted sectional models. Galloping occurred for the two cross-sections under certain wind incidence angles when a critical velocity was reached. No obvious hysteresis phenomenon of galloping was observed in the tests. The steady amplitude of galloping increased linearly with wind velocity and the increasing rate almost kept constant for different structural damping ratios. The aerodynamic nonlinearity, rather than the structural damping nonlinearity, is the main source leading to the limited amplitude oscillation. An empirical expression of galloping amplitudes for the two cross-sections was derived based on the test data. Meanwhile, the critical wind velocity was studied in a Scruton (Sc) number range of 108–4196 (as varied by changing the initial structural damping ratio between 0.093% and 3.62%). Results showed that the Den Hartog criterion was applicable to forecast the possibility of galloping, but not able to estimate the critical wind velocity for the main cable. Linear fitting method can be used to predict the critical velocity based on the experimental data. Finally, three vibration mitigation measures were studied, and a combination of structural and aerodynamic measures was recommended for galloping mitigation of main cables.

Cross-Sectional Loss Quantification for Main Cable NDE Based on the B-H Loop Measurement Using a Total Flux Sensor

In the real world, the main cables of suspension bridges are commonly inspected by conducting a periodic visual inspection of the exterior cover of the cable. Although there is a need to conduct a nondestructive evaluation (NDE) of the damage of the main cable, a suitable NDE technique has not yet been developed due to the large diameter and low accessibility of the cable. This study investigates a magnetic sensing cross-sectional loss quantification method that can detect internal and external damage to the main cables. This main cable NDE method applies an extremely low-frequency alternating current (ELF-AC) magnetization method and search coil sensor-based total flux measurement. A total flux sensor head consists of a magnetization yoke and a search coil sensor. To magnetize the main cable, a magnetic field was generated by applying a triangular ELF-AC voltage to the electromagnet yoke. The sensing part measures the magnetic flux that passes through the search coil, and the B-H loop was then obtained using the relationship between the ELF-AC voltage that has been input and the total flux that was measured. Also, the cross-sectional loss can be quantified using a variation of magnetic features from the B-H loop. To verify the feasibility of using the proposed NDE technique, a series of experiments were performed using a main cable specimen with a gradual increase in the cross-sectional loss. Finally, the relationship between the cross-sectional loss and extracted magnetic feature was determined and used to quantify the cross-sectional loss via the proposed method.

16.10: Challenges with water ingress in bridge cable systems

ABSTRACTExperiences over the last 20 years with operation and maintenance of cable borne bridges of various ages shows that water ingress in steel cable systems often occurs and causes a large risk of serious corrosion with may lead to restriction in traffic, extra ordinary inspection and maintenance costs and in worst case bridge closure. Examples of such experiences cover suspension bridges as well as cable stay bridges in USA, UK, Germany, France, Argentina, Sweden, Norway, Denmark and many other countries. The problem with water ingress is particularly critical as inspections for corrosion in cable systems are difficult to carry out and early warnings difficult to obtain.Water ingress into a cable system means that there is a significant risk of steel corrosion even with precautions by use of galvanization and HDPE coating of cable wires. Although, cable system designs generally comprise multiple barriers against corrosion, there is often a weak link in the design. This combined with an unintended outcome in the construction phase or inadequate maintenance, may allow water to start accumulating and lead to corrosion.This paper will explain and discuss cases from main cable and cable stay systems and point out the water ingress modes and their causes for main cable systems and different cable stays systems. Based hereupon, the paper discusses the weaknesses of the different steel cable concepts and different mitigations. The discussion also includes the mitigation of the water ingress problem by use of dehumidification. For main cables of suspension bridges, the concept has been in operation for more than 15 years with success. Considering the number of known problems with water in cable stays, the paper also contemplates on the possibility of using dehumidification for cable stay bridges as a way of handling the large amount of existing cable stay bridges.

Challenges of water ingress into bridge cable systems

Experience with the operation and maintenance of cable-borne bridges of various ages over the last 20 years shows that water ingress into steel cable systems often occurs and causes a high risk of serious corrosion that may lead to traffic restrictions, extraordinary inspection and maintenance costs and, in the worst case, bridge closures. Examples of such experience cover suspension bridges as well as cable-stayed bridges in the USA, UK, Germany, France, Argentina, Sweden, Norway, Denmark and many other countries. The problem of water ingress is particularly critical as inspections for corrosion in cable systems are difficult to carry out and early warnings difficult to obtain. Water ingress into a cable system means that there is a significant risk of steel corrosion even with precautions such as the use of galvanization and HDPE coating of cable wires. Although cable system designs generally comprise multiple barriers against corrosion, there is often a weak link in the design. This, combined with an unintended outcome in the construction phase or inadequate maintenance, may allow water to start accumulating and lead to corrosion. This paper will explain and discuss cases from main cable and cable-stay systems and point out the water ingress modes and their causes for main cable systems and different cable-stay systems. Based on that, the paper discusses the weaknesses of the different steel cable concepts and different mitigations. The discussion also includes the mitigation of the water ingress problem through the use of dehumidification. This concept has been successfully used for the main cables of suspension bridges for more than 15 years. Considering the number of known problems with water in cable stays, the paper also contemplates the possibility of using dehumidification for cable-stayed bridges as a way of handling the large number of existing cable-stayed bridges.

Angular change and secondary stress in main cables of suspension bridges

Three basic cable equations are proposed for evaluating the deflected shape of the main cables of suspension bridges subject to angular changes near the saddles of the main towers as well as the cable bands. The secondary stress on the tensioned parallel wires can be estimated via the combined use of the three basic cable equations that take into account the free and/or friction slip between wires as a function of the lateral restraints by cable bands and wrapping wires. A series of laboratory loading tests were carried out for a parallel wire strand to validate the proposed procedure. The proposed method was also applied to the Yi Sun-sin Bridge to demonstrate the level of secondary stress in parallel wires and to identify the factors that have an impact on the secondary stress in the completed stage as well as during the construction phase. The residual tension of the wrapping wire, which impacts the frictional resistance between wires of the main cable, was measured from field tests. The evaluated secondary stress was found to exceed 10% of the tensile strength of the wires. The findings reported herein also confirm that the distance between the tower saddle and the first cable band is a critical factor for secondary stress. Based on the experimental validation and application to an actual bridge, the proposed approach, despite being based on simplified formulations, is demonstrated to be useful in predicting the secondary stress that develops in parallel wire cables.

Monitoring the structural health of main cables of suspension bridges

In this paper, the results of a study focused on the development of a corrosion monitoring system for main cables of suspension bridges are presented. These sensors measure corrosion rate as well as quantities like temperature and relative humidity that are directly correlated to corrosion activity. Such a sensor network was first tested in a laboratory setting using a full-scale cable mock-up and, later, tested on the main cable of one of the major suspension bridges in the New York metropolitan area. Having the possibility of measuring temperature and relative humidity inside th1e cross-section of a main cable also allowed us to test the effectiveness of the cable dehumidification strategy.

Research on the Exchangeable Main Cable of Suspension bridge

Research on the Exchangeable Main Cable of Suspension bridge