Bridge Cables Research Articles

Improving the identification of dynamic parameters of bridges by UAV: approach for SHM

The structural integrity of bridges is susceptible to deterioration caused by traffic loads, environmental conditions, and weather phenomena. To maintain the safety and stability of bridges, regular inspections of their elements are required. Recent advances in the field of unmanned aerial vehicles (UAVs) provide a viable option for accurate and autonomous inspections of bridge structures without disrupting normal operations. This study focuses on the determination of the dynamic structural parameters of a suspension bridge. The methodology focuses on determining the natural vibration frequency of the bridge cables using UAV imagery. This paper contains a detailed theoretical presentation of the algorithm used, accompanied by a careful analysis of simulation results and empirical data from laboratory experiments and real case studies. In addition to the image processing-based approach for estimating the vibration frequency, the sensors on board the drone are also scrutinized and their effectiveness in detecting structural vibrations after the drone lands on the bridge surface is evaluated.

Fast Cable-Force Measurement for Large-Span Cable-Stayed Bridges Based on the Alignment Recognition Method and Smartphone-Captured Video

The accurate measurement of cable force plays an important role in the structural form, structural behavior, and safety evaluation of large-span cable-stayed bridges. A fast cable-force estimation method is proposed based on the alignment recognition method and smartphone-captured video. This method can realize real-time, non-contact, and non-destructive force measurements. Videos of bridge cables were collected using a portable smartphone, and an alignment recognition method was employed to obtain the lateral displacement along the cable, followed by numerical differentiation of the lateral displacement of the cable to acquire the acceleration time history. Based on the fundamental dynamic equation of beam elements, a unified explicit formula for cable-force calculation considering service characteristics was established in the frequency method. Finally, the method was applied to the cable-force measurement during the operation and maintenance stage of the Gengcun Dou Bridge. The measured cable forces were compared with the values obtained from the on-site monitoring system. The results show that the proposed method can accurately identify the acceleration time history at different positions of the cable, and the corresponding frequency components are essentially consistent. The average relative deviation of the measured cable forces from the reference method is within 3%. The proposed cable-force measurement method is simple as regards equipment, convenient for operation, and high in efficiency, providing a new method for the measurement of cable forces in large-span cable-stayed bridges, which can offer reliable measured cable-force data for structural analysis during bridge operation and the maintenance stage.

Research and development of corrosion monitoring sensor for bridge cable using electrical resistance probes technique

A cable corrosion monitoring sensor with a temperature compensation probe has been designed and manufactured to monitor the corrosion of high-strength steel wires in the transition zone between the cable body and the anchorage. The influence of temperature and tensile force on the resistance of steel wires was thoroughly investigated. Reliability tests were conducted on the temperature compensation probe, along with salt spray corrosion tests on the corrosion sensor. The research results demonstrated that, compared to the temperature sensor, temperature compensation probe can better reflect the actual temperature of the corrosion sensor and provide effective temperature compensation for the corrosion sensor. Moreover, the developed corrosion sensor can effectively reflect the mass loss rate of the corrosion probe. The sensor is capable of detecting a corrosion level as low as 0.02 % of the complete steel wire mass, which corresponds to an average corrosion depth of 0.412 μm.

Algorithms for Computer-Based Calculation of Individual Strand Tensioning in the Stay Cables of Cable-Stayed Bridges

This paper introduces algorithms for computer-aided calculation, based on a proposed computational model for stay cables, decomposed from a bridge’s structural system. These algorithms determine the necessary tension forces and corresponding deformations in the cables for individual strand tensioning using lightweight hydraulic jacks. Two tensioning methods are discussed: the first involves single-cycle tensioning with varying force intensities, while the second employs multiple cycles by applying forces of constant intensity until achieving an equalization of forces in all strands of the cable. The efficiency of the proposed procedures is demonstrated through a numerical example.

Full-length strain and damage monitoring for carbon fiber reinforced polymer cable based on optical frequency domain reflectometry

Lightweight, high-strength, corrosion-resistant, and fatigue-resistant carbon fiber reinforced polymer composite (CFRP) cables for cable-stayed or suspension bridges have been considered an excellent alternative to traditional steel cables. In the present paper, optical frequency domain reflectometry (OFDR) technology was applied to realize self-monitoring of the full-length strain and damage of CFRP rod-cable. The full-length axial tensile strain distribution of a 35 m CFRP cable was verified with the tensile test. The strain accuracy was verified to be 1.61 %, with a spatial resolution of ≤ 10 mm and a strain precision of 3.92 με throughout the full-length strain distribution. In comparison to the actual cable force, the cable force distribution, which is based on partial self-monitoring CFRP rods, demonstrates a deviation of approximately 1.6 %. The rod fracture damages in the CFRP cable were identified using wavelet smoothing, resulting in a localization error of ≤ 0.645 m and a quantification error of less than 15 %. According to the present study, methods to determine the cable force distribution and fracture damage for a CFRP cable were proposed.

Evaluating the load-bearing capacity of corroded cables in long-span cable-stayed bridges: A stochastic corrosion field simulation approach

In cable-stayed bridges, cables are the primary load-bearing components. The corrosion of high-strength steel wires within these cables can degrade their bearing capacity, which in turn impacts the safety and durability of long-span cable-stayed bridges. To address this concern, a three-dimensional random field model was proposed in this study to evaluate the residual bearing capacity of corroded cables. This model considers the random distribution of the strength of high-strength wires along both axial and cross-sectional directions caused by corrosion. Subsequently, a three-dimensional spatial correlation model was developed based on field test results from two stay cables in service on an actual bridge. This model represents the strength distribution of corroded high-strength steel wires within the cable. Finally, the evaluation model developed in this study was employed to assess the bearing performance of two corroded cables with different degrees of corrosion. The results were then compared with test outcomes. The results show that the proposed evaluation model can accurately estimate the bearing performance of corroded cables.

Development of multi-channel magnetic flux leakage testing system for bridge cables

Magnetic flux leakage (MFL) is one of the most popular techniques for detecting broken wire in bridge cables. MFL sensor array has attracted a lot of attention in recent years due to its capacity to measure the spatial distribution of the magnetic field of bridge cable. More sensors in the array lead to increased useful information extraction from the MFL field, allowing for more precise quantitative evaluation of bridge cable damage. This study reports the development of a cable MFL testing system capable of synchronous acquiring up to 512 channels of MFL sensors signal. Radial sensor arrays (RSA) composed of vertically placed magnetic sensors spaced at equal intervals are developed to be arranged around the bridge cable. They record the spatial distribution of the magnetic leakage field of the broken wire by collecting the MFL signal at various lift-offs. To solve the problem of multi- channel MFL signal synchronous acquisition, this study develops a MFL signal acquisition card based on multiplexing technology, capable of synchronous acquisition of up to 512 channels of MFL signal. Multiplexers are used to switch sensor channels, followed by multi-channel A/D conversion chips to convert the transmitted data. The converted data are temporally stored in the First-In-First-Out (FIFO) buffer of the Field Programmable Gate Array (FPGA) and transferred to the computer through the network port for display, storage, and signal processing. Finally, the motion control circuit, mechanical structure, and control software of the bridge cable MFL testing system are fully customized. Experiment results reveal that the system can be used in multi-channel MFL testing, laying the foundation for further multi-channel signal processing and bridge cable health evaluation.

Evaluating Stress Corrosion Damage of Steel Wires as Bridge Cables Based on the Corrosion Surface

Evaluating Stress Corrosion Damage of Steel Wires as Bridge Cables Based on the Corrosion Surface

A Simulation-Based Investigation on Thermal Responses of Suspension Bridge Tower Under Different Fire Scenarios

AbstractRecords of bridge fire incidents illustrate that bridge fires can have catastrophic consequences. The severity of these fires can be influenced by various factors such as bridge type, vehicle size, and wind. Contrary to building fires that have been extensively studied, scant attention has been paid to bridge fires and more specifically fire exposure to the suspension bridges. In addition, existing bridge fire literature is mostly concentrated on fire exposure to girders or cables of suspension bridges. Therefore, this study focused on the post-fire condition of a fire-exposed suspension bridge tower using computational fluid dynamics (CFD) modeling techniques and finite element analysis (FEA). The impacts of the main bridge fire parameters including vehicle size, exposure duration, distance between the fire source and tower, and wind effects were also evaluated. Initially, fire dynamic simulator (FDS) was used to simulate 12 different fire scenarios. The time–temperature histories obtained from each scenario were transferred to the ABAQUS finite element (FE) software to conduct transient thermal analysis and obtain the temperature development within the steel tower of the bridge. The post-fire evaluation was performed with respect to the temperature-induced reduction in the yield strength of steel. The results show that fire exposure from a fuel truck in the proximity of a steel tower could significantly reduce the strength of the tower and lead to severe damage. Early control of the fuel truck fire is crucial in reducing the severity of the damage and preventing temperature development in higher areas of the tower. Although a wind toward the tower can significantly increase the fire-induced damage to the bottom parts of the tower, it considerably reduces the temperature exposure to the higher parts of the tower. Fire exposure from a normal vehicle does not put the tower at risk of failure, and an unprotected steel tower can withstand it. However, a bus fire may lead to minor damage. The thermal strengthening of the first 20 m of the tower can help in preventing the potential fire damage.

In-plane free vibration of a two-cable network with multiple flexible cross-ties considering the effects of dynamic axial forces of the cables

Equipping cross-ties on the cables of cable-stayed bridges to form a cable network is regarded as an effective measure to suppress large cable vibrations and has been realized in practical engineering. However, most of the existing studies on the suspended cable (small sag) network have ignored the contributions of dynamic axial forces to transverse forces of the cables. More importantly, the dimension of the characteristic matrix is relatively large. Therefore, the current study introduces the transfer matrix method (TMM) to solve the in-plane free vibration problem of a two-cable network with dynamic axial forces of the cables considered simultaneously. Compared with the methodology utilized by the previous studies, the dimension of the resulting characteristic matrix is smaller and is independent of the number of cross-ties. Three cases, i.e., a two-cable network with two cross-ties, with three cross-ties and with four cross-ties, are explored in detail. Their frequencies and mode shapes are compared with those obtained by finite element model (FEM) to demonstrate the validity of the results in this paper. Meanwhile, the effects of dynamic axial forces on the first two frequencies and mode shapes are analyzed. The results show that the contributions of dynamic axial forces should be taken into account in transverse forces when calculating the first two frequencies of the cable network with flexible cross-ties.

Dynamic Response Analysis of Moving Loads over Tension Cables of Connected Tower Cable-Stayed Bridge

Due to its strong crossing ability, cable-stayed bridges have become the mainstream bridge type for large and medium spans. The connected tower cable-stayed bridge is different from traditional single span cable-stayed bridges, integrating the characteristics of split frame structure and connected tower design, and has better structural mechanical properties. However, the complex cable layout, multi tower structure, and segmented bridge deck of the cable-stayed bridge with connected towers result in essential differences in its mechanical behavior compared to traditional bridges. Therefore, studying the dynamic response of cable-stayed bridge cables when vehicle loads pass through the bridge is of great practical significance. This article comprehensively considers two factors: vehicle weight and vehicle speed, and introduces the parameter of dynamic amplification factor. The numerical simulation method is used to analyze the dynamic response of the cable when a vehicle load passes through a cable-stayed bridge with a connected tower. In order to provide key data support and important references for the construction and operation monitoring of cable-stayed bridges with connected towers.

Acoustic emission technology-based waveguide localization method for damaged internal tendons of in-service post-tensioned hollow slab bridges

Prestressing tendons are crucial load-bearing elements in post-tensioned hollow slab bridges. Damage to these tendons significantly reduces the safety, functionality, and longevity of the bridge. Regular monitoring of prestressing tendons is essential for bridge operation. Acoustic emission technology, known for its high accuracy and sensitivity to minor vibrations, is a key technique for monitoring bridge cables. This study proposes a novel dual-sensor acoustic emission localization method for detecting tendon damage in post-tensioned hollow slab bridges, utilizing waveguide technology. The effectiveness of this method is confirmed through hammering tests that simulate acoustic emission damage on operational hollow slab bridges. The proposed method, requiring only two sensors, offers a cost-effective alternative for monitoring the entire span of post-tensioned hollow slab bridges, so that effectively reduces the cost of bridge health monitoring and is easy to be promoted in actual engineering projects.

EnhancedPVE: Video Phase-Based Nonidentification Microvibration Measurement for Bridge Cables

EnhancedPVE: Video Phase-Based Nonidentification Microvibration Measurement for Bridge Cables

Corrosion protection failure test analysis of the initial damaged cable ICCP mechanism

Given the corrosion protection failure of the cable-stayed bridge cable in the actual project, the impressed current cathodic protection (ICCP) technology was used to carry out the anti-corrosion tests from steel wire scale to cable scale, analyze the corrosion protection characteristics of steel wire ICCP, deduce the corrosion factor ICCP diffusion model, and reveal the space ICCP mechanism of the initial damaged cable. The analysis shows that ICCP can effectively inhibit the corrosive effect of steel wires and cables, and reduce the loss of mechanical properties of steel wires. Its protective efficiency increases with an increase in the absolute value of its protective potential and decreases with an increase in the dead load level. ICCP has a blocking effect on the diffusion of corrosion factors in the cable space, and the corrosion spatial distribution range, corrosion factor concentration, and diffusion coefficient of the initial damaged cable decrease significantly with the increase in the absolute value of the protection potential. The open circuit potential moves in a positive direction with the development of the corrosion process, and the blocking effect of corrosive factor diffusion is transformed from the joint participation by sacrificial anode cathodic protection and ICCP to the dominance of ICCP.

Numerical Investigation on the Structural Behavior of a Short-Span Cable-Stayed Bridge with Steel and CFRP Hybrid Cables.

In this paper, a thorough investigation is presented on the static and dynamic behaviors of a short-span cable-stayed bridge (CSB) incorporating steel and carbon fiber reinforced polymer (CFRP) hybrid cables. The study focuses on the world's largest span and China's first highway, CFRP CSB. The performance of the CSB was compared using numerical simulations under four different cable patterns: steel cables, CFRP cables, and steel, and two types of hybrid cables with different structural arrangements. The results indicate that the use of the use of CFRP cables in the long cable region in the short-span CSB project investigated in this study offers improved performance in terms of stability, seismic response, and reduced displacements. In comparison to CFRP cables, hybrid cables have demonstrated a reduction of 12% in the maximum vertical displacement of the main girder. On the other hand, the hybrid cables result in reduced maximum internal forces and longitudinal and lateral displacements of the main girders and towers compared to steel cables. The difference in the arrangement of CFRP cables in the long cable region or short cable region is not obvious under dead loads, but significant differences still exist between the CFRP cable bridges in the short cable region and the long cable region in terms of live load effects, temperature effects, and dynamic characteristics.

Research on fatigue failure and structural measures of suspenders in the Jinsha River railway suspension bridge

In consideration of the significant impact of train loads on the fatigue of suspenders in railway bridges, this paper focuses on the first railway suspension bridge in China − the Jinsha River Railway Suspension Bridge. The study analyzes the force characteristics and bending failure features of the steel wire ropes in railway suspension bridges, aiming to provide insights into the design of such structures. Firstly, a finite element model of the Jinsha River Railway Suspension Bridge is established in this paper. The natural frequencies are analyzed and compared with on-site measurements to validate the accuracy of the finite element model. Secondly, the tension force amplitude and angular displacement amplitude of the suspenders are analyzed under design loads, and the failure characteristics of the cables are experimentally examined. Subsequently, a wear fatigue test for steel wire rope is designed, evaluating the fatigue life of the suspender in the bridge. The computational results are compared with experimental data to validate their accuracy. Finally, structural measures to reduce the bending fatigue of railway suspension bridge suspenders are proposed to ensure their safety during the service life. The study reveals that the presence of bending stress exacerbates the fatigue failure of suspension cables in railway suspension bridges, with the failure mode identified as fatigue failure due to the tension-bending-wear coupling effect. Furthermore, our findings indicate that the implementation of auxiliary cables can reduce the displacement differential at both ends of the suspension cables by approximately 4/5, and decrease the axial tensile stress amplitude by about 3/4. Consequently, this significantly enhances the fatigue life of the suspension cables.

Micro-crack localization for steel strands using nonlinear vibro-acoustic modulation based on modified signal bispectrum analysis

Under continuous environmental erosion and long-time high tension, fatigue micro-cracks of bridge cables appear frequently to challenge the reliability of cables. The vibro-acoustic modulation analysis is adopted because of its sensitivity to contact-type defects, especially fatigue cracks. In this paper, using multiple sets of low-frequency vibration and high-frequency ultrasonic excitation, the propagation of the ultrasonic wave in the steel strands is studied. Then, the modulated signal bispectrum is proposed to improve the detection reliability of nonlinear modulation components in the nonlinear vibro-acoustic modulation signal of the contact-type defect. The numerical simulations and laboratory tests of straight wire, helical wire, and multi-wire strands are carried out for micro-crack detection to verify the robustness of the proposed method. Compared with the traditional method, the modulated signal bispectrum can still produce clearer peak detection under high noise conditions. The results show that it provides a promising, dynamic and rapid cable defect detection technique.

PMFSE: a video phase-based micro-vibration measurement algorithm for bridge cables in complex background

The cable serves as the primary structural component in cable-stayed bridges, suspension bridges, and other cable-supported bridge designs. Accurate measurement of cable tension holds paramount importance for ensuring the overall safety and stability of bridge structures. Cable tension can be inferred from the vibration frequency, making precise measurement of cable vibration frequency of utmost practical significance. Presently, video-based methodologies, such as phase-based vibration extraction, present notable advantages in terms of speed, efficiency, and non-contact capabilities over conventional acceleration sensor approaches. However, these methods face challenges in accurately discerning the micro-vibration of cables in complex background interference. To address this problem, a phase magnification-based feature signal extraction (PMFSE) algorithm is proposed, which is suitable for detecting small vibration in complex background. The overall idea is to combine the small vibration enhancement method in spatial domain with the signal separation method in time domain. Specifically, in the spatial domain, edge phase information is amplified through phase amplitude weighting and phase enhancement techniques to mitigate non-edge noise. In time domain, cable signals are extracted based on distinguishing features between the cable signal and noise signal. The efficacy of PMFSE is evaluated in various outdoor experiments. Compared with the state-of-the-art methods, PMFSE exhibits substantial improvements on the cable micro-vibration frequency measurement in complex background.

Assessment of critical parameters affecting fretting fatigue life of bridge stay cables at saddle supports

Saddle systems are a popular solution for supporting cables in cable-stayed bridges. Fretting fatigue failure of cables at saddle supports is a primary design consideration for these systems. Critical parameters that affect the fretting fatigue life of the cables are the contact forces and the slip displacements at the contact points between the cables and the saddle. Determining these critical parameters is the first step in evaluating the fretting fatigue life of the cables. Wear in the contact points between the cables and the saddle can affect the load distribution in saddle systems and consequently affect these critical parameters. However, the effect of wear has not been studied in the previous works. This paper first discusses the methods proposed in the literature for evaluating contact forces and slip displacements in the contact points between a cable and a saddle. Then, a finite element model of the problem and a framework for modelling the wear are presented. Finally, fretting fatigue life is determined based on the different studied approaches. The main highlights of the current study are considering the effect of wear in the simulation and employing an enhanced FE model for slip displacement calculations. The results of the basic model without wear effects showed that the first contact point between the cable and the saddle is critical for fatigue failure. However, by incorporating wear in the model, the contact force at the first point dropped and the second contact point became critical; this is in line with the observations in large-scale fatigue tests of saddle systems.

A Study of Preload Detection Technology in Suspension Bridge Cable Clamp Bolts Based on the Pull-Out Method

The pull-out method is a simple and effective method for detecting the preload of suspension bridge cable clamp bolts. However, research on the pull-out method is currently limited. The force principles governing the bolt during the pulling process are unclear, and the relationship between tension force and the desired preload remains uncertain. This paper aims to explore the force principles of bolts during the pull-out method detection process through a combined approach of theoretical analysis, full-scale test, and finite element simulation. The results indicate that the bolt preload increases during the pulling process. The preload detected by the pull-out method is not the initial preload of the bolt, but rather it exceeds the initial preload. The force relationships among various components are determined as follows: the preload subtracts the change value of the force exerted by the nut at the tension end, which equals the change value of tension force. Additionally, an analysis of the impact of the length of the bolt clamping section and the bolt area on the preload was conducted. Under the same bolt area, a shorter clamping section length corresponds to a greater increase in preload. With the same clamping section length, the increment of preload increases with the bolt area. These findings can serve as references for detecting and specifying the preload of the bolts.