Large-span Bridge Research Articles

Experimental and numerical research on the uniaxial behavior of the stiffened circular concrete-filled steel tube stub columns

In large-span bridges or high-rise buildings, CFST columns with large width-to-thickness ratio are often adopted, which require proper stiffening measures to improve the mechanical behaviors. This paper presents a comparative study of circular CFST stub columns with different stiffening methods, including longitudinal stiffeners (cross-shaped, T-shaped and ordinary type), additional reinforcement and headed studs. Axial compression tests have been conducted to investigate the effects of different stiffening methods on the failure mode, ultimate strength and ductility of the circular CFST stub columns. Finite element models are established to simulate the columns’ behaviors and conduct parametric studies. Based on test and simulation results, an axial bearing capacity prediction model for circular CFST stub columns stiffened by longitudinal stiffeners is proposed. It is demonstrated that the failure modes of the steel tube and core concrete are changed by the longitudinal stiffeners. The longitudinal steel stiffeners as well as reinforcing cage can effectively improve the axial bearing capacity and ductility of the columns. The latter is more efficient in promoting the bearing capacity while the former is more efficient in improving the ductility and residual strength. A combination of the additional stirrups and the ordinary stiffeners will be a more economical choice. In addition, the proposed formula gives better prediction accuracy compared to the equations in various design codes.

Improved softened truss model of prestressed concrete box girders subjected to combined bending and torsion

Prestressed concrete (PC) box girder is an innovative structure that is widely used in large-span bridges. Under eccentric loads such as vehicles, PC girders are inevitably under combined bending and torsion. To study its bending-torsional behavior, a refined full-range analysis model based on the combined action softening truss model (CA-STM) was proposed, where a simple and effective solution procedure and failure criteria were provided. The equilibrium equation, initial estimation equation for torque, and material constitutive model were modified by considering the prestressing effect to improve the CA-STM. An optimized algorithm was also employed to simplify the solution procedure instead of the traditional trial-and-error method, thus increasing the solution rate and stability. The theoretical curves predicted from the improved CA-STM exhibited great agreement with the available experimental results, and the predicted cracking and ultimate loads were also close to the experimental values. Hence, the improved CA-STM can reasonably predict the full-range mechanical response and failure modes of PC box girders subjected to combined bending and torsion, which provides great support to the design evaluation of such bridges.

Ultimate Load-Bearing Capacity and Sustainable Performance of Pile Foundations of Yanji Suspension Bridge in Fault Zone Based on Refined Geological Model

Pile foundation is the most important foundation type of long-span bridges, of which the ultimate load-bearing capacity affects the safety and sustainable performance of bridges. When constructing large-span bridges, the bridge site may be close to the adjacent fault zones, which seriously affects the safety and long-term performance of pile foundations, causing the failure and unsustainability of long-span bridges in their life-cycle service life. At present, there are no engineering design rules or methods for assessing the load-bearing capacity of the pile foundation near the fault zones. To study the influence of the fault zone on the loading-bearing capacity and sustainable performance of pile foundations, triaxial compression tests were carried out on the mylonite at the Yanji suspension bridge site near the Xiangfan–Guangji fault zone in Hubei Province. The mechanical properties of mylonite were reflected by the Mohr–Coulomb yield criterion, and a topographic and geological modeling method based on the multi-platform was established. Then, the ABAQUS finite element software was used to study the deformation, stress, failure modes, and sustainable performance of the pile foundation under different bridge load levels, analyze the safety of the pile foundation in the fracture zone, and summarize the ultimate bearing characteristics of the pile foundation. The results show that the whole pile and surrounding rock are basically elastic under the pressure of the designed load, the plastic zone of the pile foundation is mainly concentrated at the pile bottom, and the shear stress concentration zone of the pile is mainly manifested in the joint of the cap and pile and the interface between soft and hard rock. When the load is increased to 4 times the designed load, the stress concentration area of the pile body gradually shifts upward from the pile bottom, and the surrounding rock at the bottom forms an “X-shaped” shear failure zone. After 100 years of operation, the maximum compressive stress of piles reaches 28.6 MPa, which is 120% higher than that at the beginning of the bridge construction, indicating that the sustainable performance of the piles can withstand the effect of the fault zone over the designed service years.

Rapid and Precise Measurement Method for Track Static Geometry of Large-Span Bridge Railway

Track geometry is an important parameter reflecting the safety of bridge railway, which is of great significance for the structure control of railway track. The measurement of track geometry is an indispensable part of structural health monitoring for bridge railway. However, existing methods for track static track geometry measurement are inadequate in terms of accuracy and efficiency. In order to improve the measurement method, this paper proposes a rapid and precise measurement method based on IMU/odometer aided by multiple total stations, which has the advantages of high efficiency, high accuracy, and is less affected by the environment. The proposed method uses a track measurement trolley (TMT) integrated with IMU and an odometer to collect railway track data on the bridge, and multiple total stations are used to synchronously measure the three-dimensional coordinates of the TMT. After coordinate system registration and time synchronisation, the data are then fused using a filtering algorithm to finally obtain the static geometry of the railway track. The proposed method was validated on the NanSha Port Railway Bridge across the Xijiang River in Foshan, China, and the results showed that the proposed method can make a single on-orbit measurement of a 1000 m length of large-span bridge railway track within half an hour, with an accuracy on the order of millimetres. The proposed method has obvious advantages in terms of efficiency and accuracy and is therefore an effective new measurement method with practical significance.

Engineering Mechanics Methods in Stability Studies of Bridge Structures and Innovations in Future Bridge Designs

Abstract With the development of science and technology and transportation, high pier and large-span bridges are rapidly rising. Due to the increase in span diameter and pier height, nonlinear and stability problems of bridges become more and more important. In this paper, the stability of large-span steel box-girder suspension bridges is investigated using engineering mechanics methods. Based on the finite element analysis method to solve the bridge structure of the first type of stability problems and the second type of stability problems, the use of the response spectrum method for bridge seismic response. Taking “Xiling Yangtze River Bridge” as the engineering background, the seismic response is analyzed by establishing a finite element model. The axial force of the bridge tower generated by the downstream earthquake is larger than that generated by the transverse earthquake. In the transverse direction, the bending moment MZ is larger than the bending moment MY in the transverse direction, and the bending moment of the pile foundation is larger than the bending moment of the pile foundation in the longitudinal direction. The Xiling Yangtze River Bridge plays a dominant role in transverse seismicity, and its downstream seismic excitation plays a dominant role in longitudinal seismicity. However, the energy-demand ratio corresponding to the transverse moment MY is only 1.83, and the strength of the pile section needs to be further improved. For the future innovation of bridge design, a high-performance bridge structure based on UHPC is an important direction for future development.

Multistage Graph Convolutional Network With Spatial Attention for Multivariate Time Series Imputation.

In multivariate time series (MTS) analysis, data loss is a critical issue that degrades analytical model performance and impairs downstream tasks such as structural health monitoring (SHM) and traffic flow monitoring. In real-world applications, MTS is usually collected by multiple types of sensors, making MTS and correlations between variates heterogeneous. However, existing MTS imputation methods overlook the heterogeneous correlations by manipulating heterogeneous MTS as a homogeneous entity, leading to inaccurate imputation results. Besides, correlations between different data types vary due to ever-changing environmental conditions, forming dynamic correlations in MTS. How to properly learn the hidden correlation from heterogeneous MTS for accurate data imputation remains unresolved. To solve the problem, we propose a multistage graph convolutional network with spatial attention (MSA-GCN). In the first stage, we decompose heterogeneous MTS into several clusters with homogeneous data collected from identical sensor types and learn intracluster correlations. Then, we devise a GCN with spatial attention to explore dynamic intercluster correlations, which is the second stage of MSA-GCN. In the last stage, we decode the learned features from previous stages via stacked convolutional neural networks. We jointly train these three-stage models to predict the missing data in MTS. Leveraging this multistage architecture and spatial attention mechanism makes MSA-GCN effectively learn heterogeneous and dynamic correlations among MTS, resulting in superior imputation performance. We tested MSA-GCN with the monitoring data from a large-span bridge and Wetterstation weather dataset. The results affirm its superiority over baseline models, demonstrating its enhanced accuracy in reducing imputation errors across diverse datasets.

Analysis and Research on Load Behavior of H-shaped Steel Concrete

Steel-reinforced concrete (SRC) possesses excellent strength and numerous advantages over traditional concrete, making it extensively used in high-rise buildings and large-span bridge structures. This paper commences with the constitutive relationship of steel reinforcement in SRC, the nominal stress-strain conversion, and real stress-strain transformation. It employs Abaqus for nonlinear finite element analysis to study the stress variations in compressed SRC columns subjected to reciprocating loads and examines load-displacement curves. The paper analyzes the hysteresis loops of SRC columns under reciprocating loads, the trends in skeleton curves, energy dissipation, and stiffness degradation. Consequently, it concludes that the variation of compressive stress along the axis of SRC columns is consistent with the change in bearing capacity. Under reciprocating loads, the stress at the lower end of the SRC column is greater than that at the upper end, suggesting the need for reinforcement in the lower portion. The hysteresis loop of SRC columns exhibits a rich characteristic, with increasing energy absorption as displacement increases.

Effect of steel fibres and expansive agents on compressive behaviour of circular CFST columns

Concrete filled steel tube columns (CFSTCs) are commonly used in large-span bridges and high-rise buildings. As the shrinkage of concrete may lead to significant degradation in the mechanical performance of CFSTCs, expansive concrete or fibre reinforced concrete is usually employed to improve the mechanical performance of CFSTCs. This study presents an experimental study on the combined effects of expansive agents and steel fibres on the axial compressive behaviour of circular CFSTCs. 13 CFSTCs were designed and manufactured using concrete mixes with varying expansive agent rates and steel fibre contents. The time-dependent expansive behaviours of the specimens were monitored during the concrete curing period. Then, the 13 specimens were tested under axial compression load. The failure modes, compression load-axial strain relationship, hoop strain and axial strain relationship, and ductility were investigated. The results demonstrated that the combined addition of expansive agents and steel fibres would substantially improve the compressive strength and ductile behaviour of CFSTCs.

Conceptual design and preliminary test of the novel structure of steel inner core-UHPC composite box girder

A novel steel inner core-ultra high performance concrete (UHPC) composite box girder structure is proposed, which is lightweight, economical and low-carbon emission. In this proposal, the steel inner core serves as both the load-bearing structure and the UHPC internal formwork. Eliminating the installation of longitudinal ribs in the steel inner core greatly reduces the amount of welding, minimizes sources of fatigue damage, and simplifies construction. The UHPC is externally wrapped around the steel inner core to ensure the structural durability. When the novel box girder is applied to the incremental launching continuous girder structure with a span of 70 m, the technical index per square meter of the main girder is: 163 kg of steel, 0.242 m3 of UHPC, and a self-weight of 820 kg. With the same span, the novel box girder structure exhibits significant advantages in comprehensive performance compared with other types of main girder structures. The flexural behavior of the novel box girder was investigated through a four-point bending experiment and the cracking characteristics of the test specimen on the bottom plate under different reinforcement configurations were analyzed. The test results showed that the amount of reinforcing bars in UHPC had a significant impact on the development of cracks. When arranged with a diameter of 16 mm and a spacing of 100 mm, the overall distribution of cracks was short and fine, and the crack resistance strength was 1.56–1.80 times that of the reinforcement configuration with a diameter of 16 mm and a spacing of 200 mm. The preliminary test and analysis results suggest that the proposed composite box girder can be taken as a new structural option for medium to large span bridges ranging from 40 m to 100 m.

GBDT-based multivariate structural stress data analysis for predicting the sinking speed of an open caisson foundation

ABSTRACT Open caisson foundations are often used in large-span bridge construction because of their advantageous, and an open caisson foundation gradually sinks to a predetermined position via earth excavation. Excessive sinking speed may result in various construction risks (e.g. inclination and structural damage of the open caisson). To prevent these risks, it is important to analyse the sinking situation of the foundation and predict the sinking speed during the sinking process. A sinking speed prediction model is proposed based on the gradient boosting decision tree (GBDT) algorithm, and the model can extract the data features of the structural stress monitoring data to predict the sinking speed of open caissons. Taking the supersized open caisson foundation in the Changtai Yangtze River Bridge Project as a case study, the proposed model was validated by using the monitoring data of this foundation. The validation results of this project indicate that the proposed model has high prediction accuracy, short time consumption, a good prediction effect and high practicability. Based on the model’s prediction, an earth excavation scheme can be flexibly adjusted to prevent the potential construction risks of open caissons caused by excessive sinking speed.

Study on dynamic splitting tensile mechanical properties and microscopic mechanism analysis of steel fiber reinforced concrete

With high compressive strength and high fracture toughness, steel fiber reinforced concrete is widely used in large-span bridges and high-rise buildings. Since concrete structures are subjected to strong dynamic loads such as impact blast during service, it is essential to clarify the dynamic mechanical behavior of steel fiber reinforced concrete and to propose an adapted dynamic constitutive model for structural dynamic response calculation. Therefore, in this paper, a static and dynamic splitting tensile test study was conducted on steel fiber reinforced concrete with four fiber contents (0%, 1%, 2%, and 3%), and a separated Hopkinson compression bar (SHPB) was used to conduct dynamic splitting tensile tests on steel fiber reinforced concrete to obtain the failure pattern, stress–strain curves, and basic mechanical parameters of steel fiber reinforced concrete. The results showed that the static and dynamic splitting tensile strength of steel fiber reinforced concrete increased with increased steel fiber content. The dynamic splitting tensile strength and peak deformation of steel fiber reinforced concrete increased significantly with increasing strain rate, and the dynamic splitting tensile strength of steel fiber reinforced concrete increased in the range of 1.1 to 3.3 compared with static splitting tensile strength. The enhancement of dynamic splitting tensile strength with increasing strain rate at different fiber contents showed a significant and then flattening trend. In addition, the dynamic splitting tensile strength and strain-rate sensitivity of non-steel fibered concrete are higher than that of steel fiber reinforced concrete. Meanwhile, the X-CT scanning technique was applied to reveal the strain rate reinforcement and steel fiber reinforcement mechanism from the microscopic perspective. Finally, the K&C model was modified based on the experimental results and applied to the dynamic splitting tensile simulation of SHPB to verify the accuracy and adaptability of the proposed constitutive model. The research results finally provide a theoretical basis for the mechanical response of steel fiber reinforced concrete structures under impact blast.

Mechanical properties of 2100 MPa parallel wire strands under and after elevated temperature

In this study, steady-state tensile tests were conducted at elevated temperatures and after cooling from elevated temperatures on 2100 MPa galvanized parallel wire strands (19 × 5.4 mm) used in long-span suspension bridges. Data collection was done using a charge-coupled device camera (CCDC) system. The results from tests at elevated temperatures indicate that the mechanical properties of parallel wire strands deteriorated gradually with increasing temperature. This degradation trend was well described by logistic curves. The results show that the mechanical properties after elevated temperature decreased significantly when the temperature exceeded 350 °C. By comparing with existing research, it was found that the higher the strength grade, the more severe the strength degradation after elevated temperature. During heating and cooling stages, moderate tension led to beneficial effects on residual strength of the specimens. This applies to temperatures below 400 °C. A linear-exponential-linear (L-E-L) stress-strain model was proposed to establish stress-strain equations for parallel wire strands at and after elevated temperatures. Degradation equations were also obtained for elastic modulus, yield strength, ultimate strength and proportional limit. These findings can be utilized to analyze fire resistance performance of cable systems in large-span bridges and assess post-fire damage.

Static Mechanics and Dynamic Analysis and Control of Bridge Structures Under Multi-Load Coupling Effects

With the rapid development and wide application of large-span bridges, the problem of dynamics and safety control of bridge structures under multiple loads is becoming more and more prominent. To realize the dynamic analysis and mechanical control of the girder structure, this paper designs a new type of magnetorheological (MR) mechanical damper based on the mechanistic analytical method and establishes a coupled dynamics model of the vehicle-rail-MR mechanical damper. The simulation and validation results show that the error between the semi-analytical method and the finite element theory calculation results is only 1.0%, while the kinetic simulation is consistent with the measured frequency domain trend. The analytical results show that: After applying MR mechanical damper for mechanical control, the moment live load and shear values of side spans were reduced by 27.68% and 10.79%, respectively; and the maximum moment and shear values generated at the center pivot were reduced by 28.19% and 10.81%, respectively. After applying the mechanical damper, the stress distribution of the cable-stayed bridge is more balanced, and the maximum diagonal stress of the overall structure is reduced from 3.8 MPa to 2.9 MPa. After safety control, the root-mean-square (RMS) value of the mid-span displacement amplitude was reduced by 59.32% and the maximum value was reduced by 11.46%, which improved the stability of the girder dynamics. After mechanical control, the dynamic acceleration response of the beam within the span decreased between 2 and 8 seconds and increased between 8 and 10 seconds. The overall response fluctuated around −5 m/s2 with a relatively smooth trend.

Probabilistic anomaly detection considering multi-level uncertainties for cable-stayed bridges

To model multi-level uncertainties within anomaly detection process for large-span bridges, a probabilistic anomaly detection method is proposed considering uncertain models in the data collection, thermal response separation, and trigger estimation. The uncertain model in the data collection is established with the measured value and measuring errors. The uncertain model in the thermal response separation is built through the linear Bayesian estimation. The uncertain distribution of the anomaly detection trigger is obtained via Bayesian estimation of generalized Pareto distribution. Subsequently, measurements from multi-sensors are used to detect anomalies in a probabilistic way. Evidential reasoning, a decision-level fusion tool, is used to derive a collective detection rate to distinguish sensor malfunctions from anomalous scenarios. Specifically, anomalous scenarios deserve a large collective detection rate, whilst sensor malfunctions are subject to a small collective detection rate and a large individual detection rate. Two cases (i.e., sensor malfunction and snow disaster) are illustrated based on measurements from a large span cable-stayed bridge. As a result, the sensor malfunction is detected with an individual detection rate of 89.20% and a collective detection rate of 2.77%. The snowstorm is detected by a collective detection rate of almost 100%.

Experimental and numerical investigation of the expansion mechanism of beam-end expansion devices in large-span bridge

The beam-end expansion device of a large-span bridge is critical equipment for relieving temperature stress and also a weak point. In this paper, a detailed analysis of the expansion mechanism and jamming phenomenon of the beam-end expansion device is conducted for the first time. A dynamic model of the beam-end expansion device is established using complex flexible body coupled kinematics theory. The model overcomes two major challenges in simulation: (1) the expansion function of the scissor device provides the beam-end expansion capability while transmitting force to drive the movable sleepers, and (2) the coupling effects in the longitudinal, vertical, and horizontal directions between the movable sleepers and the upper structure need to be simulated to provide not only vertical support stiffness but also force on contact surfaces during expansion motion. The phenomenon of jamming caused by the asymmetry of the scissor device is found and the reason is analyzed. By comparing the paths of load transmission caused by different types of scissor devices, the influence on scissor devices and movable steel sleepers is summarized. The conclusions derived from theoretical deductions are consistent with the simulation results and validated through four monitoring data sets. The research findings of this paper can provide insights for addressing the design, operation, and maintenance issues of beam-end expansion devices in large-span bridge projects, ensuring that they meet the requirements of engineering practice.

Seismic isolation effect of unconnected piles-caisson foundation: Large-scale shake table tests

The seismic response and isolation mechanism of a new unconnected pile-caisson foundation (UPCF) suitable for supporting deep-water large-span bridges under seismic loading were investigated by large shaking table tests. Five scaled models were constructed utilizing different cushion material (aggregate), cushion thickness and piles configuration. Each model was tested under 18 different seismic loading conditions. The tests observations were analyzed to evaluate the seismic response characteristics and isolation mechanism of UPCF. The maximum displacement of UPCF and the peak acceleration of the input ground motion were linearly related. Under strong ground motions, the foundation soil and cushion displayed a significant softening behavior manifested in reduced natural frequencies and prolonged periods, which resulted in lower acceleration amplification. However, the stiffnesses of soil and cushion were largely restored after the ground shaking ended. The cushion model with larger aggregate particles performed better in terms of the caisson residual displacement and displacement restoration rate of the caisson. It was found that the UPCF constructed with a thin cushion layer comprised of large, rounded aggregate particles exhibited acceptable seismic isolation effect and reduced the peak seismic acceleration by up to 26.7%. It was also observed that the front and middle piles experienced larger loads, and accordingly, their peak moment envelopes were greater and the location of peak moment was shallower.

Linear and nonlinear tensile creep of steam-cured UHPC

In bridges, UHPC can bear significant sustained tensile stress without cracking under service loading. Its significant impact on the long-term behavior of large-span bridges due to tensile creep characteristics becomes evident. In this paper, both linear and nonlinear tensile creep behavior of steam-cured UHPC was experimentally investigated by using dog-bone-shaped specimens under sustained direct tension for a duration of 360 days. The tensile creep test was conducted under varied tensile stress levels ranging from 0.3ft to 0.9ft. Tensile creep coefficients were calculated by using the experimental results. Nonlinear tensile creep occurs in the steam-cured UHPC when the sustained tensile stress is larger than 0.3ft. The threshold of nonlinear tensile creep is lower than that of normal-strength concrete under compression. When the sustained tensile stress is larger than 0.8ft, tensile creep failure occurs a short time after loading. The nonlinear creep impact under tension is less pronounced than that under compression due to the distinct function of steel fibers within UHPC when subjected to compression and tension force. The findings in the scanning electron microscopy (SEM) test reveal that the mechanism driving the nonlinear tensile creep of UHPC is the damage growth at the fibers-matrix interface under the high sustained tensile stress. A design-oriented model for the creep coefficient of UHPC is developed, which incorporates both linear and nonlinear creep effects. The model’s credibility is verified using the experimental results.

Equivalent conversion investigation of environmental corrosion of suspenders in long-span suspension bridge

Purpose This paper aims to investigate the equivalent relationship between accelerated corrosion tests and real environmental spectrum of suspenders in long-span suspension bridge considering multiple factors action. Design/methodology/approach Based on Faraday's law, corrosion current was used as a measure of metal corrosion, and the equivalent conversion relationship between laboratory environment and real service environment was established. The equivalent conversion method for bridge structural steel had been determined under different temperature, humidity, pH value and NaCl concentration conditions. The compilation of environmental spectra for large span bridges considering multiple factors and the principle of equivalent conversion have been proposed. Findings Environmental factors, including temperature, humidity, pH value and NaCl concentration, have significant impact on the corrosion degree of suspension steel wires, and only considering these two factors for equivalent conversion cannot accurately reflect the true service environment of the bridge. The 33.8-h salt spray accelerated corrosion test using the standard conditions can be equivalent to one year of suspenders corrosion in a real service environment. Originality/value The equivalent accelerated corrosion method for steel wires proposed in this study can effectively predict the corrosion degree of the suspenders, which has been verified to be correct and can provide theoretical guidance for the development of corrosion test plans for steel wires and engineering technical basis for anti-corrosion control and calendar life research of suspension bridge suspenders.

Book Review of Vorticity Vibration Effects,Principles and Aerodynamic Control Measures for Large-Span Bridges

With the rapid development of the world's economy and technology, bridge structures are developing in the direction of large spans. Large span means that the main girder of the bridge becomes longer, the whole bridge becomes more flexible, and the effect of the fluid, mainly wind, will be more obvious. Vortex Vibration Effects, Principles and Pneumatic Control Measures for Large-Span Bridges is a monograph in the field of wind engineering related to bridge structures written by Zhao Lin and Ge Yaojun of Tongji University (published by Tongji University Press) , which starts from the basic characteristics of vortex vibration of large-span bridges, the research progress and principles, and experimental situations, and puts forward the control countermeasures applicable to vortex vibration of a wide range of bridges and pneumatic control measures. This paper provides a brief introduction to the editors of the work, systematizes the chapter structure of the book, and explores its academic and theoretical values. The monograph shows how to apply the theory and mechanism related to vortex vibration of large-span bridges to practice, with a view to providing reference for workers and researchers in the fields of bridge structural wind engineering, disaster prevention and mitigation engineering.

Vision-based multi-point real-time monitoring of dynamic displacement of large-span cable-stayed bridges

The existing vision measurement methods face a significant challenge in the multi-point displacement monitoring of large-span bridges due to the contradiction between the measurement scale and image spatial resolution. Based on a cable-stayed bridge on a kilometer scale, a new vision-based multi-point displacement monitoring system is proposed. The bridge was designed and arranged with a camera network, consisting of a series of double-head camera stations that were connected by cooperative markers. Based on the observed multi-point deflection and lateral displacement, the deformation evolution of the bridge in the two dimensions of time and space is discussed. The results show that the proposed vision-based camera network can accurately monitor the dynamic deflection and lateral displacement across the whole span of the bridge. The measurement errors induced by the camera motion can be well compensated based on the optical constraints of the proposed camera network. The feasibility of the vision method for long-span bridge monitoring has greatly improved. The proposed system can provide a new method for displacement monitoring and fine parameters for the safety evaluation of large-span bridges.