Extraction of cable forces due to dead load in cable-stayed bridges under random vehicle loads

To extract the cable forces due to dead load in cable-stayed bridges from the monitoring data,the effects of various factors are eliminated step by step by different statistical methods.The information of cable tension sensors recorded by the health monitoring system of Nanjing No.3 Yangtze River Bridge is taken as an example. Temperature effects are eliminated by linear fitting analysis;a 5-level wavelet de-noising method is applied to eliminate the noise signal by the wavelet basis function of DB8.The rest cable force data is tested by the method of extreme-value type-Ⅲ distribution, and the fitted location parameter is selected as the cable force due to dead load.The results show that the cable force has a linear relationship with temperature. Sometimes, the temperature effect is significant.Noise effect accounts for a small percentage,and the vehicle loads effect has twice the temperature effect on the traffic volume in 2007. The calculation results of other stay cables verify the reliability and validity of the proposed method.

Determination of initial cable force of cantilever casting concrete arch bridge using stress balance and influence matrix methods

Cantilever casting concrete arch bridge using form traveller has a broad application prospect.However,it is difficult to obtain reasonable initial cable force in construction stage.In this study,stress balance and influence matrix methods were developed to determine the initial cable force of cantilever casting concrete arch bridge.The stress balance equation and influence matrix of arch rib critical section were established,and the buckle cable force range was determined by the allowable stress of arch rib critical section.Then a group of buckle cable forces were selected and substituted into the stress balance equation,and the reasonable initial buckle cable force was determined through iteration.Based on the principle of force balance,the initial anchor cable force was determined.In an engineering application example,it is shown that the stress balance and influence matrix methods for the determination of initial cable force are feasible and reliable.The initial cable forces of arch rib segments only need to be adjusted once in the corresponding construction process,which improves the working efficiency and reduces the construction risk.It is found that the methods have great advantages for determining initial cable force in cantilever casting construction process of concrete arch bridge.

Analysis of precision and error of cable force identification of cable-stayed bridge

In this paper,in order to improve the precision of cable force identification of a practical cable-stayed bridge and consider some precision problems of vibration method in surveying the cable force in the engineering application,firstly,three calculation methods for the cable force measurement are analyzed and contrasted;secondly,using the method of finite element numerical simulation and the theory of the error analysis,the effect of both bending rigidity and constraint conditions on simple formula of vibration method is investigated;and the dependence of the precision of cable frequency identification on spectrum resolution,sampling time,and the number of sampling points is studied;Finally,fundamental frequency method,frequency difference method,and peak value method are applied to the cable force calculation of a practical project;and their computational precision and error are contrasted and analyzed.It is observed that it is essential to take into account the effect of every factor on the precision of the cable force identification and make it possible to identify the cable force more accurate by vibration method;and that it simultaneously provides an effective basis for the development of a high-precision equipment.

Analysis of Key Factors in Cable Force Calculation for Cable-Stayed Bridges

Three methods for calculating cable force （analytic method, fitting method and finite element method） are analyzed and compared. The effects of boundary condition, spectrum resolution, sampling time, and number of sampling points on the precision of cable force identification are discussed, and error analysis is conducted. The results of three methods applied to a practical project are significantly less than the design value. Comparatively, the result of finite element method is the closest to the design value. Moreover, their computational precision and error are compared and analyzed. The precision of frequency identification of cables, long cables in particular, is strongly affected by frequency resolution. If the frequency resolution is included in calculating the cable force, the identification error can be reduced greatly.

Optical Fiber Grating Sensor for Force Measurement of Anchor Cable

The development of the sensor suitable for measuring large load stress to the anchor cable becomes an important task in bridge construction and maintenance. Therefore, a new type of optical fiber sensor was developed in the laboratory - optical fiber grating sensor for force measurement of anchor cable （OFBFMAC）. No similar report about this kind of sensor has been found up to now in China and other countries. This sensor is proved to be an effective way of monitoring in processes of anchor cable installation, cable cutting, cable force regulation, etc, with the accurate and repeatable measuring results. Its successful application in the tie bar cable force safety monitoring for Wuhan Qingchuan bridge is a new exploration of optical fiber grating sensing technology in bridge tie bar monitoring system.

Damage Detection for Long-Span Cable-Stayed Bridge

Based on the updated finite-element model of a cable-stayed bridge, this study investigates the technique of identifying damage existing in cable or girder by means of numerical simulation. The modal analysis is performed to identify the changes in modal fiequencies and curvatures caused by damage, and the static analysis is executed to detect the influence of damage on cable force. The results indicate a relatively significant decrease in frequencies of lower vertical bending modes due to the damage in cable and little change of frequencies due to damage in girder. Different sensitivities to the location of damaged cable are observed from the fiequency changes of different bending modes, which can be used to initially locate the damaged cable. The damage in either cable or girder can be further localized by the most significant change in curvature of girder. The damage occurred in a cable produces a remarkable change in force of nearby cables, whereas the damage in girder brings little change of cable forces. In addition, a pragmatic approach for localizing the damage in girder or cable is proposed based on a comprehensive utilization of the changes in frequency of vertical bending modes, modal curvature of girder, and force in cables.

Study and application of vibrating wire strain gauge in monitoring cable tension of FAST cable-net

A cable net structure is selected to support its reflecting triangular aluminum panels of FAST(five-hundred-meter aperture spherical radio telescope).To ensure the security and stability of the supporting structure,cable force of typical cables must be monitored on line.Considering the stringent requirements in installation,accuracy,long-term stability and EMI(Electromagnetic interference),most of the commonly used cable force measurement methods or sensors are not suitable for the cable force monitoring of the supporting cable-net of FAST.A method is presents to accomplish the cable force monitoring,which uses a vibrating wire strain gauge to monitor the strain of linear strain area at the anchor head.Experiments have been carried out to verify the feasibility.The method has a series of advantages,such as high reliability,high accuracy,good dynamic performance and durability,easiness of maintenance,technical maturity in industry and EMI shielding.Theoretical analysis shows that there is a linear relationship between the cable body force and anchor head surface strain,and experimental results proves a good linear relationship with excellent repeatability between the cable body force and anchor head surface strain measured by the vibrating wire strain gauge,with a linear fit better than 0.98.Mean square error in practical measuring is 2.5t.The relative error is better than 4%within the scope of the cable force in FAST operation which meets practical demand in FAST engineering.

A new cable truss support system for coal roadways affected by dynamic pressure

The support of coal roadways is seriously affected by intense dynamic pressures.This can lead to problems with large deformation of the roof and the two side walls of coal roadways.Rapid convergence of the walls and roof,a high damage rate to the bolts and cables,or even abrupt roof collapse or rib spalling can occur during the service period of these coal roadways.Analyzing the main support measures used in China leads to a proposed new cable truss supporting system.Thorough study of the entire structure shows the superiority of this design for roadways suffering under dynamic pressure.A corresponding mechanical model of the rock surrounding the cable truss system is described in this paper and formulas for calculating pre-tightening forces of the truss cable,and the minimum anchoring forces,were deduced.The new support system was applied to a typical roadway affected by intensive dynamic pressure that is located in the Xinyuan Coal Mine.The results show that the largest subsidence of the roof was 97 mm,the convergence of the two sides was less than 248 mm,and the average depth of the loose,fractured layer was only 6.12 mm.This proves that the new support system is feasible and effective.

Research on End-force Output of 8-cable Driven Parallel Manipulator

The return capsule needs to be launched to the moon and return back to earth in the third stage of the Chinese lunar exploration project.Therefore,it is necessary to perform simulations on the ground.This paper presents an 8-cable-driven parallel manipulator to achieve end-force output in a low-gravity environment.End-force output refers to the vector sum of the external force on the end-effector.A model of end-force output is established based on a kinematics model,a dynamic model,and a force analysis of an 8-cable driven parallel manipulator.To obtain end-force output in a low-gravity environment,the cable force has to be controlled to counteract gravity.In addition,a force-position mix control strategy is proposed to proactively control the cable force according to the force optimal distribution given by the closed-form force distribution method.Furthermore,a suitable choice for an end-force output is obtained by modeling the effect of cable force on end-force output.Experimental results show that the actual cable force agrees well with the calculated force distribution,indicating that it is feasible to realize end-force output in a low gravity environment.