Internal Force Distribution in Steel-Concrete Composite Structure for Pylon of Cable-Stayed Bridge

Adopting a steel-anchor beam and steel corbel composite structure in the anchor zone on pylon is one of the key techniques for the design of Jintang bridge, a cable-stayed bridge in Zhoushan, China. In order to ensure the safety of the steel-concrete composite structure, a stud connector model for the joint section was put forward. Experiments were conducted to obtain the relation between load and slip of specimen, the failure pattern of stud connector, the yield bearing capacity and ultimate bearing capacity of a single stud, etc. The whole process of the structural behavior of the specimen was comprehensively analyzed. The features of the internal force distribution in the steel-concrete composite structure and the strain distribution of stud connector under different loads were emphatically studied. The test results show that the stud connector is applicable for the steel-concrete composite structure for pylon of Jintang bridge. The stud has a good ductility performance and a obvious yield process before its destruction. The stud connector basically works in a state of elasticity under a load less than the yield load.

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.

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.

Comparative Study on Structural Redundancy of Cable-Stayed and Extradosed Bridges Through Safety Assessment of Their Stay Cables

This study provides new insights into the comparison of cable-stayed and extradosed bridges based on the safety assessment of their stay cables.These bridges are often regarded as identical structures owing to the use of inclined cables;however,the international standards for bridge design stipulate different safety factors for stay cables of both types of bridges.To address this misconception,a comparative study was carried out on the safety factors of stay cables under fatigue and ultimate limit states by considering the effects of various untoward and damaging factors,such as overloading,cable loss,and corrosion.The primary goal of this study is to describe the structural disparities between both types of bridges and evaluate their structural redundancies by employing deterministic and nondeterministic methods.To achieve this goal,three-dimensional finite-element models of both bridges were developed based on the current design guidelines for stay cables in Japan.After the balanced states of the bridge models were achieved,static analyses were performed for different safety factors of stay cables in a parametric manner.Finally,the first-order reliability method and Monte Carlo method were applied to determine the reliability index of stay cables.The analysis results show that cable-stayed and extradosed bridges exhibit different structural redundancies for different safety factors under the same loading conditions.Moreover,a significant increase in structural redundancy occurs with an incremental increase in the safety factors of stay cables.

Study on longitudinal wind load calculation method of cables for cable-stayed bridge

Along with the expanding of span of cable-stayed bridge,wind load becomes a more and more important controlling factor for bridge the design.A very large proportion of the wind load acting on cables has exceeded that acting on deck.There was not any detailed prescript in Chinese code for calculation of longitudinal wind load on cables due to lack of theoretical research and experiment,and conservative simplified calculation was adopted during design,which leads to conservative and uneconomical design of structures.To resolve this problem,cable force experiment was carried out during the design of Sutong Bridge.By comparing with international research results,the calculation formula of longitudinal wind drag coefficient for cables was advanced to fill the blank of bridge wind resistant code of China,and has already been adopted in the Highway Bridge Wind Resistant Design Code(JTG/T D60-01-2004)with great significance for bridge engineering.

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.

Technology for long cable erection of a thousand-meter scale cable-stayed bridge

In the background of the construction of Sutong Yangtze River Bridge(short as Sutong Bridge),the cable construction method and techniques of a thousand-meter scale cable-stayed bridge are introduced.Some key construction techniques,such as outspreading cable on deck,installing cable at pylon,pulling and fixing cable at the attachment with decks and cable PE sheath protection are discussed.

Modeling of cable vibration effects of cable-stayed bridges

The analysis of dynamic responses of cable-stayed bridges subjected to wind and earthquake loads generally considers only the motions of the bridge deck and pylons.The influence of the stay cable vibration on the responses of the bridge is either ignored or considered by approximate procedures.The transverse vibration of the stay cables,which can be significant in some cases,are usually neglected in previous research.In the present study,a new three-node cable element has been developed to model the transverse motions of the cables.The interactions between the cable behavior and the other parts of the bridge superstructure are considered by the concept of dynamic stiffness.The nonlinear effect of the cable caused by its self-weight is included in the formulation.Numerical examples are presented to demonstrate the accuracy and efficiency of the proposed model. The impact of cable vibration behavior on the dynamic characteristics of cable-stayed bridges is discussed.

Summarizing the Methods of Determination of Rational Completion Status of Cable-Stayed Bridges

Cable-stayed bridge is a high-order hyperstatic structure. The size of cable force affects the stress of the structure greatly. The key problem to determine the rational completion status of cable-stayed bridges is how to control cable force on completion status. Surrounding this problem, domestic and foreign experts and scholars have done a lot of favorable work and obtained much achievement. On the basis of comprehensive reading domestic and foreign relative documentation, the author of this article classifies rationally the current researching achievement, comments and compares advantages and disadvantages of each method and lists two synthetic methods’ detail steps and puts forward the researching emphasis of the field will deflect to synthesis several methods to determine the rational completion status of cable-stayed bridges.

Influence of Girder Vibration on Cable Damper's Performance of A Cable-stayed Bridge

The model combined by cable,girder and damper is founded to study the influence of girder vibration on cable damper 's performance of a cable-stayed bridge. The complex mode method and nondimensionalization are used to analyze the relationship between the girder's parameters and the performance of cable-related damper. The results indicate that the performance of cable-related damper will decrease greatly when the girder frequencies are near the frequencies of cable. The smaller absolute displacement of damper's piston caused by the very small vibration phase shift of girder and cable is the physical cause of the negative impact mentioned above.

Nonlinear Dynamic Reliability of Coupled Stay Cables and Bridge Tower

Nonlinear vibration can cause serious problems in long span cable-stayed bridges.When the internal resonance threshold is reached between the excitation frequency and natural frequency,large amplitudes occur in the cable.Based on the current situation of lacking corresponding constraint criteria,a model was presented for analyzing the dynamic reliability of coupling oscillation between the cable and tower in a cable-stayed bridge.First of all,in the case of cable sag,the d'Alembert principle is applied to studying the nonlinear dynamic behavior of the structure,and resonance failure interval of parametric oscillation is calculated accordingly.Then the dynamic reliability model is set up using the JC method.An application of this model has been developed for the preliminary design of one cable-stayed bridge located on Hai River in Tianjin,and time histories analysis as well as reliability indexes have been obtained.When frequency ratio between the cable and tower is approaching 1∶2,the reliability index is 0.98,indicating high failure probability.And this is consistent with theoretical derivation and experimental results in reference.This model,which is capable of computing the reliability index of resonance failure,provides theoretical basis for the establishment of corresponding rule.

Cable-Stay Bridges——Investigation of Cable Rupture

As the bridge engineering community sets sails to use longer and longer spans, more and more sophisticated analysis models have to be used in the design process. One of the significant problems represents cable rupture of cable stays. The problem is also addressed in guidelines for cable-stayed bridge design such as PTI （Post-tensioning Institute） Recommendations and EC3 by quasi-static analyses using DAF （dynamic amplification factors） to account dynamic effects, which can be conducted instead ofnsing dynamic analysis. The results show that the value DAF depends on the cable rupture location and on the type and location of the examined state. Dynamic time history analysis is recommended. Some projects examples are highlighted in the paper, where the importance of above mentioned topic has been investigated, following different regulations and approaches. Professional bridge analysis and design sottware solution RM Bridge has been used for all investigations. The application can fulfill all requirements and deliver expected and accurate results. In addition, RM Bridge Sottware also helps engineers as a tool to optimize structure design and increase resistance capacity for each element to ensure the structural safety in service stage.

Key Technologies for Design of Changqing Yellow River Super-long Bridge of Zhengzhou Ji'nan HSR

Changqing Yellow River Super-long Bridge of Zhengzhou-Ji'nan HSR is a partial cable-stayed bridge with concrete main girder and a unit length of 1,080 m.Studies are carried out on the key technologies of bridge design,and the main conclusions are as follows:The whole unit adopts the supporting system of tower pier consolidation and tower-beam separation,and each pier is provided with seismic mitigation and isolation bearing;shaped-steel reinforced concrete bridge tower is adopted to bring into full play the tensile performance of steel and the compressive performance of concrete,and avoid the construction challenges of setting up multi-layer and multi-stirrup reinforcement while improving the bearing capacity of section;a new type of double-side and bi-directional anti-skid anchorage device is adopted for the cable saddle of wire divider pipe in order to withstand the unbalanced cable force,and verify the reliability of the anti-skid anchorage device by solid model test;and large-segment cantilever pouring design is adopted for the main girder with a maximum segment length of 8 m to effectively shorten the construction period of the bridge.

Design and analysis of a bisected wheel-based cable climbing robot

To inspect inner wires of the cylindrical cables on a cable-stayed bridge, a new bisected wheel-based cable climbing robot is designed. The simple structure and the moving mode are described and the static features of the robot are analyzed. A cable with a diameter of 139 mm is selected as an example to calculate the design parameters of the robot. For safety energysaving landing in the case of electrical system failure, an electric damper based on back electromotive force and a gas damper with a slider-crank mechanism are introduced to exhaust the energy generated by gravity when the robot is slipping down along the cables. A simplified mathematical model is analyzed and the landing velocity is simulated. For the present design, the robot can climb up a cable with diameters varying from 65 to 205 mm with payloads below 3.5 kg. Several climbing experiments performed on real cables confirm that the proposed robot meets the demands of inspection.

General design of Sutong Bridge

The main span of Sutong Bridge is a double-pylon,double-plane cable-stayed bridge with steel box girder,which has the world's longest central span of 1 088 m within cable-stayed bridges.To overcome problems caused by severe meteorological conditions,perplexing hydrological conditions,deep buried bedrock and higher navigation level,many new technics and methods were created.Keys including structural system,steel box girder,stayed cable,tower,pier,tower foundation,collision avoidance system,wind-resistance,seismic-resistance,structural nonlinear response and structural static stability were presented individually in this paper.

Concrete-Filled Steel Tube Arch Bridges in China

In the past 20 years, great progress has been achieved in China in the construction of concrete-filled steel tube （CFST） arch bridges and concrete arch bridges with a CFST skeleton. The span of these bridges has been increasing rapidly, which is rare in the history of bridge development. The large-scale construction of expressways and high-speed railways demands the development of long-span arch bridges, and advances in design and construction techniques have made it possible to construct such bridges. In the present study, the current status, development, and major innovative technologies of CFST arch bridges and concrete arch bridges with a CFST skeleton in China are elaborated. This paper covers the key con- struction technologies of CFST arch bridges, such as the design, manufacture, and installation of steel tube arch trusses, the preparation and pouring of in-tube concrete, and the construction of the world＇s longest CFST arch bridge-the First Hejiang Yangtze River Bridge. The main construction technologies of rein- forced concrete arch bridges are also presented, which include cable-stayed fastening-hanging cantilever assembly, adjusting the load by means of stay cables, surrounding the concrete for arch rib pouring, and so forth. In addition, the construction of two CFST skeleton concrete arch bridges-the Guangxi Yongning Yong River Bridge and the Yunnan-Guangxi Railway Nanpan River Bridge--is discussed. CFST arch bridges in China have already gained a world-leading position; with the continuous innovation of key technologies, China will become the new leader in promoting the development of arch bridges.

The obstacle crossing ability analysis and improvement of the cable inspection robot

In this paper, the climbing obstacle capability of the previous special cable inspection robot （ Model Number： XS1T-1） is analyzed. Static equations are established to analyze the relationships between the external forces and the maximum height of an obstacle. Parameters affecting the obstacle crossing ability are obtained. According to the analysis results, an innovated small volume, simple structure and light weight climbing mechanism is proposed （Model Number： XS1T-2）. A simplified kinematics model of the mechanism is established. With two powered wheels, the obstacle crossing ability of the XSIT-2 is improved apparently. For the robot moving without deflection, the relationships of two powered input torques are deduced. The comparison of the simulation results clearly shows that the climbing ability of XS1T-2 is obviously improved, and it can meet the demands of inspection.

六塔单索面矮塔斜拉桥拉索设计研究

六塔单索面矮塔斜拉桥是目前我国比较少见的斜拉桥。从斜拉索选型、斜拉索构造、斜拉索锚固和斜拉索减振等角度对六塔单索面矮塔斜拉桥的斜拉索进行了设计与研究。该桥采用抗拉强度标准值为1 860 MPa的钢绞线斜拉索,每根钢绞线的理论直径为15.2 mm。梁端斜拉索通过锚具锚固在预应力混凝土箱梁的隔板齿块上,而在塔端,采用索鞍分丝管形式将斜拉索锚固在桥塔锚固区。斜拉索在梁端采用粘性剪切型阻尼器进行减振,在塔端采用减振圈减振。为了提高斜拉索的使用寿命和耐久性,在钢绞线斜拉索外表面包裹环氧涂层、防腐油脂和高密度聚乙烯(HDPE)保护套。最后结合未知荷载系数法,对斜拉索索力进行了优化设计,优化后的部分索力虽略有增加,但主梁截面弯矩和应力更加趋于平稳,有利于结构受力。

公铁合建钢混板-桁斜拉桥悬挑式钢锚箱受力特性及结构优化

为研究大跨度公铁合建钢混板-桁斜拉桥主梁悬挑式索梁钢锚箱结构的受力特性及结构优化,以主跨808 m的洪奇沥特大桥钢锚箱为背景,采用仿真分析方法,研究钢锚箱3个设计方案主要板件应力、焊缝应力以及推荐方案锚箱节点的传力特性和锚箱参数对钢锚箱受力的影响。结果表明:锚箱尺寸较大、顶底板加肋方案的主要板件应力最大为300 MPa,小于其他2种方案,且6条焊缝的最大应力和应力不均匀系数较优,因此确定该方案为最终设计方案;索力首先由锚垫板直接向钢锚箱顶、底板和内外腹板较为均匀传递,最终边弦杆底板、内腹板和外腹板分别承担了22.2%,46.4%和31.4%的索力;节点处副桁斜杆、近桥塔侧和远桥塔侧边弦杆、混凝土桥面、节点横梁分别传递约66.71%,9.72%,9.32%,9.68%和4.56%的斜拉索竖向分力;板件应力随顶底板厚度增加而减小,顶底板深入边弦杆长度增加可以降低底板-内腹板焊缝峰值应力,顶底板间距减小可降低内外腹板和顶底板与锚垫板接触区域应力;顶底板厚44 mm、锚箱顶底板深入边弦杆长度1800 mm、顶底板间距660 mm时较为合理。