Spatial structural analysis of main saddle for single tower spatial cable self-anchored suspension bridge

Based on the engineering background of the Jiangxinzhou Bridge in Nanjing, issues related to the spatial main saddle of the self-anchored suspension bridge are studied. The refinement finite element model is established by the secondary development technology based on the platform of the general finite element program, and a reasonable load pattern is used in its spatial structural analysis, by which its path of force transference and stress distribution are obtained. Matched with the spatial main cable, the tangency point correction method is also discussed. The results show that the lateral wall stress of the saddle groove is higher than the stress within the wall due to the role of lateral forces in the finished bridge state; the horizontal volume force of the main cable can generate a gradient distributed vertical extrusion pressure on the saddle clamping device and the main saddle body; the geometric nonlinear effect of the self- anchored suspension bridge cable system in the construction process is significant, which can be reflected in the spatial tangent point position of the main cable with the main saddle changes a lot from free cable to finished cable.

Test and numerical investigations on static and dynamic characteristics of extra-wide concrete self-anchored suspension bridge under vehicle loads

The present work is aimed at studying the mechanic properties of the extra-wide concrete self-anchored suspension bridge under static and dynamic vehicle loads. Based on the field test using 12 heavy trucks and finite element simulations, the static deformations of different components, stress increments and distributions of the girder, as well as the vibration characteristics and damping ratio of the Hunan Road Bridge were analyzed, which is the widest self-anchored suspension bridge in China at present. The dynamic responses were calculated using the Newmark-β integration method assisted by the simulation models of bridge and vehicles, the influences on the dynamic impact coefficient(DIC) brought by the vehicle parameters, girder width, eccentricity travel and deck flatness were also researched. The spatial effect of the girder is obvious due to the extra width, which performs as the stress increments distribute unevenly along the transverse direction, and the girder deflections and stress increments of the upper plate change as a "V" and "M" shape respectively under the symmetrical vehicle loads affected by the shear lag effect, cross slope and local effect of the wheels, the maximum of stress increments are located in the junctions with the inner webs. The obvious girder torsional deformation and the apparent unevenness of the hanger forces between the two cable planes under the eccentric vehicle loads, together with the mode shapes such as the girder transverse bending and torsion which appear relatively earlier, all reflect the weakened torsional rigidity of the extra-wide girder. The transverse displacements of towers are more obvious than the longitudinal ones. As for the influences on the DIC, the static effect of the heavier vehicles plays a major role when pass through with a higher speed and the changes of vehicle suspension stiffness generate greater impacts than the suspension damp. The values of DIC in the vehicle-running side during the eccentric travel, affected by the restricts from the static effects of the eccentric moving trucks, are significantly smaller than the vehicle-free side, the increase in the road roughness is the most sensitive one among the above influential factors. The results could provide references for the design, static and dynamic response analysis of the similar extra-wide suspension bridges.

Determination of reasonable finished state of self-anchored suspension bridges

A systematic and generic procedure for the determination of the reasonable finished state of self-anchored suspension bridges is proposed, the realization of which is mainly through adjustment of the hanger tensions. The initial hanger tensions are first obtained through an iterative analysis by combining the girder-tower-only finite element(FE) model with the analytical program for shape finding of the spatial cable system. These initial hanger tensions, together with the corresponding cable coordinates and internal forces, are then included into the FE model of the total bridge system, the nonlinear analysis of which involves the optimization technique. Calculations are repeated until the optimization algorithm converges to the most optimal hanger tensions(i.e. the desired reasonable finished bridge state). The "temperature rigid arm" is introduced to offset the unavoidable initial deformations of the girder and tower, which are due to the huge axial forces originated from the main cable. Moreover, by changing the stiffness coefficient K in the girder-tower-only FE model, the stiffness proportion of the main girder, the tower or the cable subsystem in the whole structural system could be adjusted according to the design intentions. The effectiveness of the proposed method is examined and demonstrated by one simple tutorial example and one self-anchored suspension bridge.

Health monitoring and comparative analysis of time-dependent effect using different prediction models for self-anchored suspension bridge with extra-wide concrete girder

The structural health status of Hunan Road Bridge during its two-year service period from April 2015 to April 2017 was studied based on monitored data.The Hunan Road Bridge is the widest concrete self-anchored suspension bridge in China at present.Its structural changes and safety were evaluated using the health monitoring data,which included deformations,detailed stresses,and vibration characteristics.The influences of the single and dual effects comprising the ambient temperature changes and concrete shrinkage and creep(S&C)were analyzed based on the measured data.The ANSYS beam finite element model was established and validated by the measured bridge completion state.The comparative analyses of the prediction results of long-term concrete S&C effects were conducted using CEB-FIP 90 and B3 prediction models.The age-adjusted effective modulus method was adopted to simulate the aging behavior of concrete.Prestress relaxation was considered in the stepwise calculation.The results show that the transverse deviations of the towers are noteworthy.The spatial effect of the extra-wide girder is significant,as the compressive stress variations at the girder were uneven along the transverse direction.General increase and decrease in the girder compressive stresses were caused by seasonal ambient warming and cooling,respectively.The temperature gradient effects in the main girder were significant.Comparisons with the measured data showed that more accurate prediction results were obtained with the B3 prediction model,which can consider the concrete material parameters,than with the CEB-FIP 90 model.Significant deflection of the midspan girder in the middle region will be caused by the deviations of the cable anchoring positions at the girder ends and tower tops toward the midspan due to concrete S&C.The increase in the compressive stresses at the top plate and decrease in the stresses at the bottom plate at the middle midspan will be significant.The pre-deviations of the towers toward the sidespan and pre-lift of the midspan girder can reduce the adverse influences of concrete S&C on the structural health of the self-anchored suspension bridge with extra-wide concrete girder.

Study of Vertical Seismic Response of Concrete Self-Anchored Suspension Bridges

Based on the variational prineiple of incomplete generalized potential energy with large deflection, the vertical nonlinear vibrational differential equation of self-anchored suspension bridge is presented by taking the effect of coupling of flexural and axial action into consideration. The linear vertical equation is obtained by omitting the nonlinear term, and the pseudo excitation method(PEM). Taking the self-anchored concrete suspension bridge over Lanqi Songhua river for an example, the expected peak responses of main beam, towers and cables are calculated. And the seismic spatial effects on vertical seismic response of self-anchored suspension bridges are discussed.

Seismic Behavior Analysis of Steel Tower of Self-anchored Suspension Bridge

Self-anchored suspension bridge is composed of tower and its foundation, stiffened beam, main cable, sling, side pier and its foundation, auxiliary pier and its foundation. The performance and importance of the components of the bridge are different. The main tower of self-anchored suspension bridge is a very important component. Once the injury and damage occur under earthquake, it is not only difficult to inspect and repair, let alone replace. This paper calculates the seismic performance of self-anchored suspen-sion bridge steel tower based on the application of Wuhan Gutian Bridge steel tower.

Study on seismic response control of a single-tower self-anchored suspension bridge with elastic-plastic steel damper

Elastic-plastic steel damper(EPSD) is a new device controlling seismic responses.The mechanical principle of EPSD was presented and a comparison was conducted between the theoretical formulas and finite element(FE) simulation of damper units.The verified force-displacement hysteretic curve of the damper system was obtained with reference to tests.The Nanjing Jiangxinzhou Bridge(NJB) was subsequently taken as the case to investigate the seismic response control effect of EPSDs on single-tower self-anchored suspension bridges.A 3-dimensional FE model of the bridge was established in ANSYS and the dynamic and static analyses of the bridge were conducted,the control effect of EPSDs under different seismic waves was further investigated through nonlinear time-history analysis based on the validated model.Results showed that both the simplified theoretical and FE simulation methods can preferable reflect the mechanical performance of EPSD,and that seismic responses of NJB with EPSDs are better than those with elastic connection device or fluid viscous damper.However,the control effect of EPSDs is influenced by seismic wave characteristics.

Calculation method on shape finding of self-anchored suspension bridge with spatial cables

Based on the spatial model,a reliable and accurate calculation method on the shape finding of self anchored suspension bridge with spatial cables was studiedin this paper.On the principle that the shape of the main cables between hangers is catenary,the iteration method of calculating the shapes of the spatial main cables under the load of hanger forces was deduced.The reasonable position of the saddle was determined according to the shape and the theoretical joint point of the main cables.The shapes of the main cables at completed cable stage werecalculated based on the unchanging principle of the zero-stress lengths of the main cables.By using a numerical method combining with the finite element method,one self-anchored suspension bridge with spatial cables was analyzed.The zero-stress length of the main cables,the position of the saddle,and the pre-offsetting of the saddle of the self-anchored suspension bridge were given.The reasonable shapes of the main cables at bridge completion stage and completed cable stage were presented.The results show that the shape-finding calculation method is effective and reliable.

Limit span of self-anchored cable-stayed suspension cooperation system bridge based on strength

The limit span of self-anchored cable-stayed suspension bridge is deduced.The relations among the geometrical parameters,loads and material characteristics are also analyzed.Based on the material strength and commonly used materials,the limit spans of self-anchored cable-stayed suspension bridges with concrete girder or steel girder under vertical static load are discussed in detail.The corresponding upper limit spans and the effect of the factors on the span are given.The results indicate that increasing rise-span ratio,height-span ratio and cable-stayed segment length or reducing the second dead load could increase the cooperation system span.

Comprehensive Optimal Control on Seismic Response of a Single-Tower Self-Anchored Suspension Bridge

Earthquake may cause severe damage to all kinds of bridge such as the falling down of the girder; therefore,effective measures should be employed to control the seismic displacement. In this paper,the method of comprehensive optimal control,com-bined with analytic hierarchy process,is employed to investigate the seismic response control of the Nanjing Jiangxinzhou Bridge,which is a single-tower self-anchored suspension bridge （SSSB）. Also,3-dimensional nonlinear seismic response analyses are con-ducted. Three types of practical connection measures for seismic response control of SSSB are investigated,and the optimal pa-rameters of the connection devices are achieved by this method. Results show that both the elastic connection devices and the damp-ers with rational parameters can reduce the seismic displacement of the bridge effectively,but the elastic connection devices will in-crease the seismic force of the tower. When all factors are consid-ered,the optimal measure is by using the elastic connection devices and the dampers together. These results can provide references for seismic response control of SSSBs.

人行悬索桥的步行参数研究

以九峰山人行悬索桥为观测点,采用视频记录与人工筛选相结合的方法获取了2236个行人样本的实测数据,进而统计得到人行悬索桥上的行人步行参数(步频、步幅和步速)的分布特性和统计值,并给出了人行悬索桥上的步频-步速、步幅-步速和步频-步幅之间的转换关系式,得到以下结论:1)在人行悬索桥上,全部行人的步行参数都服从正态分布,即步频~N(1.726,0.258)Hz、步幅~N(0.596,0.094)m、步速~N(1.013,0.260)m/s,它们的合理性也在某工程实例的应用中得以验证;2)人行悬索桥上的行人步行参数的均值(标准差)要小于(大于)其他行走环境所统计得到的行人步行参数的均值(标准差);3)中国人的步频和步幅的均值(标准差)都小于(大于)西方人的步频和步幅的均值(标准差).因此,在设计我国的人行悬索桥时,不能直接采用其他人种和行走环境的行人步行参数的统计值,而应采用适合于人行悬索桥的步行参数.

吊索断裂对人行悬索桥冲击效应的影响研究

人行悬索桥吊索断裂不但会使局部桥面坍塌,还会由于剩余构件应力重分布程度过大而引发吊索连续断裂。采用数值模拟方法对单根吊索断裂和相邻2根吊索断裂后人行悬索桥的动力响应进行分析,并通过静力重分布系数SRF、动力重分布系数DRF、振荡系数OF和动力放大系数DAF对冲击效应进行综合评估。结果表明,单根吊索瞬断后同侧相邻吊索及断索区域纵梁的静、动力重分布程度明显,但对主缆及对侧吊索产生影响较小;同侧相邻2根吊索断裂比对侧断裂对剩余吊索和断索区主梁的影响更大;除边吊索和跨中吊索外,其他剩余吊索的SRF均在50%左右,DRF均在100%左右;接近跨中区域剩余吊索的DAF均为2.0左右,但边吊索的DAF较跨中区域增大25%左右,DAF采用2.0对于边吊索偏于不安全。单根吊索断裂后其下方相应位置处纵梁弯矩的DAF值均在1.20~1.40之间。

人行索桁桥振动分析及舒适度评价

基于有限元程序Ansys,采用分块兰索斯法,分析了人行索桁桥的振动特性,采用国际标准化组织ISO 10137《结构设计基础—建筑物和人行道抗振的适用性标准》,考虑不同人行荷载形式,分析了单人荷载和人群荷载作用下人行索桁桥的侧向和竖向加速度.选取了考虑人行桥侧向与竖向耦合振动的综合评价方法,对人行索桁桥的竖向舒适度和侧向舒适度进行了综合分析.研究结果表明:在不同行人荷载作用下,人行索桁桥不会发生超越舒适度指标的振动;与其他普通悬索桥相比,由主索、桥面索和吊索组成的新型索桁桥,能够在满足使用要求、舒适度要求的同时,减轻了桥梁的质量,降低了经济成本.

龙潭果树公园3号人行景观桥桥型方案构思与设计

龙潭果树公园3号人行景观桥采用70 m双塔单跨地锚式悬索桥形式,主缆垂跨比为1/9,主梁为钢-混凝土板叠合梁,结构形式新颖美观。介绍该桥的桥型构思、方案设计,供类似人行景观悬索桥设计参考。

大跨度单索面曲线悬索桥人致振动舒适性及减振措施研究

随着桥梁美学和城市景观的追求以及新型轻质高强材料的运用,人行桥梁的跨度不断增大,基频不断降低,带来的人致振动问题也日益突出。以厦门山海健康步道节点二桥梁——单塔单索面曲线悬索桥为背景,通过行人激励下人致振动响应,分析人致振动峰值加速度和侧向锁定及其临界人数,并对安装调谐质量阻尼器(TMD)减振方案进行参数优化。结果表明:在人致振动竖向敏感频率范围内,即3 Hz以内,共有19阶模态,且模态振型耦合现象严重,不仅有主梁与桥塔、主缆耦合振型,还有主梁竖向与侧向耦合振型;第10阶和第15阶人致振动加速度峰值分别为2.127 m/s^(2)、3.778 m/s^(2),超出CL1级舒适性指标,第7阶临界锁定人数为236人,小于设计人数1235人;提出安装TMD并优化其基本参数,安装TMD后桥梁满足人致振动CL1级舒适性要求。

不同吊杆形式下人行悬索桥的力学性能分析

为了研究吊杆形式对人行悬索桥力学性能的影响,以某人行悬索桥为工程背景,采用Midas/Civil软件分别建立竖直吊杆和倾斜吊杆2种形式下的人行悬索桥有限元模型,进行合理成桥状态的找形计算,并对2种模型的静、动力性能进行分析。结果表明:1)竖直吊杆模型内部吊杆内力大小均匀,影响线均为正值,倾斜吊杆模型内部外倾吊杆内力大于内倾吊杆,且影响线有正有负。2)竖直吊杆模型主缆内力变化平缓,主梁基本不产生轴力,主缆和主梁位移较大;倾斜吊杆模型主缆内力变化梯度较大,数值较小,主梁有轴力,主缆和主梁位移较小。3)倾斜吊杆模型前10阶振动频率均大于竖直吊杆模型;在静风荷载作用下,2种模型中抗风揽体系的内力和位移差别不大,受吊杆形式的影响较小。4)倾斜吊杆模型的横向和竖向刚度均大于竖直吊杆模型,比较适合活载较小的人行悬索桥。对采用竖直吊杆体系和倾斜吊杆体系的人行悬索桥从静力和动力性能2个角度进行了全面的比较分析,为该类桥梁的结构体系优化提供了理论依据。

行人移动荷载作用下大跨悬索人行桥MTMD减振控制研究

行人移动荷载引起的桥梁结构振动是大跨桥梁设计的共性和热点问题,针对大跨悬索人行桥在行人移动荷载作用下的振动响应开展减振控制研究,采用频域分析法推导了桥梁-MTMD体系的频率响应方程,并据此对MTMD系统的数量、频带宽、阻尼比等进行了参数优化分析,进而研究了最优参数条件下桥梁-MTMD体系在不同行人移动荷载模式下的振动响应与减振效果.研究结果表明桥梁振动响应随同步频人数的增多而逐渐增大,随桥梁振动频率与激励频率的接近而逐渐增大;优化的MTMD系统能够在较宽频率范围内对大跨悬索桥结构的振动反应进行可靠、稳定的控制,有效保证了大跨悬索桥在行人移动荷载作用下的安全性和舒适性.

大跨异形悬索人行桥动力特性与抗震性能研究

以厦门健康步道“和美桥”为研究背景,基于SAP2000平台建立全桥动力计算有限元模型,采用Lanczos特征值求解方法分析了该人行桥的动力特性;同时采用时程分析法对该桥进行线性地震反应分析,探讨了大跨空间异形人行桥的地震反应特点。结果表明,该大跨异形人行桥的基本周期为1.892s,属于中等周期结构;其基本振型表现为加劲梁竖弯,且模态振型耦合现象严重。地震作用下,缆索结构内力反应较小;主梁地震轴力由两端向跨中递减,最大轴力出现在主梁与桥台连接位置;主梁弯矩和剪力最大值出现在两端位置,跨中位置的响应最小。桥塔轴力由塔顶向塔底递增;桥塔弯矩从两端向塔中位置递增。

一个行人行走激励下的悬索桥动力模型

提出了一个“双线摆模型”用于描述行人激励下悬索桥的动力行为。该模型中用两根弦和一块刚体分别代表悬索和桥面板。桥上行人行走时产生的竖向和侧向激励都用振幅为常数的简谐函数表示。在这一简化条件下根据Lagrange方法发现行人激励下悬索的动力学控制方程是一个Hill方程。利用扰动法对Hill方程进行了求解和稳定性分析,并通过数值计算证明了解析结果的正确性。利用该解析结论可以解释著名的伦敦千禧桥为何会在行人激励下出现0.48和0.96 Hz的侧向振动并伴有锁频现象。本文研究表明在人与悬索桥相互作用研究中不应该忽略悬索桥的悬挂结构特征。

三维螺旋主缆悬索桥总体构思

构思了由平行多主缆悬索桥扭转而成的三维螺旋主缆悬索桥结构,并建立了数值模型验证其结构可行性。通过多个数值模型模拟了不同扭转角下的结构竖向刚度、横向刚度和抗扭刚度的变化规律。分析表明,随着扭转角的增加,结构的横向和竖向刚度均先明显变大后稍有降低。抗扭刚度随扭转角有降低的趋势,但变化不明显。三维螺旋主缆悬索桥主缆处于全受拉状态,传力途径明确,结构稳定,可以在人行桥和景观桥上应用。主缆会在节间片上产生径向压力,大扭角的三维螺旋主缆悬索桥存在发生弹性突跳破坏的风险。