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.

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.

Mechanical performance analysis and stiffness test of a new type of suspension bridge

A new type of suspension bridge is proposed based on the gravity stiffness principle.Compared with a conventional suspension bridge,the proposed bridge adds rigid webs and cross braces.The rigid webs connect the main cable and main girder to form a truss that can improve the bending stiffness of the bridge.The cross braces connect the main cables to form a closed space truss structure that can improve the torsional stiffness of the bridge.The rigid webs and cross braces are installed after the construction of a conventional suspension bridge is completed to resist different loads with different structural forms.A new type of railway suspension bridge with a span of 340 m and a highway suspension bridge with a span of 1020 m were designed and analysed using the finite element method.The stress,deflection of the girders,unbalanced forces of the main towers,and natural frequencies were compared with those of conventional suspension bridges.A stiffness test was carried out on the new type of suspension bridge with a small span,and the results were compared with those for a conventional bridge.The results showed that the new suspension bridge had a better performance than the conventional suspension bridge.

椭圆塔空间缆自锚式悬索桥主索鞍系统设计研究

在建万龙大桥工程主桥为世界首座采用椭圆钢桥塔的空间主缆自锚式悬索桥。该桥鞍座采用铸焊结合的自适应式空间缆索主索鞍,鞍座存在以下技术难点:空间主缆主索鞍受力复杂;椭圆塔纵向刚度大,主索鞍的抗滑问题突出;鞍座底部为柔性支撑,索鞍与主塔协同变形,塔-鞍连接结构传力复杂。为掌握椭圆塔空间缆自锚式悬索桥主索鞍及塔-鞍连接结构的关键技术,运用数值分析方法开展系统研究。研究结论如下:(1)当桥梁承受(恒载+汽车+人群+自来水+温度+风)作用时,满足要求的最小摩擦系数μ为0.215,需要设置12 mm竖向摩擦板;(2)主索鞍在最大缆力工况下的最大Von Mises应力为186.2 MPa,最大竖向变形为1.572 mm,满足强度及刚度要求;(3)主索鞍与钢塔连接结构主要通过支承隔板以竖向剪力的形式将主索鞍作用力传至钢塔腹板上,端部支承隔板的剪力显著大于中间隔板,剪力传递的不均匀系数为1.29;(4)主索鞍支承板在鞍座区域的边缘存在一定转角,空缆工况最大纵向转角为0.366‰rad,在鞍座顶推施工中需要加以考虑。

圆月形独塔自锚式悬索桥总体设计

随着人们对展现城市地域特色的景观桥梁造型需求的不断增长,由于中等跨径自锚式悬索桥设计独特、极具艺术美感,备受选桥方案的青睐,成为城市地标。案例为圆月形独塔自锚式悬索桥,中等跨度;通过桥梁的方案造型,结构设计、计算分析等方面的简要介绍,为设计同类型的中等跨径自锚式悬桥提供经验借鉴。

空间刚性缆索自锚式悬索桥结构体系研究

跨河或上跨快速路的人行桥由于景观及净空的要求,梁高较小,但此种桥梁的跨径通常较大,这就造成了桥梁高跨比过小,刚度不足,振动问题突出。本文以一座实际悬索桥为例,从结构方案设计出发,针对空间缆索刚性悬索桥进行结构体系分析,研究结果表明:空间刚性缆索悬索桥的结构振型自振频率具有显著特性,需要针对性地进行结构构造设置。

大跨度悬索桥非线性静动力分析与软件开发

大跨度悬索桥是典型的柔性结构体系 ,其受力特性表现为强烈的几何非线性。介绍了适用于大跨度悬索桥空间非线性静动力有限元计算的程序的模型、原理及软件设计 ,并对一座大跨度悬索桥作了结构静动力计算。

主缆索股施工控制参数研究

基于索股线形与其无应力长度、自重荷载集度的相互关系,提出了主缆索股架设紧缆后内力重分配和紧缆实际线形的模拟算法;提出了非理想平行索股架设紧缆后的质量重分配计算假定并推导了相应的计算公式,建立了计算过程和迭代收敛准则,并运用VC++计算机语言编制了相应的计算程序;分析了各种跨度悬索桥主缆一般索股架设时采用不同间距对成缆线形及内力的影响。结果表明:适当增大一般索股架设调整时的控制间距对成缆线形基本没有影响,对索股间的内力影响有限。

悬索桥有限元计算的三节点空间鞍座单元

为了进行空间缆索悬索桥主缆与塔顶鞍座间接触非线性的计算,开发了包括塔顶鞍座及两侧主缆在内的三节点空间鞍座单元.基于空间悬链线理论及主缆与鞍座的几何关系,对单元进行状态求解,得到主缆与鞍座的切点位置及切点索力,根据静力平衡条件计算单元精确的节点力;由增量代替微分,根据切线刚度矩阵的定义计算单元刚度矩阵的元素.空间鞍座单元自动满足主缆与鞍座相切,通过修改一个参数可实现鞍座顶推的计算.计算表明:计算结果与数值解析解结果完全相同,收敛速度较快,在每次状态求解时,迭代次数在12次以内.

独柱塔自锚式悬索桥锚固横梁结构空间受力分析

南京江心洲大桥边跨主缆锚固大横梁设计独特,结构受力非常复杂。为了获得锚固横梁局部应力的大小与分布规律,对其传力途径进行研究,以通用有限元程序为计算平台,采用空间索单元模拟横梁中配置的预应力束以及主缆束股,三维块体元模拟混凝土锚固横梁,应用二次开发技术,建立精细三维有限元模型。在此基础上采用合理的加载模式对锚固横梁在空缆阶段和成桥状态2种不同工况进行应力计算与分析。结果表明:在空缆与成桥2种状态下锚固横梁的应力值与分布规律变化较大;为保证锚固横梁在施工过程中的受力状态处在合理的范围之内,锚固横梁中配置的大量预应力束应配合主缆束股的内力变化而分批次张拉。

超大跨度缆索承重桥梁结构体系

设计和建造跨海连岛大桥是新世纪桥梁工程面临的巨大挑战。超大跨度桥梁并不只是常规概念的外推,需要与之对应的结构体系。从根本上改变缆索承重桥梁的缆索体系,可以突破跨度极限。本文指出了常规结构体系向更大跨度发展的制约因素,从缆索体系的角度介绍了超大跨度斜拉桥、悬索桥以及斜拉 悬索组合桥可能采用的各种体系。这些体系试图在静力、动力方面能远远超出现有限制范围,极大地提高桥梁的跨越能力。同时,新体系的采用也给材料、设计和施工提出了很大的挑战。

从影响线角度研究3塔悬索桥力学行为

以泰州长江大桥为原型,建立相应2塔、3塔漂浮和3塔约束悬索桥空间有限元模型,研究各关键效应的影响线特征及汽车效应包络,得到如下结论:主缆抗滑、中塔受力、主梁挠跨比、梁端水平位移等在2塔悬索桥中不会引起很多关注的因素,对3塔悬索桥却成为控制指标,且由汽车作用控制;缺乏边缆的有效约束引起中塔顶水平位移增大,是导致其他效应大幅增加的原因;当一个主跨全部或部分加载,另一个主跨空载时,4个控制因素最不利,但发生的概率极低;抓住规范限制挠跨比的本质和3塔2跨悬索桥变形特点,可将其挠跨比限制放宽至1/220,行车平顺仍有充足保障;汽车与恒载应力叠加后,绝大多数运营状况下,中塔都处于受压应力状态,疲劳问题不突出。

悬索桥空间非线性分析

应用精确的空间杆单元、索单元和梁单元切线刚度矩阵，编制了悬索桥空间非线性分析程序．并通过与算例和江阴长江大桥模型试验结果的比较，验证了程序的正确性．