Dynamic performance of cable-stayed bridge tower with multi-stage pendulum mass damper under wind excitations——I:Theory

In this paper, wind-induced vibration control of a single column tower of a cable-stayed bridge with a multi- stage pendulum mass damper （MSPMD） is investigated. Special attention is given to overcoming space limitations for installing the control device in the tower and the effect of varying natural frequency of the towers during construction. First, the finite element model of the bridge during its construction and the basic equation of motion of the MSPMD are introduced. The equation of motion of the bridge with the MSPMD under along-wind excitation is then established. Finally, a numerical simulation and parametric study are conducted to assess the effectiveness of the control system for reducing the wind-induced vibration of the bridge towers during construction. The numerical simulation results show that the MSPMD is practical and effective for reducing the along-wind response of the single column tower, can be installed in a small area of the tower, and complies with the time-variant characteristics of the bridge during its entire construction stage.

Thermal Effect of the Cable-Stayed Bridge Tower

This paper studies the thermal effect of the cable-stayed bridge tower based on full time accurate measurement and finite element analysis on Xiantao Hanjiang River Highway Bridge. The measured results and the displacement variation of top tower show that the tower rotates periodically when it is exposed in sunshine. But the tower column will not decline when there is no sunshine. In spite of in winter or in summer, the period when the tower column changed smallest is from 0∶00 am to 5∶00 am. The time period when the tower column has maximum deviation lags behind the time when the tower column has maximum temperature difference, and this phenomenon is obvious in winter. The conclusions also have directive value in predicting the tower deformations and their directions in construction control of cable-stayed bridge, and in verifying the finite element program.

Aerodynamic characteristics of a high-speed train crossing the wake of a bridge tower from moving model experiments

In a strong crosswind,the wake of a bridge tower will lead to an abrupt change of the aerodynamic forces acting on a vehicle passing through it,which may result in problems related to the transportation safety.This study investigates the transient aerodynamic characteristics of a high-speed train moving in a truss girder bridge and passing by a bridge tower in a wind tunnel.The scaled ratio of the train,bridge,and tower are 1:30.Effects of various parameters such as the incoming wind speed,train speed,and yaw angle on the aerodynamic performance of the train were considered.Then the sudden change mechanism of aerodynamic loads on the train when it crosses over the tower was further discussed.The results show that the bridge tower has an apparent shielding effect on the train passing through it,with the influencing width being larger than the width of the tower.The train speed is the main factor affecting the influencing width of aerodynamic coefficients,and the mutation amplitude is mainly related to the yaw angle obtained by changing the incoming wind speed or train speed.The vehicle movement introduces an asymmetry of loading on the train in the process of approaching and leaving the wake of the bridge tower,which should not be neglected.

Dynamic performance of cable-stayed bridge tower with multi-stage pendulum mass damper under wind excitations—Ⅱ: Experiment

The possibility of using a multi-stage pendulum mass damper （MSPMD） to control wind-induced vibration of a single column tower of a cable-stayed bridge during construction was studied theoretically in part I of this work. In this paper, the performance of the MSPMD for reducing bridge tower vibration is studied experimentally. A MSPMD model and a tower model of the bridge with geometry scaling of 1：100 were designed and manufactured. Calibration of the MSPMD model with different wire lengths is conducted to verify the analytical model of the damper. A series of tests for the uncontrolled freestanding tower, tower with cables, and tower with MSPMD model are then performed under harmonic and white noise excitations. The experimental results show that the responses of the tower model significantly decrease with the installation of the MSPMD model, which demonstrates the effectiveness of the M SPMD to mitigate the vibration of the bridge tower.

Design and construction of Sutong Bridge tower

Sutong Bridge tower which is 300.4 m is the highest one in the world.The tower anchor area uses the steel-concrete composite structure,its structure and the stress mechanism are complex,so it must be paid more attention to the structure durable issue.The 300 m height makes the tower quite sensitive to the environmental factors such as wind and temperature.The wind resistance safety of tower in construction stage is especially important.In this paper,the design of composite structure is introduced.The key technologies of tower geometry control and wind resistance in construction stage are analyzed.

Shake table experimental study of cable-stayed bridges with two different design strategies of H-shaped towers

As one of the main load-carrying components of cable-stayed bridges,bridge towers are typically required to remain elastic even when subjected to severe ground motions with a 2%-3%probability of exceedance in 50 years.To fulfill this special requirement imposed by current seismic design codes,reinforcement ratios in the bridge towers have to be kept significantly higher than if limited ductility behavior of the tower is allowed.In addition,since the foundation capacity is closely related to the moment and shear capacities of the bridge tower,a large increase in bridge construction cost for elastically designed cable-stayed bridge is inevitable.To further investigate the possibility of limited ductility bridge tower design strategies,a new 1/20-scale cable-stayed bridge model with H-shaped bridge towers designed according to strong strut-weak tower column design was tested.The shake table experimental results are compared with a previous strong tower column-weak strut designed full bridge model.A comparison of the results show that ductility design with plastic hinges located on tower columns,i.e.,strong strut-weak tower column design,is another effective seismic design strategy that results in only small residual displacement at the top of the tower column,even under very severe earthquake excitations.

Geologic Survey and Stability Analysis for the South Tower Pier of Jiangyin Yangtze Highway Bridge

Jiangyin Yangtze highway bridge is a suspension bridge with main span 1 385 m. The south tower pier is located on a 70 m bedrock slope with bedding plane of strata tipping to the river channel and several weak intercalated layers. The stability of the tower pier is one of the main engineering geologic problems. On the basis of investigation and survey of relevant geologic condition analyses, the geomechanical model experiments are carried out for stability study of various foundation alternatives’ advantages and disadvantages. Pile foundation has been finally adopted and constructed, and this is justified by practice.

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.

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.

Taizhou Yangtze River Bridge——The first kilometer level three-pylon two-span suspension bridge in the world

Taizhou Bridge, located at the middle of Jiangsu Province, connecting Taizhou City and Zhenjiang City, started in Dec. 2007. The bridge is the first kilometer level three-pylon suspension bridge in the world, and it adopts longitudinal herringbone shape steel middle pylon for the first time in the world. The foundation of the middle tower is the deepest underwater caisson in soil on earth. A great many of technical innovations such as the design techniques of three-pylon suspension bridge,precisely locating and bottom-sealing techniques of the large scale caisson foundation, manufacturing, combination techniques of steel and concrete in the middle tower, welding of extra thick steel plate, manufacture and control techniques of abnormal sections of the middle tower and so on were introduced.

矮塔斜拉体系加固既有连续梁桥受力性能研究

随着服役年限的增长,大跨径预应力混凝土连续梁桥会出现腹板开裂和跨中下挠等问题。针对既有大跨预应力混凝土连续梁桥的损伤问题,以一座三跨连续梁桥为研究对象,分析其应用矮塔斜拉体系加固前后的受力状态。通过有限元模拟对比加固前后桥梁的应力分布及挠度变化,探讨加固方案的整体加固效果以及塔梁锚固区和索塔锚固区的局部受力状态。结果显示,应用矮塔斜拉体系加固方案后跨中下挠由72.61 mm改善为22.25 mm,主梁由部分截面受拉变为全截面受压。加固后横隔板、箱梁顶板等锚固区域整体应力分布合理,极小范围存在应力集中现象、可采用加强措施。验证了矮塔斜拉体系加固方法的可行性。

矮塔斜拉转体桥的BIM监测方法研究

为了优化矮塔斜拉转体桥的施工监测方法,本文介绍了工程项目概况,并详细阐述了基于BIM技术的桥梁结构模型建立过程。通过对施工关键部位的结构线形监测和拉索索力监测的探讨,分析了BIM技术在施工监测中的应用及其效果。研究提出,利用BIM模型进行实时监测和数据分析,能显著提高施工效率和安全性。研究结果表明,BIM监测方法能准确反映桥梁结构的变形和索力状态,为矮塔斜拉转体桥的施工提供了有效的技术支持。

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。

G3铜陵长江公铁大桥桥塔基础设计

G3铜陵长江公铁大桥主桥为主跨988 m的斜拉-悬索协作体系桥,桥塔采用钢筋混凝土门形结构。3号桥塔基础比选了钻孔桩基础与沉井基础方案,4号桥塔基础比选了钻孔桩基础与地下连续墙基础方案,综合考虑基础受力性能、经济性、施工风险等,均推荐采用钻孔桩基础方案。3号、4号桥塔塔座高4.5 m,承台分别为厚7 m的圆形-哑铃形和矩形-哑铃形结构,基础分别采用68根和64根φ3.0 m钻孔桩,桩长分别为95 m和79 m,按摩擦桩设计。承台系梁采用ANSYS软件进行实体有限元分析,系梁横向受力主筋、竖向抗剪箍筋采用优化分区配置,满足受力要求。

环境因素影响下钢筋混凝土索塔爬模施工仿真分析方法

为探究爬模施工进程中索塔空间温度场和应力场分布,掌握塔柱线形特性,提出一种索塔爬模施工仿真分析方法.利用Fortran编程语言开发相应子程序,对结构施加复杂温度边界,实现不同节段混凝土水化放热、收缩徐变.利用Abaqus软件对索塔爬模施工过程进行分析.结果表明:施工过程中索塔空间温度分布不均匀,塔柱表里最大温差达25.9℃,向阳面与背阴面温差最大为9℃;考虑温度效应后,塔柱所受拉应力更大,且空间应力分布具有很强的时变性,索塔线形特征与变化规律也发生改变;施工塔顶累积竖向位移先增大后减小,在爬模第16节段达到最大值20.5 mm;施工过程塔顶累计顺桥向和横桥向位移更大,最大值分别为6.5和22.3 mm.

长阳天池口清江特大桥主拱圈悬臂浇筑斜拉扣挂系统设计

长阳天池口清江特大桥主桥为净跨径242 m的非对称上承式钢筋混凝土拱桥,主拱圈采用单箱单室截面,宽9.5 m、高4.0 m。资丘岸和五峰岸半跨主拱圈各分为24个和21个节段,第1个节段采用支架现浇,其余节段采用斜拉扣挂悬臂浇筑法施工。扣索采用星式和扇形组合方式布置,位于墩顶和扣塔的扣索为星式布置,位于交界墩墩身的扣索为扇形布置,并将墩身上的扣锚索设计成连续索以避免在墩身上搭设张拉平台;扣塔由8根∅800 mm×16 mm钢管组成,两岸扣塔分别高52.68 m和60.12 m;根据锚索最大索力,设计了能承受800 kN张拉力的岩锚索。建立主拱圈悬臂浇筑施工阶段MIDAS Civil有限元模型,对斜拉扣挂系统扣锚索索力进行计算,通过拆除部分扣索和调整扣锚索索力,施工期间主拱圈截面最大拉应力、扣塔最大偏位、主拱圈成拱后线形均满足要求。

桥墩倾斜方向对自浮式防撞装置防护效果影响研究

随着航道上大跨度桥梁的建设愈加广泛,其桥墩在水面附近往往具有一定的倾斜角度。为研究桥墩倾斜方向对自浮式防撞装置防护效果的影响,文章基于装备自浮式防撞装置的2种倾斜方向的桥墩与6000DWT级散货船为研究对象进行非线性有限元仿真碰撞计算,分析桥墩倾斜方向对不同航速船舶撞击下桥墩撞击力、系统能量转换、船艏结构破坏的影响。结果表明:外倾式桥墩受到撞击力更小,其防撞装置通过变形吸收能量更多、防护效果更好。研究成果可为大跨度桥墩设计与防撞装置的开发提供重要的参考价值。

超高桥塔的气弹模型风洞试验及其等效静力风荷载

为研究超高桥塔的气弹模型风洞试验方法及其等效静力风荷载,根据某实际工程中的超高桥塔建立了有限元模型,进行了动力特性计算,进而设计了相应的气弹模型,并开展了风洞试验。在此基础上,开展了超高桥塔风致振动的非线性时程计算,并基于阵风荷载因子法,对比了以位移、内力和应力为单一目标的超高桥塔的等效静力风荷载。结果表明:斜风作用下的桥塔风致振动比较显著,其影响随着风速的增大而愈加明显;当风向角为75°~90°时,超高桥塔将在风速为35~50 m·s^(-1)的区间发生顺桥向的侧弯涡振,但幅值较小;基于应力的阵风荷载因子比基于位移或内力的阵风荷载因子更加稳定,这使得基于应力的等效静力风荷载要优于基于位移或内力的等效静力风荷载,比较适合于超高桥塔。

基于模型试验的双缆多塔悬索桥力学特性研究

为验证双缆多塔悬索桥力学特性,基于理论公式和数值分析开展了双缆多塔悬索桥模型试验。根据设计参数分别建立了传统体系和双缆体系有限元模型,对比分析了两种体系结构变形和桥塔应力;模型试验验证了双缆体系塔梁变形公式精度和动力特性。研究表明,双缆体系试验模型塔梁变形理论值与实测值及模拟值吻合良好,说明试验模型整体精度较好,验证了理论公式精度。实测与有限元模拟发现第一阶振型模态均为加劲梁一阶反对称竖弯,结构固有频率实测值与模拟值误差为6.97%,验证了模型结构振型模态和固有频率。传统体系中塔位移和加载跨加劲梁挠度是双缆体系的3倍左右,非加载跨加劲梁挠度为4倍左右;传统体系中塔塔底应力是双缆体系的3倍左右,证明双缆体系较传统体系能够有效减小中塔位移、加劲梁挠度和中塔塔底应力。