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.

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.

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.

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。

钢拱塔斜拉桥的温度耦合效应和索力预测

钢拱塔斜拉桥的受力体系与传统斜拉桥有所不同,为研究环境温度变化对这种异形桥塔斜拉桥主要受力部件的影响,以某钢拱塔斜拉桥为工程背景,首先基于在线监测获取的环境和部件温度数据,分析斜拉索索力、拱塔倾角和主梁应变的温度时变效应;然后以斜拉索为研究对象,通过该桥的有限元模型升降温模拟,分析各部件温差引起的温度耦合效应对拉索索力的影响;最后以环境温度、主梁温度、桥塔温度为输入,索力为输出,利用长短期记忆神经网络对实测索力-温度数据进行映射,实现数据压缩和特征提取,建立温度-索力预测模型,再对网络模型输入新的温度监测数据,以预测索力。研究结果表明:主梁和钢拱塔温度变化具有周期性,且滞后于环境温度;主梁应变与环境温度的变化趋势基本一致但具有一定的滞后性,环境温度变化对拱塔倾角的影响很小且没有周期性规律;索力与环境温度呈线性负相关,且需要考虑斜拉桥各部件的温差所引起的温度耦合效应;长短期记忆神经网络对带有时序特性的数据训练效果好,建立的温度-索力关系模型准确度高,可用于该桥索力的实时预测。

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。

桥梁刚度变化对高速铁路独塔斜拉桥车⁃桥耦合振动的影响分析

以高速铁路独塔斜拉桥为研究对象,建立车-轨-桥耦合系统的空间多体动力学分析模型,开展高速铁路斜拉桥的车-轨-桥耦合振动的仿真分析。通过改变材料弹性模量的方式调整桥塔和主梁刚度,研究桥梁刚度变化对桥梁车-桥-耦合振动的影响规律。研究结果表明,随着桥塔刚度的增大,主梁跨中竖向和塔顶纵向位移响应逐渐减小,其峰值减幅分别为7.57%和10%;随着主梁刚度的减小,主梁跨中竖向位移和塔顶纵向位移峰值呈逐渐递增趋势,主梁刚度变化对车体竖向加速度和Sperling竖向舒适度指标影响相对较大;相比于桥塔刚度的变化,主梁刚度变化对车-桥振动响应的影响更大;整体上,列车运行的安全性和平稳性指标满足规范要求。

随机侧风下高速列车在桥塔环境中气动载荷的时域与频域特性研究

在列车高速行驶过程中,强侧风的作用使得高速列车气动载荷急剧变化,可能会引起列车倾覆。文章对比分析了在恒定侧风和随机侧风的作用下,某型高速列车通过桥塔环境时头车所受到的气动载荷的时域特性,通过对其气动载荷进行快速傅里叶变换,得到了频谱分布特性。结果表明:在恒定侧风作用下,高速列车的气动载荷变化平缓,波动较随机侧风明显平缓;而在随机侧风的作用下,随着基频风速增大,气动载荷的极值大小基本不变,但极值点数目增加,这表明随机侧风模型和基频风速增加,对列车气动载荷变化影响显著。气动载荷功率谱密度集中出现在0~5 Hz范围内,最大值对应频率集中在0~1 Hz范围内,表明由侧风导致的列车所受非定常气动载荷的频率较低,这与列车本身的一些固有振动模态频率非常接近,易形成共振;与恒定侧风相比,随机侧风下气动载荷功率谱密度峰值更大,且随着基频风速增大而增大。

鲜花湖特大桥主桥设计研究

鲜花湖特大桥是G4222和县至襄阳高速公路舒城(千人桥)至金寨(皖豫界)段的主要控制性工程之一。主桥采用(118+220+118)m预应力混凝土部分斜拉桥,塔梁墩固结体系;上部结构采用单箱三室大悬臂斜腹板宽幅箱形主梁,人字形主塔,单索面扇形、横向双排布置斜拉索;下部结构结合现场环境,采用X形双肢薄壁墩、群桩基础。鲜花湖特大桥主桥构造新颖美观,融合了结构设计与景观需求。通过系统介绍该桥设计方案、结构和主要计算结果,以供同类项目参考。

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。

斜拉桥V形钢塔-混凝土基座结合构造方式比选

某人行景观桥为空间异型钢塔斜拉桥,主塔中2根箱型钢柱在四棱台混凝土基座上方交汇呈非对称V形,钢柱轴线与其底端钢-混连接面不垂直,基座尺寸严格受制于河道防洪要求,使塔根-基座结合部构造方式设计具有挑战性。按照造价相当的标准初步拟定3种结合方案,采用ABAQUS软件分别建立相应的有限元模型,选取塔底支座反力中平面内外弯矩绝对值相加最大的组合进行模拟计算及其结果比较和对标检验。研究结果表明:承压-传剪组合式结合部可以大幅度减小桥塔根部、基座及其中锚箱的应力,使其合理满足相关规范要求。就塔根最大位移和应力幅而言,均为传剪式最大、组合式最小。组合式方案中承压板厚度较承压式减小1/3,应力虽有上升却未超限,材料利用率提高。承压式、特别是传剪式构造方案中,混凝土基座最大主拉应力远超规范限值,无法满足抗裂要求。传剪式方案中锚箱钢板Mises应力也超限22%,且与其竖向压应力和混凝土主拉应力的最大值处于同一位置。传剪式方案不适用的原因是,锚箱中侧面竖板间距太小,矩形板与柱壁连接屈从于不利构造特点,形成大转折。无论应力大小还是变形控制,组合式方案都值得优先选择。研究成果直接服务于本工程,对类似工程也有一定的参考价值。