Experimental investigation of rain-wind-induced vibration of cables in cable-stayed bridges and its mitigation

Rain-wind-induced vibration of cables in cable-stayed bridges is presently a worldwide problem of great concern. Because it is sensitively influenced by many parameters, this peculiar phenomenon is difficult to be replicated in laboratory conditions; its mechanism has not been well explained yet. In this paper, the phenomenon of rain-wind-induced vibration of a cable model is successfully reproduced under actual rain conditions in a wind tunnel. The effects of several main factors, including the inclination angle, frequency and damping of the cable as well as the wind yaw angle, etc. on the characteristics of rain-wind-induced vibration are investigated in detail in the test. The countermeasures of double-spiral wires and dampers for the mitigation of the vibration are also experimentally studied. The results show that the size and twine direction and the pitch of the spiral wires twined on the surface of cables have great effects on the mitigation efficiency of rain-wind-induced vibration of cables.     

Accurate cable force determination using ambient vibration measurements

Knowledge of the tensile forces in cables of bridges or in external tendons is required for regular inspection and safety assessments. Force determination by lift-off tests with hydraulic jacks can result in considerable expenditure as well as the danger of damage. However, alternatively conducted vibration measurements have shown that, due to improper identification of natural frequencies or the use of over-simple force–frequency relationships, accuracies achieved up to now are sometimes not achieved. For high cable forces and short cables, errors of up to ±10% could be realized. Fast and accurate methods for assessing cable forces are thus required. The main target of this paper is the presentation of a practical applicable procedure to determine cable forces in civil engineering constructions by means of vibration measurements. By taking into account the identified natural frequencies, the bending stiffness and the boundary conditions, accuracy in the range of ±1% may be achieved.     

带转向机构HCA在杭州湾跨海大桥斜拉索减振中的应用

杭州湾跨海大桥北航道桥为主跨448m的钻石型双塔双空间索面钢箱梁斜拉桥,通航净空为47m,按双向六车道高速公路设计,设计时速100km/h。为改善行车安全性,国内首次在栏杆外侧设置了风障(高度从近塔4.27m至远塔3.4m),为了确保整桥隽秀的景观前提下开发了带转向机构的拉索减振器,对全桥拉索进行了理论分析和安装减振器后的实桥测试。     

On wind–rain induced vibration of cables of cable-stayed bridges based on quasi-steady assumption

Wind–rain induced vibration of cables of cable-stayed bridges is presently a problem of great concern. Similar to the classical galloping theory, this paper adopts quasi-steady assumption to study wind–rain induced vibration of cables. A wind tunnel test was first made to measure wind pressures and thus wind forces acting on a 3-D cable model and the upper artificial rivulet model. A new theoretical model for instability of a 2-D sectional rigid model with a moving artificial rivulet is then established and the instability criterion is proposed. The instability criterion is verified through wind tunnel test on a 2-D rigid sectional cable model with a moving artificial rivulet. Finally, theoretical models of wind–rain induced vibration of 3-D sectional cables and 3-D continuous cables are, respectively, developed based on the measured mean wind forces mentioned above, and the vibration characteristics are investigated as well as an explanation of the mechanism of wind–rain induced vibration of stay cables is made.     

Vortex-induced vibration of stay cable under profile velocity using CFD numerical simulation method

Vortex-induced vibration (VIV) of a stay cable subjected to a wind profile is numerically simulated through combining computational fluid dynamics (CFD) code CFX 10.0 and computational structural dynamics (CSD) code ANSYS 10.0. A stay cable with the inclined angle of 30° is used as the numerical model. Under a profile of mean wind speed, unsteady aerodynamic lift coefficients of the cable have been analyzed in both time domain and frequency domain when VIV occurs. The results indicate that the lift coefficient wave response of the stay cable under a wind profile is different from that of an infinitely long cable under a uniform flow in water (i.e., without consideration of profile) obtained by direct numerical simulation. Cable oscillations can severely affect the unsteady aerodynamic frequencies, change flow field distribution near the cable and affect the vortex shedding in the wake.     

索穹顶结构整体张拉成形模型试验研究

索穹顶结构既可以通过对所有拉索施加预应力完成对结构预应力的施加,也可以通过对部分拉索施加预应力,其他拉索被动受力达到整个结构被赋予预应力,根据索穹顶结构预应力施加的不同方法,探讨索穹顶结构预应力成形过程。采用不同的预应力施加方法对结构进行全过程仿真分析,表明结构的最终内力和位形与预应力施加方法无关。结合内蒙古伊旗全民健身体育中心索穹顶实际工程,制作了1∶4的试验模型,按照地面组装、分步提升、整体张拉的思路,采用ANSYS数值模拟对成形过程进行了全过程仿真分析,对索穹顶张拉成形方法进行验证。通过在模型试验过程中合理布置拉力传感器对结构从拼装到成形的全过程进行内力跟踪监测,监测结果与仿真分析结果吻合较好,从试验模型的内力变化曲线可找到内脊索开始受力即为结构由机构转变为结构的转折点。     

A new approach for simulating aerodynamic vibrations of structures in a wind tunnel—development of an experimental system by means of hybrid vibration technique

The present paper describes a newly proposed technique for simulating aerodynamic vibration of structures, which is referred to as the hybrid vibration technique or HVT. This technique is a combination of step-by-step computer calculation and measurement of the aerodynamic force acting on a model structure in a wind tunnel test. Even though the HVT can be applied effectively, problems still exist with respect to obtaining accurate simulations. These problems include response delay in controlling the model behavior and the inertia force component present in the measured aerodynamic force. Techniques for compensating for response delay and for eliminating inertia force from measured aerodynamic force are applied to a developed system based on HVT simulations of aerodynamic vibration of elastic structures and structures exhibiting elasto-plastic behavior are performed by means of the newly developed system. The effectiveness of the techniques for compensating for the response delay and eliminating the inertia force can be confirmed from the results of the simulations. In addition, the possibility and applicability of HVT is indicated.     

Geiger型索穹顶结构模型抗连续倒塌试验研究

索穹顶结构冗余度低,关键构件的破坏可能会引起结构连续倒塌。为了解索穹顶结构的抗倒塌性能,并找出影响该结构体系抗连续倒塌性能的关键构件,采用拆除构件法对跨度6 m的Geiger型索穹顶结构模型进行了抗连续倒塌试验研究。结果表明：单根构件破断后,除个别构件外,其他大多数构件的内力均减小;不同工况下,产生最大竖向位移的节点随破断构件的位置不同而不同,单根构件破断引起的结构最大竖向位移为跨度的1/14;影响索穹顶结构抗连续倒塌性能的关键构件是环索及外斜索;对于同类型构件,构件失效位置对结构抗倒塌性能的影响由内向外依次增大;保证外圈环索不失效是索穹顶结构抗倒塌的关键。     

Experimental study on the wind-induced vibration of a dry inclined cable—Part I: Phenomena

Besides rain-wind-induced vibration, field observations and a few experimental studies in recent years show that inclined cables also manifest wind-induced instability under condition when there is no precipitation. In order to further investigate these types of motion, including the limited-amplitude high-speed vortex excitations identified recently, experimental investigations were carried out. The focus of the present paper is on describing the dynamic and static model wind tunnel tests conducted and discussing the differences between divergent galloping motion and high-speed vortex excitation. Results show that the characteristics of dynamic responses and aerodynamic forces of these two types of motion are different. The former could be explained by a mechanism similar to that of classical galloping, whereas the latter might be related to vortex formation along the cable. The issues that require further investigation are also discussed.     

Experimental parametric study on wind‐induced vibration control of particle tuned mass damper on a benchmark high‐rise building

A particle tuned mass damper system is an integration of tuned mass damper and particle damper. The damping performance of such device is investigated by an aero‐elastic wind tunnel test on a benchmark high‐rise building. The robustness of the system is studied by comparing the damping performance to that of a traditional tuned mass damper, and the results show that the damper has excellent and steady wind‐induced vibration control effects. Meanwhile, the parameters (filling ratio, mass ratio, and mass ratio of the container to particles), which have great influence on the vibration reduction performance of the system, are also analyzed, and it is found that the particles filling ratio plays the most important role in deciding the damping effects of the dampers. There exists an optimum filling ratio and mass ratios in which the damper can reach the best damping state. Proper parameter selections can greatly improve the damping performance.     

吊索与钢管混凝土拱桥新型连接节点承载性能试验研究

吊索与钢管拱连接节点的设计是系杆拱桥建设中的关键技术难题。在江西吉安赣江大桥中采用的外置索座骑跨式连接节点,可很好地解决传统节点做法在施工及使用过程中存在的问题。为研究这种节点的承载性能,课题组在理论分析的基础上,在施工现场进行了足尺模型试验。本文具体介绍了这次试验的情况,包括试件制作、加载方案设计、量测技术和试验结果分析等。试验结果表明,节点的索座附近应力分布较均匀,局部变形很小,完全可满足结构承载力和变形要求。另外,这种节点构造形式简单,便于施工,是一种值得推广的节点形式。     

Experimental study on the wind-induced vibration of a dry inclined cable—Part II: Proposed mechanisms

The possibility of dry inclined cable galloping is of concern in the design of bridge stay cables. Although the phenomenon has only been observed in a few experimental studies, the fact that the mechanism of excitation is not fully understood makes it difficult to develop solutions with confidence. To clarify its physical nature, a series of dynamic and static model wind tunnel tests have been carried out in the current study. The present paper will focus on exploring the applicability of Den Hartog criterion and on an explanation of its driving mechanism. The spatial structure of the flow field surrounding an inclined cable will be examined to assist in better understanding of the phenomenon. Results show that the critical onset condition of the divergent motion predicted by the Den Hartog criterion (as applied to an inclined circular cylinder) agrees well with the experimental observation. However, satisfaction of the criterion only occurs within a critical range of Reynolds number. Further, within the critical ranges of wind speed and cable orientation, flow around the cable is found to be better organized. The resultant fluid forces acting at different longitudinal locations of the cable tend to point toward the same direction which generates greater cross-flow excitation force, and the axis-wise lift correlation is enhanced.     

Application of coupled multi-body dynamics–discrete element method for optimization of particle damper for cable vibration attenuation

With the application of the particle damping technology to cable vibration attenuation, the rootless cable damper overcomes the limit in installation height of existing dampers. Damping is achieved through energy dissipation by collisions and friction. In this paper, a coupled multi-body dynamics–discrete element method is proposed to simulate the damping of the damper–cable system under a harmonic excitation. The analyses are done by combining the discrete element method in EDEM and multi-body dynamics in ADAMS. The simulation results demonstrate the damping efficiency of rootless particle damper under different excitations and reveal the influence of the design parameters on its performance, including the filling ratio, particle size, coefficient of restitution, and coefficient of friction.     

高精度风雨模拟环境下拉索风雨激振试验研究新发现

拉索风雨激振是一种在风雨共同作用下发生的拉索大幅低频振动,现有人工降雨风雨激振试验无法准确模拟自然降雨的多种特性,难于实时再现风雨介质耦合环境拉索气动失稳现象。开发高精度人工降雨模拟装置,可对降雨强度进行精细连续调节,较为准确模拟雨滴大小、能量、均匀度等自然降雨的特性,合理地再现风雨联合作用条件下拉索风雨激振过程;系统研究风速、雨量以及风雨联合作用对拉索风雨激振的影响,揭示了拉索在低风速大雨量、高风速小雨量时,风雨激振发生规律和特点。     

铁路振动作用下双排桩屏障隔振性能试验研究

为研究铁路应用双排桩屏障的隔振性能,基于铁路振动产生的弹性波传播特性,通过场地试验测得激振频率10 Hz下地表振动加速度幅值,以双排隔振桩屏障中归一化桩间距、归一化排间距、排桩数量以及排桩布置形式为变化参数,研究改变双排桩几何参数对其隔振效果的影响。试验结果表明:随桩间距的增大,排桩屏障的隔振效果逐渐减弱。当归一化桩间距不小于3.0时,排桩屏障逐渐失去其整体隔振作用;当归一化排间距为3.0时,排桩屏障可以获得较优的隔振效果,其有效隔振面积百分比在19.52%～68.89%;随着排桩数量的增加屏障有效隔振面积随之增大,排桩数量由8增至10时,有效隔振面积百分比增大0.87%～4.74%,可以使更大区域范围达到隔振要求;当屏障整体桩数相同时,采取菱形布置形式的隔振屏障比矩形的隔振效果好,菱形布置较矩形布置有效隔振面积百分比增加1.20%～5.01%。     

考虑损伤因素的单层平面索网静力试验研究

在单层平面索网玻璃幕墙建筑的使用过程中,单层平面索网作为支承结构,不可避免地会受到各种损伤。为了研究损伤因素对单层平面索网结构静力承载性能的影响,针对尺寸为4.85m×4.85m的4×4网格索网结构足尺试验模型,分别引入索与索之间连接节点失效、索预应力损失、索锚固端破坏这三种损伤因素,进行静力加载试验研究。试验结果表明:横索与竖索连接节点失效几乎不影响单层平面索网结构的承载性能;索预应力损失时,节点索网平面外位移变化率不超过15%;锚固端破坏对结构局部影响较大,节点平面外位移变化率介于18%～36%;损伤因素对节点平面外位移的影响大于索力;损伤的影响取决于损伤程度和损伤位置;相同损伤对结构的影响程度随荷载增加而减小。     

Research and application of a new super‐long span roof based on cable structure

With the continuous development of urban processes, people's demand for large‐span space is getting stronger and stronger, and the application of large‐span building structures is becoming more and more extensive. This paper introduces a new type of suspension cable roof that uses the building's own weight to increase the tension of the cable to achieve a super‐long span. The rationality of the structural system is analyzed, and the dynamic performance, wind resistance, and seismic performance of the structure are analyzed with a simple example. At the same time, measures to further improve the structural span are proposed. Finally, it provides the forms of building that are feasible in this structural form, which provides reference and guidance for the design and construction of long‐span buildings, which is of great significance.     

斜拉桥斜拉索风雨振时索表面水线摆动作用及规律的试验研究

斜拉索表面水线的周向摆动被认为是激发索发生风雨振的重要因素。有水线的索的气动力可以认为是索本身的气动力和水线摆动产生的气动力的组合。在风洞中,通过竖向强制振动试验,测试索的气动力并算得气动导数H1*和H4*。为了模拟水线的摆动,对贴有水线的索施行两端同向强制扭转振动试验,测试振动中的气动力。通过分析水线的摆动对索竖向振动阻尼的贡献,表明水线的摆动既能促使索变得气动不稳定,也可以促使索变得气动稳定,这主要取决于水线摆动与索振动之间的位相差。同时,通过在风洞中模拟人工降雨并对水线进行跟踪观测,发现水线沿索轴向分布及摆动不均一,指出掌握风雨振时水线的各个参数对分析和理解该振动具有重要意义。     

Experimental study of traffic-induced vibration of the new CCTV headquarters building

The traffic-induced vibrations of the new CCTV Headquarters building are studied stages. In the first stage when the through experiments in two 30th floor of the northwest tower and the 38th floor of the southeast tower were finished, the traffic flows on the roads surrounding the building were investigated, and 27 setups of accelerations were measured at the roadside, on the pile cap and on the 9th floor. In the second stage when the whole steel structure was completed, l 5 setups of accelerations were measured at the roadside, on the pile cap and on the 37th and the 48th floors. The accelerations of the building under different traffic flows, in different positions are analyzed in both time domain and frequency domain. The damping ratios are estimated by the upgraded half-power bandwidth method.