模拟降雨条件下斜拉桥拉索风雨激振及控制的试验研究

斜拉桥拉索风雨激振是当前桥梁工程界和风工程研究中的国际热点和难点问题。本文在同济大学TJ -1大气边界层风洞的出口射流段中成功再现了模拟降雨状态下拉索的风雨激振现象 ,研究了几种主要参数对拉索风雨激振振动特性的影响 ,还进行了在拉索表面缠绕螺旋线来破坏水线形成从而控制拉索风雨激振的研究 ,为深入研究斜拉桥拉索风雨激振机理和风雨激振的控制提供了有益的资料     

用于索承结构中斜拉索开环振动控制的磁流变阻尼器设计

斜拉索被广泛应用于索承结构,如大跨度桥梁或屋盖结构等.由于极低的内在阻尼,斜拉索易发生因其支承的运动或天气状况影响而引起的大幅值的振动.这些振动可以危及斜拉索本身以及整个索承结构的安全与寿命,甚至引起人们对该类结构信心的降低.在斜拉索减振的诸多方法中,采用磁流变阻尼器的智能阻尼技术近来引起了人们的研究兴趣.该阻尼器的阻尼特性可以通过调节(控制)磁场的输入电流/电压而改变,从而实现在不同振动(频率及幅值)情况下的最优或次优减振效果.本文发展了一个数学模型用于评价在开环控制状态下斜拉索-阻尼器系统的阻尼比.该模型考虑了阻尼器的安装高度、阻尼系数、刚度、质量、支撑刚度、磁变阻尼力以及斜拉索的垂度与倾角等因素,推导出了一个‘广义的通用公式’用于阻尼器参数的设计与优化,即寻求可提供系统最大阻尼比的最佳阻尼器参数.本文以目前世界最长斜拉桥——苏通大桥的最长斜拉索为例,确定了能够提供足够的阻尼以抑制风雨振的阻尼器安装高度以及相应的阻尼器参数.     

Effectiveness of cable networks of various configurations in suppressing stay-cable vibration

Cross-ties have often been used as a passive mitigation system for wind- and rain-wind-induced vibrations of stay cables on cable-stayed bridges. Recently, dampers have also been incorporated in cable networks formed using cross-ties in the hope of combining the mechanisms of both systems, and to achieve improved mitigating performance. This paper presents the results from a recent study conducted to investigate the effectiveness of cross-tie and damper-cross-tie systems of various configurations. This investigation, which is based on both analytical formulation and full-scale measurement, represents a step toward the development of guidelines for the design of cable-networks for stay cable vibration mitigation.     

Vibration characteristics identification of ultra-long cables of a cable-stayed bridge in normal operation based on half-year monitoring data

Abstract

The Sutong Bridge with a span of 1088?m is supported by 272 cables, whose lengths range from 152.85?m to 576.77?m (the longest in the world). The half-year vibration acceleration data of two cables from structural health monitoring system (SHMS) is analysed, in conjunction with the wind field data, weather data and vehicle data to explore and three types of cable vibrations. The large-scale cable vibration is mainly rain-wind-induced vibrations (RWIV) when the wind direction lies in an angular range of 40°–80° relative to the cable axis, and the bridge-deck wind velocity is 4–20?m/s. The ultra-long cable also experiences in-plane vibrations, which satisfy many characteristics of vortex-induced vibrations (VIVs). Cable VIV occurs only when the bridge-deck wind velocity 4–8?m/s, with the frequency ranging from 9.5?Hz to 10?Hz. The daily small-amplitude vibration of the cables and steel girder is mainly induced by the passage of heavy trucks. There exists a positive correlation between the number of heavy trucks and the vibration level. Based on the characteristics and occurrence probabilities of these three types of cable vibrations, corresponding measures are suggested for the maintenance of ultra-long cables.     

Field observations of rain-wind-induced cable vibration in cable-stayed Dongting Lake Bridge

The cable-stayed Dongting Lake Bridge has been observed several times to exhibit large-amplitude cable oscillation under simultaneous action of rain and wind. To investigate excitation mechanism and response characteristic of the rain-wind-induced stay vibration, a series of field measurements lasting 45 days have been conducted on the Dongting Lake Bridge by deploying accelerometers, anemometers and rain gauge for continuous monitoring. This paper presents the measurement results of rain and wind excitations as well as dynamic response of a typical stay in three rain-wind excitation events. The measurement data show that under specific combination of rain and wind, the maximum acceleration response of the cable reaches 10 g and the maximum displacement response (peak-to-peak) is around 0.7 m. It is revealed that the large-amplitude rain-wind-induced stay oscillation occurs in the bridge when the mean wind velocity at deck level ranges from 6 to 14 m/s, the wind attack angle (relative yaw angle) ranges from 10° to 50°, and the rainfall is light to moderate (less than 8 mm/h). For the observed cable, the overall dominant mode of cable vibration during rain-wind excitations is the third mode. However, in the evolution process of this kind of vibration, the dominant mode may differ for different response segments.     

斜拉桥拉索风雨激振问题综述

对斜拉桥拉索风雨激振的问题和振动控制研究现状进行了总结,分析了目前研究中存在的主要问题,并指出有关拉索风雨激振研究方面有待进一步提高的问题。     

Simple model of rain-wind-induced vibrations of stayed cables

This paper proposes a single-degree-of-freedom model of rain-wind-induced vibrations in stayed cables. It is assumed that the frequency of the circumferential motion of the upper rivulet is equal to that of cable and the rivulet amplitude is set constant for a given wind speed. The obtained results are verified with the existing experimental data showing that these assumptions capture the qualitative properties of the phenomenon. The explicit, analytical expressions are derived for the aerodynamic damping and exciting force. Finally, a linear SDOF model is derived for simple estimation of the amplitude of cable vibrations induced by wind and rain.     

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.     

Interpretation of field observations of wind- and rain-wind-induced stay cable vibrations

Wind- and rain-wind-induced vibrations have been a long-standing and frequent problem for the stays of cable-stayed bridges. This paper summarizes characteristics of wind- and rain-wind-induced vibrations observed during two long-term full-scale measurement efforts. Based on these characteristics, and their relationship to the ambient meteorological environment (wind and rainfall), several distinct types of vibration are identified. The potential connection between the prevalent, large-amplitude, rain-wind-induced vibration and a type of large-amplitude dry cable vibration is explored. The characteristics of these large-amplitude vibrations are also compared to those of the classical Kármán-vortex-induced vibration, which provides considerable insight into the mechanisms of wind- and rain-wind-induced stay cable vibrations.     

Semiactive Damping of Cables with Sag

Cables, such as those used in cable–stayed bridges, suspension bridges, guy wires, transmission lines, and flexible space structures, are prone to vibration due to their low inherent damping characteristics. The mitigation of cable vibration is necessary to minimize negative impact. Transversely attached passive viscous dampers have been implemented on some cables to dampen vibration. However, it can be shown that only minimal damping can be added if the damper attachment point is close to the end of the cable. For long cables, passive dampers may provide insufficient supplemental damping to eliminate vibration problems. A recent study by the authors demonstrated that "smart" semiactive damping can provide significantly superior supplemental damping for a cable modeled as a taut string. This article extends the previous work by adding sag, inclination, and axial flexibility to the cable model. The equations of motion are given. A new control–oriented model is developed for cables with sag. Passive, active, and smart (semiactive) dampers are incorporated into the model. Cable response is seen to be reduced by semiactive dampers for a wide range of cable sag and damper location.     

拉索间距及覆冰对双索尾流驰振的影响

利用FLUENT中的SST模型对不同索距的扇形覆冰双索和无覆冰双索绕流场进行三维数值模拟,得到下游索在0°~90°风攻角下的阻力系数、升力系数以及驰振力系数,进而研究两索之间的距离、风攻角及有无覆冰等条件对双索尾流驰振稳定性的影响。结果表明:覆冰双索三维数值模拟结果与无覆冰双索三维数值模拟结果差异较大;覆冰双索比无覆冰双索更易发生尾流驰振失稳;拉索间距越近,发生尾流驰振的可能性更大,当覆冰拉索间距超过一定范围时,不会发生尾流驰振失稳;双索发生尾流驰振的风攻角范围与拉索之间的距离有关,拉索间距越近,发生尾流驰振失稳的风攻角越小;不同间距双索的绕流场存在很大差异,当拉索间距较近时,类似于单钝体绕流。     

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.     

悬挑式张弦罩棚结构的风致疲劳分析

悬挑式张弦梁结构是由传统张弦梁结构改进的高效空间结构,其单榀张弦梁结构由上拉索、弦杆以及下抗风索组合而成。由于此类结构的风致振动效应显著,有必要研究其风致疲劳效应的影响。为研究悬挑式张弦罩棚结构的风致疲劳损伤,以某体育场罩棚为研究对象,采用几何缩尺比为1∶150的ABS塑料刚性模型进行B类风场下的风洞试验,得到各测点的风压时程数据,转化为有限元模型的节点风荷载进行风致振动响应分析并得到拉索的应力时程。利用雨流计数法对拉索的应力时程进行统计计数,并结合EuroCode2中所推荐的拉索S-N曲线,采用Miner准则对拉索的疲劳损伤进行线性累积,从而对该悬挑式张弦梁结构中的拉索进行疲劳损伤评估。结果表明：拉索构件的风致疲劳损伤随风向角变化明显,最不利风向角在180°附近;由于拉索构件的几何非线性特性,其疲劳损伤随风速变化呈非线性增长趋势。     

电涡流惯质阻尼器对斜拉索振动控制研究

为提升传统被动黏滞阻尼器(VD)对斜拉索的减振效果,提出一种融合旋转式电涡流阻尼技术与滚珠丝杠两节点惯质单元的电涡流惯质阻尼器(ECIMD)斜拉索减振新方法.首先研制阻尼系数和惯性质量均可调的ECIMD样机,基于力学性能测试结果辨识ECIMD力学模型参数;然后开展ECIMD对模型拉索减振试验,获得ECIMD阻尼系数和惯...     

带索高耸结构风振的合理分析和实用方法研究

顺风向风振是随机振动 ,而索在其上作用风力时是非线性 ,因而带索的高耸结构风振是非线性结构的随机振动。本文在评述非线性结构的随机振动分析方法的基础上 ,提出较合理的分析方法和索上风力团聚在两端的线性化的实用方法。例子计算表明 ,提出方法简便又合理 ,可供应用参考。     

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。     

Parametric oscillation of cables and aerodynamic effect

This paper addresses the aerodynamic effect on the nonlinear oscillation, particularly parametric vibration of cables in cable-stayed bridges. A simplified 2-DOF model, including a beam and a stayed cable, is formulated first. Response of the cable under global harmonic excitation which is associated with wind speed is obtained using the multiple scales method. Via numerical analysis, the stability condition of the cable in terms of wind speed is derived. The method is applied to a numerical example and a long-span bridge to analyze its all stay cables. It is demonstrated that very large vibration at one of the longest cables in the middle span of the bridge can be parametrically excited when the wind speed is over around 210 km/h (58.5 m/s).     

Parametric oscillation of cables and aerodynamic effect

This paper addresses the aerodynamic effect on the nonlinear oscillation, particularly parametric vibration of cables in cable-stayed bridges. A simplified 2-DOF model, including a beam and a stayed cable, is formulated first. Response of the cable under global harmonic excitation which is associated with wind speed is obtained using the multiple scales method. Via numerical analysis, the stability condition of the cable in terms of wind speed is derived. The method is applied to a numerical example and a long-span bridge to analyze its all stay cables. It is demonstrated that very large vibration at one of the longest cables in the middle span of the bridge can be parametrically excited when the wind speed is over around 210 km/h (58.5 m/s).     

Experimental study of wind–rain-induced cable vibration using a new model setup scheme

Wind–rain tunnel test of cable section model is one of the effective ways to explore mechanism of wind-rain-induced cable vibration and its mitigation. However, most of previous model setup schemes consider vertical vibration of cable only, in which the restoring force comes from the springs that perpendicularly support the cable model at its two ends. In this short communication, a new setup scheme for experimental study of wind–rain-induced cable vibration is presented. It can simulate both horizontal and vertical vibrations of the cable, in which the restoring force of the cable model comes from cable tension forces as in the prototype cable. Furthermore, the new setup can be easily adjusted for different cable inclinations and yaw angles. The frequency equation of the cable model is first derived to facilitate the design of model setup. Vortex-induced cable vibration, galloping of cable with artificial rivulet and wind–rain-induced cable vibration are then reproduced in wind/wind–rain tunnel using the new setup scheme. The preliminary parameter study, including cable inclination, yaw angle, and rainfall, regarding wind–rain-induced cable vibration is also performed. The effectiveness of vibration control methods, such as increasing damping ratio and twining spiral wire on the cable surface, is finally investigated.     

Numerical simulation of the airflow-rivulet interaction associated with the rain-wind induced vibration phenomenon

Rain-wind induced vibration is an aeroelastic phenomenon that occurs on the inclined cables of cable-stayed bridges. The vibrations are believed to be caused by a complicated non-linear interaction between rivulets of rain water that run down the cables and the wind loading on the cables due to the unsteady aerodynamic flow field. Recent research at the University of Strathclyde has been to develop a numerical method to simulate the influence of the external air flow on the rivulet dynamics and vice versa, the results of which can be used to assess the importance of the water rivulets on the instability. The numerical approach for the first time couples a Discrete Vortex Method solver to determine the external flow field and unsteady aerodynamic loading, and a pseudo-spectral solver based on lubrication theory to model the evolution and growth of the water rivulets on the cable surface under external loading. The results of the coupled model are used to assess the effects of various loading combinations, and importantly are consistent with previous full scale and experimental observations of rain-wind induced vibration, providing new information about the underlying physical mechanisms of the instability.