风雨联合作用下大跨桥梁颤振稳定性试验研究

针对风雨联合作用下的大跨桥梁颤振稳定性,以一开槽双箱梁桥梁为研究对象,通过在大气边界层风洞中搭建的风雨联合作用试验系统,完成基于自由振动法的节段模型颤振试验。通过分析不同雨强下该桥梁主梁的颤振导数以及颤振临界风速,进而获取降雨对大跨桥梁颤振稳定性的影响规律。试验结果显示:颤振导数随雨强变化而变化,其中体现扭转气动阻尼特性的颤振导数变化较为显著,随雨强增大,颤振临界风速先增大后减小。试验结果表明:降雨对大跨桥梁的颤振导数以及颤振临界风速均有一定影响。     

桥板颤振导数的比较和敏感性分析 第一部分：试验数据分析

为评估风载下桥板的性能,通常采用多年来发展的两个独特的方法（自由和强迫振动）,从风洞模型试验中得到桥板气动弹性系数。尽管已有众多的研究者对每个技术优缺点进行分析,但文献中缺少对试验结果的系统比较。本研究的意义在于进行与长期颤振导数试验数据相关的评估,包括分析和解释自由和强迫振动两种方法的异同点。从2002年开始,美国的爱荷华州大学和日本的公立研究所着手进行桥颤振导数的研究。试验包括的截面类型很广,从矩形棱柱到改进型,尤其考虑了当前在大跨桥中采用空气动力学设计梁的趋势。同时系统地分析和比较了两种方法颤振导数的试验结果。在相关的论文中,对敏感性进行分析以研究大跨桥在气动弹性不稳定时颤振导数数据中所隐含的不同点。     

基于完全气动弹性模型的冷却塔风致响应风洞试验研究

风荷载是冷却塔设计的控制荷载,完全气动弹性模型风洞试验是研究其风致响应的有效途径。基于此,推导了冷却塔完全气动弹性模型相似关系并用有限元分析方法予以验证,据此相似关系设计并制作了某核电站200m高超大型冷却塔的1∶400完全气动弹性模型,并在风洞中模拟的B类风场对其风致响应进行测试,试验前对模型的动力特性进行检验。试验结果表明：完全气动弹性模型能较为精确模拟冷却塔结构的质量、刚度和阻尼相似;迎风面的风致变形较大,而其中又以喉部附近最大;背景响应占总响应的主导地位,动力放大效应不明显;风振系数值随高度的增加而减小,各控制点风振系数均值略小于DL/T 5339-2006《火力发电厂水工设计规范》规定值。     

风驱雨作用下桥梁主梁颤振节段模型试验研究

针对风驱雨作用下桥梁主梁的颤振问题,依据风驱雨作用和主梁振动特点,给出了分别考虑雨滴冲击和表面积水后的降雨相似关系,并探讨了其选取原则。选取大跨度桥梁较常采用的典型断面,通过节段模型试验模拟了风驱雨对主梁断面的颤振导数和颤振发生过程的影响。试验结果表明:主梁断面的颤振气动导数随雨强的变化无明显规律,各导数的变化量值相当,随风速增加,降雨引起的导数变化有所加大,但基本没有改变其随风速变化的整体趋势,试验雨强120mm/h时,模型颤振临界风速会有20%～30%左右的提高,但考虑雨强相似比后可以认为降雨对桥梁主梁的风致颤振失稳特征的影响基本可以忽略。     

薄膜结构的风致动力效应初探

由于自重轻、刚度小、距度大且具有对风荷载的敏感性，薄膜结构可能会在风荷载作用下发生破坏，其风致动力效应是从事薄膜结构研究和工程实践人员关心的问题。本文主要总结和介绍了国外在相关研究领域的进展和成果，包括薄膜结构自振特性测试结果，薄膜结构风致动力效应风洞实验结果，以及关于薄膜结构颤振失稳的讨论。     

大跨结构抗风研究现状及展望

大跨结构是典型的风敏感结构,风荷载和风致振动常常是控制结构安全性的主要因素.本文系统回顾了国内外大跨结构抗风研究领域的进展,主要涉及风洞试验、大跨结构气动弹性模型、风振系数、等效静风荷载、风致响应等方面,并对存在的不足以及进一步研究的方向提出建议.     

紊流风场中桥梁气动导数识别的随机方法

气动导数是大跨桥梁结构颤振和抖振分析的重要依据。本文提出采用随机系统识别方法来识别紊流风场中的气动导数, 与当前应用较广的瞬态激励法及强迫激励法相比, 这类方法的优势在于: (1) 将紊流看作是激励, 而不是噪声, 更能反映结构实际工作状态下的特性; (2) 识别精度不受风速的制约, 可以获得较高折减风速下的气动导数; (3) 可直接在紊流风场中结构随机响应上进行识别, 无需任何人为外在激励, 试验更为简单易行。在风洞中完成了紊流风场中桥梁节段模型测振试验, 进一步利用本文的方法识别出气动导数。与相关文献提供的类似模型在均匀场和紊流场中识别结果的对比表明: 本文识别的气动导数是可靠的, 所提出的采用随机系统识别方法来识别紊流风场中气动导数的思路是可行的。     

车辆荷载作用下公铁两用桥梁的疲劳分析

随着大量超载车辆的出现,桥梁结构损伤加剧,降低了结构使用寿命。该文首先分析了车辆动力放大系数的计算方法,其次对荷载效应计算与统计方法进行了研究,然后通过疲劳模型的建立,对车辆荷载作用下的桥梁使用寿命进行计算,最后给出了用于桥梁荷载性能估算的有限元程序,从而进一步确定了桥梁车辆荷载对桥梁疲劳性能的影响。     

大跨度桥梁风振响应问题的研究

介绍了自然风的构成,对桥梁结构风致振动的机理进行了探讨,并将该机理应用到实例的风毁分析上,成功地解释了该桥毁坏的原因。同时,对大跨桥梁风致振动控制的研究现状进行了总结,讨论了风洞试验在桥梁风致振动控制研究中的作用,并对数值风洞技术的发展及其应用前景进行了展望。     

特重车交通荷载作用下大跨拱桥动力响应分析

为研究特重车交通荷载工况作用下大跨拱桥的动力响应特点,以河北省宣大高速公路上某大桥的动态称重系统所采集的近3年的交通数据为基础,定义并提取了特重车的交通荷载工况,进而分析了不同类型特重车交通荷载工况所占比例及每个特重车交通荷载工况车辆总质量的分布规律。利用随机车流-桥梁耦合振动分析软件计算了大跨拱桥在特重车交通荷载作用下的空间动力响应,并与新旧桥梁规范中的设计车辆荷载对应的响应进行了对比。结果表明:新规范对拱桥关键部位的设计荷载定义更为保守,实测的交通荷载工况中仅有极少数特重车交通荷载工况对应的响应超过了设计车辆荷载对应的响应;对于该大跨拱桥,新桥梁规范中的设计车辆荷载能够较充分地考虑大部分特重车交通荷载作用对桥梁结构整体受力产生的不利影响。     

Control of wind-induced vibration of long-span bridges and tall buildings

With the rapid increase in scales of structures, research on controlling wind-induced vibration of large-scale structures, such as long-span bridges and super-tall buildings, has been an issue of great concern. For wind-induced vibration of large-scale structures, vibration frequencies and damping modes vary with wind speed. Passive, semiactive, and active control strategies are developed to improve the wind-resistance performance of the structures in this paper. The multiple tuned mass damper (MTMD) system is applied to control vertical bending buffeting response. A new semiactive lever-type tuned mass damper (TMD) with an adjustable frequency is proposed to control vertical bending buffeting and torsional buffeting and flutter in the whole velocity range of bridge decks. A control strategy named sinusoidal reference strategy is developed for adaptive control of wind-induced vibration of super-tall buildings. Multiple degrees of freedom general building aeroelastic model with a square cross-section is tested in a wind tunnel. The results demonstrate that the proposed strategies can reduce vibration effectively, and can adapt to wind-induced vibration control of large-scale structures in the uncertain dynamic circumstance.     

Comparative and sensitivity study of flutter derivatives of selected bridge deck sections,Part 2: Implications on the aerodynamic stability of long-span bridges

This study is the continuation of a comprehensive investigation on section-model aeroelastic coefficients for bridge decks (flutter derivatives) extracted from wind tunnel section-model tests. The original motivation emerged from the United States—Japan Benchmark Study on Bridge Flutter Derivatives, which promoted a series of systematic comparisons of experimental data extracted by two laboratories (Iowa State University, USA and Public Works Research Institute, Japan) as well as previous results available in the literature. Comparisons, which included both streamlined and bluff deck girder models, were summarized in a companion paper [Sarkar P, Caracoglia L, Haan FL, Sato H, Murakoshi J. Comparative and sensitivity study of flutter derivatives of selected bridge deck sections. Part 1: Analysis of inter-laboratory experimental data. Eng Struct 2009;31(1):159–69]. Differences in the flutter derivatives were mainly attributed to: distinct experimental methods in the wind tunnel (free or forced vibration methods), intrinsic variability between different laboratory environments and effects of amplitude dependency in the tests (for bluff sections).In this paper, a sensitivity study was performed to examine the implications of the perceived dissimilarities among flutter-derivative data sets discussed in [Sarkar P, Caracoglia L, Haan FL, Sato H, Murakoshi J. Comparative and sensitivity study of flutter derivatives of selected bridge deck sections. Part 1: Analysis of inter-laboratory experimental data. Eng Struct 2009;31(1):159–69], on the aeroelastic instability of long-span bridges.Numerical analyses were conducted to evaluate flutter instability boundaries of a set of long-span bridge configurations. Both single-mode and coupled-mode instability were considered, depending on the cross section type and characteristics. It is concluded that uncertainty in flutter derivatives occurring as a result of extraction method or intrinsic variability between different laboratories from negligibly small values to as much as fifty percent, as observed in [Sarkar P, Caracoglia L, Haan FL, Sato H, Murakoshi J. Comparative and sensitivity study of flutter derivatives of selected bridge deck sections. Part 1: Analysis of inter-laboratory experimental data. Eng Struct 2009;31(1):159–69], do not affect the variability in the predicted critical velocity in a proportional way. However, differences in the resulting critical velocities have been observed and estimated from as small as five percent to more than thirty percent, heavily depending on the type of bridge, the simulated conditions and type of instability, either dominated by a single mode or influenced by modal coupling.     

Estimation of torsional-flutter probability in flexible bridges considering randomness in flutter derivatives

Torsional-flutter instability is an aeroelastic phenomenon of interest to the bridge engineer, corresponding to a torsionally unstable vibration regime of the deck driven by wind excitation and appearing beyond a certain critical wind velocity. In this study a method for the derivation of the flutter probability for long-span bridges with bluff decks is proposed.In the first part of this study the deterministic problem is addressed. In contrast with the classical solution method in the frequency domain based on a numerical procedure for assessing the critical wind velocity, a single-mode “closed-form” algorithm for the derivation of the critical velocity was investigated. A polynomial representation of the aeroelastic-loading coefficients (flutter derivatives), necessary for torsional-flutter analysis, was utilized.In the second part an algorithm for estimating the torsional-flutter probability was developed, considering randomness in bridge properties, and flutter derivatives in particular due to their preeminent role in torsional-flutter velocity estimation.Experimental errors in the extraction of flutter derivatives from wind tunnel tests were analyzed. The “closed-form” algorithm, developed in the first part, allowed for a direct numerical solution of the flutter probability in a simple way.The torsional-flutter probability for three simulated bridge models with rectangular closed-box and truss-type girder deck was numerically determined. A set of experimental data, available from the literature, was employed. The simulations enabled the validation of the proposed algorithm.     

Wind tunnel: a fundamental tool for long-span bridge design

An overview of wind tunnel activities and methodologies to support the design of long-span suspension bridges is proposed. The most important aspects of the wind-bridge interaction are investigated considering the aerodynamic phenomena affecting the different parts of the bridge (mainly deck and towers). The experimental activities and results are proposed in the framework of a synergic approach between numerical and experimental methodologies that represent the common practice in defining the full scale aeroelastic behaviour of the bridge starting from scaled reproduction of the wind-bridge interaction. Static and dynamic wind loads, aeroelastic stability, vortex-induced vibrations will be investigated.     

Relationships among aerodynamic admittance functions, flutter derivatives and static coefficients for long-span bridges

Wind actions on long-span bridges are commonly considered as the superimposition of buffeting forces and self-excited forces, depending on the aerodynamic admittance functions and on the flutter derivatives, respectively. Since bridge deck sections are bluff bodies, the aerodynamic admittance functions and the flutter derivatives have to be determined experimentally by wind tunnel tests. This paper introduces a generalized quasi-static theory, defining new relationships among the flutter derivatives and the aerodynamic admittance functions. All the relationships are theoretically verified for the zero circular frequency; based upon experimental results, the validation of the relationships among the flutter derivatives is also provided for non-zero values of the frequency.     

Parametric study on flutter derivatives of bridge decks

The method for identification of flutter derivatives of bridge decks developed by the authors is first briefly described in this paper. To investigate the effects of dynamic parameters of a bridge deck model on the flutter derivatives a test of the sectional Jiangyin Bridge deck's models with different dynamic parameters was carried out in a boundary layer wind tunnel using the present identification method. In both smooth and simulated turbulent flow conditions, a plate model and the sectional deck model of the Jiangyin Bridge were tested to further survey the effects of turbulence on flutter derivatives. The identified results tend to indicate that the effects of parameters of the model and turbulence on the flutter derivatives are negligible.     

Flutter mechanism for rectangular prisms in smooth and turbulent flow

The aim of the present work is to clarify the flutter mechanism for suspended long span bridges via a parametric analysis on flutter instability for a set of given deck profiles. Several wind tunnel tests in the DIC-CRIACIV boundary layer wind tunnel (BLWT) have been carried out on spring suspended section models such as rectangular cylinders of different slenderness ratios B/D=5 and 12.5, where B is the longitudinal length of the prism and D is the height of the prism. The main experimental parameters needed for examining whether a given bridge profile is flutter-prone below a certain mean wind velocity are the flutter derivatives, so a system identification procedure (combined system identification method, CSIM) has been developed to extract simultaneously all flutter derivatives from two degrees of freedom (2DoF) section model test results (coupled vertical-torsional free vibration tests). The parametric analysis includes the investigation on (1) the effects of model dynamic properties on BLWT test results, (2) the consequence of turbulence on bridge stability, (3) the possible definition of an aerodynamic stability performance index (β) for rectangular cylinders for designing purposes.