大跨桥梁气动耦合抖振响应分析的实用方法

基于单模态响应的SRSS方法因其计算简便 ,是当前工程界分析大跨桥梁抖振的常用方法。但随着跨度增大 ,气动耦合效应对桥梁抖振响应的影响越来越强 ,SRSS方法计算所得的抖振响应将出现较大的误差。而目前国内外提出的考虑气动耦合效应的多模态抖振响应分析方法虽然精度比SRSS方法高得多 ,但计算过程过于复杂 ,难以被工程界接受。本文基于经典的Scanlan抖振分析方法 ,在合理简化的基础上 ,导出了多模态气动耦合抖振响应的近似闭合解 ;定义了描述模态之间耦合程度的模态耦合系数和提出了大跨桥梁气动耦合抖振响应分析的实用方法———修正的SRSS方法。最后以日本明石海峡大桥为例 ,说明了本方法的精度和实用性。     

模态间气动耦合效应对调谐质量阻尼器最优参数的影响

基于多模态耦合抖振理论,导出带有被动调谐质量阻尼器(TMD)的桥梁多模态耦合抖振系统运动微分方程,采用随机振动理论求解系统运动微分方程,并编制了桥梁多模态耦合抖振TMD控制和参数分析程序。以一座斜拉桥为算例,着重分析了模态间气动耦合效应对TMD最优参数和控制效率的影响。     

湍流风速谱有效模态的POD分析法

大跨度桥梁和极端天气的出现,使得桥梁的抖振问题备受关注。然而抖振分析的最重要参数之一是风速谱,传统的抖振分析方法认为所有频率的风速会激发桥梁的抖振响应,针对此问题本文提出了基于本征正交分解(Proper Orthogonal Decomposition)方法对风速谱分解。以某斜拉桥为算例通过对风速谱的分解研究了其有效参与模态对桥梁抖振的贡献。研究发现并不是所有频率的风速谱会激发桥梁的抖振响应,其响应与结构的自振模态和风速谱的有效湍流参与系数有关。     

大跨度斜拉桥抖振时域分析理论实例验证及影响因素分析

为了进行对现有抖振时域分析理论的实例验证,在杭州湾跨海大桥全桥模型风洞试验中,不仅对抖振位移进行了测量,还通过在塔根布设动态应变片完成了桥塔内力的实测。采用考虑桥塔风效应的抖振时域分析方法计算出大跨度斜拉桥的抖振响应,气动导纳分别取1和Sears函数,采用等效风谱法计算考虑气动导纳修正的抖振力,对风洞的空间相关性进行了测量研究并分别探讨了Sears气动导纳函数及空间相关性对抖振响应的影响,与风洞试验结果进行了对比分析。分析比较表明:当衰减因子l取实测值12.9时,风洞试验结果都介于导纳为1和导纳为Sears函数所计算的抖振响应之间,导纳取Sears函数将得到偏不安全的结果;空间相关系数对抖振响应影响较大,采用风洞实测的相关系数得到的抖振响应比采用《公路桥梁抗风设计指南》建议相关系数所得抖振响应小13%￣22%。通过杭州湾跨海大桥的实例验证发现现有抖振时域分析理论并不能完全精确预测桥梁的抖振响应,抖振响应计算值与试验值存在一定的差距。     

模态综合理论在斜拉桥抖振时域分析中的应用

在桥梁随机风场数值模拟的基础上,提出一种斜拉桥抖振时域分析的模态综合方法,建立了斜拉桥时域抖振分析计算模型.该方法简化了自激力时域化过程,并在计算中全面考虑了气动阻尼、气动刚度和气动耦合作用的影响,提高了斜拉桥抖振时域分析的效率.通过对一座大跨斜拉桥的抖振时域分析,验证了方法的正确性和可行性.     

贵阳小关桥双肢薄壁墩抖振响应试验与影响因素分析

在原有抖振时域分析方法的基础上,提出一种考虑复气动导纳函数的修正和抖振力的空间相关性的抖振时域分析方法。为对现有抖振时域分析方法的验证,以贵阳小关桥为例,对其最大悬臂状态进行全桥气弹模型风洞试验,试验中不仅对抖振位移进行测量,还通过在墩底布设动态应变片完成墩底内力的实测。气动导纳函数分别取1、Sears函数和实测的桥梁断面复气动导纳函数,采用抖振力谱法得到考虑气动导纳修正的抖振力。另外对风洞中模型抖振力的空间相关性进行测量,分析气动导纳函数和抖振力空间相关性对结构抖振响应的影响,并与风洞气弹模型试验结果进行了对比分析。分析结果表明:计算分析结果与试验结果基本一致;采用结构实际气动导纳函数的抖振响应与试验更接近;采用抖振力空间相关性计算得到的抖振响应要比采用脉动风速空间相关性的计算结果偏高。     

上海卢浦大桥抖振时域分析

用抖振时域方法对上海卢浦大桥进行了抖振计算,并与全桥气弹模型风洞试验抖振位移相互比较分析,探讨了自激力和气动导纳等因素对抖振响应的影响.气动导纳采用实测值、Sears函数和1三种不同形式,抖振位移有明显差别.全桥气弹模型试验抖振位移与采用实测气动导纳的结果很接近.气动导纳为1时的抖振位移最大,Sears函数抖振位移最小.考虑18个气动导数比不考虑侧向气动导数得到的抖振位移要略小.自激力总体上会减小抖振位移,但幅度不大,工程计算中可以偏安全地忽略自激力的影响.     

长跨柔性悬索桥风致抖振响应分析

以某主跨500 m的大跨度悬索桥为工程背景,对长跨柔性悬索桥在脉动风荷载作用下的抖振响应进行了分析和计算,得到了一些有借鉴性的结论。模态分析表明,大跨度悬索桥的自振频率较低,为典型的风敏感柔性结构。当同时考虑抖振力和自激力时,根据极值理论可以得到悬索桥主梁的抖振位移响应极值,结果表明,竖向、水平和扭转方向的最大抖振位移响应极值均发生在主跨跨中处,且数值较大,在结构设计中不容忽略。     

CFD方法的大跨度桥梁抖振荷载

采用计算流体力学(Computational Fluid Dynamic,CFD)方法替代传统的桥梁节段模型风洞试验,改进了大跨度桥梁抖振力计算方法。在香港青马大桥精细有限元模型基础上,模拟周围风场对主梁桥板压力分布,计算节点抖振力,求解局部应力响应,为桥梁抖振疲劳分析和结构健康监测打下了基础。     

北京首都机场3号航站楼风荷载和响应研究

介绍了超大跨度屋盖结构———北京首都机场 3号航站楼的模型风洞试验概况和主要结果 ,给出了屋面在最不利工况下的分块体型系数 ,清楚地显示了屋面的风压分布特征。采用考虑多模态及模态间耦合效应的CQC法计算结构风振响应 ,并以此为基础应用阵风荷载因子法计算了静力等效风荷载     

Modal coupling assessment and approximated prediction of coupled multimode wind vibration of long-span bridges

While single-mode analysis is simple and straightforward in the prediction of wind-induced responses of long-span bridges, it has adequate accuracy only for bridges with a weak modal coupling. With the increase of bridge span lengths and the adoption of streamlined cross-sections, aeroelastic modal coupling due to the interaction between the bridge and wind flow has become an important aspect of vibration. To more accurately predict wind-induced vibrations for modern long-span bridges, coupled multimode analyses of buffeting and flutter are usually required. The common approach to predicting coupled multimode response is to solve simultaneous equations with selected modes. However, quantitative information about modal coupling effects is not available in the process of selecting modes. Consequently, people can only choose much more than necessary modes to avoid missing any important ones in the coupled analysis. The objective of the present study was to quantify the modal coupling effect and provide a practical methodology to predict coupled multimode vibration without actually solving the coupled equations of motion. To achieve the objective, a closed-form spectral solution was derived by ignoring high order small coupling effects, while keeping the primary coupling effects in the solution. The modal coupling effect was then quantified using a so-called modal coupling factor (MCF). The MCF facilitates key mode selection and simplifies coupled multimode analysis. A prototype bridge was analyzed.     

Wind-induced vibration control of long span cable-stayed bridges using multiple pressurized tuned liquid column dampers

This paper explores the possibility of using multiple pressurized tuned liquid column damper (MPTLCD) to reduce wind-induced vibration of long span cable-stayed bridges. By implementing a static pressure inside two sealed air chambers at two ends of a traditional tuned liquid column damper (TLCD), a pressurized tuned liquid column damper (PTLCD) is formed and its natural frequency can be adjusted by not only the length of its liquid column but also the pressure inside its two air chambers. This special feature of PTLCD in frequency tuning greatly facilitates its application to long span cable-stayed bridges for mitigating wind-induced multi-modes of vibration. To further enhance the robustness and effectiveness of PTLCD for vibration control, MPTLCDs are explored in this study. The finite element model of MPTLCD is developed and incorporated into the finite element model of a long span cable-stayed bridge for predicting the buffeting response of the coupled MPTLCD-bridge system in the time domain. The performance of MPTLCD for suppressing combined lateral and torsional vibration of a real long span cable stayed bridge is numerically assessed. The investigations show that the MPTLCD not only provides great flexibility for selecting liquid column length but also significantly reduces the lateral and torsional displacement responses of the long span bridge under wind excitation.     

特大跨度桥梁抗风研究的新进展

主要介绍同济大学土木工程防灾国家重点实验室在国家自然科学基金重大项目资助下进行的题为“特大跨度桥梁的气动参数识别、风振及控制理论”的专题研究中所取得的主要成果 ,包括气动参数识别 ,非线性颤、抖振分析 ,桥梁数值风洞 ,颤振概率评价以及等效风荷载等方面的内容。这些成果已在许多大跨度桥梁 ,如江阴长江大桥、润扬长江大桥、南京长江二桥、苏通长江大桥和南京长江三桥中得到应用 ,显示出理论意义和实用价值。     

Investigation on influence factors of buffeting response of bridges and its aeroelastic model verification for Xiaoguan Bridge

A time-domain procedure for analyzing buffeting responses of bridges is presented and implemented in ANSYS, formulated taking into account the self-excited forces, aerodynamic admittance functions (AAFs) and the coherence of buffeting forces. The buffeting forces simulated based on the span-wise coherence of buffeting forces and also considering the aerodynamic admittance functions, together with the steady aerodynamic forces are applied as external loads to the structural model to analyze the buffeting responses in time domain. In order to account for self-excited forces, elemental aeroelastic stiffness and aeroelastic damping matrices for spatial beam elements are derived following the quasi-steady theory and are incorporated in buffeting analysis through the user-defined Matrix27 element in ANSYS. The procedure is applied to the Xiaoguan Bridge, China, during the longest double cantilever stage of construction. The wind tunnel tests of four typical bridge section models are performed to measure the aerodynamic parameters of the bridge including the steady aerodynamic coefficients and aerodynamic admittance functions. The bridge aeroelastic model testing is also carried out, and coherence functions of buffeting forces are derived from the measured buffeting forces. The measurement results of the displacements and internal forces are compared with those obtained from the analytical predictions. The influence factors, including aeroelastic effect, aerodynamic admittance functions and coherence of buffeting forces, are studied in some detail. It is shown the present method inclusive of above factors gives much closer predictions of buffeting responses to the experimental results.     

一致激励下MR阻尼器对桥梁地震反应控制效果的研究

本文应用磁流变(MR)阻尼器对桥梁结构在一致地震激励下的响应进行控制。采用子空间模态分析法建立了适合一致地震激励下桥梁振动控制分析的瞬时最优控制算法。以连续刚构桥和大跨度斜拉桥两个具体工程为例,数值仿真分析了桥梁地震反应在多种MR控制策略下的控制效果,为MR阻尼器的工程应用提供了理论依据。     

桥梁抖振反应谱研究

传统的抖振分析方法或者过于复杂而不便于工程应用 ,或者忽略了过多的因素而精度不高。根据R .H .Scanlan的桥梁颤抖振分析方法并引入气动导纳的影响 ,采用数值积分的结果 ,得到了大跨度桥梁抖振反应谱的实用公式 ,并提出了一种计入背景响应的实用方法。还研究了背景响应的变化规律 ,并进行了工程实例分析。分析结果表明 :背景响应在很多情况下不可忽略 ,现给出的实用公式具有较高的精度 ,可用于大跨度桥的梁抖振响应估算     

大跨空间结构的多目标等效静风荷载分析方法

针对大跨空间结构风荷载空间分布复杂、多振型参与结构风振以及等效静风荷载中存在多等效目标等特点,以作者提出的单目标(即等效目标)等效静风荷载分析方法为基础,提出多目标等效静风荷载的分析方法,该方法的基本思想是:根据结构风振响应特性,选择风荷载的主要本征模态和结构主导振型惯性力作为构造多目标等效静风荷载的基本向量;根据最小二乘法,得到基本向量的最优组合系数,从而得到针对多个等效目标的等效静风荷载。该分析方法的优点是:能够再现风振响应特点,又能解决工程中的多等效目标问题。最后,将该方法应用于一单层球面网壳,结果表明:一个等效静风荷载分布形式就可以实现某一类响应(如所有节点的位移)都与动力极值响应等效,验证了本文方法的有效性和精度。     

Parametric study on buffeting performance of a long-span triple-tower suspension bridge

The triple-tower suspension bridge is a brand new type of structural form that is equipped with a dominant mid-tower. The dynamic characteristics of this multiple main-span suspension bridge present a significant difference with that of the conventional single main-span suspension bridge. Hence, taking the Taizhou Yangtze River Bridge as an example, the buffeting performance of a long-span triple-tower suspension bridge under strong winds is comprehensively investigated via finite element method. Specifically, the sensitivity of structural buffeting performance to some major structural parameters, aerodynamic parameters as well as parameters of turbulence inputs is analysed in time domain. It was found that the structural buffeting performance heavily depends on the dead load of the main girder, sag-to-span ratio of the main cable, longitudinal stiffness and structural type of the mid-tower. Also, appropriate selection of aerodynamic admittance function, power spectrum model of fluctuating wind and the spatial coherence coefficient is important in the buffeting analysis. Besides, the self-excited forces have small impact on the calculation of buffeting responses of such a bridge. The analytical results can provide references for the buffeting analyses and wind-resistant design of similar long-span triple-tower suspension bridges.