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。     

高墩连续刚构桥线性抖振时程响应分析

采用Miyata T准定常气动力模型,通过双变量泰勒展开,导出12阶单元气动阻尼矩阵和气动刚度矩阵,并在ANSYS中以Matrix27单元输入来考虑桥梁结构风致抖振自激力模型,结合桥址处脉动风场的模拟,对某连续刚构桥最大双悬臂阶段和成桥运营阶段进行线性抖振时程响应分析。最后对脉动风荷载作用下的结构响应值和静阵风荷载作用结果进行了比较,得到脉动增大系数值。     

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 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.     

Time-domain buffeting simulations for wind–bridge interaction

Aeroelastic behavior of bridge deck cross-sections under the action of turbulent flow is addressed in the paper. Simulation of cross-sectional behavior is obtained in time domain, by assuming both buffeting and self-excited forces modeled by means of appropriate indicial functions extracted from flutter derivatives. The use of indicial functions for buffeting loads is justified by calculation of corresponding aerodynamic admittance functions and validated by comparison of simulated response with experimental results. A comparison with results obtained including buffeting loads modeled by a quasi-steady approach is also discussed.     

桥梁气动导纳识别的阶跃函数拟合法

基于桥梁主梁断面气动导数、阶跃函数与气动导纳之间的关系,提出一种获取气动导纳的阶跃函数拟合法。首先根据紊流风场中的抖振响应,识别桥梁结构气动导数和等效气动导纳,然后由气动导数可拟合得到阶跃函数,并根据阶跃函数系数计算得到竖向脉动风对应的气动导纳,最后结合等效气动导纳计算水平向脉动风对应的气动导纳。阶跃函数拟合法直接根据抖振响应完成了桥梁断面完整气动导纳的识别,实例研究表明,该方法对于桥梁断面气动导纳识别而言是可行的。     

Modeling hysteretic nonlinear behavior of bridge aerodynamics via cellular automata nested neural network

A new approach to model aerodynamic nonlinearities in the time domain utilizing an artificial neural network (ANN) framework with embedded cellular automata (CA) scheme has been developed. This nonparametric modeling approach has shown good promise in capturing the hysteretic nonlinear behavior of aerodynamic systems in terms of hidden neurons involving higher-order terms. Concurrent training of a set of higher-order neural networks facilitates a unified approach for modeling the combined analysis of flutter and buffeting of cable-supported bridges. Accordingly the influence of buffeting response on the self-excited forces can be captured, including the contribution of damping and coupling effects on the buffeting response. White noise is intentionally introduced to the input data to enhance the robustness of the trained neural network embedded with optimal typology of CA. The effectiveness of this approach and its applications are discussed by way of modeling the aerodynamic behavior of a single-box girder cross-section bridge deck (2-D) under turbulent wind conditions. This approach can be extended to a full-bridge (3-D) model that also takes into account the correlation of aerodynamic forces along the bridge axis. This novel application of data-driven modeling has shown a remarkable potential for applications to bridge aerodynamics and other related areas.     

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。     

桥梁气动自激力阶跃函数及时域颤振的数值算法

从航空学中机翼断面的阶跃升力函数着手,阐述其用于桥梁断面气动力表达的演变过程及存在的问题,选取适合桥梁断面气动力时域表达的升力以及升力矩阶跃函数形式并讨论其合理性。以正确模拟基于试验的桥梁断面自激力线性表达式为目标,提出阶跃函数各控制参数非线性拟合的线性搜索方法并给出合理的参数控制区间,有效地避免过大的阶跃函数瞬态值与长时间衰减过程所造成的自激力时域模拟失真现象。通过某大桥的三维颤振时域分析,对数值算法中若干关键影响因素进行讨论。     

Aerodynamic investigations for the tender design concepts of the Øresund cable-stayed bridge

For the Øresund link project two alternative tender designs were proposed, one single-level box girder solution and a double-level truss girder solution. Aerodynamic investigations, comprising wind tunnel section model tests as well as full-scale predictions, were carried out for the cable-stayed part of the two design alternatives. The section model tests covered static and dynamic tests for various configurations of bridge deck equipment, aiming at the detection of possible instabilities or vortex shedding effects and recording of the buffeting response. Cross-sectional admittance functions and aerodynamic derivatives have been estimated, and employed for full-scale predictions of dynamic displacements at a chosen value of the characteristic mean wind speed.     

Aerodynamic instability of a bridge deck section model: Linear and nonlinear approach to force modeling

The aerodynamic behavior of a bridge deck section model with a simple single-box shape was characterized in wind tunnel. At large nose-up mean angles of attack, a torsional instability arises, outlining a situation in which nonlinear aeroelastic effects may be critical. Such condition represents an interesting case to develop and validate nonlinear models for the aeroelastic problem. The experimental campaign allowed both to characterize the aerodynamic forces using forced motion tests and to study the aeroelastic behavior of the section model, when excited by actively generated turbulent wind. These aeroelastic tests are used to validate a numerical time-domain model for aerodynamic forces that takes into account the nonlinearities due to the reduced velocity and to the amplitude of the instantaneous angle of incidence. Results are critically analyzed and compared with those obtained with a linear model.     

Dynamic response of a long span suspension bridge and running safety of a train under wind action

A dynamic analysis model of a wind-train-bridge system is established. The wind excitations of the system are the buffeting and self-excited forces simulated in time domain using measured aerodynamic coefficients and flutter derivatives. The proposed formulations are then applied to a long rail-cum-road suspension bridge. The dynamic responses of the bridge and the train under wind action are analyzed. The results show that the lateral and rotational displacements of the bridge are dominated by wind, while the vertical by the gravity loading of the moving train. The running safeties of the train vehicles are much affected by wind. Under wind conditions of 30–40 m/s, the offload factors, derail factors and overturn factors of the train vehicles exceed the safety allowances, to which great attention should be paid. Translated from Engineering Mechanics, 2006, 23(2): 103–110 [译自: 工程力学]     

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     

金马大桥抖振响应的时域分析

金马大桥是一座独塔斜拉桥与两侧T构相连接的大跨度协作体系桥梁,该桥结构形式新颖且桥位处于台风多发区,因此,对该桥进行抖振响应分析是非常必要的。首先利用谐波合成法将脉动风速模拟为多个互相关的随机过程,接着给出抖振力和自激力的时域表达式,据此对金马大桥进行了抖振响应分析。结果表明,尽管该协作体系斜拉桥采用抗扭能力较差的边主梁形式,但其抗风能力是有保证的。     

大跨度桥梁结构耦合抖振响应频域分析

基于结构的固有模态坐标 ,提出了用于大跨度桥梁耦合抖振响应分析的有限元CQC(thecompletequadraticcombination)方法。在合理假设基础上 ,推导了桥梁结构的节点等效气动抖振力公式。应用随机振动理论 ,提出了桥梁结构节点位移和单元内力功率谱密度和方差的计算方法。该方法采用了含 18个颤振导数的气动自激力模型 ,可以考虑自然风的任意风谱和空间相关性以及桥梁抖振响应的多模态和模态耦合效应 ,且计算效率很高。此外 ,对主跨跨度 13 85m的江阴长江大桥的耦合抖振问题进行了分析 ,得出了一些结论。分析结果表明 ,在大跨度悬索桥中 ,多模态效应和模态耦合效应对主梁的竖向和扭转位移抖振响应有显著的影响     

Forced motion and free motion aeroelastic tests on a new concept dynamometric section model of the Messina suspension bridge

The work presents a new original experimental rig to more deeply investigate the aerodynamic behaviour of long span suspension bridges. Set-up and model are designed to grant an accurate study on main aeroelastic phenomena in bridge engineering. More in details, experimental set-up and a 1:60 scale sectional model of Messina bridge deck are presented. The complete rig—composed by dynamometric model, suspension set, experimental set-up and active turbulence generator—is designed in order to execute both forced and free motion tests, allowing to change the average position in terms of angle of attack and yaw angle and to investigate flutter derivatives, admittance functions and vortex-induced vibrations.     

桥梁断面几种气动导纳模型的合理性剖析

首先介绍非定常运动状态下的薄机翼的升力产生机制,机翼的相对运动速度用一系列固定分布模态表达成一种级数形式的广义模式。在这些速度分布模式中包括有平动模式、转动模式以及其他高阶的非线性模式。与此相对应,机翼所受的非定常升力也可根据环量理论求解成一种广义模式。由于所有频率特性的脉动风均可采用Bessel函数展开成广义形式,因而这一类方法直接得出机翼气动导纳的表达式。目前,桥梁风致抖振计算中几种应用较广的气动导纳模型均与机翼理论有关,该文的主要目标是通过对机翼理论的回顾,剖析桥梁风工程中气动导纳模型的合理性与所存在问题的根源。分析表明,任何试图通过气动导数求出气动导纳的方法都是在逻辑上不正确的。通过气动导纳的本质特征的分析,对试验测试钝体桥梁断面气动导纳的方法提出一些建议。     

Dynamics of wind-rail vehicle-bridge systems

An analytical model for dynamics of wind-vehicle-bridge (WVB) systems is presented in this paper in the time domain with wind, rail vehicles and bridge modeled as a coupled vibration system. The analytical model considers many special issues in a WVB system, which include fluid-solid interaction between wind and bridge, solid contact between vehicles and bridge, stochastic wind excitation on vehicles and bridge, time dependence of the system due to vehicle movement, and effect of bridge deck on vehicle wind load and vice versa. The models of wind, vehicles and bridge are presented with wind velocity fluctuations simulated using the simplified spectral representation method, with vehicles modeled as mass-spring-damper systems, and with bridge represented by a finite element model. The interactions between wind and bridge are similar to those considered in conventional buffeting analysis for long span bridges. In considering difficulties in measuring aerodynamic coefficients of moving vehicles on bridge deck, the cosine rule is adopted for the aerodynamic coefficients of moving vehicles to consider yaw angle effect, and expressions of wind forces on moving vehicles are then derived for engineering application. To include mutual effects of wind loads, aerodynamic parameters of vehicles and bridge deck are measured, respectively, using a composite section model test and a specially designed test device. The dynamic interaction between vehicle and bridge depends on both geometric and mechanical relationships between wheels of vehicles and rails on the bridge deck. The equations of motion of the coupled WVB system are derived and solved with a nonlinear iterative procedure. A cable-stayed bridge in China is finally selected as a numerical example to demonstrate dynamic interaction of the WVB system. The results show the validity of the present model as well as wind effects on the rail vehicles and the bridge.     

Influence of uncertainty in selected aerodynamic and structural parameters on the buffeting response of long-span bridges

Multimode-analysis methods for the study and derivation of flutter instability and buffeting response are readily available from the literature and have been successfully applied to the assessment of the susceptibility of long-span bridges to wind loading. In both cases flutter critical velocity and buffeting oscillation are usually estimated from deterministic analyses. However, the probabilistic nature of the problem is latent since uncertainties, especially those associated with the definition of wind and aerodynamic characteristics, are intrinsically present. These quantities include, for example, wind-turbulence power spectral density, static coefficients and aerodynamic derivatives, usually derived from either site observations or experimental analysis. Their effects are often neglected or usually addressed through sensitivity analyses only.While in the past uncertainty in flutter estimates has been analyzed by researchers (for example through reliability analysis), little attention has been devoted to buffeting. In this paper the effects associated with the random nature of wind and structural characteristics are analyzed through the derivation of a closed-form solution associated with the single-mode buffeting problem with selected random parameters. A specific example is provided to clarify the role of wind power spectral density, damping and selected aeroelastic derivatives.