大跨度桥梁抖振响应的直接估算方法

Direct Estimation of Buffeting Response of Long-span Bridges

大跨度桥梁结构抖振响应的预测主要通过全桥气弹模型抖振响应试验和基于节段模型试验识别气动参数的理论计算2种方法。但由于试验中大气边界层湍流特性的模拟与实际存在一定的偏差,因此无法准确估计实际桥梁结构的抖振响应。为解决实际大跨度桥梁结构抖振响应预测的精度问题,在片条假设成立的条件下,通过数学推导提出了综合传递函数的概念。该函数是气动导纳函数和考虑了自激力的机械导纳函数的组合,其将湍流的脉动特性与由湍流引起的桥梁结构的抖振响应直接联系在一起,并基于此提出了一种预测大跨度桥梁抖振响应的直接计算方法。以坝陵河大跨度悬索桥为例,在两不同风场中分别进行全桥气弹模型风洞试验,通过模型抖振响应及模拟风场测量的试验结果识别两不同风场中的综合传递函数,发现二者结果几乎一致。理论及试验分析表明:对于展宽比较大的大跨度桥梁结构,综合传递函数仅与结构固有特性及参数有关,与风场特性无关;基于综合传递函数获得抖振响应的方法省略了传统分析方法中气动参数的识别及抖振力的计算,可通过测得实桥桥址处的湍流特性,利用风洞试验中识别的综合传递函数直接计算获得实桥准确的抖振响应。最后通过算例给出了综合传递函数的应用方法,为大跨度桥梁抖振响应的准确预测提供了方法,并可为节段模型试验直接预测实桥抖振响应提供思路。

Predicting the buffeting response of long-span bridge structures is primarily achieved through a full-bridge aeroelastic model buffeting response test and theoretical calculation based on the identifies of aerodynamic parameters by section model tests. However, because of the deviation between the actual atmospheric boundary layer turbulence characteristics and the test simulations, the evaluation of the buffeting response of an actual bridge structure can be inaccurate. To solve the accuracy problem of the buffeting response prediction of actual long-span bridges, the concept of an integrated transfer function was proposed by mathematical derivation under the condition that the strip hypothesis is established. The integrated transfer function, which directly relates the fluctuation characteristics of turbulence to the buffeting response of bridge structures caused by the turbulence, combines the aerodynamic admittance function and the mechanical admittance function taking self-excited force into account. In addition, a direct calculation approach for predicting the buffeting response of long-span bridges was proposed based on this combined function. Considering Balinghe bridge as an example, wind tunnel tests of a full-bridge aeroelastic model were conducted in two wind fields. The integrated transfer functions in the two wind fields were identified based on the results of the model buffeting response and the simulated wind characteristics. Results show that the two are nearly identical. A theoretical and experimental analysis shows that for long-span bridge structures with large aspect ratios, the integrated transfer function is related only to the inherent characteristics and parameters of the structure and is independent of the wind field characteristics. The approach used to obtain the buffeting response based on the integrated transfer function omits the identities of aerodynamic parameters and the calculation of the buffeting force in the traditional analytical method. When the turbulence characteristics at the bridge site are measured, the integrated transfer function identified in wind tunnel tests can be used to calculate directly the accurate buffeting response of the actual bridge. Finally, the method of applying the integrated transfer function is given through an example, which providing a means of accurately predicting the buffeting response of long-span bridges and provides a way to directly evaluating the buffeting response of actual bridges through section model tests.