Investigation on generation mechanism of impact sound radiated from part of shoes of highway bridge and estimation of effectiveness of countermeasures for low-frequency sound

根据2005年9月中旬修正的现场实测数据，分析了伸缩缝（或鞋）位移与过桥车辆特征（车辆类型、速度等）的关系。然而，没有发现任何重要的关系。这可能是由于无法准确地获得车辆的重量以及连续的车辆必须引起复杂的振动。因此，目前对伸缩缝和伸缩鞋的性能建模还不成功。另一方面，在数值分析的基础上，研究了调谐质量阻尼器对钢结构公路桥梁低频声辐射的抑制效果。选取桥长约63米、桥宽约23米的三跨连续多主钢梁公路桥作为研究对象。这座桥目前正在维修中。采用三维多维有限元法对桥梁进行建模，得到了现场实测值与解析计算值吻合较好的固有频率。该桥上部结构共安装了12个调谐质量阻尼器。在数值分析中，采用两轴四自由度车辆模型。并考虑了一辆车、两辆车平行、两辆车连续过桥三种通行模式。采用基于Newmark’s 8法进行数值积分的有限元分析方法。声压级的计算方法是将桥面各有限元单元表面辐射的声压求和。在此计算过程中可以考虑声音的干扰现象。收声位置是垂直于桥轴线的水平距离为31米，距离桥跨中心向下的垂直距离为13米的点。结果表明：上部结构的调谐质量阻尼器可使钢结构公路桥在一阶振动模式下的低频声辐射降低3 ~ 4分贝；研究还表明，在二阶振动模式下，预计将降低约7分贝。少

Based on the field measured data corrected in the middle of September, 2005, the relation between displacement of expansion joint (or shoe) and characteristics of vehicle passing over bridge (type of vehicle, velocity, etc.) has been analyzed. However, any significant relation has not been recognized. This may be depend on the fact that the weight of vehicle could not be obtained accurately and the consecutive vehicles must cause the complicated vibration. Then the modeling on behavior of expansion joint and shoe has not been successful at present.On the other hand, the effectiveness of tuned mass damper as countermeasure for low-frequency sound radiated from steel highway bridge has been investigated based on numerical analysis. The three span continuous multi main steel girder highway bridge whose bridge length and width are about 63 meters and 23 meters, respectively is selected as the subject of study. This bridge is currently under service. The bridge is modeled based by using 3-d … More imensional finite element method so as to obtain a good agreement of natural frequencies between field measured values and analytically calculated ones. Totally twelve pieces of tuned mass dampers are equipped with the superstructure of this bridge. In the numerical analysis, a vehicle model with two axles and four degrees of freedom is adopted. And three traveling patterns, that is, one vehicle, two parallel vehicles, and two successive vehicles passing over bridge are considered in this study. Finite element analysis method where numerical integral is executed based on Newmark's 8 method is applied. Sound pressure level is calculated by summing up the sound pressure radiated from the surface of each finite element of bridge deck. An interference phenomenon of sound can be considered in this calculation procedure. Sound receiving position is the point where a horizontal distance perpendicular to the bridge axis is 31 meters and a vertical one downward away from the center of bridge span is 13 meters.The results show that equipment of tuned mass dampers with superstructure leads to 3-4 decibels reduction of low-frequency sound radiated from steel highway bridge against first-order vibration mode. It has been also revealed that about 7 decibels reduction is expected against second-order vibration mode. Less