Comparison of field measured data of low-frequency noise radiated from steel bridges with analytical ones and its reduction countermeasure

通过对位于中国高速公路上的三跨连续钢梁桥辐射声压级的数值计算结果与现场实测数据的比较，证明了本课题组开发的解析方法的正确性。研究了三跨连续钢梁桥低频声辐射的几种降噪措施的有效性。取得了以下结果。也就是说，（1）用混凝土覆盖端部防摇支撑的方法对降低低频声压级不是很有效。(2)舷梁式桥和舷上承式桥的有效性取决于桥的跨度和过桥车辆的行驶速度。(3)舷侧梁式桥和舷侧甲板式桥的有效性还取决于舷侧部分的支承条件。(4)采用定靴或销靴支撑各跨中心点的方法虽然成本较高，但效果显著。(5)桥梁辐射的低频声压级对过桥车辆进入桥梁时是否振动很敏感。因此，数值分析应引起足够的重视，本文拟对桥梁上车辆的弹性系数对桥梁低频辐射声压级的影响进行数值分析。

As the numerically calculated values of sound pressure level radiated from 3-span continuous steel girder bridge which locates on Chugoku Express Highway agree well with the field measured data, the appropriateness of analytical method developed by the head investigator's research group has been proved.By Use of the analytical method developed here, the effectiveness of several types of reduction countermeasure against low-frequency sound radiated from 3-span continuous steel girder bridge has been investigated. The following results have been obtained. That is,(1) The method in which end sway bracing is covered by concrete is not so effective to reduce the low-frequency sound pressure level.(2) The effectiveness of both sponson beam type bridge and sponson deck type bridge depends on the span length of bridge and the traveling velocity of vehicle passing over bridge.(3) The effectiveness of both sponson beam type bridge and sponson deck type bridge also depends on the supporting condition with respect to sponson part.(4) The method that central point of each span is supported with fix shoe and/or pin shoe is considerably effective although its cost becomes higher.(5) Low-frequency sound pressure level radiated from bridges is sensitive to the condition whether vehicle passing over bridge vibrates or not when it enters into the bridge. This fact means that careful attention should be paid to the numerical analysis.A numerical analysis about the effect of spring constant of vehicle passing over bridge on the low-frequency sound pressure level radiated from highway bridge will be carried out in the near future.