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

中部高速公路上三跨连续钢梁桥辐射声压级的数值计算值与现场实测数据吻合较好，证明了组长课题组所建立的分析方法的适用性。利用本文提出的解析方法，研究了几种抑制三跨连续钢梁桥低频声辐射的措施的有效性。得到了以下结果：即：(1)端部摆动支撑覆盖混凝土的方法对降低低频声压级效果不明显。(2)海绵式梁式桥梁和海绵式桥面式桥梁的有效性取决于桥梁的跨径和过桥车辆的行驶速度。(3)海绵式梁桥和海绵式桥面桥的有效性还取决于海绵式桥面部分的支承条件。(4)各跨中心点采用固定鞋和（或）销鞋支承的方法虽然成本较高，但效果较好。(5)桥梁辐射低频声压级对过桥车辆进入桥梁时是否振动的情况比较敏感。这一事实意味着应仔细注意数值分析。在不久的将来，将对过桥车辆的弹簧常数对公路桥梁辐射低频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.