U肋加劲板的声振特性研究

为分析U肋加劲板的声振特性，联合锤击试验和数值仿真方法从振动传递特性和声辐射性能2个方面进行研究。首先，以某钢箱梁为原型，设计制作一足尺U肋加劲板结构，通过锤击激励获得不同位置的振动和噪声响应。然后，以有限元计算得到的振动响应作为边界元仿真的边界条件，建立混合有限元-边界元模型预测U肋加劲板的振动声辐射，并将仿真结果与实测值进行对比。最后，通过数值仿真探讨U肋的声振贡献量，并分析结构设计参数（顶板厚度、U肋厚度和U肋间距）对顶板声功率级的影响规律。研究结果表明：相比混凝土结构，U肋加劲板的振动噪声更加明显，且频谱范围更宽，主要集中在几百至上千Hz；U肋正上方和U肋之间的顶板原点导纳差异不大；顶板原点导纳和U肋传递导纳的频谱特性相似，并在量值上具有可比性；混合有限元-边界元预测方法具有较高的精度，但计算效率不高；受到U肋自身的振动声辐射和声反射效应的影响，U肋加劲板正下方的噪声比侧方高出约10 dB（A），声压级峰值频段为400~1 250 Hz；顶板厚度和U肋间距是决定顶板声辐射大小的决定性因素，算例中顶板厚度减小6 mm或U肋间距增大300 mm时，顶板声功率级分别增加5.4 dB（A）或9.4 dB（A）；U肋厚度在6~10 mm内变化时，顶板声功率级改变不大。

Vibro-acoustic Characteristics of U-rib Stiffened Slabs

To study the vibro-acoustic characteristics of U-rib stiffened slabs, hammering test and numerical simulation are jointly introduced to investigate the vibration transmission behavior and sound radiation performance. First, based on a real steel box girder, a full-scale U-rib stiffened slab was designed and fabricated. The vibration and noise responses at different locations were measured by applying hammer excitations. Second, a hybrid finite element and boundary element model was built to predict the vibro-acoustic characteristics of the U-rib stiffened slab, where the vibrations calculated using the finite element method were regarded as the boundary condition for the boundary element simulation. The proposed prediction model was validated by comparing the simulation results with the hammering test data. Finally, based on numerical simulations, the vibro-acoustic contribution of the U-rib was discussed, and the effects of structural design parameters (e.g., top slab thickness, U-rib thickness, and U-rib spacing) on the sound power level of the top slab were analyzed. The research results show that the vibration and noise of the U-rib stiffened slabs are much more significant than that of concrete structures. Furthermore, their frequency concentrates in the range of several hundreds to 1 000 Hz, which is wider than that of concrete structures. The point accelerances of the top slab have no significant differences for the locations right above a U-rib and between neighboring U-ribs. The spectral characteristics of the point accelerances of the top slab are similar to that of the transfer accelerances of a U-rib, and their magnitudes are comparable. The hybrid finite element and boundary element prediction method has high accuracy. However, its computational efficiency is low. Owing to the sound radiated by the U-ribs and acoustic reflection effect, the noise underneath the U-rib stiffened slab is about 10 dB(A) higher than that alongside it. The peak frequency of sound pressure levels is 400~1 250 Hz. The top slab thickness and the U-rib spacing are the two decisive factors for the sound radiation of the top slab. For the illustrative case in this study, when the top slab thickness is decreased by 6 mm or the U-rib spacing is increased by 300 mm, the sound power level of the top slab increases by 5.4 dB(A) or 9.4 dB(A), respectively. When the U-rib thickness is varied from 6 mm to 10 mm, the sound power level of the top slab is hardly affected.