This paper presents the results of an operational modal analysis on a self-supporting antenna mast. The structure is instrumented with seismic accelerometers, which are moved in different setups for a detailed characterization of the mode shapes. In addition, eight strain gauges are installed, two at the bottom of each leg of the tower. Two particular challenges in the modal analysis are highlighted. First, due to the symmetry of the tower, the bending modes occur in pairs with near to identical natural frequencies and orthogonal mode shapes. These mode shapes change from one setup to another, which complicates the merging of partial mode shapes obtained from different setups. Second, the acceleration signals are polluted by radio signals. It is shown how these two issues are solved, resulting in the identification of five bending modes. The identified natural frequencies and mode shapes are very close to those predicted by a detailed finite element model of the tower, where the vertical columns are modeled using beam elements and the connections between the columns and the braces are assumed pinned. This confirms the validity of such detailed finite element models for the assessment of the dynamic response of these lattice towers under wind loading.

本文介绍了自支撑天线桅杆上的运行模态分析结果。该结构配备了地震加速度计，可以在不同的设置中移动该加速度计以详细表征振型。此外，还安装了八个应变仪，在塔的每个支腿的底部有两个。突出了模态分析中的两个特殊挑战。首先，由于塔的对称性，弯曲模式成对出现，它们具有接近相同的固有频率和正交模式形状。这些模式形状从一种设置更改为另一种设置，这会使从不同设置获得的部分模式形状的合并变得复杂。其次，加速度信号被无线电信号污染。显示了如何解决这两个问题，从而确定了五个弯曲模式。所识别的固有频率和振型非常接近于由塔的详细有限元模型预测的固有频率和振型，在该模型中，垂直梁使用梁单元进行建模，并且假定圆柱与支撑之间的连接是固定的。这证实了这种详细的有限元模型在评估风荷载作用下这些格构塔的动力响应时的有效性。