Before establishing the priority settings for the reduction of seismic risk of water supply infrastructures, it is necessary to understand the dynamic behavior of elevated water tanks, which are components of those infrastructures. Among other information, the main frequencies of vibration of these structures must be estimated and the analytical models used in their analysis and design should reproduce the frequency values obtained by in-situ dynamic tests. This work focuses exclusively on reinforced concrete (RC) elevated water tanks (200–750 m^3 of water at heights of 30–40 m), which are very common structures in the water supply systems in Portugal since the mid XXth century. This type of structures can also be seen in many regions around the world. First, a nationwide survey was conducted to determine the most common typologies in the country in terms of structural layout. Second, an in-situ campaign using ambient vibration as input was performed for a group of selected structures to determine the main frequencies of vibration and to identify modal shapes and damping values. Third, a finite element model of several different typologies was developed using the water simply as a concentrated mass at the top; the elastic properties of the model of the structure including the foundation were calibrated, so that the frequencies of various mode shapes obtained by the analytical model would match the frequencies of the real structure. Finally, an expression was derived to estimate the fundamental frequency of a group of elevated water tank typologies based on the total mass at the top of the supporting structure, which include the water, the global lateral stiffness, and the height of the tank. This study, providing important information on the frequencies of vibration of RC-elevated water tanks, contributes in a definite way to the analysis and design of such water tanks.
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机译：在建立降低供水基础设施地震风险的优先级设置之前，有必要了解高架水箱（这些基础设施的组成部分）的动态行为。除其他信息外，还必须估算这些结构的主要振动频率，并且在其分析和设计中使用的分析模型应再现通过现场动态测试获得的频率值。这项工作专门针对钢筋混凝土（RC）高架水箱（水位30–40 m处200–750 m ^ 3的水），这是自20世纪中叶以来葡萄牙供水系统中非常常见的结构。在世界许多地区也可以看到这种结构。首先，进行了一项全国性调查，以确定该国在结构布局方面最常见的类型。其次，对一组选定的结构进行了以环境振动为输入的现场运动，以确定振动的主要频率并确定模态形状和阻尼值。第三，使用水作为顶部的集中质量，开发了几种不同类型的有限元模型。对包括基础的结构模型的弹性特性进行了校准，以使分析模型获得的各种模式形状的频率与实际结构的频率匹配。最后，根据支撑结构顶部的总质量（包括水，整体侧向刚度和水箱的高度），导出了一个表达式来估算一组高架水箱类型的基本频率。这项研究提供了有关RC提升水箱振动频率的重要信息，以明确的方式有助于此类水箱的分析和设计。
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