ABSTRACT

The paper presents a survey of the historic Arch-cathedral bell tower in Vilnius induced by the appearance of cracks in the structure after a new bell system installation. An attempt is undertaken to identify the reason for the crack occurrence and to check a possible crack influence on global structural behaviour. The research is based on dynamic measurements made in the tower during ambient vibrations and during vibrations caused by swinging bells. The amplitudes of the accelerations and the spectral peaks due to the ambient and excited vibrations are compared. Magnification of the first spectral peak due to bells swinging points at resonance. The root-mean-square analysis is conducted to detect the tower section most vulnerable to swinging bells. The modal curvature approach applied to the first mode shape serves as the damage indicator. The algorithm locates damage in the region of the cracks observed in the tower; thus, the cracks are considered structural. The research proves the necessity of a dynamic survey in similar cases before important decisions are undertaken regarding the replacement of the bell system.

摘要

本文介绍了对维尔纽斯历史悠久的拱形大教堂钟楼的调查，该钟楼在安装新钟系统后结构中出现裂缝。尝试确定裂缝发生的原因并检查可能的裂缝对整体结构行为的影响。该研究基于在环境振动和摇铃引起的振动期间在塔中进行的动态测量。比较加速度的幅度和由于环境振动和激发振动引起的频谱峰值。由于钟形摆动点在共振处放大了第一个光谱峰。进行均方根分析以检测最容易受到摆钟影响的塔段。应用于第一个模态形状的模态曲率方法用作损坏指标。该算法定位在塔中观察到的裂缝区域中的损坏；因此，裂缝被认为是结构性的。该研究证明，在就更换钟系统做出重要决定之前，对类似情况进行动态调查的必要性。