Vibration-Based Investigation of a Historic Bell Tower to Understand the Occurrence of Damage

摘要

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.