Seismic Analysis of an Earthen Free-Standing Bell Tower in the Historical Center of Cusco (Peru): Ambient Vibration Testing, Model Calibration and Seismic Capacity Assessment

A remarkable feature in Peruvian’s colonial adobe church architecture in Andean region are the free-standing bell towers or campaniles. These structures are highly vulnerable to deterioration due to poor material quality, seismic activity, and environmental or human-induced loadings. Understanding their current dynamic behavior is therefore essential for their preservation. This study focuses on the Santa Ana church bell tower (17th century), located in the northwestern hills of Cusco. Two ambient vibration campaigns were carried out in November 2024 using high-sensitivity accelerometers and velocimeters. Operational Modal Analysis revealed a fundamental frequency of around 4.0 Hz, with a slightly diagonal translational mode. No clear torsional modes were identified, while higher modes (above 10 Hz) showed local out-of-plane motion of the upper walls. Based on these findings, a preliminary seismic assessment was conducted using a finite element model. A comprehensive digital reconstruction of the tower served as the basis for the model, which was calibrated using dynamic properties derived from the experimental tests. The nonlinear mechanical behavior of adobe masonry was captured through a macro-modeling approach. Modal pushover analyses identified the bell windows and upper sections as particularly vulnerable to lateral loads. Observed damage patterns include top wall out-of-plane displacement and in-plane diagonal cracking, aligning with previous post-seismic observations. While further investigation is needed, the study offers valuable insights into the seismic performance of the Santa Ana bell tower and supports future assessment and preservation efforts for similar historical structures.