Seismic Performance Assessment of Vigarano Bell Tower Using the Incremental Dynamic Analysis (IDA) Approach

This study presents a comprehensive seismic performance assessment of the historic Vigarano Bell Tower using the Incremental Dynamic Analysis (IDA) methodology within a nonlinear finite element framework. A detailed three-dimensional finite element model was developed to simulate the nonlinear dynamic response of the masonry structure using the Concrete Damage Plasticity (CDP) constitutive model. The numerical model incorporates the geometric characteristics and material properties of the tower and was subjected to large suite of recorded earthquake ground motions. Each record was incrementally scaled over an interest range of intensity levels, allowing the structural response to be investigated from the elastic regime to the onset of global instability and collapse. The seismic response was evaluated through the analysis of engineering demand parameters, including maximum top displacement, interstory drift, and damage pattern evolution. The IDA curves were employed to characterize the progressive nonlinear behavior of the structure, identify performance thresholds, and investigate the variability of the response associated with different ground motions. Particular attention was devoted to the evolution of stiffness degradation, the development and propagation of tensile damage, and the influence of higher vibration modes on the global dynamic behavior of the slender masonry tower. Based on the IDA results, probabilistic fragility curves were constructed to quantify the likelihood of exceeding predefined damage states as a function of seismic intensity. The proposed methodology provides a rigorous framework for evaluating both the seismic capacity and the uncertainty associated with the nonlinear response of historic masonry towers. The results demonstrate the capability of the IDA approach to capture the progressive deterioration of structural performance under increasing seismic demand, offering a robust basis for the probabilistic seismic assessment of slender masonry heritage structures.