Can Ancient Churches Survive Earthquakes? A Multi-Level Seismic Analysis

Title, Authors, and Publication

The paper, titled "Seismic Vulnerability Assessment of an Italian Ancient Church According to Conventional Approaches," was authored by Stefania Imperatore, Gian Piero Lignola, and Barbara Ferracuti. It was presented at the 9th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2023) in Athens, Greece, from June 12–14, 2023.

Objective and Background

This study evaluates the seismic vulnerability of an ancient masonry church in Italy using conventional assessment approaches outlined in the Italian Guidelines for Cultural Heritage Seismic Risk Evaluation. Given their large halls, weak wall connections, and insufficient floor diaphragm rigidity, historic churches are highly vulnerable to earthquakes, making their seismic assessment a priority for cultural heritage preservation.

The study applies multi-level seismic evaluation methods, particularly LV1 and LV2 approaches, to analyze the structural response and potential damage mechanisms. The results offer insights into the reliability and limitations of qualitative and quantitative seismic assessment methods, emphasizing how expert judgment influences safety evaluations.

Introduction

The seismic vulnerability of cultural heritage buildings is a major concern in Italy and Europe, as earthquakes frequently damage or collapse historical structures. Among these, masonry churches are among the most vulnerable due to their:

• Irregular geometries and complex architectural forms.
• Lack of continuous structural connections between elements.
• Presence of large openings, vaulted ceilings, and high vertical walls.

Given these vulnerabilities, the Italian Guidelines for Cultural Heritage Seismic Risk Evaluation outline a multi-tiered approach to assess seismic performance and structural stability. This study applies the LV1 (qualitative) and LV2 (quantitative) assessment methods to evaluate the structural safety of the Natività di Maria Vergine Church in Erchie, Italy.

Methodology

1. Historical and Architectural Analysis The church was built between 1081 and 1782, undergoing multiple modifications over centuries. Constructed from Pietra Leccese (local limestone), it features high vaulted ceilings and Latin-cross plan geometry. A terrestrial laser scanning (TLS) survey was conducted to digitally map the structure and create a 3D structural model.
2. LV1 (Qualitative Seismic Vulnerability Assessment) The LV1 method relies on expert observation and assigns vulnerability scores to various macroelements. A weighted vulnerability index is calculated for 21 possible failure mechanisms, such as: Fa?ade overturning Arch and vault collapse Bell tower stability
3. LV2 (Quantitative Seismic Vulnerability Assessment) The LV2 method uses numerical limit analysis to evaluate the collapse acceleration of macroelements. A pushover analysis was conducted using Aedes PCM software, considering different roof stiffness conditions. The collapse acceleration values were compared to expected seismic demands based on Italian building codes.
4. Modal Analysis for Dynamic Behavior Evaluation The church’s natural frequencies and mode shapes were analyzed under different structural configurations. Vaulted ceilings and roof flexibility significantly influenced the distribution of seismic forces.

Key Findings

1. Seismic Vulnerability Varies Across Different Structural Elements Fa?ades and tympanum are less vulnerable due to low excitation of longitudinal modal mass. Transverse walls in the nave and sacristy exhibit higher vulnerability under seismic loads.
2. LV1 vs. LV2 Results Show Discrepancies in Safety Evaluations LV1 method provides a broad vulnerability index but is highly dependent on expert judgment. LV2 method provides more precise collapse acceleration values, revealing greater vulnerability in apse and sacristy walls.
3. Collapse Acceleration Values Indicate Seismic Risk Most vulnerable elements include: Apse walls (collapse at 0.128g acceleration). Sacristy walls (collapse at 0.130g acceleration). Other elements such as fa?ades, nave walls, and transept walls have higher collapse accelerations (0.156g–0.398g), making them relatively safer.
4. Expert Judgment and Assumptions Influence Results The LV1 method may overestimate safety, especially when seismic protection devices are assumed to be effective. Masonry toothing and connection strength assumptions critically affect safety assessments.

Conclusion

This study highlights the strengths and limitations of conventional seismic vulnerability assessment methods for historical masonry churches. The LV1 method, while useful for regional evaluations, may provide overly optimistic safety estimates due to its reliance on subjective expert scoring.

The LV2 method provides more detailed collapse acceleration values, confirming that apse and sacristy walls are the most vulnerable elements. However, assumptions regarding masonry connections and roof stiffness greatly influence the results.

These findings emphasize the need for combined qualitative and quantitative approaches in seismic risk assessments to ensure accurate and reliable safety evaluations for cultural heritage structures.

Future Work and Applications

1. Refining Seismic Assessment Models Incorporating finite element simulations to improve accuracy of failure predictions.
2. Integrating Advanced Laser Scanning Techniques Expanding TLS surveys for more detailed digital modeling of heritage structures.
3. Assessing Retrofitting Strategies Evaluating seismic reinforcement techniques such as FRP jacketing and steel ties.
4. Developing Automated Risk Assessment Tools Using machine learning algorithms to predict seismic failure risks in historical buildings.
5. Expanding Case Studies Applying LV1 and LV2 methods to other historic churches across Italy and Europe.

?