Survey and numerical analysis of the structure of Villa Gazzotti by Andrea Palladio

Survey and numerical analysis of the structure of Villa Gazzotti by Andrea Palladio

Abstract

The dissertation analyses the structural behaviour of Villa Gazzotti, a Palladian villa located in the Veneto region of Italy, where nearly 4,000 Renaissance villas still exist. These buildings are culturally important due to their architecture and frescoed interiors, but they are also structurally complex because of their extensive use of masonry vaults and iron ties. Although these systems often demonstrate advanced structural intuition, they can also create vulnerabilities, especially under seismic action.

 

The study focuses on both the static and dynamic behaviour of Villa Gazzotti, selected because of its complex vaulted structure, visible masonry discontinuities, and limited restoration history. A literature review revealed that the villa incorporates a pre-existing medieval tower and was constructed in at least two phases, resulting in weak or incomplete connections between different masonry sections that significantly influence the structural response.

 

An on-site survey documented major cracks, construction traces, and structural details that helped interpret the behaviour of the building. These observations were essential for developing a finite element model used to analyse how the vault thrusts affect the walls. The analysis demonstrated that most lateral forces are transferred to iron ties and in-plane walls, while only a small portion reaches the foundations.

 

A pre-existing laser scan allowed highly precise measurement of out-of-plane wall deformations, which was used to calibrate the numerical model and validate its behaviour. Finally, a modal test supported a preliminary seismic analysis, showing that several walls are vulnerable to out-of-plane collapse during a design earthquake. One wall already presents cracks and inclination patterns indicating that such a failure mechanism may have been activated during a previous earthquake.

 

 

Introduction

The dissertation introduces the historical, architectural, and structural importance of the Venetian villas developed during the Renaissance, especially those designed by Andrea Palladio. These villas combined agricultural and residential functions and became symbols of prestige for the Venetian aristocracy.

 

Structurally, the villas are mainly composed of brick masonry with lime mortar, timber floors, and complex vaulted systems. Vaults such as barrel, groin, cloister, and pavilion vaults generate horizontal thrusts that place significant stress on the walls. Palladio and Renaissance builders frequently used iron ties to counteract these forces and reduce the need for thick buttressing walls.

 

The Veneto region is also exposed to moderate seismic activity due to its proximity to Friuli-Venezia Giulia. Although the regular geometry of Palladian villas improves structural stability, unreinforced masonry and weak diaphragm action from timber floors make these structures vulnerable to out-of-plane failures during earthquakes.

 

The thesis focuses on Villa Gazzotti in Bertesina, Vicenza, built between 1542 and 1543 and attributed to Andrea Palladio. The villa was selected because of its complex system of vaults, visible masonry discontinuities, and limited restoration history, which preserves valuable evidence of its structural behaviour.

 

The study aims to:

• Understand the static behaviour of the villa under gravity loads, especially the influence of vault thrusts;
• Investigate the effects of construction phases and masonry discontinuities;
• Build and calibrate a finite element model;
• Assess the dynamic and seismic vulnerability of the structure.

 

The research combines literature review, on-site survey, laser scanning, finite element modelling, and modal analysis.

 

1. Literature Review

1.1 The pre-existences

The literature review demonstrates that Villa Gazzotti incorporates an older medieval structure, most likely a defensive tower dating from the 13th century. This earlier construction is still visible on the east façade, where traces of infilled medieval windows and masonry discontinuities remain exposed due to the absence of plaster.

 

Research carried out by Winter and Fuchs revealed that the original tower was approximately ten metres high and divided internally by five timber floors. The foundations differ significantly from the Palladian masonry, being composed of stone and reused materials, suggesting the existence of even older structures on the site.

 

During the late 15th century, the medieval tower was adapted into a residential building with additional rooms, a basement, and a dovecote. Historical records from the sale of the property to Taddeo Gazzotti in 1533 confirm the existence of these elements. Physical traces of these earlier structures, such as stair remnants and buried floor levels, are still visible in the basement areas of the villa.

 

The location of the nearby church and cemetery restricted expansion toward the east, strongly influencing the later Palladian design.

 

Orthophotograph of the east façade. Photograph of Paolo Vedovetto, 2023.

 

 

1.2 The project and the construction

The chapter reconstructs the commissioning and construction history of Villa Gazzotti. Taddeo Gazzotti, a wealthy tax collector for the Republic of Venice, commissioned the villa around 1542–1543. However, due to financial difficulties, the construction was interrupted and the unfinished property was confiscated in 1550. Gerolamo Grimani later acquired the villa and completed the works between 1550 and 1555.

 

Architecturally, the villa presents many features characteristic of Palladio’s mature style. The façade is organised into seven bays articulated by composite pilasters, with a central loggia surmounted by a pediment. The interior plan revolves around a central salone in the shape of a Greek cross covered by a complex groin vault, while the surrounding rooms are covered with pavilion vaults and barrel vaults.

 

Elevations of Villa Gazzotti: photograph of the main façade by Renato Cevese, [8],1957; (b) lithography of the main façade by Marco Moro (1817-1885) and printed by Brizeghel, private collection, c. 1850; (c) survey by Ottavio Bertotti Scamozzi, [15], c.1778.

 

 

Comparison between Palladio’s original drawings and later surveys revealed the integration of the medieval tower into the eastern side of the building. Differences between the realised structure and Palladio’s drawings also led historians to debate whether a larger, more ambitious project had originally been planned.

 

The presence of construction joints and masonry discontinuities suggests that the villa was built in at least two phases. The front section, including the loggia and front rooms, was likely completed first, while the rear section containing the salone and avant-corps was constructed later.

 

 

1.3 The modifications

The villa underwent several transformations after its completion. The earliest important survey was carried out by Ottavio Bertotti Scamozzi in 1778, although his representations were highly idealised. Nevertheless, they show that the original layout remained substantially intact during the 18th century.

 

During the 19th century, major modifications were introduced when the villa was converted into housing for agricultural workers. An intermediate floor was inserted across the first level, new openings were created, staircases were altered, and several rooms were subdivided. Some of these changes were later reversed during restoration campaigns.

 

The chapter also discusses earthquake damage, probably associated with the 1976 Friuli earthquake. Cracks appeared in the avant-corps and several walls experienced deformations. Restoration works carried out in the early 2000s repaired many of these damages, reopened blocked windows, reconstructed staircases, and removed intrusive later additions.

 

Cross-section (idealised) of Villa Gazzotti by Ottavio Bertotti Scamozzi, [15], c.1778.

 

2. Observations of the Structure

2.1 Masonry structures

 

The structural survey revealed that the villa is almost entirely constructed from brick masonry with lime mortar. Different masonry typologies were identified according to wall thickness and construction technique. The medieval tower differs significantly from the Palladian masonry because it likely consists of brick facings filled with rubble masonry.

 

The survey also documented the various vaulted systems used throughout the villa, including barrel vaults, pavilion vaults, and the central groin vault of the salone. Inspection of the extradoses showed that the vaults were constructed using thin brick layers reinforced with ribs. In several cases, vaults were found to be structurally disconnected from adjacent walls, which strongly influences the building’s behaviour.

 

Iron ties hidden within floors, walls, and vault fillings were identified throughout the structure. These ties play a fundamental role in resisting the horizontal thrusts generated by the vaults.

Masonry details in the villa: (a) signs of masonry di costa covering the chimney duct; (b) base of the walls of the tower made of a rubble masonry of stones and pebbles; (c) foundation of the tower in front and of the Palladian walls on the left; (d) typical opening in the basement with ledge for the closing of the door.

 

 

2.2 Timber structures

 

The villa’s timber structures were analysed in detail. While parts of the basement are vaulted, the remaining areas are covered with timber floors composed of beams, boarding, and terrazzo finishes.

 

 

Several later reinforcements were identified:

• Additional beams;
• Columns;
• A central wall added to reduce excessive floor deformation.

Photographs of the timber floors of the villa: (a) basement; (b) basement underneath the main room; (c) ground floor; (d) first floor.

 

 

The roof structure includes both simple beam systems and timber trusses. Iron staples connecting some roof beams to the masonry were identified, indicating attempts to improve resistance against out-of-plane wall movements. Variations in roof construction also confirmed the existence of different building phases.

 

 

2.3 Cracks

The crack survey demonstrated that most structural damage is directly related to the thrust generated by the vaults. The pavilion vaults in the front rooms produce diagonal cracks in the vaults themselves and vertical cracks in the supporting walls. Significant outward bending of the walls was also observed.

 

The loggia vault presents cracks along its intrados and at the interfaces with the walls, indicating structural separation between the elements. Additional corner cracks developed where new Palladian masonry was connected to the medieval tower, confirming the weakness of these joints.

 

The central groin vault of the salone is comparatively stable, showing only limited cracking. However, several cracks observed in the avant-corps and west façade are attributed to seismic activity, particularly the 1976 Friuli earthquake. One major crack pattern clearly indicates the development of an overturning mechanism in the north-west section of the villa.

 

 

2.4 Traces of construction and interventions

The building preserves important construction traces that help reconstruct its construction history.

 

The survey documented:

• Construction joints;
• Masonry discontinuities;
• Putlog holes from scaffolding;
• Evidence of reused masonry;
• Variations in roof and wall construction.

The discontinuities confirm interruptions between construction phases and explain many of the present-day cracks.

 

The chapter also identifies pragmatic construction adaptations, such as local reductions in vault thickness where roof beams interfered with vault geometry.

Orthophotos of the façades with indications: (a) north; (b) south; (c) west; (d) east; (e) avant-corps west; (f) avant-corps east.

 

 

2.5 A proposition for the sequence of construction

Based on historical documentation and structural observations, the author proposes a likely sequence for the construction of the villa. The front rooms and loggia appear to have been built first. Construction was probably interrupted after the confiscation of the property, leaving parts of the structure unfinished.

 

The rear rooms and staircases were completed later, followed by the construction of the salone vault and avant-corps. In some cases, the roof structure was already in place before the vaults were completed, explaining several structural irregularities and masonry connections observed during the survey.

 

This sequence explains:

• Structural discontinuities;
• Different roof systems;
• Weak masonry connections;
• Differential structural behaviour.

 

 

3. Static Analysis

3.1 Model

A finite element model of the villa was created using DIANA FEA 10.6. The model included shell elements for walls and vaults, solid elements for vault fillings, and truss elements for the iron ties. The geometry was based on historical surveys and a recent laser scan.

 

Wall thicknesses, vault geometry, masonry discontinuities, and tie positions were introduced according to the survey results. Timber floors and roof structures were simplified as distributed loads rather than modelled explicitly.

 

The masonry was assumed to behave elastically under compression, while nonlinear cracking behaviour was introduced for tensile stresses. Material properties were initially based on Italian seismic code recommendations.

View of the model: (a) geometry; (b) mesh.

3.2 Calibration

The model was calibrated using laser scan measurements of out-of-plane wall deformations. Walls unaffected by vault thrusts were found to remain perfectly vertical, while displaced walls showed measurable deformations caused by long-term structural behaviour.

 

To reproduce the observed deformations, the Young’s modulus of the masonry had to be reduced significantly. Lower stiffness values were assigned to the medieval tower due to its rubble-filled construction.

 

The calibration also confirmed the importance of structural discontinuities around the loggia and medieval tower. Several cracks and deformations observed in reality could only be reproduced when these weak connections were incorporated into the model.

 

3.3 Behaviour of the structure

The finite element analysis clarified the structural behaviour of the villa under gravity loads. The vaults generate significant horizontal thrusts that create tensile stresses inside the walls. These stresses explain the vertical crack patterns observed during the survey.

 

The walls primarily transfer the thrusts toward iron ties and perpendicular walls rather than to the foundations through cantilever action. The analysis demonstrated that the iron ties in the front rooms and loggia are essential for structural stability. Without them, the slender walls would not be capable of resisting the vault thrusts.

 

The study also showed that some ties located in the rear section contribute little to static behaviour, although they may still be useful during seismic events. Overall, the analysis highlights Palladio’s sophisticated understanding of structural mechanics and his strategic use of concealed reinforcement systems.

Results of the finite element calculation including vault thrusts, funicular lines and cracks.

 

 

4. Dynamic Analysis

4.1 Modal test

A modal test was performed using 15 accelerometers placed throughout the villa.

 

The test aimed to:

• Identify the building’s natural vibration modes;
• Validate the numerical model.

 

Two measurement setups focused on:

• The rear section;
• The front section.

Some sensors malfunctioned, especially on the tympanum and avant-corps, limiting the available data.

 

 

4.2 Numerical modal analysis

The finite element model was adapted for dynamic analysis by introducing:

• Timber diaphragms representing floors and roof;
• Updated masonry stiffness values.

 

Calibration produced:

• 0.8 GPa for the tower masonry;
• 1 GPa for the rest of the structure.

These values are higher than those from static calibration because modal analysis reflects short-term dynamic behaviour rather than long-term deformation.

 

 

4.3 Comparison

The numerical model reproduced the first three vibration modes with acceptable accuracy:

1. Transversal translation — 3.47 Hz;
2. Longitudinal translation with rotation — 4.04 Hz;
3. Pure rotation — 4.56 Hz.

The rotational effects are strongly influenced by the stiffness contrast between the medieval tower and the rest of the villa.

MAC indices around 0.8 demonstrated good agreement between experimental and numerical results.

The calibrated model was therefore considered sufficiently realistic for preliminary seismic assessment.

 

 

4.4 Critical local mechanisms

The final chapter investigates the most vulnerable seismic mechanisms of the villa. Three critical out-of-plane overturning mechanisms were studied:

1. Overturning of the entire north façade;
2. Overturning of the upper part of the north façade;
3. Overturning of the upper west façade.

Response spectrum analysis based on Italian seismic code provisions demonstrated that these mechanisms are unsafe under a design earthquake. Existing cracks and measured wall inclinations confirm that some overturning mechanisms may already have been partially activated in the past, likely during the 1976 Friuli earthquake.

 

The study concludes that further refined seismic analysis and local strengthening interventions are necessary to ensure the long-term safety of the structure.

 

 

Conclusion

The dissertation demonstrates that Villa Gazzotti is both an architectural masterpiece and a structurally complex building shaped by:

• Multiple construction phases;
• Medieval pre-existences;
• Vault thrusts;
• Masonry discontinuities;
• Seismic vulnerability.

The historical research revealed the integration of a medieval tower into the Palladian project and confirmed that the villa was constructed in multiple phases. The structural survey documented the composition of the masonry, vaults, timber floors, and roof systems, while also identifying extensive cracking patterns linked to vault thrusts and seismic activity.

 

The finite element model successfully reproduced the observed deformations and clarified the structural role of the iron ties. The analysis demonstrated that the ties in the front portion of the villa are essential for stability and that most structural damage originates from tensile stresses generated by the vaults.

 

The modal analysis and seismic assessment further revealed that certain façades remain vulnerable to out-of-plane overturning during earthquakes. Nevertheless, the study also highlights Palladio’s remarkable structural intuition, visible in his use of ties, wall proportions, roof connections, and other preventive measures against instability.

 

Overall, the dissertation shows how advanced survey techniques, numerical modelling, and historical investigation can be combined to achieve a realistic understanding of historic masonry structures and support informed conservation strategies.