Assessment and Fragility of Byzantine Unreinforced Masonry Towers

Emmanouil-Georgios Kouris,Elias C Aifantis,Leonidas-Alexandros S Kouris,Chris G Karayannis,Avraam A Konstantinidis

doi:10.3390/infrastructures6030040

Emmanouil-Georgios Kouris, Elias C Aifantis + Show 3 more

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https://doi.org/10.3390/infrastructures6030040

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Abstract

The seismic response of five cultural heritage towers erected between the 10th and 19th century AD are investigated herein. Firstly, their architectural and modal characteristics were studied in the light of seismic events that hit the monuments. There exist several historical reports of strong earthquakes, as well as damaged structures and collapses. The limit analysis is adopted to examine the post-elastic behavior of the towers up to collapse due to out-of-plane failure. Recurrent damage modes were collected from recent earthquakes and a classification of four possible collapse mechanisms in towers and slender masonry structures is here proposed: overturning, separation of perpendicular walls, diagonal cracking, and dislocation of the belfry. A thorough examination of the towers under investigation verified the proposed damage classification. The capacity curves were derived combining the capacity curves of each of the collapse mechanisms. Damage thresholds were defined on these curves in correspondence with damage states. The studied group of structures is representative of a wider typology. A statistical approach was adopted to describe damage with seismic intensity, and vulnerability curves were generated. The results of this study will improve the understanding of the performance and the collapse mechanisms of slender masonry structures under seismic loading and provide a characterization of seismic vulnerability for the studied cultural heritage types of towers.

Highlights

Unreinforced masonry (URM) structures excited by seismic actions most often form at the ultimate response state an out-of-plane partial collapse mechanism due to weak connections and in-plane cracking [1,2,3,4]
These non-linear systems can be idealized with an equivalent linear SDOF system having an effective natural period which maximizes the response. This appears in a fraction of the ultimate displacement, which according to [40,99] is at the 40% of the ultimate displacement (0.20 m) and, the effective acceleration corresponding to the effective displacement a∗s is identified on the capacity curve (a∗s = 0.28 g = 2.79 m/s2 ) the effective secant period
The towers are located on Mount Athos, Greece and represent a large population of cultural heritage defense and monastic slender structures

Summary

Introduction

Unreinforced masonry (URM) structures excited by seismic actions most often form at the ultimate response state an out-of-plane partial collapse mechanism due to weak connections and in-plane cracking [1,2,3,4]. It is common knowledge that the main defect of URM walls is their low tensile strength; as a consequence, URM structures tend to create cracks perpendicular to the principal tensile stresses. This inefficiency had been known since ancient times and traditional reinforcement techniques have been developed involving timber and iron ties to mitigate it [3,5,6,7,8]. The interaction among the cracked parts is often merely simple

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