Seismic Vulnerability of Arches, Vaults and Domes in Historical Buildings

Introduction

The term “historical buildings” refers to any type of construction that stands witness of past civilizations in that it conveys tractable information about technology, aesthetics, and way of life, customs, religious practices, art, defense and forms of government in former times (Pantazopoulou, 2013). Due to the many environmental causes; aging, earthquakes, traffic vibrations, wind and temperature loads, air pollution, and soil settlements, the structural elements of these buildings have been found vulnerable to cracking and dangerous failure mechanisms (Pantazopoulou, 2013). Of the many possible threats to the survival of historical buildings, earthquake stands as the principal threat due to the limited earthquake resistance capacity of these buildings (Asteris, 2008).

Domes and vaults were the favored choice for large-space monumental coverings for centuries (Kuban, 1987). For such structures, the construction materials should retain their strength as they subjected to different environmental conditions. Masonry, strong in compression, has been an ideal material to fit with these structural shapes. Timber has been rarely used in such historical monumental structures.

According to historical records, many arches, vaults and domes were subjected to severe earthquakes in the past without sustaining large damages. The many historical monuments around the world that remained safe during many centuries are living examples of this fact. Furthermore, in recent years, many arches, vaults and domes had survived the effects of earthquakes with little or no damages. The Pantheon, the dome of St Peter's Cathedral, the aqueduct Pont du Gard, Nîmes, France, and the Segovia Aqueduct, Spain are few examples of the such monuments. Another more recent example of the behavior of such buildings has been demonstrated in the 1999 Kocaeli Earthquake. Most of the main compounds of mosques, having single dome with multiple semi-spherical domes, were generally intact or suffered very slight damage (JSCE, 1999; Dogangun & Sezen, 2012). Therefore, it can be concluded that each of these monuments had an inherent lateral strength that was sufficient to resist moderate sized earthquakes with an acceptable degree of damage (Palacios, 2004).

As a result of the many factors explained above, a gradual deterioration of materials or the load carrying structural system is expected to occur during the life time of the structure (Garavaglia, Anzani, & Binda, 2006; Dogangun & Sezen, 2012). Thus, it is essential to evaluate the capacity of existing structural members and assessing their retrofitting need (Dogangun & Sezen, 2012). From engineering point of view, a probabilistic measure of the damage to the building resulting from a given ground motion need to be specified. Thus, the vulnerability of an element in a historical building is defined as the probability that the said element will sustain a specified degree of structural damage given a certain level of ground motion severity (Palacios, 2004).

In general, there are two main types of vulnerability methods. The probabilistic approach (also called observed vulnerability) is, mainly, used when a group of buildings are studied and it is based on statistic of past earthquake damage. On the other hand the deterministic approach (also called predicted vulnerability) can be used in dealing with single structural units and it refers to the assessment of expected performance of buildings based on calculation and design specifications (Palacios, 2004). Studies of vulnerability of masonry structures are usually conducted within an empirical framework, based on past observation and historic damage data. However empirical approaches have limitation in terms of regional applicability and comparison among different typological and geographical context (D’Ayala & Kishali, 2012).