A critical discussion on the earthquake risk mitigation of urban cultural heritage assets

Abstract

This paper aims at providing a comprehensive review on disaster risk mitigation of urban cultural heritage assets located in historical centres, by providing a holistic framework on the features of such a complex system. From all the hazards and threats that can possibly harm cultural heritage assets, particular focus will be given to earthquake risk. The review of the state of science in which the earthquake risk mitigation concerns is considered fundamental to understand the current streams of thought and to identify new research gaps and opportunities to enhance the knowledge level on this particular field of research.

Introduction

This first section aims at highlighting some of the most relevant phenomena and external pressures affecting urban cultural heritage worldwide. In the past decades we have witnessed an increased political focus on cultural heritage, not only because of higher public interest in heritage related issues but also because cultural heritage is often seen as a means to stimulate economic activity in countries with economic downturn problems. In fact, cultural heritage is often perceived as “a powerful engine of economic development” [1], as it participates directly in the generation of economic value through, for example, tourism activities [2]. When addressing urban cultural heritage, one should adopt a holistic approach to take into account the multitude of intrinsic features of these complex systems, such as social, cultural, historic, artistic and architectural, economic, city planning and sustainable development aspects. The need for this holistic approach derives from the dynamic nature of cities, the shape of which is continually changing according to society's demands over time. Therefore, to preserve urban cultural heritage sustainably, UNESCO suggests that strategic and dynamic alliances need to be built between various actors in the urban scene, foremost between public authorities that manage the city and developers and entrepreneurs that operate in the city [3].

There are multiple causes that have been identified as responsible for transforming urban settlements and their historic areas in drivers of economic growth in many regions of the world, acquiring a new role in both cultural and social life, such as the sharp increase in the world's urban population, the scale and speed of development and the changing economy [4]. However, if this transformation and economic growth are not conducted in a controlled and sustainable manner, it may foster the development of undesirable phenomena in urban cultural heritage, such as urbanisation and globalisation, market exploitation and mass tourism, for example.

According to the United Nations [5], it is estimated that 54% of the world's population lives in urban areas in 2014. If in 1950 this percentage was estimated in 30%, by 2050 it is expected that 66% of the world's population will live in urban areas. This unprecedented and generalised urbanisation phenomenon observed in many urban areas might trigger the fragmentation and deterioration of heritage [4]. However, in many other urban areas across the globe, the opposite scenario has been observed, where several factors have been contributing to this loss of centrality and the exodus of historical centres: poor conservation state of buildings; increased air pollution rates; increased criminality and insecurity rates, and poor accessibility [6], [7]. In order to aid reversing this phenomenon up to more balanced and sustainable terms, Laprise et al. [8] have developed an innovative study about regeneration strategies for disused urban areas. In the same scope, Radoslav et al. [9] have focused on the search for new revitalisation strategies of historical city centres.

Before going into further details on this subject, it is yet opportune to clarify the concept of urban cultural heritage. To understand this concept, one should recall to the classification proposed by Abbas et al. [10], in which architectonic assets are categorised based on a strictly “mechanical” criteria that foresees the identification of the most relevant macroelements in historical buildings and on the prevailing damage mechanisms which they may be subjected to. According to the same authors [10], the need for this classification arose from the recurrent observation of certain damage patterns in function of the assets’ morphology (architectural form, proportions) and technology (type of masonry, nature of horizontal diaphragms, effectiveness of wall-to-wall and floor-to-wall connections), as these behavioural dissimilarities call for different modelling approaches and different damage variables.

In this study, attention will be given to the category of architectonic assets theoretically subjected to prevailing in-plane damage proposed by Abbas et al. [10]. Hence, the definition of urban cultural heritage assets understands not only buildings theoretically subjected to prevailing in-plane damage, but also those classified or in the process of classification, such as residential buildings, palaces and other public and service buildings with accredited cultural relevance. Moreover, this type of assets is mostly located within historical centres, as outlined in [11], [12], [13], requiring, for this reason, a distinct care, and subsequently, a different category.

From the cultural heritage viewpoint, this study aims collaterally at promoting the preservation and conservation of ancient building technologies, in order to avoid the loss of identity and the mischaracterisation of historical centres to the so-called new technologies. Moreover, in a time in which more and more economic arguments seem to dominate the decision-making process, it is indeed important to emphasise other, no less important arguments, such as the patrimonial value or the sustainability in safeguarding cultural heritage.