During the past 20 years, natural hazards such as earthquakes and tsunamis have claimed the lives of over 3.5 million people, and adversely affected the lives of a billion people worldwide.
Since World War II, economic losses associated with natural hazards such as earthquakes, have increased by a factor of eight. The risk of disasters is increasing not because the frequency or magnitude of hazards is rising, but because cities are becoming larger, so their populations are more exposed to vulnerable buildings.
While the risk of disaster in Malta due to earthquakes is perceived to be insignificant, history shows that about seven earthquakes have significantly damaged buildings in the past 400 years. One should not necessarily associate the level of risk with a possible moderate occurence of the hazard.
The vulnerability of the infrastructure and buildings, and the exposed quantity, also form part of the risk equation, together with the level of preparedness and mitigation measures. Considering that the local population has increased from less than 100,000 to over 400,000 during the past 400 years, and that the built-up area increased from about 4.5 per cent to 33 per cent in the past 50 years, the cost to recover from a devastating earthquake would be much higher if it occurred today.
Recent regional earthquakes, such as in southern Italy in 1980, Turkey in 1999, L’Aquila in 2009 and Emilia Romagna 2012, have shown that structural performance of buildings has played a crucial role in terms of disaster risk, earthquake losses and urban resilience. In many European countries, seismic design codes have only been used for the last 15 to 20 years, meaning that most of the existing building stock has not been seismically designed.
UN and World Bank initiatives encourage adequate engineering practice and the adoption of disaster risk reduction strategies. An important component of these strategies involves the quantification of possible damage in building structures in order to develop resilient urban settlements.
Most of the existing building stock has not been seismically designed
Following the introduction of new revised European standards, the author embarked on a research project as part of his Ph.D studies that involved developing computational tools to understand the performance of structures in future earthquakes, and to quantify associated damage. The research was conducted at University College, London, and funded by the Engineering and Physical Sciences Research Council, UK, and by a Strategic Educational Pathways Scholarship (Steps) part-financed by the EU European Social Fund.
The research used a statistical approach to develop relationships that relate parameters describing damage, such as deformation, with simple properties of a building, such as column and beam dimensions, and strength of materials, such as concrete as the input information.
The relationships were developed using information of experiments on buildings in literature, information of existing building stocks in Europe and in Malta, and information on the development of damage of structures in past European earthquakes. Reference was principally made to reinforced concrete structures. However, data on the performance of reinforced concrete elements in buildings constructed before the 1990s is very limited.
An extensive testing campaign simulating a seismic loading regime on reinforced concrete columns and beam-column connections representing these structures was conducted at the University of Aveiro as part of the research, and included in the data set to extend the applicability of the relationships.
Current relationships in Eurocode are developed independent of earthquake characteristics. They also refer to initiation of damage, and collapse damage states only. Nevertheless, the proposed relationships consider some seismological aspects that affect the response of buildings. The damage prediction is therefore more factual. The proposed relationships also refer to other intermediate levels of damage where the quantification of eventual damage and the assessment process are more refined.
Consequently, in the life-cycle of a building, more affordable and sustainable interventions can be made as part of the preparedness and mitigation action measures that can be taken. These include the strengthening of vulnerable structures and the repair of damaged ones.
Randolf Carl Borg is an architect and civil engineer.