- $3.8 billion per year to repair earthquake damage in Italy between 1968 to 2014
- 10% of New Zealand GDP equivalent damage during the 2010-2011 earthquakes
- $30 billion in Chile in 2010, $300 billion in Japan and $10 billion in Nepal 2015 earthquake.
Older buildings in New Zealand need to be strengthened before the next earthquake strikes or pay the price. Strengthening should not be an option, it must be mandatory for both the safety of users and reduced repair costs.
Earthquakes represent one of the most destructive natural hazards for many countries around the world, including New Zealand. For instance in Europe, although earthquakes represented only 5% of the recorded major events (natural hazards and technological accidents), in the period 1998-2009, they were responsible for about 20% of the total number of fatalities (18,864 people) and overall losses (29.2 billion euros). The cost of recent earthquakes is even larger for regions with higher seismicity. For example: Chile 2010 ($30 billion), Haiti 2010 ($14 billion – more than 100% of the country’s GDP), Christchurch 2010-2011 ($20 billion – 10% of country’s GDP), Tohoku, Japan 2011 ($300 billion associated with both earthquake and tsunami damages) and Nepal 2015 ($10 billion).
The benefit of #strengthening a structure before the earthquake strikes is usually demonstrated through a strengthening cost-benefit analysis of buildings that have damaged by an earthquake. The results of such a study are shown in Table 1. It can be seen that the cost of repairing high-risk building (structural and non-structural) is four times higher compared to the buildings with limited structural damage. It also showed that the cost of strengthening is more than double.
According to a report published by the Center of Studies of the National Council of Engineers of Italy entitled “Costs of earthquakes in Italy”, in total between 1968 and 2014 121.6 billion euros were spent for reconstructions (Fig. 1). This is equivalent to spending 2.6 billion euros per year to repair the damages caused by earthquakes. According to one of the general directors of the Civil Protection Department, Mauro Dolce, about 50 billion euros would be needed to render all public buildings earthquake-resistant. The estimation of the necessary cost for the strengthening of all private structures is not so easy since each owner can opt for a different strengthening strategy associated with costs varying from 300 to 800 euros per square meter. According to the Italian Civil Protection data, about 93.7 billion euros would be needed to provide safety of all Italian houses in the case of an earthquake, while structural interventions in zones with high seismic risk would cost approximately 36 billion euros. Considering that the reconstruction costs of 121.6 billion euros concerned only a small percentage of the Italian building stock that was exposed to earthquakes during the period 1968-2014, spending 144 billion euros for strengthening all buildings of the country is expected to be an affordable cost for a developed society to undertake on a long-term basis.
The need for seismic strengthening of structures before a strong ground shaking arrives can be illustrated by examining the seismic behavior of two identical Victorian style buildings in Santa Cruz, California during the 7.1 magnitude Loma Prieta earthquake in 1989 (http://www.earthquakesafety.com/retrofit-case-study.html). According to the owner and architect Michael O’Hearn, the twins were built 90 to 100 years ago, by the same builder, with identical materials and using the same construction techniques. He started building structural wood panels as a shear element on cripple wall framing for one of the twin buildings. The sill plate also was bolted to the foundation. Unfortunately, there was no time to install structural wood panels at the other building as well before the Loma Prieta earthquake. The non-strengthened building came apart in four sections and its five residents survived by luck. The repair cost was approximately $260,000 since the entire building had to be jacked up and slid back together on a new foundation. On the other hand, the building with the structural wood panel shear walls experienced only minor damage (repair costs of approximately $5,000). Although this cost difference might not be representative of all cases, it gives an idea about how important pre-seismic strengthening over post-seismic strengthening/repair is.
It should be also noted that all potential consequences must be considered when performing a cost-benefit analysis for the seismic strengthening of a structure, including the human dimension. The most objective way to estimate the cost of human life is insurance data. Earthquakes in developing countries, such as Haiti or Chile, might result in large amount of casualties and injuries, affecting the post-earthquake recovery, the reconstruction and also the Gross Domestic Product of the country. Moreover, since in developing countries life insurance and disaster insurance are rather uncommon, an earthquake strike can lead to poverty for a large part of the population (https://courses.edx.org/courses/course-v1:EPFLx+Tech4DRR+2016_T3/info). Developed countries (e.g. U.S.A., Japan, New Zealand, Italy) usually experience much lesser number of casualties compared to developing countries but since their GDP is based on the contribution of the tertiary sector (services, commerce, transport, tourism), damages in housing, infrastructures, and lifelines might lead to an important economic setback.
In the next few articles, I will outline the most common strengthening techniques applicable to different types of buildings.