Vulnerability of Existent Structures in Israel to Earthquakes
In Earthquake-prone countries, as Israel, the seismic aspect must be given the primary importance in designing structures located in vulnerable regions to such events. Due to the high sensitivity to man-life in Israel, lack of preparedness in facing a strong earthquake may result in a severe disaster of far-reaching significance more than in any place throughout the world.
Of course, the problem during a seismic event is the structure, which is a man-made, and not the event in itself. Against this hazard there is one and only cure, that is, designing and building earthquake-resistant structures. The Israeli seismic code, IC 413 (1995), is intended to help the designers to withstand this challenge; Its aim is to ensure that the structures are able to resist minor earthquakes without damage, to resist moderate earthquakes without structural damage, and to resist strong earthquakes without collapse and loss of life.
The present seismic design philosophy is based on qualitative but not quantitative objectives. These had demonstrated the structural resistance and the life safety protection, as for a new construction according to the recent standards, but also the severe vulnerability of the old construction.
The existent structures in Israel pose a severe hazard to life safety; it stands to reason to be of the opinion that the greatest present threat to man-life or property due to a strong or moderate earthquake in the country is the dangerous existent structures. Thus, there is an urgent need to minimize this seismic hazard in the cities all over the country.
Due to the numerous dangerous existent structures in Israel, one of the most effective ways for mitigating such a hazard is to conduct reliable estimates of the vulnerability of existent structures in urban areas, and then, the development and implementation of effective methodologies for rehabilitation of structures that were identified as dangerous. Also, to specify clear, direct, and decisive provisions for Quality Assurance, which are capable of regularizing this important issue in the seismic rehabilitation process, with unequivocal clarification and establishing settled processes for implementation by various bodies that take part in the whole process.
There is a real need to take the initiative to a national program for mitigating the seismic hazard of existent structures, with mechanism and action, taking into account the resources, the means for a rapid screening, a detailed appreciation of situation, and economic and social projections, and in order to ensure the retrofit process, there is a need to lead to adequate legislation.
A seismic rehabilitation of existent structures must result in a predictable and defined seismic performance during an earthquake with a specified severity. The base of the analysis and design is a seismic hazard criterion that reflects the relationship between the shock level and the assignment of the structure and how it will look after the specified event to which it may be exposed. This relationship must reflect the issue of the seismic safety, the structural and the nonstructural one, and thus, the degree of the population exposure to the seismic hazard is based on extents of risk with different probabilities.
Protection against earthquakes poses a problem in Israel from a point of view of economics and society, since it will take a lot from the national resources, and due to the complexity in the structure of society and the uniqueness which characterizes the tradition and the way of thinking of each part of the whole population, along with the order of national scale of priorities. However, the far-reaching economic and social results of such a disaster can be so severe that neither the government nor the society can be justified in neglecting the protection against earthquakes.