Seismic vulnerability of buildings: from intuition to evaluation

In many seismic areas of the world, there are nowadays vulnerable structures, designed and built without seismic codes or using outdated codes. The seismic vulnerability of the buildings is, sometimes, not so difficult to be intuited. However, when vulnerability is to be estimated in a numerical way, a coherent conceptual framework and a methodology, not so easy to be developed, is required. Now we are faced with a complex and complicated problem which we have to solve without disregarding the uncertainties inherent to the characteristics of the structures and of the seismic action; therefore, the methods to assess seismic vulnerability and risk require the use of a probabilistic framework. Uncertainties have a pronounced effect on the behaviour of the structures, especially when they enter in the nonlinear range during earthquakes. The effects of the May 2011 Lorca earthquake on the structures of the affected area are used herein as examples of vulnerability evaluation of buildings and to test the capacity of the vulnerability assessment methods. The damages produced in the structures of Lorca by the earthquake, obtained through inspection after the earthquake, are compared herein with those calculated by means of a probabilistic risk analysis.