Seismic vulnerability assessment of classes of reinforced concrete structures

Abstract

The modern seismic design is based on the concept to meet different performance levels, for each of which the structure should not exceed the predetermined degrees of damage. The analysis of elastic-linear benefit from the simplicity of use and theoretical understanding, but are not able to predict the inelastic deformation capacity offered by a structure, for that reason they are unsuitable for a modern seismic design (based on the concept of performance), where the non-linear behavior and the conditions close to the collapse are investigated. To achieve an accurate and realistic prediction of the seismic response of a structure is necessary to have analytical tools that allow to figure out the nonlinear behavior and its evolution over time. The IDA, the Incremental Dynamic Analysis (designed by Prof. D. Vamvatsikos - foreign tutor's writer - and Professor C. A. Cornell), addresses the need to want to investigate the dynamic behavior of a structure at various levels of seismic intensity. Given an accelerogram, different dynamic analyzes on the same structure but with a seismic increasingly scaled input are performed, up to the collapse of the structure or until a predetermined level of deformation or displacement takes place. The incremental dynamic analyzes are clearly preferable like nonlinear analysis, because only with the previous is possible to grasp the dynamic behavior of the structure resulting in potential savings in terms of actions to be pursued. This is the concept on which is based the study carried out during this period: the evaluation of seismic vulnerability, especially of reinforced concrete structures, using the analysis above described Very significant and useful for the purpose of the research was the period spent abroad, during which a probabilistic and a statistical technique to assess losses caused by earthquakes of entire urban areas was developed. The used approach is "multi-level", for classes of buildings that represent the building types that are in the examined area. The starting point was the observation of an area inside the City Hall of Zografou, the district within which the NTUA (National Technic University of Athens) is located, by detecting some significant features of 305 surveyed buildings (such as number of floors, irregularities in height and in plant, year of construction). Each of these characteristics has been considered as discriminatory for the belonging of the particular building to a specific group. Homogeneous groups were then treated with techniques of statistical type, including the Clustering method, by which the number of the models (12 models) is resulted much lower than the number of the buildings analyzed, representative of the structures present in the whole area examined. Taking as a reference the legislation in force at time of the construction of each model to designing it (making choices about the statistical characteristics of the materials used), the results related to static analysis and IDA, have been considered for the assessment of seismic losses the whole area they represent. The approach based on "damage factor" compared to other models for which are known seismic losses, led to further evaluation in terms of statistical dispersion of results. The steps are repeatable, with the necessary precautions, in other areas, and they give the opportunity to describe the seismic fragility of the heritage of entire cities. The results are useful to provide valuable information to organizations such as the Civil Protection and / or insurance agencies