VALUTAZIONE DI VULNERABILITA’ SISMICA DI ELEMENTI IN C.A.: MODELLI DI CAPACITA’ A FLESSIONE E TAGLIO

The evaluation of seismic vulnerability of RC buildings is a topic of great concern and actuality, due to the fact that they constitute a relevant part of the Italian existing assets. Thanks to their historical and architectural value, many buildings belong to the cultural heritage, the conservation and protection of which is important. This work intends to provide specifications and guidelines for capacity assessment of RC buildings, in terms of strength and ductility, for state of stress that occurs in presence of seismic action. An in-depth study of two main topics is carried out in this work: the first concerns flexural deformation capacity of RC structures, and the second concerns the evaluation of capacity models for shear strength of RC elements. The in-depth study was justified and aimed at researching of specifications and guidelines to be implemented in professional practice. For this reason, for both topics, a critical comparative analysis of capacity models available in current international standards and guidelines were developed and useful tables and tools for vulnerability assessment of RC elements are given. This thesis, therefore, consists of two main parts: the first is devoted to flexural deformation capacity models and the second is devoted to shear capacity models, fundamental to evaluate mechanisms and appearances of ductile and brittle failure. As specified above, in dealing with both topics particular attention was paid to regulatory aspects. The first part of the thesis deals with some specific aspects related to the assessment of ductility required by current standards with a view to the seismic vulnerability evaluation of existing structures and to design new seismic-resistant structures. After a brief overview of fundamental concepts of both curvature and displacement ductility, specific aspects of the ductility assessment of existing structures and newly constructed structures are discussed. For existing structures, it has been proposed an immediate evaluation by using tabular approach, with reference to rotation capacity assessment of beams and columns. For new structures, on the other hand, reference was made to ductility assessments in the context of linear analysis methods, trying to retrace what was proposed by the current code, from curvature ductility demand to the calculation of the corresponding capacity, proposing evaluations and comparison in respect of construction detail rules, an alternative to explicit assessment to the satisfaction of ductility requirements. In the second part of the thesis, the topic shear strength has been addressed with particular reference to capacity models. The objective of this thesis has been on one hand, comparing different current standards and guidelines and on the other hand, systematically collecting the larger number of shear tests of RC beams and columns found in literature, creating a specific database usable for purpose of study or research. Specifically, the database, containing 2’858 tests, was created from different sources such as PEER and ACI-DAfStb, along with Collins at al. (2005) and Cavagnis (2017) works. This second part of the thesis begins by retracing the main steps that have marked the history of knowledge evolution and regulatory requirements related to the evaluation of shear strength of RC elements trying to find the genesis of current standards and guidelines. To this end, capacity models found in the literature were investigated, derived from mechanical and/or empirical approaches, which represents the fundamental of the models adopted in the current standards. In addition to the Italian national code and the European codes, capacity models of other five international codes were considered. The comparison between these codes is made with reference to the experimental results of the database developed in this work with over 170 beams and columns with shear reinforcement and over 2000 members without shear reinforcement.