Records, capacity curve fits and RC damage states within a performance based earthquake engineering framework
De Luca, Flavia (2011) Records, capacity curve fits and RC damage states within a performance based earthquake engineering framework. [Tesi di dottorato] (Inedito)
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Earthquake engineering aims at the goal of controlling the seismic risk to socio-economically acceptable problems, encompassing multidisciplinary efforts from various branches of science and engineering. Such efforts in the last decades allowed structural engineering progressing towards an approach that can fit the general framework of the assessment and the control of seismic risk: performance based earthquake engineering (PBEE). PBEE represents a common platform for researchers and engineers. It is the frame in which the topics of this research have grown up. The first step of PBEE, hazard and ground motion, is discussed in the first part of this research. The employment of advanced intensity measures (IM) in Probabilistic Seismic Hazard Analysis (PSHA) is investigated. New prediction equations for inelastic displacement and equivalent number of cycles based on the ITalian ACcelerometric Archive are provided as IMs for both peak and cyclic inelastic response of structures. This tool goes towards further enhancements of PSHA. Moreover it can be a tool for the validation of simulated scenario for a robust employment in the assessment of critical facilities and finally for it can play a role in future perspective of large scale risk assessment. Issues regarding ground motion selection for nonlinear dynamic analyses are then examined: the reliability of artificial records, wavelet adjusted and linearly scaled records is investigated within a code-based framework. The inelastic displacement of such records was shown to be statistically equivalent to the one of unscaled real records, given the same spectral constraint suggested by codes; on the other hand, regarding cyclic response artificial records showed their statistically significant overestimation that can cause problem when employed for specific facilities in which cyclic response has a significant role in the assessment of the seismic performances. The second step discussed is the aspect of seismic demand prediction and estimation. Analysis methodologies are described and their level of accuracy is discussed, focusing on specific code prescriptions concerning structural analysis. Some critical issues of the recent Italian Code regarding choice and applicability conditions of analysis methods are emphasized. Special attention is given to the static pushover analysis, a methodology nowadays in the between of research and practice. A review of the approximations implicit in this methodology is provided, focusing the attention on the piecewise linear approximation of the capacity curve. A methodology for the systematical investigation of this aspect is presented and then employed for the definition of an optimized fit for capacity curves allowing a reduction and, above all, a quantification of the error introduced by this step when performing nonlinear static analysis. The third step within the PBEE framework, and the final one of this research, deals with modeling of damage states. The damage measures for reinforced concrete (RC) structures are investigated. Limit states for reinforced concrete structures are considered, focusing on the aspects of brittle failures in existing reinforced concrete structures. The latter represents one of the most critical issues for existing reinforced concrete structures, given the absence of capacity design. Brittle failures in reinforced concrete (RC) elements are analyzed according to code provisions, considering different code approaches and the analytical models are finally compared with experimental data. Non conventional brittle modes of failures such as the sliding shear mechanism are reviewed, with special attention to the structural details that allow the development of sufficient capacity against this failure mode. Finally the influence of masonry infill on the whole structural behavior of RC structures is investigated. The whole aspect of damage measures in reinforced concrete structures is further examined by means of the result of a reconnaissance post earthquake campaign. 6th April 2009 L’Aquila event is considered, and performances of existing reinforced concrete buildings during the earthquake are reviewed. Finally the results of the in-field campaign allowed the analytical study of a soft storey collapse. The back analysis of the case study structure selected emphasized the critical aspects regarding brittle mode of failure and singles out the likely causes of the structural collapse. The whole research, through the above three step path, aims to focus on some critical issues providing some tools, suggesting enhancements in methodologies and procedures and finally outlining possible future perspectives for the PBEE framework. In fact, this consolidated spine for earthquake engineering, allows a separate focus on issues that can then be recombined in the multidisciplinary context of assessment and control of the seismic risk.
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