Resumen de Análisis estructural sísmico de edificios de acero: un enfoque probabilista
The main objective of this thesis is the probabilistic assessment of the expected seismic damage in steel buildings located in Mexico City. Although a deterministic analysis is performed both, seismic actions and buildings, are considered in a probabilistic way. A broad acceleration database, with 7132 records (3 components) of the 180 stations in the city, 1363 with peak ground acceleration (PGA) above 0.01 g, is analyzed; this analysis, allows having data representative for each one of the 6 seismic zones of the city; the seismic action in each zone is defined by means of 20 accelerograms compatible and with controlled error, in the sense that the mean value and standard deviation of the 20 spectra match well the design spectrum and a predefined error function, respectively. Concerning structures, the study is based on low- (3 stories), mid- (7 stories) and high-rise (13 stories) buildings and on 3 structural configurations: i) Special Moment Frames (SMF) ii) Special Concentrically Braced Frames (SCBF) and (iii) Buckling Restrained Braced Frames (BRBF). The mechanical properties are considered in a probabilistic way by means of appropriate probability distributions; Monte Carlo simulation and Latin hypercube based sampling techniques are used. The deterministic analysis is performed by using mean values of buildings and accelerograms. 2D models, Nonlinear Static Analysis (NLSA), Non Linear Dynamic Analysis (NLDA) and Incremental Dynamic Analysis (IDA) are used. NLSA allows obtaining capacity spectra, fragility curves, mean damage state curves and relations between PGA and the displacement of the performance point. IDA allows obtaining relations among PGA, maximum roof displacement and Park and Ang damage index. The results show that buildings perform properly. However, BRBF show the best performance; SMF the worst. The highest expected damage is obtained for high-rise buildings and, particularly, for SMF buildings; this result is attributed to soft-soil¿s amplification effects, affecting more to high buildings. Uncertainties in the response increase with the severity of the earthquake and they are dominated by uncertainties in the seismic action; however, the influence of uncertainties of the mechanical properties of buildings, although minor, is also significant. Static analysis provides good results, when compared with the ones of the dynamic analysis; but, this consistency is lower for high-rise buildings. The deterministic analysis shows a good consistency with the median values of the probabilistic analysis, although the probabilistic approach allows analyzing uncertainties and, in this sense, it should be preferred.
In this thesis, innovative methods for the analysis of the seismic action and for damage assessment have been implemented. Concerning to seismic action, a comprehensive study of directionality effects in Mexico City has been performed; also, the design spectra have been compared with the ones of the recorded accelerograms. Concerning to damage analysis the performance point is obtained by using an energy-balance based method. The parametric model for capacity curves has been applied; this model completely defines capacity curves/spectra with 5 independent parameters. In addition, two damage indices that are compatible with the Park and Ang index have been obtained; these two damage indices are calculated from the capacity curve, in a straightforward way. In addition, a probabilistic assessment of the collapse damage state, is performed. Finally, as a practical and useful contribution, several developments of this thesis, are implemented in an interactive software; it is intended that the computer program, "Probabilistic Seismic Risk" (PSRv1.0), be an easy and efficient tool allowing a fast assessment of the seismic risk.
