Innovative engineering applications are proposed to satisfy the current necessities of earthquake engineering, which are well established from a conceptual perspective, and frequently, the development of some missing inputs is only required to employ them, such as the case of the correlations between spectral values at different vibration periods. Accordingly, we computed the correlation between spectral accelerations at two vibration periods using ground motions from interplate and, alternatively, intraslab events, recorded in firm ground of Mexico City. Results show that the spreading of correlation values depends on the rupture mechanism. Then, based on hypothesis test analyses, we used four correlation models available in the literature to predict our correlation values. According to the findings, we proposed a predictive correlation mathematical model for interplate and, separately, for intraslab seismic events. We evaluated the influence of the predictive correlation models on the results corresponding to two earthquake engineering applications. The first refers to compute conditional mean spectra and the second to perform probabilistic seismic hazard analysis (PSHA) using I Np and, alternatively, Sa avg , intensity measures. We found that while the conditional mean spectra might be affected in the region of short vibration periods, the computations of the PSHA with improved intensity measures are not affected significantly.
Abstract. For earthquake resistant design, structural degradation is considered using traditional strength modification factors, which are obtained via the ratio of the nonlinear seismic response of degrading and non-degrading structural single degree of freedom (SDOF) systems. In this paper, with the aim to avoid the nonlinear seismic response to compute strength modification factors, a methodology based on probabilistic seismic hazard analyses (PSHA) is proposed in order to obtain strength modification factors of design spectra which consider structural degradation through the spectral-shape intensity measure INp. PSHA using INp to account for structural degradation, and Sa(T1) which represents the spectral acceleration associated with the fundamental period and does not consider such degradation, are performed. The ratio of the uniform hazard spectra in terms of INp and Sa(T1), that represent the response of degrading and non-degrading systems, provide new strength modification factors without the need to develop nonlinear time history analysis. A mathematical expression is fitted to the ratios that correspond to systems located in different soil types. The expression is validated by comparing the results with those derived from nonlinear time-history analyses of structural systems.
El análisis dinámico modal espectral es ampliamente utilizado en el diseño sísmico de edificaciones. Este tipo de análisis generalmente define la acción símica mediante un espectro de pseudoaceleraciones elástico, cuyas ordenadas pueden alterarse por medio de factores de modificación de resistencia; existen, por ejemplo, factores de modificación por ductilidad, sobrerresistencia, redundancia, irregularidad, asimetría en fluencia, etc. En el presente estudio se propone una metodología orientada a obtener factores de modificación de resistencia para considerar el efecto de degradación estructural, aplicables a espectros de sitio de diseño sísmico de la Ciudad de México (CDMX). La metodología se basa en análisis probabilistas de peligro sísmico (APPS) utilizando dos medidas de intensidad sísmica: a) Sa(T1), la cual representa la aceleración espectral en el periodo fundamental de una estructura, y b) INp, que considera el alargamiento del periodo fundamental que presenta la estructura como consecuencia de la degradación estructural. Primeramente, se estiman espectros de peligro uniforme, correspondientes a diferentes sitios de la CDMX, en términos de Sa(T1) y, alternativamente, de INp, los cuales representan la respuesta de sistemas con comportamiento no degradante y degradante, respectivamente. Enseguida, a través del cociente entre dichos espectros INp/Sa(T1), se obtienen factores de modificación de resistencia, sin la necesidad de realizar análisis no-lineales. Finalmente, se ajusta una expresión matemática a dichos cocientes espectrales, aplicable a estructuras desplantadas sobre diferentes tipos de terreno de la CDMX. La expresión propuesta se compara con resultados de otras investigaciones basados en análisis no-lineales tiempo-historia
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