Abstract
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 (PSHAs), is proposed in order to obtain strength modification factors of design spectra which consider structural degradation through the spectral-shape intensity measure INp. PSHAs 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), which represent the response of degrading and non-degrading systems, provides 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.
Highlights
Structures subjected to cyclic loading induced by intense ground motions can exhibit stiffness and/or strength degradation due to the inelastic nonlinear behavior of their structural elements, which can give place to lengthening of the structural fundamental vibration period T1
probabilistic seismic hazard analyses (PSHAs) are associated with Sa(T1) and alternatively with INp intensity measures, where Sa(T1) represents the spectral acceleration at the fundamental period of a structure, and INp is an intensity measure that accounts for the period lengthening due to structure-degrading behavior (INp is defined below)
We consider that there is no optimal period range for Saavg(T1 . . . TN ) that meets the entire range of structural vibration periods; here we propose that TN should depend on the structural vibration period, which is in agreement with Tsantaki et al (2012, 2017)
Summary
Structures subjected to cyclic loading induced by intense ground motions can exhibit stiffness and/or strength degradation due to the inelastic nonlinear behavior of their structural elements, which can give place to lengthening of the structural fundamental vibration period T1. The simplified nonlinear approach is available in FEMA P-58 (2012) methodology Another example is the Manual for Civil Structures Design (MCSD, 2015), developed by the Federal Commission of Electricity of Mexico, which specifies a degrading factor that increases or decreases the design spectral ordinates, due to structural deterioration. Soil–structure interaction (SSI) was not taken into account to compute the structure-degrading modification factors for seismic design spectra; notice that the effect of SSI is more important for stiff structures located on soft soil, in such a way that for this type of structure, the ordinates of the response spectra tend to increase while the opposite occurs for flexible structures (Avilés and Pérez-Rocha, 2007). The results obtained in the present study could be modified to include the effect of SSI via the current Mexico City Building Code (MCBC, 2017) which provides recommendations about this issue
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