Browsing by Author "Miranda, Eduardo"

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    A Simplified and Versatile Element Model for 2 Elastomeric Seismic Isolation Bearings
    (2021) Miranda, Sebastián; Miranda, Eduardo; Llera, Juan Carlos de la
    A novel approach for two-dimensional modeling of elastomeric bearings using three springs in parallel is presented. This simplified element model considers as follows: (1) an elastoplastic spring with a smooth transition between branches; (2) a linear elastic spring; and (3) a non-linear elastic spring, and is fully defined by only six parameters. The main advantages of the simplified model are twofold: (1) versatility, as a single model is capable of accurately reproducing the main characteristics of the hysteretic behavior of different types of rubber-based seismic isolators, including low damping rubber bearings (LDRBs), high damping rubber bearings (HDRBs), and lead-core rubber bearings (LRBs) and (2) simplicity, as it requires fewer parameters and it is easier to calibrate from experimental cyclic test results than most currently available models. Model parameters’ identification is illustrated using quasi-static cyclic and earthquake simulator tests of HDRBs and LRBs, demonstrating that the model shows a good agreement between the test-measured and model-predicted hysteretic behavior. Different objective functions are evaluated in the optimization procedure, and their effect on the identified parameters is studied and discussed. This practitioner-oriented model is particularly amenable for implementation in general-purpose structural analysis software. Its usage is strongly recommended as an initial-stage design tool to select the optimal isolation system for a specific project.
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    The effect of spectral shape on damping modification factors
    (2020) Miranda, Sebastián; Miranda, Eduardo; Llera, Juan Carlos de la
    The main objective of this study is to investigate the effect of spectral shape on damping modification factors η used in equivalent static and response spectrum analyses of structures with damping ratios that are different from 5% critical damping. Record-to-record variability of η is also evaluated through a statistical analysis of 5270 ground motions records from 1137 interface earthquakes recorded in Chile. The effect of spectral shape is studied using recently developed spectral shape metrics SaRatio and epsilon (ε) and evaluating their use as possible predictors for η. Similarly to previous investigations, this article also examines the effect of oscillator period, earthquake magnitude, and earthquake duration for different levels of damping ratio. Results suggest that SaRatio is an effective predictor of η, particularly for highly damped structures. However, results also indicate that for rock and firm sites, earthquake faulting mechanism and site class do not have a significant influence on η. A simple period-independent regression model for η as a function of SaRatio and damping ratio is proposed. A comparison between median η from this study and those in current Chilean seismic codes shows that code factors are unconservative.
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    Uncertainty on measurement of elastomemeric isolators effective properties
    (2021) Miranda, Sebastián; Llera, Juan Carlos de la; Miranda, Eduardo
    Elastomeric isolators are subjected to a series of non-destructive tests with several repeated deformation cycles. For each cycle, effective properties are calculated and afterward averaged. Despite their variability, and therefore their inherent uncertainties, these properties are treated as deterministic values by seismic design procedures. In this research, these uncertainties are quantified, based on the Guide to the expression of Uncertainty in Measurement, GUM, and Monte-Carlo simulations, considering variability between repetitions and instrumentation errors. Uncertainties were calculated for a dataset of 2,498 isolators' test results, finding that the maximum relative expanded uncertainty was 12%. The GUM and Monte-Carlo methods lead to similar results, and higher-order effects in the GUM assessment were negligible. A comprehensive analysis to evaluate the influence of the directly-measured quantities in the properties uncertainties was performed. Results showed that forces and displacements measurement errors are equally relevant in stiffness uncertainties, but force measurement errors primarily control damping uncertainties.

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