Browsing by Author "Candia, G."

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    Collapse assessment of a chilean code-conforming reinforced concrete office building
    (Earthquake Engineering Research Institute, 2018) Araya Letelier, Gerardo Andrés; Parra Torres, Pablo Fernando; López-García, Daniela; García Valdés, Óscar Andrés; Candia, G.; Lagos, R.
    Chilean buildings are periodically subjected to earthquakes and their satisfactory performance preventing collapse is widely known. Yet, as a result of the Mw 8.8 2010 Chile earthquake, one reinforced concrete building collapsed and many others were severely damaged, raising concerns about the collapse margin of these structures. Modifications to the Chilean codes were introduced after this earthquake, but Chilean codes are still prescriptive and assessments of the collapse risk of current Chilean buildings is limited. This study evaluates the collapse potential of a code-conforming reinforced concrete office building in Santiago, Chile, whose structural system has a core of two cantilever C-shaped walls surrounded by intermediate moment frames. The architectural layout was designed based on a statistical analysis of the building inventory in Santiago. Incremental dynamic analyses using 45 Chilean earthquakes were performed over a nonlinear model of the building to estimate its collapse fragility, which was combined with a site specific seismic hazard analysis to estimate the mean annual frequency of collapse (γc), and the probability of collapse in 50 years (Pc(50)). Results of γc and Pc(50) were 1.2x10-4 and 0.6%, respectively, and deaggregation of γc is dominated by small to medium earthquake intensities.
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    Correlations of spectral accelerations in the Chilean subduction zone
    (2020) Candia, G.; Poulos Campbell, Alan John; Llera Martin, Juan Carlos de la; Crempien de la Carrera, Jorge Gustavo Federico; Macedo, J.
    The correlation between spectral accelerations is key in the construction of conditional mean spectra, the computation of vector-valued seismic hazard, and the assessment of seismic risk of spatially distributed systems, among other applications. Spectral correlations are highly dependent on the earthquake database used, and thus, region-specific correlation models have been developed mainly for earthquakes in western United States, Europe, Middle East, and Japan. Correlation models based on global data sets for crustal and subduction zones have also become available, but there is no consensus about their applicability on a specific region. This study proposes a new correlation model for 5% damped spectral accelerations and peak ground velocity in the Chilean subduction zone. The correlations obtained were generally higher than those observed from shallow crustal earthquakes and subduction zones such as Japan and Taiwan. The study provides two illustrative applications of the correlation model: (1) computation of conditional spectra for a firm soil site located in Santiago, Chile and (2) computation of bivariate hazard for spectral accelerations at two structural periods.
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    Earthquake response sensitivity of complex infrastructure networks
    (2020) Llera Martin, Juan Carlos de la; Monsalve, Mauricio; Ferrario, Elisa; Allen, E.; Chamorro, A.; Castro, S.; Alberto, Yolanda; Arróspide, Felipe; Poulos, Alan; Candia, G.; Aguirre, P.
    Resilience of complex infrastructure networks is critical in achieving earthquake resilience in urban environments. Perhaps due to their modeling complexity, very few research studies have addressed sensitivity of the network response to a severe earthquake hazard field. This research aims to characterize earthquake response sensitivity as a function of different topological parameters of 5 critical complex networks in central Chile, covering the electric, transportation, and drinking water networks. Central Chile was selected because it amounts for almost 50% of the country’s population. What is also particular about this setting, is that the seismic characteristics of the region lead to extended (essentially) N-S strike fault ruptures, which run along the subduction margin defined by the E-W convergence between the South American and Pacific Ocean plates at an unusual rate of about 68 mm/year, thus involving in the strong-motion hazard field geographic scales in the hundreds of kilometers. It is concluded that node and link topological structures differ considerably between these complex systems, which are characterized by several different well-known centrality parameters and other interesting indices and network-class discriminators. Secondly, a component criticality analysis under an earthquake hazard field is also presented just in terms of connectivity/service loss, which enables, at least, a rough identification of the robustness of each network as nodes and links are removed. Results from these topological analyses are useful to identify which components are essential in generating larger earthquake resilience. This is the first time such results are obtained for central Chile using very detailed models of these complex networks
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    Machine learning techniques for estimating seismic site amplification in the Santiago basin, Chile
    (2022) Diaz, J. P.; Saez, E.; Monsalve, M.; Candia, G.; Aron, F.; Gonzalez, G.
    Seismic site amplification and seismic hazard maps are crucial inputs for decision making and risk evaluation in places where seismicity imposes a significant risk to human life and infrastructure. In this work, we propose a novel machine learning (ML) based methodology to integrate qualitative and quantitative data to map the degree of seismic amplification in an area of Chile, one of the most seismically active countries on Earth. Our method uses measurements of surface shear wave velocities (Vs30) and predominant frequencies (f0) combined with gravity anomaly maps to update the geographic extension of seismic amplification classes. Additionally, we trained the predictive models to interpolate and extrapolate Vs30 and f0 to the unsampled sites. Applying this method to the Santiago basin resulted in (i) a refined seismic amplification map, and (ii) maps of Vs30 and f0 estimated with improved accuracy. The best predictions, obtained by ML techniques and validated through crossvalidation, are possibly due to the inclusion of spatial covariates for algorithm training, enhancing the ability of the model to capture the spatial correlations of geological, geophysical and geotechnical data. The estimation of predominant frequencies (f0) is improved considerably by including gravity as a covariant. The accuracy of the f0 predictions apparently depends more on the choice of covariates than on the algorithm used, while the Vs30 predictions are more sensitive to the chosen algorithm. These results illustrate the great potential of machine learning predictive algorithms in digital soil mapping, which surpass traditional geostatistical techniques. The major contribution of this work is to introduce a novel methodology, based on artificial intelligence models, to extend local measurements of site-specific dynamic properties. This information can be used to quantitatively estimate seismic hazard over a regional scale.
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    Modelling of earthquake-induced pounding between adjacent structures with a non-smooth contact dynamics method
    (2021) Llera Martin, Juan Carlos de la; Langlade, T.; Bertrand, D.; Grange, S.; Candia, G.
    This article presents the kinematic analysis of two adjacent structures with pounding using the framework of finite element dynamic analysis and a non-smooth contact dynamics (NSCD) method for treating contact-impact. The latter consists of a Moreau-Jean implicit integration scheme that uses Moreau's sweeping process and Newton's impact law. Test cases are carried out to prove the efficiency of the implementation and accuracy of the results relative to the widely used penalty method (PM). Furthermore, finite element simulations are compared with shaking table results of two structures susceptible to pounding. Models are steel frames 2.5 m to 5 m high, 3 m in span, have reinforced-concrete slabs, and distant 0 to 5 cm. Floor displacements, number and time of occurrence of impacts, as well as shape of the response spectra are in good agreement with experimental observations. Moreover, using the building pounding frame and the NSCD method, an estimation of a constant value for the coefficient of restitution was carried out. It is concluded that the NSCD method is a very numerically efficient tool in terms of reduction of CPU time and description of the impact physics. Consequently, this approach is amenable for fragility analysis of the dynamic response of structures involving a contact-impact phenomenon