DSpace Repository :: Browsing by Author "Candia, Gabriel"

Browsing by Author "Candia, Gabriel"

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A Consistently Processed Strong-Motion Database for Chilean Earthquakes
(2022) Castro, Sebastián; Benavente, Roberto; Crempien, Jorge G.F.; Candia, Gabriel; Llera, Juan Carlos de la
Since the 1985 M 8.0 central Chile earthquake, national strong‐motion seismic networks have recorded ten megathrust earthquakes with magnitudes greater than M 7.5 at the convergent margin, defined by the contact between the Nazca and South American plates. The analysis of these earthquake records have led to improved hazard analyses and design codes for conventional and seismically protected structures. Although strong‐motion baseline correction is required for a meaningful interpretation of these records, correction methods have not been applied consistently in time. The inconsistencies between correction methods have been neglected in the practical use of these records in practice. Consequently, this work aims to provide a new strong‐motion database for researchers and engineers, which has been processed by traceable and consistent data processing techniques. The record database comes from three uncorrected strong motion Chilean databases. All the records are corrected using a four‐step novel methodology, which detects the P‐wave arrival and introduces a baseline correction based on the reversible‐jump Markov chain Monte Carlo method. The resulting strong motion database has more than 2000 events from 1985 to the date, and it is available to download at the Simulation Based Earthquake Risk and Resilience of Interdependent Systems and Networks (SIBER‐RISK) project website.
A framework to account for structural damage, functional efficiency and reparation costs within the optimal design of countermeasures: Application to snow avalanche risk mitigation
(2022) Favier, Philomène; Eckert, Nicolás; Faug, Thierry; Bertrand, David; Ousset, Isabelle; Candia, Gabriel; Llera, Juan Carlos de la
In mountain areas, long-term snow avalanche risk evaluation is of paramount importance for land use planning. In avalanche-prone areas, when real estate demand is high, for instance, building protective structures may be a sensible choice for reaching a compromise between safety and development. Specifically, minimizing the risk within a quantitative framework can provide optimal defense structure configurations (size, localization, construction technology, etc.). However, existing approaches based on a proper theoretical decision-making framework still suffer from limitations making them hardly usable in practice. It is herein proposed to account for the physical, functional, and monetary dimensions of a protective measure within the assessment of total risk. Total risk, which is calculated as the mean expected loss, is quantified within a four-state system in which the failure of the dam and the failure of the dwellings to be protected are assessed with specific vulnerability relations. Bounds for the risk and subsequent optimal dam design values are quantified using minimum and maximum (min/max) functional efficiency relations of the dam. Additional assumptions regarding the functional-structural efficiency relation allow for the optimal design and corresponding minimum risk to be reached. An application is proposed with a case study from the French Alps. A comprehensive parametric study shows that the min/max bounds risk quantification is worth implementing in some cases, such as, for instance: if there is a high uncertainty of the functional efficiency of the dam, of if the assets to be protected have a monetary value. However, when the failure of the dam is unlikely to occur (due to its location or to its material resistance), it is shown that quantification of the intermediate risk without the min/max bounds approach is sufficient. In the future, the framework could be extended to many other mountain hazards (debris flows, landslides, etc.), more complex elements at risk, and even to problems going beyond the sole question of land-use planning such as traffic road regulation.
A New State-of-the-Art Platform for Probabilistic and Deterministic Seismic Hazard Assessment
(2019) Candia, Gabriel; Macedo, Jorge; Jaimes, Miguel A.; Magna-Verdugo, Carolina
A new computational platform for seismic hazard assessment is presented. The platform, named SeismicHazard, allows characterizing the intensity, uncertainty, and likelihood of ground motions from subduction-zone (shallow interface and intraslab) and crustal-zone earthquakes, considering site-specific as well as regional-based assessments. The platform is developed as an object-oriented MATLAB graphical user interface, and it features several state-of-the-art capabilities for probabilistic and deterministic (scenario-based) seismic hazard assessment. The platform integrates the latest developments in performancebased earthquake engineering for seismic hazard assessment, including seismic zonation models, ground-motion models (GMMs), ground-motion correlation structures, and the estimation of design spectra (uniform hazard spectra, classical conditional mean spectrum (CMS) for a unique tectonic setting). In addition to these standard capabilities, the platform supports advanced features, not commonly found in existing seismic hazard codes, such as (a) computation of source parameters from earthquake catalogs, (b) vector-probabilistic seismic hazard assessment, (c) hazard evaluation based on conditional GMMs and user-defined GMMs, (d) uncertainty treatment in the median ground motions through continuous GMM distributions, (e) regional shaking fields, and (f ) estimation of CMS considering multiple GMMs and multiple tectonic settings. The results from the platform have been validated against accepted and well-documented benchmark solutions.
Assessment of fragility models based on the Sept 19th, 2017 earthquake observed damage
(2019) Román de la Sancha, A.; Mayoral, J.M.; Hutchinson, T.C.; Candia, Gabriel; Montgomery, J.
Seismic vulnerability evaluations of buildings and critical infrastructure in densely populated cities strongly rely on fragility curves to estimate the probability of reaching or exceeding a given state of damage. Currently, however, the predicting capabilities of these models is limited. This paper presents a critical study of the accuracy of fragility curves for buildings, urban bridges, tunnels, overpasses, main roads, avenues and metro stations, aiming at establishing its advantages and shortcomings, when using them in seismic vulnerability and resilience assessments. Data gathered from one of the most damage areas during the 7.1 Mw September Mexico-Puebla 2017 earthquake was used in this study. Measured peak ground accelerations, PGA, and permanent ground deformations, PGD, along with appropriate fragility curves were used to establish the probability of having minor, moderate, large damage or collapse of buildings and critical infrastructure components. The damage on the study area documented during field reconnaissance was compared to that which would have been predicted using the fragility curves. Although in some cases, there was a good agreement between predicted and observed damage, overall it was clearly identified the need for developing fragility models that account for soilstructure interaction, and specific structural and ground conditions, to ensure a more reliable risk characterization of the City building stock and infrastructure during an earthquake.
Collapse risk assessment of a Chilean dual wall-frame reinforced concrete office building
(2019) Araya-Letelier, G.; Parra, P.F.; Lopez-Garcia, D.; Garcia-Valdes, A.; Candia, Gabriel; Lagos, R.
Several code-conforming reinforced concrete buildings were severely damaged during the 2010 moment magnitude (Mw) 8.8 Chile earthquake, raising concerns about their real collapse margin. Although critical updates were introduced into the Chilean design codes after 2010, guidelines for collapse risk assessment of Chilean buildings remain insufficient. This study evaluates the collapse potential of a typical dual system (shear walls and moment frames) office building in Santiago. Collapse fragility functions were obtained through incremental dynamic analyses using a state-of-the-art finite element model of the building. Site-specific seismic hazard curves were developed, which explicitly incorporated epistemic uncertainty, and combined with the collapse fragility functions to estimate the mean annual frequency of collapse (λc) values and probabilities of collapse in 50-years (Pc(50)). Computed values of λc and Pc(50) were on the order of 10−5–10−4, and 0.1–0.7%, respectively, consistent with similar studies developed for buildings in the US. The results also showed that the deaggregation of λc was controlled by small to medium earthquake intensities and that different models of the collapse fragility functions and hazard curves had a non-negligible effect on λc and Pc(50), and thus, propagation of uncertainty in risk assessment problems must be adequately taken into account.
Correlations of spectral accelerations in the Chilean subduction zone
(2020) Candia, Gabriel; Poulos, Alan; Llera, Juan Carlos de la; Crempien, Jorge G.F.; Macedo, Jorge
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.
Cost-Benefit Analysis of Seismic Mitigation Measures for Wine Barrel Stacks
(2017) Jaimes, Miguel A.; Candia, Gabriel; Favier, Philomène
This study conducts a cost-benefit analysis of alternative seismic risk mitigation methods for wine barrel stacks. The Chilean wine industry is presented as an illustrative case study, in which performance metrics such as the expected annual loss and benefit-cost ratios are computed for wineries at different locations. By computing seismic risk within a consistent framework, this study shows the value of cost-benefit simulations for defining the best mitigation strategies and allocating economic resources. Likewise, this approach helps to communicate information to decision-makers because it is presented in a simple and transparent way, even if they are not familiar with formal risk studies. For 3-level wine barrel stacks, it was observed that the Cradle Extender® (MS1) prevents a large number of barrel collapses and provides the highest benefit-cost ratio. On the other hand, for 6-level wine barrel stacks, the pre-stressed cable (MS2) is more effective than MS1 as it prevents the barrel stack from overturning. No significant reduction of loss is apparent in 4 and 5-level wine barrel stacks with the use of mitigation strategies; indeed the mitigation strategies could generate greater losses and, therefore, other alternatives must be
Demanda sísmica en túneles superficiales en depósitos de suelo
(Universidad del Desarrollo. Facultad de Ingeniería, 2022) Gutiérrez Vega, Carlos Alfonso; Candia, Gabriel
Los túneles de metro son estructuras críticas en las redes de transporte, las cuales pueden resultar gravemente dañadas durante un terremoto producto del colapso o deformaciones del terreno. Por lo cual, una correcta evaluación de la demanda sísmica en túneles superficiales en depósitos de suelo es crucial. Para realizar esta evaluación, la presente investigación se desarrolló considerando dos objetivos principales: (i) caracterizar la demanda sísmica en túneles circulares emplazados en ambientes de subducción y (ii) desarrollar un modelo predictivo para determinar deformaciones horizontales en el túnel. Para alcanzar estos objetivos, se implementó un modelo de elementos finitos para evaluar la respuesta sísmica un túnel circular de hormigón de 6 m de diámetro, a profundidades de clave de 12 m y 24 m. Ambas unidades se encuentran emplazadas en un depósito de arena fina de 140 m de ancho y 60 m de profundidad, modelados por medio de elementos finitos (2D) en el software de código abierto OpenSees®. Para modelar el comportamiento histerético de la arena se utilizó el modelo PressureDepenMultiYield (PDMY), considerando tres densidades relativas (𝐷𝑟) para el estudio del depósito de suelo (55%, 65% y 75%). Los modelos numéricos anteriormente descritos fueron rigurosamente validados y calibrados en función de un modelo de elementos finitos de prueba que reproduce los ensayos en centrifuga geotécnica estudiados por Lanzano et al., 2012. Adicionalmente, para la correcta validación de los parámetros del modelo PDMY, se realizó una prueba de respuesta de un elemento a corte simple y una prueba de respuesta de una columna de suelo en campo libre. Por otro lado, se evaluó la demanda sísmica considerando que las unidades de estudio se encuentran emplazadas en la ciudad de Santiago de Chile, y la selección de registros de aceleración se realizó por medio de la metodología Conditional Scenario Spectra o CSS (Abrahamson & Yunatci, 2010; Arteta & Abrahamson, 2019). El desarrollo de esta metodología permitió seleccionar un conjunto de 𝑛𝐶𝑆𝑆 =122 registros de aceleración con sus correspondientes tasas de excedencia y factores de escala. Los resultados de los modelos numéricos se presentaron en función de cuatro parámetros de diseño de ingeniería (EDPs) de interés: (i) Cargas axiales máximas (N), momentos flectores en el revestimiento del túnel (M), razones de drift (∆) y asentamiento sobre el eje central del túnel (𝛿𝑧). Posteriormente y por medio de la metodología CSS, se generaron curvas de demanda sísmica (SDHC) considerando tasas de excedencia entre los 10−4 y 10−1 eventos/año, lo que permitió comprender la influencia de la profundidad del túnel y las densidades de suelo para el diseño de ingeniería de este tipo de estructuras. Finalmente, se propone una ley de atenuación para determinar deformaciones máximas (𝛾𝑚𝑎𝑥) de un depósito de suelo en condiciones de campo libre, considerando parámetros clave como la altura del depósito de suelo, su periodo fundamental y la velocidad máxima del suelo ante un evento sísmico.
Evaluación de Riesgo Sísmico de Túneles Circulares en Depósitos de Suelo
(Universidad del Desarrollo. Facultad de Ingeniería, 2019) Lyon, Benjamín; Candia, Gabriel
Los túneles urbanos son un componente importante de los sistemas de transporte modernos y transportan diariamente a millones de personas. Por este motivo, es esencial que su diseño incorpore los efectos de un evento sísmico severo y que este satisfaga los criterios de serviciabilidad e integridad estructural. En general, los túneles sufren menores niveles de daño que las estructuras superficiales, sin embargo, terremotos recientes (e.g., Niigataken-Chuetsu 2004, o Düzce 1999) han causado daños estructurales de consideración. Debido a la incertidumbre que aún persiste en la evaluación de la respuesta sísmica de túneles, y a la luz de los últimos estudios experimentales, esta investigación tiene como objetivo el desarrollo de curvas de fragilidad y riesgo con la finalidad de aportar información relevante para los tomadores de decisiones acerca de la respuesta sísmica de túneles. Como caso estudio se consideró un túnel circular de 6 m de diámetro en un depósito de arena seca media densa y a 12 m de profundidad. Se desarrolló un modelo de elementos finitos en OpenSees R considerando una ley constitutiva no-lineal para la arena y elementos lineales para el túnel; el modelo numérico fue validado con los resultados de un ensayo centrífuga y con un análisis lineal equivalente 1D de una columna de suelo en campo libre. El modelo numérico reproduce correctamente la rigidez y amortiguamiento del suelo, y la propagación de ondas en el depósito. Asimismo, el modelo numérico reproduce la distribución de esfuerzos internos en el túnel que predice la teoría de elasticidad. Se evaluó la respuesta sísmica del túnel usando 285 registros sísmicos de terremotos corticales escalados a valores de PGA entre 0.08 g y 4.92 g y se desarrollaron funciones de fragilidad para distintos parámetros de respuesta. Los resultados indican que la respuesta media del túnel (e.g., esfuerzos internos, aceleraciones máximas, drifts, deformación diametral, etc.) varía linealmente con tres medidas de intensidad analizadas. Se evaluó el riesgo sísmico para un túnel hipotético ubicado en Oakland, CA; los resultados muestran que la deformación de corte en el suelo y el drift en el túnel son comparables para periodos de retorno Tr < 2475 años, lo cual permite para este caso el uso del método simplificado de campo libre. Asimismo, las deformaciones diametrales en el túnel para periodos de retorno de 1000 y 2475 años son consistentes con los valores estimados según el procedimiento simplificado de AASHTO-2010 para un túnel en suelo tipo D. La presente investigación incorpora el estado del arte en el cálculo del riesgo sísmico compatible con las metodologías de diseño basado en desempeño, y la metodología empleada permite estimar riesgo para distintas configuraciones de túneles y en otras regiones sísmicas.
Evaluación sísmica de desplazamientos permanentes para deslizamientos de taludes en roca : metodología para la obtención de curvas de fragilidad y riesgo de desplazamiento
(Universidad del Desarrollo. Facultad de Ingeniería, 2018) Allendes Aránguiz, Diego Antonio; Candia, Gabriel
Experimental modeling of seismic earth pressures on retaining walls
(Soil Dynamics and Earthquake Engineering, 21/09/2016) Candia, Gabriel; Mikola, R.; Sitar, Nicholas
Geotechnical Aspects of the 20115 M-w 8.3 Illapel Megathrust Earthquake Sequence in Chile
(01/05/2017) Candia, Gabriel; Pascale, Gregory de; Montalva, Gonzalo; Ledezma, Christian
The 2015 Illapel earthquake sequence in Central Chile, occurred along the subduction zone interface in a known seismic gap, with moment magnitudes of M-w 8.3, M-w 7.1, and M-w 7.6. The Main event triggered tsunami waves that damaged structures along the coast, while the surface ground motion induced localized liquefaction, settlement of bridge abutments, rockfall, debris flow, and collapse in several adobe structures. Because of the strict seismic codes in Chile, damage to modern engineered infrastructure was limited, although there was widespread tsunami-induced damage to one-story and two-stories residential homes adjacent to the shoreline. Soon after the earthquake, shear wave measurements were performed at selected potentially liquefiable sites to test recent Vs-based liquefaction susceptibility approaches. This paper describes the effects that this earthquake sequence and tsunami had on a number of retaining structures, bridge abutments, and cuts along Chile's main highway (Route 5). Since tsunami waves redistribute coastal and near shore sand along the coast, liquefaction evidence in coastal zones with tsunami waves is sometimes obscured within minutes because the tsunami waves entrain and deposit sand that covers or erodes evidence of liquefaction (e.g., lateral spread or sand blows). This suggests that liquefaction occurrence and hazard may be under estimated in coastal zones. Importantly, the areas that experienced the greatest coseismic slip, appeared to have the largest volumes of rockfall that impacted roads, which suggests that coseismic slip maps, generated immediately after the shaking stops, can provide a first order indication about where to expect damage during future major events.
Ground Motion Correlations from Recorded Mexican Intermediate-depth, Intraslab Earthquakes
(2021) Jaimes, Miguel A.; Candia, Gabriel; López-Castañeda, Alhelí; Macedo, Jorge
Predictive models to estimate correlation coefficients between peak ground acceleration, peak ground velocity, and spectral acceleration residuals for Mexican intermediate-depth, intraslab earthquakes recorded on rock sites are presented in this study. The models were developed for the total, between-events, and within-event residuals using a recent ground-motion prediction equation (GMPE) and an updated ground-motion database. The results support the use of region- and mechanism-specific correlation models for the subduction intraslab zone of Mexico. An example of the application of the proposed correlation coefficient models consisting in evaluating a conditional mean spectrum (CMS), based on the Mexican seismic design normative, is presented.
Interperiod correlation model for Mexican interface earthquakes
(2019) Jaimes, Miguel A.; Candia, Gabriel
This article presents a correlation model for pseudo-acceleration, peak ground acceleration, and peak ground velocity residuals using a database of Mexican subduction interface earthquakes at rock sites (NEHRP Class B). A mixed-effect regression model, a ground motion model, and 40 event recordings (418 records) with moment magnitude between five and eight were used to develop a magnitude-independent correlation model. This region-specific model yields consistently higher correlation values compared with similar studies developed for shallow crustal regions and other subduction zones worldwide, particularly for pseudo-acceleration values at distant periods. These results support the idea of using a region-specific and mechanism-specific correlation model for Mexico’s subduction zone.
Machine learning techniques for estimating seismic site amplification in the Santiago basin, Chile
(2022) Díaz, J.P.; Sáez, E.; Monsalve, M.; Candia, Gabriel; Aron, F.; González, 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 cross-validation, 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.
Modelling of earthquake-induced pounding between adjacent structures with a non-smooth contact dynamics method
(2021) Langlade, T.; Bertrand, D.; Grange, S.; Candia, Gabriel; de la Llera, Juan Carlos
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
New developments for the performance-based assessment of seismically-induced slope displacements
(2020-11) Macedo, Jorge; Candia, Gabriel; Lacour, Maxime; Liu, Chenying
This study presents new developments for the performance-based assessment of seismically-induced slope displacements (D). Performance-based procedures enable a hazard-consistent and rational seismic design of slope systems; hence, their use in practice is appealing. However, they are not the standard in engineering practice because their use is considered too complex to be used for non-critical projects. The developments presented in this study allow the straightforward estimation of displacement hazard curves (DHC) for a wide range of slope systems subjected to earthquakes in different tectonic settings (i.e., shallow crustal, and subduction), considering a rigorous quantification of the existing uncertainties. The new developments include 1) full integration of probabilistic seismic hazard assessments (PSHA), and the estimation of DHCs, 2) automatic estimation of DHC for D models with multiple intensity measures through vector PSHA, 3) estimation of DHC for systems with contributions from multiple tectonic settings, 4) uncertainty treatment (i.e., epistemic and aleatory) on DHCs, through a logic tree scheme, 5) deaggregation of earthquake scenarios from DHCs, and 6) uncertainty quantification on DHCs through the polynomial chaos theory. The new developments are implemented in a MATLAB graphical user interface (GUI) to facilitate its use by engineers and researchers. We discuss illustrative examples and guidelines for the application of the GUI to evaluate the seismic performance of different slope systems that are affected by earthquakes from multiple tectonic settings.
Observed building damage patterns and foundation performance in Mexico City following the 2017 M7.1 Puebla-Mexico City earthquake
(2019) Franke, Kevin W.; Candia, Gabriel; Mayoral, J.M.; Wood, Clinton M.; Montgomery, Jack; Hutchinson, Tara; Morales-Velez, Alesandra C.
The September 19th, 2017 M7.1 Puebla-Mexico City earthquake introduced strong ground motions into the Mexico City basin, which contains very soft lacustrine soils, dense urban infrastructure, and millions of inhabitants. As a result, 38 mid-rise structures collapsed and several hundred more were damaged. This paper reports the observations related to building performance, damage patterns, and foundation performance made by the two UNAM-GEER engineering reconnaissance teams sent to investigate the geotechnical aspects of the earthquake. The methodology used to perform building damage mapping following the 2017 event is described. Comparisons are made between the observed building damage patterns following the September 19th, 1985 and the 2017 earthquake, and the distinct differences in the damage pattern distribution between the two earthquakes are summarized. Overall, building and foundation performance were observed to be quite good during the 2017 event, especially when compared to the 1985 event. Structures that were observed to be heavily damaged or collapsed were all built prior to 1985, and incorporated poor structural design and/or construction which resonated with the soil column on which they were constructed, and/or were built upon very soft soils that contributed to significant foundation deformations. Detailed building damage pattern maps of specific neighborhoods that were investigated are provided, and lessons learned from this event are summarized.
Performance-based analysis of Transit tunnels in the Chilean subduction zone
(2022) Lyon, Benjamín; Candia, Gabriel; Gutiérrez, Carlos; Macedo, Jorge
In this article, we study the seismic response of a shallow metro tunnel in a subduction zone environment and the use of a performance-based approach to develop seismic demand hazard curves (SDHC) of key engineering demand parameters, such as drift ratio, surface settlement, bending moment, and axial loads. The tunnel consists of a 6-m diameter sprayed concrete lining in medium dense soil and is located in Santiago, Chile. To simulate its seismic response, a finite element model of the soil–tunnel system was implemented in OpenSees and validated against centrifuge test results, linear-equivalent solutions for a 1D soil column, and single elements in cyclic simple shear. The tunnel response was computed for 112 ground motions, selected and scaled using the conditional scenario approach. This approach assigns a rate of occurrence to each ground motion and therefore, allows for a direct computation of annual exceedance rates of the tunnel response parameters. For instance, at this specific location, the 2500-yr return period drift ratio in the lining is approximately 0.25% as a result of large deformations imposed by the surrounding soil. Likewise, axial loads between 0.3 and 1.0 MN/m and vending moments of ±0.2 MN∙m/m are apparent from the axial load-moment interaction diagrams; these results are of great value for the design and verification of the tunnel based on the collapse or life-safety limit states. Notably, the current formulation relaxes the assumption of scaling ground motions to a particular intensity measure and can be a computationally efficient alternative to standard incremental dynamic analyses
Performance-based assessment of the seismic pseudo-static coefficient used in slope stability analysis
(2020) Macedo, Jorge; Candia, Gabriel
Pseudo-static slope stability procedures are often employed to evaluate the seismic performance of geotechnical slope systems, at least in the initial evaluation stages. To yield meaningful results, these methods should rely on parameters that are representative of the existing seismic demand and the properties of the geotechnical slope system being evaluated. This study proposes a performance-based probabilistic procedure to estimate the seismic pseudo-static coefficient (SPC) in a rational and transparent manner. The proposed procedure has its cornerstone on the evaluation of seismically-induced displacement (D) hazard curves, and it provides SPC estimations that are consistent with the allowable D level that a geotechnical structure can sustain, the properties of the sliding mass, and the seismic demand at the slope site. In addition, the calculated SPC can be directly associated with a return period or hazard design level for D. The proposed procedure can be applied to evaluate the seismic performance of a wide range of geotechnical slope systems potentially affected by earthquakes from different tectonic settings, such as subduction and shallow crustal earthquake zones (or a combination of both). The proposed procedure is implemented in a computational platform that facilitates its straightforward use in engineering practice. The implementations are fully automated for South America (i.e., Peru, Chile, Ecuador), Mexico, and the United States, but the proposed framework can be applied worldwide. Finally, an illustrative example for the application of the procedure in the seismic stability assessment of a slope system is provided.

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