Browsing by Author "Bazáez, Ramiro"

Now showing 1 - 7 of 7
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    33
    (33, 33) Aldea, Sofía; Bazáez, Ramiro; Heresi, Pablo; Astroza, Rodrigo; 33
    Bridges are one of the most critical and costly structures on road networks. Thus, their integrity and operation must be preserved to prevent safety concerns and connectivity losses after seismic events. Recent large-magnitude earthquakes have revealed a series of vulnerabilities in multi-span highway bridges. In particular, skewed bridges have been severely damaged due to their susceptibility to developing excessive in-plane deck rotations and span unseating. Although seismic design codes have been updated to prescribe larger seating lengths and have incorporated unseating prevention devices, such as shear keys and cable restrainers, research on the seismic performance of skewed bridges with passive energy-dissipation devices is still limited. Therefore, this study focuses on assessing the effectiveness of implementing hysteretic dampers on skewed bridges. With that aim, dampers with and without recentering capabilities are designed and incorporated in representative Chilean skewed bridges to assess their contribution to seismic performance. Three-dimensional nonlinear finite element models, multiple-stripe analysis, and fragility curves are utilized to achieve this objective. The results show that incorporating bidirectional dampers can effectively improve the seismic performance of skewed bridges at different hazard levels by limiting in-plane deck rotations independently of their skew angle. Additionally, the influence of external shear keys and damper hysteretic behavior is analyzed, showing that these parameters have a low influence on bridge performance when bidirectional dampers are incorporated.
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    33
    (33, 33) Birrell, Matías; Astroza, Rodrigo; Murcia-Delso, Juan; Hernández, Francisco; Bazáez, Ramiro; 33
    This paper proposes a simplified tri-linear model for the lateral force-displacement relationship of monolithic exterior shear keys in reinforced concrete bridges, failing in sliding shear. To allow for implementation compatibility with a widely used simplified model for shear keys failing in diagonal tension (DT), this model is presented in a tri-linear formulation that builds on past experimental data and expressions for the capacity of shear keys. Capacity points are adapted from previously published work on sliding shear (SS) and sliding friction (SF) failing shear keys, and displacement points are devised around available experimental data and numerical studies. These consider the effective stiffness of concrete members, dowel action in vertical steel reinforcement, and empirical observations from monolithic shear key tests. Model parameters are probabilistically characterized in a Bayesian parameter estimation framework, to incorporate experimental data. The calibrated expressions are then validated by comparing sampled predictions to experimental observations, and finally a single distribution for model parameters is suggested. The goal of this model is to provide a simplified formulation to be implemented alongside DT failure in time-history response simulations of structure-level finite element models of bridges, thus covering both major failure mechanisms in monolithic reinforced concrete shear keys.
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    (33, 33) Pinto, Francisco J.; Toledo, José; Birrell, Matías; Bazáez, Ramiro; Hernández, Francisco; Astroza, Rodrigo; 33
    Bridges are essential structures in the logistic chain of countries, making it critical to design them to be as resilient as possible. One way to achieve this is through performance-based seismic design (PBSD), which involves using nonlinear Finite Element (FE) models to predict the response and potential damage of different structural components under earthquake excitations. Nonlinear FE models need accurate constitutive models of material and components. Among them, seismic bars and laminated elastomeric bearings play an important role in a bridge’s response to earthquakes; therefore, properly validated and calibrated models should be proposed. Only default parameter values from the early development of the constitutive models widely used by researchers and practitioners for these components tend to be used, and low identifiability of its governing parameters and the high cost of generating reliable experimental data have prevented a thorough probabilistic characterization of their model parameters. To address this issue, this study implements a Bayesian probabilistic framework using Sequential Monte Carlo (SMC) for updating the parameters of constitutive models of seismic bars and elastomeric bearings and proposes joint probability density functions (PDF) for the most influential parameters. The framework is based on actual data from comprehensive experimental campaigns. The PDFs are obtained from independent tests conducted on different seismic bars and elastomeric bearings, to then consolidate all the information in a single PDF for each modeling parameter by means of the conflation methodology, where the mean, coefficient of variation, and correlation between calibrated parameters are obtained for each bridge component. Finally, findings show that the incorporation of model parameter uncertainty through a probabilistic framework will allow for a more accurate prediction of the response of bridges under strong earthquakes.
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    (33, 33) Pinto, Francisco; Astroza, Rodrigo; Bazáez, Ramiro; Hernández, Francisco; Navarro, Nibaldo; 33
    Deterioration mechanisms, such as chloride-induced corrosion, affect bridges in aggressive environments, making them more vulnerable to extreme events like earthquakes. Although many studies have assessed the impact of chloride-induced corrosion on the seismic vulnerability of reinforced concrete (RC) highway bridges, several gaps still need to be addressed. Accordingly, this research primarily focuses on evaluating the seismic performance of RC highway bridges in aggressive environments susceptible to chloride-induced corrosion and earthquakes. To achieve this, a probabilistic framework is employed, which incorporates uncertainties associated with corrosion progression, seismic events, and the impact of different modeling approaches for boundary condition. The framework considers the time-dependent effects of corrosion on the physical and material properties of steel and concrete in bridge columns. Monte Carlo Simulations (MCS), probabilistic seismic hazard analysis (PSHA), and record selection strategies are utilized to address the uncertainties in corrosion and seismic demand. Nonlinear dynamic models and multiple stripe analysis (MSA) are employed to obtain fragility surfaces and curves for main bridge components and the entire system under different boundary conditions. The study focuses on a five-span highway bridge with simply-supported prestressed concrete I-girder and RC multi-column bents located in Chile. The results reveal that elastomeric bearings are the most vulnerable components, exhibiting varying vulnerability levels under different corrosion exposure and boundary conditions. Abutments, although the second most susceptible, are unaffected by corrosion uncertainty in terms of seismic fragility. Bridge columns are identified as the third most vulnerable components, with the probability of exceeding slight damage state consistently increasing with more prolonged corrosion exposure. It is noted that only flexure failure mode in column is analyzed and possible shifting to shear or flexure-shear modes is not accounted for. The findings of this study underscore the exceptional resilience of Chilean highway bridge columns to seismic demand and corrosion uncertainties, contrasting with the situation in US regions where columns are more vunerable. Additionally, the study indicates that Soil-Structure Interaction (SSI) tends to reduce bridge vulnerability under combined corrosion and earthquake effects. The insights obtained from this study and the proposed framework can inform the development of maintenance programs based on bridge performance expectations and enhance the seismic resilience of bridge systems worldwide.
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    (33, 33) Pinto, Francisco; Astroza, Rodrigo; Pizarro, Alonso; Bazáez, Ramiro; Hernández, Francisco; 33
    Bridges are vital infrastructures but face compounding risks from scouring and seismic events. Although recent studies have explored these individual and overlapping hazards, they often utilize deterministic approaches and focus on specific bridge types in limited geographical areas. This study addresses these gaps by introducing a probabilistic framework for assessing the seismic performance of multi-span reinforced concrete (RC) highway bridges in the presence of scour-related uncertainties. A time-dependent scour model, informed by a Bayesian approach and literature-based uncertainties, is integrated into the framework. Probabilistic Seismic Hazard Analysis (PSHA) and record selection strategies are employed to define the seismic demand probabilistically. Monte Carlo simulation (MCS) is utilized to propagate combined uncertainties during the analysis, considering different scour scenarios defined according to the discharge peak condition of the flood event at the specific location of the bridge. In the last step of the probabilistic framework, fragility analyses are conducted on individual components and the entire system by means of nonlinear dynamic models and multiple stripe analysis (MSA). An actual five-span bridge with simply supported prestressed concrete girders, located in Chile, is used as application example of the proposed approach, considering measured hydrological data and seismic hazard of the real location of the bridge. The study identifies distinct vulnerabilities across various bridge components under scour conditions. Elastomeric bearings are particularly susceptible in scenarios characterized by low scour depths (low discharge peak condition). Conversely, abutments display heightened vulnerabilities as scour depth increases (medium discharge peak condition). Piles also exhibit notable vulnerability, escalating in scenarios with great scour depth (medium discharge peak condition). Notably, piles tend to be more susceptible than columns to scour effects, especially in bents featuring shorter columns. These disparities in vulnerability are influenced by the bridge design philosophy, as well as the synergistic effects of seismic forces and varying scour depths. System fragility curves further elucidate that the likelihood of exceeding specific damage thresholds varies according to different scour scenarios, with the deeper scour depth scenario, displaying the higher vulnerabilities.
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    Bayesian inference for calibration and validation of uniaxial reinforcing steel models
    Birrell, Matias; Astroza, Rodrigo; Restrepo, José I.; Loftizadeh, Koorosh; Carreño, Rodrigo; Bazáez, Ramiro; Hernández, Francisco
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    Cyclic Behavior of U-Shaped Flexural Plates for Their Implementation in Multidirectional Energy Dissipation Devices
    González, Jorge; Barriuso, Fernando; Bazáez, Ramiro; Pérez, Luis; Lara-Rodríguez, Gabriel; Astroza, Rodrigo; Heresi, Pablo