4 research outputs found
Parametric Probabilistic Seismic Performance Assessment Framework for Ordinary Standard Bridges
This paper focuses on the assembly and implementation of a full-fledged parametric probabilistic seismic performance assessment framework for ordinary standard bridges (OSBs) in California. The framework stems from the performance-based earthquake engineering (PBEE) assessment methodology developed under the auspices of the Pacific Earthquake Engineering Research (PEER) Center. It involves a sequential execution of analytical steps to arrive at estimates of performance measures which, for example as considered in this study, are the mean return periods (MRPs) of exceedances for a selected set of limit-states (LSs). Improvements from state-of-the-art literature related to various stages of the PEER PBEE assessment framework are incorporated. This includes: (1) introduction of an improved intensity measure (IM), i.e., average spectral acceleration over a period range, for probabilistic seismic hazard analysis (PSHA), (2) conditional mean spectrum (CMS)-based site-specific risk-consistent ground motions selection for ensemble nonlinear time-history analyses involved in probabilistic seismic demand hazard analysis (PSDemHA), (3) introduction of material strain-based engineering demand parameters (EDPs), (4) identification of practical damage LSs, and (5) development of strain-based fragility functions required in probabilistic seismic damage hazard analysis (PSDamHA) for the considered LSs. Four distinct testbed OSBs are selected for the study. A two-dimensional design parameter space is defined in terms of typical primary design variables involved in seismic design of OSBs, i.e., the column diameter and the column longitudinal steel reinforcement ratio. Computational models of the as-designed bridges as well as their re-designs spawned by varying the primary design variables subject to practical constraints are assessed using the implemented framework. For each testbed OSB, and for each of the considered LSs, a smooth surface is fitted to the MRPs computed for all the re-designs of the bridge in the primary design parameter space. Topologies of these surfaces are explored. Feasible design domains in the two-dimensional design parameter space are identified. Safety of the as-designed version and feasibility domain for the re-designs of each testbed OSB are examined and discussed.Support of this research by the California Department of Transportation under Grant No. 65A0594, Task No. 2880 is gratefully acknowledged. Opinions and findings in this study are those of the authors and do not necessarily reflect the views of the sponsor
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Risk-targeted Performance-based Seismic Assessment and Design of Bridges
Driven by the necessity to meet changing public expectations in the wake of natural disasters, such as earthquakes, the structural engineering community has been moving towards rational, risk-informed, and transparent approaches to structural design, amidst which probabilistic performance-based seismic design (PBSD) has emerged as the most scientific and promising one. The main objective of this research is to formulate a simplified yet rigorous framework for risk-targeted PBSD of Ordinary Standard Bridges (OSBs), which, despite being simple bridges, constitute an integral part of lifeline infrastructure systems, especially in earthquake-prone regions such as California. A seismic performance assessment methodology integrating site-specific seismic hazard analysis, structural demand analysis, and damage analysis in a comprehensive and consistent probabilistic framework is computationally implemented as a modular tool unifying several state-of-the-art advancements related to the field. This tool is used for a parametric probabilistic performance assessment of four different testbed OSBs over a primary design parameter space to investigate the effects of varying key structural design parameters on targeted structural performance measures. Erratic performance levels exhibited by these real-world traditionally designed bridges, compared to expert-opinion-based target performance levels, expose the inconsistency and opacity of current (prescriptive) design principles that do not explicitly state, analyze, and design for risk-targeted performance objectives but implicitly expect them to be satisfied. A comprehensive risk-targeted simplified yet rigorous PBSD method is distilled out and proposed, and its efficacy is validated using four real-world bridges as cases in point. The framework is then enhanced by the inclusion and consistent propagation of pertinent sources of uncertainty (typically ignored in practice) to obtain a more complete picture of seismic performance, thereby leading to a more comprehensive, transparent, and reliable design of OSBs, facilitating effective and risk-informed decision-making in the face of uncertainty. It is believed that the adoption of the proposed PBSD methodology, although non-traditional in its format, will be highly beneficial in the medium to long term. This initial venture will also prove crucial in supporting and fostering future research work and innovative technological developments in bridge infrastructure engineering
Preparation of FeCo/Cu Core Shell Magnetic Nanoparticles
FeCo/Cu core shell structure with FeCo as a core andcopper as the shell has been successfully synthesized bydisplacement reaction. The morphology, grain size, lattice strain,and magnetic properties of all the samples were examined byusing transmission electron microscopy (TEM), X-ray diffraction(XRD), and vibrating sample magnetometer (VSM). Annealingtemperatures and its effect on magnetic properties of theFeCo/Cu core shell particles was investigated. A maximumcoercivity (Hc) of 398.84 Oe was recorded for the sample heattreated in magnetic field. The blocking temperatures (TB) andsquareness (Mr/Ms) of the sample gradually increased due to theinfluence of temperature and magnetic field