@article{vaishanav_bodda_gupta_2024, title={Computationally efficient approach for risk-informed decision making}, volume={167}, ISSN={["1878-4224"]}, DOI={10.1016/j.pnucene.2023.104983}, abstractNote={Probabilistic risk assessment (PRA) is used as an essential tool for risk-informed decision-making in the nuclear industry. The fault and event trees play a crucial role in PRA to estimate the probability of system failure based on the failure probabilities of components. The fault trees or event trees for an actual power plant unit can be fairly large in size with several different types of logic gates, interconnected events, dependent events, etc. A large fault tree can include hundreds of gates, basic events (BEs), multiple occurring events (MOEs), and dependent events. Complex connectivities can give rise to excessive computational demand and storage requirements for the analysis. Fault and event trees can be solved using the minimal cut-set approaches, or advanced quantification techniques such as Binary decision diagrams or Bayesian networks. However, these techniques can be computationally inefficient for larger fault trees and can run out of memory/storage space. This study focuses on developing and proposing a new approach for accurate estimation of the system-level risk while improving the computational efficiency significantly. More specifically, an attempt is made to reduce the complexity of the analysis of MOEs and dependent events in fault trees. The proposed algorithms in this study present a significant improvement over traditional approaches which makes it highly promising for additional development. The computational efficiency of the proposed approach over the traditional approach is illustrated for fault trees with a varying number of events and different types of logic gate connections.}, journal={PROGRESS IN NUCLEAR ENERGY}, author={Vaishanav, Pragya and Bodda, Saran Srikanth and Gupta, Abhinav}, year={2024}, month={Feb} }
 @article{wang_lee_nimawat_han_gupta_2024, title={Integrated 4D Design Change Management Model for Construction Projects}, volume={150}, ISSN={["1943-7862"]}, url={https://doi.org/10.1061/JCEMD4.COENG-14246}, DOI={10.1061/JCEMD4.COENG-14246}, number={5}, journal={JOURNAL OF CONSTRUCTION ENGINEERING AND MANAGEMENT}, author={Wang, Liannian and Lee, Joomyung and Nimawat, Jatin and Han, Kevin and Gupta, Abhinav}, year={2024}, month={May} }
 @misc{sandhu_bodda_gupta_2023, title={A Future with Machine Learning: Review of Condition Assessment of Structures and Mechanical Systems in Nuclear Facilities}, volume={16}, ISSN={["1996-1073"]}, DOI={10.3390/en16062628}, abstractNote={The nuclear industry is exploring applications of Artificial Intelligence (AI), including autonomous control and management of reactors and components. A condition assessment framework that utilizes AI and sensor data is an important part of such an autonomous control system. A nuclear power plant has various structures, systems, and components (SSCs) such as piping-equipment that carries coolant to the reactor. Piping systems can degrade over time because of flow-accelerated corrosion and erosion. Any cracks and leakages can cause loss of coolant accident (LOCA). The current industry standards for conducting maintenance of vital SSCs can be time and cost-intensive. AI can play a greater role in the condition assessment and can be extended to recognize concrete degradation (chloride-induced damage and alkali–silica reaction) before cracks develop. This paper reviews developments in condition assessment and AI applications of structural and mechanical systems. The applicability of existing techniques to nuclear systems is somewhat limited because its response requires characterization of high and low-frequency vibration modes, whereas previous studies focus on systems where a single vibration mode can define the degraded state. Data assimilation and storage is another challenging aspect of autonomous control. Advances in AI and data mining world can help to address these challenges.}, number={6}, journal={ENERGIES}, author={Sandhu, Harleen Kaur and Bodda, Saran Srikanth and Gupta, Abhinav}, year={2023}, month={Mar} }
 @article{sandhu_bodda_sauers_gupta_2023, title={Condition Monitoring of Nuclear Equipment-Piping Systems Subjected to Normal Operating Loads Using Deep Neural Networks}, volume={145}, ISSN={["1528-8978"]}, DOI={10.1115/1.4062462}, abstractNote={Abstract}, number={4}, journal={JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Sandhu, Harleen Kaur and Bodda, Saran Srikanth and Sauers, Serena and Gupta, Abhinav}, year={2023}, month={Aug} }
 @article{lee_gupta_proestos_2023, title={Performance-Based Characterization and Quantification of Uncertainty in Damage Plasticity Model for Seismic Fragility Assessment of Concrete Structures}, volume={9}, ISSN={2376-7642}, url={http://dx.doi.org/10.1061/AJRUA6.RUENG-913}, DOI={10.1061/AJRUA6.RUENG-913}, abstractNote={Seismic probabilistic risk assessment requires explicit consideration and quantification of all sources of uncertainty. Although uncertainties in earthquakes and basic material properties, such as nominal concrete compressive strength, strain at maximum stress, and modulus of elasticity of concrete, have been considered in some studies, uncertainties in parameters used to model the nonlinear behavior of concrete are often not considered. Recent recommendations in design standards have incorporated performance-based limit states in the design and risk assessment of nuclear power plants. These recommendations have implicitly mandated that the uncertainty in the nonlinear behavior of concrete needs to be characterized and quantified in accordance with different performance limit states. This study focused on nonlinear model parameters in the concrete damage plasticity model (CDPM) and their characterization in terms of material strength parameters. Furthermore, a performance-based characterization and quantification of uncertainties in nonlinear model parameters was also conducted. Data from existing experimental studies were used to study the uncertainties in CDPM and were used as a basis for the proposed quantification.}, number={1}, journal={ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Lee, Sangwoo and Gupta, Abhinav and Proestos, Giorgio T.}, year={2023}, month={Mar} }
 @article{sandhu_bodda_gupta_2023, title={Post-hazard condition assessment of nuclear piping-equipment systems: Novel approach to feature extraction and deep learning}, volume={201}, ISSN={["1879-3541"]}, DOI={10.1016/j.ijpvp.2022.104849}, abstractNote={Over the past decade, the use of artificial intelligence techniques in the field of health-monitoring has gained significant interest, especially for structures such as building and bridges. However, applications to industrial systems such as equipment-piping systems in nuclear plants have not been explored. In this paper, it is shown that the existing techniques developed for buildings and bridges cannot be extended directly to equipment-piping systems as the response of such systems is governed by multiple localized modes unlike that in buildings and bridges. This paper proposes a new approach that consists of three key aspects: (i) a novel vector of degradation-sensitive features extracted from measured data, (ii) using a deep Artificial Neural Network (ANN) for diagnosis of degradation location and degradation severity, and (iii) consideration of uncertainty in degradation severity when training the ANN. Degradation in piping-equipment systems can occur due to flow-accelerated erosion and corrosion. These locations can potentially exhibit damage such as localized yielding or initiation of cracking due to an external event such as an earthquake. Moreover, such locations can at times go undetected by current inspection techniques. Therefore, a robust framework is needed for detection of degradation after a seismic event. This manuscript proposes a proof-of-concept framework, which utilizes data collected from sensors to generate a deep ANN database for predicting degraded locations and severity in a piping-equipment system. Degradation severity is classified as minor, moderate, and severe. In the suggested methodology, a novel vector of degradation-sensitive features is extracted from the sensor data to train the ANN. A simple piping-equipment system is selected to demonstrate feature extraction as a means to simplify pattern recognition, explore the design and parameters of an ANN, and develop a sensor placement strategy. The effectiveness of the proposed framework is demonstrated on a realistic primary safety system of a two-loop nuclear reactor. It is shown that the proposed post-hazard condition assessment framework is able to detect degraded locations along with the severity levels, including minor degradation, with considerably higher accuracy.}, journal={INTERNATIONAL JOURNAL OF PRESSURE VESSELS AND PIPING}, author={Sandhu, Harleen Kaur and Bodda, Saran Srikanth and Gupta, Abhinav}, year={2023}, month={Feb} }
 @article{patel_gupta_kwon_2023, title={Rocking stiffness of electrical cabinets with tubular base in nuclear power plants}, volume={414}, ISSN={["1872-759X"]}, DOI={10.1016/j.nucengdes.2023.112603}, abstractNote={Safe operation of nuclear power plants during an earthquake requires continued operation of safety related electrical equipment as intended. Such equipment are mounted in electrical cabinets and are seismically qualified by using an in-cabinet response spectra (ICRS). Generation of ICRS requires a good understanding of the cabinet’s dynamic characteristics. Past studies have shown that the rotational stiffness associated with the cabinet base and the mounting arrangement plays a primary role in the dynamic behavior of the cabinet. This rotational stiffness is needed to evaluate and characterize the global rocking mode of cabinet vibration. Existing studies have developed formulations to calculate the rocking stiffness for a few mounting arrangements that are typically found in United States and some other western countries. However, existing formulations could not be applied to cabinets in South Korean nuclear plants due to the differences in cabinet mounting type. This study is focused on consideration of tubular mounting arrangement that is typically found in South Korean plants. First, closed-form formulations are developed using fundamental principles of mechanics for two separate cases of this mounting arrangement. Then, detailed nonlinear finite element (FE) analyses are conducted for different mounting arrangements corresponding to different properties and dimensions of the tubular base. The FE models are used to calibrate the proposed closed-form formulations for various different configurations and structural or geometrical properties of tubular members. The proposed formulations provide a simple and accurate estimation of cabinet rocking stiffness which otherwise is difficult to evaluate without a shake table test or a detailed finite element analysis.}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Patel, Parth and Gupta, Abhinav and Kwon, Yangsoo}, year={2023}, month={Dec} }
 @article{nie_bodda_sandhu_han_gupta_2022, title={Computer-Vision-Based Vibration Tracking Using a Digital Camera: A Sparse-Optical-Flow-Based Target Tracking Method}, volume={22}, ISSN={["1424-8220"]}, url={https://doi.org/10.3390/s22186869}, DOI={10.3390/s22186869}, abstractNote={Computer-vision-based target tracking is a technology applied to a wide range of research areas, including structural vibration monitoring. However, current target tracking methods suffer from noise in digital image processing. In this paper, a new target tracking method based on the sparse optical flow technique is introduced for improving the accuracy in tracking the target, especially when the target has a large displacement. The proposed method utilizes the Oriented FAST and Rotated BRIEF (ORB) technique which is based on FAST (Features from Accelerated Segment Test), a feature detector, and BRIEF (Binary Robust Independent Elementary Features), a binary descriptor. ORB maintains a variety of keypoints and combines the multi-level strategy with an optical flow algorithm to search the keypoints with a large motion vector for tracking. Then, an outlier removal method based on Hamming distance and interquartile range (IQR) score is introduced to minimize the error. The proposed target tracking method is verified through a lab experiment—a three-story shear building structure subjected to various harmonic excitations. It is compared with existing sparse-optical-flow-based target tracking methods and target tracking methods based on three other types of techniques, i.e., feature matching, dense optical flow, and template matching. The results show that the performance of target tracking is greatly improved through the use of a multi-level strategy and the proposed outlier removal method. The proposed sparse-optical-flow-based target tracking method achieves the best accuracy compared to other existing target tracking methods.}, number={18}, journal={SENSORS}, author={Nie, Guang-Yu and Bodda, Saran Srikanth and Sandhu, Harleen Kaur and Han, Kevin and Gupta, Abhinav}, year={2022}, month={Sep} }
 @article{crowder_lee_gupta_han_bodda_ritter_2022, title={Digital Engineering for Integrated Modeling and Simulation for Building-Piping Systems Through Interoperability Solutions}, ISSN={["1943-748X"]}, DOI={10.1080/00295639.2022.2055705}, abstractNote={Abstract Designing piping systems for nuclear power plants involves engineers from multiple disciplines (i.e., thermal hydraulics, mechanical engineering, and structural/seismic) and close coordination with the contractors who build the plant. Any design changes during construction need to be carefully communicated and managed with all stakeholders in order to assess risks associated with the design changes. To allow the quick assessment of building and piping design changes through a streamlined building-piping coupled analysis, this paper presents a novel interoperability solution that converts bidirectionally between building information models (BIMs) and pipe stress models. Any design changes during construction that are shown in an as-built BIM are automatically converted into a pipe stress model. Any further design changes due to building-piping interaction analyses are converted back to the BIM for the contractor and other designers to access the latest model. Two case studies are presented to illustrate the bidirectional conversion that allows an integrated coupled analysis of the building-piping system to account for their interactions.}, journal={NUCLEAR SCIENCE AND ENGINEERING}, author={Crowder, Nicholas and Lee, Joomyung and Gupta, Abhinav and Han, Kevin and Bodda, Saran and Ritter, Christopher}, year={2022}, month={May} }
 @article{lin_athe_rouxelin_avramova_gupta_youngblood_lane_dinh_2022, title={Digital-twin-based improvements to diagnosis, prognosis, strategy assessment, and discrepancy checking in a nearly autonomous management and control system}, volume={166}, ISSN={["1873-2100"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85115958204&partnerID=MN8TOARS}, DOI={10.1016/j.anucene.2021.108715}, abstractNote={The Nearly Autonomous Management and Control System (NAMAC) is a comprehensive control system that assists plant operations by furnishing control recommendations to operators in a broad class of situations. This study refines a NAMAC system for making reasonable recommendations during complex loss-of-flow scenarios with a validated Experimental Breeder Reactor II simulator, digital twins improved by machine-learning algorithms, a multi-attribute decision-making scheme, and a discrepancy checker for identifying unexpected recommendation effects. We assess the performance of each NAMAC component, while we demonstrate and evaluated the capability of NAMAC in a class of loss-of-flow scenarios.}, journal={ANNALS OF NUCLEAR ENERGY}, author={Lin, Linyu and Athe, Paridhi and Rouxelin, Pascal and Avramova, Maria and Gupta, Abhinav and Youngblood, Robert and Lane, Jeffrey and Dinh, Nam}, year={2022}, month={Feb} }
 @article{eidelpes_bolisetti_gupta_shafieezadeh_2022, title={Fission Battery transportation and siting aspects}, volume={152}, ISSN={["1878-4224"]}, DOI={10.1016/j.pnucene.2022.104362}, abstractNote={Fission Batteries (FBs) are envisioned to be highly mobile, autonomously operating, and economically competitive small nuclear power reactor systems useable for generating electric power or heat. Such novel systems will face unique challenges pertaining to siting and transportation. This paper presents the findings and recommendations of the 2021 Idaho National Laboratory FB Initiative workshop on the transportation and siting of FBs. Regulatory and technical subject matter experts on the transportation and storage of radioactive materials, licensing of nuclear power plants, innovative sensing technologies, etc., participated in this workshop and shared their professional experiences and perspectives. Based on these conversations, the paper describes the lessons learned from nuclear reactor siting and licensing, as well as from the siting and transportation of radioactive materials such as fresh or spent nuclear fuel. It then explores the applicability of these lessons and practices to FB siting and transportation. In addition, associated regulatory and technological challenges are identified, such as a changing FB source term, criticality safety aspects, neutron activation and embrittlement of structural components, site development, transportation uncertainties, the current regulatory framework, modeling and simulation uncertainties, and limited inspections. Additionally, research and development activities are suggested to address these gaps and challenges, including the development of modeling and simulation tools for FB design, strategies for rapid FB transportation, innovative FB shell materials, procedures for onsite handling of FBs, transportation-accident-proof criticality control mechanisms, self-monitoring and self-testing capabilities, regulatory requirements, and probabilistic risk assessment tools. Carrying out these research initiatives is expected to help accelerate the evolution of FBs and facilitate their design, licensing, and deployment.}, journal={PROGRESS IN NUCLEAR ENERGY}, author={Eidelpes, E. and Bolisetti, C. and Gupta, A. and Shafieezadeh, A.}, year={2022}, month={Oct} }
 @article{dubey_gupta_cho_2021, title={A Closed-Form Solution to Characterize the Behavior of Piping T-Joints}, ISSN={["2093-6311"]}, DOI={10.1007/s13296-021-00511-z}, journal={INTERNATIONAL JOURNAL OF STEEL STRUCTURES}, author={Dubey, Ankit R. and Gupta, Abhinav and Cho, Sung Gook}, year={2021}, month={Jul} }
 @article{bodda_keller_gupta_senfaute_2021, title={A Methodological Approach to Update Ground Motion Prediction Models Using Bayesian Inference}, ISSN={["1420-9136"]}, DOI={10.1007/s00024-021-02915-8}, abstractNote={In recent decades, prediction of ground motion at a specific site or a region is of primary interest in probabilistic seismic hazard assessment (PSHA). Historically, several ground motion prediction equation (GMPE) models with different functional forms have been published using strong ground motion records available from NGA-West and European databases. However, low-to-moderate seismicity regions, such as Central & Eastern United States and western Europe, is characterized by limited strong-motion records in the magnitude–distance range of interest for PSHA. In these regions, the available data for the development of empirical GMPEs is very scarce and limited to small magnitude events. For these regions, the general practice in PSHA is to consider a set of GMPEs developed from data sets collected in other regions with high seismicity. This practice generates an overestimation of the seismic hazard for the low seismicity regions. There are two potential solutions to overcome this problem: (1) a new GMPE model can be developed; however, development of such a model can require significant amount of data which is not usually available, and (2) the existing GMPE models can be recalibrated based on the data sets collected in the new region rather than developing a new GMPE model. In this paper, we propose a methodological approach to recalibrate the coefficients in a GMPE model using different algorithms to perform Bayesian inference. The coefficients are recalibrated for a subset of European Strong-Motion (ESM) database that corresponds to low-to-moderate seismicity records. In this study, different statistical models are compared based on the functional form given by the chosen GMPE, and the best model and algorithm are recommended using the concept of information criteria.}, journal={PURE AND APPLIED GEOPHYSICS}, author={Bodda, Saran Srikanth and Keller, Merlin and Gupta, Abhinav and Senfaute, Gloria}, year={2021}, month={Nov} }
 @article{bodda_gupta_sewell_2021, title={Application of Risk-Informed Validation Framework to a Flooding Scenario}, volume={7}, ISSN={["2376-7642"]}, DOI={10.1061/AJRUA6.0001172}, abstractNote={AbstractIn recent years, the use of advanced simulation tools for modeling the behavior of flooding at a nuclear power plant has gained significant importance. The credibility of advanced simulatio...}, number={4}, journal={ASCE-ASME JOURNAL OF RISK AND UNCERTAINTY IN ENGINEERING SYSTEMS PART A-CIVIL ENGINEERING}, author={Bodda, Saran Srikanth and Gupta, Abhinav and Sewell, Robert T.}, year={2021}, month={Dec} }
 @article{patel_bodda_gupta_2021, title={Modeling the behavior of reinforced concrete slabs subjected to impact}, volume={385}, ISSN={["1872-759X"]}, DOI={10.1016/j.nucengdes.2021.111512}, abstractNote={In recent years, safety of nuclear power plants against external missile impacts such as those due to tornadoes has gained significant attention. In many cases, advanced simulation tools based on finite element method (FEM) or smooth particle hydrodynamics (SPH) are being employed to simulate missile impact behavior and to evaluate vulnerability of nuclear facilities. Due to the complex nature of impact behavior, it requires appropriate calibration of parameters in the advanced simulation models that are used to represent them. In this manuscript, we propose a novel approach for modeling the behavior of reinforced concrete slabs subjected to missile impact. First, we use data from one experimental study to develop and calibrate various models needed to conduct the finite element analysis. Then, the calibrated models are used to conduct a predictive analysis for a different experimental setup. A comparison of the experiment and the analytical results for the new test provides confidence in the predictive capability of the simulation approach with calibrated parameters.}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Patel, Parth and Bodda, Saran Srikanth and Gupta, Abhinav}, year={2021}, month={Dec} }
 @article{gupta_dubey_cho_2021, title={Seismic Fragility of Piping Nozzles in Nuclear Power Plants: A Case for Updating the Current State-of-Practice}, volume={143}, ISSN={["1528-8978"]}, DOI={10.1115/1.4051136}, abstractNote={Abstract}, number={6}, journal={JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Gupta, Abhinav and Dubey, Ankit R. and Cho, Sung-Gook}, year={2021}, month={Dec} }
 @article{singh_gupta_2021, title={Seismic response of electrical equipment subjected to high?frequency ground motions}, volume={374}, ISSN={["1872-759X"]}, DOI={10.1016/j.nucengdes.2020.111046}, abstractNote={Recent ground motion studies conducted at nuclear facilities indicate that in Central and Eastern United States, the ground motion response spectra exceed the safe–shutdown earthquake spectra at high frequencies. Even though high–frequency ground motions do not cause structural damage, high–frequency accelerations may propagate through the structure and interfere with the output of the safety–related equipment such as relays required to ensure safe shutdown of the plant during a seismic event. Hence, it is essential to seismically qualify electrical equipment subjected to high–frequency accelerations. The seismic qualification is conducted by comparing in–cabinet response spectra evaluated at the equipment locations with the capacities of equipment obtained from shake table tests. The in–cabinet response spectrum is obtained from analysis of nuclear power plant building and electrical cabinet in which the equipment are mounted. This study is based on the hypothesis that the high–frequency motions do not reach the equipment as the small displacements induced by such motions are filtered out by the geometric nonlinearities. The effect of two different types of nonlinearities are studied: (1) a gap in the connection between electrical cabinet and floor; (2) sliding friction between electrical cabinet's base and the floor. The results from an analyses of various different cases show that the high–frequency motions do not reach the relays if the maximum displacement of building floor is less than the gap. Even if the displacement is larger than the gap, the in–cabinet spectral accelerations are not excessively high. On the contrary, results from a conventional linear analysis give excessively high unrealistic spectral accelerations.}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Singh, Sugandha and Gupta, Abhinav}, year={2021}, month={Apr} }
 @article{kwag_gupta_baugh_kim_2021, title={Significance of multi-hazard risk in design of buildings under earthquake and wind loads}, volume={243}, ISSN={["1873-7323"]}, DOI={10.1016/j.engstruct.2021.112623}, abstractNote={• Development of a performance-based framework to consider multiple hazards. • Significance of multi-hazard design is shown through retrofit solutions in buildings. • Cost-effective damper design is explored under two different hazards. Traditionally, external hazards are considered in the design of a building through the various combinations of loads prescribed in relevant design codes and standards. It is often the case that the design is governed by a single dominant hazard at a given geographic location. This is particularly true for earthquake and wind hazards, both of which impart time-dependent dynamic loads on the structure. Engineers may nevertheless wonder if a building designed for one of the two dominant hazards will satisfactorily withstand the other. Prior studies have indicated that in some cases, when a building is designed for a single dominant hazard, it does not necessarily provide satisfactory performance against the other hazard. In this paper, we propose a novel framework that builds upon performance-based design requirements and determines whether the design of a building is governed primarily by a single hazard or multiple hazards. It integrates site-dependent hazard characteristics with the performance criteria for a given building type and building geometry. The framework is consistent with the burgeoning area of probabilistic risk assessment, and yet can easily be extended to traditional, deterministically characterized design requirements as illustrated herein.}, journal={ENGINEERING STRUCTURES}, author={Kwag, Shinyoung and Gupta, Abhinav and Baugh, John and Kim, Hyun-Su}, year={2021}, month={Sep} }
 @article{singh_gupta_2021, title={Understanding the seismic response of electrical equipment subjected to high-frequency ground motions}, volume={140}, ISSN={["1878-4224"]}, DOI={10.1016/j.pnucene.2021.103915}, abstractNote={Ground motion studies in Central and Eastern United States (CEUS) show that the ground motion response spectra exceeds design spectrum of nuclear power plants in high–frequency range. To ensure safe shutdown of nuclear power plants in events where design spectrum is exceeded, the safety–related digital control systems and electrical equipment such as relays must be seismically qualified for high–frequency ground motions. Conventionally, uncoupled linear analysis of building and electrical cabinet is conducted and then seismic demands on equipment are evaluated. The conventional analysis ignores effects of various factors such as geometric nonlinearities, mass interaction between primary (building) and secondary (electrical cabinet) systems, etc. Ignoring such factors leads to unnecessarily high seismic demands on equipment. In this study, the seismic demands on equipment are evaluated by conducting both coupled and uncoupled analysis of linear primary system and linear as well as nonlinear secondary system. Various cases are analyzed where at least one mode of primary system is tuned with one mode of secondary systems. Each case is subjected to both low–frequency and high–frequency ground motions to compare the difference in response to each ground motion. The seismic demands on equipment are compared for coupled and uncoupled analysis as well as for linear and nonlinear systems. The results show reduction in seismic demands on electrical equipment for various nonlinear coupled analysis cases. The high seismic demands evaluated from linear uncoupled analysis may lead to exclusion of some electrical equipment which can be avoided by conducting coupled nonlinear analysis of primary–secondary systems and obtaining the realistic seismic demands on equipment.}, journal={PROGRESS IN NUCLEAR ENERGY}, author={Singh, Sugandha and Gupta, Abhinav}, year={2021}, month={Oct} }
 @article{tadinada_gupta_2020, title={A Bayesian Inference driven computational framework for seismic risk assessment using large-scale nonlinear finite element analyses}, volume={130}, ISSN={["0149-1970"]}, DOI={10.1016/j.pnucene.2020.103556}, abstractNote={Nuclear engineers are increasingly relying on large-scale simulations particularly for seismic risk assessment. Experimentally validated simulation models are used to consider the effects of uncertainties and evaluate fragilities by conducting multiple nonlinear analyses. However, such an approach becomes computationally prohibitive and care is needed to achieve desired degree of accuracy with a reasonable amount of computational effort. In this paper, a statistical framework is presented to minimize the total computational effort needed in conducting large-scale simulations for seismic risk assessment. The salient features of the framework are: (i) use of Bayesian inference to allow consideration of data from diverse sources like experiments, field data, existing or simplified approaches, and data from large-scale simulations, and (ii) embedment of Bayesian methods within an iterative process to plan and allocate adequate computing resources such that the desired accuracy is achieved using minimum possible simulations. The applicability and efficiency of the proposed framework is illustrated using the example of a box-shaped reinforced concrete shear wall.}, journal={PROGRESS IN NUCLEAR ENERGY}, author={Tadinada, Sashi Kanth and Gupta, Abhinav}, year={2020}, month={Dec} }
 @article{dubey_gupta_coleman_2020, title={A Framework for Simulation-Based Internal Flooding Risk Assessment}, volume={142}, ISSN={["1528-8978"]}, DOI={10.1115/1.4045028}, abstractNote={Abstract}, number={1}, journal={JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Dubey, Ankit R. and Gupta, Abhinav and Coleman, Justin}, year={2020}, month={Feb} }
 @article{dubey_gupta_cho_2020, title={Characterization of Limit State for Seismic Fragility Assessment of T-Joints in Piping System}, volume={142}, ISSN={["1528-8978"]}, DOI={10.1115/1.4047041}, abstractNote={Abstract}, number={5}, journal={JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Dubey, Ankit R. and Gupta, Abhinav and Cho, Sung Gook}, year={2020}, month={Oct} }
 @article{vaishanav_gupta_bodda_2020, title={Limitations of traditional tools for beyond design basis external hazard PRA}, volume={370}, ISSN={["1872-759X"]}, DOI={10.1016/j.nucengdes.2020.110899}, abstractNote={Probabilistic risk assessment (PRA) is being used increasingly by the nuclear industry for safety during normal operations as well as for the protection against external hazards. Computation of total risk in an external hazard PRA is dependent on hazard assessment, fragility assessment, and systems analysis. A systems analysis for propagation of component fragilities is conducted using event and fault trees. The event and fault trees for an actual power plant can be fairly large in size, which imposes computational challenges. Hence, certain assumptions are employed for computational efficiency. These assumptions typically represent the conditions imposed during the design basis (DB) scenario. The traditional PRA tools based on these assumptions are also widely applied to perform risk assessment in the context of beyond design basis (BDB) scenarios. However, some of these assumptions may not be valid for certain BDB scenarios. In addition, the probability of dependent failures also increases in BDB scenarios due to common cause failures (CCF) which usually results from design modifications, human errors, etc. In this manuscript, a simple and a relatively more complex illustrative examples are used to show the limitation of these assumptions in the numerical quantification of risk for the case of BDB conditions. Case studies with CCF events across multiple fault trees are also presented to illustrate the effect of these assumptions when traditional approach is used in BDB risk assessment. It is shown that the assumptions are valid for the case of DB conditions but may lead to excessively conservative risk estimates in the case of BDB conditions. A Bayesian network based top-down algorithm is proposed as an alternative tool for accurate numerical quantification of total risk in systems analysis.}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Vaishanav, Pragya and Gupta, Abhinav and Bodda, Saran Srikanth}, year={2020}, month={Dec} }
 @article{bodda_gupta_dinh_2020, title={Risk informed validation framework for external flooding scenario}, volume={356}, ISSN={["1872-759X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85074190032&partnerID=MN8TOARS}, DOI={10.1016/j.nucengdes.2019.110377}, abstractNote={Safety of nuclear plants against external flooding has gained significant attention following the accident at Fukushima Daiichi nuclear power station. In United States, Oyster Creek nuclear plant was safely shutdown when high storm surge during hurricane Sandy caused a potential flooding threat. Subsequently, the nuclear energy industry experienced a significant activity in Probabilistic Risk Assessment (PRA) for external flooding. Increasingly, methods of computational fluid dynamics including advanced simulation codes are being considered to evaluate the sequence of events during different scenarios of flooding at a plant. One of the key limitations in the use of advanced codes for external flooding is related to a lack of credibility of such simulations. The motivation of this study is to develop a formal validation approach that provides a basis to quantify credibility of risk assessments that are based on advanced simulation codes. In this study, we illustrate the application of existing performance based risk-informed validation framework to an external flooding event. However, it is determined that a direct application of this approach to flooding is restricted due to a lack of relevant data to evaluate experimental fragilities for flooding failures. Therefore, we take a simple synthetic example to evaluate the applicability of the proposed framework to validation of flooding PRA scenario and update the proposed framework as needed.}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Bodda, Saran Srikanth and Gupta, Abhinav and Dinh, Nam}, year={2020}, month={Jan} }
 @article{gupta_cho_hong_han_2019, title={Current state of in-cabinet response spectra for seismic qualification of equipment in nuclear power plants}, volume={343}, ISSN={["1872-759X"]}, DOI={10.1016/j.nucengdes.2018.12.017}, abstractNote={Many nuclear power plants in the south eastern region of South Korea are undertaking seismic qualification studies due to the recent earthquake in Gyeongju region. The records from this earthquake contain high frequency content compared to the frequency exhibited in most of the design basis Safe Shutdown Earthquakes used in the design of nuclear power plants. While the high frequency ground motions are not detrimental to the structures due to relatively smaller displacements, such motions can lead to functionality related failures in electrical equipment and systems such as control relays. The seismic qualification of relays and other such instruments require characterization of in-cabinet response spectra (ICRS) in the cabinet or control panels where they are mounted. The current practice of generating ICRS, in many cases, uses constant amplification factors which are based on studies containing low frequency ground motions. Cabinets can often have higher frequency modes which can amplify the motion if it contains high frequency pulses. Finite element analysis to evaluate the dynamic characteristics of cabinet is highly impractical because each cabinet is vastly different from other cabinets and a given plant contains hundreds of such cabinets and control panels. Therefore, a method is needed to evaluate accurate dynamic characteristics of cabinets and control panels in a relatively simple manner. This paper presents the details of such a method called Ritz vector approach and also compares the ICRS of an actual cabinet for a high frequency input motion with that for a low frequency input motion.}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Gupta, Abhinav and Cho, Sung-Gook and Hong, Kee-Jeung and Han, Minsoo}, year={2019}, month={Mar}, pages={269–275} }
 @article{ryu_gupta_ju_2019, title={Fragility Evaluation in Building-Piping Systems: Effect of Piping Interaction With Buildings}, volume={141}, ISSN={["1528-8978"]}, DOI={10.1115/1.4039004}, abstractNote={Many studies assessing the damage from 1971 San Fernando and 1994 North Ridge earthquakes reported that the failure of nonstructural components like piping systems was one of the significant reasons for shutdown of hospitals immediately after the earthquakes. This paper is focused on evaluating seismic fragility of a large-scale piping system in representative high-rise, midrise, and low-rise buildings using nonlinear time history analyses. The emphasis is on evaluating piping's interaction with building and its effect on piping fragility. The building models include the effects of nonlinearity in the performance of beams and columns. In a 20-story building that is detuned with the piping system, critical locations are on the top two floors for the linear frame building model. For the nonlinear building model, critical locations are on the bottom two floors. In an eight-story building that is nearly tuned with the piping system, the critical locations for both the linear frame and nonlinear models are the third and fourth floors. It is observed that building nonlinearity can reduce fragility due to reduction in the tuning between building and piping systems. In a two-story building, the nonlinear building frequencies are closer to the critical piping system frequencies than the linear building frequency; the nonlinear building is more fragile than the linear building for this case. However, it is observed that the linear building models give excessively conservative estimates of fragility than the nonlinear building models.}, number={1}, journal={JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Ryu, Yong Hee and Gupta, Abhinav and Ju, Bu Seog}, year={2019}, month={Feb} }
 @article{ryu_gupta_ju_2019, title={Probabilistic Characterization of an Allowable Design Moment in a Piping Elbow}, volume={141}, ISSN={["1528-8978"]}, DOI={10.1115/1.4042907}, abstractNote={The design of a nuclear power plant piping requires consideration of the effects of pressure and moment loads according to the appropriate design equation, which is Piping design equation (9) in NC/ND-3600, Section III of the ASME Boiler and Pressure Vessel Code. The design moment is influenced significantly by the definition of the B2 stress index in piping elbows. This paper presents a study on reliability-based design for piping elbows on the level D service limit in the design code. Probability density functions (PDFs) of the design moment were calculated using the ASME equation and modified B2 equations. The PDFs of the design moment were evaluated by the collapse moment using the closed-form equations. The probability distribution of the design moment using the modified B2 equation was closer to the distributions of the collapse moment than its design moment using the ASME B2 equation. Probabilistic analyses were conducted to evaluate reliability levels in straight pipe as well as piping elbows using the ASME and modified B2 equations. It was observed that the minimum reliability level (MRL) of the design equation for the straight pipe was slightly higher than the MRL of the elbow. The MRLs of the design equation using the ASME and modified B2 equations were similar for the same values of bend parameter h, and the MRL of the design equation did not show influence of changes in bend parameter, piping type, and B2 stress index.}, number={3}, journal={JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Ryu, Yonghee and Gupta, Abhinav and Ju, Bu Seog}, year={2019}, month={Jun} }
 @article{kwag_gupta_2018, title={Computationally efficient fragility assessment using equivalent elastic limit state and Bayesian updating}, volume={197}, ISSN={["1879-2243"]}, DOI={10.1016/j.compstruc.2017.11.011}, abstractNote={Conventionally, the seismic response of primary structures such as buildings and secondary systems such as piping is evaluated through uncoupled analyses. Many studies have illustrated that the two systems interact in many different ways (mass interaction, non-classical damping, phasing, etc.). An analysis of the coupled system is not only rational but also eliminates the excessive conservatism that exists in an uncoupled analysis. Consequently, fragility assessments based on uncoupled analysis are also incorrect and a coupled analysis must be conducted in such evaluations. However, nonlinear analyses of such complex systems particularly in the context of fragility assessment, which requires a large number of nonlinear analyses, becomes computationally prohibitive. Tadinada and Gupta (2017) presented an equivalent elastic limit state concept with an intent to reduce the computational effort needed in these assessments and yet evaluate the seismic fragility with sufficient accuracy. This paper outlines some of the limitations that have been experienced in the use of originally proposed equivalent limit-state formulation and presents valuable enhancements. The novel contribution of this study is focused on accounting for the effect of uncertainty in nonlinear characteristics and the effect of non-classical damping. Unlike the originally proposed formulation, the proposed formulation also considers the asymmetric variation of the equivalent limit state with respect to tuning ratio. Furthermore, a Bayesian approach is incorporated into the proposed methodology for increasing the accuracy of seismic fragilities in the case of tuned or nearly tuned primary-secondary systems. Numerical examples are used to illustrate that the modified form improves the accuracy for both the tuned and the detuned systems. In summary, the proposed approach provides an efficient framework of seismic fragility assessment and risk evaluation for coupled systems.}, journal={COMPUTERS & STRUCTURES}, author={Kwag, Shinyoung and Gupta, Abhinav}, year={2018}, month={Feb}, pages={1–11} }
 @article{kwag_gupta_dinh_2018, title={Probabilistic risk assessment based model validation method using Bayesian network}, volume={169}, ISSN={["1879-0836"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85030567554&partnerID=MN8TOARS}, DOI={10.1016/j.ress.2017.09.013}, abstractNote={Past few decades have seen a rapid growth in the availability of computational power and that induces continually reducing cost of simulation. This rapidly changing scenario together with availability of high precision and large-scale experimental data has enabled development of high fidelity simulation tools capable of simulating multi-physics multi-scale phenomena. At the same time, there has been an increased emphasis on developing strategies for verification and validation of such high fidelity simulation tools. The problem is more pronounced in cases where it is not possible to collect experimental data or field measurements on a large-scale or full scale system performance. This is particularly true in case of systems such as nuclear power plants subjected to external hazards such as earthquakes or flooding. In such cases, engineers rely solely on simulation tools but struggle to establish the credibility of the system level simulations. In practice, validation approaches rely heavily on expert elicitation. There is an increasing need of a quantitative approach for validation of high fidelity simulations that is comprehensive, consistent, and effective. A validation approach should be able to consider uncertainties due to incomplete knowledge and randomness in the system's performance as well as in the characterization of external hazard. A new approach to validation is presented in this paper that uses a probabilistic index as a degree of validation and propagates it through the system using the performance-based probabilistic risk assessment (PRA) framework. Unlike traditional PRA approaches, it utilizes the power of Bayesian statistic to account for non-Boolean relationships and correlations among events at various levels of a network representation of the system. Bayesian updating facilitates evaluation of updated validation information as additional data from experimental observations or improved simulations is incorporated. PRA based framework assists in identifying risk-consistent events and critical path for appropriate allocation of resources to improve the validation.}, journal={RELIABILITY ENGINEERING & SYSTEM SAFETY}, author={Kwag, Shinyoung and Gupta, Abhinav and Dinh, Nam}, year={2018}, month={Jan}, pages={380–393} }
 @article{ju_gupta_ryu_2018, title={Seismic Fragility of Steel Piping System Based on Pipe Size, Coupling Type, and Wall Thickness}, volume={18}, ISSN={["2093-6311"]}, DOI={10.1007/s13296-018-0100-4}, number={4}, journal={INTERNATIONAL JOURNAL OF STEEL STRUCTURES}, author={Ju, Bu Seog and Gupta, Abhinav and Ryu, Yonghee}, year={2018}, month={Nov}, pages={1200–1209} }
 @article{tadinada_gupta_2018, title={Simulation of Constrained Variables in Engineering Risk Analyses}, volume={72}, ISSN={["1537-2731"]}, DOI={10.1080/00031305.2016.1255660}, abstractNote={ABSTRACT The problem of sampling random variables with overlapping pdfs subject to inequality constraints is addressed. Often, the values of physical variables in an engineering model are interrelated. This mutual dependence imposes inequality constraints on the random variables representing these parameters. Ignoring the interdependencies and sampling the variables independently can lead to inconsistency/bias. We propose an algorithm to generate samples of constrained random variables that are characterized by typical continuous probability distributions and are subject to different kinds of inequality constraints. The sampling procedure is illustrated for various representative cases and one realistic application to simulation of structural natural frequencies.}, number={2}, journal={AMERICAN STATISTICIAN}, author={Tadinada, Sashi Kanth and Gupta, Abhinav}, year={2018}, pages={130–139} }
 @article{gupta_saigal_ryu_2017, title={Performance-Based Reliability of ASME Piping Design Equations}, volume={139}, ISSN={["1528-8978"]}, DOI={10.1115/1.4034584}, abstractNote={In this paper, we present an exploratory study on the evaluation of reliability levels associated with the piping design equations specified by ASME Boiler and Pressure Vessel (BPV) Code, Section III. Probabilistic analyses are conducted to evaluate reliability levels in straight pipe segments with respect to performance functions that characterize the different failure criteria using advanced first-order reliability method (AFORM). One important failure criterion considered in this study relates to the plastic instability which forms the basis of piping design equations for emergency and faulted load level conditions as defined in the ASME code. The code-specified definition of plastic instability is based on the evaluation of a collapse moment which is defined using the moment–curvature curve for a particular component. In this study, we use elastic-perfectly plastic, bilinear kinematic hardening, and multilinear kinematic hardening stress–strain curves to develop closed-form expressions for the moment–curvature relationship in a straight unpressurized pipe. Both the pressurized and the unpressurized loading conditions are considered. The closed-form reliability is evaluated using Monte Carlo simulation because of the complex nature of the closed-form expression. The reliability values are calculated with respect to the maximum allowable moment specified by the code design equations that use deterministic safety factors.}, number={3}, journal={JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Gupta, Abhinav and Saigal, Rakesh K. and Ryu, Yonghee}, year={2017}, month={Jun} }
 @article{ju_gupta_ryu_2017, title={Piping Fragility Evaluation: Interaction With High-Rise Building Performance}, volume={139}, ISSN={["1528-8978"]}, DOI={10.1115/1.4034406}, abstractNote={Many recent studies have emphasized the need for improving seismic performance of nonstructural systems in critical facilities in order to reduce the damage as well as to maintain continued operation of the facility after an earthquake. This paper is focused on evaluating system-level seismic fragility of the piping in a representative high-rise building. Piping fragilities are evaluated by incorporating the nonlinear finite-element model of a threaded Tee-joint that is validated using experimental results. The emphasis in this study is on evaluating the effects of building performance on the piping fragility. The differences in piping fragility due to the nonlinearities in building are evaluated by comparing the fragility curves for linear frame and nonlinear fiber models. It is observed that as nonlinearity in the building increases with increasing value of peak ground acceleration, the floor accelerations exhibit a reduction due to degradation/softening. Consequently, the probabilities of failure increase at a slower rate relative to that in a linear frame. It is also observed that a piping located at higher floor does not necessarily exhibits high fragilities, i.e., the fundamental building mode is not always the governing mode. Higher order building modes with frequencies closest to critical piping modes of interest contribute more significantly to the piping fragility. Within a particular building mode of interest, a good indicator of the amplification at different floor levels can be obtained by the product of mode shape ordinate and modal participation factor. Piping fragilities are likely to be higher at floor levels at which this product has a higher value.}, number={3}, journal={JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Ju, Bu Seog and Gupta, Abhinav and Ryu, Yong Hee}, year={2017}, month={Jun} }
 @article{kwag_gupta_2017, title={Probabilistic risk assessment framework for structural systems under multiple hazards using Bayesian statistics}, volume={315}, ISSN={["1872-759X"]}, DOI={10.1016/j.nucengdes.2017.02.009}, abstractNote={Conventional probabilistic risk assessment (PRA) methodologies (USNRC, 1983; IAEA, 1992; EPRI, 1994; Ellingwood, 2001) conduct risk assessment for different external hazards by considering each hazard separately and independent of each other. The risk metric for a specific hazard is evaluated by a convolution of the fragility and the hazard curves. The fragility curve for basic event is obtained by using empirical, experimental, and/or numerical simulation data for a particular hazard. Treating each hazard as an independently can be inappropriate in some cases as certain hazards are statistically correlated or dependent. Examples of such correlated events include but are not limited to flooding induced fire, seismically induced internal or external flooding, or even seismically induced fire. In the current practice, system level risk and consequence sequences are typically calculated using logic trees to express the causative relationship between events. In this paper, we present the results from a study on multi-hazard risk assessment that is conducted using a Bayesian network (BN) with Bayesian inference. The framework can consider statistical dependencies among risks from multiple hazards, allows updating by considering the newly available data/information at any level, and provide a novel way to explore alternative failure scenarios that may exist due to vulnerabilities.}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Kwag, Shinyoung and Gupta, Abhinav}, year={2017}, month={Apr}, pages={20–34} }
 @article{gupta_bose_2017, title={Significance of non-classical damping in seismic qualification of equipment and piping}, volume={317}, ISSN={0029-5493}, url={http://dx.doi.org/10.1016/J.NUCENGDES.2017.03.020}, DOI={10.1016/J.NUCENGDES.2017.03.020}, abstractNote={This paper presents a discussion on the significance of non-classical damping in coupled primary-secondary systems such as building-equipment or building-piping. Closed-form expressions are used to illustrate that the effect of non-classical damping is significant in systems with tuned or nearly tuned uncoupled modes when the mass-interaction is sufficiently small. Further, simple primary-secondary systems are used to illustrate that composite modal damping is another form of classical damping for which the transformed damping matrix, obtained after pre- and post-multiplication of the damping matrix with the modal matrix, contains only diagonal terms. Both the composite and the classical damping give almost identical results that can be much different from the corresponding results for non-classical damping. Finally, it is shown that consideration of classical damping (ignoring the off-diagonal terms) can give excessively conservative results in nearly tuned primary-secondary systems. For perfectly tuned primary-secondary systems, however, classical damping can give responses that are much lower than what they should be.}, journal={Nuclear Engineering and Design}, publisher={Elsevier BV}, author={Gupta, Abhinav and Bose, Mrinal K.}, year={2017}, month={Jun}, pages={90–99} }
 @article{tadinada_gupta_2017, title={Structural fragility of T-joint connections in large-scale piping systems using equivalent elastic time-history simulations}, volume={65}, ISSN={["1879-3355"]}, DOI={10.1016/j.strusafe.2016.12.003}, abstractNote={The main focus of the paper is to evaluate seismic fragility of nonlinear connections in large piping systems. Piping systems in general exhibit damage due to excessive inelastic deformation at discrete locations such as T-joints, elbows, valves, etc., and low ductility corresponding to failure. Since the supporting structure remains primarily elastic, this study evaluates the effectiveness of using linearization techniques to describe the localized nonlinearities with equivalent elastic properties. A concept called "Equivalent Elastic Limit State" is introduced. A large number of representative nonstructural systems which are essentially linear but characterized by localized fragile nonlinearities are studied to propose a model for computing seismic fragility curves using only elastic time-history simulations. It is shown that the seismic fragility evaluated using elastic analyses is close to the actual fragility. Fragility estimated using this approach can be used as a very reliable prior estimate within Bayesian fragility models so that the posterior estimate of fragility curve can be obtained using a very few number of nonlinear time-history analyses. The efficacy of the model is illustrated for seismic fragility analysis of a full-scale piping system in a hospital with fragile 2″ T-joint connections.}, journal={STRUCTURAL SAFETY}, author={Tadinada, Sashi Kanth and Gupta, Abhinav}, year={2017}, pages={49–59} }
 @article{ryu_gupta_jung_ju_2016, title={A Reconciliation of Experimental and Analytical Results for Piping Systems}, volume={16}, ISSN={["2093-6311"]}, DOI={10.1007/s13296-016-0019-6}, number={4}, journal={INTERNATIONAL JOURNAL OF STEEL STRUCTURES}, author={Ryu, Yonghee and Gupta, Abhinav and Jung, WooYoung and Ju, BuSeog}, year={2016}, month={Dec}, pages={1043–1055} }
 @inproceedings{kwag_gupta_2016, title={Bayesian network technique in probabilistic risk assessment for multiple hazards}, booktitle={Proceedings of the 24th International Conference on Nuclear Engineering, 2016, vol 4}, author={Kwag, S. and Gupta, A.}, year={2016} }
 @inproceedings{bodda_sandhu_gupta_2016, title={Fragility of a flood defense structure subjected to multi-hazard scenario}, DOI={10.1115/icone24-60508}, abstractNote={The March 2011 Fukushima Daiichi nuclear power plant disaster has highlighted the significance of maintaining the integrity of flood protection systems in the vicinity of a nuclear power plant. In the US, Oyster Creek nuclear plant was shut down when high storm surge during hurricane Sandy threatened its water intake and circulation systems. A gravity dam located upstream of a power plant can undergo seismic failure or flooding failure leading to flooding at the nuclear plant. In this paper, we present the results from a study on evaluating the fragilities for failure of a concrete gravity dam under both the flooding and the seismic events. Finite element analysis is used for modeling the seismic behavior as well as the seepage through foundation. A time-dependent analysis is considered to account for appropriate nonlinearities. Failure of dam foundation is characterized by rupture, and the failure of dam body is characterized by excessive deformation for the flooding and seismic loads respectively. The study presented in this paper has focused on a concrete gravity dam because of the need of validation of models which exist in prior studies only for concrete gravity dams. However, the concepts are directly applicable to any concrete flood defense structure.}, booktitle={Proceedings of the 24th International Conference on Nuclear Engineering, 2016, vol 4}, author={Bodda, S. S. and Sandhu, H. K. and Gupta, A.}, year={2016} }
 @inproceedings{chatterjee_gupta_2016, title={Seismic qualification of equipment: A pra-consistent framework}, DOI={10.1115/icone24-60674}, abstractNote={The seismic probabilistic risk assessment (SPRA) for a nuclear power plant involves the estimation of fragility curves for plant equipment. The seismic qualification of an equipment based on testing requires the equipment to continue to function when subjected to a specific test response spectrum (TRS). Broad banded ground motions have been found to cause more damage to equipment than the filtered narrow banded excitations. As a result, the definition of acceleration capacity used in the fragility models use clipped response spectra for both test response spectrum (TRS) and required response spectrum (RRS). The main purpose of the clipping factors is to convert a narrow banded response spectrum to a broad banded spectrum. The broadband correction factor and the modal interaction correction factors together contribute to the definition of clipping factor. The current study involves reconciliation with previous research by generating the mean response factor for different waveforms and subsequently the root-mean-square (RMS) severity ratio as a function of bandwidth. This ratio can be estimated for real earthquakes from their peak-to-rms values and the peak spectral values. In addition it can be shown that in case of real narrow banded earthquakes, this ratio is even lower and therefore the clipping would be greater. The modal interaction correction factor which considers the effect of interaction between different modes in case of broad banded time histories has also been investigated. The primary objective of this work is to study the existing Conservative Deterministic Failure Margin (CDFM) and Probabilistic approaches for estimating these factors as per the guidelines of EPRI [2] and apply the same to real life ground motions. It has been observed that the recommended practices are based on studying the behavior of random ground motions generated artificially for different bandwidths and center frequencies. The present study aims towards a more realistic fragility estimation of equipment by studying the spectral response of equipment based on actual ground motions. The purpose is to evaluate clipping factors that are consistent with Seismic Probabilistic Risk Assessment.}, booktitle={Proceedings of the 24th International Conference on Nuclear Engineering, 2016, vol 1}, author={Chatterjee, P. and Gupta, A.}, year={2016} }
 @article{syed_gupta_2015, title={Seismic fragility of RC shear walls in nuclear power plant Part 1: Characterization of uncertainty in concrete constitutive model}, volume={295}, ISSN={["1872-759X"]}, DOI={10.1016/j.nucengdes.2015.09.037}, abstractNote={This two part manuscript proposes a framework for seismic fragility assessment of reinforced concrete structures in nuclear energy facilities. The novelty of the proposed approach lies in the characterization of uncertainties in the parameters of the material constitutive model. Concrete constitutive models that comprehensively address different damage states such as tensile cracking, compression failure, stiffness degradation, and recovery of degraded stiffness due to closing of previously formed cracks under dynamic loading are generally defined in terms of a large number of variables to characterize the plasticity and damage at material level. Over the past several years, many different studies have been presented on evaluation of fragility for reinforced concrete structures using nonlinear time history simulations. However, almost all of these studies do not consider uncertainties in the parameters of a comprehensive constitutive model. Part-I of this two-part manuscript presents a study that is used to identify uncertainties associated with the critical parameters in nonlinear concrete damage plasticity model proposed by Lubliner et al. (1989. Int. J. Solids Struct., 25(3), 299) and later modified by Lee and Fenves (1998a. J. Eng. Mech., ASCE, 124(8), 892) and Lee and Fenves (1998b. Earthquake Eng. Struct. Dyn., 27(9), 937) for the purpose of seismic fragility assessment. The limitations in implementation of the damage plasticity model within a finite element framework and hence its direct use in a simulation based fragility assessment is addressed. A methodology to overcome these limitations by combining the damage plasticity based constitutive model with some existing closed-form expressions is presented in this study. A simulation-based fragility evaluation framework that incorporates the damage plasticity model and the closed-form expressions for evaluating damage variables and application of this framework to an experimentally tested shear wall is presented in the Part-II companion paper.}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Syed, Sammiuddin and Gupta, Abhinav}, year={2015}, month={Dec}, pages={576–586} }
 @article{syed_gupta_2015, title={Seismic fragility of RC shear walls in nuclear power plant part 2: Influence of uncertainty in material parameters on fragility of concrete shear walls}, volume={295}, ISSN={["1872-759X"]}, DOI={10.1016/j.nucengdes.2015.09.038}, abstractNote={Part 2 of this two-part manuscript builds upon the conclusions from Part 1 by evaluating whether or not it is important to considering uncertainties in material constitutive model parameters in the fragility assessment of concrete shear walls. A particular application of a box-shaped shear wall is considered because this particular specimen was tested in the past under the JNES/NUPEC program in Japan and has been used extensively by various researchers around the world to conduct studies on reconciliation of experimental and analytical results. A simulation-based fragility evaluation framework is presented in this paper. The uniqueness of this framework lies in incorporation of the uncertainties and randomness associated with the parameters of damage plasticity model as well as earthquake input motions, which are essential for estimating the demands. Unlike most of the previous studies that focus mostly on shear capacity, two different performance limit states based on maximum shear strains and maximum shear force are considered in the fragility assessment. For each performance limit state, variation in the probability of failure due to uncertainties in the material constitutive model is determined for illustrating the significance of considering such uncertainties.}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Syed, Sammiuddin and Gupta, Abhinav}, year={2015}, month={Dec}, pages={587–596} }
 @article{ju_gupta_2015, title={Seismic fragility of threaded Tee-joint connections in piping systems}, volume={132}, ISSN={["1879-3541"]}, DOI={10.1016/j.ijpvp.2015.06.001}, abstractNote={This paper proposes a methodology to evaluate seismic fragility of threaded Tee-joint connections found in typical hospital piping systems. Existing experimental data on threaded Tee-joints of various sizes subjected to monotonic and cyclic loading indicates that the "First Leak" damage state is observed predominantly due to excessive flexural deformations at the Tee-joint section. The results of the monotonic and cyclic loading tests help us evaluate the characteristics for a given pipe size and material. A non-linear finite element model for the Tee-joint system is formulated and validated with the experimental results. It is shown that the Tee-joint section can be satisfactorily modeled using non-linear rotational springs. The system-level fragility of the complete piping system corresponding to the "First Leak" damage state is determined from multiple time-history analyses using a Monte-Carlo simulation accounting for uncertainties in demand.}, journal={INTERNATIONAL JOURNAL OF PRESSURE VESSELS AND PIPING}, author={Ju, Bu Seog and Gupta, Abhinav}, year={2015}, pages={106–118} }
 @inproceedings{gupta_2013, title={Evolution of Organic Matter and Organic Nitrogen in Leachates with Landfilling Age: A Size Distribution and Hydrophobicity Study}, ISBN={9780784412947}, url={http://dx.doi.org/10.1061/9780784412947.249}, DOI={10.1061/9780784412947.249}, abstractNote={Landfill leachates are frequently discharged to publically owned treatment works (POTWs). The presence of UV quenching substances in leachate interferes with UV disinfection at the POTWs. Also, the biorefractory organic nitrogen contained in the leachate contributes to the plant’s effluent nitrogen making it difficult to meet the tightening total nitrogen effluent regulations in some regions of the country. To study the changes in organic carbon and nitrogen with landfill age, leachate samples with landfilling ages ranging from 2 to 30 years from a large landfill in Kentucky were collected and fractionated on the basis of their particle size (molecular weight cut off) and hydrophobicity into humic acids (HA), fulvic acids (FA) and a hydrophilic (Hpi) fraction. The results identified the hydrophilic component which was mostly < 1 kDa as the major source of the total organic carbon and organic nitrogen. This component tends to persist even in the older stabilized leachates whereas the HA fraction gets degraded or converted into FA fraction. The effectiveness of biological treatment for leachates at different ages was examined to develop an understanding that might help design on-site treatment methods. It was observed that on-site biological treatment was able to degrade organic matter measured as total organic carbon (TOC) but was not effective for removal of UV quenching substances, especially for the older leachates. This pointed to the possibility that the microorganisms with the capability to degrade the UV absorbing substances need a detention time of around 10-20 years which cannot be provided by on-site biological treatment. It was also observed that one-third of the organic nitrogen was from proteins which were mainly concentrated in the Hpi fraction.}, booktitle={World Environmental and Water Resources Congress 2013}, publisher={American Society of Civil Engineers}, author={Gupta, Abhinav}, year={2013}, month={May} }
 @article{budai_tselev_tischler_strelcov_kolmakov_liu_gupta_narayan_2013, title={In situ X-ray microdiffraction studies inside individual VO2 microcrystals}, volume={61}, ISSN={1359-6454}, url={http://dx.doi.org/10.1016/j.actamat.2012.09.074}, DOI={10.1016/j.actamat.2012.09.074}, abstractNote={Synchrotron X-ray microdiffraction provides quantitative structural measurements with submicron spatial resolution, and hence enables investigations of how local microstructural inhomogeneities affect materials' properties. A combination of polychromatic and monochromatic X-ray microdiffraction was used to investigate domain formation, interface orientations and strain distributions inside individual vanadium dioxide (VO2) microcrystals. Using in situ measurements near the VO2 metal–insulator phase transition, it was found that the observed phase evolution is critically dependent on external strain. Substrate-induced strains or inhomogeneous sample heating can directly alter phase stability and affect the local domain orientations. In different clamped or freely suspended single-crystal samples, all the predicted twin laws for the M2 phase in VO2 were observed, except one. When the rutile and M2 phases coexist, it was found that different interphase boundary orientations can be stabilized by sample size and by interfacial elastic strain. The large variations in phase sequences and domain orientations observed in relatively simple, small single crystals provide insight into the mechanisms responsible for the broad structural and electronic transitions observed in epitaxial VO2 films.}, number={8}, journal={Acta Materialia}, publisher={Elsevier BV}, author={Budai, J.D. and Tselev, A. and Tischler, J.Z. and Strelcov, E. and Kolmakov, A. and Liu, W.J. and Gupta, A. and Narayan, J.}, year={2013}, month={May}, pages={2751–2762} }
 @inproceedings{ju_tadinada_gupta_2012, title={Fragility analysis of threaded T-joint connections in hospital piping systems}, booktitle={Proceedings of the ASME Pressure Vessels and Piping Conference, PVP 2011, vol 8}, author={Ju, B. S. and Tadinada, S. K. and Gupta, A.}, year={2012}, pages={147–155} }
 @article{tadinada_gupta_2012, title={Sampling of closely-spaced ordered set of uniformly distributed random variables}, volume={89}, ISSN={["0029-5981"]}, DOI={10.1002/nme.3248}, abstractNote={SUMMARY}, number={3}, journal={INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING}, author={Tadinada, Sashi Kanth and Gupta, Abhinav}, year={2012}, month={Jan}, pages={354–370} }
 @article{kripakaran_hall_gupta_2011, title={A genetic algorithm for design of moment-resisting steel frames}, volume={44}, ISSN={["1615-1488"]}, DOI={10.1007/s00158-011-0654-7}, abstractNote={This paper presents computational approaches that can be implemented in a decision support system for the design of moment-resisting steel frames. Trade-off studies are performed using genetic algorithms to evaluate the savings due to the inclusion of the cost of connections in the optimization model. Since the labor costs and material costs vary according to the geographical location and time of construction, the trade-off curves are computed for several values of the ratio between the cost of rigid connection and the cost of steel. A real-life 5-bay 5-story frame is used for illustration. Results indicate that the total cost of the frame is minimal when rigid connections are present only at certain locations. Finally, “Modeling to Generate Alternatives—MGA,” is proposed to generate good design alternatives as the solution from optimization may not be optimal with respect to the unmodeled objectives and constraints. It provides a set of alternatives that are near-optimal with respect to the modelled objectives and that are also farther from each other in the decision space. Results show that a final design could be chosen from the set of alternatives or obtained by tinkering one of the alternatives.}, number={4}, journal={STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION}, author={Kripakaran, Prakash and Hall, Brian and Gupta, Abhinav}, year={2011}, month={Oct}, pages={559–574} }
 @article{tadinada_gupta_2011, title={Consideration of uncertainties in seismic analysis of non-classically damped coupled systems}, volume={241}, ISSN={["1872-759X"]}, DOI={10.1016/j.nucengdes.2011.02.011}, abstractNote={Abstract This paper proposes a method to evaluate the design response of a non-classically damped coupled primary–secondary system by statistically incorporating the effects of uncertainties in modal properties of its constituent uncoupled systems. Within the framework for the coupled system seismic analysis, the uncertainties can be accounted for by modeling the uncoupled modal properties of primary and secondary systems as random variables. Gupta and Choi (2005) proposed the Square-Root-of-Mean-of-Squares (SRMS) method which employs a limited Monte Carlo simulation to evaluate the design response of the secondary system statistically. The SRMS approach was illustrated to work well with representative single degree of freedom (SDOF) primary–SDOF secondary systems. In this paper, we study the applicability of SRMS methodology to MDOF primary–MDOF secondary systems. In such systems, two or more modes are likely to have closely spaced frequencies. The individual probability density functions of the closely spaced frequencies overlap with each other. Simulation of such closely spaced frequencies as independent random can give incorrect set of frequencies in the sense that the frequencies do not remain as ordered sets. Rejection of these incorrect sets does not resolve the problem as the simulated density functions no longer maintain the originally assumed distribution. The simulation of ordered sets of natural frequencies of an MDOF structure can be achieved by using a joint density function that considers the necessary constraints. The SRMS method for MDOF primary–MDOF secondary coupled systems is modified by incorporating a closed-form formulation for the joint density function of closely spaced frequencies. The modified SRMS approach is validated for MDOF secondary systems that are both singly as well as multiply connected to the MDOF primary system.}, number={6}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Tadinada, Sashi Kanth and Gupta, Abhinav}, year={2011}, month={Jun}, pages={2034–2044} }
 @article{gupta_narayan_dutta_2010, title={Near bulk semiconductor to metal transition in epitaxial VO2 thin films}, volume={97}, number={15}, journal={Applied Physics Letters}, author={Gupta, A. and Narayan, J. and Dutta, T.}, year={2010} }
 @article{gupta_narayan_kumar_2009, title={Magnetic Properties of Self-Assembled Ni Nanoparticles in Two Dimensional Structures}, volume={9}, ISSN={["1533-4899"]}, DOI={10.1166/jnn.2009.214}, abstractNote={A pulsed laser deposition technique has been used to synthesize a uniform distribution of Ni nanoparticles of controllable size in Al2O3 thin film matrix. The ability to control particle size in confined layers provides a very convenient means to tune the magnetic properties from superparamagnetic to ferromagnetic. The coercivity of these particles was measured at various temperatures as a function of particle size. The results indicate that the magnetic transition from single- to multi-domain region occurs at a larger particle size at higher temperature than at lower temperature. Stronger magnetic interaction among particles at lower temperatures is believed to lead to the formation of smaller sized domains for any given particle size in order to minimize the interaction energy.}, number={6}, journal={JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY}, author={Gupta, A. and Narayan, J. and Kumar, Dhananjay}, year={2009}, month={Jun}, pages={3993–3996} }
 @article{gupta_aggarwal_gupta_dutta_narayan_narayan_2009, title={Semiconductor to metal transition characteristics of VO2 thin films grown epitaxially on Si (001)}, volume={95}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3232241}, DOI={10.1063/1.3232241}, abstractNote={We report semiconductor to metal transition (SMT) characteristics of vanadium dioxide (VO2) grown epitaxially on Si (001) at 500 °C. The epitaxial integration with Si (001) was achieved by using epitaxial tetragonal yttria-stabilized zirconia (YSZ) as an intermediate buffer layer, which was grown in situ. From x-ray (θ-2θ and ϕ-scan) and electron diffraction studies, we established that VO2 and YSZ grow in (020) and (001) orientations, respectively, on Si (001) substrate and epitaxial relationship was established to be “VO2[001] or VO2[100]”//YSZ[110]//Si [100] and VO2(010)//YSZ(001)//Si(001). VO2/YSZ/Si(001) heterostructures showed approximately three orders of magnitude reversible change in resistivity and hysteresis of ∼6 K upon traversing the transition temperature. A 10 °C increase in the SMT temperature of these VO2 films, compared to the value reported for bulk VO2, has been explained on the basis of uniaxial stress along the c-axis, which can stabilize the covalent monoclinic phase up to higher temperatures. A correlation between in-plane orientations of the film and the transition width has also been suggested, which is consistent with our previously published thermodynamic model.}, number={11}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Gupta, A. and Aggarwal, R. and Gupta, P. and Dutta, T. and Narayan, Roger J. and Narayan, J.}, year={2009}, month={Sep}, pages={111915} }
 @article{azmy_gupta_pugh_2008, title={Computational Modelling of Genome-Side Transcription Assembly Networks Using a Fluidics Analogy}, volume={3}, ISSN={["1932-6203"]}, DOI={10.1371/journal.pone.0003095}, abstractNote={Understanding how a myriad of transcription regulators work to modulate mRNA output at thousands of genes remains a fundamental challenge in molecular biology. Here we develop a computational tool to aid in assessing the plausibility of gene regulatory models derived from genome-wide expression profiling of cells mutant for transcription regulators. mRNA output is modelled as fluid flow in a pipe lattice, with assembly of the transcription machinery represented by the effect of valves. Transcriptional regulators are represented as external pressure heads that determine flow rate. Modelling mutations in regulatory proteins is achieved by adjusting valves' on/off settings. The topology of the lattice is designed by the experimentalist to resemble the expected interconnection between the modelled agents and their influence on mRNA expression. Users can compare multiple lattice configurations so as to find the one that minimizes the error with experimental data. This computational model provides a means to test the plausibility of transcription regulation models derived from large genomic data sets.}, number={8}, journal={PLOS ONE}, author={Azmy, Yousry Y. and Gupta, Anshuman and Pugh, Franklin}, year={2008}, month={Aug} }
 @article{kripakaran_gupta_matzen_2008, title={Computational framework for remotely operable laboratories}, volume={24}, ISSN={["0177-0667"]}, DOI={10.1007/s00366-008-0089-y}, abstractNote={Decision-makers envision a significant role for remotely operable laboratories in advancing research in structural engineering, as seen from the tremendous support for the network for earthquake engineering simulation (NEES) framework. This paper proposes a computational framework that uses LabVIEW and web technologies to enable observation and control of laboratory experiments via the internet. The framework, which is illustrated for a shaketable experiment, consists of two key hardware components: (1) a local network that has an NI-PXI with hardware for measurement acquisition and shaketable control along with a Windows-based PC that acquires images from a high-speed camera for video, and (2) a proxy server that controls access to the local network. The software for shaketable control and data/video acquisition are developed in the form of virtual instruments (VI) using LabVIEW development system. The proxy server employs a user-based authentication protocol to provide security to the experiment. The user can run perl-based CGI scripts on the proxy server for scheduling to control or observe the experiment in a future timeslot as well as gain access to control or observe the experiment during that timeslot. The proxy server implements single-controller multiple-observer architecture so that many users can simultaneously observe and download measurements as a single controller decides the waveform input into the shaketable. A provision is also created for users to simultaneously view the real-time video of the experiment. Two different methods to communicate the video are studied. It is concluded that a JPEG compression of the images acquired from the camera offers the best performance over a wide range of networks. The framework is accessible by a remote user with a computer that has access to a high-speed internet connection and has the LabVIEW runtime engine that is available at no cost to the user. Care is taken to ensure that the implementation of the LabVIEW applications and the perl scripts have little dependency for ease of portability to other experiments.}, number={4}, journal={ENGINEERING WITH COMPUTERS}, author={Kripakaran, Prakash and Gupta, Abhinav and Matzen, Vernon C.}, year={2008}, month={Oct}, pages={405–415} }
 @article{kripakaran_gupta_baugh_2007, title={A novel optimization approach for minimum cost design of trusses}, volume={85}, ISSN={["1879-2243"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-36049020582&partnerID=MN8TOARS}, DOI={10.1016/j.compstruc.2007.04.006}, abstractNote={This paper describes new optimization strategies that offer significant improvements in performance over existing methods for bridge-truss design. In this study, a real-world cost function that consists of costs on the weight of the truss and the number of products in the design is considered. We propose a new sizing approach that involves two algorithms applied in sequence – (1) a novel approach to generate a “good” initial solution and (2) a local search that attempts to generate the optimal solution by starting with the final solution from the previous algorithm. A clustering technique, which identifies members that are likely to have the same product type, is used with cost functions that consider a cost on the number of products. The proposed approach gives solutions that are much lower in cost compared to those generated in a comprehensive study of the same problem using genetic algorithms (GA). Also, the number of evaluations needed to arrive at the optimal solution is an order of magnitude lower than that needed in GAs. Since existing optimization techniques use cost functions like those of minimum-weight truss problems to illustrate their performance, the proposed approach is also applied to the same examples in order to compare its relative performance. The proposed approach is shown to generate solutions of not only better quality but also much more efficiently. To highlight the use of this sizing approach in a broader optimization framework, a simple geometry optimization algorithm that uses the sizing approach is presented. This algorithm is also shown to provide solutions better than the existing results in literature.}, number={23-24}, journal={COMPUTERS & STRUCTURES}, author={Kripakaran, Prakash and Gupta, Abhinav and Baugh, John W., Jr.}, year={2007}, month={Dec}, pages={1782–1794} }
 @article{saigal_gupta_2007, title={Combination of modal responses: A closed-form formulation for rigid response coefficient}, volume={237}, ISSN={["0029-5493"]}, DOI={10.1016/j.nucengdes.2007.04.003}, abstractNote={Recent studies conducted by US Nuclear Regulatory Commission (USNRC) for combining modal responses in a response spectrum method of seismic analysis and design have emphasized that each modal response quantity should be separated into damped-periodic and rigid parts before combining the contributions from different modes. The damped-periodic parts of modal responses are combined using the double-sum equation whereas the rigid parts are combined algebraically. A particular modal response quantity is separated into damped-periodic and rigid parts using the “rigid response coefficient”. The USNRC sponsored study recommends the calculation of rigid response coefficient by either the Lindley–Yow approach or Gupta method. While Lindley–Yow's method has a heuristic basis and gives incorrect results in low frequency region, Gupta's method is based on numerical studies of free-field earthquake motions and works well in the frequency regions of interest for a free-field ground motion. A closed-form solution was developed by Hahn and Valenti in 1997 using a frequency domain approach. With appropriate simplifications, their work can be shown to result in an expression which is very similar to that given by Gupta. It must be noted that the earthquake input to the secondary systems such as piping and equipment is defined by a floor motion and not a free-field ground motion. The frequency characteristics of a floor motion are very different from those of a free-field ground motion. In this paper, we study the validity of existing formulations for the case of floor motions and develop a closed-form solution based on a time domain approach to explain the behavior of rigid response coefficient. The formulation is then used to explain the nature of variation in rigid response coefficient for ground as well as floor motions. It is shown that the proposed formulation and its simplified form gives results that are identical to those evaluated numerically in the complete frequency region of interest.}, number={19}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Saigal, Rakesh K. and Gupta, Abhinav}, year={2007}, month={Oct}, pages={2075–2082} }
 @inproceedings{cropper_gupta_2006, title={Analytical and Experimental Investigation of the Damping Matrix in Shear Building Models}, ISBN={9780784408896}, url={http://dx.doi.org/10.1061/40889(201)83}, DOI={10.1061/40889(201)83}, abstractNote={In this paper, we present a study conducted on investigating the nature of damping matrix associated with multi degree of freedom simple shear building models. The various conventional methods of creating damping matrices in structures are summarized and numerical examples are used to illustrate the inconsistencies among them. Numerical examples are also used to illustrate the significance of non-zero off diagonal terms in the transformed damping matrix obtained after pre and post multiplication with mode shape matrix, i.e. the significance of non-classical nature of damping matrix in certain cases. The analytical study is followed by the description of a laboratory experiment that is developed to evaluate the validity of analytical results. The results from experimental studies of a simple 2-DOF shear building model are presented to validate the inconsistencies associated with the conventional methods of creating damping matrices in structures. It is also shown that the incorrect formulation of damping matrix results in highly incorrect responses.}, booktitle={Structures Congress 2006}, publisher={American Society of Civil Engineers}, author={Cropper, Michael E. and Gupta, Abhinav}, year={2006}, month={Oct} }
 @inproceedings{kripakaran_gupta_2006, title={Computational Approaches for Decision Support in Structural Performance Evaluation}, ISBN={9780784408780}, url={http://dx.doi.org/10.1061/40878(202)17}, DOI={10.1061/40878(202)17}, abstractNote={Structural engineers face complex decision making in the design and performance evaluation of structural systems. The complexity of the problem is generally determined by factors like continuous and/or discrete nature of its decision variables and presence of multiple objectives. Often, many solutions are available for the problem-at-hand and significant time is spent in identifying the final solution due to the iterative nature of the design process. Formulating this problem as an optimization problem has enabled the application of numerous approaches from operations research. Previously, these approaches were not applicable in most cases either due to the enormity of the decision space or the computational complexities associated with the design problem. The availability of processing power and memory as a result of recent advances in computing technology, has now evoked interest in the application of sophisticated optimization techniques like genetic algorithms for structural optimization. But, current research in structural optimization suffers from two major limitations that are related to the way optimization is currently employed for supporting the decision-making process. The first limitation is related to the adaptation of mathematical optimization techniques for application in structural engineering. Researchers have tended to use optimization techniques like black-boxes. It is possible to develop special adaptations to the mathematical optimization techniques for the particular problem-in-hand that may significantly improve their overall performance. An example of such an adaptation may be related to adapting Genetic Algorithms (GA) to problem-dependent implementation based upon knowledge of structural behavior. Another limitation of current optimization studies lies in their suggested use to find a single “optimal” solution. The final solution from an optimization approach is rarely the best solution because optimization formulations often exclude certain objectives and constraints due to the difficulty in quantifying them. One way of overcoming this drawback is by using optimization to generate a set of “good” alternatives. Then, the engineer will have the opportunity to study these alternatives, conduct what-if analyses, make minor changes if needed and pick the best solution from the set. The engineer can then employ professional judgment and expertise to evaluate these alternatives with respect to unmodeled factors. Many structural design problems belong to the class of discrete optimization. For example, the types of available products for various members in a truss are often chosen from a discrete 17 ANALYSIS AND COMPUTATION SPECIALTY CONFERENCE th}, booktitle={Structures Congress 2006}, publisher={American Society of Civil Engineers}, author={Kripakaran, Prakash and Gupta, Abhinav}, year={2006}, month={Oct} }
 @article{wirgau_gupta_matzen_2006, title={Internet-enabled remote observation and control of a shake table experiment}, volume={20}, DOI={10.1061/(ASCE)0887-3801(2006)20:4(271)}, abstractNote={This paper describes a computational framework and the corresponding interfaces required to convert a shake table experiment for remote access including control, observation, and protection from misuse. The laboratory environment is expanded by this research to include remote controlling of the experiment, multiuser viewing, data storage, and download capabilities. The software technology selected for programming this application is LabVIEW and its real-time counterpart, LabVIEW RT. Practical and intuitive control panels coupled with easy to follow data flow block diagrams are made possible by using LabVIEW, which is also capable of handling the data acquisition. The setup in this laboratory environment connects an administrator-controlled host computer to a real-time board that controls the DAQ through a TCP/IP connection. The information sent and received through the DAQ card is processed by LabVIEW RT code embedded upon the real-time board. The information is then sent back to the host computer for saving, visualization, and distribution to remote clients. Data visualization is implemented through a graphical user interface that is intended to serve the functions of an oscilloscope for displaying the accelerations from both the table and the structure in real time. Physical visualization is made possible by way of a real-time video stream. Protection of the experimental system from unintended or accidental damage required sufficient safety protocols.}, number={4}, journal={Journal of Computing in Civil Engineering}, author={Wirgau, S. and Gupta, A. and Matzen, V.}, year={2006}, pages={271–280} }
 @inbook{kripakaran_gupta_2006, title={MGA - A mathematical approach to generate design alternatives}, volume={4200}, ISBN={978-3-540-46246-0}, DOI={10.1007/11888598_37}, abstractNote={Optimization methods are typically proposed to find a single solution that is optimal with respect to the modeled objectives and costs. In practice, however, this solution is not the best suited for design as mathematical models seldom include all the costs and objectives. This paper presents a technique – Modeling to Generate Alternatives (MGA), that instead uses optimization to generate good design alternatives, which the designer may explore with respect to the unmodeled factors. The generated alternatives are close to the optimal solution in objective space but are distant from it in decision space. An application of this technique to design of moment-resisting steel frames is illustrated.}, booktitle={Intelligent computing in engineering and architecture ?h [electronic resource] : ?b 13th EG-ICE Workshop 2006, Ascona, Switzerland, June 25-30, 2006 : revised selected papers / ?c Ian F. C. Smith (ed.).}, publisher={Springer}, author={Kripakaran, P. and Gupta, A.}, year={2006}, pages={408–415} }
 @article{gupta_choi_2005, title={Consideration of uncertainties in seismic analysis of coupled building piping systems}, volume={235}, ISSN={["0029-5493"]}, DOI={10.1016/j.nucengdes.2005.05.013}, abstractNote={In this paper, we present an analytical study for incorporating the effect of uncertainties in modal properties of uncoupled primary and secondary systems in the seismic analysis of non-classically damped coupled systems such as building piping by response spectrum method. Monte Carlo simulation is used to illustrate that the secondary system design response when defined at a non-exceedence probability of 0.84 over the individual responses obtained from multiple response spectrum analyses by considering uncertainties in modal parameters is excessively higher than the design response specified at the same non-exceedence probability over the responses obtained from multiple time history analyses. This is so because the earthquake input in a response spectrum method is characterized by a design spectrum which by itself is specified at a non-exceedence probability of 0.84 over the multiple time histories with normalized peak ground acceleration. Accurate evaluation of design response at a non-exceedence probability of 0.84 in the response spectrum method requires that the individual modal responses be defined at appropriate probability levels that may be different than the conventionally used non-exceedence probability value of 0.84. The required probability values are evaluated by using first order reliability method. It is shown that the modal responses, when defined at a non-exceedence probability of 0.84, would give relatively accurate values of design response only if the individual modes are perfectly correlated or a single mode contributes to the particular response quantity of interest. For all other cases, the design response would be excessively high. The accurate probability values needed to specify each modal response evaluated using the first order reliability method cannot be incorporated directly in a response spectrum analysis due to computational inefficiency. Two simplified methods, based on total probability theorem, are developed in this paper to overcome this limitation. It is shown that these methods give design response values that are very close to the true values obtained from multiple time history analyses.}, number={17-19}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Gupta, A and Choi, B}, year={2005}, month={Aug}, pages={2071–2086} }
 @article{gupta_kripakaran_mahinthakumar_baugh_2005, title={Genetic algorithm-based decision support for optimizing seismic response of piping systems}, volume={131}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-14544294041&partnerID=MN8TOARS}, DOI={10.1061/(asce)0733-9445(2005)131:3(389)}, abstractNote={This paper describes computational approaches used in a prototype decision support system (DSS) for seismic design and performance evaluation of piping supports. The DSS is primarily based on a genetic algorithm (GA) that uses finite element analyses, and an existing framework for high performance distributed computing on workstation clusters. A detailed discussion is presented on various issues related to the development of an efficient GA implementation for evaluating the trade-off between the number of supports and cost. An integer string representation of the type used in some existing studies, for instance, is shown to be inferior to a binary string representation, which is appropriate when supports are modeled as axially rigid. A novel seeding technique, which overcomes the inefficiencies of conventional methods in the context of pipe support optimization, is also presented. Finally, an efficient crossover scheme is proposed for generating trade-off curves and the approach is validated with respect ...}, number={3}, journal={Journal of Structural Engineering}, author={Gupta, A. and Kripakaran, P. and Mahinthakumar, G. K. and Baugh, J. W.}, year={2005}, pages={389–398} }
 @inproceedings{gupta_gabr_matzen_2004, title={Alternatives in the implementation of internet-enabled laboratory experiments in undergraduate civil engineering courses}, booktitle={ASEE 2004 annual conference & exposition$h[electronic resource] :June 20-23, 2004, Salt Lake City, Utah : Engineering education reaches new heights : conference proceedings}, publisher={Washington, D.C.: American Soceity for Engineering Education}, author={Gupta, A. and Gabr, M. A. and Matzen, V. C.}, year={2004} }
 @article{rustogi_gupta_2004, title={Modeling the dynamic behavior of electrical cabinets and control panels: Experimental and analytical results}, volume={130}, DOI={10.1061/(asce)0733-9445(2004)130:3(511)}, abstractNote={Ritz vector approach for evaluating the dynamic properties of electrical cabinets is based on the premise that a single significant cabinet mode is sufficient to calculate accurate incabinet spectra needed in the seismic qualification of electrical instruments mounted inside the cabinet. It uses mathematical functions to characterize the significant mode shapes that can be either a local mode shape of the structural member or a superposition of the global cabinet and the local mode shapes. The significant modes for typical cabinets have been identified from fixed-base finite element analyses. In this paper, modal data from in situ and shake table tests for two different cabinets is used to evaluate not only the validity of finite element analysis results but also the premise for developing Ritz vector approach. A key difference observed in the test data is related to the existence of a global rocking in cabinets that are anchored at the base. A rigid body rocking due to base plate uplift cannot be evaluated from fixed-base finite element models that were used in the development of the Ritz vector approach. Finite element analyses after modifications for incorporating cabinet rocking due to base plate uplifting give results that are close to the test data. Even though the test data and the new analyses show that the significant cabinet mode is different from what has been considered in the past, the basic premise for Ritz vector approach remains unchanged. Minor modifications needed in the Ritz vector approach for incorporating cabinet rocking superimposed with local mode shapes are also presented.}, number={3}, journal={Journal of Structural Engineering (New York, N.Y.)}, author={Rustogi, S. K. and Gupta, A.}, year={2004}, pages={511–519} }
 @article{wang_gupta_tiwari_zhang_narayan_2004, title={TaN-TiN binary alloys and superlattices as diffusion barriers for copper interconnections}, volume={33}, ISSN={0361-5235 1543-186X}, url={http://dx.doi.org/10.1007/S11664-004-0300-X}, DOI={10.1007/S11664-004-0300-X}, number={1}, journal={Journal of Electronic Materials}, publisher={Springer Science and Business Media LLC}, author={Wang, H. and Gupta, A. and Tiwari, Ashutosh and Zhang, X. and Narayan, J.}, year={2004}, month={Jan}, pages={L5–L5} }
 @article{gupta_choi_2003, title={Reliability-based load and resistance factor design for piping: an exploratory case study}, volume={224}, ISSN={["0029-5493"]}, DOI={10.1016/S0029-5493(03)00133-X}, abstractNote={This paper presents an exploratory case study on the application of Load and Resistance Factor Design (LRFD) approach to the Section III of ASME Boiler and Pressure Vessel code for piping design. The failure criterion for defining the performance function is considered as plastic instability. Presently used design equation is calibrated by evaluating the minimum reliability levels associated with it. If the target reliability in the LRFD approach is same as that evaluated for the presently used design equation, it is shown that the total safety factors for the two design equations are identical. It is observed that the load and resistance factors are not dependent upon the diameter to thickness ratio. A sensitivity analysis is also conducted to study the variations in the load and resistance factors due to changes in (a) coefficients of variation for pressure, moment, and ultimate stress, (b) ratio of mean design pressure to mean design moment, (c) distribution types used for characterizing the random variables, and (d) statistical correlation between random variables. It is observed that characterization of random variables by log-normal distribution is reasonable. Consideration of statistical correlation between the ultimate stress and section modulus gives higher values of the load factor for pressure but lower value for the moment than the corresponding values obtained by considering the variables to be uncorrelated. Since the effect of statistical correlation on the load and resistance factors is relatively insignificant for target reliability values of practical interest, the effect of correlated variables may be neglected.}, number={2}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Gupta, A and Choi, B}, year={2003}, month={Sep}, pages={161–178} }
 @article{yang_rustogi_gupta_2003, title={Rocking stiffness of mounting arrangements in electrical cabinets and control panels}, volume={219}, ISSN={["0029-5493"]}, DOI={10.1016/S0029-5493(02)00279-0}, abstractNote={Several studies have shown that the consideration of a rigid body-rocking mode in a cabinet is necessary to evaluate accurate incabinet spectra. Observations from finite element analyses are used to study cabinet rocking behavior and to show that accurate representation of the boundary conditions at the cabinet base is essential in the evaluation of correct rocking mode. Simple formulations for evaluating the rocking stiffness are developed by conducting detailed analytical studies for three different types of cabinet mounting arrangements. Availability of these formulations enables incorporation of a cabinet rocking mode in the Ritz vector approach [Nucl. Eng. Des. 190 (1990) 225] for evaluating the cabinet dynamic properties in significant mode and for generating the incabinet response spectra.}, number={2}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Yang, JF and Rustogi, SK and Gupta, A}, year={2003}, month={Feb}, pages={127–141} }
 @article{wang_gupta_tiwari_zhang_narayan_2003, title={TaN-TiN binary alloys and superlattices as diffusion barriers for copper interconnects}, volume={32}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-003-0081-7}, number={10}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Wang, H and Gupta, A and Tiwari, A and Zhang, X and Narayan, J}, year={2003}, month={Oct}, pages={994–999} }
 @article{bray_gupta_parsons_2002, title={Effect of hydrogen on adsorbed precursor diffusion kinetics during hydrogenated amorphous silicon deposition}, volume={80}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000174623300040&KeyUID=WOS:000174623300040}, DOI={10.1063/1.1467616}, abstractNote={Fractal analysis of the surface topography is used to study the effects of hydrogen dilution on the surface transport kinetics during the plasma deposition of hydrogenated amorphous silicon. Images obtained from atomic force microscopy are examined using dimensional fractal analysis, and surface diffusion lengths of growth precursors are estimated from the measured correlation lengths. The addition of small amounts of hydrogen (H2/SiH4 ratios <10/1) during deposition leads to a decrease in the diffusion length, but larger hydrogen dilutions result in increased diffusion length. Moreover, the measured surface diffusion activation barrier is reduced from 0.20 eV for deposition from pure SiH4 to 0.13 eV with high hydrogen dilution. Results are consistent with recent models for precursor surface transport during low-temperature deposition, and give insight into critical processes for low-temperature silicon crystallization.}, number={13}, journal={Applied Physics Letters}, author={Bray, KR and Gupta, A and Parsons, Gregory}, year={2002}, pages={2356–2358} }
 @article{gupta_yang_2002, title={Modified Ritz vector approach for dynamic properties of electrical cabinets and control panels}, volume={217}, ISSN={["0029-5493"]}, DOI={10.1016/S0029-5493(02)00133-4}, abstractNote={Often, the simple methods used for evaluating incabinet spectra needed in the seismic qualification of safety related electrical instruments ignore the dynamic characteristics of the electrical control panels and cabinets. Gupta et al. (Nucl. Eng. Des. 190 (1999a) 255) developed a Ritz vector approach for evaluating the dynamic properties of the cabinets and the incabinet spectra. This approach is based on the conclusions drawn from detailed finite element analyses of several cabinets. In the present paper, we illustrate the limitations of the originally proposed Ritz vector approach that were encountered during subsequent applications to actual cabinets. Modifications to the originally proposed formulations are presented and their accuracy evaluated by comparison of results for actual cabinets with the corresponding results obtained from finite element analyses. The modified Ritz vector approach can account for actual rotational constraints imparted by supporting structural members such as stiffeners. It can also be applied to bench board type cabinets in which instruments are mounted on plates or frames that are inclined to the global axes as well as to frames in which parallel frame members can vibrate in different vibration shapes due to differences in boundary conditions and non-uniform mass distribution.}, number={1-2}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Gupta, A and Yang, JF}, year={2002}, month={Aug}, pages={49–62} }
 @article{zhao_gupta_2002, title={Redundancy in residual vectors for missing mass effect in coupled modal synthesis}, volume={128}, DOI={10.1061/(asce)0733-9445(2002)128:9(1231)}, abstractNote={It has been illustrated in the past that a modal synthesis gives incorrect modal properties and seismic response of nonclassically damped coupled systems when all the modes of uncoupled primary and secondary systems are not included. The effect of missing mass contained in the truncated high frequency modes can be represented using residual modal vectors. This paper illustrates two possibilities in which the residual modal matrix may contain redundant vectors leading to a breakdown of the originally proposed method. First, secondary systems with a support inclined to the primary system orthogonal connecting degrees of freedom can have residual vectors that are scalar multiple of each other (parallel). Second, the number of residual and nonrigid modal vectors can be more than the total number of secondary system modes (equal to the number of secondary system degrees of freedom) in multiply connected simple secondary systems. A solution is presented to identify and eliminate both these types of redundant ve...}, number={9}, journal={Journal of Structural Engineering (New York, N.Y.)}, author={Zhao, J. and Gupta, A.}, year={2002}, pages={1231–1235} }
 @article{yang_gupta_2002, title={Ritz vector approach for static and dynamic analysis of plates with edge beams}, volume={253}, ISSN={["0022-460X"]}, DOI={10.1006/jsvi.2001.4047}, abstractNote={Abstract A Ritz vector approach is used to develop new formulations for evaluating the static and the dynamic characteristics of rectangular plates with edge beams. Unlike previous studies in which stiffness coefficients with specified distributions along the plate edges are used to represent the effect of edge restraints, the effect of elastic edge restraints is accounted for by including appropriate integrals for edge beams in the expressions for total kinetic and potential energies in a Rayleigh–Ritz approach. The effect of various types of boundary conditions at the beam ends is accounted for by considering the corresponding Ritz vectors. The contribution of beam mass to the total kinetic energy is also considered in the proposed approach. This effect has often been neglected in the previous studies but can be significant in some applications. The results obtained from the application of the proposed approach to a variety of examples are compared with the corresponding results obtained from the finite element analysis.}, number={2}, journal={JOURNAL OF SOUND AND VIBRATION}, author={Yang, J and Gupta, A}, year={2002}, month={May}, pages={373–388} }
 @article{gupta_parsons_2000, title={Bond strain, chemical induction, and OH incorporation in low-temperature (350-100 degrees C) plasma deposited silicon dioxide films}, volume={18}, ISSN={["1071-1023"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000087654200131&KeyUID=WOS:000087654200131}, DOI={10.1116/1.591468}, abstractNote={New device concepts are being considered with very demanding requirements for low-temperature processing. In this article, infrared transmission and ellipsometry is used to compare silicon oxide films formed by plasma chemical vapor deposition using SiH4, N2O, and either He or H2 dilution gas between 350 and 100 °C. The Si–O asymmetric stretching mode is affected by bond strain and chemical induction, and monitoring the Si–O peak position gives insight into the effect of process conditions on local bond structure. Hydrogen is expected to affect surface processes during growth, for instance, to enable the removal of surface SiOH bonds through H-mediated abstraction, leading to improved bonding structure at low temperature. We find that exposing the surface to hydrogen atoms during growth helps eliminate isolated SiOH bonds, leading to Si–Si bond formation. However, an increase in associated SiOH bonding groups, stabilized by hydrogen bonding, is also observed. The density of associated SiOH groups is larger at low temperature where the rate of water desorption is reduced, suggesting that the associated OH is formed by physisorbed water produced during OH removal. Films deposited with hydrogen dilution show somewhat improved electrical performance at <200 °C, but further work is required to produce high quality films at very low temperatures.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Gupta, A and Parsons, GN}, year={2000}, pages={1764–1769} }
 @article{gupta_rustogi_gupta_1999, title={Ritz vector approach for evaluating incabinet response spectra}, volume={190}, ISSN={["0029-5493"]}, DOI={10.1016/S0029-5493(99)00076-X}, abstractNote={A new method is proposed for evaluating accurate incabinet response spectra for seismic qualification of electrical instruments. Finite element analysis of several typical cabinets shows that only few (often one) modes contribute significantly to the spectral accelerations at critical instrument locations inside the cabinet. In most cases the significant mode is a local mode of the cabinet component like door or back wall on which the instrument is mounted. In some cases it can also be a global cabinet mode or a superposition of the global cabinet and local component modes. Dynamic properties of the significant modes can be calculated using Rayleigh–Ritz method. The engineering effort and computational time taken by the new method is a minute fraction of that by the finite element method.}, number={3}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Gupta, A and Rustogi, SK and Gupta, AK}, year={1999}, month={Jun}, pages={255–272} }
 @article{gupta_gupta_1998, title={Missing mass effect in coupled analysis. I: Complex modal properties}, volume={124}, DOI={10.1061/(asce)0733-9445(1998)124:5(490)}, abstractNote={New formulations are developed to account for the effect of uncalculated high frequency rigid modes in the seismic analysis of coupled primary–secondary systems by modal synthesis approach. The effect of uncalculated rigid modes is included in terms of residual modal vectors for both the uncoupled primary and the multiply supported secondary systems. The reduced eigenvalue problem, obtained by transforming the original equation of motion in which the displacements at the secondary system degrees of freedom (DOF) are expressed relative to the base of the primary system, gives incorrect results when all the modes of the secondary system are not included and the effect of high frequency modes is included through residual modal vectors. An alternate formulation is presented in which the original equation of motion is transformed such that the displacements at the secondary system DOF are expressed relative to the primary system connecting DOF. The reduced eigenvalue problem is solved using the transformed equ...}, number={5}, journal={Journal of Structural Engineering (New York, N.Y.)}, author={Gupta, A. and Gupta, A. K.}, year={1998}, pages={490–495} }
 @article{gupta_gupta_1998, title={Missing mass effect in coupled analysis. II: Residual response}, volume={124}, DOI={10.1061/(asce)0733-9445(1998)124:5(496)}, abstractNote={This is the second paper of two papers that describe the procedures to include the effect of uncalculated high frequency modes in coupled modal synthesis. Because the residual modal vectors of a multiply supported secondary system cannot be included directly in a coupled modal synthesis, formulations are developed to calculate the residual response due to “missing mass” contained in the uncalculated high frequency rigid modes and combine it with the response due to nonrigid modes. A criterion is developed to determine a rigid (cut-off) frequency for the uncoupled secondary system modes and estimate the upper bound of error in the secondary system residual response.}, number={5}, journal={Journal of Structural Engineering (New York, N.Y.)}, author={Gupta, A. and Gupta, A. K.}, year={1998}, pages={496–500} }
 @book{gupta_gupta_1997, title={CREST-IRS: A computer program for generating instructure response spectra (Version 1.0)}, publisher={Center for Nuclear Power Plant Structures, Equipment and Piping in the Department of Civil Engineering}, author={Gupta, A. and Gupta, A. K.}, year={1997} }
 @article{gupta_gupta_1997, title={Seismic response of tuned single degree of freedom secondary systems}, volume={172}, ISSN={["0029-5493"]}, DOI={10.1016/S0029-5493(96)00003-9}, abstractNote={Modal synthesis procedure for evaluating spectral acceleration in the single degree of freedom (SDOF) secondary system oscillator is studied. Problems encountered in the evaluation of response for secondary oscillators that are tuned or nearly tuned with the primary system modes are discussed and solutions to these problems are presented. A new hybrid approach is proposed that gives accurate spectral acceleration in tuned secondary systems for both cases of zero and non zero mass ratio in structures that are nonclassically damped. Formulations are developed to evaluate the interaction-free (zero mass ratio) instructure spectral accelerations for perfectly tuned secondary oscillators in a coupled primary-secondary system when the two uncoupled systems have same damping characteristics (classical damping case).}, number={1-2}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Gupta, A and Gupta, AK}, year={1997}, month={Jul}, pages={17–25} }