A robust method for reliability updating with equality information using sequential adaptive importance sampling

Reliability updating refers to a problem that integrates Bayesian updating technique with structural reliability analysis and cannot be directly solved by structural reliability methods (SRMs) when it involves equality information. The state-of-the-art approaches transform equality information into inequality information by introducing an auxiliary standard normal parameter. These methods, however, encounter the loss of computational efficiency due to the difficulty in finding the maximum of the likelihood function, the large coefficient of variation (COV) associated with the posterior failure probability and the inapplicability to dynamic updating problems where new information is constantly available. To overcome these limitations, this paper proposes an innovative method called RU-SAIS (reliability updating using sequential adaptive importance sampling), which combines elements of sequential importance sampling and K-means clustering to construct a series of important sampling densities (ISDs) using Gaussian mixture. The last ISD of the sequence is further adaptively modified through application of the cross entropy method. The performance of RU-SAIS is demonstrated by three examples. Results show that RU-SAIS achieves a more accurate and robust estimator of the posterior failure probability than the existing methods such as subset simulation.Comment: 38 pages, 6 tables, 9 figure

2-Dimensional Simulation of Deterioration Process for Life-cycle Performance Assessment of RC Structures in Marine Environment

The reliability-based durability design approach doesnt account for neither the surface deterioration of structures over service lives, nor the possible life-cycle maintenance. The paper employs the 2-dimentional (2D) simulation technique based on random field theory and Monte Carlo simulation method, to analyze the life-cycle performance of reinforced concrete structures under chloride attack, which is illustrated through the surface deterioration modelling of immersed tube tunnel segment of Hong Kong-Zhuhai-Macao (HZM) sea-link project. Then, the paper compares the maintenance demands imposed to different durability design specifications with different life-cycle performance target. The results may provide useful information in future durability design and aid the decision making process

Seismic Fragility Analysis of Precast RC Shear Wall-Frame Structures with Connection Defects

As observed in many evidences during past earthquakes, the quality of precast concrete (PC) connections is one of the main factors that affect the seismic reliability of PC structures. In the context of Chinas rapid development of PC structures in high seismic regions, it is important to assess the effect of connection deficiency on their seismic performance. This paper proposes a framework for seismic fragility analysis of PC shear wall-frame structures whose wall panels are assembled through grout sleeve connections that are susceptible to insufficient grouting. The uncertainties associated with the defected sleeve connections are taken into account, and then the probabilistic response of shear wall model is estimated through Point Estimate (PE) method. Then, a generic shear wall-frame building is modeled on platform of OpenSees. Seismic fragility analysis is performed to the structures with different degrees of connection deficiency, showing that the seismic performance is significantly affected by connection deficiencies, and great effort should be taken for the quality control of grout sleeve connections in construction site

Evaluating Seismic Performance of Water Supply System with Multiple-Functionality-Based Measurement

Water supply system (WSS) is an essential part of the infrastructure system of a city and plays an important role in resisting and recovering from natural disasters. Disruption of WSS due to seismic damage of pipelines would impair its city functionalities including fire suppression, water supply of critical facilities and domestic water supply. Some metrics have been proposed in existing literatures to evaluate the performance of WSS subjected to disaster events. Nevertheless, these metrics, aiming at a specific functionality of WSS, e.g. fire suppression or domestic water supply, cannot give a comprehensive evaluation with its multiple functionalities included. In this regard, this paper proposes an economic loss-based metric to evaluate integratedly the consequence of disruption of two functionalities, fire suppression and domestic water supply, of WSS subjected to hazard event. The direct economic losses associated with the two broken functionalities are estimated and compared through the case study of a water distribution network of a city in South-West China subjected to earthquake. It is found that the two functionality losses have small correlation and the strategy to improve the seismic performance should consider both of them integratedly

Evaluation of the neonatal sequential organ failure assessment and mortality risk in neonates with respiratory distress syndrome: A retrospective cohort study

BackgroundRespiratory distress syndrome (RDS) is one of the leading causes of neonatal death in the neonatal intensive care unit (NICU). Previous studies have suggested that the development of neonatal RDS may be associated with inflammation and lead to organ dysfunction. The neonatal sequential organ failure assessment (nSOFA) scoring system is an operational definition of organ dysfunction, but whether it can be used to predict mortality in neonates RDS is unknown. The aim of this study was to clarify the performance of the nSOFA score in predicting mortality in patients with neonatal RDS, with the aim of broadening the clinical application of the nSOFA score.MethodsNeonates with RDS were identified from the Medical Information Mart for Intensive Care (MIMIC)-III database. Cox proportional hazards model were used to assess the association between nSOFA score and mortality. Propensity score matched analysis were used to assess the robustness of the analytical results.ResultsIn this study of 1,281 patients with RDS of which 57.2% were male, death occurred in 40 cases (3.1%). Patients with high nSOFA scores had a higher mortality rate of 10.7% compared with low nSOFA scores at 0.3%. After adjusting for confounding, multivariate Cox proportional risk analysis showed that an increase in nSOFA score was significantly associated with increased mortality in patients with RDS [adjusted Hazards Ratio (aHR): 1.48, 95% Confidence Interval (CI): 1.32–1.67; p < 0.001]. Similarly, the High nSOFA group was significantly associated with higher mortality in RDS patients (aHR: 19.35, 95% CI: 4.41–84.95; p < 0.001) compared with the low nSOFA group.ConclusionThe nSOFA score was positively associated with the risk of mortality in cases of neonatal RDS in the NICU, where its use may help clinicians to quickly and accurately identify high risk neonates and implement more aggressive intervention

Mathematical Formulation of Tools for Assessment of Fragility and Vulnerability of Damaged Buildings

Performance-Based (PBE) and Consequence-Based (CBE) are new approaches to seismic design, evaluation and risk assessment, in which design criteria are devised to achieve stated performance objectives, and regional losses to civil infrastructure are mitigated through selective interventions for critical components of a civil infrastructure. These new approaches give engineers more flexibility in achieving performance goals but require substantial additional computational resources to fully achieve performance goals. As a step toward making such approaches feasible, this dissertation develops a number of computationally efficient methods for performing finite element-based structural system dynamic response analysis and reliability assessment. The Enhanced Uncoupled Modal Response History Analysis (EUMRHA) procedure developed herein is an efficient response analysis procedure to make the analysis of dynamic structural response to earthquakes in the nonlinear range less time-consuming. This technique is used to investigate the potential for aftershocks to cause additional damage to steel moment frame buildings, utilizing a technique designed to enhance the efficiency of Monte Carlo simulation in estimating low-probability events. Relatively simple probabilistic tools are proposed for purposes of rapid structural evaluation and condition assessment of damaged buildings. Finally, an analysis-based inspection scheme based on an associated probability model of connection damage is proposed for assessing the safety condition of existing buildings, and a procedure to assess the likely performance of an un-repaired building during a future earthquake is developed.Ph.D.Committee Chair: Ellingwood, Bruce R; Committee Member: Craig, James I.; Committee Member: DesRoches,Reginald; Committee Member: Goodno, Barry; Committee Member: Haj-Ali,Rami

Energy Saving Thermal Management of Space Remote Sensor and Validation

An energy-efficient thermal control management method for space remote sensors using optical, mechanical, electrical, and thermal integration is proposed. The satellite power resources are insufficient, so an energy-efficient loop heat pipe (LHP) is designed for six intermittently operating detectors. The charge-coupled device (CCD) has a total heat generation of 72 W and operates for 8 min per orbital cycle. The LHP includes a capillary pump, six cold plates, and two radiators. The working fluid of the LHP is high-purity ammonia and the material of the wick is ceramic. The drive power on the capillary pump evaporator automatically switches between 30 W and 90 W depending on the operating mode of the remote sensor, resulting in an average power saving of about 58.2% compared to a conventional LHP. For the optical structure, a three-stage insulation technology was developed to save heater power and improve temperature stability. A transient numerical simulation model of the LHP was developed to study the vapor–liquid zone of two radiators under the condition of rapid power change. Vacuum thermal tests were conducted and the test data agreed well with the numerical simulation results. The in-orbit temperature data showed that the temperature fluctuations of the optical structure and CCD were less than ±0.2 °C and ±0.8 °C, respectively