Aging concrete structures: a review of mechanics and concepts

The safe and cost-efficient management of our built infrastructure is a challenging task considering the expected service life of at least 50 years. In spite of time-dependent changes in material properties, deterioration processes and changing demand by society, the structures need to satisfy many technical requirements related to serviceability, durability, sustainability and bearing capacity. This review paper summarizes the challenges associated with the safe design and maintenance of aging concrete structures and gives an overview of some concepts and approaches that are being developed to address these challenges

Cross-Layer Resiliency Modeling and Optimization: A Device to Circuit Approach

The never ending demand for higher performance and lower power consumption pushes the VLSI industry to further scale the technology down. However, further downscaling of technology at nano-scale leads to major challenges. Reduced reliability is one of them, arising from multiple sources e.g. runtime variations, process variation, and transient errors. The objective of this thesis is to tackle unreliability with a cross layer approach from device up to circuit level

Risk-Based Approach for Life-Cycle Assessment and Management of Bridges and Ship Structures

Existing civil and marine structures and infrastructures have to maintain their serviceability and safety under the effects induced by normal events and to withstand the effects of extreme events . Although the quantification of the performance of a structural system is usually conducted considering only structural aspects, in this study consequences arising from the occurrence of potential disruption of service due to failure/malfunction of structural components are also considered, leading to risk assessment.Uncertainties are unavoidable in planning, design, and maintenance of structural systems. Advanced probabilistic methods, such as Monte Carlo simulations based on Latin Hypercube sampling, finite element and response surfaces analyses are used in this study in order to account for uncertainties and their propagation over time.The main focus of this study is to develop a risk-based approach for the life-cycle assessment and management of civil and marine structures with emphasis on single highway bridges, groups of bridges, and ship structures. Risk is assessed for highway bridges under the effects of multiple hazards, including traffic, environmental attacks, scour, and earthquakes, whereas the effects of traffic and earthquake are accounted for groups of bridges. Other performance indicators, including reliability, redundancy, and resilience to disasters, are also investigated. For ship structures, a novel approach is developed for the evaluation of time-variant reliability, redundancy, and risk accounting for different limit states of the ship hull, potential effects induced by corrosion, and considering different ship operational conditions over time.Risk is assessed based on reliability analysis by accounting several limit states and quantifying the associated potential monetary losses for a spectrum of consequences, including operating costs and accident costs.A novel approach for near real-time multi-criteria optimal ship routing, integrating risk and structural health monitoring data is developed considering different damage scenarios and generic operational conditions.The developed approaches are applied to several structures, including a highway bridge crossing the Wisconsin River in Wausau, WI, a highway bridge carrying a segment of the northbound I-15 crossing the Temescal Wash located close to the city of Corona, CA, a group of existing bridges located north of the San Diego metropolitan area, and a NAVY\u27s Joint High-Speed Sealift

Maintenance and safety of deteriorating systems: a life-cycle perspective

This paper reviews the key aspects associated with maintenance and safety of deteriorating infrastructure systems from a life-cycle perspective. The main conceptual aspects related to probabilistic optimization of maintenance and rehabilitation of structural systems are discussed. These aspects include life-cycle risk and sustainability assessment, risk-informed and utility-based decision making, and multi-objective optimization of interventions. In general, sustainability assessment is performed by quantifying economic, social, and environmental impacts associated with infrastructure management activities. This keynote paper also reviews various methods for determining optimum life-cycle maintenance, repair, and rehabilitation types and times, as well as the impact of such activities on the total life-cycle cost. The role of probabilistic performance indicators including reliability and risk, the sustainability assessment of deteriorating infrastructure systems, and risk- and utility-informed decision making are highlighted herein

Investigation of Ageing Effects Using the Probabilistic Safety Assessments - Proceedings of the European Workshop on Probabilistic Safety Assessment

JRC – IE Petten organized with the support of the Kernkraftwerk Gösgen-Däniken, Switzerland, an EC Workshop on Investigation of Ageing Effects using the Probabilistic Safety Assessments. The goal of the workshop was to present and discuss the developed methods and approaches and the results obtained for application of reliability and PSA techniques on evaluation and management of NPP ageing. For the units which have approached the end of initial design lifetime and especially for those which are planning to extend the lifetime, it has to be demonstrated that the plant safety level will remain adequate until the end of operation, and to do that, is necessary to evaluate the effects of ageing phenomena on the plant performance and safety. The workshop contained a general session, dedicated to activities of different organizations in PSA field, and a technical session, focused on the results obtained in application of reliability and PSA techniques on evaluation and management of NPP ageing. Based on the presentations and participants experience, discussions about topics considered interested to be developed further were organized. The arising conclusions are presented.JRC.F.5-Nuclear Reactor Safety Assessmen

Control Strategies for Improving Reliability and Efficiency in Modular Power Converters

The significance of modular power converters has escalated drastically in various applications such as electrical energy distribution, industrial motor drives and More Electric Aircraft (MEA) owing to the benefits such as scalability, design flexibility, higher degree of fault tolerance and better maintenance. One of the main advantages of modular systems is the ability to replace the faulty converter cells during maintenance instead of the entire system. However, such maintenance cycles can result in a system of converter cells with different aging. A system with cells having different aging arises the threats of multiple maintenance, lower reliability and availability, and high maintenance costs. For controlling the thermal-stress based aging of modular power converters, power routing strategy was proposed. The thesis focuses on the different implementation strategies of power routing for modular converters. Power semiconductors are one of the most reliability critical components in power converters, and thermal-stress has been identified as the main cause of their failure. This thesis work concentrates on the power semiconductor reliability improvement algorithms. For improving system lifetime, virtual resistor based power routing algorithms for single stage and multi-stage modular architectures have been investigated through simulations and validated with experiment. A unified framework for routing the power in complex modular converter architectures is defined based on graph theory. Popular converter architectures for Smart Transformer (ST) and MEA applications are modeled as graphs to serve as the basis for developing power flow optimization. The effectiveness of graph theory for optimizing the power flow in modular systems is demonstrated with the help of proposed algorithms

Multi-criteria optimization for energy-efficient multi-core systems-on-chip

The steady down-scaling of transistor dimensions has made possible the evolutionary progress leading to today’s high-performance multi-GHz microprocessors and core based System-on-Chip (SoC) that offer superior performance, dramatically reduced cost per function, and much-reduced physical size compared to their predecessors. On the negative side, this rapid scaling however also translates to high power densities, higher operating temperatures and reduced reliability making it imperative to address design issues that have cropped up in its wake. In particular, the aggressive physical miniaturization have increased CMOS fault sensitivity to the extent that many reliability constraints pose threat to the device normal operation and accelerate the onset of wearout-based failures. Among various wearout-based failure mechanisms, Negative biased temperature instability (NBTI) has been recognized as the most critical source of device aging. The urge of reliable, low-power circuits is driving the EDA community to develop new design techniques, circuit solutions, algorithms, and software, that can address these critical issues. Unfortunately, this challenge is complicated by the fact that power and reliability are known to be intrinsically conflicting metrics: traditional solutions to improve reliability such as redundancy, increase of voltage levels, and up-sizing of critical devices do contrast with traditional low-power solutions, which rely on compact architectures, scaled supply voltages, and small devices. This dissertation focuses on methodologies to bridge this gap and establishes an important link between low-power solutions and aging effects. More specifically, we proposed new architectural solutions based on power management strategies to enable the design of low-power, aging aware cache memories. Cache memories are one of the most critical components for warranting reliable and timely operation. However, they are also more susceptible to aging effects. Due to symmetric structure of a memory cell, aging occurs regardless of the fact that a cell (or word) is accessed or not. Moreover, aging is a worst-case matric and line with worst-case access pattern determines the aging of the entire cache. In order to stop the aging of a memory cell, it must be put into a proper idle state when a cell (or word) is not accessed which require proper management of the idleness of each atomic unit of power management. We have proposed several reliability management techniques based on the idea of cache partitioning to alleviate NBTI-induced aging and obtain joint energy and lifetime benefits. We introduce graceful degradation mechanism which allows different cache blocks into which a cache is partitioned to age at different rates. This implies that various sub-blocks become unreliable at different times, and the cache keeps functioning with reduced efficiency. We extended the capabilities of this architecture by integrating the concept of reconfigurable caches to maintain the performance of the cache throughout its lifetime. By this strategy, whenever a block becomes unreliable, the remaining cache is reconfigured to work as a smaller size cache with only a marginal degradation of performance. Many mission-critical applications require guaranteed lifetime of their operations and therefore the hardware implementing their functionality. Such constraints are usually enforced by means of various reliability enhancing solutions mostly based on redundancy which are not energy-friendly. In our work, we have proposed a novel cache architecture in which a smart use of cache partitions for redundancy allows us to obtain cache that meet a desired lifetime target with minimal energy consumption