Minimum expected cost-oriented optimal maintenance planning for deteriorating structures: application to concrete bridge decks

Civil engineering structures are designed to serve the public and often must perform safely for decades. No matter how well they are designed, all civil engineering structures will deteriorate over time and lifetime maintenance expenses represent a substantial portion of the total lifetime cost of most structures. It is difficult to make a reliable prediction of this cost when the future is unknown and structural deterioration and behavior are assumed from a mathematical model or previous experience. An optimal maintenance program is the key to making appropriate decisions at the right time to minimize cost and maintain an appropriate level of safety. This study proposes a probabilistic framework for optimizing the timing and the type of maintenance over the expected useful life of a deteriorating structure. A decision tree analysis is used to develop an optimum lifetime maintenance plan which is updated as inspections occur and more data is available. An estimate which predicts cost and behavior over many years must be refined and reoptimized as new information becomes available. This methodology is illustrated using a half-cell potential test to evaluate a deteriorating concrete bridge deck. The study includes the expected life of the structure, the expected damage level of the structure, costs of inspection and specific repairs, interest rates, the capability of the test equipment to detect a flaw, and the management approach of the owner towards making repairs.     

声学测量技术20年

文章扼要评述近20年来在声频范围内声学测量技术的重要进展。对若干 涉及诸如声强测量，传递函数法及膺噪声等方面测量技术的主题分别作了讨论。     

On development of fractional calculus during the last fifty years

Fractional calculus generalizes integer order derivatives and integrals. During the last half century a considerable progress took place in this scientific area. This paper addresses the evolution and establishes an assertive measure of the research development.     

Deep flow in the Madagascar-Mascarene Basin over the last 150,000 years

The SW Indian Ocean contains at least four layers of water masses with different sources: deep Antarctic (Lower Circumpolar Deep Water) flow to the north, midwater North Indian Deep Water flow to the south and Upper Circumpolar Deep Water to the north, meridional convergence of intermediate waters at 500-1500 m, and the shallow South Equatorial Current flowing west. Sedimentation rates in the area are rather low, being less than 1 cm ka(-1) on Madagascar Ridge, but up to 4 cm ka(-1) at Amirante Passage. Bottom flow through the Madagascar-Mascarene Basin into Amirante Passage varies slightly on glacial-interglacial time-scales, with faster flow in the warm periods of the last interglacial and minima in cold periods. Far more important are the particularly high flow rates, inferred from silt grain size, which occur at warm-to-cold transitions rather than extrema. This suggests the cause is changing density gradient driving a transiently fast flow. Corroboration is found in the glacial-interglacial range of benthic delta18O which is ca. 2 per thousand, suggesting water close to freezing and at least 1.2 more saline and thus more dense glacial bottom waters than present. Significant density steps are inferred in isotope stage 6, the 5e-5d, and 5a-4 transitions. Oxygen isotope data suggest little change by mixing in glacial bottom water on their northward path. Benthic carbon isotope ratios at Amirante Passage differ from glacial Southern Ocean values, due possibly to absence of a local productivity effect present in the Southern Ocean.     

近15年国内桥梁坍塌事故的原因和风险分析

预制节段拼装桥墩存在施工周期短,对交通和环境影响小等优势。随着经济的快速发展和城市化进程的加快,车辆撞击桥墩的事件增加,在极端情况下可能还会导致桥梁整体倒塌。然而,关于这种结构形式的抗车辆撞击性能研究仍较为匮乏,因此,非常有必要开展这方面的研究。该文基于显式动力分析软件ANSYS/LS-DYNA对车辆撞击预制混凝土节段拼装桥墩开展数值模拟工作,在保证数值模型合理性与准确性的基础上,探究几何与构造等因素对节段拼装桥墩抗车辆撞击性能的影响,具体包括截面类型、预应力筋以及剪力键布置等。结果表明：圆形截面相比于方形截面具有更好的抗车辆撞击性能;周边布置预应力筋相较于中心布置能够给节段拼装桥墩提供更好的抗车辆撞击性能;圆柱形混凝土剪力键能够通过提高节段拼装桥墩的整体性来提升节段拼装桥墩的抗车辆撞击性能。基于研究结果的综合考虑,对于实际工程应用问题,应将预制拼装桥墩按圆形截面设计,并采用周边布置预应力筋及节段中心布置剪力键的形式。     

Scientometric analysis of the development of nuclear physics during the last 50 years

A new method for author groups formation and decay processes is proposed. With the help of a special mathematical model time distribution of authors and their publications was established and group productivity, composition and stability, annual change of the total number of short-term and long-term authors, their renovation etc. as well as the time dependence of these quantities was determined. Particularities of activity of authors working in nuclear physics are investigated. It is shown that the most rapid development in this field took place in the pre-war years, it was at high level up to 1960 and then began to decrease. The method used permits to forecast the development of science and to analyse the activity of author units in particular scientific centers.     

The expected time lost due to an extra risk

Tsunamis are normally generated by underwater earthquakes. The earthquakes are normally easily detected by seismographs. However, the earthquake may not always generate a tsunami. Further, the severity of the earthquake is not linearly related to the severity of the tsunami. The tsunami may be detected by a deep-sea pressure transducer communicating through a surface rider buoy, through satellites to a tsunami warning centre. The detectors are expensive to build and maintain, need to be placed near surface-rider buoys, and the placement of these detectors needs to be optimal. The provision of adequate warnings from the network of detectors, called the tsunami warning potential, depends on the network of the deployed detectors, the number of detectors used, and the response times of the detectors, warning centre, and of the emergency services which need to convey the warning. The warning potential is also a function of the number in the population at risk. The sensitivity of the warning potential is analysed for first-order effects, particularly with respect to time delays arising from detection and operation of the emergency services to deliver the warning to the population. The sensitivity of the warning potential to population shifts is also considered. Areas for improvement are identified, together with suggestions of how the system can be optimised.     

Are “Sleeping Beauties” to be expected?

Summary A paper that is little cited ('sleeps') for a long period of time and then becomes much cited ('is awakened'), has been termed by van Raan (2004) a 'Sleeping Beauty', or a paper that was 'ahead of its time'. The inference is that the importance of the paper was not initially recognised, only later was it (re)discovered. On the other hand, much theoretical work in informetrics views the citation process as being purely random - modelled by an appropriate stochastic process. From this point of view, the 'awakening' could simply be a matter of chance without necessarily saying anything about the worth of the paper. The question therefore arises as to whether such awakenings can be explained or expected purely by the random nature of the model or whether they are so unlikely that an alternative explanation should be sought. In this note we express the notion of a Sleeping Beauty in terms of a well-known stochastic model and seek to answer this question, at least in general terms.     

New single four-arm bridge for measuring low-resistance four-terminal resistors

Translated from Izmeritel'naya Tekhnika, No. 1, pp. 36–38, January, 1988.     

New method for separate balancing of ac bridge circuits

Conclusions It should be noted that the possibility of separate balancing of bridge circuits is very important not only for manually-operated bridges, but also for designing automatic bridges. In particular, on the basis of the above method of separate balancing it becomes possible to design a digital automatic bridge for evaluating both components of an impedance by the digit-by-digit measuring method and, thus, eliminate the well-known difficulties which arise in using tracking systems.     

Long-term hurricane risk assessment and expected damage to residential structures

This paper presents results from a study to evaluate long-term hurricane risks in the Southeastern United States using event-based simulation procedures. These risks are defined by (1) the statistical extreme wind climate, and (2) the expected insured losses from damage to residential structures. A probabilistic hurricane event model developed by the authors is used to evaluate long-term risks. The event model parameters were derived from a statistical analysis of storms affecting the Southeastern United States and include radius of maximum winds, central pressure difference, landfall location, storm track, and decay rate. The 50-year mean recurrence interval (MRI) gradient-level and surface gust wind speeds are evaluated for the region investigated using results from the simulation analysis. When coupled with a damage model, also developed by the authors, the results from the event-based simulation analysis are used to provide estimates of the expected losses. The states of North Carolina, South Carolina, and Florida are used to demonstrate the applicability of this procedure for evaluating expected losses. Implications for setting design wind speeds as well as risk-consistent insurance rates are discussed.     

Drivetrains on floating offshore wind turbines: lessons learned over the last 10 years

This paper presents lessons learned from own research studies and field experiments with drivetrains on floating wind turbines over the last ten years. Drivetrains on floating support structures are exposed to wave-induced motions in addition to wind loading and motions. This study investigates the drivetrain-floater interactions from two different viewpoints: how drivetrain impacts the sub-structure design; and how drivetrain responses and life are affected by the floater and support structure motion. The first one is linked to the drivetrain technology and layout, while the second question addresses the influence of the wave-induced motion. The results for both perspectives are presented and discussed. Notably, it is highlighted that the effect of wave induced motions may not be as significant as the wind loading on the drivetrain responses particularly in larger turbines. Given the limited experience with floating wind turbines, however, more research is needed. The main aim with this article is to synthesize and share own research findings on the subject in the period since 2009, the year that the first full-scale floating wind turbine, Hywind Demo, entered operation in Norway.

     

Design criterion for fatigue strengthening of riveted beams in a 120-year-old railway metallic bridge using pre-stressed CFRP plates

This study presents a design criterion developed for fatigue strengthening of a 120-year-old metallic railway bridge in Switzerland and presents a pre-stressed un-bonded reinforcement (PUR) system developed to apply the strengthening. The PUR system uses carbon fiber reinforced polymer (CFRP) plates; however, unlike conventional pre-stressed CFRP reinforcement methods, preparation of the existing metallic bridge surface is not required. This decreases the time required for on-site strengthening procedures. The principle of the constant life diagram (CLD) and two fatigue failure criteria (Johnson and Goodman) are described. Analytical formulations are developed based on the CLD method to determine the minimum CFRP pre-stress level required to prevent fatigue crack initiation. The PUR system uses an applied pre-stress force to reduce the mean stress level (and stress ratio) to shift an existing fatigue-susceptible metallic detail from the ‘at risk’ finite life regime to the ‘safe’ infinite life regime. The applied CLD method is particularly valuable when the stress history of the detail is not known and it is difficult to assess the remaining fatigue life. Moreover, it is shown that the currently adopted approach in many structural codes which emphasizes stress range as the dominant parameter influencing fatigue life are non-conservative for tension–tension stress patterns (i.e., stress ratios of 0 < R < 1). Analyses show that the modified Johnson formula accurately reflects the combined effect of stress range, mean stress level, and material properties, and offers a relatively easy design procedure. Details of a retrofit field application on members of a riveted wrought iron railway bridge are given. A wireless sensor network (WSN) system is used for long-term monitoring of the on-site CFRP stress levels and temperature of the retrofitted details. WSN measurements indicate that increases in ambient temperature result in increased CFRP pre-stress levels.