Pre-posterior analysis of inspections incorporating degradation of concrete structures

The framework of pre-posterior decision analysis has a large potential as a decision support tool in structural engineering. It seems ideally suited to tackle problems related to determining the value of Structural Health Monitoring and is commonly applied in inspection and maintenance planning. However, the application of this methodology for integrated life-cycle cost decision making related to monitoring of time-dependent and spatial degradation phenomena in concrete structures, needs further investigation. In this work, the timedependent and spatial degradation phenomena will be coupled to the pre-posterior decision making approach and applied on concrete beams under bending, subjected to corrosion of the reinforcement. A framework is set up to determine the value of information of inspections enabling adequate decision-making. The methodology incorporates Bayesian updating based on the uncertain inspection outcomes. The framework will be illustrated by application on a simply supported reinforced concrete beam

Development of conformity criteria for durability and its influence on service life predictions

To ensure the quality of produced concrete batches, it is often verified whether a specified concrete compressive strength is reached by the application of conformity control. The conformity criteria used for this purpose are related to the probability of accepting a batch, in relation to a specified quality. Batches fulfilling the conformity criteria are accepted, whereas others are rejected. In this way, the outgoing quality of the accepted concrete is higher than without the application of conformity control. This is the result of the filtering effect of conformity control and affects the probability of failure of concrete structures. Instead of only applying conformity control to the concrete compressive strength, a similar procedure could be applied to durability related variables. One example hereof is the diffusion coefficient of the concrete. When conformity criteria are defined and applied in relation to the diffusion coefficient, the result will be a filtering effect on the distribution of the diffusion coefficient. The outgoing distribution will have a lower mean value and standard deviation compared to the incoming distribution. This will influence the time-dependent reliability of reinforced concrete structures. This paper investigates the effect of conformity criteria for diffusion coefficients on the service life and failure probabilities of reinforced concrete elements. The filtering effect is investigated by a numerical study applying analytical methods and numerical integration

Calibration of partial factors for temporary structures

The Eurocodes currently do not provide a coherent reliability-based justification for the semi-probabilistic design format of temporary structures. Besides the need for suitable target reliability levels, a coherent definition of partial factors is needed, adjusted according to the chosen target reliability level and the intended reference period considered for the design of the temporary structure. When developing such a partial factor approach, attention should be given to the coherency with current Eurocodes to avoid conceptual discrepancies between the design of long-term and temporary structures. In this contribution a full-probabilistic framework for the structural reliability quantification of temporary structures is developed, based on Latin hypercube sampling. A sensitivity study is performed to detect the most important variables to be considered for the reliability analysis. The framework is subsequently used to determine the inherent reliability levels of scaffolds associated the design guidelines and partial factors according to current standards. Furthermore, recommendations for the target reliability levels for temporary structures are proposed, considering an economic optimization procedure. Finally, adjusted partial factors for temporary structures are derived, enabling a rather simple and straightforward, but objective and coherent safety evaluation of temporary structures by practitioners. Such adjusted partial factors are obtained using two methods: (1) an optimization procedure and (2) the Adjusted Partial Factor Method, which was originally developed for adjusting partial factors for existing structures

A nationwide study on reproductive function, ovarian reserve, and risk of premature menopause in female survivors of childhood cancer: design and methodological challenges

<p>Abstract</p> <p>Background</p> <p>Advances in childhood cancer treatment over the past decades have significantly improved survival, resulting in a rapidly growing group of survivors. However, both chemo- and radiotherapy may adversely affect reproductive function. This paper describes the design and encountered methodological challenges of a nationwide study in the Netherlands investigating the effects of treatment on reproductive function, ovarian reserve, premature menopause and pregnancy outcomes in female childhood cancer survivors (CCS), the DCOG LATER-VEVO study.</p> <p>Methods</p> <p>The study is a retrospective cohort study consisting of two parts: a questionnaire assessing medical, menstrual, and obstetric history, and a clinical assessment evaluating ovarian and uterine function by hormonal analyses and transvaginal ultrasound measurements. The eligible study population consists of adult female 5-year survivors of childhood cancer treated in the Netherlands, whereas the control group consists of age-matched sisters of the participating CCS. To date, study invitations have been sent to 1611 CCS and 429 sister controls, of which 1215 (75%) and 333 (78%) have responded so far. Of these responders, the majority consented to participate in both parts of the study (53% vs. 65% for CCS and sister controls respectively). Several challenges were encountered involving the study population: dealing with bias due to the differences in characteristics of several types of (non-) participants and finding an adequately sized and well-matched control group. Moreover, the challenges related to the data collection process included: differences in response rates between web-based and paper-based questionnaires, validity of self-reported outcomes, interpretation of clinical measurements of women using hormonal contraceptives, and inter- and intra-observer variation of the ultrasound measurements.</p> <p>Discussion</p> <p>The DCOG LATER-VEVO study will provide valuable information about the reproductive potential of paediatric cancer patients as well as long-term survivors of childhood cancer. Other investigators planning to conduct large cohort studies on late effects may encounter similar challenges as those encountered during this study. The solutions to these challenges described in this paper may be useful to these investigators.</p> <p>Trial registration</p> <p>NTR2922; <url>http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=2922</url></p

Applied Bayesian pre-posterior and life-cycle cost analysis for determining and optimizing the value of structural health monitoring for concrete structures

In Vlaanderen is meer dan 60% van het bestaande brugpatrimonium gebouwd voor 1981 en meer dan 25% zelfs voor 1945, waardoor een aanzienlijk budget wordt besteed aan het onderhouden en herstellen van deze constructies. Daarom trachten ingenieurs steeds betere tools te ontwikkelen om rationeel gefundeerde beslissingen te maken met betrekking tot de besteding van de beschikbare budgetten. In het bijzonder worden daarbij nauwkeurigere berekeningsmethoden ontwikkeld die toelaten de resterende levensduur van bestaande constructies in te schatten. Hierbij is er nood aan een methodologie om de betrouwbaarheid van bestaande (soms gecorrodeerde) betonconstructies in te schatten, rekening houdend met informatie van inspecties en monitoring. In dit proefschrift is aangetoond hoe op basis van (een combinatie van) verschillende types meetdata en visuele waarnemingen de degradatietoestand van een bestaande betonconstructie kan worden ingeschat. Een betere inschatting van deze degradatietoestand leidt ook tot een betere beoordeling van de constructieve veiligheid en de resterende levensduur, die tevens worden gekwantificeerd. Verder is een rekenmethode uitgewerkt om strategieën voor monitoring van (bestaande) constructies te optimaliseren, rekening houdend met de kosten over de gehele levenscyclus van de constructie. Zo kunnen de beschikbare budgetten zo optimaal mogelijk worden benut

Conformity control of concrete durability parameters and its filtering effect on the design service life

Conformity control is applied in order to safeguard the quality of produced lots. Conformity criteria are characterized by an operating characteristic curve, quantifying the probability of acceptance in relation to a concrete lot with a specific quality. By applying conformity control, certain lots of concrete are accepted or rejected. This induces a filtering effect, which in case of conformity control of durability parameters leads to an effect on the design service life. For durability, limiting values for durability-related properties can be proposed. Specifying conformity criteria for the durability parameters of concrete can enable to safeguard the quality of concrete products in relation to durability. This conformity control has a filtering effect on the distribution of these durability parameters. When, for example, considering the diffusion coefficient of concrete, this filtering effect results in a lower mean value and standard deviation, consequently (positively) influencing the service life. In this paper, conformity criteria for durability parameters are developed, and their effect on the design service life of reinforced concrete elements is quantified

Development of conformity criteria for diffusion coefficients of concrete and their influence on the service life of reinforced concrete structures

Conformity control is often applied on concrete compressive strength in order to safeguard the quality of produced concrete lots. Conformity criteria are mostly characterized by an operating characteristic curve, indicating the probability of acceptance in relation to a concrete lot with a specific quality. By applying this conformity control, certain lots of concrete are accepted and others are rejected. This induces a filtering effect, leading to an effect on the failure probability as a result of the quantitative quality control process. For durability criteria, often limiting bounds for durability related properties are proposed. Specifying conformity criteria for example to the diffusion coefficient of the concrete can enable to safeguard the quality of concrete products in relation to durability properties. Also this type of conformity control has a filtering effect, i.e. on the distribution of the diffusion coefficient, resulting in a lower mean value and standard deviation, influencing consequently the service life. This paper investigates for the first time the effect of conformity criteria for diffusion coefficients as well their effect on the service life of concrete elements