Reliability-based Assessment of Concrete Dam Stability

Risk management is increasingly used in dam safety and includes risk analysis, risk evaluation and risk reduction. Structural Reliability Analysis (SRA) is a probabilistic methodology that may be used in the risk assessment process. SRA has been frequently used for calibration of partial factors in limit state design codes for structures (not dams). In a reliability analysis a mathematical description of the failure mode, a limit state function, is defined. All parameters describing the limit state function should be random variables and are described by stochastic distributions (or, where appropriate, a deterministic value). The safety index (or probability of failure) may be determined by e.g. First Order Reliability Method and the result is compared to a target safety index to determine if the structure is safe enough. Several difficulties exists in the use of SRA for concrete dams, mainly due to the fact that only a few examples of such analysis for dams exist. One difficulty is how to define the failure modes. In this thesis a complete system of failure modes is identified, where failure is considered as a series system of “failure in the concrete part”, “failure in the concrete-rock interface” and “failure in the rock mass”. Failure in the concrete-rock interface may occur due to sliding or overturning. Sliding is the joint occurrence of sliding with a partially bonded contact (fails at very small displacement) and sliding with broken contact (fails at larger displacement) and both have to occur for sliding to occur, hence they are treated as a parallel system. Adjusted overturning is a combination of overturning and crushing of the concrete or crushing of the rock. A substantial part of the work has been to define the necessary input data. - Cohesion in the interface is very important. Due to the expected brittle failure in a partly intact interface, treatment of the shear resistance as a brittle parallel system is proposed. - Description of the headwater results in a series system; either failure occurs for water levels at retention water level (rwl) or for water levels above rwl, the latter described by an exponential distribution. - Uplift is one of the most important loads. A geostatistical simulation procedure is presented, where the hydraulic conductivity field of the foundation is described by a variogram and uplift is simulated by a FE-analysis. This methodology is demonstrated to be very useful and gives estimates of the statistical distribution of uplift. Three papers on this subject are included; the first is a description of the methodology, the second presents a sensitivity analysis performed for a large number of different combinations of input data and the last is an application to a Brazilian dam, where water pressure tests and monitoring results are available. In two papers SRA is applied to concrete dams and the system reliability is determined. In the first paper a spillway section where information of e.g. cohesion, friction angles etc. were available is analysed. In the last paper an idealized dam and a power intake structure are analysed. The conclusions are that SRA may be used for assessment of concrete dam stability and that it is well fitted for the dam safety risk management process. Every dam is a unique prototype and SRA enables specific behaviour and properties of a certain structure to be taken to consideration. The system reliability analysis is a very valuable tool in understanding the relationship between failure modes and enables the safety for the whole structure to be determined. In a reliability analysis the most important parameters may be identified and thus safety measures can be focused where it gives the best possible output. A general safety consideration is that development of the safety concept for concrete dams, from deterministic to probabilistic or semi-probabilistic, will give a known and more uniform level of safety

Samband mellan tidig ålder vid avskiljning och missriktat diande hos föl

By tradition horses are weaned at an age of 5-6 months. This study illuminates weaned foals misdirected suckling behaviour, which means that they try to suckle another foal. Since no information about this issue is presented, we decided to perform a behaviour study on weaned foals. The misdirected suckling behaviour was studied on a group with 7 foals, with both fillies and colts. In the group the weaning age varied between 147 days and 215 days, and the first time we observed them, they had been separated from the mares for 12 days. We found that age at weaning is correlated with the emergence of this non-nutritional suckling behaviour. It was revealed that the older colts were most frequent to give suck. Beside our behaviour study we review the natural relationship between mare and her offspring, natural weaning and the suckingbehaviour in foals. Suckling is an important factor for the foals´ social and emotional welfare. When human wean foals at a young age, they are exposed for stress that could lead to stereotypic and other behaviour problems

Postvaccination immune responses and risk of primary total hip arthroplasty—A population-based cohort study

Objective To investigate the relationship between individual postvaccination immune responses and subsequent risk of total hip arthroplasty (THA) due to idiopathic osteoarthritis (OA) or rheumatoid arthritis (RA). Method Results of tuberculin skin tests (TSTs) following the Bacille Calmette–Guerin (BCG) vaccination were used as a marker of individual immune responses. TST results from the mandatory mass tuberculosis screening program 1948–1975 (n = 236 770) were linked with information on subsequent THA during 1987–2020 from the Norwegian Arthroplasty Register. The multivariable Cox proportional hazard regression was performed. Results A total of 10 698 individuals received a THA during follow-up. In men, there was no association between TST and risk of THA due to OA (Hazard ratio [HR] 1.01, 95% confidence interval [CI] 0.92–1.12 for positive versus negative TST and HR 1.06, 95% CI 0.95–1.18 for strong positive vs negative TST), while the risk estimates increased with increasingly restrictive sensitivity analyses. In women, there was no association with THA due to OA for positive versus negative TST (HR 0.98, 95% CI 0.92–1.05), while a strong positive TST was associated with reduced risk of THA (HR 0.90, 95% CI 0.84–0.97). No significant associations were observed in the sensitivity analysis for women or for THA due to RA. Conclusion Our results suggest that an increased postvaccination immune response is associated with a nonsignificant trend of increased risk of THA among men and a decreased risk among women, although risk estimates were small.publishedVersio

Increasing but levelling out risk of revision due to infection after total hip arthroplasty: a study on 108,854 primary THAs in the Norwegian Arthroplasty Register from 2005 to 2019

Background and purpose — Focus on prevention, surveillance, and treatment of infection after total hip arthroplasty (THA) in the last decade has resulted in new knowledge and guidelines. Previous publications have suggested an increased incidence of surgical revisions due to infection after THA. We assessed whether there have been changes in the risk of revision due to deep infection after primary THAs reported to the Norwegian Arthroplasty Register (NAR) over the period 2005–2019. Patients and methods — Primary THAs reported to the NAR from January 1, 2005 to December 31, 2019 were included. Adjusted Cox regression analyses with the first revision due to deep infection after primary THA were performed. We investigated changes in the risk of revision as a function of time of primary THA. Time was stratified into 5-year periods. We studied the whole population of THAs, and the subgroups: all-cemented, all-uncemented, reverse hybrid (cemented cup), and hybrid THAs (cemented stem). In addition, we investigated factors that were associated with the risk of revision, and changes in the time span from primary THA to revision. Results — Of the 108,854 primary THAs that met the inclusion criteria, 1,365 (1.3%) were revised due to deep infection. The risk of revision due to infection, at any time after primary surgery, increased through the period studied. Compared with THAs implanted in 2005–2009, the relative risk of revision due to infection was 1.4 (95% CI 1.2–1.7) for 2010–2014, and 1.6 (1.1–1.9) for 2015–2019. We found an increased risk for all types of implant fixation. Compared to 2005–2009, for all THAs, the risk of revision due to infection 0–30 days postoperatively was 2.2 (1.8–2.8) for 2010–2014 and 2.3 (1.8–2.9) for 2015–2019, 31–90 days postoperatively 1.0 (0.7–1.6) for 2010–2014 and 1.6 (1.0–2.5) for 2015–2019, and finally 91 days–1 year postoperatively 1.1 (0.7–1.8) for 2010–2014 and 1.6 (1.0–2.6) for 2015–2019. From 1 to 5 years postoperatively, the risk of revision due to infection was similar to 2005–2009 for both the subsequent time periods Interpretation — The risk of revision due to deep infection after THA increased throughout the period 2005–2019, but appears to have levelled out after 2010. The increase was mainly due to an increased risk of early revisions, and may partly have been caused by a change of practice rather than a change in the incidence of infection.publishedVersio

Antibiotic-loaded bone cement in prevention of periprosthetic joint infections in primary total knee arthroplasty: A register-based multicentre randomised controlled non-inferiority trial (ALBA trial)

Introduction The current evidence on the efficacy of antibiotic-loaded bone cement (ALBC) in reducing the risk of periprosthetic joint infections (PJI) after primary joint reconstruction is insufficient. In several European countries, the use of ALBC is routine practice unlike in the USA where ALBC use is not approved in low-risk patients. Therefore, we designed a double-blinded pragmatic multicentre register-based randomised controlled non-inferiority trial to investigate the effects of ALBC compared with plain bone cement in primary total knee arthroplasty (TKA). Methods and analysis A minimum of 9,172 patients undergoing full-cemented primary TKA will be recruited and equally randomised into the ALBC group and the plain bone cement group. This trial will be conducted in Norwegian hospitals that routinely perform cemented primary TKA. The primary outcome will be risk of revision surgery due to PJI at 1-year of follow-up. Secondary outcomes will be: risk of revision due to any reason including aseptic loosening at 1, 6, 10 and 20 years of follow-up; patient-related outcome measures like function, pain, satisfaction and health-related quality of life at 1, 6 and 10 years of follow-up; risk of changes in the microbial pattern and resistance profiles of organisms cultured in subsequent revisions at 1, 6, 10 and 20 years of follow-up; cost-effectiveness of routine ALBC versus plain bone cement use in primary TKA. We will use 1:1 randomisation with random permuted blocks and stratify by participating hospitals to randomise patients to receive ALBC or plain bone cement. Inclusion, randomisation and follow-up will be through the Norwegian Arthroplasty Register. Ethics and dissemination The trial was approved by the Western Norway Regional Committees on Medical and Health Research Ethics (reference number: 2019/751/REK vest) on 21 June 2019. The findings of this trial will be disseminated through peer-reviewed publications and conference presentations. Trial registration number NCT04135170.publishedVersio

Geostatistical approach for statistical descripion of uplift pressures: Part I

The possibilities of the use of structural reliability analysis in concrete dam design and assessment is investigated in Sweden. For such analysis, statistical descriptions of the loads and resistances are necessary. Uplift pressure has a large impact on safety, and is difficult to quantify. This paper describes the methodology of a geostatistical approach to simulate the uplift pressure, and an example is given of the results. In ‘Geostatistical approach for statistical description of uplift pressures: Part II’, these results are described in more detail. In the approach used, simulation of the hydraulic conductivity beneath the concrete dam (2D) was performed by means of geostatistics. The spatial dependence was described using a variogram, and input data was the mean value, and variance, of the hydraulic conductivity and spatial range. For a given field of hydraulic conductivity a finite element model could be used to derive the uplift pressure, uplift force and uplift moment. Since the variance and spatial range was unknown, a thorough sensitivity analysis was performed by analyzing twenty-nine combinations of variance and range. For each combination, 1000 realizations of random fields of the hydraulic conductivity were derived, and the uplift was found for each. The resulting histograms for uplift force and uplift moment were best fitted to a Beta distribution. For increasing range, the uplift force distribution transforms from narrow and normal-like to wide and rectangular in shape, while the uplift moment distribution becomes more triangular

Service Oriented Architecture – An Archival- and Information perspective on Service Oriented Architecture

The starting point of this paper has to do with rapid changes within the information technology and the need for agile and fast systems. The primary goal is to investigate what happens with recordkeeping practices in agile environments like service oriented architecture (SOA). It is in the possible transfer between IT architecture and digital archive the area of this paper resides. The paper relates to the Records Continuum model by which records will be considered historical and active at the time of creation. In the Records Continuum model recordkeeping practices and archival requirements will have to be taken into account at the time of creation. This paper concerns SOA from the perspective of Archival and Information science. It describes the different parts that make it possible to achieve a SOA with emphasis on those parts which have the most impact on the requirements of a digital archive. The main requirements discussed in this paper are the principle of provenance, the need to ensure that records remain authentic, reliable and keep their integrity and usability over time. The issue of keeping track of information and activities in a SOA is also discussed. It is established that records which need to fulfil the requirements mentioned above do exists in a SOA. The purpose of this paper is to investigate whether or not the principle of provenance and the archival requirements will be affected by SOA, and whether or not the requirements can be fulfilled over time. Information collection for this paper is basically through studies of literature and information gathering on the Internet. The method is descriptive and comparison between the information gathered has been made. In addition one short interview has been undertaken with Skatteverket, a government that are in the process of implementing both SOA and a digital archive. The main purpose with the interview was to find out if there are any collaboration between SOA and the digital archive at Skatteverket. The results indicate that a lot of the problem concerning preservation of digital records over time also applies for SOA, such as the lack of sustainable format and media and the potential loss of information. However some successful implementations of digital archives based on the OAIS-model with SOA as tool for realising the digital archive has been found. The archival requirements and the principle of provenance will be affected by SOA but it is only when there is a connection between SOA and a digital archive that it is possible to secure some of the archival requirements

Reliability-based evaluation of concrete dams

Swedish concrete dams are designed and assessed based on deterministic design using safety factors. The combination of increasing age, new methods for calculation of design floods and increasing demands by society to ensure a high level of safety, has resulted in upgrading and rebuilding needs for dams. When safety is re-evaluated it is important that evaluation is based on modern safety concepts. The objective of this thesis is to describe how reliability based methodology can be used for assessment of concrete dams, how it fits into the dam safety risk management process and the present state of knowledge of relevant statistic information of resistance and load parameters. Risk management is becoming more frequently used in dam safety all over the world and structural reliability analysis can be used for safety assessment of existing dams. Since object specific information, monitoring results, known loads etcetera can be included in the analysis it gives more reliable results than a more general assessment procedure based on traditional dam safety design guidelines. In this thesis the sliding and overturning failure modes are used for analysis, but there are reasons to further analyse the failure mode formulation. Overturning is not considered in several guidelines, instead resultant location is used as an indicator, and failure is associated with sliding or overstressing. The Swedish guideline on dam safety, RIDAS, does not, unlike guidelines used elsewhere in the world, take account to cohesion when the sliding stability is estimated. Even so, cohesion is included in the sliding criterion used for analysis in this thesis. In structural reliability analysis the failure mode of interest is described by a limit state function, which is a function of a number of basic variables, described by their statistical distribution. For a concrete dam the basic variables for the sliding failure mode are self-weight (G), cohesion (c), base area (A), friction angle (φ), uplift pressure (U), hydrostatic water pressure (H) and ice load (I) and the limit state function becomes Limit state functions for overturning or other failure modes can be defined in the same way. When statistical distributions are known for the basic variables, the safety index, β, can be calculated. β is related to the probability of failure by , where Φ is the standardized normal distribution function. For safety evaluation, β is compared to a target safety index, βT. For dams no such target value exists. There are different approaches how to set a target and the most straightforward is calibration to existing practice, but there are also reasons to believe that target safety for dams should be based also on tolerable risk concepts. The basic variables affecting concrete dam stability are described and special attention is given to uplift, where a thorough state-of-the art is given, as it has been shown in previous research to have a large influence on dam stability. Uplift varies depending on temperature (higher uplift during cold periods), due to loads (increasing water levels may give rise to uplift pressure to increase more than the linear design assumption), is highly dependant on foundation treatment and drainage and is difficult to monitor (uplift in one point represent only a local area). A promising approach on how to use geostatistical modelling to derive statistical distribution for uplift is shown. The hydraulic conductivity beneath the dam is assumed to have certain properties (mean value and variance) and is quantified by a spatial correlation structure. Flow and uplift pressure distribution is then solved by use of a finite element program. A large number of simulations is used to obtain a statistical distribution of uplift force and moment on the whole dam base area. The uplift force active on the dam is described as where u is the uplift force, calculated from the linear uplift reduction assumption used in design, and C is a random variable based on the simulations. The treatment of moment of uplift is similar. This concept can and should be further developed, e.g. by investigating real rock properties and analyzing 3-D modelling of hydraulic conductivities. Even though there are questions to be solved, this approach gives useful results. In the first of two examples, the capacity of a wall in a spillway chute is analyzed. The result is that the wall can withstand approximately 20 % higher water levels than that resulting from design according to RIDAS. In the second example a dam, fulfilling the requirements in RIDAS, is analysed. The results reveal that the cohesion and the friction coefficient gives the largest contribution to the uncertainty of β for sliding failure, whereas self-weight, followed by uplift and ice load, dominates the uncertainty for overturning failure. The main conclusions are that structural reliability analysis can be used as a tool in the dam safety risk management process and that the most important factors for further analysis are cohesion, friction coefficient, ice load, uplift and self-weight. The examples shown, and the results of a master thesis, indicates that today’s guideline (RIDAS) results in a number of “problems”, among them that the safety index seems to be dependant on dam type and dam height and that cross-sectional design is, at least in one example, conservative

Geostatistical approach for statistical description of uplift pressures: Part II

The possibilities of using structural reliability analysis in concrete dam design and assessment is investigated in Sweden. For such analysis statistical descriptions of the loads and resistances are necessary. Uplift pressure has a large impact on the safety and is difficult to quantify. In ‘Geostatistical approach for statistical description of uplift pressures: Part 1’*, the methodology of a geostatistical approach to simulate the uplift pressure was described, while in this paper the results are thoroughly represented. The uplift force was found possible to describe as it is received from the assumption usually used in design, multiplied by a random parameter, C. Due to physical limitations C varies between 0-2. Similarly, for the moment from uplift pressure, Cm varies between 0-1.5. Hydraulic conductivity beneath the dam was described as a random field with certain properties. A sensitivity analysis was performed for different variance and range. The results are stable for a range >4m, while the variance is more important. For small variance the pdf of C and Cm are narrow and normal-like, while for large variance they become wide and rectangular- or triangular-shaped, respectively. The methodology is also tested for dams with drains and grout, buttress dams of different geometry. and for rock with an anisotropic correlation structure. The conclusion is that the methodology is useful and gives a valuable statistical descriptions of the uplift pressure. This may be used as input when performing structural reliability analysis. For further improvement experimental data and three-dimensional simulation could be used

Service Oriented Architecture – An Archival- and Information perspective on Service Oriented Architecture

The starting point of this paper has to do with rapid changes within the information technology and the need for agile and fast systems. The primary goal is to investigate what happens with recordkeeping practices in agile environments like service oriented architecture (SOA). It is in the possible transfer between IT architecture and digital archive the area of this paper resides. The paper relates to the Records Continuum model by which records will be considered historical and active at the time of creation. In the Records Continuum model recordkeeping practices and archival requirements will have to be taken into account at the time of creation. This paper concerns SOA from the perspective of Archival and Information science. It describes the different parts that make it possible to achieve a SOA with emphasis on those parts which have the most impact on the requirements of a digital archive. The main requirements discussed in this paper are the principle of provenance, the need to ensure that records remain authentic, reliable and keep their integrity and usability over time. The issue of keeping track of information and activities in a SOA is also discussed. It is established that records which need to fulfil the requirements mentioned above do exists in a SOA. The purpose of this paper is to investigate whether or not the principle of provenance and the archival requirements will be affected by SOA, and whether or not the requirements can be fulfilled over time. Information collection for this paper is basically through studies of literature and information gathering on the Internet. The method is descriptive and comparison between the information gathered has been made. In addition one short interview has been undertaken with Skatteverket, a government that are in the process of implementing both SOA and a digital archive. The main purpose with the interview was to find out if there are any collaboration between SOA and the digital archive at Skatteverket. The results indicate that a lot of the problem concerning preservation of digital records over time also applies for SOA, such as the lack of sustainable format and media and the potential loss of information. However some successful implementations of digital archives based on the OAIS-model with SOA as tool for realising the digital archive has been found. The archival requirements and the principle of provenance will be affected by SOA but it is only when there is a connection between SOA and a digital archive that it is possible to secure some of the archival requirements