An inverse problem analysis for the determination of probalistic parameters of concrete behavior modeled by a statistical approach

When the Monte Carlo method is used to simulate the heterogeneous behavior of concrete in the framework of a finite element probabilistic analysis, N samples of the vector of random variables (tensile strength, Young's modulus, etc.) are generated from a specific probability density function. If the uncertainties of these material parameters are assumed to vary spatially following a normal distribution, the N samples corresponding to a simulation are function of the mean and the standard deviation that define the Gauss density function. The problem is that these statistical moments are not known,a priori, for the characteristic volume of the finite elements for which the problem has been discretized. In this paper an algorithm is proposed to evaluate the parameters characterizing the statistical distribution (e. g. for a normal distribution: the mean and the standard deviation) for a given response of the structure (for instance, a mean load-displacement curve) following an inverse analysis procedure. A very simple mechanical system is used to verify the feasibility of the procedure. By way of example, it is shown that this kind of inverse problem for the identification of statistical parameters is suitable for concrete.

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Résumé Si la méthode de Monte-Carlo est utilisée pour simuler l'hétérogénéité du béton dans le cadre d'une analyse probabiliste par éléments finis, N échantillons du vecteur des variables aléatoires (résistance à la traction, module d'Young, etc.) sont générés à partir d'une fonction de densité de probabilité donnée. Si la dispersion de ce matériau peut être représentée par une distribution normale, les N échantillons correspondant à une simulation, sont fonction de la moyenne et de l'écart type qui définissent la fonction de densité de Gauss. Le problème c'est que ces moments statistiques ne sont pas connus,a priori, pour le volume caractéristique des éléments finis selon lesquels le problème a été discrétisé. Dans cet article, on propose un algorithme pour l'évaluation des paramètres qui caractérisent la distribution statistique (comme exemple, pour une distribution normale: la moyenne et l'écart type) correspondant à la réponse donnée d'une structure (par exemple: une courbe force-déplacement) suivant un processus d'analyse inverse. Un système mécanique très simple est utilisé pour vérifier la faisabilité du processus. Il est montré, à partir d'un exemple, que ce type d'analyse inverse peut être utilisé pour le béton.

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Editorial note COPPE/UFRJ and LCPC are RILEM Titular Members.     

Modeling of Early-Age Creep of Shotcrete. II: Application to Tunneling

This paper presents the application of the material model presented in the companion paper to the structural analysis of tunnels driven according to the new Austrian tunneling method (NATM). On the one hand, two-dimensional simulations of the excavation of a tunnel driven according to the NATM are presented. They show the significance of shotcrete creep for the soil-shotcrete compound structure. These simulations constitute the main part of the paper. On the other hand, as an outlook, a hybrid method is addressed that combines, (in the framework of nonlinear finite-element analyses) the aforementioned material law with three-dimensional in situ displacement measurements performed continuously during the construction process of NATM tunnels. This method enables continuous safety assessment of tunnels and, hence, contributes essentially to online monitoring of tunnels.     

The production and application of cuprous oxide and cupric hydroxide

Copper compounds are crucial for major areas of application, basically due to the biological impact of small amounts of copper. Thus, on the one hand, copper is used in the form of cuprous oxide as a coating for the hulls of ships to prevent algae growth or as cupric hydroxide as a fungicide in wine or coffe plantations; on the other hand, it is indispensable as a trace element in animal foodstuffs. Other applications (e.g., the manufacture of catalysts or pigments) are presently quantitatively small. Adalbert Lossin earned his Ph.D. in incorganic chemistry at the University of Hannover in 1993. He is currently the head of research and development at Norddeutsche Affinerie. Franz-Josef Westhoff earned his Dr. Ing. in nonferrous metallurgy at Tu Clansthal-Zellerfeld in 1990. He is currently a general superinterdent at the Metais and Chemicals Division of Norddeutsche Affinerie.     

Spontaneous rise of fetal platelet counts despite increasing anti-HPA-5b antibodies

A 47-year-old woman with seronegative polyarthritis, diarrhea, and photosensitivity dermatitis was found to have Crohn's disease and pellagra. The presence of high values of 5-hydroxyindolacetic acid in the urine began the exhaustive investigations and finally enterotomy. No mass lesion was found. Argyrophilic cells were not increased in areas of inflamed intestinal mucosa or the normal mucosa. The disagreement between biochemical and histologic findings was attributed to sampling error. Antiinflammatory treatment for Crohn's disease was given and the gastrointestinal and articular symptoms improved, excretion of 5-hydroxyindolacetic acid returned to normal and there was no relapse of pellagra. Pellagra as a complication of Crohn's disease has been described in 4 cases; malnutrition and intestinal malabsorption were the proposed mechanisms for the niacin deficiency and pellagra of those patients. In the current case, the pathogenesis of pellagra may be accounted to wastage of tryptophan by an increased pool of intestinal argyrophilic cells, suggested by increased urinary excretion of 5-hydroxyindolacetic acid.     

Proteases and their inhibitors are indicative in gestational disease

OBJECTIVE: To assess whether various proteolytic factors which are involved in trophoblast invasion show different concentrations in plasma and placenta of patients with HELLP syndrome, pre-/eclampsia and highly pathological Doppler flow measurements but without additional complications (hpD). DESIGN: Case control and observational study; 18 women with HELLP syndrome, 21 with pre-/eclampsia, 13 with hpD, as well as healthy pregnant women (matched pairs); statistical analysis: sign test and Wilcoxon test. RESULTS: Urokinase-type plasminogen activator (uPA), uPA receptor, tissue-type plasminogen activator (tPA), plasminogen activator inhibitor 1 (PAI-1), matrix metalloproteinases MMP-8, MMP-9 and tissue inhibitor of metalloproteinases TIMP-1 were measured by ELISA. PAI-1 plasma levels are significantly elevated in all three groups studied. In HELLP syndrome, tPA and TIMP-1 are also elevated, and in patients with hpD, MMP-8 is increased, whereas MMP-9, and TIMP-1 are lower. In placenta extract, only pre-/eclampsia shows reduced MMP-9 concentrations. CONCLUSIONS: The increased frequency of small-for-gestational-age infants observed in all three study groups is an expression of impaired placental implantation and remodelling processes. These disturbances manifest themselves in the form of changes in some of the factors in plasma and placenta extract that are involved in these processes.     

Long-term results of endoscopic treatment of biliary duct obstruction due to pancreatic disease

BACKGROUND/AIMS: Endoscopic stenting has become an established method of providing palliative treatment in cases of malignant biliary obstruction, as well as in benign biliary stenosis. Several problems associated with the types of stent used have not yet been resolved, and an ideal stent has yet to be designed. Observation of the clinical course for patients with biliary obstruction of various etiologies, and evaluation of the results with various treatment methods are the aims of this study. METHODOLOGY: In 1993 and 1994, biliary obstruction was treated endoscopically in 47 patients with a malignant pancreatic tumor and in 18 patients with chronic pancreatitis. The primary intervention was assessed retrospectively on the basis of the patients' records, and information concerning the clinical course was obtained by contacting the patients or their relatives or general practitioners. RESULTS: Primary endoscopic drainage was successful in all cases. Only one of the patients with pancreatic tumors is still alive; survival after stent placement averaged 6.2 months. Metal stents remained patent significantly longer than plastic stents and percutaneous transhepatic biliary drains (PTBDs)(8.2 versus 3.5 or 1.9 months; p < 0.001). In cases of chronic pancreatitis, three of the nine patients who received only endoscopic treatment, without stenting, were able to continue without stents in the longer term, whereas seven of the nine who underwent surgery had no further problems. CONCLUSIONS: Endoscopic drainage of biliary obstruction provides excellent short-term results. In long-term treatment for purely palliative purposes, metal stents remain patent for longer than plastic stents. In chronic pancreatitis, surgical treatment clearly seems to provide better long-term results than endoscopic therapy.     

Three-dimensional ultrasound evaluation of fetal tooth germs

Thirty children have had percutaneous endoscopic gastrostomy (PEG) inserted for feeding purposes. During a follow-up period of 5-45 months (mean 24 months), complications were recorded in 13 patients. Some patients had more than one complication. Complications included colocutaneous fistula, gastro-oesophageal reflux, wound infection, granulation tissue formation, tube leakage, tube blockage and bleeding. The authors present a retrospective review of the results and discuss the management of these complications.