TY - JOUR A1 - Most, Thomas A1 - Bucher, Christian T1 - Stochastic simulation of cracking in concrete structures using multi-parameter random fields JF - International Journal of Reliability and Safety N2 - Stochastic simulation of cracking in concrete structures using multi-parameter random fields KW - Angewandte Mathematik KW - Strukturmechanik Y1 - 2006 SP - 168 EP - 187 ER - TY - THES A1 - Most, Thomas T1 - Stochastic crack growth simulation in reinforced concrete structures by means of coupled finite element and meshless methods N2 - The complex failure process of concrete structures can not be described in detail by standard engineering design formulas. The numerical analysis of crack development in concrete is essential for several problems. In the last decades a large number of research groups have dealt with this topic and several models and algorithms were developed. However, most of these methods show some difficulties and are limited to special cases. The goal of this study was to develop an automatic algorithm for the efficient simulation of multiple cracking in plain and reinforced concrete structures of medium size. For this purpose meshless methods were used to describe the growth of crack surfaces. Two meshless interpolation schemes were improved for a simple application. The cracking process of concrete has been modeled using a stable criterion for crack growth in combination with an improved cohesive crack model which can represent the failure process under combined crack opening and crack sliding very well. This crack growth algorithm was extended in order to represent the fluctuations of the concrete properties by enlarging the single-parameter random field concept for multiple correlated material parameters. N2 - Das komplexe Versagensverhalten von Betonstrukturen kann in der Regel nicht mit Standardbemessungsformeln beschrieben werden. Eine detaillierte numerische Analyse der Rissentwicklung in Beton ist für einige Problemstellungen unverzichtbar. In den letzten Jahrzehnten haben sich eine Vielzahl von Forschergruppen mit dieser Thematik aus-einandergesetzt. Dabei wurden verschiedene Modelle und Algorithmen entwickelt. Die meisten dieser Verfahren weisen jedoch verschiedene Probleme auf oder sind nur für Spezialfälle anwendbar. Das Ziel dieser Arbeit war die Entwicklung eines automatischen Algorithmus zur effizienten Simulation von mehrfacher Rissentwicklung in Beton- und Stahlbetonstrukturen mittlerer Größe. Dabei wurden netzfreie Verfahren angewendet, um die Änderung der Rissoberflächen abzubilden. Zwei netzfreie Interpolationstypen wurden im Hinblick auf eine unkomplizierte Anwendung angepaßt. Der Versagensprozess des Betons wurde mit Hilfe eines stabilen Risskriteriums in Kombination mit einem erwei-terten kohäsiven Rissmodell abgebildet. Dieses erweiterte Modell kann die Zusammenhänge bei kombinierter Rissöffnung und -gleitung sehr gut wiedergeben. Der entwickelte Algorithmus zur Risssimulation wurde in Hinblick auf eine stochastische Modellierung erweitert. Zu diesem Zweck wurde das Zufallsfeldkonzept für die Abbildung mehrerer untereinander korrelierter Materialparameter ergänzt. T2 - Stochastische Rissfortschrittsberechnung in bewehrten Betonstrukturen unter Kopplung der Finiten Elemente Methode mit netzfreien Verfahren KW - Gitterfreie Methode KW - Stochastik KW - Risssimulation KW - Stahlbeton KW - Meshless method KW - stochastic KW - crack simulation KW - reinforced concrete Y1 - 2005 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20051219-7623 ER - TY - JOUR A1 - Most, Thomas A1 - Bucher, Christian T1 - Probabilistic analysis of concrete cracking using neural networks and random fields JF - Probabilistic Engineering Mechanics N2 - Probabilistic analysis of concrete cracking using neural networks and random fields KW - Angewandte Mathematik KW - Strukturmechanik Y1 - 2007 SP - 219 EP - 229 ER - TY - JOUR A1 - Kirichuk, A. A1 - Most, Thomas A1 - Bucher, Christian T1 - Numerical nonlinear analysis of kinematically excited shells JF - International Journal for Computational Civil and Structural Engineering N2 - Numerical nonlinear analysis of kinematically excited shells KW - Angewandte Mathematik KW - Strukturmechanik Y1 - 2003 SP - 61 EP - 74 ER - TY - JOUR A1 - Most, Thomas A1 - Bucher, Christian T1 - New concepts for moving least squares: An interpolating non-singular weighting function and weighted nodal least squares JF - Engineering Analysis with Boundary Elements N2 - New concepts for moving least squares: An interpolating non-singular weighting function and weighted nodal least squares KW - Angewandte Mathematik KW - Strukturmechanik Y1 - 2008 SP - 461 EP - 470 ER - TY - CHAP A1 - Most, Thomas ED - Gürlebeck, Klaus ED - Könke, Carsten T1 - ESTIMATING UNCERTAINTIES FROM INACCURATE MEASUREMENT DATA USING MAXIMUM ENTROPY DISTRIBUTIONS N2 - Modern engineering design often considers uncertainties in geometrical and material parameters and in the loading conditions. Based on initial assumptions on the stochastic properties as mean values, standard deviations and the distribution functions of these uncertain parameters a probabilistic analysis is carried out. In many application fields probabilities of the exceedance of failure criteria are computed. The out-coming failure probability is strongly dependent on the initial assumptions on the random variable properties. Measurements are always more or less inaccurate data due to varying environmental conditions during the measurement procedure. Furthermore the estimation of stochastic properties from a limited number of realisation also causes uncertainties in these quantities. Thus the assumption of exactly known stochastic properties by neglecting these uncertainties may not lead to very useful probabilistic measures in a design process. In this paper we assume the stochastic properties of a random variable as uncertain quantities caused by so-called epistemic uncertainties. Instead of predefined distribution types we use the maximum entropy distribution which enables the description of a wide range of distribution functions based on the first four stochastic moments. These moments are taken again as random variables to model the epistemic scatter in the stochastic assumptions. The main point of this paper is the discussion on the estimation of these uncertain stochastic properties based on inaccurate measurements. We investigate the bootstrap algorithm for its applicability to quantify the uncertainties in the stochastic properties considering imprecise measurement data. Based on the obtained estimates we apply standard stochastic analysis on a simple example to demonstrate the difference and the necessity of the proposed approach. KW - Angewandte Informatik KW - Angewandte Mathematik KW - Architektur KW - Computerunterstütztes Verfahren KW - Computer Science Models in Engineering; Multiscale and Multiphysical Models; Scientific Computing Y1 - 2010 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170314-28732 UR - http://euklid.bauing.uni-weimar.de/ikm2009/paper.html SN - 1611-4086 ER - TY - JOUR A1 - Most, Thomas A1 - Bucher, Christian T1 - Energy-based simulation of concrete cracking using an improved mixed-mode cohesive crack model within a meshless discretization JF - International Journal for Numerical and Analytical Methods in Geomechanics N2 - Energy-based simulation of concrete cracking using an improved mixed-mode cohesive crack model within a meshless discretization KW - Angewandte Mathematik KW - Strukturmechanik Y1 - 2007 SP - 285 EP - 305 ER - TY - JOUR A1 - Most, Thomas A1 - Bucher, Christian A1 - Schorling, York T1 - Dynamic stability analysis of non-linear structures with geometrical imperfections under random loading JF - Journal of Sound and Vibration N2 - Dynamic stability analysis of non-linear structures with geometrical imperfections under random loading KW - Angewandte Mathematik KW - Strukturmechanik Y1 - 2004 SP - 381 EP - 400 ER - TY - JOUR A1 - Most, Thomas A1 - Ishii, H. A1 - Geng, X. A1 - Bolzern, P. A1 - Colaneri, P. A1 - De Nicolao, G. T1 - Discussion on Almost sure stability of stochastic linear systems with ergodic parameters JF - European Journal of Control N2 - Discussion on Almost sure stability of stochastic linear systems with ergodic parameters KW - Angewandte Mathematik KW - Strukturmechanik Y1 - 2008 SP - 124 EP - 130 ER - TY - CHAP A1 - Most, Thomas A1 - Bucher, Christian T1 - Application of the "fictious crack model" to meshless crack growth simulations N2 - In this paper a meshless component is presented, which internally uses the common meshless interpolation technique >Moving Least Squares<. In contrast to usual meshless integration schemes like the cell quadrature and the nodal integration in this study integration zones with triangular geometry spanned by three nodes are used for 2D analysis. The boundary of the structure is defined by boundary nodes, which are similar to finite element nodes. By using the neighborhood relations of the integration zones an efficient search algorithm to detected the nodes in the influence of the integration points was developed. The components are directly coupled with finite elements by using a penalty method. An widely accepted model to describe the fracture behavior of concrete is the >Fictitious Crack Model< which is applied in this study, which differentiates between micro cracks and macro cracks, with and without force transmission over the crack surface, respectively. In this study the crack surface is discretized by node pairs in form of a polygon, which is part of the boundary. To apply the >Fictitious Crack Model< finite interface elements are included between the crack surface nodes. The determination of the maximum principal strain at the crack tip is done by introducing an influence area around the singularity. On a practical example it is shown that the included elements improve the model by the transmission of the surface forces during monotonic loading and by the representation of the contact forces of closed cracks during reverse loading. KW - Bruchmechanik KW - Rissbildung KW - Modellierung Y1 - 2003 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20111215-3359 ER -