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Brno, Czech Republic

Brno University of Technology is a university located in Brno, Czech Republic. Being founded in 1899 and initially offering a single course in civil engineering, it grew to become a major Czech university with over 24,000 students enrolled at 8 faculties and 2 university institutes. Wikipedia.

Kala Z.,Brno University of Technology
Engineering Structures | Year: 2011

The article presents the sensitivity and statistical analyses of the load-carrying capacity of a steel portal frame. It elaborates a typical stability problem of a system comprising two single-storey columns loaded in compression. The elements of this system mutually influence each other, and this fact, in conjunction with the random imperfections, influences the load-carrying capacity variance. This mutual interaction is analysed using the Sobol' sensitivity analysis. The Sobol' sensitivity analysis is applied to identify the dominant input random imperfections and their higher order interaction effects on the load-carrying capacity. Majority of imperfections were considered according to the results of experimental research. Realizations of initial imperfections were simulated applying the Latin Hypercube Sampling method. The geometrical nonlinear solution providing numerical result per run was employed. The frame was meshed using beam elements. The columns of the plane frame are considered with two variants of boundary conditions. The dependence between mean and design load-carrying capacities and column non-dimensional slenderness is analysed. © 2011 Elsevier Ltd. Source

Kala Z.,Brno University of Technology
Thin-Walled Structures | Year: 2011

The objective of the paper is to analyse the influence of initial imperfections on the load-carrying capacity of a single storey steel plane frame comprised of two columns loaded in compression. The influence of the variance of initial imperfections on the variance of the load-carrying capacity was calculated by means of Sobol' sensitivity analysis. Monte Carlo based procedures were used for computing full sets of first order and second order sensitivity indices of the model. The geometrical nonlinear finite element solution, which provides numerical results per run, was employed. The mutual dependence of sensitivity indices and column non-dimensional slenderness is analysed. The derivation of the statistical characteristics of system imperfections of the initial inclination of columns is described in the introduction of the present work. Material and geometrical characteristics of hot-rolled IPE members were considered to be random quantities with histograms obtained from experiments. The Sobol sensitivity analysis is used to identify the crucial input random imperfections and their higher order interaction effects. © 2010 Elsevier Ltd. All rights reserved. Source

This paper presents a number of theoretical and numerical results regarding correlation coefficients and two norms of correlation matrices in relation to correlation control in Monte Carlo type sampling and the designs of experiments. The paper studies estimation formulas for Pearson linear, Spearman and Kendall rank-order correlation coefficients and formulates the lower bounds on the performance of correlation control techniques such as the one presented in the companion paper Part I. In particular, probabilistic distributions of the two norms of correlation matrices defined in Part I are delivered for an arbitrary sample size and number of random variables in the case when the sampled values are ordered randomly. Next, an approximate number of designs with perfect uncorrelatedness is estimated based on the distribution of random correlation coefficients. It is shown that a large number of designs exist that perfectly match the unit correlation matrix. © 2011 Elsevier Ltd. All rights reserved. Source

Kala Z.,Brno University of Technology
Journal of Civil Engineering and Management | Year: 2012

The random load carrying capacity of steel plane frames with bracing stiffness is studied. The load carrying capacity is evaluated using the geometrically non-linear FEM analysis. The incremental stiffness matrix of a slightly curved element utilized in the non-linear incremental analysis is listed. Initial imperfections are considered as random variables. Statistical analysis and Sobol sensitivity analysis are performed using the Latin Hypercube Sampling method. The effect of initial random imperfections on the load carrying capacity is studied, whilst assuming constant slenderness of the columns. The evaluation parameters are the pair of non-random values of elastic bracing stiffness, and system length of the columns. The paper illustrates that the load carrying capacity is very sensitive to initial crookedness of the columns in the event that the non-sway (symmetric) and sway (anti-symmetric) buckling modes coincide. In this case, the design load carrying capacity obtained from statistical analysis according to the EN 1990 (2002) standard is relatively very small (of low safety). Results show that the reliability of design of a steel frame according to EUROCODE 3 (1993) is significantly misaligned. The significance of the first and the second buckling forces as indicators of sensitivity of the load carrying capacity to the imperfections is discussed. Copyright © 2012 Vilnius Gediminas Technical University (VGTU) Press Technika. Source

Ficker T.,Brno University of Technology
Construction and Building Materials | Year: 2012

The properties of the fracture surfaces of hydrated Portland cement pastes were investigated. Analyses of fracture surfaces proved to be capable to provide information about the actual values of compressive strength. Since the compressive strength of cement pastes, σ c, is dependent mainly on capillary porosity and the porosity is a controlling factor of height irregularities of fracture surfaces, the compressive strength, as a consequence, shows a functional dependence on the height irregularities. As a measure of height irregularities the 3D profile and roughness parameters were employed. The 3D surface profiles of the fractured specimens were registered by the confocal microscope. The parameters SP a and SP q, i.e. the arithmetic average and the quadratic mean (rms) heights, respectively, were found to be statistically reliable indicators of surface irregularity and thus the dependences σ c(SP a) and σ c(SP q) were also shown to be relevant indicators of compressive strength. It is hypothesized that the height irregularities of fracture surfaces might become a basis for the microscopic assessment of the compressive strength of cement pastes. © 2011 Elsevier Ltd. All rights reserved. Source

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