Ústav stavební mechaniky

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Numerical Modelling of Cylindrical Fluid Filled Tank
(WSEAS, 2024-09-03) Kotrasová, Kamila; Frantík, Petr; Kormaníková, Eva
The demand for drinking and service water storage is rising with changing climate conditions and increasing life expectancy. The tanks are commonly used to store large volumes of liquids and materials in various fields of the economy. This paper presents the model of the numerical simulation for the steel tank filled with fluid, using the finite element method. The results of the tank filled with water are presented, by the results: the pressure of the fluid the effective stress, and the maximum deformation of the tank solid domain. The correctness of the pressure values was verified by the simple calculation of the fluid pressure. Finally, the paper documents the results for various fluid fillings with a considered range of fluid densities. The influence of the fluid filling height on the behavior of the solid domain of the fluid filling container loaded by the static loading as well as the effect of the width of the tank on the behavior of the solid domain of the fluid filling container. © 2024, World Scientific and Engineering Academy and Society. All rights reserved.
Nonlinear global design resistance: Case studies of post-tensioned concrete bridges made of I-73 and KA-61 girders
(ERNST & SOHN, 2024-08-28) Lipowczan, Martin; Novák, Lukáš; Lehký, David; Novák, Drahomír
The paper portrays a comprehensive computational procedure for determining the global structural resistances of two existing bridges made of I-73 and KA-61 precast post-tensioned concrete girders using advanced statistical assessment methods in combination with nonlinear fracture mechanics-based finite element method analysis. Although this combination is a powerful tool for realistic modeling of structures, its practical application is still very time consuming. Therefore, a statistical sampling approach for the determination of the structural design resistance is compared to selected efficient semi-probabilistic methods based on the estimation of coefficient of variation-estimation of coefficient of variation (ECoV) method according to fib Model Code 2010 and improved approach called Eigen ECoV method. Load-bearing capacity is determined for the ultimate as well as several serviceability limit states. The sensitivity of the input parameters burdened with uncertainties on the response of the structure is quantified using a sensitivity analysis supported by a surrogate model based on polynomial chaos expansion. The paper shows that the applicability of nonlinear modeling with respect to uncertainties is possible when using these ECoV methods and a surrogate model and can be applied in a routine manner. The shortcomings and advantages of all the used safety design/assessment methods are discussed.
Damage detection of riveted truss bridge using ANN-aided AMS optimization method
(CRC Press, 2024-07-12) Šplíchal, Bohumil; Lehký, David; Lamperová, Katarína
Aging transport infrastructure brings increased economic burden and uncertainties regarding the reliability, durability and safe use of structures. Early damage detection to locate incipient damage provides an opportunity for early structural maintenance and can guarantee structural reliability and continuing serviceability. This paper describes the use of the hybrid identification method, which combines a metaheuristic optimization technique aimed multilevel sampling with an artificial neural network-based surrogate model to approximate the inverse relationship between structural response and structural parameters. The method is applied to identify damage in existing riveted truss bridge. The effect of the damage rate and location on the identification speed and the accuracy of the solution is investigated and discussed.
Finite element analysis of concrete slab exposed to high velocity pressure wave – simplified vs. smoothed-particle hydrodynamics (SPH) method
(EDP Sciences, 2024-05-24) Jindra, Daniel; Hradil, Petr; Kala, Jiří
Many structures are required to sustain the structural resistance also under extreme loading conditions, for example impacts of high-velocity objects (airplane crash into nuclear power plant), impacts of projectiles (defence structures), or while exposed to high velocity pressure wave caused e.g. by explosion of various chemicals in industry, nature gas, or also conventional weapons. Numerical analyses of these phenomena are feasible while utilizing explicit approach of the finite element method (FEM), available in commercially accessible software LS-Dyna. In order to predict the behaviour of the structure properly, advanced nonlinear material models are required to be considered, which are often mathematically described by numerous input parameters. Several approaches to model the exposure to blast load exist, from simplified, where the blast wave is considered as timedependent pressure based on empirical equations, to more advanced ones, where the propagation of the pressure wave itself through the surrounding environment is being modelled Arbitrary Lagrangian Eulerian, (ALE method), or so called smoothed-particle hydrodynamics (SPH) method, which might be used to model the blast itself. In this paper, FEM analyses of a simply supported concrete slab with basalt fibre reinforced polymer (BFRP) bars exposed to close range explosion of TNT charge are presented. 3D numerical models are analysed utilizing explicit solver of LS-Dyna. Karagozian and Case (K&C) nonlinear material model for concrete is used, which is suitable when high strain rates are present in the quasi brittle materials. Two variants of the blast loads modelling are compared. The simplified empirical approach, which is less demanding on computational power, and feasible for utilization in case of simple structure geometry, and more demanding method using SPH method to model the TNT detonation and interaction with the exposed concrete slab. The results of these numerical analyses are compared with experimental data based on available literature, and properly discussed.
Global Sensitivity Analysis of Structural Reliability Using Cliff Delta
(MDPI, 2024-07-07) Kala, Zdeněk
This paper introduces innovative sensitivity indices based on Cliff's Delta for the global sensitivity analysis of structural reliability. These indices build on the Sobol' method, using binary outcomes (success or failure), but avoid the need to calculate failure probability P-f and the associated distributional assumptions of resistance R and load F. Cliff's Delta, originally used for ordinal data, evaluates the dominance of resistance over load without specific assumptions. The mathematical formulations for computing Cliff's Delta between R and F quantify structural reliability by assessing the random realizations of R > F using a double-nested-loop approach. The derived sensitivity indices, based on the squared value of Cliff's Delta delta(2)(C), exhibit properties analogous to those in the Sobol' sensitivity analysis, including first-order, second-order, and higher-order indices. This provides a framework for evaluating the contributions of input variables on structural reliability. The results demonstrate that the Cliff's Delta method provides a more accurate estimate of Pf. In one case study, the Cliff's Delta approach reduces the standard deviation of Pf estimates across various Monte Carlo run counts. This method is particularly significant for FEM applications, where repeated simulations of R or F are computationally intensive. The double-nested-loop algorithm of Cliff's Delta maximizes the extraction of information about structural reliability from these simulations. However, the high computational demand of Cliff's Delta is a disadvantage. Future research should optimize computational demands, especially for small values of P-f.

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