Jiri Kala

Sensitivity analysis of the effect of initial imperfections on the (i) ultimate load and (ii) fatigue behaviour of steel plate girders

Abstract The study is divided into two parts: (i) in the first one, the plate girder (Fig 1) is considered to be exposed to quasi‐constant loading (ie to loads which are either constant or repeated in a very small number of cycles), while (ii) in the other one, the girder is assumed to be subjected to repeated loading. Then it is understandable that the objective of the first part should be to look into the influence of initial imperfections on the static ultimate load of the girder related to the formation of a plastic failure mechanism in it, while that of the second part was to study the effect of imperfections on the stress state under considerably lesser loads, viz under such as to correspond to the development of fatigue cracks in the girder and, consequently, to its fatigue limit state. In this case the state of stress was measured by bending stresses developing in the crack‐prone areas (Fig 4) of the web “breathing” under the repeated loads, which ‐as demonstrated by the Prague experiments ‐ occur...

Assess of the Nuclear Power Plant Structures Residual Life and Earthquake Resistance

The paper deals with the seismic analysis of safety related structures of an operating nuclear power plant. At present time the nuclear power plants of VVER-400/213 type operate for over thirty years and there are arising requirements to verify the actual state of structures in order to assess their residual life in general. A sophisticated computation model has been developed for the seismic structural analysis using the ANSYS program package. The model involves the complex of all constrained structures of two main production blocks with equipment. In order to get a general view at the seismic load effects, seismic response analysis has been performed using direct integration of equations of motion in 25 sec interval at 0.01 sec step with excitation described by accelerograms. Combinations of dead loads and seismic loads have been considered in the stress assessment of the structures. The results of the performed analyses form a base for residual life prediction of selected structures

Calculation of Timber Outlook Tower with Influence of Behavior of “Steel-Timber” Connection

The paper describes the dynamics analysis of the timber truss tower structure located near Bohdaneč village. Regular static analysis and response on dynamic wind action detailed calculations of tower was performed. Article contents description of elaborated analysis, results summary and qualifying reliability of the structure considering dynamic wind effect in direction of the flow, vortex excitation and pedestrians’ movement action.

Analysis of the Shear Failure of a Reinforced Concrete Wall

This paper proposes a 3D computational Finite Element model of a shear wall test that includes the test device with the tested concrete slab. A modified Drucker-Prager model was used for the modelling of the nonlinear behaviour of the concrete. The condition of plasticity is formed from two criteria with which it is possible to realistically describe the strength of concrete under pressure, tension and shear stress. The simulation results are compared to measured data.

Response of Water Tower on Wind Induced Vibration Considering Interaction of Fluid and Structure

The paper deals with the numerical analysis of forced vibrations of a slender water tower structure. The computation model has been developed using finite elements in the ANSYS program environment. For CFD (Computational Fluid Dynamics) analysis the CFX module was used. The computation model includes the precisely modeled thin-walled steel structure and two variants of fluid domain. Elements FLUID30 formulated for direct description of the fluid pressure field has been applied and Lagrange description FLUID80. The Raleigh’s model of energy dissipation has been used. Similarity of normal modes of vibration has been applied as the criterion for defining the relations between computed natural frequencies of the empty tank and filled with water. To obtain accurate wind induced forces the CFD model of air surrounding was modeled. From this model the relation between velocity of unaffected stream and vortex separation frequency. Forced vibrations of the tower excited by vortex shedding harmonic pulsations have been computed.

Optimization of the material parameters of the continuous surface cap model for concrete

Modeling the nonlinear behavior of concrete within the problems of continuum mechanics for designing protective and military structures is now undoubtedly the subject of effort of staff of many scientific institutes. Striving for modeling real nonlinear behavior of concrete through sophisticated material models implemented in an even more sophisticated computing systems based mainly on the finite element method, however, brings with it certain problems. The main problem is especially a lack of knowledge of material constants (parameters) that must be defined to ensure proper function of a particular model. One possibility, which today enables the mentioned problem successfully solved, is the use of optimization procedures in order to find the correct values of the material parameters. Parameter optimization goes hand in hand with experimental investigation of concrete structures, while it trying to find parameter values of used material model of concrete so that the resulting data obtained from the numerical simulation will best approximate the experimental data. This paper deals with parameter optimization of nonlinear material model of concrete, which is implemented in a computing system LS-Dyna, with the use of optimization procedures and experimental data obtained from the direct tensile tests performed on specific concrete test specimens.

Simulating randomized failure of concrete targets

A new approach of involving the concrete-like materials heterogeneity into the simulations is described in the paper. The reason why the topic is so attractive is based on a need to capture the behaviour of real-world processes as well as possible. In case of protective structure design there is always a question which material should be used for the construction. And if the concrete-like material is chosen, how far one should go with its simulation complexity. With the Smoothed Particle Hydrodynamics (SPH) method we are able to simulate high speed loadings without any numerical difficulties. On the other hand, there is no approach of how to simply involve material heterogeneity (randomness) into the simulations using SPH. The main idea of this process (algorithm) is presented in the paper. The mathematical background as well as the numerical simulation example are described. All the aspects which need to be maintained to ensure algorithm functionality are described, too.

Study on Identification of Material Model Parameters from Compact Tension Test on Concrete Specimens

Identification of a concrete material model parameters using optimization is based on a calculation of a difference between experimentally measured and numerically obtained data. Measure of the difference can be formulated via root mean squared error that is often used for determination of accuracy of a mathematical model in the field of meteorology or demography. The quality of the identified parameters is, however, determined not only by right choice of an objective function but also by the source experimental data. One of the possible way is to use load-displacement curves from three-point bending tests that were performed on concrete specimens. This option shows the significance of modulus of elasticity, tensile strength and specific fracture energy. Another possible option is to use experimental data from compact tension test. It is clear that the response in the second type of test is also dependent on the above mentioned material parameters. The question is whether the parameters identified within three-point bending test and within compact tension test will reach the same values. The presented article brings the numerical study of inverse identification of material model parameters from experimental data measured during compact tension tests. The article also presents utilization of the modified sensitivity analysis that calculates the sensitivity of the material model parameters for different parts of loading curve. The main goal of the article is to describe the process of inverse identification of parameters for plasticity-based material model of concrete and prepare data for future comparison with identified values of the material model parameters from different type of fracture tests.