Applied Mechanics and Materials Vols. 725-726

Abstract: The article is devoted to the problem of numerical simulation of unbounded domains in structural mechanics. Nowadays there are many numerical methods to analyze structural mechanics problems in infinite domains. A brief analytical review of existing numerical methods is presented. Among them are finite difference method, boundary element method (BEM), finite element method (FEM) and scaled boundary finite element method (SBFEM). No one suggests general approach for all kinds of problem statements. Vast majority of industrial software realize FEM. Considering this fact it is more reasonable to modify FEM for mechanical problems in unbounded domains. New variational differential method and new FEM modification, based on the approach of quasi-uniform grids modelling in finite difference method, are proposed. New numerical methods enable to solve problems in semi-infinite and infinite domains without introduction of artificial boundaries and setting special non-reflecting conditions. The article shows basic steps of new numerical algorithms for problems in one-dimensional semi-infinite computational domain.

Abstract: This article is about the nonlinear problems of the theory of elastic Cosserat – Timoshenko’s rods in the material (Lagrangian) description with energy conjugated vectors of forces, moments and strains. The variational formulations of static problems was given. The differential equations of the plane stability problems were obtained from the second variation of the Lagrangian functional. The exact solutions of the stability problems for basic types of the end fixities of the rod were obtained for the Timoshenko’s rod (taking into account only bending and shear stiffness). It appears that classical well-known equilibrium stability functional and stability equations for the Timoshenko’s rod are incorrect. Also well-known Engesser formula (with bending and shear stiffness) is incorrect. The numerical solution of the stability problems for hinged Timoshenko’s rod with rigid support was obtained. Also, simplified formula for this problem was derived using asymptotic analysis.

Abstract: In this work we consider a mathematical model for granular medium. Here we claim that Reduced Cosserat continuum is a suitable model to describe granular materials. Reduced Cosserat Continuum is an elastic medium, where all translations and rotations are independent. Moreover a force stress tensor is asymmetric and a couple stress tensor is equal to zero. Here we establish the variational (weak) form of an initial boundary-value problem for the reduced Cosserat continuum. We calculate the variation of corresponding Hamiltonian to obtain motion differential equation.

Abstract: This paper presents the procedure for stability analysis of frames in elastic-plastic domain using the concept of the tangent modulus. When the buckling of structure occurs in plastic domain, it is necessary to replace the constant modulus of elasticity E with the tangent modulus E_t. Tangent modulus is stress dependent function and takes into account the changes of the member stiffness in the inelastic range. Formulation of the corresponding stiffness matrices is based upon the solution of the equation of bending of the beam according to the second order theory. Numerical analysis was performed using the code ALIN, developed in the C++ programming language

Abstract: The paper is devoted to development and numerical implementation for a numerical method for investigation of stress-strain state of the solids with large elastic-plastic deformations. Calculation algorithm is based on the linearized equation of virtual work, defined to actual state. The arc-length method is used. A spatial discretization is based on the finite element method. The developed algorithm of investigation of large elastic-plastic deformations is tested on the solution of the necking of circular bar problem and a conical shell subjecting to a constant ring load.

Abstract: The problem that this work deals with, relates to the analysis of behavior of the lattice girder joint. We will analyse a strained diagonal, roof lattices, presented on picture 1, in which the maximum influence of a normal force is 509.1kN and there are two profiles L100x100x10 adopted, both turned backwards (to each other). The connection between the angle bar and joint sheet metal, 15mm thick, is achieved via 4 angle stitches, 7mm thick and 250mm long, that will, besides diagonal itself, be the topic of this work. Steel concerned is S235.

Abstract: In recent years, Italian technical-scientific community has increased its interest on the evaluation of the seismic response of existing structures. Among this wide range of structures, reinforced concrete bridges stand out for their strategic relevance and technical complexity. Most of these structures were built between 60ies and 70ies, according to design procedures which ignored nowadays knowledge in seismic engineering. Thus, the necessity to evaluate the real strength capacity of these structures with modern analysis techniques has become essential, leading to the determination of their safety level in case of an earthquake. In particular, for the assessment of several bridges of a motorway network, a multi-modal pushover analysis approach has been considered. This analysis technique allows considering the nonlinear behaviour and the complex dynamic response of such structures without exceeding in high computational costs. Some basic rules were defined (constitutive laws of materials, finite element type, plastic hinge models, etc.) for the modelling of bridges, in order to guarantee homogeneous comparable results among different structures of a network. At the end, some of the results are compared to see the variation of the verification level with respect to both the number of modes considered and the analysis’s accuracy in terms of number of loading steps.

Abstract: This article describes the process of examining bridges. AB road bridge, founded on the columns by the Karpoš system and damaged due to erosive action of the river, is given as an example. The first tests of the bridge are conducted​​ on the impact load of V 300, because of the appearance of longitudinal cracks. The results of the columns testing are presented in this paper, as well as the rehabilitation measures thus increasing the load capacity of the column.

Abstract: Practical approach of strain gauges using is introduced. The use of strain gauges and signal processing of measured data at static experimental load testing of a concrete beam are carried out. The ability of the strain gauge sensor to pick up the specific deformation / strain signals during loading is investigated. The Fast Fourier Transformation (FFT) is applied to obtain the signal in frequency domain and reverse FFT to transform the processed signal back to time domain. The measurements are confirmed with some inductive transducers and total station. This approach is tested on 2.7 m long concrete beam in laboratory. A practical use of strain gauges with bridge constructions under complex inspection is described.

Abstract: Today there are a lot of sophisticated methods to measure and analyse a bridge during load tests as a GPS, photogrammetric measurements, laser scanning, etc., The use of an classical techniques as trigonometric hights is still good enough for most demanding field observations. In practice control measurements are performed with the help of geodetic measurements, of which the basic goal is to capture any geometric changes in the measured object, or its displacements and deformations are found. In this article the use of trigonometric hights during a load test on the biggest Slovenian viaduct “Črni Kal” is introduced, displacement measurements on the viaduct and an analysis of results, with particular stress on the accuracy of the calculations.