Applied Mechanics and Materials Vol. 617

Abstract: This paper deals with the application of the method of impedance spectroscopy to testing of cement-based composites prepared from a mix of cement mortar and quartz sand, which were intentionally degraded by high-temperature treatment (in the temperatures range from 25 °C to 400 °C). The monitoring of structural changes in the thermal stress is very important, for example for determining the reliability of the whole structure. Based on the Debye theory of dielectric the models were created, their applications and received parameters measured dielectric material is characterized and discussed the uniqueness of determining the values of model parameters. Development of electrical parameters and permittivity at each temperature areas reliably show these structural changes and thus the structural reliability.

Abstract: Fatigue of steel specimens at low temperatures is treated in present paper. Micro-mechanical modeling is used for numerical analysis of the problem. The numerical treatment of non-linear problems appearing is made by updated Lagrange formulation of motion. Each step of iteration approaches the solution of the linear problem. Numerical and experimental assessment is submitted in order to demonstrate the efficiency of the approach suggested.

Abstract: The article compares results of temperature and heat flux measurements in the external wall of a real timber structure with results obtained by numerical modeling using the finite element method in the ANSYS software. The measured temperature values are compared with results obtained from numerical simulation of dynamic heat transport using non-stationary boundary conditions. In the article there is evaluated a suitability of theoretical numerical calculations for a thermal field and heat flux prediction in a building structure.

Abstract: The authors proposed the results of fire resistance evaluation of steel-concrete beams with external sheet reinforcement at standard temperature range of fire in the room and justified specifications for flame-retardant coat due to design standards. In order to analyze fire resistance the three-dimensional computer models were developed taking into account the basic conditions of beams loading and bearing as well as non-linear "stress-strain" dependencies of concrete and external reinforcement.

Abstract: The purpose of the paper is to perform a static analysis of a thin-wall cold-rolled steel cross-section of a trapezoidal sheet by means of a mathematical model developed in ANSYS, commercially available software applications. The trapezoidal sheets are used typically as an external cladding which covers the structures of steel halls. Investigating into behaviour of the trapezoidal sheets subjected to extreme loads represents an urgent issue in wind engineering. A physical tension test has been performed in order to verify and confirm the mathematical model. Experiments have been performed to prove results of the static analysis into the behaviour of a load-carrying structure formed by a thin-wall cross-section.

Abstract: The torsion of the mast shaft has been monitored on several masts in the Institute of Theoretical and Applied Mechanics (ITAM) since 2005. The occurrence of this phenomenon is conditioned by the fact that the guy ropes are attached out of the axis of the mast shaft. An experimental mast-shaft model of 15 m height guyed in 3 directions was used for the more detailed study of its rotational motion. The excitation was realized by transversal auxiliary rope drawn by harmonic human force in resonance. The displacement of the shaft top results in translation caused by the guy force and the rotation, caused by the eccentricities of the guy-ropes, attached out of the shaft axis. The resulting movement of the shaft support is an elliptical orbit. The shaft of our experimental mast was equipped in two levels with accelerometers for registration of horizontal x, y motions. The two x, y signals in two levels were monitored and analysed.

Abstract: This article is about the nonlinear dynamic stability problems of the exact (Cosserat) theory of elastic rods. There is examined the general geometrically nonlinear theory with no restrictions on displacements and rotations being imposed. In this article, it is shown that the variational problem can be defined as the search for the stationary point of the Hamilton’s functional. The new exact solutions of the stability problems for different types of the end fixities of the rod were obtained taking into account bending, shear and longitudinal stiffness.

Abstract: Fatigue analysis of steel parts of structures, which are subjected to complex irregular loading programs caused by wind, thermal, wave loads, earthquakes and combined imposed actions, requires in some cases using special methods of stress-strain evaluation. The model of the low cycle fatigue nonlinear damage accumulation is developed with taking into account the history of the deformation process. The damage is defined on the base of considering the quasi-static accumulation of maximal strain (stress) and hysteresis loops. The identification of material constants of the model is discussed. Application of the damage model for fatigue analysis of the antennas, pipelines, basements and fasteners units is considered and a comparison with experiments is given.

Abstract: This paper deals with some problems of the ceiling plate, made of the Cobiax-system. Cobiax provides a system to produce voided, biaxial, flat plate slabs as a high-quality concrete solution for large spans and slim slabs. Plastic voids in the shape of spheres or flattened spheres are contained in steel cages and put into concrete structures to create longer spans and reduce vertical loads. The presented plate is made of cobiax balls with a diameter of 27 cm located outside the area of columns. Probability analysis of Monte-Carlo method in Ansys is presented. Input parameters are changing according to Gauss or triangular distribution.

Abstract: Strain-Life approach to fatigue analysis of structures being developed since early 1960s recently was considered applicable in Civil Engineering, in particular, for fatigue evaluation of bridge structure with integrated abutments. To exemplify the approach and display the problems of its implementation in fatigue design, in-service reliability of structures, an example of fatigue design of a ship superstructure critical detail is presented. The detail is located at expansion joint ending in the superstructure which is frequently applied in ship design aimed at reducing stresses in a long superstructure caused by the general bending deformation of ship hull. Specific of the detail is the high local stress concentration which may result in fatigue damage menacing integrity of the ship hull. In the example of fatigue design of the expansion joint the modified «Strain-Life» criterion for fatigue of material is applied along with empirical relationship providing evaluation of the local strain. This version of the approach allows assessment of fatigue properties of the detail without utilizing Neuber’s formula and presenting the loading history in the block-type format. The results of analysis allowed selection of the expansion joint detail of the superstructure geometry and construction procedure at a shipyard providing necessary reliability.