Geometry functions for edge cracks in steel bridge under three- and four- point bending with various span

Fatigue cracks are found during the regular structural inspections. To precisely describe/suggest propagation of fatigue cracks throughout structure and it’s designed service life, the knowledge of geometry functions describing the stress situation in front of the crack tip for relative crack lengths are important. The cracks usually propagate/initiated from the edge or the surface of the structural element, where the maximum value of applied load is achieved. The theoretical model of fatigue crack propagation is based on linear fracture mechanics (Paris law). Steel structural elements are subjected to various bending load (three-, four- point bending and pure bending etc.). The geometry functions for the edge cracks are calculated for various span according to real steel bridge elements and appropriate polynomial functions independent on the distance are proposed for three- and four- point bending load

Cubic nonlinear squeezing and its decoherence

Squeezed states of the harmonic oscillator are a common resource in applications of quantum technology. If the noise is suppressed in a nonlinear combination of quadrature operators below threshold for all possible up-to-quadratic Hamiltonians, the quantum states are non-Gaussian and we refer to the noise reduction as nonlinear squeezing. Non-Gaussian aspects of quantum states are often more vulnerable to decoherence due to imperfections appearing in realistic experimental implementations. Therefore, a stability of nonlinear squeezing is essential. We analyze the behavior of quantum states with cubic nonlinear squeezing under loss and dephasing. The properties of nonlinear squeezed states depend on their initial parameters which can be optimized and adjusted to achieve the maximal robustness for the potential applications.Comment: 17 pages, 10 figure

Investigation of eigenvalue problem of water tower construction interacting with fluid

The paper concerns problems, in which both the structural and fluid responses of a complex construction to mechanical actions are strongly coupled. Particularly, there are treated problems, in which the structural dynamic response to actions is significantly affected by the presence of the fluid in the structure. The work presents the evolution of the way of solving that problem of the complex solution of the generalized problem of the structure using multiphysical ANSYS program package. The formulation of fluid finite elements is discussed, considering both pressure (Euler) with/without sloshing and displacement (Lagrange) approaches. The solution is demonstrated on thin-walled steel water tower structure

Inverse Identification of the Material Parameters of a Nonlinear Concrete Constitutive Model Based on the Triaxial Compression Strength Testing

The aim of this paper is to perform the inverse identification of the material parameters of a nonlinear constitutive model intended for the modeling of concrete which is known as the Karagozian & Case Concrete model. At present, inverse analysis is frequently used because it allows us to find the optimum parameter values of nonlinear material models. When applying such parameters, the resulting response of the structure obtained from a computer simulation is very similar to the real response of the structure based on the related experimental measurement. This condition then undoubtedly constitutes one of the progressive steps to refine the current numerical approaches. For the purposes of the inverse analysis performed in this paper the experimental data was obtained from the triaxial compression strength tests carried out on the concrete cylinders

Study of the Efficiency and Accuracy of Optimisation Algorithms within Inverse Identification of the Parameter Values of a Nonlinear Concrete Material Model

The inverse identification of the parameter values of nonlinear material models, which have been developed for, inter alia, concrete modelling, is currently a process that is widely used and investigated in the field of research and development. Today there are several approaches that can be employed for the inverse identification process. One of the most significant of these approaches involves the use of optimisation algorithms which, however, often demonstrate varying levels of precision and efficiency within specific tasks. These aspects are the subject of the research presented in this contribution

Mesh Size Influence of the Concrete Slab FE Model Exposed to Impact Load for Various Material Models

Numerical approach using the FEM has been used to model the behaviour of the reinforced concrete specimen subjected to the pressure blast wave. The concrete structure is a slab freely supported around the perimeter by a steel plate and a concrete base. A simplified 3D blast model has been used, which involves the pure Lagrangian approach of FEM. The analyses have been conducted using explicit solver. 3 different non-linear material models of concrete have been used to capture the concrete behaviour: CSCM (Continuous surface cap model), Schwer Murray continuous surface cap model, and JHC (Johnson-Holmquist-Cook) material model. Influences of various mesh sizes on the final results (crack patterns, vertical deflection, strain-time dependence) are being monitored, compared with physical experiment data and discussed.Ostrav

Optimal adjustment od FE model of concrete slab exposed to impact loading

Numerical approach using FEM has been used to describe the behaviour of concrete slab exposed to impact loading. 3D parametrical numerical model has been created, and the influence of various parameters values on model response is being investigated. The analyses have been conducted using explicit numerical solver of commercially available software LS-Dyna. The optimal adjustment of the model has been determined

Requirements of technical standards for the dynamic analysis of the load-bearing structures of footbridges

The load-bearing structures of footbridges are designed to be slender and feature spans of considerable length. It can be expected that the natural frequencies of such load-bearing structures range from 0.5 Hz to 5.0 Hz. These low natural frequencies are problematic as regards the effects caused by the dynamic component of wind or the movement of persons. Increased acceleration values can lead to the serviceability limit state of structures being exceeded or the heightening of stress which can result in damage to the structure mainly in the area of details prone to fatigue. The contribution deals with the requirements concerning the execution of dynamic analyses which are listed in the relevant technical standards. It will present procedures for the determination of dynamic loading, methods of solving dynamic tasks as well as design criteria enabling delicate bridge structures to be designed correctly

Stress relaxation of concrete beams caused by creep and shrinkage effects

Shrinkage and creep are two important physical properties of concrete material which cause increase of the deformation of the constantly loaded structure over long period of time, the feature known as rheology. Additional deformation of concrete structures at the end of the design working period (most commonly 50 years) caused by these phenomena is circa three times larger than the value of the immediate elastic deformation (or even larger in some cases). Hence, in accordance with the corresponding European standard, these effects should be taken in account while evaluating the serviceability limit state of concrete structures, and if significant, consideration of these phenomena is also needed for the verification of the ultimate limit state. In concrete material, creep occurs at all stress levels, and is dependent on many parameters, as cement class, concrete grade, relative humidity of the environment, surface of the structure in contact with the ambient air (drying surface), and the age of concrete (after casting) at the loading moment. Shrinkage of the concrete is independent on loading. It is caused by decrease of the pore water content in the hardened concrete, and is predominantly dependent on the ambient relative humidity. Relaxation describes stress reduction at a constant material strain, usually in prestressing steel tendons. In this study, the physical experiments of multiple concrete beams over time with respect to rheological processes are described. Each experimental system consists of two C35/45 beams horizontally bounded by a prestressed steel cylinder. Decrease of these pretension forces in cylinders over time have been monitored (stress relaxation). All together time histories of two forces are documented, based on measurements conducted in interior environment of an agricultural building. The experimental time histories of the pretension forces are then compared with the results of the finite element numerical analyses conducted in ANSYS software. Creep and shrinkage effects of the concrete material have been considered based on the corresponding European standard for design of the concrete structures. The time-histories of the forces in prestressed cylinders obtained from the numerical simulations are then compared with the experimental data, and discussed. It is concluded, that the estimation of the force decrease over analysed time with the creep and shrinkage effects considered according to the corresponding European standard appears to be slightly larger than the experimentally measured decrease of the force value, hence the assumption is more conservative