Pavel Manas

Methodology for risk assessment of road bridges endangered by blast attack

Malfunction of bridges due to natural or man-made hazards causes severe consequences in transportation networks. Decision making about protective measures should take basis in optimising expected costs. Uncertainties in input data should be treated by probabilistic methods. In general, total costs cover initial and operational costs, and direct and indirect consequences of structural failure. Bayesian (causal) networks provide an appropriate tool for such considerations. Case studies indicate that particularly the analysis of bridge response to a blast attack is a complex issue.

Research of Prospective Materials for Military Protective Structures

Different types of composite materials with potential application in ballistic protection of static objects are discussed and compared in present study. The studied solutions include: 1) the concretes with or without reinforcement, 2) the metallic boxes with internal gap filled with different materials and 3) the ceramics-metallic composite armours. Besides the ballistic resistance, the areal weight and the price are taken into account. The weight of solutions is important in case of static objects mainly from logistic point of view. The proposals of ballistic compositions presented in the study can facilitate the choice of solutions according to specific requests.

Temporary bridges used in the Czech Republic

The paper presents temporary bridge constructions, which are owned by state organizations in the Czech Republic. These bridge constructions would be used in case of replacement of permanent bridges during crisis. The structures are compared especially with regard to their load capacity, the possibility of building by units of the Armed Forces of the Czech Republic (ACR) and amount of material in warehouses.

A comparison of the MLC of wheeled and tracked vehicle according to the STANAG 2021

The article deals with the determination of MLC (Military Load Classification) of vehicles. The two loading sets (tracked vehicle and the semi-trailer with the vehicle) are compared to the bending moment imposed to structure. The loads are applied to various spans from 10 to 100 meters, loading classes are calculated according to the STANAG 2021, Ed. 8. The aim of the article is to evaluate the MLC of proposed combined tracked vehicle in comparison with the vehicle on the semi-trailer and towing vehicle.

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.

Reliability assessment of existing bridges for military use — Appropriate values of partial factors for traffic loads

Freedom of movement and manoeuvre are key assumptions to success in any military operation and one of the core responsibilities for each corps of army engineers. The calculation of military loading capacity of any civilian bridge is one of the essential tasks to achieve this target. Partial factors for the traffic loading in standards for civilian use fail to adequately reflect conditions for assessing existing bridges under well-defined military loads. Based on the safety format adopted in an upcoming edition of STANAG 2021, the submitted contribution illustrates on how the partial factor for military traffic can be adjusted considering various crossing conditions. The numerical study, focused on a crossing of a MLC80 class vehicle over an existing bridge, reveals that the partial factor of the military traffic load can range from 1.1 up to 1.4, depending on the chosen crossing conditions and the target reliability level selected for the crossing mode under consideration.

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.

Determination of the Material Properties of Recycled Rubber for Explicit FEM Simulation

Recycled rubber materials are one of cheap and suitable materials for energy absorbers in protective structures. Standard tests of elastomers in uniaxial or biaxial tension is not suitable and efficient for energy absorbers made of recycled car tires. Simple compression test and simple impact test are described material properties from those tests are determined and compared with simulation in ANSYS/AUTODYN.

The Influence of Plasma Nitriding Process on Mechanical Properties of 14NiCr14 Steel

The article deals with an alteration of mechanical properties of plasma nitrided steel. Experimental work was focused on evaluation of influence of plasma nitriding process on the notch toughness of steel. Experiments were realized on V-notch samples of size 10x10x55 mm (according to ISO 148-1 standard) from 14NiCr14 steel. The 14NiCr14 steel was heat treated prior plasma nitriding. The heat treatment consisted of hardening at 850 °C and tempering on elimination of internal stress at 200 °C. Heat treated experimental samples were plasma nitrided at 450 °C, 500 °C and 550 °C. The notch toughness tests of steel were carried out using the instrumental Charpy hammer at test temperatures-40 °C, +21 °C and +70 °C. The notch toughness of plasma nitrided samples achieved nearly identical values as heat treated samples thus plasma nitriding did not reduce the values of notch toughness. The increase in temperature of the plasma nitriding process even led to achievement of higher values of notch toughness compared with heat treatment specimens namely at all test temperatures.

Analysis of acoustic emission signal generated by timber under load

The nature of acoustic emission (AE) signal depends on the character of the wave source (deformation or crack of the material) and properties of the material. In the case of wood materials the species, anisotropy and moisture content have also significant influence on the AE wave propagation through the material. To better understand the processes inside the specimen under load both the deformation and AE signal were measured. The acoustic emission signal was preamplified and recorded using Vallen AMSY-5 AE measurement system. The recorded data were analysed using Fourier transform. The results have proved significant differences between specimens of respective species (beech and spruce wood). AE signal monitoring makes possible to determine the allowable load for a particular specimen without any danger of permanent damage.