1. A general analytical solution to the one-dimensional consolidation problem for unsaturated soil under various loading conditionsJiwei Li, Changfu Wei, Yanlin Zhao, 2018, original scientific article Abstract: A general analytical solution is developed for the onedimensional consolidation problem of unsaturated soil under various time-dependent loading conditions based on a differential transformation method (DTM). In particular, analytical solutions are obtained for different relationships between the coefficients in the governing equations for unsaturated soil consolidation. The Fourier series expansion technique is adopted to account for both the continuous differentiable loading and the periodic piecewise loading. A comparison between the results of the current solution and the existing theoretical solution indicates that the proposed solution yields excellent results, while it is straightforward to obtain the analytical solution of the unsaturated consolidation problems. It was also found that the variations in the coefficients in the governing equations can significantly influence the dissipation of both the excess pore-air pressure and the excess pore-water pressure, though the magnitudes of their variations are different.
Keywords: one-dimensional consolidation problem, unsaturated soil, analytical solution, time-dependent loading
Published in DKUM: 11.10.2018; Views: 983; Downloads: 424
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2. Numerical study of the dynamic active lateral earth pressure coefficient of cohesive soilsMehrab Jesmani, Hossein Alirezanejad, Hamed Faghihi Kashani, Mehrad Kamalzare, 2017, original scientific article Abstract: Retaining walls are proposed in many projects, such as bridges, coastal structures, road constructions and wherever lateral support is required for the vertical surface of an excavation. The active lateral pressure coefficient of soil, Ka , is an important parameter for studying the static and dynamic behaviors of these retaining walls. Many studies have evaluated this coefficient in static situations, but in most previous dynamic studies, researchers have worked on the behavior of cohesionless backfill soil or made simplifying assumptions (e.g., pseudo-static status) for cohesive soils as backfill soil. In this study, the size of the active lateral earth pressure coefficient (Ka) was studied in a full dynamic situation (Kae). A retaining wall with cohesive backfill soil is evaluated using the finite-difference method (FDM) and the effects of important soil and loading properties are assessed. The model is based on Mohr-Coulomb failure criteria under seismic loading. The results show that the value of Kae at the top of the wall, where it is highly sensitive to any variation in the soil and loading properties, is greater than one due to the high pressure value induced by the horizontal dynamic acceleration and the presence of tension cracks.
Keywords: dynamic active lateral earth pressure coefficient (Kae), cohesive backfill soil, finite difference method (FDM), tension cracks, retaining wall, seismic loading
Published in DKUM: 18.06.2018; Views: 1044; Downloads: 85
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3. Experimental and numerical studies of T-shaped footingsNihat Kaya, Murat Ornek, 2013, original scientific article Abstract: In addition to vertical axial loads, the footings of structures are often subjected to eccentric loads caused by the forces of earth pressures, earthquakes, water, wind, etc. Due to eccentric loading, the two edges settle by different amounts, causing the footing to tilt and then the pressure below the footing does not remain uniform. The T-shape is proposed as a footing shape for improving the bearing capacity of shallow footings against the action of eccentric loads. The vertical insertion of the rigid T-shaped footing, into the bearing soil, provides considerable resistance, against both of sliding and overturning, enough to regain the reduction in bearing capacity and increase in settlement. In this study, a series of experimental and numerical results from the ultimate loads and settlement of T-shaped footings are reported. A total of 48 model tests were conducted for investigating the effects of different parameters, such as the problem geometry and soil density. The problem geometry was represented by two parameters, the load eccentricity (e) and the insertion depth (H) of the T-shape into the loose and dense sand soil. After the experimental stage, the numerical analyses were carried out using a plane strain, two-dimensional, finite-element-based computer program. The behaviour of the T-shape footing on sand beds is represented by the hardening soil model. The results of the experimental and numerical studies proved that the ultimate bearing capacity of a footing under eccentric loads could be improved by inserting a vertical central cut-off rigidly connected to the footing bottom. The load settlement curves indicate that the higher load eccentricity results in a decrease in the bearing capacity of the strip footing. It was also proved that the ultimate bearing capacity values can, depending on the soil density, be improved by up to four times that of the loose sand case. This investigation is considered to have provided a useful basis for further research, leading to an increased understanding of the T-shaped footing design.
Keywords: model test, finite-element method, T-shaped footing, eccentric loading, sand
Published in DKUM: 14.06.2018; Views: 817; Downloads: 50
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4. Prediction of the pile behaviour under dynamic loading using embedded strain sensor technologyAndrej Štrukelj, Mirko Pšunder, Helena Vrecl-Kojc, Ludvik Trauner, 2009, original scientific article Abstract: A standard dynamic loading test of the pile was performed on the highway section Slivnica - Hajdina near Maribor, Slovenia. Parallel to standard testing procedures the new monitoring technology based on specially developed strain sensors installed inside the pile body along the pile axis was introduced. On the basis of the measured results the normal strains along the pile axis were measured. Taking into consideration the elastic modulus of the concrete the normal stresses in the axial direction of the pile were also calculated and afterwards the shear stresses along the pile shaft have been estimated as well as the normal stresses below the pile toe. The estimation was made by considering a constant value for the pile diameter. The measured results were also compared with the computer simulation of the pile and the soil behaviour during all the successive test phases. The strain measurements inside the pile body during the standard dynamic loading test in present case did not have the purpose of developing an alternative method of pile loading tests. The presented monitoring technology proved itself as a very accurate and consistent. It gave in the first place the possibility of a closer look at the strains and stresses of the most unapproachable parts of different types of concrete structure elements especially piles and other types of deep foundations.
Keywords: piles, deep foundations, dynamic loading test, strain measurement technologies, elasto-plastic modelling, finite-element method
Published in DKUM: 06.06.2018; Views: 946; Downloads: 71
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5. The assesment of pile shaft resistance based on axial strain measurements during the loading testAndrej Štrukelj, Stanislav Škrabl, Ksenija Štern, Janko Logar, 2005, original scientific article Abstract: Near Maribor, a new bridge over the Drava river is being under construction. Before the main works actually started, static and dynamic loading tests of piles were performed. The goal of the static loading test was to determine the bearing capacitiy of the test pile. It was also interesting to determine the share of the axial load distributed on the shaft and pile toe. In order to measure the distribution of the axial force along the pile, a specially made steel canal was built in the pile before concreting. Inside this canal the strain gauges were distributed evenly at the distance of one meter. The strains were measured for each loading phase in all measuring points. The distribution of the axial force was assessed from the obtained results and based on the distribution of the axial force the shaft resistance could be determined. The unexpectedly high bearing capacity of the pile shaft made the obtained results highly interesting. In this paper, measuring methods and measuring results are discussed. Behaviour of the pile and the soil during the loading test were also modelled by axial symmetric and three dimensional models. The calculated and measured results show a very good agreement.
Keywords: civil engineering, bridges, soil mechanics, pile shaft resistance, loading test, strain measurements, elastoplastic soil modelling, finite element method
Published in DKUM: 16.05.2018; Views: 1055; Downloads: 63
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6. A multiscale approach to deformation and fracture of heat-resistant steel under static and cyclic loadingP. O. Maruščak, Denys Baran, Vladimir Gliha, 2013, original scientific article Abstract: Regularities of static and cyclic deformation, damage and fracture of heat-resistant steel 25Kh1M1F, based on the approaches of physical mesomechanics and 3D interferometry method, are presented in this paper. The applicability of these techniques for different hierarchy levels of deformation was studied. The investigation of scanning microscope photos was conducted for several dissipative structures, fragmentation of the material, localisation of macrodeformation and subsequent failure on macro- and mesolevel. It is shown that the used modern techniques of experimental analysis are very efficient in understanding deformation and damage evolution in materials.
Keywords: fracture, heat-resistant steel, cyclic loading, fatigue, plastic deformation
Published in DKUM: 18.08.2017; Views: 966; Downloads: 330
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7. Behavior of metallic foam under shock wave loadingMatej Vesenjak, Matej Borovinšek, Zoran Ren, Seiichi Irie, Shigeru Itoh, 2012, original scientific article Abstract: In this manuscript, the behavior of metallic foam under impact loading and shock wave propagation has been observed. The goal of this research was to investigate the material and structural properties of submerged open-cell aluminum foam under impact loading conditions with particular interest in shock wave propagation and its effects on cellular material deformation. For this purpose experimental tests and dynamic computational simulations of aluminum foam specimens inside a water tank subjected to explosive charge have been performed. Comparison of the results shows a good correlation between the experimental and simulation results.
Keywords: metal foam, shock wave loading, experimental testing, dynamic simulation
Published in DKUM: 21.06.2017; Views: 1051; Downloads: 373
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8. Experimental and numerical evaluation of the mechanical behavior of strongly anisotropic light-weight metallic fiber structures under static and dynamic compressive loadingOlaf Andersen, Matej Vesenjak, Thomas Fiedler, Jehring, Lovre Krstulović-Opara, original scientific article Abstract: Rigid metallic fiber structures made from a variety of different metals and alloys have been investigated mainly with regard to their functional properties such as heat transfer, pressure drop, or filtration characteristics. With the recent advent of aluminum and magnesium-based fiber structures, the application of such structures in light-weight crash absorbers has become conceivable. The present paper therefore elucidates the mechanical behavior of rigid sintered fiber structures under quasi-static and dynamic loading. Special attention is paid to the strongly anisotropic properties observed for different directions of loading in relation to the main fiber orientation. Basically, the structures show an orthotropic behavior; however, a finite thickness of the fiber slabs results in moderate deviations from a purely orthotropic behavior. The morphology of the tested specimens is examined by computed tomography, and experimental results for different directions of loading as well as different relative densities are presented. Numerical calculations were carried out using real structural data derived from the computed tomography data. Depending on the direction of loading, the fiber structures show a distinctively different deformation behavior both experimentally and numerically. Based on these results, the prevalent modes of deformation are discussed and a first comparison with an established polymer foam and an assessment of the applicability of aluminum fiber structures in crash protection devices is attempted.
Keywords: aluminum fiber, fiber structure, orthotropy, sintering, compression, static loading, dynamic loading, energy absorption, numerical simulation
Published in DKUM: 21.06.2017; Views: 784; Downloads: 438
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9. Computer simulation of needle and take-up lever mechanism using the ADAMS software packageDarja Žunič-Lojen, Karl Gotlih, 2003, original scientific article Abstract: A knowledge of the interactions between a sewing machinećs mechanisms and the sewing thread in the stitch formation process should help us to understand thread loadings in the sewing process. The aim of this work is to analyse the needle bar's kinematics with the thread take-up lever by using computer simulation. A cyclogram was drawn on the basis of modelling and kinematic simulation of a needle bar with a thread take-up lever, and measurements of the thread tension forces in the sewing process. This cyclogram enables analysis of the interactions between the thread and the elements of the sewing machine. The results of these simulations are curves that describe the movements at characteristic points on the mechanism. These give the possibility of pinpointing the exact positions of the mechanism's elements with respect to the main shaft rotation in the sewing machine.
Keywords: textiles, garment manufacturing, sewing, thread, stitch fomation, thread loading, cyclogram, computer simulation
Published in DKUM: 01.06.2012; Views: 1835; Downloads: 33
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10. Assessment of the consequences of accident scenarios involving dangerous substancesZorka Novak-Pintarič, 2007, original scientific article Abstract: This paper highlights the major steps in the procedure for evaluating the consequences of accidents involving dangerous substances, especially during storage, loading and unloading activities. The procedure relies on identifying accident scenarios that could be encountered in particular plants, followed by modelling of these scenarios by means of available modelling systems. Finally, the resultant outcomes are identified, together with their effects on both people and property. The resources needed to perform this proceedure are discussed, in order to clarify the roles of operators, external experts and other institutions when evaluating any accident conesquences. Four examples, all relevant in industrial practice, are given in order to illustrate the procedure: the releasing of liquefied petroleum gas, flammable organic solvents, toxic chlorine, and fuel oil. The results of these studies may be used for a quick order-of-magnitude estimation of accidents consequences.
Keywords: chemical industries, dangerous substances, transportation, storage, risk, accidents, consequences estimation, Seveso II, loading, unloading, safety report
Published in DKUM: 01.06.2012; Views: 2112; Downloads: 98
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