VGTU Journals (Vilnius Gediminas Technical University - Vilnius Tech)
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Ground compaction zone of structures and structural strength of soil
No full textGround compaction zone develops under action of structure foundation. Boundaries of it could be limited by a distance at which pressure from structure action is equal to structural strength of the soil. The structural strength of soil can be expressed by the parameters of shear resistance—the cohesion and the angle of the internal friction. These parameters are obtained by the experiment and corresponded to the strength at the beginning of the soil movement The ground compaction zone of structure will be at a depth, where the values of additional pressure is equal to the value of the structural strength of soil.Using the theory of soil limits the formula for the calculation of the structural strength state could be obtained:
where c—soil cohesion; Φ—the angle of the internal friction. Values c and Φ are obtained experimentally. They corresponds to the strength when shear movement starts.
Article in Lithuanian.
Pastato pagraindo deformacijų zona ir grunto strukūrinis stipumas
First Published Online: 26 Jul 201
Plazma ARC joining of thin plate constructions
No full textHeat and fluid flow exist not only in ingots or big size welds but also in small size microplasma ARC melted weld pool. Edge weld pool geometry depend from interfacial energy, direction of the fluid flows in the weld pool caused by thermocapilary convection. Thermocapilary convection is the dominant flow mechanism under downhand welding conditions. Comparision are made between calculated size of edge weld and experimental results.
Article in Lithuanian.
Plazminis plonalakščių konstrukcuijų sujungimas
First Published Online: 26 Jul 201
The quantitative assessement of the location of building projects in a territory
No full textIn many research works concerning the dispersion of building projects the influence of this dispersion on organizational structures of building enterprise management has not been almost touched upon. However, the territorial concentration of production is one of the most important structural factor. The quantitative evaluative analysis allows us to answer the question: why is there no common oppinion on this problem? The main reason is that the fields and aims of applying this factor by various researchers are different.When the dispersion is considered as a structural factor, it\u27s index must reflect the influence of dispersion on the organizational structure of the enterprise management. The index may be represented by the number of building sitez or the amount of work per territorial unit.
Article in Lithuanian.
Statybos objektų sklaidos kiekybinis įvertinimas
First Published Online: 26 Jul 201
The equilibrium finite elements in computation of elastic structures
No full textA problem of elastic structures stress-strain field determination is considered in this article. A theoretical background and computation algorithms of equilibrium finite element method are presented there. The different external effects are estimated, namely: load, prestressing, inicial strains and support settlements. The dual relationships (equilibrium and geometrical equations, stiffness and flexibility equations) of equilibrium element, also the expressions of stiffness and flexibility matrices are given. These relationships describe the stress-strain field of the finite element and allow to transforme the flexibility matrix to the stiffness matrix and on the contrary. There are presented direct and variational formulations of the problem. The algorithms of the forces method and displacements method are made for their solution. Easier is the algorithm of displacements method, because making equations of the forces method needs to solve the system of equilibrium equations. But the formulation and solving of the displacements equations can be changed by direct formulation of global flexibility matrix of the structure. In these cases, when the degree of static indeterminacy of the discrete model of structure is quite less than the number of freedom degrees, suth the change can be effective.The computational results illustrate the high accuracy of equilibrium elements not only with respect to forces, but also to displacements. The direct stiffness method in equilibrium elements makes it possible not only to simplify significantly implementation of the equilibrium element method, but also to include equilibrium elements in libraries of geometrically compatible elements.
Article in Russian.
First Published Online: 26 Jul 201
Dual limit analysis problems with discontinuity of displacement velocities
No full textThe general dual mathematical models (static and kinematic formulations) of the limit load and rigidplastic body parameters optimization problems are formed on the basis of extremal energy principles and theory of duality. Yield conditions are controlled not only in volume of finite elements, but also at the surfaces between elements. Therefore the possible discontinuity of displacement velocities and velocity energy dissipation between the elements are evaluated.
Article in Russian.
Dualūs ridinės pusiausvyros uždaviniai su poslinkių greičių trūkiais
Santrauka. Sudarytos standaus—plastinio kūno parametrų ir ribinės apkrovos optimizacijos uždavinių dualūs matematiniai modeliai statinėje ir kinematinėje formuluotėje. Juose takumo sąlygos tikrinamos ne tik baigtinių elementų tūryje, bet ir jų paviršiuose. To pasekoje dualiose formuluotėse įvertinami galimi poslinkių greičių trūkiai ir energijos disipacijos greitis paviršiuose tarp elementų.
First Published Online: 26 Jul 201
Sound absorption qualities of a cylinder-shaped isolated acoustic resonator
No full textIn the article, an isolated acoustic resonator consisting of a cylinder-shaped hole of variable volume and with large and variable diameter is theoretically analyzed.Theoretical formulaes by which sound absorption of such resonator is computed are presented. The computations incorporate the influence exerted by overtones, i.e. odd harmonics, and supplementary resonator mass upon sound absorption. A change in the sound absorbtion depending on the resonator hole diameter, the angle of sound wave incidence and its volume, i.e. the distance to the rigid surface, has been established. Sound absorption reaches its maximum at low frequencies and it depends strongly on the hole diameter. Under constant hole diameter, sound absorption does not depend on the resonator volume, i.e. the distance to the rigid surface. Absorption notably depends on the angle of sound wave incidence. When this angle increases, absorption also increases at resonant frequency, while the frequency itself moves towards higher frequencies. When the sound wave incidence is 90 degrees with respect to resonator, maximum absorption is already observed at high frequencies.Real and imaginary parts of the radiation impedance of cylindric hole and of the impedance of the hole itself, as well as their dependency on frequency are computed. In this case, hole impedance consists of the impedances of the hole and air resiliency. The influence exerted by the real and imaginary parts upon sound absorption has been established. The resonance takes place when the imaginary parts of radiation and hole impedances intersect.
Article in Lithuanian.
Cilindrinės formos vienetinio akustinio rezonatoriaus garso absorbcinės savybės
First Published Online: 26 Jul 201