Higher School of Civil Engineering

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Aleksandrov Y.,Higher School of Civil Engineering
Bulgarian Journal of Agricultural Science | Year: 2017

In this paper are reviewed several solutions for panel walls and panel connections, representing a part of the enclosing structure of the chambers of fruit storehouses, which are often subject to hits coming from various sources, including during extreme situations. The solutions represent patented inventions, representing an integral part of the dissertation of the author [1]. BG 401 (Y1)-"Connection between panels"; This solution integrates an elastic protective screen, which can be dismounted in case of premature runout; the hits produced by root fruits and vegetables, stored in bulk are absorbed by the screen, which is suspended over pins, which transfer the energy of the hits to the bearing construction of the wall panels. BG 62742 (B1)-“Wall panel”; the hit absorption is ensured with the help of elastic screens and coverings, suspended and connected to the sides of the panel. BG 63218 (B1)-“Multilayer panel with impact-protection and connection between panels.”{ The covering of the panels is made of elastic materials and it integrates star-shaped elements, which are inserted into the surface layers of the panel. Membranes, stretched over tensegrity-structures are able to offer protection against harmful impact, e.g. acid rain, volcanic ash, overheating, etc., whereas the refrigerators for fruits and vegetables are situated under these membranes. The membranes are made of transparent materials, e.g. polyketone, reinforced by carbon fiber, whereas the hothouse effect occurring beneath them can be used to maintain positive temperatures inside the chambers of the refrigerators for fruits and vegetables. Additional protection against premature runout of the external covering of the enclosing structure is ensured by transparent protective membranes. Positive temperature inside of the chambers of the refrigerators is a result of the use of solar energy. The protection of the refrigerators for fruits and vegetables with transparent membranes is especially important in case of extreme situations of various origin. © 2017, National Centre for Agrarian Sciences. All rights reserved.


Partov D.,Higher School of Civil Engineering | Kantchev V.,HSCE L.Karavelov
Central European Journal of Engineering | Year: 2011

The paper presents analysis of the stress and deflections changes due to creep in statically determinate composite steel-concrete beam. The mathematical model involves the equation of equilibrium, compatibility and constitutive relationship, i.e. an elastic law for the steel part and an integral-type creep law of Boltzmann - Volterra for the concrete part. On the basis of the theory of the viscoelastic body of Arutyunian-Trost-Bažant for determining the redistribution of stresses in beam section between concrete plate and steel beam with respect to time "t", two independent Volterra integral equations of the second kind have been derived. Numerical method based on linear approximation of the singular kernal function in the integral equation is presented. Example with the model proposed is investigated. The creep functions is suggested by the model CEB MC90-99 and the "ACI 209R-92 model. The elastic modulus of concrete Ec(t) is assumed to be constant in time 't'. The obtained results from the both models are compared. © Versita sp. z o.o.


Aleksandrov Y.,Higher School of Civil Engineering
Bulgarian Journal of Agricultural Science | Year: 2017

Here are reviewed new solutions for fruits and vegetables that use solar energy in order to achieve positive temperatures. Furthermore, the main aspects of the basic requirements for their implementation are taken into consideration. Three typical solutions with inventive step of the author are reviewed. These are: BG63644 (B1). Built-up refrigeration chamber (Aleksandrov, 2002). The triangular panels 5, situated on the walls and the roof of the refrigerator chamber can be also made of transparent structures, whereas the chamber is directly situated on the respective terrain over a ribbed plate; the ribs form ventilation channels. BG № 111651/09.12.2013 г. Moveable cold storage chamber for positive temperature. BG111651 (A) (Aleksandrov, 2013a.) Transparent angular two-plane elements are used for the direct lighting of the floor and the ceiling of the refrigeration chamber, the penetration of solar beams is directed by sunblinds, which are controlled by sensors. BG № 111658/17.12.2013. System for solar heating of cooling chamber with positive temperatures. BG111658 (A). (Aleksandrov, 2013b) Solar water collectors are used for heating and hot water supply to meet various demands, e.g. to cover the technical needs (e.g. washing of root fruit and vegetables, etc.) In extreme situations, the refrigerators for fruits and vegetables which operated under positive temperatures can be used for various other purposes, e.g. medical purposes - as premises for the situation of operating rooms. The transparent elements will allow the penetration of natural light, whereas water collectors will provide hot water for medical purposes. The application of tension membranes and tensegrity structures as a way of executing protective screens on refrigerators for fruits and vegetables under other harmful external conditions - acid rain, falling volcanic ash, formations of smog and others is also described. © 2017, National Centre for Agrarian Sciences. All rights reserved.


Kazakov K.,Higher School of Civil Engineering | Yanakieva A.,Bulgarian Academy of Science
Comptes Rendus de L'Academie Bulgare des Sciences | Year: 2012

This research is devoted to an investigation of the computational effective- ness of the Augmented Lagrange method versus Penalty method and Lagrange multiplier method in the FEM numerical models of bond-slip between plain steel bars and concrete. Such a mechanical process of extraction can be simulated by 3D finite elements in order to discretize both steel bar and concrete and reproduce contact between bodies through contact elements. The contact equilibrium equations are part of the FEM global system of equations, concerning the entire computational model. In principle, the contact elements are non-linear finite elements and this objective yields non-linearity of the global system of equations. The contact stiffness coefficients are function of the displacements, and the method of generation and solution of the equations is important for the effectiveness and adequacy of the computational results.


Bozic B.,University of Belgrade | Fan H.,KTH Royal Institute of Technology | Milosavljevic Z.,Higher School of Civil Engineering
Survey Review | Year: 2013

This paper deals with the estimation of the quality of the baseline for the calibration of distance measurement devices which was established by Serbian Military Geographic Institute for military use. The basic characteristics of the baseline are explained, and a plan for the checking of the baseline quality is proposed. The measurements realised so far can be grouped into two phases. The measurements have been processed, and the estimates of the distances of this length standard have been obtained. The standard deviations of the least squares estimates of the lengths were better than 0?3 mm in each epoch. This precision offers the possibility to check all measurement devices with a minimum uncertainty of the calibrations, of ¡(1 mmz1 ppm). The stability of the pillars is also analysed. The conventional deformation analysis method was applied to three datasets and the results obtained by evaluating them are shown. © 2013 Survey Review Ltd.


Partov D.,Higher School of Civil Engineering | Partov D.,Brno University of Technology | Kantchev V.,Higher School of Civil Engineering | Kantchev V.,Sofia University
ACI Structural Journal | Year: 2014

The paper presents an analysis of the stress and deflections changes due to creep in statically determinate composite steelconcrete beams. The mathematical model involves the equation of equilibrium, compatibility, and constitutive relationship, that is, an elastic law for the steel part and an integral-type creep law of Boltzmann-Volterra for the concrete part. Based on the theory of the viscoelastic body of Arutyunian-Trost-Ba'ant for determining the redistribution of stresses in beam sections between a concrete plate and steel beam with respect to time t, two independent Volterra integral equations of the second kind have been derived. A numerical method based on linear approximation of the singular kernal function in the integral equation is presented. An example with the proposed model is investigated. The creep functions are suggested by the Gardner and Lockman model. The elastic modulus of concrete Ec(t) is assumed to be constant in time t. Copyright © 2014, American Concrete Institute.


Davidov J.,Bulgarian Academy of Science | Davidov J.,Higher School of Civil Engineering | Grantcharov G.,Florida International University | Mushkarov O.,Bulgarian Academy of Science | Yotov M.,Florida International University
Communications in Mathematical Physics | Year: 2011

In this paper we consider pseudo-bihermitian structures - pairs of complex structures compatible with a pseudo-Riemannian metric. We establish relations of these structures with generalized (pseudo-) Kähler geometry and holomorphic Poisson structures similar to that in the positive definite case. We provide a list of compact complex surfaces which could admit pseudo-bihermitian structures and give examples of such structures on some of them. We also consider a naturally defined null plane distribution on a generalized pseudo-Kähler 4-manifold and show that under a mild restriction it determines an Engel structure. © 2011 Springer-Verlag.


Ganchev G.,Bulgarian Academy of Science | Milousheva V.,Bulgarian Academy of Science | Milousheva V.,Higher School of Civil Engineering
Journal of Mathematical Physics | Year: 2012

A marginally trapped surface in the four-dimensional Minkowski space is a spacelike surface whose mean curvature vector is lightlike at each point. We associate a geometrically determined moving frame field to such a surface and using the derivative formulas for this frame field we obtain seven invariant functions. Our main theorem states that these seven invariants determine the surface up to a motion in Minkowski space. We introduce meridian surfaces as one-parameter systems of meridians of a rotational hypersurface in the four-dimensional Minkowski space. We find all marginally trapped meridian surfaces. © 2012 American Institute of Physics.


Ganchev G.,Bulgarian Academy of Science | Milousheva V.,Bulgarian Academy of Science | Milousheva V.,Higher School of Civil Engineering
International Journal of Geometric Methods in Modern Physics | Year: 2013

A marginally trapped surface in the four-dimensional Minkowski space is a spacelike surface whose mean curvature vector is lightlike at each point. We introduce meridian surfaces of parabolic type as one-parameter systems of meridians of a rotational hypersurface with lightlike axis in Minkowski 4-space and find their basic invariants. We find all marginally trapped meridian surfaces of parabolic type and give a geometric construction of these surfaces. © World Scientific Publishing Company.


Partov D.,Higher School of Civil Engineering | Kantchev V.,Higher School of Civil Engineering
ACI Structural Journal | Year: 2014

The paper presents an analysis of the stress and deflections changes due to creep in statically determinate composite steel-concrete beams. The mathematical model involves the equation of equilibrium, compatibility, and constitutive relationship, that is, an elastic law for the steel part and an integral-type creep law of Boltzmann-Volterra for the concrete part. Based on the theory of the viscoelastic body of Arutyunian-Trost-Bažant for determining the redistribution of stresses in beam sections between a concrete plate and steel beam with respect to time t, two independent Volterra integral equations of the second kind have been derived. A numerical method based on linear approximation of the singular kernal function in the integral equation is presented. An example with the proposed model is investigated. The creep functions are suggested by the Gardner and Lockman model. The elastic modulus of concrete Ec(t) is assumed to be constant in time t.

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