Papers by Lyubomir Zdravkov
Using GNIA or GMNIA in new, still unmade shells is related with a large scope, heavy and continuo... more Using GNIA or GMNIA in new, still unmade shells is related with a large scope, heavy and continuous calculations. Main difficulty is modeling of imperfections with correct values. Ordinary designers who are usually hard pressed by time and are not familiar with computing software, enabling full GNIA or GMNIA analysis of shells, require simplified procedures in which imperfections are not included. Such a procedure, called LBA-MNA, is presented here. It allows analysis of real shells, modelled as perfect structures.
Bookmarks Related papers MentionsView impact
The concerned spatial dome with radial girders and circular elements is roof on tank T016 in La R... more The concerned spatial dome with radial girders and circular elements is roof on tank T016 in La Reunion, France. The roof is self-supporting, supported only on the shell of the tank .Sections of dome roof are designed on two independent ways-manual and FEA analysis are performed. Controlling company, "Bureau Veritas", did not approve our design methods and it was necessary to make additional, nontraditional analysis of roof structure. За La Reunion и Martinique, Франция, са проектирани група вертикални стоманени цилиндрични резервоари, в които ще се съхраняват нефтопродукти. Всички конструктивни изчисления по резервоарите са предавани за проверка и одобрение първоначално на възложителя, а след това-на контролната фирма "Bureau Veritas". Една от отправените към нас забележките е, че приетите от нас изкълчвателни дължини на радиалните ребра не са верни. Препоръчано ни беше да приемем изчислителни дължини, равни на половината диаметър на резервоара, както е посочено...
Bookmarks Related papers MentionsView impact
Open road structure of steel railway bridges is constructed of longitudinal (LB) and transverse (... more Open road structure of steel railway bridges is constructed of longitudinal (LB) and transverse (TB) beams. The longitudinal beams pass over or through the transverse beams and transmit their vertical loads through common joints. Since nodes are rigid, i.e. they provide mutual rotation of items, LB and TB form plain rigid structure that is statically indeterminate system. Internal forces in elements of plain rigid structure caused by vertical moving loads depends on the location of loads on LB, and the ratio of the bending stiffness of LB and TB. Forces in steel members of plain structure could be determined analytically, using simplified methods, or precisely, using FEA. Main question is how much is difference between two methods? Key words: railroad bridge, opened road structure, forces, FEA Open type road structure of steel railroad bridges is built by longitudinal (LB) and transverse (TB) beams. When bridge has only one railway track, longitudinal beams are two and the distance ...
Bookmarks Related papers MentionsView impact
Beams are structural elements subjected to bending loads transverse to their longitudinal axis. F... more Beams are structural elements subjected to bending loads transverse to their longitudinal axis. For steel beams, which compressed flange is not laterally restrained, checking loss of overall stability is often authoritative in determining their section. In engineering practice are known various approaches to verify the assurance of the steel beam against lateral-torsional buckling. In this article the attention is focused to the methods and their characteristics, described in actual version of the European standard EN1993-1-1.
Bookmarks Related papers MentionsView impact
In 2011 has finished design of 16 aboveground steel tanks for Oiltanking Terneuzen B.V, the Nethe... more In 2011 has finished design of 16 aboveground steel tanks for Oiltanking Terneuzen B.V, the Netherlands. These tanks are with double shells, single bottom and dome roofs. On level of top angles of the tanks, between tanks are mounted pedestrian steel bridges for inspection and maintenance. They have various spans, as follow: L = 18 750 mm, L = 18 450 mm, L = 18 000 mm, L = 16 688 mm, L = 11 550 mm и L = 9 450 mm. As a result of weak soils under the tanks and lack of reinforced concrete foundations it is expected extremely high levels of settlements-500 mm in vertical direction and ±200 mm-in horizontal. These significant settlements lead to specific decisions such:-use of moving bearings with large scope of horizontal deflection;-stationary bearings should have large capacity of rotation;-steel bridges should have as many degrees of freedom;-to ensure a walkway without gaps in case of horizontal deflection of supports in opposite directions. 1. Introduction The design of 16 abovegro...
Bookmarks Related papers MentionsView impact
Modern programs for analysis and design of building structures often have modules which can help ... more Modern programs for analysis and design of building structures often have modules which can help us to determine critical values of loads in which elements will lose overall stability. These modules are especially useful for complex spatial structures where the boundary conditions are not quite clear and it is difficult to determine who is who supports (bear). For accurately determining the critical values of loads is very important used programs to have a correct mathematical algorithms. Unfortunately, these algorithms are not visible to us, their users. However, not everything is in foreign hands. With some simple tests we could to gain approximate idea of the reliability of the results we get. The materials used in the construction works increase their strengths. As a result, sections of girders and columns became smaller and smaller, and elements-thinner. As a consequence of it, the elements can easily lose their local or general stability. This problem is especially relevant in...
Bookmarks Related papers MentionsView impact
Domes on circular base are widespread-silos, tanks, bulk storage, sport facilities, exhibition ha... more Domes on circular base are widespread-silos, tanks, bulk storage, sport facilities, exhibition halls. They are light, nice and could cover big spans without internal columns. Steel domes successfully cover spans with diameter D ≤ 40,0 m, but aluminium domes could cover spans with diameter D ≤ 120,0 m Bigger part of domes on circular base has radial girders, circular elements-rings and cover plates. Usually they are steel made. The domes are spatial statically undetermined systems, so it is difficult to obtain the design stresses and forces without finite element analysis (FEA) model. Accurate design of the elements of the roof structure can be achieved only by using adequate program product and taking into account the rigidity of the elements and flexibility of the joints.
Bookmarks Related papers MentionsView impact
Gasholders are well known structures and used in industry for a long time ago. Their purpose, as ... more Gasholders are well known structures and used in industry for a long time ago. Their purpose, as prompt their name, is to keep and storage gas. Often the gas is waste of another production. Using gasholders that gas could be captured, storage and after that-utilized. Classical structure of gasholders is two steel vessels, which could move between them. On this way they change their volume at constant pressure. With a development of new technologies new structural decisions for gasholders are used. In some gasholders the second vessel is replaced with a moving cellar, in others-with a flexible membrane. Газхолдерите са строителни съоръжения, отдавна известни и ползвани в практиката. Тяхното предназначение, както подсказва името им, е да задържат и съхраняват газ. Често този газ е отпадъчен продукт от друга дейност и чрез газхолдерите той може да бъде съхранен и впоследствие-оползотворен. Класическата конструктивна схеми при газхолдерите представлява 2-а стоманени съда, които могат да...
Bookmarks Related papers MentionsView impact
The concerned spatial dome with radial girders and circular elements is roof on tank T016 in La R... more The concerned spatial dome with radial girders and circular elements is roof on tank T016 in La Reunion, France. The roof is self-supporting, supported only on the shell of the tank .Sections of dome roof are designed on two independent ways – manual and FEA analysis are performed. Controlling company, „Bureau Veritas”, did not approve our design methods and it was necessary to make additional, nontraditional analysis of roof structure.
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
When a building structure is spatial (3D), all elements work together. They influence and support... more When a building structure is spatial (3D), all elements work together. They influence and support each other. On that situation is very difficult to determine who is supporting and who is supported member. It is impossible to calculate directly their effective lengths. These lengths are used in classic equations of standards to check elements for loss of stability. On that reason is reasonably to use General method, described in European standard EN 1993-1-1. This method is convenient to use, but unfortunately it could not be used without good computer skills and specialised structural software possessing Buckling Analysis module. Когато строителната конструкция е пространствена, всички елементи в нея са натоварени заедно и едновременно. Те взаимно си влияят и се подпират един друг. В този случай е много трудно да бъде определено кой елемент е подпрян и кой е подпиращ. Невъзможно е да бъде определено в явен вид тяхната ефективна изкълчвателна дължина, а тя се използва в класическите...
Bookmarks Related papers MentionsView impact
The roofs of steel tanks can be classified in groups as follow: а) according to the shape of the ... more The roofs of steel tanks can be classified in groups as follow: а) according to the shape of the roof :-cone roof ;-dome roof;-hanging roof;-floating roof. b) according to static scheme:-self supporting-cone and dome ;-supported roofs-cone and hanging roofs. c) according to the position of the roof stricture:-situated under the roof cover plates;-situated above the roof cover plates. The most expedient shape of roofs, from the technical end economical point of view, must be determined depending on the geometrical dimensions of AST, the stored product inside, the conditions during the exploitation. Important is the tradition of design and erection of steel tanks:-in Europe and in particular in Bulgaria most popular are self supporting roofs when the tanks have small diameter and the stored product has slight evaporation;-in the USA and in the Near East the most used fixed roofs are supported cone roofs. 1. Purpose of the research It is possible to use different types of roofs-dome, c...
Bookmarks Related papers MentionsView impact
Cylindrical steel tanks with double shell become to be popular in Bulgaria. They have common stee... more Cylindrical steel tanks with double shell become to be popular in Bulgaria. They have common steel bottom for shell and catching basin. Projection of bottom outside of main reservoir is a much more than 0,05 m, as is in traditional tanks. In this case will be mistake to use methodology in standards. Results will be wrong. It is necessary to use new methods for assessment of stress in annular bottom plates. 1. Въведение Напреженията в долния опорен възел на стоманените резервоари, където се снаждат корпусът и дъното, зависят от множество фактори, един от които е "излизането" С на дъното извън корпуса. При традиционните стоманени цилиндрични резервоари, диаметърът на дъното е по-голям от вътрешния диаметър на корпуса с 100 ÷ 150 mm. При резервоарите с двоен корпус, които масово се строят в Германия, Чехия, Унгария, Полша, а вече навлизат и в България, диаметърът на дъното значително надвишава диаметърът на вътрешния корпус (фиг.1). Приемането на "излизането" С = 0,...
Bookmarks Related papers MentionsView impact
Aboveground steel tanks are spatial thin shell structures. Their main parts are bottom, shell and... more Aboveground steel tanks are spatial thin shell structures. Their main parts are bottom, shell and roof. The most responsible, the most long and heavy loaded structural element is the shell. It has to be ensured against:-tearing from loads of stored liquid and internal pressure-lose of stability in radial and longitudinal direction World known standards [2], [3], [4], [5] have differences in methodology about ensure the shell against lose of stability. In result we have divergences in necessary thickness of courses and / or necessity of intermediate wind girders on the shell. Стоманените вертикални цилиндрични резервоари са тънкостенни пространствени строителни съоръжения. Техните основни конструктивни елементи са дъно, корпус и покрив. Най-отговорният, най-продължително и най-тежко натоварен елемент е корпусът, който трябва да бъде осигурен срещу:-разкъсване от хидростатичния товар от съхранявания продукт и свръхналягане. При тази проверка якостта на стоманата е от съществено значен...
Bookmarks Related papers MentionsView impact
The vertical cylindrical steel tanks are not eternal facilities. They bear the unfavorable impact... more The vertical cylindrical steel tanks are not eternal facilities. They bear the unfavorable impacts of the environments and of the products stored in them. In order to increase the safety of their exploitation they shall be inspected at a determinate period of time and the obtained results shall be used for calculations for bearing capacity of their elements. In Bulgaria the analysis of their behavior during the seismic influence is an integral part of this type of calculation.
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Dome roofs are most light structure to cover cylindrical tanks. When they are steel made they cou... more Dome roofs are most light structure to cover cylindrical tanks. When they are steel made they could not be used to cover serious spans, respectively big tanks. Author has checked the possibilities to use steel dome roof as cover of aboveground cylindrical tank with V=70000 m 3 capacity and diameter D=64 m. The investigation was made with appropriate 3D software. It is used nonlinear solution, accounting large displacements of steel structure for more accuracy. Most serious problem is vagueness of snow distribution and combination of wind and snow loads. При едни и същи условия на експлоатация е възможно проектирането и използването на различни видове постоянни покриви-сферични, конични самоносещи или подпряни. При всяко от конструктивните решения количеството вложен метал и цената на съоръжението са различни. Сферичните куполи са най-леките стоманени постоянни покриви с пълностенна конструкция. Те могат да работят при повишено вътрешно налягане, нямат конфликт с вътрешния плаващ пок...
Bookmarks Related papers MentionsView impact
Challenge Journal of Structural Mechanics, 2022
Bridges are facilities that are in exploitation outdoor. Often the wind is the leading horizontal... more Bridges are facilities that are in exploitation outdoor. Often the wind is the leading horizontal force in the transverse direction. Therefore the bridges have received the due attention in the standards for wind loading. Unfortunately, in all available standards for wind load on the bridges, one, summarized value of the aerodynamic coefficient is indicated. It is related to the entire cross-section of the facility. There is no differentiation for the individual longitudinal girders and/or roadway. Information about the specific wind pressure on each of the bridge’s element is required for the correct design of their supporting systems, whether they are framed or braced type. To fill this gap, the author has built several models of bridges with longitudinal girders, using a Computational Fluid Dynamics (CFD) analysis. Through them he determined the values of the aerodynamic coefficients for each of the bridge girders under the roadway and the cross-section of the bridge as a whole. ...
Bookmarks Related papers MentionsView impact
New tendency of design of steel roofs of cylindrical tanks is to put cover plates under steel str... more New tendency of design of steel roofs of cylindrical tanks is to put cover plates under steel structure. This type of roof has only radial girders. Joints between cover plates are made with overlapping and filled welds. Usually these joints are single-welded. The author made research about real work of the thin roof cover plates and filled welds. Comparison between traditional methods of design and nonlinear solution with ANSYS is made.
Bookmarks Related papers MentionsView impact
Cylindrical steel tanks for oil and oil products storage have a limited time for exploitation. Un... more Cylindrical steel tanks for oil and oil products storage have a limited time for exploitation. Under the influence of the storage product, external environment, settlement of foundation, their working condition continuously goes to be worse. In this case the tanks should be periodically inspected, analyzed and if it is necessary-to be repaired or to be out of service. When the steel tanks are inspected and analyzed correctly and on time, damaged elements could be repaired or replaced. The time for exploitation could be elongated and could be several times bigger than design period of exploitation.
Bookmarks Related papers MentionsView impact
Uploads
Papers by Lyubomir Zdravkov