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Temperaturno-vlažnostna analiza masivnega betona z izpeljanim končnim elementom : diplomska naloga
Raspet, Erik (Author), Schnabl, Simon (Mentor) More about this mentor... This link opens in a new window, Kryžanowski, Andrej (Co-mentor), Logar, Janko (Thesis defence commission member), Bosiljkov, Vlatko (Thesis defence commission member)

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Abstract
V diplomski nalogi je predstavljena problematika masivnih betonov, tj. betonov, pri katerih je potrebna kontrola zaradi povišanja temperature v betonskem prerezu, ki je posledica sproščanja hidratacijske toplote ob vezanju cementa, in s tem povezanim nastankom razpok. Opisana je sestava cementa in vpliv sestave cementa na sproščanje hidratacijske toplote. Hidratacija je opisana po fazah, ki si sledijo med vezanjem cementa. Natančneje sta predstavljeni dve vrsti cementa, in sicer CEM I 42,5 R ter CEM III/B 32,5 N SR-LH, ki se med seboj bistveno razlikujeta glede na količino sproščene hidratacijske toplote. Podan je tudi izraz za opisovanje hitrosti sproščanja toplote med procesom hidratacije. V nadaljevanju naloge je prikazana diskretizacija problema in izpeljava enačb končnega elementa za povezan problem temperature in vlage. Izpeljane enačbe so nato uporabljene za sestavo sistema linearnih algebrajskih enačb, s pomočjo katerega izračunamo vrednosti temperature in koncentracije vlage v izbranih točkah. S pomočjo izpeljanih enačb je bil izdelan računalniški program v programskem okolju MATLAB, ki nam v nadaljevanju služi za numerično temperaturno vlažnostno analizo masivnega betona. V zadnjem delu diplomske naloge so predstavljeni rezultati treh analiz. Najprej analiziramo stopnjo povezanosti problema, pri čemer dobimo pri nepovezanem in delno povezanem problemu pričakovane rezultate. Nasprotno so pri povezanem problemu rezultati nezanesljivi, zato v nadaljevanju slednjega ne obravnavamo.. Z drugo analizo pokažemo, da za oceno temperature in koncentracije vlage v betonu upoštevanje delne povezanosti problema med fazo hidratacije ni potrebno, saj je razlika med povezanim in delno povezanim problemom zanemarljiva. S tretjo analizo pa pokažemo nujnost uporabe cementov z nizko stopnjo hidratacijske toplote pri izdelavi masivnih betonov.

Language:Slovenian
Keywords:gradbeništvo, UNI, dipl., temperatura, koncentracija vlage, masivni beton, metoda končnih elementov, diskretizacija, povezan problem, hidratacija cementa, MATLAB, metoda uteženih rezidualov
Work type:Undergraduate thesis (m5)
Tipology:2.11 - Undergraduate Thesis
Organization:FGG - Faculty of Civil and Geodetic Engineering
Year:2015
Publisher:[E. Raspet]
Number of pages:XVI, 77 str.
Place:Ljubljana
COBISS.SI-ID:7152481 Link is opened in a new window
Views:934
Downloads:335
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Secondary language

Language:English
Title:Hygrothermal analysis of mass concrete by derived finite element
Abstract:
The present thesis deals with problems regarding mass concrete, in which the temperature rises due to the heat of cement hydration during the curing phase. A rise of temperature in concrete may result in cracking of young concrete. In the first part of the thesis cement composition and its influence on the released hydration heat is described. The hydration process is explained by its individual phases which occur during hardening of concrete. Two types of cement are presented, the CEM I 42,5 R and CEM III/B 32,5 N SR-LH. The hydration heat released by those two types of cement differs significantly. Also an analytical expression is given for evaluation of heat release of cement. Next, the discretization of the problem and the derivation of the coupled equations is made for a single finite element. The derived equations are used to form a system of linear algebraic equations, which is needed for calculation of the temperature and moisture distribution. Also the derived equations are used to write a computer program in MATLAB environment. The program is used as a tool for numerical hygrothermal analysis of mass concrete. The last part of the thesis presents the results of three different. The purpose of the first analysis is to investigate the influence of the coupling degree between heat and moisture transfer. While the results of non-coupled and semi-coupled models seem reliable, the results of a fully-coupled model are not realistic and therefore are not used in further analyses. The second analysis confirmed there is not much influence of semi-coupling on temperature fields, so the equations can be solved separately and still give useful results. The third analysis shows the necessity of low heat cement use in mass concrete structures.

Keywords:graduation thesis, civil engineering, temperature, moisture, mass concrete, Finite Element Method, discretisation, coupled problem, cement hydration, MATLAB, Weighted Residuals Method

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