magistrsko delo
Martin Hostnik (Author), Janko Logar (Mentor), Janko Logar (Thesis defence commission member), Jurij Karlovšek (Thesis defence commission member)

Abstract

geotehniki, predvsem v predorogradnji, je uporaba brizganega betona zelo razširjena. Za razliko od klasičnega litega betona, kjer se pri načrtovanju in gradnji upošteva lastnosti otrdelega betona, je pri uporabi brizganega betona nujno poznavanje mehanskih lastnosti v začetni in zgodnji starosti. Od tega je namreč odvisna varnost med gradnjo in hitrost napredovanja izkopa. Razlog je v tem, da mora brizgan beton že takoj prevzeti obremenitev, ki izhaja iz lastne teže materiala. Z nadaljevanjem izkopa in posledično relaksacijo okoljske hribine mora že v začetni in zgodnji starosti zagotavljati ustrezen podporni tlak. V magistrskem delu je obravnavano numerično modeliranje brizganega betona z uporabo konstitutivnih modelov, ki imajo vgrajeno časovno odvisnost mehanskih lastnosti. Poleg tega nekateri obravnavani modeli opisujejo odziv brizganega betona po preseženi vrhunski natezni oziroma tlačni trdnosti. Cilj naloge je ugotoviti prednosti in slabosti uporabe naprednih modelov v primerjavi z enostavnimi linearno-elastičnimi in elasto-plastičnimi modeli, ki se trenutno večinoma uporabljajo pri načrtovanju podzemnih objektov. V prvem delu so opisani uporabljeni konstitutivni modeli, ki so vključeni v na področju geotehnike in predorogradnje najbolj razširjena numerična programska orodja Abaqus, ZSoil in Plaxis. Največja težava naprednih konstitutivnih modelov je veliko število vhodnih parametrov, med katerimi so nekateri težko določljivi. Posledično se v praksi uporabljajo ocenjene ali na podlagi izkušenj privzete vrednosti ter priporočene vrednosti s strani proizvajalca programske opreme. Najbolj zanesljive parametre pridobimo s povratnimi analizami laboratorijskih ali in-situ preiskav brizganega betona, s katerimi se v fazi priprav na gradnjo potrjuje receptura brizganega betona. Tekom dela so bili pridobljeni rezultati laboratorijskih preiskav enoosne tlačne trdnosti pri različnih starostih in rezultati preizkusa žilavosti materiala. Nato so bile v nadaljevanju narejene povratne analize laboratorijskih testov in s tem določeni oziroma preverjeni splošno uporabljani vhodni parametri za napredne konstitutivne modele. V zadnjem delu je prikazana praktična uporaba konstitutivnih modelov s povratno analizo obstoječega predora Tabor na hitri cesti Razdrto % Nova Gorica. Nato so v zaključku predstavljeni rezultati raziskave ter prednosti in slabosti uporabe nelinearnih konstitutivnih modelov za brizgani beton.

Keywords

gradbeništvo;magistrska dela;brizgani beton;predorogradnja;numerične analize;nelinearnost;elasto-plastičnost;konstitutivni modeli;časovna odvisnost;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FGG - Faculty of Civil and Geodetic Engineering
Publisher: [M. Hostnik]
UDC: 624.19:666.97.033.14(043.3)
COBISS: 8206689 Link will open in a new window
Views: 1286
Downloads: 907
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Other data

Secondary language: English
Secondary title: Numerical modelling of shotcrete using advanced constitutive models
Secondary abstract: structures. The fundamental difference between sprayed and cast concrete is that shotcrete has to support its own weight immediately after being placed even on overhanging surfaces, therefore its initial and early strength development are crucial for the stability of structure as well as the safety of personnel. Sprayed concrete has to provide sufficient support pressure at these early ages to allow fast continuation of works. In structural design on the other hand, properties of hardened concrete i.e. final reached values govern the behaviour of structure. Thesis deals with the advanced constitutive models for sprayed concrete with incorporated time dependence of strength and stiffness parameters. Some of the analysed models account also for the postpeak behaviour in both compression and tension. The main goal of the presented thesis is to explore advantages and disadvantages of the advanced non-linear constitutive models in comparison to the simple linear-elastic and bilinear elasto-plastic models currently used in the industry. Descriptions of constitutive models implemented in the most commonly used commercial software in the industry such as Abaqus, ZSoil and Plaxis are provided in the first part of the thesis. The biggest disadvantage of presented advanced models is the abundance of required input parameters. Some of them cannot be obtained from simple laboratory or in-situ tests. For this reason, experience based or recommended values by the software developer are mainly used. Nevertheless, the most reliable parameters can be only obtained by the back calculation of the pre-construction testing of sprayed concrete samples. To conduct the back calculation analysis, the results of uniaxial compressive strength at different ages and the results of energy absorption tests were obtained from foreign laboratories. Back calculations of these tests were performed to determine or confirm the commonly used input parameters for advanced sprayed concrete models. Further on, the practical implication of advanced constitutive models is presented on a case history from the Tabor tunnel, located at the Razdrto % Nova Gorica motorway in Slovenia. Main findings of the performed research and discussion on the advantages and disadvantages of use of advanced material models for sprayed concrete in the tunnelling industry conclude the presented thesis.
Secondary keywords: civil engineering;master thesis;sprayed concrete;tunnelling;numerical analysis;non-linearity;elastoplasticity;cyclic resistance ratio;constitutive models;time dependent behaviour;
Type (COBISS): Master's thesis/paper
Study programme: 0
Thesis comment: Univ. v Ljubljani, Fak. za gradbeništvo in geodezijo
Pages: X, 62 str., 1 pril.
ID: 10910810