Končni elementi za modeliranje lokaliziranih porušitev v armiranem betonu

doktorska disertacija

Miha Jukić (Avtor), Boštjan Brank (Mentor), Dušan Petrovič (Član komisije za zagovor), Igor Planinc (Član komisije za zagovor), Gordan Jelenić (Član komisije za zagovor), Adnan Ibrahimbegović (Komentor)

Povzetek

Ključne besede

Built Environment;civil engineering;doctoral thesis;materials;cement;

Podatki

Jezik:	Angleški jezik
Leto izida:	2013
Izvor:	Ljubljana
Tipologija:	2.08 - Doktorska disertacija
Organizacija:	UL FGG - Fakulteta za gradbeništvo in geodezijo
Založnik:	[M. Jukić]
UDK:	624.012.45:624.042.2:624.042.7(043.3)
COBISS:	6453345
Št. ogledov:	1683
Št. prenosov:	507
Ocena:	0 (0 glasov)
Metapodatki:

Ostali podatki

Sekundarni jezik:	Slovenski jezik
Sekundarni naslov:	Finite elements for modeling of localized failure in reinforced concrete
Sekundarni povzetek:	In this work, several beam finite element formulations are proposed for failure analysis of planar reinforced concrete beams and frames under monotonic static loading. The localized failure of material is modeled by the embedded strong discontinuity concept, which enhances standard interpolation of displacement (or rotation) with a discontinuous function, associated with an additional kinematic parameter representing jump in displacement (or rotation). The new parameters are local and are condensed on the element level. One stress resultant and two multi-layer beam finite elements are derived. The stress resultant Euler-Bernoulli beam element has embedded discontinuity in rotation. Bending response of the bulk of the element is described by elasto-plastic stress resultant material model. The cohesive relation between the moment and the rotational jump at the softening hinge is described by rigid-plastic model. Axial response is elastic. In the multi-layer beam finite elements, each layer is treated as a bar, made of either concrete or steel. Regular axial strain in a layer is computed according to Euler-Bernoulli or Timoshenko beam theory. Additional axial strain is produced by embedded discontinuity in axial displacement, introduced individually in each layer. Behavior of concrete bars is described by elasto-damage model, while elasto-plasticity model is used for steel bars. The cohesive relation between the stress at the discontinuity and the axial displacement jump is described by rigid-damage softening model in concrete bars and by rigid-plastic softening model in steel bars. Shear response in the Timoshenko element is elastic. The multi-layer Timoshenko beam finite element is upgraded by including viscosity in the softening model. Computer code implementation is presented in detail for the derived elements. An operator split computational procedure is presented for each formulation. The expressions, required for the local computation of inelastic internal variables and for the global computation of the degrees of freedom, are provided. Performance of the derived elements is illustrated on a set of numerical examples, which show that the multi-layer Euler-Bernoulli beam finite element is not reliable, while the stress-resultant Euler-Bernoulli beam and the multi-layer Timoshenko beam finite elements deliver satisfying results.
Sekundarne ključne besede:	Grajeno okolje;gradbeništvo;disertacije;materiali;cement;
URN:	URN:NBN:SI
Vrsta datoteke:	application/pdf
Vrsta dela (COBISS):	Doktorsko delo/naloga
Komentar na gradivo:	Univ. v Ljubljani, Fak. za gradbeništvo in geodezijo, Podiplomski študij gradbeništva, Doktorski študij
Strani:	XVIII, 200 str., [22] str. pril.
Vrsta dela (ePrints):	thesis
Naslov (ePrints):	Finite elements for modeling of localized failure in reinforced concrete
Ključne besede (ePrints):	porušna analiza;metoda končnih elementov;armirani beton;lokalizirana porušitev;vgrajena nezveznost;rezultantni model;večslojni model;Euler-Bernoullijev nosilec;Timošenkov nosilec
Ključne besede (ePrints, sekundarni jezik):	failure analysis;finite element method;reinforced concrete;localized failure;embedded discontinuity;stress-resultant;multi-layer;Euler-Bernoulli beam;Timoshenko beam
Povzetek (ePrints):	V disertaciji predlagamo nekaj formulacij končnih elementov za porušno analizo armiranobetonskih nosilcev in okvirjev pod monotono statično obtežbo. Lokalizirano porušitev materiala modeliramo z metodo vgrajene nezveznosti, pri kateri standardno interpolacijo pomikov (ali zasukov) nadgradimo z nezvezno interpolacijsko funkcijo in z dodatnim kinematičnim parametrom, ki predstavlja velikost nezveznosti v pomikih (ali zasukih). Dodatni parametri so lokalnega značaja in jih kondenziramona nivoju elementa. Izpeljemo en rezultantni in dva večslojna končna elementa za nosilec. Rezultantni element za Euler-Bernoullijev nosilec ima vgrajeno nezveznost v zasukih. Njegov upogibni odziv opišemo z elasto-plastičnim rezultantnim materialnim modelom. Kohezivni zakon, ki povezuje moment v plastičnem členku s skokom v zasuku, opišemo s togo-plastičnim modelom mehčanja. Osni odziv je elastičen. V večslojnih končnih elementih vsak sloj obravnavamo kot betonsko ali jekleno palico. Standardno osno deformacijo v palici izračunamo v skladu z Euler-Bernoullijevo ali s Timošenkovo teorijo nosilcev. Vgrajena nezveznost v osnem pomiku povzroči dodatno osno deformacijo v posamezni palici. Obnašanje betonskega sloja opišemo z modelom elasto-poškodovanosti, za sloj armature pa uporabimo elasto-plastični model. Kohezivni zakon, ki povezuje napetost v nezveznosti s skokom v osnem pomiku, opišemo z modelom mehčanja v poškodovanosti za beton in s plastičnim modelom mehčanja za jeklo. Strižni odziv Timošenkovega nosilca je elastičen. Večslojni končni element za Timošenkov nosilec nadgradimo z viskoznim modelom mehčanja. Za vsak končni element predstavimo računski algoritem ter vse potrebne izraze za lokalni izračun neelastičnih notranjih spremenljivk in za globalni izračun prostostnih stopenj. Delovanje končnih elementov preizkusimo na več numeričnih primerih. Ugotovimo, da večslojni končni element za Euler-Bernoullijev nosilec ni zanesljiv, medtem ko rezultantni končni element za Euler-Bernoullijev nosilec in večslojni končni element za Timošenkov nosilec dajeta zadovoljive rezultate.
Povzetek (ePrints, sekundarni jezik):	In this work, several beam finite element formulations are proposed for failure analysis of planar reinforced concrete beams and frames under monotonic static loading. The localized failure of material is modeled by the embedded strong discontinuity concept, which enhances standard interpolation of displacement (or rotation) with a discontinuous function, associated with an additional kinematic parameter representing jump in displacement (or rotation). The new parameters are local and are condensed on the element level. One stress resultant and two multi-layer beam finite elements are derived. The stress resultant Euler-Bernoulli beam element has embedded discontinuity in rotation. Bending response of the bulk of the element is described by elasto-plastic stress resultant material model. The cohesive relation between the moment and the rotational jump at the softening hinge is described by rigid-plastic model. Axial response is elastic. In the multi-layer beam finite elements, each layer is treated as a bar, made of either concrete or steel. Regular axial strain in a layer is computed according to Euler-Bernoulli or Timoshenko beam theory. Additional axial strain is produced by embedded discontinuity in axial displacement, introduced individually in each layer. Behavior of concrete bars is described by elasto-damage model, while elasto-plasticity model is used for steel bars. The cohesive relation between the stress at the discontinuity and the axial displacement jump is described by rigid-damage softening model in concrete bars and by rigid-plastic softening model in steel bars. Shear response in the Timoshenko element is elastic. The multi-layer Timoshenko beam finite element is upgraded by including viscosity in the softening model. Computer code implementation is presented in detail for the derived elements. An operator split computational procedure is presented for each formulation. The expressions, required for the local computation of inelastic internal variables and for the global computation of the degrees of freedom, are provided. Performance of the derived elements is illustrated on a set of numerical examples, which show that the multi-layer Euler-Bernoulli beam finite element is not reliable, while the stress-resultant Euler-Bernoulli beam and the multi-layer Timoshenko beam finite elements deliver satisfying results.
Ključne besede (ePrints, sekundarni jezik):	failure analysis;finite element method;reinforced concrete;localized failure;embedded discontinuity;stress-resultant;multi-layer;Euler-Bernoulli beam;Timoshenko beam
ID:	8313080