Dinamična analiza prostorskih jeklenih okvirjev v požaru : doktorska disertacija

Ogrin, Anita (author), Saje, Miran (mentor), Hozjan, Tomaž (comentor)

V doktorski disertaciji obravnavamo toplotno in mehansko fazo požarne analize prostorskih jeklenih linijskih konstrukcij. Pri jeklenih prerezih, zaščitenih s protipožarnimi oblogami, vpeljemo iterativni postopek za določitev temperature zraka v zaprtem prostoru med oblogo in tankostenskim jeklenim prerezom, v katerem upoštevamo prenos toplote med oblogo, prerezom in notranjim zrakom tako s konvekcijo kot s sevanjem. Predstavljamo nov matematični model ravninskega prenosa toplote po intumescentnem premazu, ki služi kot požarna zaščita jeklenega prereza. V modelu so upoštevane bistvene značilnosti intumescentnih premazov, kot so postopno ekspandiranje ter temperaturno in časovno odvisne termične lastnosti. Te so določene po pravilu mešanice na osnovi deležev temperaturno odvisnih lastnosti posameznih materialnih faz. Upoštevamo intaktno, ekspandirano in zoglenelo materialno fazo premaza. Deleže posameznih faz izračunamo iz trenutnega stanja kemijske reakcije pirolize. Potek reakcije opišemo z Arrheniusovo enačbo. Za račun mehanskega odziva prostorskih jeklenih okvirjev v požaru uporabimo nedavno izpeljani matematični model za dinamično analizo prostorskih linijskih elementov, ki upošteva Reissnerjevo geometrijsko točno teorijo nosilcev, multiplikativno naravo prostorskih rotacij in za osnovne neznanke sistema vodilnih enačb končnega elementa uporabi krajevne odvode hitrosti in kotnih hitrosti. Ta model razširimo tako, da je omogočeno upoštevanje vpliva temperature. Tako razširjen model lahko upošteva temperaturno odvisne mehanske lastnosti jekla, temperaturne deformacije jekla, Harmathyjev eksplicitni model viskoznega lezenja jekla, plastično utrjevanje materiala in različne nelinearne napetostno-deformacijske materialne zveze. Izpeljane matematične modele za vsako od obeh faz požarne analize preskusimo z numeričnimi primeri in validiramo z eksperimentalnimi in numeričnimi rezultati iz literature. Vpliv nekaterih bistvenih parametrov numeričnih modelov preverimo tudi s konvergenčnimi študijami. Rezultati predstavljenih matematičnih modelov kažejo, da z njimi mehanski odziv prostorskih jeklenih okvirjev v požaru opišemo realistično in natančno.

• Language: Slovenian
• Keywords: grajeno okolje, gradbeništvo, disertacije, prostorski jekleni okvirji, požar, matematični modeli, intumescentni premaz, toplotna analiza, mehanska analiza, materialni modeli, točne kinematične enačbe nosilcev, dinamika
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FGG - Faculty of Civil and Geodetic Engineering
• Publisher: [A. Ogrin]
• Year: 2017
• PID: 20.500.12556/RUL-99215
• UDC: 624.014.2:624.072.33:614.84(043)
• COBISS.SI-ID: 8202849
• Publication date in RUL: 08.01.2018

Licences

• License: CC BY-NC 4.0, Creative Commons Attribution-NonCommercial 4.0 International
• Link: http://creativecommons.org/licenses/by-nc/4.0/
• Description: A creative commons license that bans commercial use, but the users don’t have to license their derivative works on the same terms.
• Licensing start date: 08.01.2018

Secondary language

• Language: English
• Title: Dynamical analysis of three-dimensional steel frames in fire : doctoral dissertation

Abstract

In the present PhD thesis, the thermal and mechanical phases of the fire analysis of spatial steel beamlike structures are addressed. An iterative procedure for the determination of air temperature in the void space between the fire-protective boards and the steel cross-section surfaces is proposed, accounting for the heat transfer with convection and radiation. A novel mathematical model for the planar heat transfer over the steel cross-section, protected with an intumescent coating is also presented. The model considers all main phenomena of intumescent coatings such as a progressive expansion, and time and temperature dependent thermal properties of the coating. These are determined from the rules of mixtures as the ratios of temperature dependent properties of material phases; virgin, intumesced and charred material phases are considered. The ratios of each material phase are based on the current progress of the chemical reaction of pyrolysis. The reaction is modelled by the Arrhenius equation. A fully new mathematical model is also presented for the determination of the mechanical response of spatial steel frames in fire. The recently developed model for the dynamical analysis of spatial beam-like structures is based on Reissner%s geometrically exact beam theory which properly considers multiplicative properties of spatial rotations. The first spatial derivatives of the velocities and the angular velocities are chosen as the basic unknowns of our new numerical model. The model has been expanded to account for temperature dependent mechanical properties of steel, and considers thermal deformations, Harmathy%s model of viscous creep, plastic hardening and softening of material and several non-linear stress-strain relations. The model has been validated against experimental and numerical results from literature. The effects of numerical, mechanical and thermal parameters have been assessed. The results show that the present thermal and mechanical models well enable us to determine the mechanical response of spatial steel frames in fire realistically and accurately.

• Keywords: building environment, civil engineering, thesis, spatial steel frames, fire, mathematical models, intumescent coating, thermal analysis, mechanical analysis, material models, geometrically exact beam theory, dynamics