Vpliv viskoznega lezenja na mehansko obnašanje jeklenih konstrukcij v primeru požara : magistrsko delo

Blumauer, Urška (author), Hozjan, Tomaž (mentor), Planinc, Igor (comentor)

Magistrsko delo obravnava vpliv viskoznega lezenja jekla pri povišanih temperaturah na obnašanje jeklenih konstrukcij med požarom. Obširneje so v delu predstavljeni modeli viskoznega lezenja jekla pri povišanih temperaturah, ki jih zasledimo v strokovni literaturi. Tako so v magistrskem delu za Harmathy-jev model viskoznega lezenja jekla in bilinearni materialni model jekla, na osnovi eksperimentalnih rezultatov natezne palice določene vrednosti materialnih parametrov za konstrukcijsko jeklo kvalitete S355. Podobno so določene tudi vrednosti materialnih parametrov Harmathy-jevega viskoznega modela lezenja jekla v kombinaciji z modificiranim Poh-ovim materialnim modelom, ki je bil vgrajen v program POZAR. Program je dopolnjen tudi z modificiranim inkrementno–iteracijskim postopkom, ki bistveno poveča hitrost računske analize. V primeru požarne analize upogibnega nosilca pri 50% mejni obtežbi je računska analiza z modificiranim algoritmom vsaj 57x hitrejša. V nadaljevanju magistrskega dela smo validirali predhodno določene vrednosti materialnih parametrov Harmathy-jevega modela viskoznega lezenja jekla pri povišanih temperaturah. Primerjava med eksperimentalnimi in numeričnimi rezultati, ki so izračunani z Harmathy-jevim modelom viskoznega lezenja, je pokazala dobro ujemanje rezultatov le pri nizkih nivojih napetosti. Natančna parametrična analiza pa je pokazala, da so kritični časi značilnega jeklenega okvirja za predhodno določene vrednosti Harmathy-jevega modela viskoznega lezenja jekla pri visokih temperaturah primerljivi. To velja tako za standardno požarno krivuljo, kot tudi za naravna požara s hitrim in počasnim naraščanjem temperatur v požarnem prostoru. Razlikujejo se le deformabilnosti okvirjev, saj je model skladno s SIST EN 1993-1-2 bistveno bolj tog.

• Language: Slovenian
• Keywords: gradbeništvo, magistrska dela, viskozno lezenje jekla, jeklena okvirna konstrukcija, modificirana Pohova napetostno deformacijska zveza jekla, nazivna požarna krivulja, požarni scenarij
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FGG - Faculty of Civil and Geodetic Engineering
• Place of publishing: Ljubljana
• Publisher: [U. Dolinar]
• Year: 2016
• Number of pages: XVI, 64 str.
• PID: 20.500.12556/RUL-84996
• UDC: 614.84:624.01(043.3)
• COBISS.SI-ID: 7588705
• Publication date in RUL: 19.09.2016

Secondary language

• Language: English
• Title: Influence of viscous creep on mechanical behavior of steel structures in fire

Abstract

This thesis deals with the influence of viscous creep of steel at elevated temperatures on the behavior of steel structure during fire. Models of viscous creep of steel at elevated temperatures are being extensively presented. For Harmathy's model of viscous creep of steel and bilinear material model of steel, new values of material parameters for Harmathy model were proposed for structural steel grade S355, based on experimental results of tensile bar. Similarly, for Harmathy's model of viscous creep of steel and modified Poh material model of steel, new values of material parameters were proposed for structural steel grade S355. Modified Poh material model was additionaly built into the program POZAR. The program is also complemented by a modified incremental–iterational process, which significantly increases the speed of computational analysis. In case of fire analysis of simply supported beam at 50 % of critical load, the computational analysis, with usage of modified algorithm, ends at least 57 times faster. The proposed values of material parameters for Harmathy viscous creep model at elevated temperatures were validated. Comparison between experimental and numerical results which were determined with proposed material parameters for Harmathy viscous creep model shows good agreement between the results only at low stress values. Accurate parametric analysis shows that the critical times of the typical steel frame for proposed values of material parameters for Harmathy viscous creep model are comparable. This applies to both the standard fire curve, as well as natural fire with fast and slow temperature increase in the fire area. The only difference is the deformability of frames, due to the model proposed by standard SIST EN 1993-1-2 being significantly stiffer.

• Keywords: viscous creep of steel, steel frame structure, Poh modified material model, nominal fire curve, fire scenario