Sztywność zginanych elementów żelbetowych poddanych działaniu temperatury pożarowej

Michał Jan Głowacki

Abstract

The aim of the thesis was to investigate possible stiffness changes of bent reinforced concrete elements exposed to load and high temperature simultaneously. The above issue plays a critical role in the advanced analysis of complex concrete structures subjected to fire. In order to examine this issue an experimental study of 24 reinforced concrete beams was performed. All beams were divided into 8 series according to 3 factors: (1) zone of crosssection exposed to high temperature (tension or compression zone), (2) reinforcement ratio – 0.44 or 1.13%, (3) load level in reference to ultimate load capacity in room temperature – 50 or 70%. The pure bending part of the beam was heated. Cross-section stiffness was calculated on the basis of beam deflection. This thesis also presents the review of the test results available in the literature. Based on analysis it has been determined that in beams with heated tension zone a decrease of cross-section stiffness from 60 to 80% in reinforcement temperature in the range of 200¸300°C is observed. When reinforcement temperature is about 500°C, the cross-section stiffness may be only 10¸15% of value in room temperature. It has also been found that the model recommended in Eurocode 2-1-2 characterizing mechanical properties of tensile steel in high temperature may be used for adequate prediction of decrease of cross-section stiffness with heated tension zone. This thesis presents a simple approach to estimate crosssection stiffness with heated reinforcement. The test results show that decrease of crosssection stiffness with heated tension zone, to some extent, depends on load level. It cannot be concluded that stiffness depends on the reinforcement ratio. In elements where the compression zone is exposed to high temperature, an apparent increase of cross-section stiffness at initial heating stage should be expected. The less concrete of compression zone is loaded, the bigger increase of cross-section stiffness. The decrease of cross-section stiffness occurs only at the later heating stage independent of concrete load level. This decrease happens when contraction of compressed concrete caused by reduction of its mechanical properties in high temperature begins to exceed its free thermal elongation. Cross-section ultimate load capacity with heated reinforcement decreases much faster than cross-section ultimate load capacity with heated compression zone.
Diploma typeDoctor of Philosophy
Author Michał Jan Głowacki (FCE / ICE)
Michał Jan Głowacki,,
- The Institute of Civil Engineering
Title in PolishSztywność zginanych elementów żelbetowych poddanych działaniu temperatury pożarowej
Languagepl polski
Certifying UnitFaculty of Civil Engineering (FCE)
Disciplineconstruction / (technology domain) / (technological sciences)
Start date30-09-2016
Defense Date04-07-2017
End date12-07-2017
Supervisor Robert Kowalski (FCE / ICE)
Robert Kowalski,,
- The Institute of Civil Engineering

Pages164 + [ z1 - z3.4]
Keywords in Englishreinforced concrete, high temperature
Abstract in EnglishThe aim of the thesis was to investigate possible stiffness changes of bent reinforced concrete elements exposed to load and high temperature simultaneously. The above issue plays a critical role in the advanced analysis of complex concrete structures subjected to fire. In order to examine this issue an experimental study of 24 reinforced concrete beams was performed. All beams were divided into 8 series according to 3 factors: (1) zone of crosssection exposed to high temperature (tension or compression zone), (2) reinforcement ratio – 0.44 or 1.13%, (3) load level in reference to ultimate load capacity in room temperature – 50 or 70%. The pure bending part of the beam was heated. Cross-section stiffness was calculated on the basis of beam deflection. This thesis also presents the review of the test results available in the literature. Based on analysis it has been determined that in beams with heated tension zone a decrease of cross-section stiffness from 60 to 80% in reinforcement temperature in the range of 200¸300°C is observed. When reinforcement temperature is about 500°C, the cross-section stiffness may be only 10¸15% of value in room temperature. It has also been found that the model recommended in Eurocode 2-1-2 characterizing mechanical properties of tensile steel in high temperature may be used for adequate prediction of decrease of cross-section stiffness with heated tension zone. This thesis presents a simple approach to estimate crosssection stiffness with heated reinforcement. The test results show that decrease of crosssection stiffness with heated tension zone, to some extent, depends on load level. It cannot be concluded that stiffness depends on the reinforcement ratio. In elements where the compression zone is exposed to high temperature, an apparent increase of cross-section stiffness at initial heating stage should be expected. The less concrete of compression zone is loaded, the bigger increase of cross-section stiffness. The decrease of cross-section stiffness occurs only at the later heating stage independent of concrete load level. This decrease happens when contraction of compressed concrete caused by reduction of its mechanical properties in high temperature begins to exceed its free thermal elongation. Cross-section ultimate load capacity with heated reinforcement decreases much faster than cross-section ultimate load capacity with heated compression zone.
Thesis file
rozprawa doktorska_mgr inż. Michał Głowacki.pdf 5.59 MB

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