Research Presentation: Jiaqing Pei, “Burnout Resistance of Concrete Structures under Natural Fires”

April 30, 2021





Master’s Candidate

Jiaqing Pei

Thursday, May 6, 2021

11:30 AM

Contact Elena Shichkova for access to this presentation.

Burnout Resistance of Concrete Structures under Natural Fires

The current fire resistance design method for structures is based on the consideration of a monotonically increasing fire exposure such as ISO 834 or ASTM E119. However, this method fails to address the possibility of structural collapse in the cooling phase of real fires, which can have disastrous consequences for fire fighters and severe socio-economic impacts. To address this shortcoming, the burnout resistance concept was recently proposed to quantify the ability of structural members to survive until full burnout under real fires exposure.

In this research, the relationship between burnout resistance, standard fire resistance and the cooling phase is analyzed for reinforced concrete columns, beams and walls. First, a standardized natural fire model is proposed for systematic quantification of burnout resistance. The fire model is based on the Eurocode parametric model with a linear cooling phase calibrated on observed cooling rates. Then, burnout resistance analyses are performed on several standard fire tests and designs according to ACI. Finite element modeling, including thermal and mechanical modeling, is applied and calibrated to reproduce the standard tests. Using the calibrated FE models, the members are analyzed under the proposed standardized natural fire model. An iterative computational procedure is applied to subject the members to increasing durations of fire exposure until finding the shortest standardized fire that cannot be survived until burnout, from which the burnout resistance metrics is defined. It is found that the cooling phase has a great influence on the burnout resistance. Several fire severity concepts are explored but none of them can fit all the tests well due to the complex behavior of concrete members under natural fire exposure. Finally, simple equations are formulated for evaluating the burnout resistance of concrete columns, beams and walls from their fire resistance and the rate of cooling. Such equations can support design for complete burnout which has benefits for safety of fire brigades, as well as for property protection and resilience of the built environment.

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