Keywords: fire resistance, concrete filled tubular, nonlinear finite element analysis, high strength concrete.

An advanced numerical model for predicting the fire response of axially loaded concrete filled tubular columns is presented in this paper. This model includes a wide range of realistic and innovative considerations that have not been previously taken into account by other researchers (e.g. the real gap conductance evolution with temperature at the steel-concrete interface). A sequentially coupled thermal-stress analysis was designed for this research. The analysis was performed by first conducting a pure heat transfer analysis for computing the temperature field and afterwards a stress/deformation analysis for calculating the structural response. Nodal temperatures were stored as a function of time in the heat transfer analysis results and then read into the stress analysis as a predefined field.

By means of this model, the fire behaviour of normal and high strength concrete filled columns was investigated. The values adopted for the main variables of the problem were a result of an extensive sensitivity analysis conducted in this research.

The numerical model was validated by comparing the simulation results with fire tests available in the literature. The model showed good agreement with the tests for the normal strength concrete (NSC) filled specimens both quantitative, producing acceptable results in the fire resistance rating, and qualitative, capturing the overall axial displacement response with respect to time.

Despite the real fire behaviour of those columns filled with NSC was accurately represented by means of this model, when the range of the "medium" strengths (i.e. concrete strengths between 40 and 60 MPa) was explored, the numerical response started to deviate from the tests. This fact was magnified when studying specimens filled with high strength concrete (HSC), over 60 MPa. This deviation from the tests was due to the complexity of spalling taking place in the HSC when subjected to elevated temperatures, phenomenon which the numerical model was not able to predict at this level of development.

It becomes clear from the findings of this investigation that without accounting for the moisture movement and development of pore pressures within the concrete core, a conventional numerical model will not be able to capture the real fire behaviour of the HSC filled specimens. Thus, a more advanced thermo-hydro-mechanical model capable of capturing the occurrence of spalling will be needed in order to accurately predict the fire response of the HSC filled hollow section columns. It will be the aim of the authors to model these parameters for capturing the occurrence of spalling and thus make the model valid for a wider range of concrete strengths.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £145 +P&P)