Numerical and experimental investigation of the behavior of high strength concrete columns in fire

The effect of structural boundary conditions and explosive spalling on performance of concrete elements in fire is still an area of interest within the research community. This paper presents the results of experimental research executed on 30 high strength concrete columns. The parametric study investigated the high strength concrete columns under five loading levels (0.2, 0.3, 0.4, 0.5 and 0.6) subjected to two heating rates, with special attention directed towards explosive spalling. The second part of the paper represents a three-dimensional finite element (FE) model of the reinforced concrete columns, taking into account exposure to high temperatures. The effects of tension softening are included in the model and are based on the Hordjik, Cornelissen and Rienhardt curve. The concrete columns were modelled taking into account the embedded reinforcement and crack formation and propagation using the smeared cracks model, which allowed a nonlinear transient structural analysis to be conducted. The comparison of the results of the FE analysis and the tests performed showed a reasonable agreement and a divergence in some cases due to concrete spalling. An assessment of stresses generated in the high strength concrete columns under fire using the FE model is also presented in the paper. The evaluation shows that mechanical and thermal tensile stresses could reach up to 8.69 MPa, which is high enough to cause concrete spalling.