Model fire test and similarity relationship development of RC columns subjected to uneven fire exposure

Abstract

The model fire test of reinforced concrete components typically requires a furnace temperature-rising curve that is significantly higher than that of the prototype, according to traditional similarity theory. However, this requirement can sometimes render the model fire test infeasible due to surpassing the heating capacity of the furnace. To address this challenge, the present study conducts experiments and finite element analysis (FEA) on geometrically similar, reinforced, square concrete columns of various sizes exposed to fire from two or three sides, using the ISO 834 standard fire curve for all columns. The fire resistance results from experiments and FEA are utilized to derive similarity relationships for the time scale of the model to prototype columns. The similarity in the thermal–mechanical response of the model and prototype columns under the proposed time scale is evaluated and validated using experimental data from this study and previous research. The findings indicate that good similarity between the mechanical response and fire resistance of the model and prototype columns can be attained as long as the model and prototype columns exhibit similar average sectional temperatures and similar temperatures near the rebar. By normalizing the time scale using s1.19 for 2-sided heating and s1.29 for 3-sided heating, where s represents the geometric scale factor of model to prototype, the data from the model column under standard fire effectively predicts the axial deformation development and fire resistance of the prototype column. Although there is a certain deviation in the temperature near the fire exposure surface and concrete center of the model and prototype columns under the proposed time scale factor, this discrepancy does not significantly affect the similarity of their mechanical response.