Effect of fire on in-plane and out-of-plane behavior of reinforced concrete frames with and without masonry infills

The present study develops a generic three-dimensional (3D) finite element (FE) model to characterize the in-plane and out-of-plane behavior of masonry infill reinforced concrete (RC) frames under fire exposure. The developed FE model accounts for critical factors governing thermo-mechanical behavior of these structural systems such as: temperature-dependent material properties, geometric and material non-linearities, cracking and crushing of concrete and masonry, and shear and tension debonding at interfaces. The developed model is validated using appropriate experimental data from the literature, and the validated FE model is subsequently utilized to investigate post-fire in-plane and out-of-plane behavior of masonry filled RC frames under standard and parametric fire exposures. The results from extensive parametric studies demonstrate that fire has a strong potential for degrading the in-plane stiffness and inducing significant out-of-plane instability in these structural systems, even for a small fire exposure duration of one hour. The results also reveal that the mechanism of degradation in in-plane stiffness of infill-frame is more intricate than that of RC frame, and presence of infill exacerbates the out-of-plane instability of RC frame under fire exposure. The developed model can be further utilized as a tool to develop performance-based design framework for rational fire design approach of these structural systems.