Modelling and analysis of the bottom frames of multi-story masonry buildings exposed to fire

The multi-story masonry buildings with reinforced concrete frames on ground floors collapse more easily than pure frames when bottom frames exposed to fire, for reasons that fire load of its ground floors is relatively large, and the ratio of dead load to the total loads is also large, deformations of joists caused by fire produce adverse effect on arch mechanism of masonry. For the purpose of loading temperature on steel bars and concrete for fire resistance analysis of reinforced concrete structures in ABAQUS, separated loading method is proposed firstly in this article. The Hill yield criterion for compression and the Rankine yield criterion for tension are adopted to establish anisotropic elasto-plastic material model for masonry. The process simulation from temperature rises to buildings collapse is realized. A parametric study is conducted to investigate the effects on fire resistance of the bottom frames when the bottom floors exposed to fire due to the change in effective load ratio, section size and reinforcement ratio. The study shows that the failure mode of the bottom frames exposed to fire is mainly due to columns collapse. Bottom fames designed with seismic class I and II have relatively more safety storage than non-seismic designed bottom frames to resist the fire load effect, and they can satisfy time limits of fire resistance.