High Temperature Performance Research For Seismic-damaged Reinforced Concrete Beamunder Post-Earthquake Fire

Besides huge life and property loss brought by post-earthquakefire(PEF),seismicdamaged components and structures are also threatened seriously. At present, PEF research on components and structures is less. Based on the on-site investigations of the earthquake damage and shaking table tests.In this paper,combination of cracking and concrete cover spallingis the main form of damage to reinforced concrete beam.By use of the ABAQUS software to set up the finite element calculation model of seismic-damaged reinforced concrete beam(SDRCB) and to do the analysis of the temperature field of which suffers ISO834 curve.Cross section temperature field characteristics, the influence of geometric features on temperature field, temperature difference under the condition of considering and ignoring reinforcements in the same location of section, the influence of reinforcements on the beam temperature field areanalyzed,the bending capacity of SDRCB is calculated and the influence of geometric features on bending capacity is also analyzed. Calculation formulas of the bending capacity reduction coefficient are fitted. The principal conclusions of this paper are as follows:(1) The cross sectiontemperature field contours of SDRCB with combination of cracking and concrete cover spalling aresingle axial symmetry. The relative crack depth has not obvious influence on the temperature field ofSDRCB. Location of concrete cover spalling has effect on the temperature field of SDRCB. That is, isotherm of corner of cover spalling is not parallel to the axis of the beam.(2) Temperature of rebar node at the bottom of the beam splitting section is slightly lower than the same location of seismic-damaged plain concrete beam. The temperature is almost the same between stirrup node on the side of SDRCB and the same location ofseismic-damaged plain concrete beam. Temperature of rebar node on the top of SDRCB is lower than the same location of seismic-damaged plain concrete beam, but the difference is approached rapidly. Temperature of stirrup node on the top of SDRCB is higher than the same location of seismic-damaged plain concrete beam, however the difference is very small, the highest difference between them is 18℃. Generally speaking, the temperature difference is small between rebar node in SDRCB andthe same location of seismic-damaged plain concrete beam, which can be ignored.(3)Reinforcements have some effect on the temperature of SDRCB. However, the scope of the impact is confined to small range of itself and a limited period. After the heat reaches equilibrium and the temperature is almost the same between steel and concrete, there is no influence on the temperature field of SDRCB by reinforcements.So, the influence of reinforcements can be ignored in temperature analysis of SDRCB approximately. That is, the temperature of concrete can instead of the reinforcements temperature in the same location of the section. In this case, the calculation models are simplified; the calculation time is shortened under the condition of guaranteeing the accuracy.(4)The bending capacity of SDRCBcompressive zone has something to do with location of concrete cover spalling and relative crack depth. The bending capacity will be affected by the spalling position of concrete cover, which will affect the heat absorption and dissipation of concrete and steel bar. The bending capacity decreases with the increasing of relative crack depth. Because the bigger the relative crack depth increases, the smaller the compressive zone of crack section, and thus the bending capacity of concrete are decreased.(5)The bending capacity of SDRCBtensile zone has something to do with location of concrete cover spalling. However, it has nothing to do with the relative crack depth. Due to the limited thickness of cover, its ability to isolate high temperature is weak.The longer the beam suffers high temperature, the weaker the influence on bending capacity which caused by location of cover spalling.(6)The bending capacity reduce rate of SDRCB tension zoneis higher than SDRCB compressive zone. It means that tensile zone of section subjected fire is worse for the safety of components or structures.