约束混凝土梁的升降温全过程弯矩分析

利用SAFIR程序，开展了约束混凝土梁的升降温全过程梁端弯矩分析；考察了转动约束刚度比、轴向约束刚度比、截面尺寸、荷载比、全截面配筋率和升温时间等参数对梁端弯矩的影响规律，并与单调升温时的相应规律进行对比，给出了梁端弯矩的实用计算方法。研究结果表明：对于先升温、后降温的约束混凝土梁梁端弯矩的变化，总体表现出与单调升温类似的特征，主要区别在于后期因降温作用而呈现出缓慢降低的趋势；转动约束刚度比对梁端弯矩的影响集中在升温前期，在此时段内，梁端弯矩随着转动约束刚度比的增加而增大，但增幅逐渐趋缓；升温后30min以内，轴向约束刚度比的改变对梁端弯矩几乎没有影响；之后，梁端弯矩随着轴向约束刚度比的增加而逐渐减小。

Bending Moments of Restrained RC Beams during Heating and Cooling Phases

Using the computer program of SAFIR, the influences of some parameters （i. e. , rotational restraint ratio, axial restraint ratio, sectional dimensions, load ratio, reinforcement ratio and heating time, etc. ） on bending moments at the ends of restrained concrete beams exposed to ISO834 standard fire with cooling phase are analyzed, and compared with those exposed to ISO834 standard fire without cooling phase. Based on the simulation results, a practical calculation method for bending moments at the ends of beams subjected to fire with cooling phase is proposed. Simulation results show that： （a） the bending mo- ments at the ends of beam in fire with cooling phase and those without cooling phase appear to follow a common trend on the whole, and the main difference lies in the later stage of fire due to the cooling phase; （b） the influence of rotational restraint ratio on the bending moments at the ends of beam concentrates on the earlier stage of fire, and the bending moments increase with the increasing of rotational restraint ratio; and （c） the effect of axial restraint ratio on the bending moments at the ends of beam is very limited within the first 30 min of fire, and then the bending moments decrease with the increasing of axial restraint ratio.