约束混凝土柱的升降温全过程轴力分析

Axial Force in Restrained RC Columns during Heating and Cooling Phases

利用SAFIR程序,开展了约束混凝土柱的升降温全过程轴力分析。考察了轴向/转动约束刚度比、截面边长、荷载比、荷载偏心率、配筋率、升温时间等参数对ISO834标准升降温过程作用下约束混凝土柱的轴力的影响规律,并与单调升温时的相应规律进行了比较。通过对2880种工况的计算分析,建议给出了该类构件轴力变化系数的实用计算方法。研究结果表明:对于轴向/转动约束混凝土柱,无论单调升温还是先升温后降温,轴力变化系数总体都呈现出先逐渐增大而后有所减小或基本保持稳定,最后以较大速率持续降低的趋势,主要区别在于后期单调升温对应的降低速率一般比先升温后降温时更大;对于先升温后降温的轴向/转动约束混凝土柱,转动约束刚度比、柱长和混凝土保护层厚度对轴力变化系数影响较小,而轴向约束刚度比、荷载偏心率和配筋率越大或荷载比和截面边长越小,轴力变化系数的峰值就越大。

Using the computer program of SAFIR,the influences of some parameters（i.e.,axial/rotational restraint ratio,sectional dimension,load ratio,load eccentricity ratio,reinforcement ratio,and heating time,etc.） were analyzed on axial forces in restrained concrete columns exposed to ISO834 standard fire with cooling phase,compared with those in the standard fire without cooling phase.Based on the simulation results of 2880 cases,a practical calculation method for axial force in column was proposed.It was shown that：（a） for axially-and-rotationally restrained columns in fire with or without cooling phase,the enhancement coefficient of axial force increased gradually first,and then reduced gently or kept constant,and finally decreased quickly.However,in the late stage,the enhancement coefficient corresponding to fire without cooling phase dropped more significant than that with cooling phase;and（b） the influences of the rotational restraint ratio,column length and thickness of concrete cover on the enhancement coefficient of axial force in axially-and-rotationally restrained columns were limited subjected to fire with cooling phase,while the peak value of the enhancement coefficient increased with the increase of the axial restraint ratio,load eccentricity ratio and reinforcement ratio or with the decrease of the load ratio and sectional dimension.