抗震钢筋混凝土框架底层柱底截面弯矩增强系数合理取值的讨论

Discussion on Rational Value for the Moment Amplification Coefficients at the Bottom Sections of Columns in Aseismic RC Frames

以我国 8度区 (设计基本地震加速度 0 2 g)二级抗震钢筋混凝土框架结构为例 ,选取底层柱底截面的三档弯矩增强系数与上部各层柱端抗弯能力的两档增强措施相组合 ,设计出 6榀典型平面框架 ;再以采用单分量模型和改进武田滞回模型的杆系结构弹塑性动力反应分析程序PL AFJD对这些框架依次进行了相当于罕遇地震水准的 4条地面运动输入下的地震反应分析。分析结果初步表明 ,要使结构全面满足抗震设计要求 ,底层柱下端截面弯矩增强系数的取值应与上部各层柱的增强措施相匹配 ;修订后规范 8度区二级抗震等级框架上部各层柱的增强措施与修订前相比虽已有提高 ,但提高幅度尚嫌不足 ;底层柱底增强系数也宜在修订后规范取值 1 2

Six RC frames of seismic grade 2 in earthquake intensity 8 regions were designed by combination of three moment amplification coefficients at the bottom sections of columns in the ground floor and two different amplification methods of columns in upper stories.By means of nonlinear dynamic analysis program PL AFJD,the seismic response analysis under major earthquake was carried out by inputting four ground motions.The results indicate that the moment amplification coefficient at the bottom section of columns in the ground floor should be compatible to that of the upper stories;for the RC frames of seismic grade 2 in earthquake intensity 8 regions,the amplification method of columns in upper stories is not sufficient in the revised code,and the moment amplification coefficient at the bottom section of columns is advised to be increased greater than the current value of 1 25.