柱子的xtract是类似的，不同的是输出的是PMM曲线
区别是在loading里面选择PM interaction
图10 sap里面定义 Column“弯矩—轴力”屈服曲线（PMM曲线）
对于柱截面，定义PMM（轴力—弯矩耦合铰）来拟合构件的非线性行为，将xtract计算结果输入程序中形成PMM屈服面，如图8所示。在任一轴力P作用下，截面“弯矩—转角”关系如上M3铰所述，屈服弯矩（SF）根据PMM屈服面中相应轴力P对应的屈服弯矩给定。
附注：箱型截面：
命令流放在最后（复制到txt里面，另存beam。xbj文件，拖入到xtract图标）： # Project file generated by XTRACT # Created by: 红亮
# WARNING: When this file is read into XTRACT, data consistency checks are NOT performed. If inappropriate
# input data is read into the software, unexpected results may ensue. Before modifying this file, it is advised to
# save a back up copy. The order of the file in not important, nor is the spacing. The file must contain Global
# data as described below. Note that if this file is saved outside XTRACT, the associated output file will be
# automatically deleted when the file is opened.
# Define the global parameters for the file separated by Begin_Global and End_Global
# Version, Units and Name are required.
Begin_Global NAME = beam VER = 3.03 UNITS = N-mm HAS_ANALYZED = True
# Optional parameters Author = 红亮 Company = 大学
Job_Name = 截面M-φ曲线分析 Job_Number = beam
Time_Stamp = 2012/7/1 15:33:16 End_Global
#---------------------------------------
# Begin material definition with Begin_Material and end with End_Material Begin_Material NAME = Steel1
TYPE = Strain Hardening Steel Fy = 360.0 Fu = 360.0 esh = .002 esu = .09 Es = 200.0E+3 End_Material
#---------------------------------------
Begin_Material NAME = C40