有限元建模对结构自振频率计算的影响

Effect of FEM Modeling on Natural-Frequency Calculating

以室外大比例框架结构(1∶2)模型自振频率测试结果为基础,采用Nastran程序分5种有限元模型4种工况计算了结构的自振频率,工况中包括了单元类型、单元位置偏置、地基条件和结构配筋等因素的影响.计算表明,考虑土结构相互作用(SSI)的计算结果比考虑刚性地基的结果低;较为准确的有限元计算模型应采用实体单元,并考虑配筋及上下部共同作用;在小震情况下,采用现行框架结构设计方法建模计算偏于不安全,这与通常的设计结论不一致.

Based on the test results of natural frequency of large-scale frame structure （1：2）, a Finite Element Method（FEM） program using Nastran was adopted to calculate the natural frequency of five models for four cases. In the cases, the effects of some factors were considered such as element type, element offset , subsoil condition and reinforcement. The calculation showed that the frequency results of Soil Structure Interaction （SSI） system were less than those of rigid soil. For accurate FEM modeling, solid elements should be selected , reinforcement and upper-lower structure interaction should be considered. In case of small earthquake, modeling according to the current frame-structure design method is not safe, which is not consistent with the usual design conclusions.