考虑大变形影响的框架极限荷载计算

Computation of Limit Load for Frames by FEM with Consideration of Large Deformations

本文用有限元法研究了考虑大变形影响的平面框架结构的极限荷载的计算问题。对大变形引起的几何非线性效应按带动坐标的二阶理论进行分析,单元杆弦允许有大的刚体位移而相对弯曲服从梁柱理论。结构材料假设为理想弹塑性,极限弯矩考虑轴力影响。对此双重非线性问题采用荷载增量法与切线刚度迭代法相结合的算法。算例说明本文方法可行、程序正确。同时表明,某些框架结构因受大变形影响极限荷载将有一定的减小,应该予以考虑。

The FEM for determing the limit load of plane elastic-plastic frames in consideration of large deformations is studied.The analysis of geometric nonlinear effect caused by large deformations is based on the second-order theory,in which large rigid body displacements of the member chord are allowed and local member force-deformation relationships are based on the beam-column theory.The material is assumed to be ideally elastic-plastic.The effect of axial forces on plastic moment capacity is considered.A computational technique for solving the dual nonlinear problem is proposed,in which an incremental lead approath with a Newton-Raphson type of iteration is employed.To demonstrate the feasibility of the method of analysis and the reliability of the computer program,numerical examples are presented.Numerical results indicate that the values of the limit load of some elastic-plastic frames are reduced to a certain extent due to the influence of large structural deformations,and this point merits attention.