1、The element siiffness matrix and the geometric stiffness matrix etc. are explicitly presented.
2、The stiffness matrix and geometric stiffness matrix of rectangular tube-in-tube element of which the cross-section has bisymmetric axes are developed.
3、The three-node beam element tangent stiffness matrix including the geometric stiffness matrix is developed according to the nonlinear finite element theory.
4、In this paper, a improved geometric stiffness matrix of a column element considering axial force-lateral displacement effects is derived.
