Rigid Body Motion Test for Nonlinear Analysis with Beam Elements

A rigid body motion test is proposed for verifying the legitimacy of a finite element to be used in a geometrically nonlinear analysis. The test requires that the initial forces acting on an element rotate or translate with the rigid body motion while the magnitudes of the initial forces remain unchanged, so as to preserve the equilibrium of the element during the rigid body motion. Such a test is consistent with basic physical laws, and is, therefore, more rational than previous considerations on rigid body motions. This paper also demonstrates the significance of using a consistent procedure for calculating the member forces in an incremental nonlinear, solution process. When a consistent element is used along with a consistent force calculation procedure, convergent and accurate solutions can be obtained for various nonlinear problems.