EFFECTS OF RIGID BODY AND STRETCHING ON NONLINEAR-ANALYSIS OF TRUSSES

According to the law of rigid body motion, a body initially acted upon by a set of forces in equilibrium will experience no additional straining when subjected to a rigid body motion, and will remain in equilibrium after the rigid body motion. When such a law is not strictly followed in an incremental-iterative nonlinear analysis, especially in the element force recovery procedure, fictitious forces may occur at each intermediate step, which eventually may result in the deviation of the calculated behavior of a structure from its true response. From the point of view of solution accuracy, the rigid body effect plays a more important role than the stretching effect in determining which higher-order terms should be included in a force-recovery procedure. In this paper, both of these effects are considered in the derivation of the nonlinear stiffness matrices for a truss element. Each term involved in the formulation is examined with clear physical meanings given. Comparisons are made with previous results in the numerical examples. © ASCE.