Kinematic and Elastic Mobility

Abstract

Mobility, either virtual or kinematic, is a definitive feature of underconstrained structural systems. The two types of mobility are intricately intertwined. For instance, when a quasi-variant system (type III) made of a real, flexible material is subjected to a perturbation load, it undergoes displacements and constraint variations bringing it out of its singular configuration. As a result, the system acquires kinematic mobility, i.e., the possibility of finite displacements without any additional constraint variations. Under the same conditions, a quasi-invariant system (type II) behaves differently: in a new configuration it loses even its virtual mobility and becomes capable of supporting an arbitrary load.