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The deployable structures investigated in this paper are prefabricated space frames made of basic units consisting of two straight bars connected to each other by a pivot, the so called scissor-like-elements. They can be stored in a compact folded configuration, and can be easily deployed into large, load carrying forms by simple articulation. In order to avoid major disadvantages of previous designs, the structures examined here obey strict geometric rules so that they are self-standing and stress-free in both their folded and deployed configurations. During deployment however, geometric incompatibility between member lengths results in a geometrically nonlinear structural behaviour. The optimum design of such a structure has to provide a compromise between desired stiffness in the deployed configuration, and desired felxibility during deployment.

Deployable-collapsable structures have many potential applications. ranging from emergency shelters and facilities, through relocatable semipermanent structures, to space-station components. A new concept of selfstabilized/self-supported "clicking" structures -featuring stable, stress-free states in both deployed and collapsed forms -shows even greater promise. This article highlights the state-of-the-art in the field of deployable-collapsable structures and discusses their advantages and limitations. A unique concept of "clicking" structures is introduced, and its basic capabilities are presented and discussed. Finally future research needs are mapped out.

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This paper presents further developments in the geometric design of deployable structures that are self-standing and stress-free in both the deployed and collapsed configurations. The basic geometric design philosophy of these structures has been explained in previous publications. Furthermore. guidelines for the geometric design of polygonal and trapezoidal units for flat and curved structures have been proposed. The size of the joints has been assumed to be infinitesimally small.In reality however. the joints have certain discrete dimensions that have to be taken into account. This paper presents a more realistic geometric design procedure allowing for discrete joint sizes. First, a simple but accurate model is adopted for the joints that treats them as a grid of bars that are hinged to the members of the structure. Then. the geometric constraints and deployability conditions derived earlier are modified to account for joint size. Regular polygonal units for flat and curved structures. and trapezoidal units for flat structures are covered. An example of a medium size model is presented. where adjustments for the joint size had to be made during geometric design. Finally. the influence of joint size in the structural response during deployment is illustrated.