Expandable Structures are a special kind of mechanism that can be used in several different geometries. The geometry of structures based on scissors is introduced to explain concepts necessary to design a wide range of forms like masts, archs, plane spatial structures, cylindrical and spherical bar structures.
This study describes a self-tensioning system in which the gravitational loads acting on a horizontal structural element are automatically converted to a posttensioning force on that component. The self-tensioning effect has a variable intensity, constantly adjusted depending on the applied service loads. The selftensioning is eccentrically applied over the cross-section, and it generates a negative moment that compensates the deformations due to the gravitational loads. The system can be utilized in beams, slabs and structural framings of different materials and can be implemented using different mechanical and hydraulic solutions. The study describes the operation of a mechanical solution for the self-tensioning system and analyzes its behavior in large-span timber floor framings. When combined with conventional pre-tensioning, the selftensioning system notably improves the strength and deformation behavior and permits a design of timber floor framings with a total height of 0.03 times the span length, achieving relative deflections below 1/1000 of the span for the service loads of the structure. Headings Post-tensioning, self-tensioning, prestressing, pre-tensioning, tensioning systems, long-span, timber flooring, wooden structures.
Crosspiece deployable grids are assemblies formed by groups of bars with two joints at their ends and one or more that lie inward and that can vary their angular position with respect to each other. In practice, this variation means that assemblies can change their form from a folded position, where they occupy very little space, to an unfolded position that is usable as an enclosure or covering. The evolution betwen the two extreme positions of this geometry is determined by compatibility limitations. In this paper, the performance of spherical grids composed of two-way crosspieces is studied. A way of generating them from grids which subdivide the surface of a sphere is also presented.
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