Doctor of Philosophy
Department of Civil and Mining Engineering
Li, Hewen, Shape formation of space trusses, Doctor of Philosophy thesis, Department of Civil and Mining Engineering, University of Wollongong, 1997. http://ro.uow.edu.au/theses/1265
This thesis is principally concerned with the shape formation of different forms of space trusses with non-zero Gaussian curvature by means of a post-tensioning technique. The space truss that is shaped and erected by a post-tensioning procedure, rather than by traditional techniques involving cranes and scaffolding, is called a post-tensioned and shaped space truss.
The construction procedure for a post-tensioned and shaped space truss initially involves the assembly of a planar truss with a single-layer of chords, together with out-of-plane web members, at ground level. In proportion to the desired space shape, certain bottom chords are given gaps. The bottom chords comprise shorter tubes and strands that pass through the tubes and through the bottom joints. The initially too-short chords are used to create pre-defined gaps, while the tensioning strands are used to close the gaps. By means of post-tensioning, a planar layout can be deformed and erected to its desired space shape at the same time.
In this thesis, the principles of the post-tensioned and shaped space trusses, together with the essential aspects that lead to shape formation and self-erection, are investigated theoretically and are verified by experimental models. In addition to theoretical work, seven domes and one hypar have been constructed by means of a post-tensioning method under laboratory conditions. Also, a pyramidal unit of a full-size practical space truss has been tested. After the shape formation tests, three post-tensioned and shaped domes and one hypar space truss have been loaded to failure in order to observe the ultimate load carrying capacity.
The post-tensioned and shaped space trusses have satisfactory ultimate load capacity. The post-tensioning process m a y increase or reduce the ultimate load capacity of posttensioned and shaped space trusses, due to the resulted prestress forces in some critical members. Compared with the simplicity in construction and erection procedure, the post-tensioned and shaped space trusses still have evident advantages in economy, even if the ultimate load capacity is reduced. Furthermore, the ultimate load capacity of a posttensioned and shaped space truss can be improved by stiffening only a few critical members according to the test results.