Experimental Study On Shape Formation And Vertical Ultimate Load Capacity Of Post-tensioned And Shaped Hypar Space Truss

The post-tensioned and shaped space truss is an innovative kind of space structure, combining traditional space truss with post-tensioning technology. Initially assembled on the ground level, the space truss can be deformed into a curved shape and erected into a space position by post-tensioning method. The basic structural module of the post-tensioned and shaped space truss is the single chord space truss (SCST), which is composed of a single layer of chords, together with out of plane web members. As a result of the different position of prestressing strands, the structure system has multiform space shape, such as barrel vault, hypar and dome. The research by scholars at Wollongong University showed that post-tensioned and shaped space truss can resist significant load.Based on the previus research, a modified post-tensioned and shaped hypar space truss is studied in this paper, the experiment includes shape formation and vertical ultimate load capacity.Different from the former shape formation experiment, two technical innovations is introduced in the post-tensioned and shaped space truss, which consist of a new type of bottom joint reducing eccentricity to some great extent, and a novel post-tensioning technology, called Suspa BBRV, could double the speed of prestressing and labour cost was halved. The force sensor is applied to measure the cable tension, and more accurate result is acquired, compared with the strain gauge method.Several new ways are carried out in the shape prediction. Different connector elements are used to simulate the bolt connection of the top joint, and the end of web. Based on both geometry and material nonlinearity, new FEM refering 'tube to tube' contact based on beam and truss elements, is employed to shape prediction. The newmethod is relatively much more accurate, and rise-span ratio is larger although necessary prestess is less.The experimental and theoretical result demonstrate that shape formation is attributed to the flexual deflection of top chords, little axial deformation is observed in the test.According to the lay out of space truss model, vertical load could not be applied to the top joints by the conventional loading system, Hence, a new type of loading system, including rope and pulleys, is presented and its tension loss mechanism was analysed. The valuable guideline are presented and applied to the loading installation. The actual ultimate vertical load is gained after the test space truss collapses.According to the vertical load capacity experiment result, the overall instability is not the main failure pattern of this new kind of structure, the focus of research should be the structural stiffenss. Axial force is the controlling interior force of the bars. The primary reason for failure is the high Mises stress zones induced by the pretension in the shape forming, which exist in some top joints, developing rapidly into fracture during vertical load test, make the structural stiffenss almost decrease to zero.Finally, the advisable guideline is presented for the further study.