PRELIMINARL SUTDY ON LOADING TEST FOR PNEUMATICALLY PRESTRESSED COLUMN

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Publication year 2023
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Title PRELIMINARL SUTDY ON LOADING TEST FOR PNEUMATICALLY PRESTRESSED COLUMN
Author Takara Muto,Ken’ichi Kawaguchi,Yosuke Nakaso,Junichi Kikuchi,Koichi Taniwaki,Mieko Tamegai
Summary Pre-tensioning can reduce self-weight of the structure, but rigid boundary condition or fine struts, both of which are very heavy, are usually required to get reaction force to introduce the pre-tension. However, air pressure is possible to introduce the pre-tension by combining an inflatable cushion and cables, without increasing its self-weight. The structure keeps its ultra lightweight. We call the structure as “Pneumatically Prestressed Structure”. In this report we made pneumatically prestressed column, which is the column type of pneumatically prestressed structure, with a cylindrical inflatable tube of 3 m length. Then, loading test was performed for it. The prototype consists of an inflatable tube, cables, and rigid plate. The length and diameter of the tube is 3.0m, 1.2m, respectively. The tube is made of thin sheet of PVC, which thickness is 0.3mm. A net is wound on the lateral surface of the tube as reinforcement. The net takes tension instead of the tube, therefore thin sheet is suited to make the tube with less material. The plate is attached to both ends of the tube via Velcro and fastener. The ends of 8 cables are connected to corners of the plate and the cables are arranged like the alphabet X. Loading test was performed by putting metal weight on the upper plate of the specimen from above, one by one. At every loading step, vertical and horizontal displacements were measured. The results are summarized as follows.
1. We made the prototype of pneumatically prestressed column, which had 0.7% assembling error. The prototype was inflated at 4.0 kPa. It is essential to control of the length of cable in advance.
2. Inserting swim rings contributed to reduce initial geometrical imperfection of the inflated tube.
3. The specimens displaced linearly to the load and the horizontal displacement was within 3 mm, but it increased drastically after 2.6 kN. Then, the specimens displaced by 18 mm at maximum load, 3.17 kN.
4. Pretension of cables at initial state was as much as 73% of air pressure.
5. The following items are to be considered; the replacement of swim ring to restrict the shape of the inflated tube, rigidization of net, and high air-tightness of the membrane including seaming line and valves.