Experimental Research On Joint Of Space Cross-truss At Tension And Torsion

The space cross-truss is a new kind of steel structure. It's applied for the"Ticou"of Guotai art center being built in Chongqing. Each single truss composed space cross-truss is paralled to the others in the same height, but it's vertical to the others above and below nearby. So, the poles in the single trusses belong to different height can't be in the same plane. Some kinds of special joints must be applied for these poles to connect them, so that each single truss can be connected to the other above and below nearby, which makes each single truss be the space cross-truss. The"Ticou"of Guotai art center is hanging system on structure, the highest three layers of single trusses become a big cantilever truss, the rest 29 layers of single trusses are hung under the big cantilever truss by special joints. As the consequence, the special joints are tensed by the gravity of the single trusses below. When the big cantilever truss is bended, the special joints will be shear because of the bending deformation of the whole hanging system. What's more, each single truss is paralled to the others in the same height, but the cantilever length of single truss is different with each other. So, there is difference on axis deformation of chord, which causes the different shearing force between layers, and that will cause torsion to special joint. Because the force on special joint is complex, and the special joint is a key link for structure, it is necessary to take experimental study on the special joints.By the experiment mentioned in the paper, three total scale specimens for each kind of special joints applied to space cross-truss are tested at tension and torsion, the stress and deformation are measured, the failure mode and the ultimate capacity is obtained. The result from the paper shows that the distribution of the stress at the joint region is complex, the steel of some part gets plastic, the stress redistribute occurs. The weld between the major tube and secondary tube cracked, which caused the structure got failure. The distruction is brittle fracture. The truss got destruct before the joint region, which means the weld between the joint and pole of truss is safe in static force, the same to the joint region. Finally, after the safety is considered, an advisable joint will be recommended in three kinds of special joints.