Experimental investigation of failure mechanism of grid structure with bolted spherical joints

Abstract Under strong earthquakes, the grid structure members may frequently bear plastic strain so that the grid failure, which is characterized by ultra-low cyclic fatigue. In the present study, the ultra-low cycle fatigue test of three full-scale grid structures, which are under vertical cyclic large plastic strain load, is carried out. The hysteretic and skeleton curves, energy consumption capacity, ductility performance, bearing capacity degradation, and stiffness change are obtained. Also, the macroscopic morphology of rod fracture is analyzed. In addition, the corresponding recommendations are made based on the failure mechanism of the rod and the deformation characteristics of the joint. It was found that the ultra-low cycle fatigue damage of the lower chord is the main cause of grid failure. Also, the failure behavior of the rod in the structure is very similar to that in the member test. The coupling effect of ultra-low circumferential fatigue and local buckling causes the strain to concentrate in the middle of the rod. The computational analysis of such structures under strong earthquakes should consider the degradation of joint stiffness.