Bolted spherical joints are widely used in space grid structures. However, the preload loss, which may arise from fabrication error, insufficient twist of the screw and some other unknown reasons can undermine the structural integrity and even lead to the collapse of the whole structure. Therefore, a method for evaluating the preload status of bolted spherical joints is vital to the structural health monitoring of the space grid structures. To this end, a non-destructive evaluation of the preload loss of bolted spherical joints based on time reversal acoustics (TRA) is presented. In this method, an excited signal generated by a lead zirconate titanate (PZT) patch at the bolted sphere is reconstructed after the signal recorded by another PZT patch at the bar is time-reversed and re-emitted. The deviation of the reconstructed signal from the initial signal allows identification of preload loss of the bolted spherical joint. This method is demonstrated to be effective by a finite element simulation. Furthermore, the effect of preload loss of the bolted spherical joint on its ultimate flexural capacity is studied, which highlights the necessity for the non-destructive evaluation.

Bolt-ball joints are widely adopted in grid structures due to their high installation accuracy and short construction period. Since the bolt is inside the joint, it is challenging to evaluate its health status from outside the structure. A finite-element plane-truss structure model, based on the actual grid structure, was constructed to investigate the influence of the rod’s preload on the overall stiffness and bearing capacity of the grid structure. Moreover, a model of the grid structure, with a bolt-ball joint connection, was constructed to analyze the influence of the preload loss in bolted-ball joints on the overall mechanical performance of the local members and structures. The results show that the release of preload on the outer web rod is less effective in terms of the overall stiffness and bearing capacity of the structure than on the inner web rod. The preload of the larger span direction rod plays an important role, and the preload of the upper chord has a greater impact, while the preload of the web rod and the upper chord in the smaller span direction has no significant effect on the normal stress in the surrounding rods.