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The high-strength bolts’ fatigue is critical for the bolt–sphere joints of grid structures under the action of suspended cranes. High-strength bolts with a huge diameter are used more commonly when the span of grid structures and the burden of suspended cranes increase. However, few works have explored the fatigue performance of high-strength bolts with a huge diameter in bolt–sphere joints of grid structures. Thus, this paper examines M60 high-strength bolts with a huge diameter used in the bolt–sphere joints of grid structures. To this end, an AMSLER fatigue testing machine performed fatigue tests on 27 specimens under constant amplitude. The stress–fatigue life (S–N) curve was obtained by regression analysis and the corresponding constant-amplitude fatigue design method was established. The test results were compared with those of high-strength bolts in other specifications. The results showed that the M60 high-strength bolt has a higher fatigue strength. Furthermore, scanning electron microscopy (SEM) analyzed the macroscopic and microscopic fatigue fracture of the specimens, and the mechanism of the fatigue failure was examined. Our findings provide important experimental data for revising relevant Chinese and international codes and promote the application of high-strength bolts with a huge diameter used in the bolt–sphere joints of grid structures with suspended cranes. This study could fill the gap of fatigue performance data of high-strength bolts in different specifications for bolt–sphere joint grid structures, and provide a basis for further studies.

Grid structures with bolt-sphere joints are widely used in industrial plants. With the installation of suspension cranes, high-strength bolts are subjected to repeated alternating loads and cause fatigue problems. Due to their dispersive nature, the degree of difficulty and cost of fatigue tests are extremely high. Due to the lack of a recognized fatigue design method, engineering designers have encountered great difficulties, and the promotion and application of such methods are severely restricted. In this paper, we successfully implemented a constant-amplitude fatigue test of M39 high-strength bolt specimens on an American MTS Landmark 370.50 fatigue testing machine and obtained the corresponding S-N curve from the statistical analysis of the test data. Using the nominal stress amplitude Δσ and the hot point stress amplitude Δσk as the design parameters, we established a corresponding constant-amplitude fatigue design method. We performed a microscopic analysis of the fracture surface using a TESCAN Mira3 LMH scanning electron microscope and revealed the fatigue failure mechanism of the high-strength bolts.

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