High Strength Bolt Stress And Fatigue Performance Study

High-strength bolts become an important connection in the building structure because of its high strength and removability. Since the connection has a complex stress mechanism, there are still some problems to solve. In one hand, our current specification underestimated bearing capacity under certain conditions, such as the shear capacity of the pressure type high strength bolt connection. In the other hand, our current specification lacks rules for the bolt fatigue design under tension. This thesis uses the numerical experimentation and theoretical derivation to study the two problems mentioned above.(1)The principle of virtual work was used to deduce the pre-stress simulation method. This method can simulate pre-stress properly.(2)The numerical experimentation method was adopted to analyze the loading process of bearing-type joints. Results show that, without considering the friction forces between connecting plates, when the bearing capacity of connection is controlled by bolt strength, the shear capacity of high-strength bolted bearing-type joints will be underestimated. In this thesis, a reasonable method was proposed to calculate shear capacity of high-strength bolted bearing-type joints.(3)Stress concentration in bolt screw was studied in the thesis through theoretical derivation and numerical analysis. Ignoring lead angle, the variation of axial force gradient was obtained according to deformable coordination condition. In addition, thread displacement factor and thread force were determined by numerical computation. Stress concentration factor in bolt screw was gotten through iteration by local modeling. Compared with the calculation results of whole model, the method proposed in this thesis has higher computing accuracy and efficiency.(4)After getting stress concentration factors, the fatigue life of40Cr high-strength steel bolts were estimated by two kinds of S-N methods. The design formulas of fatigue were proposed considering stress amplitude and stress ratio. Compared with other existing experimental results, our estimation results have higher safety and precision in high-cycle fatigue.(5)Fracture mechanics was used to analyze the stress strength factors of I fissure, bolts lifetime was estimated for different initial fissure lengths, and influences of different fissure lengths on the fatigue lifetime were studied. In accordance with the engineering assumptions, fatigue lifetime of initial fissure length0.5mm was assumed to be the bolt fatigue lifetime. Compared with the experimental data, results show that the estimated lifetime of initial fissure length0.5mm is fairly safe and precise. In addition, fissure length has important impact on bolt fatigue life.