Experimental Research On Fatigue Failure Of Connecting Nodes With High-strength Bolts

Basing on the background engineering of the world's largest long-span steel truss arch bridge—Chongqing Chaotianmen Yangtze River Bridge engineering, the fatigue property of high strength bolt connection at cross joint of horizontal and transverse direction of light rail in the lower deck is focused on in this paper. The following studies are involved.The comparative analysis on calculation method of bridge load spectrum is completed in accordance with home and abroad specifications. According to Miner linear cumulative damage rule, the equivalent amplitude of internal force is determined. By ignoring the minor factors, the fatigue property of high strength bolt connection at the cross joint is taken into account and the simplification design for half-scale model is carried out.Two million times of fatigue tests under designing amplitude of loading for cross joint have been completed. The theoretic analysis and fatigue tests have both verified the reliability of this type of cross joint working under service loading. The subsequent tests are gradually increasing the designing amplitude of fatigue loading from 1.5 to 3.0 and observing the behavior of testing beam along with the increased amplitude of fatigue loading and repeat counts. The observations are composed of lateral wobble, filings at the surface of the connection, looseness of high strength bolts, and fatigue crack of welding at web and lower flange.Basing on the previous home and abroad studies, deep study on complete procedure of the looseness of one bolt has been finished. The influence of axial impact loading, lateral wobble, dynamic shearing loading of screw on the motion model and mechanic behavior of bolts have been analyzed. Formula of bolt looseness has been deduced by theory of kinematics and mechanic, and the failure criterion on the looseness of high strength bolt has also been discussed.In view of the model test, the force of transfer path in the model and the influence from the secondary internal force in the cross beam have been studied. It puts emphasis on the mechanism of looseness of high strength bolt at the joint by the force of pry. The calculation formula of the pry for T-joint has been deduced. The corresponding amplitude of fatigue loading to the looseness of joint bolt has been verified. And the complete procedure of failure for this type of high strength bolt has been generalized.