STUDY ON FATIGUE CRACKING OF JOINT IN A HALF-THROUGH CFST TRUSS ARCH RIB JOINT

To analyze the reason why fatigue cracking appeared on the rib joint of a half-through concrete filled steel tubular (CFST) truss arch, finite element (FE) analysis is carried out by establishing the full-bridge FE model using the software of MIDAS/CIVIL. By studying the variation of the stress amplitude of the arch rib joint under different vehicle loads and geometric parameters of the arch rib joint respectively, the influence of overloading, medium loading and unbalanced loading on the stress amplitude is analyzed. Furthermore, the influence of geometric parameters of the arch rib joint on the stress amplitude is also discussed. It is found that the stress amplitude of the arch rib joint linearly increases with the variation of overloading percent, including 30%, 50%, 100% and 150%, respectively, and the maximum value of the stress amplitude reaches 155 MPa. Besides, the stress amplitude caused by a BS5400 fatigue vehicle model is the maximum comparing with others. However, the value of the stress amplitude caused by unbalanced loading is 1.2 times as that caused by medium loading under a China 550 kN-vehicle model. Thus, overloading and unbalanced loading lead to fatigue cracking and the unsymmetrical distribution of fatigue cracks on the arch rib joint of a CFST truss bridge respectively. The stress amplitude of the joint decreases with the increase of the ratio of brace thickness to chord thickness, but with the increase of the ratio of brace diameter to chord diameter, chord diameter to thickness and brace diameter to thickness, the stress amplitude increases first and then decreases.