PREDICTION OF FATIGUE LIFE FOR WELDED T-JOINTS OF CONCRETE-FILLED CIRCULAR HOLLOW SECTIONS BASED ON FRACTURE MECHANICS

The basic theory of linear elastic fracture mechanics was used to predict the fatigue life of welded T-joints in concrete-filled steel circular hollow section trusses. Firstly, some fatigue tests of the joints was carried out, which would be reference data for the validation of fatigue life prediction. Secondly, a model and a flowchart were set up for the numerical simulation of fatigue life based on fracture mechanics. APDL macro commands were developed by means of the software ANSYS, and then the prediction of fatigue life of the joints was implemented. Finally, the behavior of fatigue crack propagation was investigated. It is concluded that the numerical model based on fracture mechanics can better predict the fatigue life of complicated steel-concrete composite joints. The different size of an initial crack does not cause a significant influence in the condition of normal welding quality. The rate of crack propagation in length is faster than that in depth. Before the depth of a crack come to a half of the chord thickness, the crack propagates quite slowly in depth and a large proportion of fatigue life undergoes this period. Hereafter, it propagates more quickly in the direction of depth.