Experimental Study on Fatigue Performance of Full Penetration Welded Joints of U-shaped Rib-plate

Abstract

The U-shaped rib-plate welded joint of an orthotropic bridge deck is a part where multiple fatigue cracks can occur. In order to improve the fatigue performance of U-shaped rib-plate welded joints, the fatigue design requirements of this structural detail for the current specification and the reasons why fatigue problems still exist were analyzed. Since partial penetration welding is mainly adopted at present, full penetration welding is introduced to improve the fatigue performance. This study focuses on the fatigue performance of a new U-shaped rib-plate full penetration welded joint and carries out structural detail and full-scale segment model test research. The results show that the full penetration fatigue cracks start at the welding toe of the inner side of the U-shaped rib and develop along the thickness direction of the U-shaped rib web. However, the fatigue cracks of partial penetration welding mainly start at the welding root of the unfused weld and develop along the welding throat until penetrating the entire welding throat. Under the same loading condition, the loading cycles of the full penetration welding for producing cracks were obviously higher than that of partial penetration welding. The hot spot stress in the test was consistent with the theoretical calculation value. The stress concentration in the weld toe of the U-shaped rib is obvious, and the inner side was in a tensile state while the outer side was in a compressive state, which indicates that the fatigue crack was initiated on the inner side of the weld toe of the U-shaped rib. The hot spot stress fatigue strength was 263.8 MPa after regression calculation. The corresponding loading cycles of the fatigue loading amplitude for the fatigue test were converted into loading cycles corresponding to a single wheel load of 60 kN under highway bridge specifications, which exceed 120 million cycles for two fatigue specimens, and the full penetration welded joints of the U-shaped rib-plate still had no fatigue cracks. Thus, the full penetration welded joint of the U-shaped rib-plate exhibited good fatigue resistance.