U肋-面板全熔透焊接接头疲劳性能试验

正交异性桥面板U肋-面板焊接接头为疲劳裂纹多发部位，为了提高U肋-面板焊接接头疲劳性能，分析目前规范中对该构造细节的疲劳设计要求以及疲劳问题依然存在的原因，在目前主要采用部分熔透焊形式的背景下，考虑引入全熔透焊接以期达到提高疲劳性能的目的。研究围绕一种全新的U肋-面板全熔透焊接接头的疲劳性能分别开展构造细节和节段足尺模型试验研究。试验结果表明：全熔透疲劳裂纹都是始于U肋内侧焊趾处，沿着U肋腹板厚度方向发展，部分熔透焊裂纹主要始于未熔透焊缝的焊根部位，沿焊喉方向发展，直至贯通整个焊喉，且在同样加载条件下，全熔透焊裂纹产生的加载次数明显高于部分熔透焊；全熔透焊的热点应力试验测试值与理论计算值基本一致，U肋焊趾部位应力集中明显，内侧受拉外侧受压，解释了疲劳裂纹起始点为U肋焊趾内侧；经回归计算得到热点应力疲劳强度为263.8 MPa；将足尺节段疲劳试验加载幅度对应的加载次数换算为公路桥梁规范单车轮轮载60 kN所对应的加载次数，2个试件加载次数都超过1.2亿次，且U肋-面板全熔透焊接接头依然没有疲劳裂纹产生，表明U肋-面板全熔透焊接接头具备优良的抗疲劳性能。

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

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.