The Study on Improvement Method of Fatigue Strength of Steel Bridge Weld member

从焊缝金属的影响和焊趾后处理的影响两个方面研究了提高焊接接头疲劳强度的方法。在这项研究中，纵向焊接接头和纵向焊接肋接头进行了研究。因此，获得了以下三个主要结果。(1)采用纵向焊接接头，通过试验和统计分析，研究了焊缝金属的欠匹配对焊接接头疲劳强度的影响。结果表明，低匹配使焊接接头处的残余拉应力降低，焊接缺陷产生的概率降低，疲劳裂纹萌生的概率降低。(2)采用纵向焊接肋接头，研究了焊缝金属和焊趾后处理对焊接接头疲劳强度的影响。结果表明，焊缝金属的变化和后处理对焊缝（包括焊趾）的形态、硬度和焊接残余应力有影响。选择合适的焊缝金属和焊趾后处理提高了焊接接头的疲劳强度。(3)为了验证上述两个结果（1）（2）在真实的钢桥结构中的应用，进行了大型钢梁试件的疲劳试验。大梁试件与（1）（2）中使用的小梁试件具有相同的焊接条件。结果表明，焊缝金属的欠匹配和TIG熔修均能提高疲劳强度，本文所评价的改进方法对真实的钢桥结构是有效的。

The improvement methods of fatigue strength of weld joints were studied at the following two view points, 1.the effects of weld metal, 2.the effects of post-treating of weld toe. In this study, longitudinal weld joints and longitudinal weld rib joints were investigated. Consequdntly, the following three main results were obtained.(1) Using longitudinal joints, the effects of undermatching of weld metals on fatigue strength of weld joints were investigated experimentally and statistically. The results showed that the undermatching makes the weld tensile residual stress at the weld joints, probability of weld defect occurrence, and probability of fatigue crack initiation from the weld defects decrease.(2) Using longitudinal weld rib joints, the effects of weld metal and post-treating of weld toe on fatigue strength of weld joints. The results showed that changes of weld metals and post-treating affected on the configuration of weld bead (including weld toe), hardness, and weld residual stresses. And choosing appropriate weld metals and post-treating of weld toe improved the fatigue strength of weld joints.(3) To evaluate the application of the above-mentioned two results (1) (2) to real steel bridge structure, fatigue tests with large girder specimens were performed. The large girder specimen had same wedl condition as small specimens which were used in (1) (2). The results showed that undermatching of weld metals and TIG-dressing improved the fatigue strength, and that the improvement method evaluated in this sutyd were effective on the real steel bridge structures.