点焊对钢桥细部焊接结构疲劳寿命的影响

Effect of spot welding on the fatigue life of small welded structures of orthotropic steel bridge

为了研究点焊对正交异性钢桥细部焊接结构疲劳寿命的影响,制作了桥面板与U肋细部构造疲劳试样,试样分为有点焊、点焊打磨和无点焊三种形式。在试样的焊缝根部和焊趾位置周围布置应变片进行疲劳试验,得到每组试样的疲劳寿命以及裂纹发生位置。通过对疲劳试样进行精细化有限元计算可知,点焊位置焊趾处应力明显大于焊缝根部的应力,点焊后打磨应力集中明显减小。分析结果表明,1有限元分析结果与试验结果相符,点焊不仅改变了疲劳裂纹的发生位置,而且导致疲劳寿命明显下降;而点焊后打磨试样的疲劳寿命与无点焊试样寿命较为一致。2建议该构造细节无点焊或点焊后打磨时采用Eurocode3细节分类100的疲劳曲线或者《铁路桥梁钢结构设计规范》中疲劳容许应力幅类别为Ⅶ的疲劳曲线,若点焊不做处理时则疲劳曲线应降级使用,建议采用Eurocode3-80或者BS5400-E。3要提高构造细节疲劳寿命,应尽量减小点焊或将点焊进行打磨处理。

To research the effect of spot welding on the fatigue life of small welded structures of orthotropic steel bridge, the fatigue specimens of bridge cover and U-rib with spot welding, with pol- ished spot welding and without spot welding were designed and produced. Fatigue tests were per- formed by arranging strain gauges around weld roots and weld toe to obtain the fatigue life and crack position of the specimens. The elaborate finite element calculation was carried out for the fatigue specimens, and the following results were obtained. The stress at the weld toe with spot welding is significantly greater than that at the weld root, and the stress concentration of the specimens with polished spot welding is reduced obviously. And the analysis results show that the finite element a- nalysis results were consistent with the experimental results, and the position of fatigue cracks changed with spot welding which led to the decrease of fatigue life obviously. The fatigue life of the specimens with polished spot welding was almost the same as that of those without spot welding.Comparing the fatigue test data with the specifications for steel structure, the tollowmg aovlces can be given ： for the specimens without spot welding or with polished spot welding, it is recommended to use detail category 100 of Eurocode3 specification or detail category VII in the code for design of steel structure of railway bridge ; for the samples with spot welding, the fatigue curve should be downgrad- ed, and detail category 100 of Eurocode3 specification or detail category E of BS5400 specification is suggested to be used. To improve the fatigue life of small welded structures, it is necessary to minimize spot welding or polish the spot welding.