Effect of crack-closure treatment on fatigue durability of cracked rib-to-deck welded joints in steel bridge decks

Abstract

To evaluate the effect of treating long cracks with the impact crack-closure retrofit (ICR) technique, three rib-to-deck welded specimens with a crack length of about 100 mm were tested. The metallographic structure, crack section, crack propagation life, and stress variation were analyzed. Finite-element models were also developed, and some optimal values of certain parameters are suggested according to the simulated results. The results show that new crack sources are generated on both sides of the ICR-treated region because of the stress distribution. The fatigue lives of cracked specimens with long cracks are significantly improved by the technique. Considerable residual compressive stress is also induced, and so it is suggested that the optimal impact angle to be applied to real bridges should be 70°. The stress at the weld root is distributed uniformly with the crack closed, and the optimal crack-closure depth is 4 mm. To evaluate the effect of different crack-closure depths in tests, it is recommended that a hot-spot stress method which is extrapolated by three reference points should be adopted.

摘要

为分析气动冲击技术对长裂纹的修复效果, 选取了三个裂纹长度均为100 mm 以上的顶板与U 肋试件, 开展了气动冲击修复试验及修复后疲劳加载, 并分析了微观结构变化、裂纹断面、裂纹扩展 速率、应力幅等。同时, 建立了相关有限元模型, 基于分析结果提出了部分关键的技术参数。研究表 明, 由于锤击后的应力重分布, 在锤击区域的两侧会产生新的疲劳源区, 但具有长裂纹试件的疲劳寿 命依然得到了显著的提高。气动冲击可产生可观的残余压应力, 为取得最佳效果, 气动冲击角度建议 为70°。裂纹闭合后焊根应力呈不均匀分布, 最佳的闭合深度为 4 mm。在裂纹闭合深度影响的试验研 究中, 建议采用三点外推得到的热点应力作为评判指标。