A Study on Life-Prediction and Life-Expansion of Existing Steel Bridge

近年来，公路、铁路钢桥出现疲劳破坏的现象时有报道。在此背景下，评估桥梁寿命的预测方法和制定有效的维修计划就显得尤为重要。本文以建立钢桥寿命预测和延寿方法为目标，开展了以下几个方面的研究：1）为了对既有桥梁进行寿命预测，了解既有桥梁疲劳裂纹的位置、类型和产生原因是非常重要的。首先，本研究建立了日本、美国公路、铁路钢桥疲劳破坏的数据库; S. 2）其次，为了探讨疲劳破坏的发生机理，进行了应力测量和有限元分析。最后，针对钢桥的延寿问题，采用焊接接头小试件，研究了钢桥疲劳寿命的改善方法（例如平面外角撑板焊接接头，平面内节点板焊接节点和十字形焊接节点）和包括部分焊接节点（如腹板节点板、翼缘节点板和竖向加劲肋）的梁试件。作为提高疲劳强度的方法，本文研究了焊接电极的欠匹配和焊趾处的焊后处理，如TIG修整、修磨毛刺和锤击等。

Recently, it has been often reported that fatigue failure occurred in many steel highway and railway bridges. From this background, now it becomes much important to estimate the way to predict of life of bridge and to make an efficient plan of maintenance work. In this study, aiming to establish the way of life prediction and life-expansion of steel bridges, the following studies were carried out considering fatigue.1) In order to predict life of existing bridges, it is very important to know location, type, and reason of fatigue crack in Existing bridge. First, in this study, to establish the data-base, fatigue failure occurred in steel highway and railway bridge in Japan and U. S. A were rearranged2) Next, in order to discuss the mechanism of occurrence of fatigue failure, stress measurement and FEM analysis were carried out. Here, scallop detail and cross-connection detail were studied in testing laboratory and also actual bridges considering secondary stress and deformation mode.3) Finally, aiming life-expansion of steel bridges, some fatigue improvement methods were studied with using small welded joint specimens (such as out-of-plane gusset welded joint, in-plane gusset welded joint and cruciform welded joint) and girder specimen including some welded joints (such as web gusset, flange gusset and vertical stiffener). As fatigue strength improvement method, under-matching weld electrode and post-welding processing at welded toe such as TIG-dressing, burr-grinding and hammer peening were dealt with in this study.