首都大学東京, 2015-09-30, 博士（工学）, 甲第582号首都大学東

Nguyen Xuan Tung

首都大学東京博士（工学）首都大学東京, 2015-09-30, 博士（工学）, 甲第582号doctoral thesi

グエン, シュアン トウン

16700

Nguyen, Xuan Tung

Tokyo Metropolitan University Institutional Repository Miyako-Dori / 首都大学東京機関リポジトリ

  氏 名  NGUYENグ エ ン XUANシ ュ ア ン TUNGト ウ ン 所     属  都市環境科学研究科 都市環境科学専攻 都市基盤環境学域 学 位 の 種 類   博士（工学） 学 位 記 番 号   都市環境博 第 163号 学位授与の日付  平成 27年 9月 30日 課程・論文の別  学位規則第４条第１項該当 学位論文題名  Evaluation of the corrosion state of gusset-plate connections on  steel truss bridge and corrosion inspection recommendations  （鋼トラス橋格点部の腐食形状評価とその点検方法に関する研究） 論文審査委員   主査 教 授 野上 邦栄    委員 教 授 宇治 公隆    委員 准教授 中村 一史   【論文の内容の要旨】 In the world today, numbers of steel structures are increasing rapidly. In parallel with the new construction of steel structures, numbers of aging structures are also increasing recently. Japan is not an exception to this situation. In Japan, many steel bridges were built during the period of high economic growth from the 1950s to the 1970s, so the number of aging bridges in the country is now growing rapidly. With this rising number of bridges over 50 years old, there have been reports of serious corrosion damage, including the cases of the Kiso river bridge on National Highway Route 23 and the Honjo bridge on National Highway Route 7 in 2007. Around the same time, the Minneapolis I-35W truss bridge suddenly collapsed. Normally, in steel truss bridge, there is the damage tendency on its members and the connections between them. These damages detected when inspecting steel truss bridges and steel arch bridges is mostly corrosion of steel members or their connections. Sectional loss of the main structural members of a steel bridge may lead to the loss of structural integrity. It is clear that an evaluation method is needed for the health of steel bridges based on corrosion loss. Besides, in order to verify the safety of an entire bridge system, there is a need for an inspection and maintenance regime that evaluates the impact of such corrosion efficiently and properly. Up to now, numbers of research on investigation of corrosion state of gusset plate connection on the actual steel truss bridge, the effects of corrosion damage of connections to the ultimate strength of the whole structure are still a few. The purpose of this research is corrosion damage assessment by detailed corrosion measurement and corrosion state evaluation of gusset plates connections on actual steel truss bridge. The targeted bridge in this study is the Choshi bridge, a five-span cantilever steel truss bridge, crossed the estuary of Tone river. This bridge was removed in accordance with the opening of new bridge in 2009 after approximately 50 years of service. Due to the influence of salt attack, the corrosion damage occurred severely on every members of this bridge even the repainting was carried out several times in its service life. Moreover, during its service life, the diagonal members, the gusset plate connections, floor beams were reinforced and the lateral bracing was replaced. Besides, the corrosion also occurred severely at the transition areas and the bolt area because of stagnant water and the lack of coating thickness, respectively. The load carrying capacity and the earthquake resistance of the bridge also were decreased due to the corrosion damage on superstructure and concrete spall on the RC piers because of severe corrosion of inner reinforcement caused by water leaking. Because of the severe damage, the Choshi bridge was dismantled in 2009, with several parts (connections and diagonal members) were cut off for corrosion research. Furthermore, as part of the research effort to determine the influence of corroded connections on the ultimate strength of the whole bridge system, this study investigated crevice corrosion at contact surfaces on gusset plate connections, which has not been clarified until now. The 5 connections used in this study were cut from a dismantled Choshi steel truss bridge, the upper connections on the second span (P25d), the upper connections on the forth span (P51u), one upper (P73d)  and two lower (P72d and P72u) connections on the fifth span. Among these 5 connections, the crevice corrosion specimens were cut from two selected connections, P51u and P72u, for further evaluation of corrosion state at the contact surfaces. The contact surfaces of these specimens were measured in detail in order to clarify their corrosion states. This study focuses on the following main objectives: 1) to investigate the corrosion state of the five connections on the steel truss bridge; 2) to investigate the crevice corrosion state of the two specific connections; 3) to propose the corrosion inspection and maintenance guidelines for new and existing steel truss bridge.      This dissertation is composed of six chapters. Chapter 1 is the introduction that contains the background, motivation, and objectives of this study. A comprehensive review of literature and a description of the scopes and method were presented in this chapter. In chapter 2, the corrosion measurement devices and measurement method were presented.  In this chapter, the measurement methods were introduced, normally there are two methods, direct and indirect, and also their devices. For examples, direct method (contact with the specimen’s surface) uses resonance, ultrasonic, mechanical and electromagnetic devices, while camera and laser meter are used in the indirect method (in a distance from the specimen’s surface). In this chapter, the mechanical and electromagnetic devices were introduced in detail. Besides, as the indirect measurement, the newly-developed device, laser measurement equipment that was used for measurement on the whole research time was presented. In chapter 3, the corrosion states of the five connections were revealed. These five typical connections were selected on the five-span cantilever steel truss bridge (two connections on the second span and three remaining ones on the fifth span). In this chapter, the corrosion of five connections were measured in detail and then the corrosion depth profiles of outer and inner surfaces and several narrow surfaces of each connection were created. Besides, the corrosion state of the transition area between gusset plates and flange of diagonal member was also investigated in this chapter. Chapter 4 presents the crevice corrosion state of the two connections among the five ones that mentioned above. Since the corrosion state between the contact surfaces of connection has not been investigated previously, in this study, the two connections were prepared as specimens for study: the gusset plate was cut off from an upper connection, P51u,; and attached plates on a lower connection, P72u, that used for reinforcement by high strength bolts to satisfy loading capacity requirements during the service life of the bridge in 2002 were removed. These specimens were then measured using laser measurement equipment and evaluated in detail to clarify the actual state of crevice corrosion on these gusset plate connections and the reinforced area. Further, deformation of the rivets on to the tensile diagonal member of connection P51u was also evaluated. Chapter 5 summarizes the corrosion types in detail of the five connections in chapter 3, 4 Furthermore, the corrosion inspection and maintenance guidelines for new steel bridge and existing steel bridge were proposed.  Chapter 6 summarizes the research results and presents the overall conclusions of the thesis. 

Evaluation of the corrosion state of gusset-plate connections on steel truss bridge and corrosion inspection recommendations

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鋼トラス橋格点部の腐食形状評価とその点検方法に関する研究

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