A study on improvement of corrosion environment of a steel plate girder bridge by installing metallic sandwiched panel

金属サンドイッチパネル設置による鋼鈑桁橋の腐食環境改善に関する研究

A study on improvement of corrosion environment of a steel plate girder bridge by installing metallic sandwiched panel

Degree Grantors Yamaguchi University

With the deterioration of bridges as social infrastructure, appropriate maintenance and life extension are required. However, aging degradation of individual bridges is not the same. Since traffic volume and bridge environment are different for each bridge, the degree of deterioration of the bridge is also different. Therefore, it is necessary to identify and eliminate the cause of individual deterioration and to take appropriate measures.
This paper focuses on weathering steel bridge that the formation of dense rust is greatly influenced by the environment. The purpose of this study is to clarify the effect of anticorrosion by the environmental improvement which covers the whole steel girder with the metal sandwich panel for weathering steel bridge. Since the space in the girder covered with the metal sandwich panel cannot be expected to have the effect of washing by rainwater or drying and wetting by the flow of wind, the adoption of the metal sandwich panel for weatherproof steel bridge has not been judged until now. In this thesis, the corrosion behavior of weathering steel and the effectiveness of corrosion protection are shown by exposure test, and the corrosion protection effect of environmental improvement by metal sandwich panel is clarified. In addition, this study examines the economical advantages by the metal sandwich panel installation by calculating the life cycle cost.
This paper consists of six chapters.
Chapter 1 describes the background and purpose of this research.
Chapter 2 summarizes previous studies on corrosion protection methods used in steel bridges.
In Chapter 3, exposure tests were conducted inside and outside the metal sandwich panel and the following finding were obtained.
1) In the girder covered with the metal sandwich panel, fluctuation range of temperature and humidity is small throughout the year, and it does not follow the sudden weather change of outside of the panel. Since the difference between the temperature and dew point in the panel is large, the wet time in the panel is suppressed to 1/5 or less of the wet time of outside the panel.
2) At the structure which has thin floor slab and low height girder, the temperature rise in the panel may be unavoidable depending on season. However, since the humidity in the panel is low and the wet time is also greatly reduced, the anticorrosive effect can be expected in the steel bridge including the weathering steel bridge.
3) Amount of air born salt into the panel after the metal sandwich panel installation was not detected.
In Chapter 4, a small test specimen was placed in the inside space of the steel girder, and the transition of corrosion, anticorrosion effect by environmental improvement and inner surface painting were examined.
1) The untreated steel and the uncoated steel in the ingrown rust region evaluated by the ion permeation resistance method are kept almost same condition after five years.
2) It is also conceivable that the initial salinity of the steel material subjected to the substrate adjustment by blasting exists even after the substrate adjustment, and that the adhering salinity penetrates into the inside of the steel plate at the time of rust formation. However, the increase rate of rust thickness due to aging is slow, and a method of installing a metal sandwich panel after blasting is also effective.
3) Although the effect of environmental isolation from outside the girder was confirmed, it became clear that it was difficult to completely suppress the progress of rust.
Chapter 5 examined the economic effects of installing metal sandwich panels on new girders from the beginning and installing them on overbridges 50 years after the star of service.
1) If repainting is required even 1 time during the during the design service period of 100 years, the anticorrosion method by environmental improvement of the metal sandwich panel is economically superior.
2) Accumulating the cost of close visual inspection (for 50 years) of the overbridge that has been in service for 50 years increases the maintenance cost.
Chapter 6 summarizes this research and describes future issues.

Creators Tachibana Shuusaku