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- 검색키워드
- 저자 : Katashi Fujii (검색결과 3 건)
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Naoyuki Asao,Katashi Fujii 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.10
In Japan, many steel railway bridges were constructed during the period of rapid economic growth in the 1960s. Now, as over 50 years have passed, the condition of these aging structures has become conspicuous, and a major social problem. In particular, the deterioration and damage due to corrosion in steel plate girder railway bridges with open deck system is becoming pronounced. Nevertheless, the remaining strength evaluation and the methods of reinforcing corroded structures are not always sufficient. Therefore, the purpose of this study is to propose an analytically-based evaluation method, and a reliable measure of reinforcement in the field of steel railway bridge maintenance. The following is noted: 1) Regarding the shear capacity of plate girders with corrosion near supports, the remaining strength depends on the condition of the corroded surface of each component of the member, such as a web or a vertical stiffener. Also, according to the form and degree of corrosion, the fracture mode also changes from the buckling of web to the buckling of cross-shape columns which consisting of the web and vertical stiffener. The result shows that the corroded web has more effect on the shear capacity than the vertical stiffener. 2) Regarding situation of separation between the web and bottom flange due to corrosion near supports, the remaining strength is found to deteriorate more rapidly than in the Case 1 above when the separation area lengthens to more than that of the sole plate area. 3) To enhance the remaining shear capacity in the Cases 1 and 2 above, the load bearing capacity can be improved dramatically by unsophisticated attachments applied as reinforced members.
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Remaining Strength Estimation Methods of Plate Girders with Corrosion and the Practical Evaluations
Naoyuki Asao,Katashi Fujii 대한토목학회 2019 KSCE Journal of Civil Engineering Vol.23 No.1
In steel plate girder railway bridges with open deck system, damage caused by local corrosion of the upper flanges under sleepers is well-known. This damage reduces ultimate strength of the main girders significantly (e.g., in the case of 50%-corroded upper flanges, approximately 30 percent reduction in bending strength). This paper presented a simple evaluation method for estimating the remaining strength of the plate girders that have local corrosion damage under sleepers. Remaining strength of the damaged plate girders can be calculated by taking into account both the remaining strength for local load (hereinafter referred to as “patch load”) that acts directly on the upper flanges under the sleepers, and the remaining strength for bending load that acts on the main beam itself. This new evaluation method using the equations proposed in this paper, is based on the idea that the remaining strength under pure bending load can be obtained as the minimum value of strengths calculated in light of the various buckling modes of the compression flange, while taking the thickness reduction due to corrosion into account. Thereafter, the remaining strength under patch load only can be calculated by using an equation which is further simplified based on Takimoto’s original equation. Finally, the remaining strength of the plate girder as a whole is obtained from the strength interaction curve between patch and bending loads. In addition, by comparing the estimated remaining strengths obtained through this method with those obtained from nonlinear Finite Element Method (FEM) analyses using full-scale beam models, it could be concluded that the simple evaluation method by using both new and original equations can estimate the remaining strength of plate girders with corroded flanges under sleepers with around 95 percent accuracy.
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An enhanced method of predicting effective thickness of corroded steel plates
Tatsumasa Kaita,J.M. Ruwan S. Appuhamy,J.M. Ruwan S. Appuhamy,Katashi Fujii 국제구조공학회 2012 Steel and Composite Structures, An International J Vol.12 No.5
Many steel bridge infrastructures in the world are getting older, and a large number of these structures are in need of maintenance, rehabilitation or replacement. Most of them are subjected to corrosion due to exposure to aggressive environmental conditions and inadequate maintenance, causing reduction of their carrying capacities. In order to have an adequate bridge management, it is of paramount importance to develop an efficient, accurate and rapid condition assessment method which can be used to make reliable decisions affecting the cost and safety. Therefore, a simple and accurate method of calculating remaining yield and tensile strength by using a concept of representative effective thickness with correlation of initial thickness and maximum corroded depth is proposed in this study, based on the results of many tensile coupon tests of corroded plates obtained from a steel plate girder with severe corrosion, used for about 100 years. Furthermore, a strength reduction diagram which will be very useful for bridge inspection engineers to make rational decisions about the maintenance management of aged steel bridge infrastructures is presented.
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