Defects induced by the welding procedure are recognized to be important factor for the joint strength . In the previous report, we described the experimental results and fracture analysis on brittle fracture in the butt joints with edge through thickness defects. There the observed strength of notched specimens by electric discharge cutting is lower than the expected value. This report discusses the relevant analysis on the above phenomena, attributing degradation of fracture toughness caused by NC gas cutting process.

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In the Electroslag welding (ESW) joint used for high-rise buildings, under large earthquake, it is worried about an early brittle fracture in the tip of a slit between a skin plate and a backing strip. In order to grasp the relationship between the toughness of the ESW joint and the fracture strength, material testing, tensile loading test of partial model and analytical study by FEM were carried out. The conclusion of this study can be summarized as follows; 1) the brittle fracture in the elastic range of joint is generated from the HAZ section of skin plate; 2) the brittle fracture after plastic behavior is generated from the welding metal and the joint showed sufficient strength; 3) in comparison with FEM analysis and the test results, a starting point of fracture can be presumed by considering the critical stress of cleavage fracture.

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Steels manufactured in around 1920 contain more sulfur and phosphorus comparing with present steels contain. Steels used in a bridge for a long term were welded by using a general filler wire, no defects or cracks occurred without dealing with special treatment like as pre-/post-heating. The welded joints with steels used for a long term had enough mechanical properties comparing with SM400A welded joints had. In the welded joints with steels used for a long term, Charpy absorbed energy was the smallest in the base metal. Brittle fracture percentage of the base metal was extremely high comparing with that of SM400A. Even if welding was used for joining in repair/reinforcement on the existing steel bridges, there were no problems in the welded joints. It was rather necessary that the base metal should be much noted.

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Surface profile of structural members sometimes gives valuable information to estimate mechanical behavior of existing structures. In this study, based on stereography technique, a simple method to measure the surface profile was developed, and apllied to a corroded steel plate surface. The method gave good results even for corroded steel plate surface which has few image patters and characteristics. The accuracy of the method was also discussed on the results for a variety of system conditions, such as camera position and camera resolution.

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This paper discussed fatigue characteristics of steel pipe structure with gusset plate connection in which branch tube axis is eccentric for the main tube axis. The authors conducted the static experiment in order to ask for the buckling strength of a main tube as past research using the test specimen that consists of a main tube and a branch tube. On the basis of the past researches, this experiment performs low-cycle repeat loading to a branch tube while carrying out loading of the fixed load to a main tube. Based on this study result, the stress behavior and fatigue characteristics of the main tube of steel pipe structure that have the eccentric joint were clarified.

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In a steel framework, composing beam-to-column connections with only bolt connections is one of the possible way to avoid brittle fracture in weld connections under strong earthquakes. In this study, cyclic loading tests of subassemblage frames including H-section beam-to-H-section column bolted connection are performed, and the semi-rigidity of the beam-to-column connection, which is caused by out-of-plane deformation of plate element in H-section member, is chiefly investigated. Reinforcing effect of doubler plates at column web attached with high strength bolts is also investigated.

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In this research, high strength and high ductility long bolts with waisted shank are applied to the semi-rigid column anchor connection as a type of long bolted tensile connections. The mechanical behavior of the semi-rigid column anchor connection with the waisted shank long bolts is investigated by a FEM analysis considering the contact/non-contact behavior between the bottom base plate and the footing concrete. Discussed in the paper is the effect of the long high strength bolts with waisted shank on the ultimate strength and the behavior up to the ultimate state of the anchor connection of the column specimens subjected to bending. The performance of the column anchor connections with high strength bolts with waisted shank is compared with that of the connections with normal high strength bolts. The connection with high strength bolts with waisted shank can increase the ultimate horizontal displacement of the top of the column specimens with this type of anchor connection and improve energy absorption capacity due to the high deformability compared with the column specimens with the anchor connection by normal high strength bolts.

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Loading tests are carried out using prestressed steel box girder model with external cables to confirm the propriety of structural design of long spanned architectural structure prestressed by external cables. The tests are performed for four girder models, which have different supporting system and loading pattern. It is found that the test results show sufficient bearing capacity. The test results are compared to the numerical results obtained by the beam theory and the calculation method based on the infinitesimal theory using beam and cable element.

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By Japan Bridge Standard V, bridges must be installed aseismic strengthening systems for earthquake level II. Aseismic strengthening systems are representative connected to the main girder by high tension bolts. Bridges must be strengthened for transmitting the earthquake force smoothly and keeping their damage minimum. When we design strengthening structures. we meet with some difficulties. that are the installation means. joints of strengthening beams, a relation between earthquake force and strengthening structures. In the case of a box girder. such difficulties are remarkable because aseismic forces are large . In this paper. strengthening brakets and beams for a box girder of existing urban highway bridges are designed . then, FEM models are made up and FEM analysis results are discussed.

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This paper proposed new type steel plate floor girder, as the bridge for rebuilding. This new type bridge is taking in for the steel plate floor of CT-shaped ribs and using section steel for all steel materials other than a deck plate. And this structure, the longitudinal joint of bridge was joined the adjoined angle steel web with the high-strength bolt in the deck plate lower part. This attained curtailment of manufacture cost and labor saving of local construction. And the static loading test was conducted about proposed steel plate floor girder, FEM nonlinear analysis was carried out simultaneously. Those results understand nonlinear characteristic of the structure of proposed steel plate floor girder and checked the structure performance as a highway bridge, and proposed the design technique of the high strength bolt connection. This paper proposed new type steel plate floor girder, as the bridge for rebuilding. This new type bridge is taking in for the steel plate floor of CT-shaped ribs and using section steel for all steel materials other than a deck plate. And this structure, the longitudinal joint of bridge was joined the adjoined angle steel web with the high-strength bolt in the deck plate lower part. This attained curtailment of manufacture cost and labor saving of local construction. And the static loading test was conducted about proposed steel plate floor girder, FEM nonlinear analysis was carried out simultaneously. Those results understand nonlinear characteristic of the structure of proposed steel plate floor girder and checked the structure performance as a highway bridge, and proposed the design technique of the high strength bolt connection.

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