Robinson type composite deck, in which concrete and a base steel plate stiffened with transverse ribs are connected by headed studs, is a typical and major one among composite decks in Japan. Through the past fatigue tests for the composite decks under running wheel load, fatigue failure of the studs was confirmed to be an important phenomenon and to be designed based on reasonable fatigue data. Then the fatigue tests on an isolated stud by giving rotating shear force were carried out and a fatigue design method was proposed in 1997. Shortly afterwards, fatigue test machine giving a rotating shear force was improved and new fatigue data were obtained. Furthermore, welding method of the stud was also improved to increase fatigue life by improved welding ferule. The new data with the improved ferule have shown about 3 times longer fatigue lives from the ordinary ferule.
 In this study, analytical investigations were carried out on two points. The first one is to get a reliable fatigue design method of the studs in the composite deck on the relation between the fatigue data of studs in a composite deck under wheel running machine and the S-N data of studs obtained from the recent rotating shearing fatigue tests on isolated stud. The second one is proofing the fatigue life elongation by changing welding methods using new ferule from the ordinary one. The both analytical investigations are based on the shearing stress analysis at the welding boundary of welded stud and a base steel plate. Three dimensional FEM analyses were carried out with detailed modeling of the welded collar shape and the above mentioned numerical investigations were obtained with the higher reliability.

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 With the earthquake records obtained during the last 23 years, analyses of the transfer function, the cross spectrum and the coherence function have been carried out for a rockfill dam, called Aratozawa dam (74.4m high and with central clay core). Based on analysis results the fundamental frequencies and acceleration amplification factors of the dam body are investigated. It is found that the fundamental frequencies and the acceleration amplification factors of the dam body sharply declined temporarily, shuck by the Iwate-Miyagi Nairiku Earthquake, June 14, 2008. However, these characteristics almost recovered to their original status about a week after the main shock. As for the propagating behavior of the seismic waves in the dam-foundation system, it has been pointed out that in the low frequency domain up to the fundamental frequency of the dam, the response of the dam crest mainly depends on the seismic motions of the lower bedrock. On the other hand, in the higher frequency domain, the contribution from the seismic motions of both banks may become dominant at some frequencies. It has been also found that such features temporarily changed due to the mentioned strong earthquake.

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 Carbon fiber reinforced polymer, CFRP, plates bonding method for cracked steel structures is one of the new repair methods. In this study, to evaluate the extended bending fatigue life of out-of-plane gusset joint by plate bonding, stress intensity factor (SIF) of cracked steel plate and that of cracked out-of-plane gusset joint by plate bonding was calculated by finite element and simple calculation based on linear fracture mechanics. Furthermore, bending fatigue tests of out-of-plane gusset joint were carried out, to reveal the extended bending fatigue life by bonding CFRP plates. Finally, crack propagation analysis was conducted and the extended bending fatigue life by bonding CFRP plates was estimated. As the results of the crack propagation analysis, the estimated fatigue life of cracked out-of-plane gusset joint repaired by bonding CFRP plates was good agreed with the fatigue life given by the tests.

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 In plate girder railway bridges with open deck system, the local corrosion on the upper flange under sleepers is well-known as a typical damage, which makes the ultimate strength decreases significantly. This paper presents a simple evaluation method for remaining strength of plate girder with local corrosion under sleepers. The remaining bending strength can be obtained as the minimum value among the strengths based on the several buckling modes of the compressive flange. Then the remaining strength of the plate girder is finally obtained by the interaction curve between ultimate patch-load strength and the bending strength. Comparing with the remaining strengths both of loading tests and nonlinear FEM analyses, it can be concluded that the method proposed herein can evaluate the remaining strength of the corroded plate girder reliably.

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 For the maintenances of high strength bolted connections in actual steel bridges, it is required to clarify the relationship between corrosion behaviors of individual parts of fastener and slip resistance. This paper presents a study on relationship between corrosion behaviors of spliced plates and slip resistance. In this study, firstly the corrosion behavior is inspected using the corroded spliced plates which were cut off from the steel bridge girder removed. Moreover, the pressure distribution tests under the axial force of a high strength bolt and various tensile tests are performed on those corroded specimens.
 From the test results, it can be clear that the yield of back side of a bolt hole, i.e., the side subjected to compression force in the bolt hole and slip resistance correlate closely with each other. Moreover, the diagnostics for corroded spliced plate of friction type of high strength bolted connections are proposed.

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 The steel plate bonding method has been widely adopted as a reinforcing method for deteriorated and damaged RC structures. This research presents a technique for the quantitative estimation of the thickness of water layer stagnated on the upper surface of a steel plate, debonded from a RC slab structure due to bonding re-degradation. The proposed technique is a non-destructive inspection which utilizes ultrasonic guided waves on the bottom side of a steel plate. The verification of the proposed technique has been conducted via the comparison of the results between the theoretical analysis and the experiments. In the verification, we examined various combinations for thicknesses of steel plate and water layer, considering not only the steel plate bonding slab but also a steel plate-concrete composite slab and a concrete filled I-beam grid deck, whose bottom surfaces are also covered with steel plates. The comparison provides a good agreement between the theoretical solutions and the experimental results and concludes that our proposed technique is a promising nondestructive testing for the detection and evaluation of the water ponding on the upper surface of the steel plates.

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 For the joints with zinc-aluminum alloys sprayed surfaces, hot-dip galvanized bolts are applied and such bolts are tightened by turn-of-nut method. However, it is unclear how much axial force is induced into the bolts in the joints with this metal-sprayed surfaces. In order to examine slip coefficient of the bolted joints with zinc-aluminum alloys-sprayed contact surfaces slip tests of high strength bolted joints were carried out. On the basis of above examinations, the slip coefficient with this metal-sprayed surfaces is proposed in this paper. To clarify the induced axial force of the bolts, bolt-tightening tests were carried out. Considering bolt diameter, bolt length, induced axial forces and their relaxation, nut rotation angles are proposed in relation to different bolt size.

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 This study proposes a failure mechanism and a method for evaluating the flexural response of RC beams subjected to close-in explosion to develop a safety assessment method and protective design of structure subjected to explosive loads. First, to examine the spatial distributions, explosion tests were conducted with C-4 explosives. Approximation formulae for the spatial distributions of the peak over-pressure and impulse were proposed by using the variables of explosive mass, stand-off distance, and target member length. Secondly, close-in explosion tests on RC beams using C-4 explosives were conducted. The measurement parameters were pressure acting on the beam, maximum and residual displacements at the center of the beam, strain of the lower longitudinal reinforcing bar, and reaction force. The failure mechanism of RC beams subjected to close-in explosion was examined. Finally, the method for evaluating the flexural response of RC beams considering the blast load distribution owing to close-in explosion was proposed.

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 In this study, a power generation type TMD with electromagnetic damping device is newly proposed. By applying electromagnetic damping device, damping characteristics can be easily adjusted only by changing resistance, and in addition, the TMD with the electromagnetic damping device can generate electric power during the vibration energy absorption. In this study, considering an actual bridge condition, characteristics of electromagnetic damping device under different levels of resistance were investigated through experiments and simulations. Based on the results, a power generation type TMD was developed by exchanging oil dampers to the electromagnetic damping devices, and was applied to an actual expressway bridge to examine its performance of vibration energy absorption and power generation.

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 The effects of partial fairings on reducing hydrodynamic forces on bridges during tsunami or flood were studied. Covering the entire sides with fairings is difficult under some circumstances, especially at the bridge ends because of the complexity of the work required. Therefore, this study conducted hydraulic experiments and numerical simulations to determine an effective fairing-covering ratio. The results show that fairings are effective to reduce drag, but have limited effect on reducing lift depending on the wave height. Further, fairings that cover more than half the width of the bridge can reduce drag and lift, and a fairing that covers 75% of the width of a bridge model exhibits a similar reduction as a full width fairing. However, a 25% width fairing results in a low reduction in tsunami-induced forces.

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 Laminated rubber bearings are the most major devices for base-isolation of buildings and bridges. This paper presents a 2D mechanical model of laminated rubber bearings based on the wildly-used 1D bi-linear elasto-plastic model. At fist, the 1D bi-linear model is extended into 2D one through the classical plasticity theory, and its numerical algorithm is also developed. Then, the 2D bi-linear model is complemented by adding two hardening functions and one damage function, in order to express typical mechanical behavior of the bearings such as hardening and Mullins' effect. Finally, bi-axial loading experiments of a small high damping rubber bearing are conducted, and their results are compared with the proposed model. As a results, it is found that the model can well reproduce the experimental results.

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 Lightweight orthotropic steel decks are widely used in the bridges of an urban expressway in Japan. However, it is observed in the existing bridges that fatigue cracks occur in the orthotropic steel deck. As a countermeasure of this problem, we have developed a light weight highway-bridge deck with high durability using ultra-high strength fiber-reinforced concrete (UFC). Developed UFC deck slab consists slab of 40 mm thickness and ribs of 83 mm in height. This deck slab has an extremely thin thickness as compared to that in the concrete deck slabs. Since UFC deck developed has very thin components as compared with conventional concrete decks, we validated the safety of this thin deck structure using finite element analysis. The bending stiffness of the UFC deck is smaller than that of the conventional deck. We also verified serviceability using the vibration test and the load test. The characteristic frequency and impact factor of the deck were calculated by these tests.

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 Lightweight orthotropic steel decks are widely used in the bridges of an urban expressway in Japan. However, it is observed in the existing bridges that fatigue cracks occur in the orthotropic steel deck. As a countermeasure of this problem, we have developed a light weight highway-bridge deck with high durability using ultra-high strength fiber-reinforced concrete (UFC). Developed UFC deck slab consists slab of 40 mm thickness and ribs of 83 mm in height. This deck slab has an extremely thin thickness as compared to that in the concrete deck slabs. We also verified its fatigue resistance and mechanical characteristic using the wheel running test. We verified from the tests that the fatigue resistance of the UFC deck and feasibility for its application. We conducted a wheel running test to evaluate the fatigue performance of the deck, in which a wheel load was applied 200,000 times (100,000 cycles), and the magnitude was varied from 100 kN to 220 kN. As the result, there was no damage under the design load. When a load roughly two times larger than the design load was applied, minor cracks were detected on the side faces of the ribs. However, there was no reduction of stiffness. We confirm that the fatigue resistance of the UFC deck is sufficiently high.

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 The present study focuses on input loss of rigid-frame viaduct with pile foundations. It is well known that existence of pile foundation causes the input loss due to the effect of the kinematic interaction between soil and pile. Higher effect of input loss is expected for such a rigid-frame viaduct, because the rigidity for out-of-plane direction of the girder and beams would restrain the behavior of free field along the longitudinal direction. Though the input loss effect caused by the entire viaduct system has not been well known yet. Therefore, the characteristics and evaluation method of input loss of the rigid-frame viaduct with pile foundation are investigated in detail.

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 Over the last decade, fatigue cracks have been observed at welded joints between trapezoidal ribs and deck plates in many orthotropic steel deck bridges in Japan. Considering a fatigue crack at rib-to-deck welded joints can cause pavement damage and thus compromise transportation safety, it is necessary to detect and repair it at the early stage of its development.
 This paper presents the accuracy of crack sizing with an electrically driven phased array ultrasonic scanner (PAUT scanner) developed for inspection of rib-to-deck welded joints in orthotropic steel decks. The PAUT scanner simultaneously examines a deck plate and a weld bead into either of which cracks propagate from a weld root. Moreover, it can detect the cracks as remained in the steel members.
 In this research, firstly an internal crack is induced at rib-to-deck welded joints by using a plate bending fatigue testing machine where crack sizes are controlled by monitoring stresses at regions closed to weld beads. Subsequently, the joints are inspected with the PAUT scanner. Appropriate sizing methods are determined for the crack going through a deck plate and a weld bead, respectively, and the accuracy of crack sizing is evaluated by comparing with real cracks on the joints. In addition, the influence of paint coatings on the accuracy in crack sizing is examined. As a result of these investigation, it is demonstrated that the PAUT scanner has enough crack sizing performance.

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 There are many corrosion damaged bridges in cold or snowy districts because deicing salts are spread to prevent freeze on road. The amount of spread deicing salts has increased every year since the use of studded tires was prohibited in Japan. Corrosion due to scatter of deicing salts are reported on parallel bridges with different height of the road surface and/or on bridge close to the ground in Japan. However, it has not been clear enough that the influence of scattered deicing salts on the corrosion of steel bridges. In this paper, the relation between the amount of spread deicing salt and adhered salt to girder is observed, and the relation between scattered salt and corrosion of test piece using weathering steel is observed. Furthermore the evaluation of applicability of weathering steel bridge in spread deicing salt are is discusses.

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