During the Kobe earthquake, unexpected brittle fracture was occurred in a corner of steel bridge bent. In this study, based on the temperature rise which was obtained from elastic-plastic FEM considering heat transfer and the transition temperature shift of critical CTOD curve due to the strain rate, dynamic loading effect on the fracture origin during the earthquake was estimated. As a result, it was shown that, the effect of dynamic loading acted to inhibit the brittle fracture because amount of rise in temperature exceeded that of transition temperature shift due to the strain rate. Besides, it was confirmed that, even if it was affected by the effect of dynamic loading, brittle fracture could be occurred by the effect of strain history.

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 In general, designing a structure that minimizes a total cost, including not only construction but also repairing costs after severe earthquake, requires considerable number of calculations in a trial-and-error basis. In this research, a new design nomograph that gives combinations of demanding natural period, ductility and yielding coefficient in view of minimizing a total cost of structure is proposed by means of nonlinear numerical simulations. It is clarified through comparison of the nomograph and current design spectra based on past earthquake records that the structures comply with current design code meet the demands of preventing severe damage and minimizing the total cost simultaneously.

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 Rocking behavior of unfixed body is affected by center of mass, material coefficient of restitution and so on. 2/5 scale metal cask model considering these parameter was used for seismic test to evaluate stability of grounding metal cask attached to a transfer pallet under the influence of long-period earthquake motion.
 The newest knowledge from seismic test indicates seismic motion with high velocity over 100 kine not always cause the raise of response velocity of metal cask because of energy consumption by cask sliding and impact deformation of concrete. And new estimation method (called "Window energy spectrum method") of earthquake response spectrum gives suitable evaluation of response energy.

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 The ultimate strength of aluminum alloy plates in in-plane bending is investigated considering joining locations and plate width by the elastic-plastic large deflection analysis with FEM. The aluminum alloys taken into account are heat-treated A6061-T6 and A6005C-T5 and non-heat-treated A5083-O. The softening of material and the residual stresses caused by the friction stir welding (FSW) and the MIG welding are introduced in the analysis. It is shown that the joining locations and the width of plate have a great influence on the ultimate strength. The formula which gives the curves for the ultimate strength of plates in in-plane bending considering joining locations and plate width are proposed, based on the results of the FEM analysis.

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 Recently, various metallic coating systems have been adopted for steel bridges. In order to examine the performance of repaired painting on steel plates with four types of deteriorated metallic coating systems, acid rain combined cyclic corrosion tests were performed. The four types of metallic coating systems were zinc hot dip galvanized coating, zinc-aluminum alloy coating, zinc-aluminum pseudoalloy coating and aluminum coating. The effect of remaining thickness of metallic coating on the performance of repair paint was discussed. Finally, the lifecycle cost analysis was performed for various repair strategies for the four types of metallic coating systems.

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 Continuous composite girders with pre-cast concrete slab have the advantages on rationality of structure, economical efficiency and short construction period. However, the configuration of shear studs in a pre-cast concrete slab segment is considerable restricted in comparison with standard in-site concrete slab owing to structural limitation of the pre-cast segment. In this paper, behavior of shear connectors which connect steel girder with pre-cast concrete slab is discussed. Push-out tests of shear connectors and bending tests of composite girders were carried out. Furthermore, finite element analyses were conducted to verify the test results. According to the tests and analyses, it was shown that longitudinal spacing of studs can be expanded than that based on conventional design.

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 In this research, additional welding with low temperature transformation welding material and improvement method which combined cleaning treatment with a grinder and hammer peening treatment have been investigated. The improvement effect is clarified from the fatigue test of girder specimen with the out-of-plane gusset plate. Although the improvement effect by peening treatment varied, the fatigue strength at weld toe of out-of-plane welded joint increased to more than D class. The improvement effect by the additional welding decreases since the compressive residual stress on the front side is lost due to the additional welding on rear side. When using maximum principal stress range for structural hot spot stress range, the effects of shear stress and the difference of stress concentration on fatigue strength improvement can be considered.

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 The objective of this study is to understand the relationship between damage and the change of dynamic characteristics in an existing bridge for vibration-based structural health monitoring. Focused bridge is a demolished pedestrian bridge, which is a composite steel girder with two main girders. The first damages are slits by gas cutting, which are given to a lower flange in the lateral direction. Then, outstanding plate in the lower flange is removed along the span. Vibration measurement was carried out in each damage case. As a result, it was confirmed that natural frequencies decreased depending on the progress of damage. Its reduction rate was greater in the modes without torsion. For reproducible analysis, spectral element and finite element analyses were carried out. Analytical results also showed the similar reduction of natural frequencies to measurement.

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 In this study, the heavy vehicle with excitation system that can control its axle forces passed over a bridge associated with a cargo and a passenger's vehicle to evaluate the vibration transfer between the bridge and vehicles. As a result, it was found that when the bridge vibrates on some level at a frequency close to cargo's eigenfrequency, dominant frequencies corresponding to those found in the bridge vibration can be also found in the cargo vibration. As for the passenger's vehicle, its vibration behavior was complicated due to high sensitivity of road roughness and it was difficult to find the frequencies corresponding to the bridge vibration in the vibration of passenger's vehicle.

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 This paper presents failure mechanism of the scabbing of concrete plates subjected to high velocity impact and effects of fiber sheet reinforcement. Prior to impact tests, strain measurement method using acrylic bar with strain gauges is validated by conducting impact test to concrete bar specimen. Then, impact tests are carried out to examine the failure mechanism of scabbing of concrete plates. In the tests, the strain measurement method is applied and strain behavior inside the concrete plate is discussed. After that, impact tests of fiber sheet reinforced concrete plates are conducted. Based on failure mode and strain behavior, effects of fiber sheet reinforcement on the failure of concrete plates are examined.

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 The Japanese design specifications of guard fences were revised in 2004. Since this revision, it has been regulated to improve the choking rate from vehicles, and also to satisfy the requirements of the design specifications, a new bridge railing guard fences are designed. This study verified that the impact performance of the fence posts of new bridge railing guard fences satisfied the performance requirements of the design specifications. By comparing the new and existing types of fence posts, it was quantitatively verified that the fence posts of new types absorbed the impact energy by the lateral-torsional buckling behavior at the compression parts, and had better shock-absorbing properties than the fence post of existing types.

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 Slip coefficient of high-strength bolt friction joints is well known to depend on the condition of contact surfaces. The coefficient is determined as 0.4 in the Specifications for Highway Bridges and the Design Standards for Railway Structures and Commentary (Steel Structures) in Japan, in the condition of roughened contact surfaces with mill scale removed or painted contact surfaces with inorganic zinc rich paint. However, the slip coefficient with metal-sprayed surfaces is not clear. For the joints with metalsprayed 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 metal-sprayed surfaces. In order to examine slip coefficient of the bolted joints with metal-sprayed contact surfaces slip tests of high strength bolted joints were carried out. On the basis of above examinations, the slip coefficient with 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 paper studies the earthquake response of steel portal frames when the shear collapse occurs at the centre of the beam. The pseudodynamic simulation technique for the earthquake response analysis of the frames is developed in correspondence to the pseudodynamic substructure testing method. For the thin-walled box element under shear force in the middle of beam, the numerical process is utilized by a general-purpose finite element analysis program. The numerical results show the shear collapse behaviour in stiffened box beams and corresponding restoring force - displacement relationship of frames. The advantages of shear collapse of beams for the use in frames during earthquakes are discussed from the point of view of the hysteretic energy dissipated by the column base.

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 Fatigue cracks have been recently reported at weld root of deckplate-U type rib connection in orthotropic steel deck bridges on heavy traffic route. These cracks propagate to the upper surface of deckplate, that makes it difficult to detect them during visual inspection. With the purpose of developing a reliable and practical non-destructive inspection method for the cracks, this paper discusses an ultrasonic testing method using SV waves by critical angle beam probe. A reliable technique for the sensitivity calibration was proposed. Based on ultrasonic testing for fatigue crack specimens and a damaged deckplate on actual bridge, applicability of the proposed ultrasonic inspection method was confirmed.

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 Recently, the construction number of steel girder bridge using thick plates has been increasing. It is afraid that residual stress in the thick plates affects the load carrying capacity of the girder. Therefore, this study aims to measure the distribution of residual stresses in the thick plates by mechanical cutting method. Herein, simplified measurement method is proposed for the measurement in the thickness direction. As a result, it was found that the slope of stress distribution in the thickness direction becomes large as the thickness of the plate increases. Then, after considering the equilibriums of residual stress three-dimensionally, the residual stress was introduced into a finite element analysis model, which is the modeling of an existing bridge at the intermediate support. It was confirmed that residual stress in the thick plate does not affect the load carrying capacity of steel girder in bending.

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 A perfobond strip is generally used as the shear connector in the various steel-concrete hybrid structures and a few design formulas for evaluating the shear resistance of the perfobond strip are proposed. However, these design formulas are not always applicable to the one employed in the steel-concrete rigid frame bridge, since the formulas are established based on the standard push-out specimen for the stud shear connector in which some cracks may occur in the concrete block of the specimen during the test. In this paper, the shear resistance of the perfobond strip are examined experimentally by employing the simple push-out specimen different from the standard one for the stud shear connector. As a result, the design formula is proposed for evaluating the shear resistance of the perfobond strip taking into account the proportion of the concrete block as well as the perforation size and the concrete compressive strength.

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 Salt is known to accelerate the corrosion of weathering steel bridges. The origin of salt around girders is valuable information in terms of the maintenance for anti-corrosion of steel bridges. Salt around girders generally originates from sea-salt and deicing salt. Since salt of both origin increases in winter, contribution of deicing salt is hard to be estimated only from fluctuation of total abundance of salt around the bridge. In this study, abundance of Mg²⁺ as well as that of Cl^- in salt sampled under bridges is analyzed. As a result, this study revealed that the supply of deicing salt declines Mg²⁺/Cl^- ratio of salt on the girder. In addition, examination of Mg²⁺/Cl^- ratio of salt sampled under the examined bridge near sea revealed that the fluctuation of quantity of air-born salt under the bridge is ascribed to the fluctuation of supply of sea salt.

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 Many weathering steel bridges has been constructed due to its advantage in Life Cycle Cost. With the expansion of number of weathering steel bridges, occurrence of corrosive rust on weathering steel has been reported in recent years. However, repair technique of corroded weathering steel is not established yet. At the time of repair painting, ablation of the adherence rust and the adherent salt on surface of weathering steel will become major problem. This paper propose a flow of repair painting for weathering steel bridges based on Rc-I painting method that was established to painting bridges. By the results of aplication of this flow to on site repair, availability of proposed method was confirmed.

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 Enormous damage occurred to the fishing port facilities and natural slopes behind the port in Genkai Island during the 2005 west off Fukuoka prefecture earthquake (M_J7.0). The evaluation of the strong seismic motion is very important to clarify the failure mechanism. In this study, seismic waveform at this site was estimated based on empirical site amplification and phase effects. The estimated seismic waveform is useful in the detailed study of seismic performance evaluation.

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 Many landslides occurred in the near-source region of the 2007 Niigataken Chuetsu-oki Earthquake. A large scale landslide and disaster occurred in Oumigawa, Kashiwazaki City. Therefore, to clarify the landslide mechanism, it is necessary to estimate strong motions at the landslide with sufficient accuracy, taking into account site effects. In this study, seismic waveform at the landslide was estimated based on site-effect substitution method. The site effects at the landslide were evaluated based on newly conducted seismic observation near the landslide. Difference of the site effects between the landslide site and the permanent observation stations was indicated.

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 Rational and efficient management is required for maintenance of infrastructure stock. In this study, the stock management model based on linear feedback control system theory, previously proposed by authors, is extended to include the effect of preventive maintenance. Optimization of preventive maintenance to minimize cost for target stock condition level is studied based on this model. Preventive maintenance is found to be more important when requirement for stock condition is higher. Also, the model is applied to corrosion and painting of steel bridges, and optimization of maintenance strategies is discussed.

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 The 2008 Wenchuan earthquake with a surface wave magnitude of 8.0 induced numerous landslides along the Longmen Mt. zone in Sichuan Province of China. The authors investigated into various influential factors on the slope stability of 119 landslides in Wenchuan prefecture, such as horizontal peak ground acceleration, slope angle, slope height, rock materials and geological structures. The authors developed hanging wall and footwall's acceleration attenuation formulae from 115 seismic stations and the formulae confirmed hanging-foot wall effect had notable influence on landslide distribution density and occurrence probability. The results of multivariable analysis clarified that slope height, horizontal peak ground acceleration and geological structures were more influential to sliding area and volume than slope angle and rock materials. Furthermore, the authors discussed the effectiveness of reinforcements on the slope stability and showed that anchor cable, frame beam and soil nailing wall had good anti-seismic property, however, shotcrete with bolts had limited ability to enhance slope stability during the earthquake.

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