Brittle fractures could occur from shallow surface cracks on welded parts of steel structures during earthquakes. Since the occurrence of that fracture is significantly influenced by the shape of the welded parts, the existing methods cannot predict the fractures. This study focused on a modified Weibull stress which considers the processes of nucleation and propagation of microcracks, and affirmed the applicability to evaluation of the brittle fracture initiation during earthquakes. Additionally, the relationship between critical deformation of a steel bridge bent corner to the fracture from a shallow crack and its weld toe radius was quantitatively evaluated as an example of actual use of the modified Weibull stress based evaluation.

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 A new type of post for the bridge railing has been developed using the extruded multi-hollow-type shape of aluminum-alloy to have the improved landscape and permeability. First, static tests and numerical analyses simulation have been performed using model posts made from aluminum alloy plate to determine the multi-hollow-type sectional dimensions. Then, extruded posts have been tested and analysed to prove the performance following the code for the design of the railing in Japan. The new type of post can be used for different strength types of bridge railing changing the width when cutting the extruded member.

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 In order to improve the quality of repair welding for existing steel bridges, the effect of residual stress relaxation of welded part by heat treatment with a sheet-type portable heater was investigated through the experiment and analysis on box welded out-of-plane gusset joints. The thermal history required for heat treatment was controlled with high accuracy. The welding residual stress around the yield stress could be relaxed by the heat treatment. The stress relaxation mechanism was elucidated by the thermal elastic plastic analysis considering the high temperature creep characteristics. The fatigue life in the low stress range (100MPa) of joints of which the residual stress was relaxed became twice as long as that of the joints as welded.

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 In I-cross-section of a steel bridge subjected to tensile stress, high strength bolted friction type joints with staggered bolts arrangement are often used. Because the effective cross-sectional area can be large at the outside section of the joint by using staggered bolts arrangement. In this study, an elasto-plastic finite element analysis for high strength bolted friction joints is conducted. The analytical parameters considered in this study are the bolt arrangement, the number of bolts in a line and a row, the ratio of the design slip strength to the design yield strength. The influence that these parameters give to strength and load transferring mechanism is discussed. Furthermore the design method of high strength bolted friction type joints with staggered bolts arrangement over 8 rows of bolts in a line is considered.

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 Three-dimensional dynamic cracking propagation analysis was conducted to evaluate seismic safety of concrete gravity dams with transverse joints. Analytical models were constituted by reservoir, base rock, dam body using smeared crack model and transverse joints, which have non-liner behavior based on Mohr-Coulomb's failure criteria. Crack pattern, crack propagation and failure pattern of dam body were discussed comparing with/without transverse joints. It was realized that crack propagation of the dam body with transverse joints is not spread more than without ones. Moreover, residual ligament height defined from crack propagation was introduced for index of earthquake-resistant safety concerning utilization of reservoir. The relationship between residual ligament height and input acceleration was investigated to evaluate seismic safety of concrete gravity dams with/without transverse joints.

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 To mitigate earthquake damage to highway bridges, many laminated rubber bearings were installed in Japan following the 1995 Great Hanshin-Awaji Earthquake. Recently, deterioration of these rubber bearings, which affects the seismic performance of the bridges, has been reported. However, an accurate assessment of damage to rubber bearings (for early warning) is difficult because of a rubber covering that interferes with checking inside.
 This study evaluates the acoustic emission (AE) method, a non-destructive test (NDT), for evaluating damage to these rubber bearings. Verification of the method was conducted by laboratory tests as well as field measurements. The AE activities and the parameters of the deteriorated bearings were compared with new ones. Many AE hits and a large amount of AE energy were observed from the deteriorated rubber bearings through the laboratory tests and the field measurements. On the other hand, few AE activities were observed from new bearings. Internal damage to deteriorated bearings was verified with microscopic observation of the cut plane after the loading tests. The results showed that internal damage to these rubber bearings can be accurately estimated using AE.

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 There are a number of examples of viaduct and normal bridge damaged seriously by fire accident in Japan, USA and other countries. Some of those bridges were fallen down by fire attack and self-weight of bridge. For these reasons, it is pointed out that the fire design for bridges should not be obligated in the design codes in such countries. For designing of steel concrete composite girder, the safety under the action of the normal force, shearing force, bending moment and their combination shall be confirmed at high temperature state. Therefore, in this paper, the interaction equations between bending moment (M) and shearing force (Q), normal compressive force (N) and bending moment (M), and N-Q-M are discussed and numerical results are reported.

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 A bridge vibration energy harvester has been proposed in this paper using a Tuned Mass Damper (TMD) system, named hereafter tuned mass energy harvester. To harvest and make use of the unused reserve of energy the aforementioned damper system absorbs, an electromagnetic transducer has been applied. To investigate the configuration of the tuned mass energy harvester considering performances of bridge vibration control and energy harvesting, single-mass and dual-mass systems where one or two masses are connected in series with the electromagnetic transducer and spring are proposed. According to the theory of vibrations and electric circuits, it has been clarified that dual-mass systems have several advantages over single-mass systems for power generation and vibration control. It has also been clarified that for effective energy harvesting or vibration control, it is essential to consider the power factor of electromagnetic transducer and electric circuit.

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 Numerical analysis of tsunami loads on bridges has become an important issue since the 2011 Tohoku earthquake and tsunami disaster in Japan. This paper details a two-dimensional multi-phase turbulence flow analysis using OpenFOAM, which is open-source software. The wave height and velocity time histories were provided at the upstream boundary, and the flow regime was calculated using the k-epsilon and SST k-omega turbulence models. The results were used to simulate a tsunami flow acting on a bridge girder model having a rectangular cross-section, and the tsunami loads and associated pressures on the bridge model were calculated. The results using the SST k-omega turbulence model showed good agreement with tsunami loads obtained from actual hydraulic experiment. Negative pressure was generated on the upstream side at the base of the bridge model, but the estimated negative pressure was lower than the experimental value. The pressure on other parts of the model was estimated with good precision. Furthermore, the flow regime around the bridge model was qualitatively reproduced by the simulation.

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 At a tunnel portal of a high-speed railway, a hood is build to reduce a micro-pressure wave generated by a train entering into a tunnel. A conventional hood has a rectangular cross-section larger than that of a tunnel, and in order to minimize the construction costs, we have developed a porous round hood with the same cross-section as the tunnel. In this study, we examine the effect of this round hood on a micro-pressure wave and other pressure waves. The result of an experiment with a scale model shows that the round hood can reduce a micro-pressure wave as much as the conventional rectangular hood. Then, the round hood is constructed at the Yamanashi Maglev test line, and a field measurement is conducted. The result agrees with the experimental result and shows that the round hood can reduce both a micro-pressure wave and a pressure wave at a tunnel portal enough for the environmental standard criteria.

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