In bridge maintenance and design, it is important to know the response to an external force under live load. The use of a micro-electro mechanical systems (MEMS) accelerometer is proposed for the purpose. Accelerometer are easy to install on a painted metal surface using magnets, inexpensive, and compact. Furthermore, unlike conventional methods such as those using laser displacement meters, the use of MEMS accelerometers does not require a steady point, so that improved workability is expected.
 In this study, “Portable-Weigh-In-Motion” was developed as a bridge monitoring using MEMS accelerometer. In order to enhance the accuracy of vehicle detection, secondary differential filter was first applied to the response at the time of the vehicle passage. Next, using the sharpened vehicle response and free vibration method, bridge displacement was determined from acceleration. Then, based on the difference of the vehicle kinds and vehicle passing speed, the accuracies of the determined displacement were verified. Thirdly, the system of Portable-Weigh-In-Motion was developed using the determined bridge displacement. Finally, we conducted the measurement on an actual bridge to examine the effectivity of the proposed system by comparing the result of conventional WIM system using strain gauge.

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 This study showed the applicability of using the posterior distributions of model parameters to the structural reliability analysis of existing bridges. The target here was a steel plate-girder bridge that showed corrosions and deterioration in its girders, bearings, and concrete slab. The mean and variance of resonant frequencies were acquired by multiple measurements of traffic vibration for the use as observation data in the Bayesian inference, and a nominal finite element (FE) model of the target bridge was constructed. The prior distributions of model parameters that represented the uncertainties due to the deteriorations were then determined based on the inspection data, and the parameters that had sensitivities to resonant frequencies were extracted by the analysis of variance (ANOVA) to prevent the ill-posedness. The posterior distributions of the spring stiffness at the ends of steel girders, which were given to represent performances of the corroded bearings in the FE model, and the density of the concrete slab were estimated by applying the surrogate modeling and the Markov Chain Monte Carlo (MCMC). It was then recognized that the uncertainties of those model parameters could be reduced, and those posterior distributions could explain the actual deteriorations. The posterior distributions were used to calculate the structural reliability index β of the target bridge. The probability density functions of maximum Misesstress on the steel girders under the design load were firstly obtained by the Monte Carlo FE model calculations using the prior and posterior distributions, respectively. In the results, the reliability index against the variability of steel yield stress in the case of posterior distributions became higher than that in the case of the prior. It was then concluded that the procedure presented in this study realized the understanding of structural reliability of existing bridges quantitatively.

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 In the steel deck plate stiffiened with trough rib, fatigue crack in the longitudinal welding between steel deck and trough rib is classified in “deck plate penetration type” to progress in deck plate top surface direction and “bead penetration type” to progress in bead surface direction. In this study, a newly developed phased array non-destructive testing system was applied to detect both type of fatigue crack in the steel box girder bridge with steel deck under operating condition, and the performance of this system was evaluated.

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 Sn-bearing steel containing a small amount of tin (Sn) was newly developed by noting the effect of adding such kind of trace alloy element for improving the corrosion resistance of steel. In order to investigate the corrosion deterioration characteristics around paint-coat defect of the coated Sn-bearing steel, accelerated exposure test was performed. During the test, the appearance and surface shape of paint coated Sn-bearing steel were examined for evaluating the degree of deterioration. The corrosion deterioration was evaluated by focusing on the blister of paint coating around the initial defect scribed in X shape. After the test, the corroded volumes of specimens were examined. The blister areas from the cross scribe paint defect of the Sn-bearing steel was respectively 90% in A-type coating and 50% in C-type coating of those of the SM490 steel at 2400 cycles. The corroded volumes from the cross scribe paint defect of the Sn-bearing steel were respectively 80% in A-type coating and 60% in C-type coating of those of the SM490 steel after the test.

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 In order to achieve the effective management of huge number of existing railway bridges, it is important to estimate the structural performance estimation based on simple measurement. This study proposed two, MCMC based inverse analysis and modal identification based simple evaluation, methods by employing the beam dynamics theory to be able to estimate not only vibration properties but also displacement and impact factor that are also used in the design. The numerical calculations revealed that the inverse analysis can estimate accuracy more than existing identification methods such, as FFT and so on. Although interaction effect with passing train has a dominant influence on the estimation accuracy, the proposed method can estimate the maximum displacement within 2% error based on acceleration. By application to the acceleration measured on actual bridges, estimation errors on the maximum displacement were -3% to +6% in case of the proposed inverse analysis method.

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 In previous studies, anti-corrosion characteristics of alloy thermal spraying coating has been investigated by various corrosion tests. However, the characteristics of Al-5Mg alloy thermal spraying coating remains largely unknown. In this research, to evaluate the characteristics, accelerated corrosion tests, electro-chemical tests and tensile adhesion tests were conducted. In addition, similar corrosion tests were carried out to compare the characteristics with other coatings by Zn-15Al alloy thermal spraying and C-5 heavy-duty anticorrosive coatings. From these test results, corrosion resistance of Al-5Mg alloy thermal spraying coating is much greater than that of Zn-15Al alloy and C-5 anticorrosive coatings. Al-5Mg alloy coating with a cross-cut has enough anti-corrosion performance against highly corrosive environment with NaCl corresponding to 2,000cycles of cycle-D specified in JIS K 5600-7-9.

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