For three large cable-supported bridges, namely the Yokohama Bay Bridge, Rainbow Bridge and Tsurumi Tsubasa Bridge, a study on seismic retrofit to resist level-2 ground motions was made. For the bridge components that were expected to be damaged in view of the response values obtained by nonlinear dynamic analyses, the ultimate strength and maximum deformation capacity were further calculated by inelastic analyses using a three-dimensional finite element method. Based on these analyes, a damage tree in the bridge system was prepared. Then, retrofit designs were considered to limits the damage to be an allowable.

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Relation between maximal fault displacement and magnitude of inland earthquakes in Japan is investigated using observed data and found to depend on slip types. The dependence is explained by the difference of slip absorption in surface layer and the maxmal slip in rupture area. The relation is compared with the average slip in the rupture area derived from the scaling law of inland earthquakes. Magnitude-dependance of the ratio of earthquakes caused surface fault rupture and those possibly identified prior to its occurance is examined.

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This paper presents the effect of bilateral excitation on the seismic performance of cantilevered reinforced concrete bridge columns with a square cross section. Hybrid loading test was conducted on six 1.35m tall reinforced concrete columns with a 400mm x 400mm section. Both unilateral and bilateral excitations were imposed to the columns. Furthermore, the result of hybrid loading test was compared with the result of cyclic loading test. Fiber element analysis was conducted to simulate the test results. It is found from the experiments and analysis that flexural strength and ductility capacity of reinforced concrete columns significantly deteriorate under the bilateral excitation than the unilateral excitation.

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1999 Chi-Chi Earthquake in Taiwan seriously damaged transmission towers, which was unprecedented in Japan.
This study firstly shows the latest findings of damage investigation of an extra high voltage tower. Secondly, it suggests a single model of a steel tower briefly considering how cable system affected this damage. Then it focuses on the fact that the largest 345kV steel tower #203, the only one completely collapsed, was a steel tower with unequal legs and analytically examines the possibility that the seismic vibration caused this collapse.
As a result, when seismic waves monitored in the vicinity were given, there appeared a high possibility of overall buckling at the bottom of the steel tower #203.
Lastly, given the restoration work of the steel tower #203, where its foundation was altered to connected foundation, this study points out that it is effective in improving earthquake-resistance in case of unequal land subsidence.

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In this paper, a methodology to estimate the Markovian transition probability model is presented to forecast the deterioration process of bridge components. The deterioration states of the bridge components are categorized into several ranks, and their deterioration processes are characterized by hazard models. The Markovian transition probabilities between the deterioration states which are defined for the fixed intervals between the inspection points in time, are described by the exponential hazard models. The applicability of the estimation methodology presented in this paper is investigated by the empirical data set of steel bridges in New York city.

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In this paper, the average cost calculation, which is not rely on discount rates, is investigated to evaluate the life cycle cost for the bridge components management. By assuming that the concerned bridge is under the perpetual usage, it is shown that the average cost evaluation becomes free from the conditionality for life-cycle cost evaluation : i.e., the setting of the target year of evaluation period as well as the current health-states of the bridge components. The expected cumulative life cycle cost defined for the arbitrary duration starting from the present time can be divided into the sum of the average annual cost and the relative cost conditionally defined upon the health states of the bridge components at the present time. It is also discussed that the average optimal maintenance strategies, which are evaluated by the evaluation scheme presented in the paper, can be obtained by the average cost minimizing Markov decision model. The validity of the model is investigated by a case study dealt with an actual highway bridge.

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Recently, in the metropolitan expressway, fatigue cracks on steel bridge bents have been reported. The purpose of this study is to clarify the fatigue strength and improve the fatigue strength of beam-circular column connections of steel bridge bents. Fatigue tests and FEM analyses were carried out on large scale specimens by reproducing actual beam-circular column connection. It was found that fatigue performance of that connection has low fatigue strength due to high stress concentration and existence of inherent weld defects at corner of that connection. As a retrofit result of rib-installation, although there is existence of inherent weld defects, rib-installation could improve fatigue strength of that connection.

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The modal damping evaluation method is investigated for structural cables which diameters are comparative large with the length and which sag ratios are comparatively small. An energy-based representation of modal damping is theoretically derived considering both axial and bending stiffness. It is shown that the modal damping is expressed by parameters ξ concerning cable stiffness in transverse direction and λ concerning cable sag. It clarified that the modal damping tends to be influenced of bending stiffness when these parameters are small. Moreover, the approximation evaluation formula is proposed. As a result of applying to the cable-stayed bridge cables, it is confirmed that this method is practical by giving a suitable loss factor.

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Seismic performance and correlation characteristics of reinforced concrete columns subjected to torsional moment, bending moment and axial force are clarified by experimental research. Interaction curves among those three sectional forces, which are necessary in nonlinear time history analysis, have not been proposed yet.
In this study 25 specimens with different rate of bending and torsional moments, pitch of hoop reinforcement are tested by newly developed loading system. The test specimen has 400^*400 mm cross section and 1600 mm length. The axial force is 0,5,10% of concrete compressive strength, i.e. 0,2,4 MPa. Pitches of hoop reinforcement are 30mm and 60mm. (volume ratios are 1.16% and 0.58% respectivily). Types of loading are pure bending, pure torsion and combined loading of bending moment and torsional moment. Bending and torsional moments are cyclic loadings, but axial forces are maitained to be constant during test.

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This study aims at presenting a new framework for probabilistic seismic hazard analysis with focus on Fourier amplitude and group delay time to calculate ground motion time histories corresponding to target annual probability of exceedence, considering source, path and site amplification effects especially due to deep subsurface profiles. Instead of depending on ground motion indices such as peak acceleration or acceleration response spectrum, the present method makes use of the linear operation among source, path and site effects on Fourier amplitude spectra, and directly calculates ground motion time histories with the stochastic Green's function method. In this paper, in addition to the methodology, an application of the method to the sites in Kanto region is illustrated.

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This paper presents three-dimensional free vibration analysis of orthotropic thick plates with arbitrary boundary conditions using the B-spline solid element method based on the theory of orthotropic elasticity.
To demonstrate the convergence and accuracy of the present method, several examples are solved, and results are compared with those obtained by exact and other numerical methods based on the theory of elasticity and classical thin plate theory. Good convergence and accuracy are obtained by the present method regardless of plate geometries.
The effects of thickness to width ratio, aspect ratio and boundary conditions on dimensionless frequency parameters and mode shapes of orthotropic thick rectangular plates are investigated.

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This paper presents analytical solutions for an elastic medium due to stress release method using cylindrical measuring device. It is assumed that the medium is an anisotropic body, while other layers are isotropic. And various three-dimensional loadings are treated. Also, it is possible to exactly apply this theory to measurements by small-diameter overcoring. Therefore, this paper can be expanded past analytical studies which assumed large-diameter overcoring. In numerical calculations, effects of hardness of measuring device or overcoring radius on measurement results are discussed.

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Rubber bearings show large changes in their performances when they are used for a long time. However, the quantitative evaluation and the design method considering their performance changes are not established because of few data of the deterioration. In this research, the deterioration characteristics of natural rubber materials of bridge bearings due to the heat oxidation which is the most important factor were investigated experimentally. From the test results, performance changes of natural rubber materials at any site could be estimated.

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In a hybrid loading test, actuators are usually pin connected to a specimen at one end and a loading frame at the other end. Under this condition, if the structure is loaded, a secondary force is induced by actuators due to P-Δ action of actuators. This paper presents a numerical simulation and a bench mark test to show the importance of modification of the P-Δ action in a hybrid loading test. It was found that if the P-Δ action of actuators is disregarded, a larger residual drift is likely to be developed. The bench mark tests provide responses which are quite close to the responses predicted by the fiber model. This shows the effectiveness of the modification.

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A number of fatigue cracks have been detected in orthotropic steel decks of highway bridges. The most effective retrofitting method is considered to be improvement of stiffness of the deck because the previous measurements and analysis have shown that the major cause of fatigue damage is the lack of stiffness in bending behavior of the deck. The static loading test with actual trucks was carried out with the specimens applied several types of retrofitting works. In this paper, the results of the loading test and the effectiveness of retrofitting method are presented and discussed.

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Filling a steel tube with concrete strengthens flexural strength of a tube, but it also makes the tube brittle. To prevent steel tube failure due this brittleness, there are two kinds of reinforcement methods, i.e., putting reinforcement bars in Concrete Filled Steel Tubular (CFT) or welding semicircular steel around the tube on the outside. These two methods are evaluated by two types of experiments. First, the weight dropping test is carried out to damage the reinforced CFT, and then the static cantilever bending test is performed to measure the residual performance of the damaged CFT. Comparing with the result of non-reinforced CFT, the reinforcement effect concerning ductility is investigated.

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