An active optimal control algorithm is presented for the suppression of self-excited vibration such as galloping in towers of long span bridges. Quasi-steady theory is applied to model the aerodynamic forces and multimode response is considered to observe the intermode interaction. Gust load is considered as a random phenomenon and modeled by the power spectra of the along and across wind fluctuating velocities. The possible error in the response prediction, due to uncertainty in the quasi-steady theory and the random gust phenomenon, is rectified by the introduction of an observer. An optimal observer is used to minimize its effect on the increment of the objective function. The effect of the observer on the change in system parameter and gust intensity is examined, also the time delay effect on the performance of the controller is investigated.

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Retrofitted reinforced concrete structures were modeled using fiber modeling technique extended to include the stress-strain relation of repair material such as grouted epoxy resin or covered steel plates. Earthquake response analysis was then conducted using inelastic hysteretic rules. Effectiveness of seismic retrofit was evaluated through comparison of ductility, hysteretic energy and damage index with the original members. The proposed method was verified by the test results of retrofitted RC beam members. As an application of this method, earthquake response of a strengthened RC bridge pier was simulated. The bridge pier with reinforcements terminated at mid-height was modeled including retrofitting by steel jackets. Thin steel jacket showed higher capacity than thick one because of its larger ductility.

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A closed form solution for the 2-dimensional problem to evaluate the displacement and stress of an elastic fullspace subject to sudden distributed forces is developed. The force is expressed in a form of multinormal function of space and time variables over strips and time increments. The solution procedure is to utilize the Fourier-Laplace domain transform with the Cagniard-de Hoop method for the inversion. The application to the boundary-initial value problems is demonstrated for the Lamb's problem and for the seismic wave scattering propagation problem. The former makes the validation of the present solution and the latter provides the useful information on ground motions at irregular sites.

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Concrete structures in the natural circumstances are going to detoriorate gradually, affected by carbonation (neutralization). The possibility of corrosion of reinforcement steel is considered to be significant when carbonation reaches its cover thickness. Also, the carbonation velocity of concrete is much affected by the natural circumstances. In this paper, to estimate the optimal cover thickness which contains the lifecycle term, the concept on reliability based total cost munimum technique is used. Furthermore, to evaluate the ambiguity of influences of natural circumstances that affects the carbonation velocity, fuzzy algebla is adopted.

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This paper deals with a method to estimate the amplitude of vortex-induced vibration of long span bridge girder under natural wind based on the test results of conventional spring-mounted model test in smooth flow. A series of experiments were conducted to clarify the effects of vibration mode, turbulence intensity and scale on bridge response, and the results indicate that turbulence effect is remarkable; it was found that the effect of turbulence intensity which is the most important parameter depends on cross-sectional shape of girder, width to depth ratio (B/D) and so on. Observation of vortex-induced vibration of an actual bridge is consistent with the test results obtained in the present study.

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This paper proposes high precision stiffness equations for large-size quadrilateral plate elements, that can be applied in the analysis of plate structures composed by one or more panels.
Displacements and stress resultants can be applied to the elements, whose arbitrary boundary conditions are obtained by the superposition of fundamental solutions in a single trigonometric series for the problem of semi-infinite plates in one of the directions. The nodal conditions along the element edge were considered by combining the analytical method above mentioned with a numerical method (point-matching method).
The accuracy of the results obtained in the numerical calculations confirms the usefulness of the stiffness equations proposed herein.

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Investigated is the mechanical behavior of beam-to-column connections with bolted Tstubs. The objective of this study is to establish the design guide to beam-to-column connections with split-tee joints. Experiments of beam-to-column connections with various joint surface conditions are carried out, in order to obtain qualitative and quantitative effects of joint surface conditions on the mechanical behavior of the beam-to-column connections. It is revealed that the mechanical behavior is greatly influenced by the joint surface conditions, and that angular welding distortion and curve welding distortion work advantageously in the mechanical view point when the distortions are convex-wise.

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Chracteristics of multiple tuned mass dampers (MTMD), whose natural ferquencies are distributed to some band width around the natural frequency of ateucture, are investigated. Perturbation solutions of modal properties of MTMD-steucture system are obtained neglecting the effect of non-proportional damping It is shown that in an efficient MTMD all the TMD are strongly coupled with structurc in any mode Optimal band width is derived on the basis of perturbation solution.

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Efficiency of multiple tuned mass dampers (MTMD), whose natural frequencies are distributed to some band width around the natural frequency of a structure, are investiagated through perturbation solutions of modal properties of MTMD-structure damped system. Useful formulas to estimate the performance of MTMD subjected to various extermal forces are derived. Numerical study confirmed accuracy of these formulas. Optimal design parameters of the MTMD are also proposed.

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As a passive control means to reduce traffic-induced vibration of viaducts caused by running vehicles, viscous dampers are studied. Complex eigenvalue analysis of a simple beam with two viscous dampers shows that high modal damping can be added to lower modes. An approximate formula for the modal damping ratio is derived. Through comparison with TMD and an active control method using simulation analysis, it was indicated that viscous dampers as well as the active control method are effective for traffic-induced girder vibration. However, it is also found that the three control methods considered here are not effective in reducing the dynamic reaction force in viaducts.

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This paper presents a method for the determination of rational characteristics of bilinear restoring force of bearings for seismic isolation in a bridge with multispan. The bilinear restoring force characteristics equivalent to a linear one-degree-of-freedom system can be easily determined by using the inverse of the equivalent linearization techniques without iterating calculation, and in the condition of the fixed ratio between two stiffnesses before and after yielding of a bearing, the unique bilinear characteristics with the maximum damping constant are determined. As computational results of seismic responses of a bridge, it is shown that the maximum response values can be obtained by using linear response spectra and bearings for seismic isolation can be rationally designed as well as easily.

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A circuit breaker fixed to a spread footing is modeled by a mass-rigid body system. The breaker is represented by a mass and the footing by a rigid body. The mass and the rigid body is connected by a spring and damper. The rigid body is supported by horizontal and rotational springs and their corresponding dampers. By using the recorded input and response data earthquake, parameters for soil-structures interaction are estimated by structural identification techniques based on Gauss-Newton method.

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Impulsive response of an elastic layered medium in the in-plane wave field is presented. The procedure for calculating the impulsive response is based on a thin-layered element and discrete wave number method. The elastic wave equation is transformed into an ordinary differential equation by the thin-layered element and discrete wave number method, and an Hermitian matrix appears in the equation. The impulsive responses can be calculated by superposing the eigensolutions of the ordinary differential equation. From the numerical calculations and process of the formulation, the vibration characteristics of the surface layer on the rigid basement are investigated.

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This paper presents a nonlinear seismic response analysis method for three dimensional soil-structure interaction systems using FEM. In the method, material nonlinearity is introduced by employing the Mohr-Coulomb failure law in the full three dimensional stress space. To treat the nonlinearity, we developed the method of evaluating the unbalanced tensor at every interation in the load transfer method. In addition, we proposed a new method to treat the boundaries of FEM model in order to reduce the number of freedom. The detailed examples show the validity of the method to analyze the material nonlinearity and the effectiueness of the proposed boundany treatment.

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In the previous paper, the authors pointed out the advantage of the nonlinear goal programming. In this paper, its utility is applied to the minimum weight designs of Nielsen bridges considering the stress adjustment of the hanger cables. Namely, the constraint conditions for the cable stress as well as the total weight are treated as the objective functions of one-sided goal programming technique, in which the sectional dimensions of the members and the prestress of the cables are used for the design variables. Moreover, the validity of the present technique is shown by the numerical calculations.

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This study was done in order to find a method whereby the useful results obtained from the analysis by the use of yield strength ratio R₁ or R₂, which are often used in inelastic earthquake response analysis, could be used interchangeably. The transformation coefficient C_R of the R₁ to R₂ was derived from their definition, and the regression equation of the C_R was deduced, on the basis of numerical results of elastic response analysis for SDOF structures, excited by thirty artificial earthquakes prepared in this study. The result of verification of this equation, by using the numerical examples of the required yield strength ratios R_1r and R_2r, showed that the ratios R₁ and R₂ are interchangeable with each other within an acceptable range of accuracy.

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