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Ikeda Y.,Kajima Technical Research Institute
Earthquake Engineering and Structural Dynamics | Year: 2016

This paper verifies the feasibility of the proposed system identification methods by utilizing shaking table tests of a full-scale four-story steel building at E-Defense in Japan. The natural frequencies, damping ratios and modal shapes are evaluated by single-input-four-output ARX models. These modal parameters are prepared to identify the mass, damping and stiffness matrices when the objective structure is modelled as a four degrees of freedom (4DOF) linear shear building in each horizontal direction. The nonlinearity in stiffness is expressed as a Bouc-Wen hysteretic system when it is modelled as a 4DOF nonlinear shear building. The identified hysteretic curves of all stories are compared to the corresponding experimental results. The simple damage detection is implemented using single-input-single-output ARX models, which require only two measurements in each horizontal direction. The modal parameters are equivalent-linearly evaluated by the recursive Least Squares Method with a forgetting factor. When the structure is damaged, its natural frequencies decrease, and the corresponding damping ratios increase. The fluctuation of the identified modal properties is the indirect information for damage detection of the structure. © 2016 John Wiley & Sons, Ltd.

Tanaka Y.,University of Tokyo | Hibiya T.,University of Tokyo | Niwa Y.,University of Tokyo | Iwamae N.,University of Tokyo | Iwamae N.,Kajima Technical Research Institute
Journal of Geophysical Research: Oceans | Year: 2010

Tide-induced strong diapycnal mixing in the Kuril straits is thought to be one of the essential processes controlling water mass formation in the North Pacific. In order to make a definite quantification of diapycnal diffusivity in the Kuril straits, we drive a three-dimensional numerical model and examine the generation, propagation, and dissipation features of internal waves which play an essential role in transferring energy from the predominant K1 barotropic tide to diapycnal mixing processes. It is shown that most of the internal wave energy subtracted from the K1 barotropic tide is dissipated within the Kuril straits such that the local dissipation efficiency becomes 0.8-1.0, about three times the value previously employed. This is because the K1 tidal frequency is subinertial in this area so that significant amount of K1 tidal energy is fed into coastal trapped waves (CTWs) which stay around each island without propagating away from the straits; CTWs induce strong velocity shear near the ocean bottom causing bottom-confined intense mixing with a vertical decay scale ∼200 m, less than half the value previously employed, although there remains some uncertainties resulting from the employed parameterizations of viscosity and diffusivity. The average diapycnal diffusivity in the Kuril straits becomes ∼25 × 10-4 m2 s-1, about three times the value previously estimated, although it is still an order of magnitude less than assumed for the Kuril straits in the existing ocean general circulation models. © 2010 by the American Geophysical Union.

Fukumoto T.,Kajima Technical Research Institute
Journal of Structural and Construction Engineering | Year: 2016

This paper proposes a new formulation for ultimate shear strength considering restriction stress for concrete in perfobond strip shear connections. The formulation provides ultimate shear strength by multiplying shear cracking strength by the ratio of ultimate shear strength to shear cracking strength. In the investigation, a regression formula for the relationship between the ratio and restriction stress is proposed based on a database including previous test results using no-cover simple-specimen loaded restriction force. This paper proposes a method of transforming the effect of restraining concrete around a steel plate hole by reinforced concrete cover and penetrating rebars, and transforming it into restriction stress in the ultimate shear strength formulation. Predictions from the proposed formulation almost agree with test results.

Mahaboonpachai T.,University of Tokyo | Matsumoto T.,Hokkaido University | Inaba Y.,Kajima Technical Research Institute
International Journal of Adhesion and Adhesives | Year: 2010

This paper aims to investigate interfacial fracture toughness between concrete and polymer-cement mortar (PCM) in an external wall tile structure under various shear to tensile stress ratio by using interface elements in a finite element method (FEM). A constitutive material model of interface elements was developed, and its corresponding values that have a relation to the interfacial fracture toughness were calibrated with three four-point bending set-ups and one high shear test. Then, the developed interface element was verified by applying to analyze the failure of tiles in the tiled column compression test. With this method, the interfacial fracture toughness of the current interface was successfully obtained for the whole range of the shear to tensile stress ratio. Finally, the result is further discussed with the other interfaces, consisting of cementitious materials. © 2009 Elsevier Ltd. All rights reserved.

Fukumoto T.,Kajima Technical Research Institute
Journal of Structural and Construction Engineering | Year: 2015

This paper proposes a new practical model of a restoring force characteristic on the panel zone within steel beam-to-concrete filled circular steel tube column moment connections for predicting the elastoplastic behavior of the panel zones including strength reduction after ultimate strength. The proposed model for a skeleton curve is provided as a multi-linear model having a cracking strength point, a yield strength point, an ultimate strength point and strength reduction points for 95%, 90% or 80% of ultimate strength. The skeleton curve model up to the ultimate strength point is based on the previous shear force-deformation model proposed by the writer, while the deformations of these strength reduction points is provided as new regression formulations obtained from previous test results. The writer proposes a new hysteresis loop model including stiffness reduction. The proposed models agree approximately with experimental results up to large deformations.

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