The Experts below are selected from a list of 11286 Experts worldwide ranked by ideXlab platform
Izuru Takewaki - One of the best experts on this subject based on the ideXlab platform.
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unified analysis of kinematic and inertial earthquake pile responses via the single input response spectrum method
Soil Dynamics and Earthquake Engineering, 2014Co-Authors: Kotaro Kojima, Kohei Fujita, Izuru TakewakiAbstract:Abstract In the seismic response of a structure–pile–soil system, a kinematic response due to the forced displacement of the surface ground is important, especially in a soft ground, together with the inertial response due to the inertial forces from superstructures. In this paper it is shown that a response spectrum method in terms of complex modal quantities can be used in the evaluation of the maximum kinematic and inertial seismic responses of the structure–pile–soil system to the ground motion defined at the engineering bedrock surface as an acceleration response spectrum. The notable point is that the kinematic response, the inertial response and the total response can be evaluated by the same analysis model and method by changing the model parameters. Then it is discussed which of the simple sum or the SRSS of the kinematic and inertial responses is appropriate even in resonant cases for the evaluation of the maximum pile-head bending moment. It is concluded through many examples that the validity of the simple sum or the SRSS depends on the relation between the Fundamental Natural Period of the surface ground and that of the superstructure while an averaged evaluation is valid in resonant cases.
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soil structure random response reduction via tmd vd simultaneous use
Computer Methods in Applied Mechanics and Engineering, 2000Co-Authors: Izuru TakewakiAbstract:A new systematic method for optimal viscous damper (VD) placement in building structures with a tuned mass damper (TMD) is developed taking into account the response amplification due to the surface ground. Non-linear amplification of the surface ground is described by an equivalent linear model and local interaction with the surrounding soil is incorporated with a horizontal spring and a dashpot. Hysteretic damping of the surface ground and radiational damping into the semi-infinite visco-elastic ground are included in the model. An original steepest direction search algorithm is applied to the interaction model with a TMD. Closed-form expressions of the inverse of the coefficient matrix (tri-diagonal matrix) enable one to compute the transfer function and its derivative with respect to design variables very efficiently. It is shown that simultaneous use of a TMD and added viscous dampers is very effective in response reduction and the ratio of the Fundamental Natural Period of the structure to that of the surface ground is a key parameter for characterizing the optimal damper placement. Several examples with and without a TMD for different soil conditions are presented to demonstrate the effectiveness and validity of the present method.
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inverse stiffness design of shear flexural building models including soil structure interaction
Engineering Structures, 1999Co-Authors: Izuru TakewakiAbstract:Abstract A new efficient seismic stiffness design procedure is developed for a shear-flexural building–pile–soil system. A set of design earthquakes is defined at the bedrock (beneath surface soil layers) to take into account the effects of surface soil layers on the design of building super-structures. It is shown that a closed-form solution to a hybrid inverse eigenmode problem can be utilized in developing the efficient seismic stiffness design procedure by regarding the Fundamental Natural Period of the total system and the lowest-mode deformation quantities as the principal parameters for adjustment of the story deformations. Physical interpretation of the governing equations enables one to transform a set of formally nonlinear equations into a set of simultaneous linear equations. A model twenty-story building supported by a pile–soil system with ten sublayers is presented to demonstrate the usefulness of this design procedure.
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sequential stiffness design for seismic drift ranges of a shear building pile soil system
Earthquake Engineering & Structural Dynamics, 1996Co-Authors: Tsuneyoshi Nakamura, Izuru Takewaki, Y AsaokaAbstract:A shear building supported by a prescribed pile-soil system is subjected to bedrock earthquake input. A new design procedure is presented for generating a sequence of stiffness designs satisfying the constraints on interstorey drifts. The mean peak interstorey drifts of the shear building subjected to a set of spectrum-compatible ground motions at the bedrock are evaluated by a modal combination rule. Tuning of the Fundamental Natural Period of a shear building with a fixed base with that of a shear beam ground results in a non-monotonic sequence of stiffness designs with respect to a ground stiffness parameter and previous approaches cannot be applied to such a problem. This difficulty in finding such a non-monotonic sequence is overcome by utilizing the ground stiffness parameter and the superstructure stiffness parameter alternately in multiple design phases and by developing a new multi-phase perturbation technique. Fundamental characteristics of this sequence of stiffness designs and the effect of ground stiffnesses on the design of the shear building are disclosed. It is further shown that the stiffness contour method is also useful for the design procedure such that a scattering effect in the estimates of ground stiffnesses is taken into account. The usefulness of the proposed procedure of sequential stiffness design and contour line method is demonstrated through several sequential design examples.
Y Asaoka - One of the best experts on this subject based on the ideXlab platform.
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sequential stiffness design for seismic drift ranges of a shear building pile soil system
Earthquake Engineering & Structural Dynamics, 1996Co-Authors: Tsuneyoshi Nakamura, Izuru Takewaki, Y AsaokaAbstract:A shear building supported by a prescribed pile-soil system is subjected to bedrock earthquake input. A new design procedure is presented for generating a sequence of stiffness designs satisfying the constraints on interstorey drifts. The mean peak interstorey drifts of the shear building subjected to a set of spectrum-compatible ground motions at the bedrock are evaluated by a modal combination rule. Tuning of the Fundamental Natural Period of a shear building with a fixed base with that of a shear beam ground results in a non-monotonic sequence of stiffness designs with respect to a ground stiffness parameter and previous approaches cannot be applied to such a problem. This difficulty in finding such a non-monotonic sequence is overcome by utilizing the ground stiffness parameter and the superstructure stiffness parameter alternately in multiple design phases and by developing a new multi-phase perturbation technique. Fundamental characteristics of this sequence of stiffness designs and the effect of ground stiffnesses on the design of the shear building are disclosed. It is further shown that the stiffness contour method is also useful for the design procedure such that a scattering effect in the estimates of ground stiffnesses is taken into account. The usefulness of the proposed procedure of sequential stiffness design and contour line method is demonstrated through several sequential design examples.
Tsuneyoshi Nakamura - One of the best experts on this subject based on the ideXlab platform.
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sequential stiffness design for seismic drift ranges of a shear building pile soil system
Earthquake Engineering & Structural Dynamics, 1996Co-Authors: Tsuneyoshi Nakamura, Izuru Takewaki, Y AsaokaAbstract:A shear building supported by a prescribed pile-soil system is subjected to bedrock earthquake input. A new design procedure is presented for generating a sequence of stiffness designs satisfying the constraints on interstorey drifts. The mean peak interstorey drifts of the shear building subjected to a set of spectrum-compatible ground motions at the bedrock are evaluated by a modal combination rule. Tuning of the Fundamental Natural Period of a shear building with a fixed base with that of a shear beam ground results in a non-monotonic sequence of stiffness designs with respect to a ground stiffness parameter and previous approaches cannot be applied to such a problem. This difficulty in finding such a non-monotonic sequence is overcome by utilizing the ground stiffness parameter and the superstructure stiffness parameter alternately in multiple design phases and by developing a new multi-phase perturbation technique. Fundamental characteristics of this sequence of stiffness designs and the effect of ground stiffnesses on the design of the shear building are disclosed. It is further shown that the stiffness contour method is also useful for the design procedure such that a scattering effect in the estimates of ground stiffnesses is taken into account. The usefulness of the proposed procedure of sequential stiffness design and contour line method is demonstrated through several sequential design examples.
George Gazetas - One of the best experts on this subject based on the ideXlab platform.
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4th Ishihara lecture: Soil-foundation-structure systems beyond conventional seismic failure thresholds
Soil Dynamics and Earthquake Engineering, 2015Co-Authors: George GazetasAbstract:A new paradigm has now emerged in performance-based seismic design of soil-foundation-structure systems. Instead of imposing strict safety limits on forces and moments transmitted from the foundation onto the soil (aiming at avoiding pseudo-static failure), the new dynamic approach "invites" the creation of two simultaneous "failure" mechanisms: substantial foundation uplifting and ultimate-bearing-capacity slippage, while ensuring that peak and residual deformations are acceptable. The paper shows that allowing the foundation to work at such extreme conditions may not only lead to system collapse, but it would help protect (save) the structure from seismic damage. A potential price to pay: residual settlement and rotation, which could be abated with a number of foundation and soil improvements. Numerical studies and experiments demonstrate that the consequences of such daring foundation design would likely be quite beneficial to bridge piers, building frames, and simple frames retrofitted with a shear wall. It is shown that system collapse could be avoided even under seismic shaking far beyond the design ground motion. Three key phenomena are identified as the prime sources of the success; they are illustrated for a bridge-pier: (i) the constraining of the transmitted accelerations by the reduced ultimate moment capacity of the foundation, to levels of about one-half of those developing in a conventional design; (ii) the beneficial action of the static vertical load of the structure which pushes down to "re-center" the leaning (due to uplifting and soil yielding) footing, instead of further distressing the plastic hinge of the column of the conventional design; and (iii) the substantial increase of the Fundamental Natural Period of the system as uplifting takes place, which brings the structure beyond the significant Period range of a ground motion, and hence leads to the abatement of its severe shaking.
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seismic soil structure interaction beneficial or detrimental
Journal of Earthquake Engineering, 2000Co-Authors: George Mylonakis, George GazetasAbstract:The role of soil-structure interaction (SSI) in the seismic response of structures is reex-plored using recorded motions and theoretical considerations. Firstly, the way current seismic provisions treat SSI effects is briefly discussed. The idealised design spectra of the codes along with the increased Fundamental Period and effective damping due to SSI lead invariably to reduced forces in the structure. Reality, however, often differs from this view. It is shown that, in certain seismic and soil environments, an increase in the Fundamental Natural Period of a moderately flexible structure due to SSI may have a detrimental effect on the imposed seismic demand. Secondly, a widely used structural model for assessing SSI effects on inelastic bridge piers is examined. Using theoretical arguments and rigorous numerical analyses it is shown that indiscriminate use of ductility concepts and geometric relations may lead to erroneous conclusions in the assessment of seismic performance. Numerical examples are pres...
Venkata Dilip Kumar Pasupuleti - One of the best experts on this subject based on the ideXlab platform.
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empirical expression for the Fundamental Natural Period of buildings on slopes
2020Co-Authors: Ajay Kumar Sreerama, Sreenath Gundoji, Bharat Prakke, Venkata Dilip Kumar PasupuletiAbstract:Seismic codes worldwide provide empirical formulas for estimating the Fundamental Natural Period of vibrations (Ta), preferably suitable for regular buildings. As per IS 1893:2016, the Fundamental Natural Period is an inherent building property which is a function of height and base dimensions of the building. However, the formula specified in the existing code is not suitable for a building that is irregular both in plan and elevation. One such case of irregular buildings is building structures on slopes, which are supported on foundations at different horizontal levels leading to non-uniform column heights, where the present Period formula is not suitable for estimation of Ta. In the present study, an attempt is made to develop an empirical expression for estimating Ta for buildings on slopes, by performing a regression analysis of numerically obtained Natural Periods. A total of 180 RC moment-resisting frame structures with varying floor heights and slope angles have been modelled and analyzed using SAP 2000 for the study and an empirical expression has been presented.
