bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental assessment of low‐aspect‐ratio, reinforced concrete shear wall stiffness
Authors: Farrar Charles R. , Baker William E. 
Published: April 2007

AbstractLow‐aspect‐ratio, reinforced concrete shear walls are the primary lateral‐load‐carrying element in many structures designed for protective purposes. A review of the technical literature shows that considerable uncertainty exists regarding the elastic stiffness these structures will exhibit during seismic excitation. Because of this uncertainty, current design practice often employs a stiffness reduction factor. In an attempt to develop accurate information regarding the stiffness of these structures, 13 shear wall elements were tested statically; dynamically, with simulated seismic base excitations on a shake table; and with experimental modal analysis procedures. Results of these tests show that the shear wall's stiffness can be accurately estimated with a mechanics‐of‐materials analysis that accounts for shear deformation.
Symmetric modes of vibration for A circular plate using finite dynamic elements
Authors: Fergusson N. J. , Pilkey W. D. 
Published: April 2007

AbstractThe dynamic element method has been shown previously to provide a computational advantage over the ordinary finite element method for various beam elements. The Taylor expansions are computed here for the dynamic shape functions (two terms) and dynamic stiffness matrix (four terms) for the axisymmetric vibrations of an annular plate element. The complicated matrices which result are made more tractable by expressing them as power series in powers of the aspect ratio. The percentage error in the natural frequencies is then calculated using both the two‐ and the three‐term dynamic stiffness matrix, demonstrating the increased accuracy for a given number of elements.
Influence of time‐domain dam–reservoir interaction on cracking of concrete gravity DAMS
Authors: Wepf Dieter H. , Feltrin Glauco , Bachmann Hugo 
Published: April 2007

AbstractBased on a non‐linear dam‐reservoir interaction model, a study investigating the earthquake response of concrete gravity dams is presented. For the propagation of cracks in unreinforced mass concrete, a discrete crack approach formulation based on the finite element method is applied. A special crack element is used to follow a fictitious crack in order to account for a zone of microcracks developing at the crack tip. The reservoir is modelled using the boundary element method. At a fictitious boundary dividing the irregular finite part of the reservoir from the regular infinite part, the loss of energy due to pressure waves moving away towards infinity is taken into account rigorously. Analyses are performed on the tallest non‐overflow monolith of the Pine Flat Dam located in Kern County, California. The interaction of a dam, which may exhibit cracks in mass concrete, with a reservoir domain of arbitrary geometry extending to infinity is studied. Some main parameters are investigated. The importance of tools capable of handling the non‐linear dam‐reservoir interaction is emphasized.
Parametric study of vertical vibrations of circular flexible foundations on layered media
Authors: Gucunski Nenad , Peek Ralf 
Published: April 2007

AbstractThe paper presents results of a parametric study of vertical oscillations of a flexible circular plate on the surface of an elastic half‐space and an elastic layered system. The solution of the problem is based on the ‘ring method’. Vertical oscillations have been analysed to determine the displacement and soil reaction distributions at the soil‐plate interface and the impedance functions. Parameters of the study include material and geometrical properties of a soil system and a plate and the load distribution on the plate. The results indicate significantly different behaviour of a flexible plate from that of a rigid one. Based on the observed behaviour, a classification of plates has been suggested.
Seismic response controlled structure with Active Variable Stiffness system
Authors: Kobori Takuji , Takahashi Motoichi , Nasu Tadashi , Niwa Naoki , Ogasawara Katsura 
Published: April 2007

AbstractThe Active Variable Stiffness (AVS) system is proposed as a seismic response control system. It actively controls structural characteristics, such as stiffness of a building, to establish a non‐resonant state against earthquake excitations, thus suppressing the building's response. It consumes a relatively small amount of energy and maintains the safety of the building in moderate to severe earthquakes. In order to accumulate practical data and investigate them, a building has been constructed as a trial. This paper describes the applied system, the control algorithm, verification of stiffness selection, results of tests for verifying system characteristics, some observed earthquake records and simulation analyses. Responses in controlled and uncontrolled states have been compared to show the effectiveness of the proposed system.
CQC modal combination rule for high‐frequency modes
Authors: Kiureghian Armen Der , Nakamura Yutaka 
Published: April 2007

AbstractThe CQC rule for modal combination is extended to include the quasi‐static contribution of truncated modes and the effects of input narrow‐bandedness and cut‐off frequency. A simple measure of the error in approximating a high‐frequency modal response by its quasi‐static contribution is derived. The extended rule is applicable to structures with high‐frequency modes and to seismic inputs which may not be regarded as wide band. Numerical examples demonstrate the significance of input bandwidth and cut‐off frequency on modal cross‐correlation coefficients, and on the error resulting from truncation of high‐freqeuncy modes.
Seismic cracking and energy dissipation in concrete gravity dams
Authors: Bhattacharjee S. S. , Léger P. 
Published: April 2007

AbstractA finite element method for seismic fracture analysis of concrete gravity dams is presented. The proposed smeared crack analysis model is based on the non‐linear fracture behaviour of concrete. The following features have been considered in the development of the model: (i) the strain softening of concrete due to microcracking; (ii) the rotation of the fracture band with the progressive evolution of microcrack damage in finite elements; (iii) the conservation of fracture energy; (iv) the strain‐rate sensitivity of concrete fracture parameters; (v) the softening initiation criterion under biaxial loading conditions; (vi) the closing‐reopening of cracks under cyclic loading conditions. The seismic fracture and energy response of dams and the significance of viscous damping models to take account of non‐cracking structural energy dissipation mechanisms are discussed. The influences of global or local degradation of the material fracture resistance on the seismic cracking response of concrete dams were also studied. Two‐dimensional seismic response analyses of Koyna Dam were performed to demonstrate the application of the proposed non‐linear fracture mechanics model.
Maximum response of asymmetric structures subject to A multicomponent earthquake
Authors: Li B. , Al‐Bermani F. G. A. , Kitipornchai S. 
Published: April 2007

AbstractA simple and general technique to obtain a six‐component earthquake input motion of a rigid foundation using three‐linear‐components earthquake record is presented. Using the multicomponent input, the maximum structural response to an arbitrarily oriented earthquake is derived. The method is applied to determine the response spectrum for a two‐d.o.f. laterally and torsionally coupled linear system. The effects of foundation geometry, structural properties and apparent wave velocity on the structural response are investigated. It is found that increasing the foundation size reduces the peak values of the input motion; this reduction is more pronounced for a square foundation than for a circular one.
Theoretical and experimental studies on rectangular liquid dampers under arbitrary excitations
Authors: Koh C. G. , Mahatma S. , Wang C. M. 
Published: April 2007

AbstractThis paper presents a study on the behaviour of rectangular liquid dampers under a horizontal excitation of arbitrary time history. The theoretical model to predict motion of a shallow liquid in a rectangular tank is adapted from a previous researchers' model which was developed for sinusoidal excitations. The model includes an energy dissipation term arising from liquid viscosity. In the present consideration of arbitrary excitations, the energy dissipation term is derived in a straightforward way, without resorting to the equivalent linearization method or assumption of harmonic response as used by earlier researchers. The up‐crossing rate of wave height is used in furnishing the Reynolds number required for the evaluation of shear stress in the boundary layer. Since there was no known precedent study involving arbitrary excitations, experiments have been performed accordingly to verify the model. Generally, the theoretical model furnishes results which are found to be in close agreement with the experimental ones. The results also illustrate the strong dependency of liquid motion upon the natural frequency of the damper, amplitude and frequency content of the excitation spectrum. The model is then applied to study the effectiveness of tuned liquid dampers in vibration control of a single‐degree‐of‐freedom structure subjected to earthquake excitations. Significant suppression of structural vibration can be achieved using tuned liquid dampers.
Response analysis of reinforced concrete structures under seismic excitation
Authors: Mørk K. J. 
Published: April 2007

AbstractThe theoretical background and capabilities of a program for response analysis of reinforced concrete structures under seismic excitation are presented. The emphasis is on the analysis of stiffness and strength degradation due to severe plastic deformations.An extended version of the model of Roufaiel–Meyer is utilized as the constitutive moment–curvature relation. This takes into account the transition from uncracked to cracked sections, including a mechanism for strength deterioration. The finite length of plastic end zones is taken into account by controlling the plasticity in certain sections and at internal cross sections of the members. Incremental bending stiffness corresponding to the local bending axes of the elements between these control sections is determined by linear interpolation.The stochastic earthquake excitation may be specified either as a standardized acceleration time‐series applied at the earth surface and scaled with stochastically varying maximum acceleration and duration, or as an intensity modulated Gaussian white noise process filtered through a Kanai–Tajimi filter. Based on Monte‐Carlo simulation, the program calculates the mean values and standard deviations of storey displacements, bending moments in critical sections and maximum softening damage indicators, defined from the lower time‐averaged eigenperiods.An adaptive system reduction scheme has been implemented based on a truncated expansion of external nodal point degrees‐of‐freedom in the linear eigenmodes of the initial undamaged structure. A full description of the internal degrees‐of‐freedom controlling the hysteresis is maintained.In order to demonstrate the ability of the program to predict the actual seismic response of reinforced concrete structures, computed results were compared to the experimentally recorded results of a 10‐storey 4‐bay reinforced concrete model.
Iterative methods for non‐classically damped dynamic systems
Authors: Udwadia Firdaus E. , Kumar Ravi 
Published: April 2007

AbstractNon‐classically damped structural systems do not easily lend themselves to the modal superposition method because these systems yield coupled second‐order differential equations. In this paper, a variety of new computationally efficient iterative methods for determining the response of such systems are developed. The iterative approaches presented here differ from those presented earlier in that they are computationally superior and/or are applicable to the determination of the responses of broader classes of structural systems. Numerical examples, which are designed to evaluate the efficacy of these schemes, show the vastly improved rates of convergence when compared to earlier iterative schemes.
Dynamic stiffness of unbounded medium based on damping‐solvent extraction
Authors: Song Chongmin , Wolf John P. 
Published: April 2007

AbstractIn the damping‐solvent extraction method, to calculate the dynamic‐stiffness matrix of an unbounded medium, a finite region of the medium, adjacent to the structure is analysed in the first step, whereby hysteretic material damping is introduced artificially as a solvent. This leads to the dynamic‐stiffness matrix of the damped bounded medium, which is assumed in the second step to be equal to that of the damped unbounded medium. In the third step, the effect of the material damping on the dynamic‐stiffness matrix is eliminated, i.e. the damping solvent is extracted, resulting in the dynamic‐stiffness matrix of the unbounded medium. The damping‐solvent extraction method permits an efficient calculation of the dynamic‐stiffness matrix of an unbounded medium by analysing the adjacent bounded medium only, which exhibits the same dynamic characteristics as the (bounded) structure. The familiar standard finite‐element method is sufficient for the analysis and the hysteretic damping is introduced by multiplying the elastic moduli by 1 + 2i£. The introduced hysteretic material damping, the solvent, is extracted at the end of the analysis for each coefficient of the dynamic‐stiffness matrix and for each frequency independently of the others by a very concise equation based on a Taylor expansion.The method is evaluated thoroughly for dynamic soil‐structure interaction and for seismic reservoir‐dam interaction using stringent simple cases with analytical solutions available and is also applied to practical examples, by calculating the dynamic‐stiffness matrix of a semi‐infinite wedge and an embedded foundation.
Neural network for earthquake selection in structural time history analysis
Authors: Cheng M. , Popplewell N. 
Published: April 2007

AbstractA neural network is employed to select earthquake waves in a time history approach for structural dynamics. The neural network is a preferable alternative to an expert system because knowledge can easily be renewed. It involves a back propagation model having three layers (one input, one hidden and one output layer) and is used to avoid inappropriate earthquake input prior to practical numerical computations. Knowledge to categorize the earthquake waves is acquired through network training with earthquake response spectra and structural responses. The trained network is tested by categorizing the responses of three types of unknown structures caused by 50 previously recorded earthquakes. Comparisons are made with analogous data from the traditional site dominant period method. Results demonstrate that, unlike the latter method, a neural network is generally more successful as the number of training patterns increases.
Seismic response of a cylindrical shell embedded in a layered viscoelastic half‐space. I: Formulation
Authors: Luco J. E. , de Barros F. C. P. 
Published: April 2007

AbstractA method to obtain the three‐dimensional harmonic response of a infinitely long cylindrical shell of circular cross‐section embedded in a layered viscoelastic half‐space and subjected to harmonic plane waves impinging at an oblique angle with respect to the axis of the shell is presented. The procedure combines an indirect integral representation for the field in the exterior half‐space with a model of the pipeline or tunnel based on Donnell shell theory. The integral representation for the soil is based on the use of moving Green's functions for the layered viscoelastic half‐space. The accuracy of the formulation is tested by comparison of results obtained by using different discretizations. Extensive comparisons with previous two‐ and three‐dimensional results for the case of a shell embedded in a uniform half‐space and some new numerical results for a shell embedded in a multilayered half‐space are presented in a companion paper.
Dynamic soil pressures on rigid cylindrical vaults
Authors: Veletsos A. S. , Younan A. H. 
Published: April 2007

AbstractA critical evaluation is made of the dynamic pressures and the associated forces induced by ground shaking on an upright, circular, rigid vault that is embedded in a uniform viscoelastic stratum of constant thickness and infinite extent in the horizontal plane. Both the vault and the stratum are presumed to be supported on a non‐deformable base undergoing a space‐invariant, uniform horizontal motion. The effects of both harmonic and earthquake‐induced excitations are examined. Simple approximate expressions for the responses of the system are formulated, and comprehensive numerical data are presented which elucidate the underlying response mechanisms and the effects and relative importance of the various parameters involved. The parameters investigated include the height to radius ratio for the vault, the conditions at the vault‐medium interface, and the material properties of the stratum. In addition to valuable insights into the response of the particular system being examined, the results presented provide a conceptual framework for the analysis and interpretation of solutions for more involved systems as well.
Formulation of hydrodynamic pressures in cracks due to earthquakes in concrete dams
Authors: Tinawi René , Guizani Lotfi 
Published: April 2007

AbstractA new analytical development of the seismic hydrodynamic pressure inside pre‐existing cracks on the upstream face of concrete dams is presented. The finite control volume approach is utilized to derive an expression for the seismic hydrodynamic pressure using the continuity principle and the linear momentum theorem for the fluid inside the crack. The derived pressure expression is a function of the relative crack‐opening acceleration and velocity. The acceleration and velocity terms are then recast in the form of added mass and damping matrices which can then be included at the nodes inside the discrete crack of a finite element model. This procedure linearizes the solution of the problem. A dam, 55 m high and having an initial crack opening of 2 mm at the base or near the crest and subjected to two different accelerograms, is analysed. For high‐frequency ground motion, the seismic hydrodynamic pressure inside the crack, at the base of the dam, appears to be 50 per cent higher than the corresponding hydrostatic pressure.
Performance of a high damping rubber bearing base isolation system for a shear beam structure
Authors: Chen Yu , Ahmadi Goodarz 
Published: April 2007

AbstractPerformance of High Damping Laminated Rubber Bearing (HD‐LRB) base isolation system in protecting the structure and the structural content is studied. A non‐uniform shear beam structural model is considered, and the generalized non‐stationary Kanai–Tajimi model for the El Centro 1940 earthquake is used as excitation. The technique of equivalent linearization is utilized and the mean‐square response statistics of secondary systems and primary structure are evaluated. Statistically estimated peak responses of the secondary system and the primary structure are evaluated and the results are compared with the response spectra for the actual earthquake accelerogram. Comparison of the stochastic responses for base‐isolated structures with the HD‐LRB and the linear Laminated Rubber Bearing (LRB) and the fixed‐base structure is also carried out. It is shown that the HD‐LRB system significantly reduces the mean‐square, as well as the peak acceleration and deflection responses without generating large base displacements. Furthermore, the non‐linear behaviour of the HD‐LRB somewhat improves the performance of the bearing in reducing the peak responses of the secondary system and the primary structure when compared with the linear LRB model.
Dynamic characterization of multiple tuned mass dampers and some design formulas
Authors: Abé Masato , Fujino Yozo 
Published: April 2007

AbstractMultiple Tuned Mass Dampers (MTMD) consist of a large number of small oscillators with natural frequencies distributed around the natural frequency of a controlled mode of the structure. In the present paper, the modal characteristics and efficiency of the MTMD are studied analytically. Perturbation solutions for the modal properties of the MTMD–structure system are obtained and the modal characteristics are discussed. An explicit formula to estimate the effectiveness of the MTMD subjected to harmonic forces is also derived. It is shown that the MTMD is efficient when at least one of the oscillators is strongly coupled with the structure in any mode. Based on this observation, a critical bandwidth of the natural frequencies of the MTMD to make the system multiply tuned is derived in a simple form, and furthermore a robustness criterion for the frequency tuning under a given bandwidth is proposed. It is shown that, when properly designed, the MTMD can be much more stable (robust) than a conventional single TMD while maintaining more or less the same efficiency. Numerical studies verify the accuracy of the perturbation solutions and the proposed formulas.
Site response analysis in the valley of Mexico: Selection of input motion and extent of non‐linear soil behaviour
Authors: Ordaz M. , Faccioli E. 
Published: April 2007

AbstractIt is well known that seismic waves in the lake‐bed zone of Mexico city are dramatically amplified, and that the soft clays in this region exhibit an unusually large elastic range. New field and laboratory data show that clays in certain areas within the Valley of Mexico have lower elastic thresholds and, hence, non‐linear soil behaviour would be more likely to take place. In this paper, we analyse geotechnical and strong‐motion data to model, using a one‐dimensional (1‐D) approach, the non‐linear soil response at two sites in Mexico City during the September 19, 1985 (Ms = 8.1) Michoacán earthquake. Results suggest that, even for motions as large as those recorded during the 1985 Michoacán event, a linear viscoelastic behaviour must be assumed for the examined area, although, as far as it is presently known, the clays from this area show the greatest modulus reduction among the Mexico City clays. Thus, a linear 1‐D propagation analysis continues to be a suitable engineering option in computing expected ground motions at soft sites for the Valley of Mexico. Caution, however, is warranted when selecting input motions, since, as shown in this paper, large differences can result depending on the choice of outcrop motions.
Dynamic‐stiffness matrix in time domain of unbounded medium by infinitesimal finite element cell method
Authors: Wolf John P. , Song Chongmin 
Published: April 2007

AbstractTo calculate the dynamic‐stiffness matrix in the time domain (unit‐impulse response functions) of the unbounded medium, the infinitesimal finite element cell method based solely on the finite element formulation and working exclusively in the time domain is developed. As in the cloning algorithm, the approach is based on similarity of the unbounded media corresponding to the interior and exterior boundaries of the infinitesimal finite element cell. The derivation can be performed exclusively in the time domain, or alternatively in the frequency domain. At each time station a linear system of equations is solved. The consistent‐boundary method to analyse a layered medium in the frequency domain and the viscous‐dashpot boundary method are special cases of the infinitesimal finite element cell method. The error is governed by the finite element discretization in the circumferential direction, as the width of the finite‐element cell in the radial direction is infinitesimal. The infinitesimal finite element cell method is thus ‘exact in the finite‐element sense’. This method leads to highly accurate results for a vast class of problems, ranging from a one‐dimensional spherical cavity to a rectangular foundation embedded in a half‐plane.