bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic stiffness of rigid rectangular foundations on the half‐space
Authors: Triantafyllidis Th. 
Published: March 2007

AbstractThe dynamic soil–structure interaction of a rigid rectangular foundation with the subsoil represents a mixed‐boundary value problem. This problem is formulated in terms of a system of coupled Fredholm integral equations of the first kind. The subsoil is modelled by a homogeneous, linear‐elastic and isotropic half‐space which is perfectly bonded to the rigid, rectangular foundation. An approximate solution for the resultant loads between the foundation and the half‐space due to a unit forced displacement or rotation is obtained using the Bubnov–Galerkin method. Using this method the displacement boundary value conditions are exactly satisfied and the contact stress distributions between the foundation and the half‐space are approximated by series expansions of Chebyshev polynomials. This method provides a simple means of studying the soil‐structure interaction of rectangular foundations with different inertia properties.
Stability of elastic frames subjected to earthquake excitations
Authors: Ahmadi Goodarz , Abdel‐Rahman Samir 
Published: March 2007

AbstractDynamic stability of elastic multistorey frame structures subjected to vertical earthquake ground accelerations is studied. Different stationary, non‐stationary, white and non‐white random models for earthquake strong motion are considered. The concepts of mean‐square and almost‐sure stability are reviewed and the corresponding stability theorems are presented. Several general criteria regarding the dynamic stability of the equilibrium state of multistorey frames subjected to random excitations are developed. A few examples concerning the stability of single and multi‐degree‐of‐freedom structures under earthquake excitations are presented. The stability of motion of frames under combined horizontal–vertical acceleration is also briefly discussed.
Transient waves in a rod subjected to impulsive end loading
Authors: Thambiratnam David P 
Published: March 2007

AbstractHerein the propagation of transient waves in a rod due to impulsive end loading is investigated using the method of wavefront expansion. The Mindlin–Herrmann equations which include the Poisson effect are used to model the rod. Since this rod theory is restricted to lower values of Poisson's ratio (< 0.283), the present work also has the same restriction. The impulsive end loading on the rod can be prescribed in the form of stress, strain, velocity or acceleration boundary conditions. The analysis is based on the concept of a wave as a carrier of discontinuities in the field variables and their derivatives. These discontinuities are determined from a set of recurrence relations which are in turn generated by the use of time harmonic asymptotic series solutions to the equations of motion. Transients due to both velocity and strain (or stress) boundary conditions are treated. Numerical examples are presented to illustrate the method of solution. The results indicate the distortion of the transient waves due to the dispersive nature of the governing equations. Transients due to other boundary conditions at the rod end can be treated by using the results presented in the paper.
Inferred displacements, velocities and rotations of a long rigid foundation located at el centro differential array site during the 1979 imperial valley, california, earthquake
Authors: Niazi Mansour 
Published: March 2007

AbstractDigitally recorded acceleration time histories of the 1979 Imperial Valley earthquake by the five elements of the El Centro Differential Array are used to estimate the induced torsional and rocking vibrations of long structures in the near field of strong earthquakes. The underlying assumptions in these estimates are high rigidity of the foundation relative to the surrounding soil and its negligible mass. Based on these analyses, the peak rotation amplitude of an 18 m long foundation within 5 km of the fault is approximately 1 × 10−3 rad, or nearly 0·06 degrees, and decreases rapidly for larger foundation dimensions for either the rocking or torsional mode. The strongest impulses of rotations coincide with arrival of the S phase. This paper examines the sensitivity of the resulting peak displacement and particle velocity amplitudes to the foundation dimension. It is inferred that the base averaging effects of displacement and velocity fields at frequencies contributing to peak values (f < 1 Hz) are negligibly small. Rocking and torsional amplitudes for the specific site and geometry considered here show a tendency to reduce with the increase of foundation dimensions.
Random vibration of hysteretic systems under bi‐directional ground motions
Authors: Park Y. J. , Wen Y. K. , Ang A. H‐S. 
Published: March 2007

AbstractA random vibration method is developed for the response analysis of hysteretic structural systems under stochastic two‐dimensional earthquake excitations. The biaxial hysteretic restoring force is modelled by coupled non‐linear differential equations; the response statistics are obtained using the equivalent linearization technique. The validity of the proposed model is appraised using available biaxial loading tests of reinforced concrete columns. A parametric study was performed to examine the significance of the effects of biaxial interaction under earthquake excitations. A practical method to evaluate the extreme response statistics is also presented.
Simplified analysis of dynamic response of rigid foundations with arbitrary geometries
Authors: Chow Y. K. 
Published: March 2007

AbstractA simple, efficient numerical procedure is presented for the analysis of the steady‐state dynamic response of rigid foundations of arbitrary shape on a homogeneous, isotropic elastic half‐space. The contact area of the foundation and soil medium is discretized into square subregions. The influence of the rigid square subregion is approximated by that of an equivalent rigid circular base with the same contact area. This approximation is a better representation of a rigid square subregion than a uniformly stressed subregion used in earlier approaches. Simple expressions are used to determine the influence of the subregion on itself and on the rest of the subregions, without the expense of numerical integration procedures. The present method is demonstrated to converge rapidly. The accuracy of this method is examined by comparison with available published theoretical and experimental results.
An index for measuring the effects of topography on seismic ground motion intensity
Authors: Sánchez‐sesma Francisco J. , Faccioli Ezio , Fregonese Roberto 
Published: March 2007

AbstractAn index is proposed for the quantitative evaluation of topographical effects, as may be required in seismic microzoning and structural design applications. This topographical effects index (TEI) is defined as the relative Arias intensity for a given position.As an example, the TEI is calculated for a semicircular canyon excited by an earthquake signal that consists of plane elastic SH waves and is characterized by a theoretical spectrum of accelerations. The analytical solution by Trifunac15 provides the transfer functions for this problem. The behaviour and spacial distribution of the calculated TEI values are illustrated for different incidence angles and spectral parameters.The proposed index appears useful for generating quantitative criteria which, after proper confirmation by instrumental recordings, could be considered in earthquake code provisions.
Dynamic modelling of axisymmetric foundations
Authors: Chen Cheng‐Hsing , Penzien Joseph 
Published: March 2007

AbstractA boundary impedance matrix to characterize a homogeneous half‐space with a cylindrical cavity is formulated by the global Ritz method. This method, which is basically the same as the indirect boundary element method, uses a very limited number of distributed sources to generate Ritz vector sets representing the far‐field impedances. The resulting impedance matrix is fully‐coupled, complex‐valued, frequency‐dependent and can be combined with any compatible finite element near field for carrying out soil–structure interaction analyses. The numerical results obtained by this method for surface supported and embedded foundations are very close to corresponding published results obtained by different procedures. Combining the boundary impedance matrix with a finite element near field provides an hybrid model which is effective and efficient in carrying out dynamic soil–structure interaction analyses.
Modal analysis for random vibration of hysteretic frames
Authors: Baber T. T. 
Published: March 2007

AbstractAn algorithm is presented for the direct stiffness formulation of hysteretic frames which is suitable for random vibration analysis under zero mean or non‐zero mean random excitation. A modal transformation is used to reduce the number of active degrees of freedom. First and second order response statistics are presented for two example frames using stochastic equivalent linearization and Monte Carlo simulation. The modal transformation stabilizes the stationary response calculation algorithm by eliminating superfluous higher modes. The iterations for transient response calculations under non‐zero mean excitations are destabilized by elimination of too many modes. The modal transformation allows reasonable response estimates to be obtained with significant reductions in computing time. The expected lower modes dominate the response, but inclusion of several higher modes is necessary to provide reasonable response estimates.
A model for system identification of degrading structures
Authors: Iwan Wilfred D. , Cifuentes Arturo O. 
Published: March 2007

AbstractThis paper presents a physically motivated model for the gross dynamic behaviour of degrading hysteretic structures subjected to damaging earthquake motions. The model is intended to provide a vehicle for gaining insight into the nature of the non‐linear response of such structures and to be used in system identification studies. A concept is presented for identifying the model parameters based on examination of the gross restoring force characteristic of a real structure. The model is applied to data from two damaged structures: the Bank of California building in the 1971 San Fernando earthquake and the Imperial County Services building in the 1979 Imperial County earthquake.
Structural response to non‐stationary non‐white stochastic ground motions
Authors: Langley R. S. 
Published: March 2007

AbstractA numerical procedure is presented for calculating the survival probability of a linear multidegree of freedom structure subjected to non‐stationary non‐white ground motions using the concept of qualified envelope crossings. The moment equations governing the covariances of the structural response and its Hillbert transform are derived, and efficient techniques for calculating various convolution integrals which appear in these equations are discussed. Numerical integration of the moment equations yields the statistics of the response and the response envelope, from which the survival probability can be estimated. Excellent agreement is found with published analytical results for the response variances of a three storey building, and it is shown that the method can readily deal with cases for which there is no analytical solution.
Vertical vibration of ring foundations
Authors: Veletsos Anestis S. , Tang Yu 
Published: March 2007

AbstractA comprehensive analysis is made of the harmonic response of vertically excited, massless, rigid ring foundations supported at the surface of an homogeneous elastic halfspace. The parameters considered include the thickness to radius ratio for the ring, the frequency of the exciting force and of the resulting steady‐state response, and Poisson's ratio for the supporting medium. The response quantities examined include the stiffness and damping coefficients of the system in an equivalent spring–dashpot representation of the supporting medium, the displacements of the foundation and of points on the ground surface away from the foundation, and the normal pressure at the foundation–medium interface. The results in each case are compared with those obtained for a solid disk having the same radius as the outer radius of the ring, and a simple approximate model is used to interpret the results and to provide insight into the action of the system. The reported data are computed by a method of analysis that takes due account of the mixed boundary conditions at the surface of the halfspace, and are believed to be of high accuracy.
Dynamic stability of liquid‐filled cylindrical shells under vertical excitation, Part II: Theoretical results
Authors: Chiba M. , Tani J. 
Published: March 2007

AbstractTheoretical analyses are presented for the dynamic stability of a clamped‐free cylindrical shell partially filled with liquid, under vertical excitation. In the analyses, the dynamic version of the Donnell equations and the velocity potential theory were used for the motions of the shell and the liquid, respectively. The problem was solved by using the modified Galerkin method so as to satisfy the boundary conditions. The equations of motion coupling the shell and the liquid were derived from a type of coupled Mathieu's equation. It is found that the parametric principal resonance could occur, as well as the parametric combination resonance of the sum type, involving two natural vibrations with the same circumferential wave number but with different axial mode number. The latter type of parametric resonance apparently has not been previously studied. The instability regions where parametric resonance occurs were determined by using Hsu's method.17 To compare with the experimental results which had been stated in a companion paper,15 detailed numerical calculations were carried out for the two test cylinders partially filled with water. Excellent agreement between theory and experiment was demonstrated for the instability regions.
Impedance functions for foundations embedded in a layered medium: An integral equation approach
Authors: Apsel R. J. , Luco J. E. 
Published: March 2007

AbstractAn integral equation technique to calculate the dynamic response of foundations embedded in a layered viscoelastic half‐space when subjected to external forces and moments is presented. The technique is based on representing the radiated field as resulting from a set of sources distributed over a surface internal to the actual boundary of the foundation and by imposing the boundary conditions in an integral sense. The resulting non‐singular integral equation with symmetric kernel is solved by discretization and reduction to a system of linear algebraic equations. The technique is validated by comparison with previous results for cylindrical foundations with different embedment ratios.
Finite element analysis of the seismic response of anchored and unanchored liquid storage tanks
Authors: Barton D. C. , Parker J. V. 
Published: March 2007

AbstractThe seismic response of liquid‐filled cylindrical storage tanks has been investigated using finite element techniques implemented in the general purpose structural analysis computer code ANSYS. Both added mass concepts and displacement‐based fluid finite elements were employed to allow for the effects of the liquid. Simplified response spectrum modal analyses of a tank making use of the axisymmetric harmonic displacement patterns of the principal modes of deformation were found to give accurate predictions of the tank behaviour with a rigidly anchored base. Time history analyses of three‐dimensional finite element models of unanchored and flexibly anchored tanks, with gap conditions between the tank base and the supporting floor to allow lift‐off of the base, indicated that stresses in the tank and resultant loads on the floor can be much greater than for a rigidly restrained tank. These results demonstrate the importance of carefully considering the restraint conditions when performing seismic design calculations on storage tanks.
Marginal cost based seismic decision: A probabilistic approach
Authors: Parisi Maria A. 
Published: March 2007

AbstractAmong various methodologies for seismic risk mitigation, the use of the marginal cost of saving a life as decision variable, proposed in the literature, does not require to assign a cost to human life. Also, optimization of resources over a territory can be profitably performed in terms of such a variable. Parameters of different type (seismic, structural, financial) enter into the analytical definition of the marginal cost of saving a life. These parameters are subject to intrinsic variability and uncertainty that are bound to affect the decision variable. This aspect was not originally taken into account systematically. The influence of the uncertainty in the various basic parameters on the decision variable is studied here. A procedure is suggested to develop constant probability of exceedance contours of the decision variable versus the design coefficient to be selected. The suggested procedure is exemplified for two regions of different seismicity.
Cumulative experimental errors in pseudodynamic tests
Authors: Shing Pui‐Shum B. , Mahin Stephen A. 
Published: March 2007

AbstractIn pseudodynamic tests, experimental feedback errors are accumulated in the step‐by‐step integration procedure. In this paper, the growth of cumulative experimental errors is examined. Approximate cumulative error bounds are derived for linear single‐ and multi‐degree‐of‐freedom systems, based on realistic models of random and systematic feedback errors. These studies show that the rate of cumulative error growth with respect to the integration time step increases rapidly with the natural frequency of the specimen and the integration time interval used. Hence, the higher modes of a multi‐degree‐of‐freedom system are more sensitive to experimental errors than the lower ones. Furthermore, it is shown that some systematic errors are extremely undesirable. Rational criteria for assessing the reliability of pseudodynamic test results are presented.
Eigenproperties of non‐classically damped primary structure and equipment systems by a perturbation approach
Authors: Suarez L. E. , Singh M. P. 
Published: March 2007

AbstractClosed‐form expressions are obtained to calculate the approximate complex eigenvalues and eigenvectors of a system composed of a non‐classically damped primary structure and a single degree of freedom oscillator. The expressions are obtained through a systematic second order perturbation analysis of a transformed eigenvalue problem of the combined system. The possibility of tuning between the structure and equipment is considered. The dynamic properties of the combined system are derived in terms of the complex eigenvalues and eigenvectors of the supporting structure and the frequency, mass and damping ratio of the equipment. Examples demonstrating the accuracy of the expressions for the eigenvalues and eigenvectors are presented. These eigenproperties are used for generation of floor response spectra for non‐classically damped structures to incorporate the dynamic interaction effects between the structure and equipment.
Diabetes mellitus and risk of breast cancer: A meta‐analysis
Authors: Larsson Susanna C. , Mantzoros Christos S. , Wolk Alicja 
Published: March 2007

AbstractDiabetes mellitus has been associated with an increased risk of several types of cancers, but its relationship with breast cancer remains unclear. We conducted a meta‐analysis of case–control and cohort studies to assess the evidence regarding the association between diabetes and risk of breast cancer. Studies were identified by searching MEDLINE (1966–February 2007) and the references of retrieved articles. We identified 20 studies (5 case–control and 15 cohort studies) that reported relative risk (RR) estimates (odds ratio, rate ratio/hazard ratio, or standardized incidence ratio) with 95% confidence intervals (CIs) for the relation between diabetes (largely Type II diabetes) and breast cancer incidence. Summary RRs were calculated using a random‐effects model. Analysis of all 20 studies showed that women with (versus without) diabetes had a statistically significant 20% increased risk of breast cancer (RR, 1.20; 95% CI, 1.12–1.28). The summary estimates were similar for case–control studies (RR, 1.18; 95% CI, 1.05–1.32) and cohort studies (RR, 1.20; 95% CI, 1.11–1.30). Meta‐analysis of 5 cohort studies on diabetes and mortality from breast cancer yielded a summary RR of 1.24 (95% CI, 0.95–1.62) for women with (versus without) diabetes. Findings from this meta‐analysis indicate that diabetes is associated with an increased risk of breast cancer. © 2007 Wiley‐Liss, Inc.
Central bank intervention with limited arbitrage
Authors: Neely Christopher J. , Weller Paul A. 
Published: March 2007

AbstractShleifer and Vishny (SV) pointed out some of the practical and theoretical problems associated with assuming that rational risk‐arbitrage would quickly drive asset prices back to long‐run equilibrium. In particular, they showed that the possibility that asset price disequilibrium would worsen, before being corrected, tends to limit rational speculators. Uniquely, SV showed that ‘performance‐based asset management’ would tend to reduce risk‐arbitrage when it is needed most, when asset prices are furthest from equilibrium. We analyse a generalized SV model for central bank intervention. We show that increasing availability of arbitrage capital has a pronounced effect on the dynamic intervention strategy of the central bank. Intervention is reduced during periods of moderate misalignment and amplified at times of extreme misalignment. This pattern is consistent with empirical observation. Copyright © 2007 John Wiley & Sons, Ltd.
The diffusion process of sodium hyaluronate (Na‐Ha) and Na‐Ha‐n‐alkyl derivatives films swelling
Authors: Mráček Aleš , Benešová Karolína , Minařík Antonín , Urban Pavel , Lapčík Lubomír 
Published: March 2007

AbstractThe process of diffusion of sodium hyaluronate and its hydrophobically modified alkyl derivatives in water was studied by measuring the kinetics of solid polymer film swelling. The following fundamental thermodynamic parameters of the swelling process were calculated: the apparent diffusion coefficient of swelling by water Ds determined at three temperatures (25, 37, and 45°C), the activation enthalpy of diffusion connected with the swelling ΔHD,s and the activation enthalpy of the swelling process ΔHs. The thermodynamic activity of the solvent for the given sodium hyaluronate and its four alkyl derivatives has been expressed through the internal quantity RAδ,s, that is expansion work of polymer coil accomplished by the action of the internal pressure. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007