bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrodynamic coefficients of a monolithic circular offshore structure
Authors: McCormick Michael E. 
Published: April 2007

AbstractExpressions for both the rectilinear and rotational inertial and damping coefficients for a circular monolithic tower of uniform radius are derived. The analysis matches the fluid velocity, derived from potential theory, with the structural velocity in sway. That is, the motions of the tower are assumed to be in a vertical plane. The analysis is then applied to a tower composed of (lumped‐mass) elements, where the expressions for the added‐mass and damping coefficients are shown to be functions of wave number. The added‐mass is shown to be a product of two wave systems: a travelling wave system, which is responsible for the radiation damping, and a standing wave system, called the evanescent system, which is attached to the structure.The added‐mass of the evanescent system is negative for small wave numbers, while that of the travelling waves is positive. The negative sign simply means that the inertial force of the evanescent waves is 180° out of phase with that of the travelling system. Furthermore, it is shown that the contributions of the two wave systems to the total added‐mass of the structure counteract each other, resulting in a total added‐mass which varies gradually with the wave number.Finally, the analysis is applied to an experiment, and results of the analysis and the experiment are found to agree rather well.
An evaluation of the ductility reduction factor q in the 1976 regulations for the federal district of mexico
Authors: Hadjian A. H. 
Published: April 2007

AbstractThe reduction of the spectral accelerations to account for inelastic response of structures as given by the 1976 Regulations for the Federal District of Mexico is evaluated relative to the records obtained at the Secretaria de Communicaciones y Transportes (SCT) during the September 19, 1985 Mexico earthquake. It is concluded that the 1976 Regulations do not treat all types of structural systems equally. On a relative basis the 1976 Regulations provide less protection for those structures designed to larger values of ductility factors. This could have contributed, together with other characteristics of the ground motions and construction practices, to the heavy damage of highrise buildings in Mexico City.
A mathematical model for the in‐plane non‐linear earthquake behaviour of unreinforced masonry walls. Part 1: Experiments and proposed model
Authors: Mengi Yalcin , McNiven Hugh D. 
Published: April 2007

AbstractIn this study a mathematical model is proposed to predict the non‐linear in‐plane behaviour of clay brick masonry walls when subjected to dynamic excitations. Owing to its length, the study is divided into two parts. This part is devoted to a description of the appropriate experiments and to the development of the mathematical model, including use of experimental data. In Part 2 the model is completed by establishing the parameter functions appearing in it.The form of the non‐linear model is established by developing a simple, linear model from more complicated ones previously developed by the authors, and then extending this simple model to cover behaviour in the non‐linear range. The model contains two types of parameter function. One describes elasto‐plastic stresses and depends on strains; the other describes viscous stresses and is a function of strain rates.The experimental work was carried out using the shaking table of the Earthquake Engineering Research Center, University of California, Berkeley. The experiments involved in‐plane horizontal earthquake excitations. The intensity of excitation, starting with a small value, was increased gradually through the beginning of cracking until damage was complete. Time histories of accelerations and displacements relative to a fixed frame were recorded at the upper and lower edges, and at the mid‐height of the wall specimen.At the end of this part, the experimental data are processed to obtain the data for a ‘complex frequency response function’ of the wall specimen. The reduced data will be used in the optimization analysis in Part 2.
A mathematical model for the in‐plane non‐linear earthquake behaviour of unreinforced masonry walls. Part 2: Completion of the model
Authors: McNiven Hugh D. , Mengi Yalcin 
Published: April 2007

AbstractIn this part, the parameter functions for clay brick masonry appearing in the non‐linear model are established for the wall material used in the experiments by means of experimental data and a particular type of optimization. This special optimization makes use of the fact that the wall behaves linearly at the intensity level of each excitation, as described in Part 1, and involves matching in frequency space the experimental and theoretical complex frequency response functions relating the Fourier transforms of the top and base accelerations of the wall.It is found that the envelope curves for the parameter functions are bilinear and that the dynamic values of mechanical properties of masonry differ greatly from their static values.The completed model is appraised by comparing how the wall will respond to strong earthquake excitations when predicted using the model and how it actually responded on the shaking table. The predicted response is remarkably close to the experimental.
Ambient vibration survey of the bosporus suspension bridge
Authors: Brownjohn J. M. W. , Dumanoglu A. A. , Severn R. T. , Blakeborough A. 
Published: April 2007

AbstractTraffic and wind excitation has been used to obtain the dynamic characteristics of the first Bosporus (Bogazici) Suspension Bridge. Structural symmetry and the absence of suspended side‐spans allowed attention to be focused on the main span and the Asian tower. For the main span, 18 vertical and 20 lateral modes were obtained, including torsional modes. For the tower, 12 longitudinal and 12 lateral modes were identified. All these models lie in the range 0–1‐1 Hz.A detailed comparison is given between these modes and corresponding calculated modes, obtained by use of a three‐dimensional finite element model which includes a geometric stiffness matrix. Of particular interest is the validity of the theoretical model used for the box‐deck, because of its subsequent use in response studies of asynchronous seismic excitation.Comparison with a more limited study made in 1973 shows that the bridge continues to behave as it was designed to behave, particularly with regard to the deck‐tower interface. From natural frequency measurements of two hangers, the load which they carry was assessed.
Elastic wave scattering by inhomogeneous and anisotropic bodies in a half space
Authors: Hirose Sohichi , Kitahara Michihiro 
Published: April 2007

AbstractScattering of elastic waves by inhomogeneous and anisotropic bodies in a half space is considered. The integral equation method is formulated by using the fundamental solution of a homogeneous isotropic body in elastostatics and regarding the resulting inhomogeneous terms as equivalent body forces. Numerical examples are presented for the wave scattering by inhomogeneous and/or anisotropic alluvial valleys and for the dynamic analysis of an inhomogeneous dam. The effect of inhomogeneities and anisotropy on the dynamic behaviour of alluvial valley and dam is discussed.
Earthquake analysis of a class of torsionally‐coupled buildings
Authors: Hejal Reem , Chopra Anil K. 
Published: April 2007

AbstractAn effective procedure is summarized without derivation for estimating the maximum response of a class of torsionally‐coupled, multi‐storey buildings due to earthquake ground motion characterized by response spectra. The analysis procedure is shown to be efficient and to provide insight into torsional coupling effects because the maximum response of such a torsionally‐coupled, N‐storey building in its njth mode of vibration is determined exactly by analysing (i) the response in the jth vibration mode (j = 1,2, N) of the corresponding torsionally‐uncoupled, N‐storey system; and (ii) the response in the nth vibration mode (n = 1, 2 for a one‐way symmetric plan) of an associated torsionally‐coupled, one‐storey system. It is also demonstrated that an earlier, simpler approach in which the total (considering all vibration modes) response of the building is determined from the total response of the two simpler systems is strictly valid only under restrictive conditions, which are identified, but the simpler approach leads to results that are accurate to a useful degree.
Earthquake analysis of intake‐outlet towers including tower‐water‐foundation‐soil interaction
Authors: Goyal Alok , Chopra Anil K. 
Published: April 2007

AbstractThe available procedure for earthquake analysis of axisymmetric intake‐outlet towers is extended to towers of arbitrary geometry, but with two axes of plan symmetry, and to include the effects of tower‐foundation‐soil interaction. The total system is represented as four substructures: tower, surrounding water, contained water and the foundation supported on flexible soil. The substructure representation of the system permits use of the most effective idealization for each substructure. An example earthquake response analysis is presented to demonstrate the results obtained from the analysis procedure. Computation times for several cases are included to demonstrate the efficiency of the analysis procedure.
Recursive evaluation of interaction forces of unbounded soil in the time domain
Authors: Wolf John P. , Motosaka Masato 
Published: April 2007

AbstractThe interaction forces representing the contribution of the linear unbounded soil to the equations of motion of a nonlinear soil‐structure‐interaction analysis are specified in the form of convolution integrals. They can be evaluated recursively in the time domain. In this procedure, the forces at a specific time are computed from the displacements at the same time and from the most recent forces and most recent past displacements. It is, in principle, only approximate. When the dynamic‐stiffness coefficients can be expressed as the ratios of two polynomials in frequency, the appropriately chosen recursive equations are exact.Two possibilities of choosing a recursive equation are discussed.
The impulse‐invariant method, where the unknown recursive coefficients are calculated by solving a system of equations which are established by equating the rigorous and recursive formulations for a discretized unit impulse displacement.
In the segment approach, the dynamic‐stiffness coefficients in the time domain are interpolated piecewise. Applying the z‐transformation analytically then results in an explicit recursive equation without solving a system of equations.
The recursive evaluation of the convolution integrals in the time domain leads to a dramatic reduction in the computational effort up to two and three orders of magnitude and in the storage requirement. This makes the time‐domain analysis using the substructure method computationally competitive with the corresponding direct (non‐recursive) frequency‐domain procedure of determining the complex response which is, however, applicable only to a linear (total) system.
Recursive evaluation of interaction forces of unbounded soil in the time domain from dynamic‐stiffness coefficients in the frequency domain
Authors: Wolf John P. , Motosaka Masato 
Published: April 2007

AbstractThe interaction forces of the linear unbounded soil in a non‐linear soil‐structure‐interaction analysis can be calculated recursively, starting directly from the dynamic‐stiffness coefficients in the frequency domain.Two possibilities of choosing a recursive equation are discussed.
The recursive equation in the frequency domain. For each frequency, the interaction force at a specific time station is expressed as a function of the corresponding interaction force at the previous time station and of the displacements at the current time station and at the two most recent past time stations. This recursive evaluation of the convolution integral. which can be derived using the z‐transformation, is rigorous. By using interpolation in the frequency domain, an approximate procedure results, which leads to a significant reduction in computational effort.
The recursive equation in the time domain. By approximating the dynamic‐stiffness coefficients as the ratios of two polynomials in frequency using a curve‐fitting technique based on the least‐squares method and by applying the partial‐fraction expansion and using the z‐transformation, the recursive coefficients can be determined explicitly. Alternatively, the ratio of two polynomials can also be transformed to an ordinary differential equation together with the initial conditions.
The recursive equations using interpolation in the frequency domain and based on a ratio of two polynomials lead to a reduction in the computational effort of one and up to three orders of magnitude, respectively.
Stability and dynamics of beams on winkler elastic foundations
Authors: De Rosa Maria Anna 
Published: April 2007

AbstractThe dynamical properties of a foundation beam on a Winkler soil have been recently discussed by using the power series method14 and the finite element method.15, 17 – 19 The first method can be applied only if the Winkler soil is linearly distributed along the whole span: on the contrary, the second method is more general, but it requires considerable computational efforts.In this paper a recently developed discretization method has been shown to be particularly well suited for dynamic analysis of foundation beams, in the presence of second order destabilizing effects. The procedure is based on the Hamilton principle, and the equation of motion is deduced from the corresponding Lagrange equations.According to the proposed method, the structure is reduced to a set of rigid bars, connected together by elastic cells. The convergence of the method is shown to be quite rapid, so that a small number of Lagrangian coordinates has to be introduced, and the resulting eigenvalue problem can be easily solved.Numerical comparisons are also performed with the available data of the literature, and the agreement is shown to be excellent. Two particularly unusual cases are illustrated, in order to emphasize the method's peculiarities.Finally, the influence of the axial forces on the fundamental vibration frequency is discussed, both for conservative and non‐conservative forces.
Seismic response of steel frame structures with added viscoelastic dampers
Authors: Zhang Ri‐Hui , Soong T. T. , Mahmoodi P. 
Published: April 2007

AbstractThe feasibility of using viscoelastic (VE) dampers to mitigate earthquake‐induced structural response is studied in this paper. The properties of VE dampers are briefly described. A procedure for evaluating the VE damping effect when added to a structure is proposed in which the damping effect of VE dampers is incorporated into modal damping ratios through an energy approach. Computer simulation of the damped response of a multi‐storey steel frame structure shows significant reduction in floor displacement levels.
Transient Scattering of Elastic Waves by Dipping Layers of Arbitrary Shape Part 1: Antiplane Strain Model
Authors: Eshraghi Hossein , Dravinski Marijan 
Published: April 2007

AbstractScattering of elastic waves by two dimensional multilayered dipping sediments of arbitrary shape embedded in an elastic half‐sapce is investigated by using a bondary method. The displancement field is evaluated throughout the elastic media for both steady state and transient incident SH waves. The unknown scattered field is expressed in terms of wave functions which satisfy the equation of motion, traction‐free boundary condition and appropariate radiation conditions. The transient response is constructed from the steady state solution by using the fast Fourier transform technique.The numerical results presented demonstrate that scattering of waves by subsurface irregularities may cause locally very large amplification of surface ground motion. The motion can be affected greatly by the scattered surface waves in the sediments. The results clearly indicate that the surface ground motion depends upon a number of parameters present in the problem, such as frequency and the angle of incidence of the incoming wave, impedance contrast between the layers and location of the observation point.
Transient scattering of elastic waves by dipping layers of arbitrary shape. Part 2: Plane strain model
Authors: Eshraghi Hossein , Dravinski Marijan 
Published: April 2007

AbstractScattering of elastic waves by dipping layers of arbitrary shape embedded within an elastic half‐space is investigated for a plane strain model by using a boundary method. Unknown scattered waves are expressed in the frequency domain in terms of wave functions which satisfy the equations of motion and appropriate radiation conditions at infinity. The steady state displacement field is evaluated throughout the elastic medium for different incident waves so that the continuity conditions along the interfaces between the layers and the traction‐free conditions along the surface of the half‐space are satisfied in the least‐squares sense. Transient response is constructed from the steady state one through the Fourier synthesis.The results presented show that scattering of waves by dipping layers may cause locally very large amplification of surface ground motion. This amplification depends upon the type and frequency of the incident wave, impedance contrast between the layers, component of displacement which is being observed, location of the observation station and the geometry of the subsurface irregularity. These results are in agreement with recent experimental observations.
In‐plane free vibration of supported/free parabolic cables
Authors: Darbre Georges R. 
Published: April 2007

AbstractThe free‐vibration analysis of parabolic cables fixed at the lower end and free to move in the horizontal direction at the upper end is performed. The dynamic stiffness of such cables is zero at the natural frequencies and this property is used to obtain the governing frequency equation. Double‐frequency points at which two consecutive natural frequencies are identical occur for specific values of stiffness parameters. Expressions for the natural modes of vibration and for the contribution of the extensional and inextensional cable resistances to the modal potential energy are given.
Seismic response of base isolated buildings including p‐Δ effects of isolation bearings
Authors: Koh Chan Ghee , Balendra Thambirajah 
Published: April 2007

AbstractIn order to achieve a low isolation frequency, elastomeric bearings used for base isolation of buildings usually have low shear rigidity which leads to a significant reduction in the buckling load. The effects of compression load on the bearing behaviour are therefore an important consideration. A study of seismic response of base isolated buildings is presented in this paper, fully accounting for the P‐Δ effects of isolation bearings. An analytical procedure is formulated that treats separately the superstructure and the supporting bearings and assembles the governing equations via the interaction forces at the base deck. The resulting equations are then solved step‐by‐step numerically. Numerical results obtained for a base isolated five‐storey shear building show that neglecting the P‐Δ effects can lead to considerable errors in the computed seismic response when the buckling safety factor of bearings is low.
On rigid foundations subjected to seismic waves
Authors: Pais Artur L. , Kausel Eduardo 
Published: April 2007

AbstractIn the analysis of structural foundations for seismic loads, it is customary to distinguish two types of soil‐structure interaction effect: kinematic interaction (or wave passage), and inertial interaction. The former refers to the phenomenon of wave scattering, which occurs because the foundation is much stiffer than the surrounding soil and cannot accommodate to its distortions. Inertial interaction, on the other hand, is caused by feedback of kinetic energy of the structure into the soil. This paper is concerned only with the first phenomenon.The rigorous analysis of rigid, embedded foundations subjected to seismic disturbances requires, in general, substantial computational effort. Indeed, a typical analysis would normally require models with finite elements and/or boundary elements. Although such methods may be used to find an accurate solution to the problem of kinematic interaction, their use is not always warranted, given the many uncertainties involved and the multitude of assumptions that must be considered. Hence, approximate solutions are attractive for this problem. One such approximate method is the remarkably simple algorithm proposed by Iguchi.3 This paper presents first an appraisal of this method by way of a comparison with accurate numerical solutions for cylindrical foundations; next the algorithm is applied to rectangular (prismatic) foundations. It is found that Iguchi's method gives results that are adequate for engineering purposes, even if not entirely accurate.
Arch dam system identification using vibration test data
Authors: Mau S. T. , Wang S. 
Published: April 2007

AbstractIn an effort to study the dynamic characteristics of an arch dam system from the vibration test results, a systematic method of frequency‐domain system identification is developed. The governing equations for system identification are based on a non‐classical modal superposition method. The non‐classical model is shown to be derivable from a general matrix formulation of the dam system. The conventional classical modal formulation becomes a special case of the general non‐classical formulation. The modal parameters of the non‐classical and the classical formulation are to be identified.The system identification method includes a single‐mode sweep procedure for initial parameter estimation and a progressive multiple‐mode parameter identification scheme that contains an information criterion for the determination of the optimal number of modes to be included in the identification process. The method is applicable to data measured at more than one point on the dam and to data that include both the amplitude response and the phase response.The method is applied to the vibration test data of two dams. Based on the results of these applications, the adequacy of the classical model and the non‐classical model is compared and the effect of the phase data on the parameter determination is discussed.
Optimal vibration abatement of mechanical systems
Authors: Ebrahimi N. D. 
Published: April 2007

AbstractIn this paper, a method is presented for forced vibration suppression of multi‐degree‐of‐freedom systems with damping. The technique pursued in this investigation is based on applying control forces at a certain number of the system's degrees of freedom. The problem is organized as an unconstrained, non‐linear optimization formulation so that the peak vibration amplitudes of a certain number of degrees of freedom would be minimized. An efficient mathematical programming algorithm is used to solve this optimization problem numerically. It will be shown that the scheme illustrated in this paper is remarkably effective in reducing the vibration of the system. In particular, the vibration amplitudes at selected degrees of freedom may be diminished substantially.