bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of an axisymmetric body with obliquely incident seismic waves by global local finite elements
Authors: Avanessian V. , Dong S. B. , Muki R.
Published: April 2007

Asymmetric steady‐state structure‐media interaction due to obliquely incident body waves is investigated via a version of the global local finite element method. In the present version, a local region that houses an axisymmetric structure is modelled by conventional finite elements, while the behaviour in the remaining portion of the homogeneous semi‐infinite medium is presented by the spherical harmonics that are the eigensolutions of the entire space problem. The solution scheme involves (1) full displacement and traction continuity along the boundary between the local and the exterior regions and (2) satisfaction of the traction‐free requirement on the surface of the half‐space beyond the discretized region by virtue of a sequence of integral constraints of the non‐zero weighted surface tractions of the spherical harmonics. The numerical results presented are for a perfectly bonded rigid circular foundation resting on the surface of the half‐space and subjected to obliquely incident body waves. Dependence of the displacement response of the footing upon incident angles and dimensionless wave numbers is thoroughly studied.
Hydrodynamic coefficients of a monolithic circular offshore structure
Authors: McCormick Michael E.
Published: April 2007

Expressions 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

The 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

In 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

In 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

Traffic 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

Scattering 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

An 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

The 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

The 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

The 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

The 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

The 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

Scattering 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

Scattering 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

The 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

In 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

In 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

In 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

In 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.
Rotational components of surface strong ground motion
Authors: Oliveira Carlos S. , Bolt Bruce A.
Published: April 2007

Rotational components of seismic waves have been estimated using the strong motion array in Taiwan, SMART‐1. The inner rings of accelerographs, covering an approximately circular area of 3 km2, permit a decomposition of travelling waves with wavelengths in the range 0.5 to 5.0 km and frequencies from 0.1 to 5 Hz.

Rotational components of the strain field, obtained from station pairs and averaged over the array using stacking techniques, were computed for five different earthquakes with Ms magnitude 5.7 to 7.8, and epicentral distances 6 to 84 km. The results indicate peak rotation values about a vertical axis on the order of 4 × 10−5 rad at an approximately 2.5 s period. The measured values for pure rotation and rocking are in agreement with the spatial coherency structure observed in these earthquakes. For comparison, significant effects to engineered structures generally appear when curl u > 10−4 rad. The estimates are important for design of scaled engineered models for soil‐structure interaction experiments.
Water pressures on rigid gravity dams with finite reservoir during earthquakes
Authors: Aviles Javier , Sanchez‐Sesma Francisco J.
Published: April 2007

An approximate analytical solution is presented for earthquake‐induced hydrodynamic pressures on rigid gravity dams with a finite reservoir and incompressible fluid. Using the Trefftz‐Mikhlin method, the solution is constructed with function expansions of solutions of the problem's governing equation which satisfy boundary conditions at the bottom and free surface. Unknown coefficients of the linear combinations are obtained from a continuous least‐squares treatment of the remaining boundary conditions at the upstream dam face and reservoir wall. Numerical results are presented for different geometries of the dam‐water and wall‐water interfaces. Out‐of‐phase motion at the end of the reservoir is considered. When the upstream dam face and reservoir wall are vertical, the known solution for in‐phase dam and wall movement is recovered.
A generalized least‐squares family of algorithms for transient dynamic analysis
Authors: Kujawski Jerzy , Gallagher Richard H.
Published: April 2007

By use of the generalized least‐squares procedure, in conjunction with a finite element approximation in time, a simple three‐time‐level family of time integration schemes is derived. This results in fourth‐order accurate unconditionally stable algorithms and stable eighth‐order accurate non‐dissipative algorithms. Numerical examples show the accuracy of the proposed schemes in comparison with the Fox‐Goodwin formula and Newmark's average acceleration method.
Seismic response of the superstructure and attached equipment in a base‐isolated building
Authors: Tsai Hsiang‐Chuan , Kelly James M.
Published: April 2007

Base isolation can be used both to protect the structure and simultaneously to reduce the response of internal equipment. The seismic response of a base‐isolated structure has been studied through the shaking table test or numerical calculation before. The object of this paper is to analyse a base‐isolated structure by a different analytical approach—perturbation analysis.

Recognizing that the horizontal stiffness of an isolation system is much smaller than that of the superstructure, the mathematical expressions of the modal properties of base‐isolated structures are derived by the perturbation method in terms of the modal properties of the superstructure and used to study the dynamic response of superstructure and attached equipment in the base‐isolated building.

This study shows that the first base‐isolated mode not only controls the superstructural response but also dominates the response of high‐frequency attachment. The contribution of higher modes to the response of base‐isolated structures, which is proportional to the horizontal stiffness of isolation system, is very small.
Formulae for errors for initial displacement and velocity problems using the Newmark method
Authors: Warburton G. B.
Published: April 2007

A standard test of the Newmark method in structural dynamics is its application to the determination of the response of a damped or undamped single‐degree‐of‐freedom system to a prescribed initial displacement or velocity. In this paper formulae for the error, Δj, in the response, after applying the Newmark method for j time‐steps each of duration Δt, are proposed and their acceptable accuracy is demonstrated.
Effects of concrete cracking on the earthquake response of gravity dams
Authors: Vargas‐Loli Luis M. , Fenves Gregory L.
Published: April 2007

Tensile stresses exceeding the tensile strength of concrete can develop in concrete dams subjected to earthquake ground motion. This study examines the earthquake response of gravity dams including tensile cracking of the concrete. The interaction between the dam and compressible water is included in the analysis using a numerical procedure for computing the non‐linear dynamic response of fluid‐structure systems. The crack band theory is used to model tensile cracking with modifications to allow for the large finite elements necessary for dam analysis. The earthquake response of a typical gravity dam monolith shows that concrete cracking is an important non‐linear phenomenon. Cracking is concentrated near the base of the dam and near the discontinuities in the face slope. The extensive cracking, which develops due to ground motion typical of maximum credible earthquakes, may affect the stability of dams during and after strong earthquakes.
Soil‐pile‐structure interaction effects on the seismic response of a cooling tower
Authors: Ahn Kijun , Gould Phillip L.
Published: April 2007

A study of the effects of soil‐pile‐structure interaction on the response of rotational shell structures supported by a group of vertical piles is presented. The interaction effects are included in the dynamic analysis through the development of a frequency dependent boundary system at the interface between the shell and the underlying foundation. The substructure method is used to simplify the connection problem between the shell and the pile foundation. A free vibration analysis of a cooling tower is carried out to investigate the dynamic properties of rotational shells with four different foundation stiffnesses. The effects of soil‐pile‐structure interaction on the response in the shell are demonstrated by a complex response analysis of a cooling tower.
Attenuation of seismic intensity in Albania and Yugoslavia
Authors: Trifunac M. D. , Todorovska M. I.
Published: April 2007

Average and standard deviations of hypocentral distances to selected isoseisms are presented for Albania and Yugoslavia. The results apply for the Medvedev‐Karnik‐Sponheuer (MKS) intensity, provided that all data are corrected to a unified MKS equivalent intensity as defined by Shebalin et al.19 The results should be useful in general macroseismic studies in these two countries, but are essential for the development of microzonation maps when the seismicity is described in terms of the locally available intensity catalogues.

The observed attenuation of the intensities versus the hypocentral distance is similar to the attenuation of the Modified Mercalli Intensity (MMI) in the western United States of America. This finding should facilitate the use of other empirical scaling relations, developed in California, for various predictions of the characteristics of strong earthquake shaking in Albania and Yugoslavia.
Modal identification of self‐adjoint distributed‐parameter systems
Authors: Norris Mark A. , Silverberg Larry
Published: April 2007

A new method is introduced for the identification of modal quantities of self‐adjoint distributed‐parameter systems. The method uses the temporal and spatial orthogonality properties of distributed‐parameter systems to form a pseudo‐Rayleigh quotient. The stationary values of the pseudo‐Rayleigh quotient can be determined by the solution of an eigenvalue problem, where the eigenvalues and eigenfunctions provide the frequencies and natural modes of the distributed‐parameter system. By way of formulation, the method is insensitive to zero mean measurement noise and is applicable to continuous as well as discrete systems. Numerical examples are presented in which the modal quantities of a simply‐supported beam and a discrete model of a membrane are identified. The results are compared with another modal identification technique, namely, the Ibrahim time domain method.
An improved implicit‐explicit time integration method for structural dynamics
Authors: Miranda Isidoro , Ferencz Robert M. , Hughes Thomas J. R.
Published: April 2007

An explicit predictor‐corrector algorithm is derived from the implicit α‐method. This explicit algorithm is shown to have better stability and accuracy properties than its Newmark‐based predecessor. This algorithm is then combined with the implicit α‐method, resulting in an implicit‐explicit α‐method which can be effectively utilized for linear and non‐linear structural dynamics calculations.
Response analysis of hysteretic multi‐storey frames under earthquake excitation
Authors: Nielsen S. R. K. , Mørk K. J. , Thoft‐Christensen P.
Published: April 2007

Local incremental stiffness relations are formulated for a class of elasto‐plastic beam elements. The earthquake acceleration is modelled as a filtered white noise process. The Itǒ differential equations of the integrated system made up of the structural system and the excitation process are then formulated. Instead of the original system an equivalent nonlinear system is considered, in which the drift vector is given by a series expansion of order n ≧ 1, where n = 1 represents the well‐known case of equivalent linearization. Only components of the drift vector representing the non‐analytieal constitutive equations are replaced by a polynomial expansion. The coefficients of this expansion are determined from a least mean square criterion, and are sequentially updated. Especially an equivalent system with a cubic expansion to the drift vector is investigated. The hierarchy of statistical moment equations is closed by a cumulant neglect closure scheme. The method has been applied to a two‐storey frame. The results are compared to those of numerical simulation, and provide substantial improvements compared to equivalent linearization.
Analytic solutions for soil‐structure interaction in layered media
Authors: Liou Gin‐Show
Published: April 2007

The total system studied in this paper is a layered soil stratum with a rigid bedrock and a cylindrical cavity on the surface. Analytic solutions for the layered medium with prescribed harmonic displacement time history on the surface of the cylindrical cavity are presented. The whole soil domain is divided into interior and exterior domains. The interior domain is the projection of the cylindrical cavity down to the rigid bedrock, whereas the exterior domain is then the soil medium complement to the interior domain. The displacement and stress fields in both domains are expanded as an infinite series of Fourier components with respect to the azimuth. For each Fourier component in the infinite series, the solutions for both domains are found independently by solving the general differential equations of wave propagation satisfying the boundary conditions of the top surface and the lower rigid boundary. Displacement and stress continuity conditions are then imposed on the vertical interface between the two domains using the formulation of a weighted residual. For the soil‐structure interaction problem, the impedance matrix at the interface between the structure and the soil medium can be easily generated using the analytic solutions, which can then be combined with the finite element model of the structure. A simple example is presented to demonstrate the effectiveness of the procedure presented.
The dynamics of interstructural connection to prevent pounding
Authors: Westermo Bruce D.
Published: April 2007

This paper examines the dynamic implications of connecting closely neighbouring structures for the purpose of eliminating pounding during earthquakes. To prevent this destructive contact the structures are connected by a link and beam system which transmits the connection forces to the floors of the structures. Four specific cases are used as examples of the effects.

The coupled system is modelled as a combined mass and stiffness matrix problem which allows the traditional methods for analysis. The mode shapes and natural frequencies for these cases are examined, and it is shown that the general response characteristics can be derived from the coupled system's frequencies and modes. Estimates of the fundamental frequency of the coupled system are derived. Both the harmonic and earthquake response are examined for the four cases. In all circumstances the linkage reduces the relative overlap deflection of the structures at large amplitudes, but it also increases the base shear on the stiffer of the two structures at excitation frequencies below the fundamental frequency. It is shown that bounds on the base shear are derivable from the change in the fundamental frequencies. The dependence of the response characteristics on the stiffness of the coupling beam is also examined.
Seismic responses of deck‐type arch bridges
Authors: Dusseau Ralph A. , Wen Robert K.
Published: April 2007

The dynamic responses of three deck‐type arch bridges, with main spans of 59,213 and 518m, are presented. The ratios of natural period to arch span were found to be quite close for all three bridges. Artificial ground motions were applied separately in three directions to finite‐element models of each bridge. Three acceleration levels were considered—0.09g, 0.22g and 0.50g—corresponding to the AASHTO Seismic Risk Zones I, II and III, respectively. Responses to uniform lateral motion were generally the largest, while the responses to vertical motion were generally lower than those due to lateral or longitudinal motion. In all cases considered, none of the total stresses in the main members exceeded the yield stress. Connection and secondary member responses were also calculated and are presented. In addition, the effects of unequal motions at the supports were sampled by various deterministic inputs. While the effects of such motions in the vertical and lateral directions were less than the responses to uniform motion, the effects of unequal longitudinal motions at the supports were substantial.
Symmetrical fft technique and its applications to earthquake engineering
Authors: Katukura Hiroshi , Ohno Susumu , Izumi Masanori
Published: April 2007

The objective of this paper is to propose an FFT technique symmetrical for time and frequency, in which the symmetrization is done by introducing generating functions. By the symmetrical treatment, it becomes possible to derive several complementary relations in the time and frequency domains. Based on the idea of the symmetrical FFT technique, the phase problem of seismic waves is discussed not only in the frequency domain but also in the time domain. Furthermore, the deconvolution technique to evaluate the minimum‐phase‐shift and all‐pass functions of seismic waves, which is not discussed sufficiently in earthquake engineering, is developed in the two domains. Numerical examples to present these basic ideas are also illustrated in the symmetrical framework.
Soil‐structure interaction experiment using impulse response
Authors: Mita A. , Yoshida K. , Kumagai S. , Shioya K.
Published: April 2007

A new experimental method using a finite soil model with no special treatement on its boundaries is employed for soil‐structure intration problems to simulate the semi‐infinitenesss of the actual soil medium. The present method utlizies the characteristics of transient response to an impluse load to obtain the impedance functions and effective input motions for surface and embedded foundations. This technique is applicable to a linear elastic system whose impulse response decreases to a small enough value before observing the reflected waves. The experimentally obtained impedance functions and effective input motions are compared with those obtained by the direct boundary integral equation method and the hybrid approach. Good agreement between the xperimental and analytical results validates the present method as well as the accuracy of the numerical tools.
Base‐isolated buildings with soil‐structure interaction
Authors: Novak M. , Henderson P.
Published: April 2007

The equations of motion of building systems with soil‐structure interaction are formulated for foundations comprising a joint mat or a set of individual spread footings. The influence of soil‐structure interaction and the possible effects of building and foundation rocking are examined by investigating the modal properties. Simplifications in the analysis are also suggested.
A study of seismic response characteristics of structures with friction damping
Authors: Malushte S. R. , Singh M. P.
Published: April 2007

The effectiveness of introducing Coulomb damping in structures to reduce seismic response is evaluated. Response characteristics of simple one‐degree‐of‐freedom structures with sliding interfaces between the top slab and supporting frame and between the base and foundation are studied and compared. It is shown that, analytically, the top slab sliding system is a special case of the base sliding system. The slab sliding system is seen to offer certain advantages over the base sliding system inasmuch as it provides a more effective reduction in the lateral forces in the supporting frame as well as a better isolation of supported secondary systems, as depicted by a significantly reduced level of floor spectrum response. The analytical ease of predicting the response of the slab sliding system is also demonstrated. The required unobstructed sliding displacements seem to be reasonable except, may be, for flexible systems. The similarities and differences between the hysteretic and slab sliding systems are also highlighted by comparison of their response results.
On the rotational components of seismic motion
Authors: Castellani A. , Boffi G.
Published: April 2007

The surface motion during an earthquake is different from point to point depending on the propagation properties of the seismic waves. Rocking and torsion are thus present in the free field, in proportion to the spatial derivatives of the surface motion with respect to a given direction. These derivatives are inversely proportional to the apparent wave velocity in that direction, so the smaller the wave apparent velocity, the more important its contribution to the rotations. In this respect, a marked contribution to surface rotations from surface waves is expected.

A mathematical model is presented, based on a detailed representation of soil impedance, an approximate identification of surface waves and a deconvolution of body waves in P and SV contributions. Through this model the surface motion obtained from the records of strong‐motion accelerometers can be expressed as a superposition of plane waves of known wavelengths.

Rocking response spectra are computed and results are compared with previously published spectra. A sensitivity analysis is performed on some parameters of the model.
Influence of lateral‐load‐resisting system on the earthquake response of structures—a system identification study
Authors: Papageorgiou Apostolos S. , Lin Bing‐Chang
Published: April 2007

Analysis and comparison of the dynamic responses of three well instrumented (with accelerographs) high‐rise buildings shaken during the 1984 Morgan Hill earthquake are presented. The buildings examined in the present work are (i) the Town Park Towers Apartment building, a 10‐storey, concrete shear wall building; (ii) the Great Western Savings and Loan building, a 10‐storey building with concrete frames and shear walls; and (iii) the Santa Clara County Office building, a 13‐storey, moment‐resistant steel frame building. The structures are located within 2 km of each other and, as may be confirmed by visual inspection of the recorded seismograms, experienced similar ground motions. One‐dimensional and three‐dimensional linear structural models are fitted to the observations using the modal minimization method' for structural identification, in order to determine optimal estimates of the parameters of the dominant modes of the buildings. The time‐varying character of these parameters over the duration of the response is also investigated. Comparison of the recorded earthquake response of the structures reveals that the type of lateral‐load‐resisting system has an important effect on the dynamic behaviour of the structures because it controls the spacing of the characteristic modes on the frequency axis. The Santa Clara County Office building has closely spaced natural frequencies and exhibits strong torsional response and modal coupling. Its dynamic behaviour is contrasted with that of the Great Western Savings and Loan building which has well separated natural frequencies and exhibits small torsional response and no modal coupling. Strong modal coupling causes a beating‐type phenomenon and makes earthquake response of structures different from that envisioned by codes.
Full‐scale dynamic testing of the Alamillo cable‐stayed bridge in Sevilla (Spain)
Authors: Casas Juan R.
Published: April 2007

Accelerations and displacements due to dynamic excitation by simulated traffic consisting of two trucks, were measured on the deck and tower of the Alamillo cable‐stayed bridge. Also the dynamic testing program included the measurement with accelerometers of the free‐damped vibration of the 26 cables achieved by means of quick‐releasing force. From these measurements it was possible to obtain the dynamic parameters of the bridge (natural frequencies and damping ratios) and the real forces in the cables. In the paper, only the tests, results and conclusions related to dynamic parameters of the bridge are presented. The objective of the dynamic tests herein described was to validate the mathematical modelling and the wind‐tunnel models used in the dynamic analysis of the bridge in front of traffic and wind‐forces. As the agreement between dynamic parameters of the real bridge and theoretical and scaled models was very satisfactory, the correct dynamic behaviour of the bridge in response to traffic and wind (vortex shedding, flutter, etc.) can be deduced jointly with the correct alignment and expected internal forces in the permanent state in tower and deck.