bluuebunny/crossref_metadata_2025 huggingface dataset:
Impedances of embedded rigid strip foundations
Authors: Rajapakse R. K. N. D. , Shah A. H.
Published: March 2007

This paper is concerned with the dynamic response of rigid strip foundations of arbitrary geometry embedded in a homogeneous elastic half‐space. The embedded rigid foundation is modelled by an equivalent domain in a uniform half‐space which is subjected to an appropriate body force field. The components of the impedance matrix are determined through the solution of a linear simultaneous equation system which is established by invoking rigid body displacements of discrete locations within the equivalent domain and appropriate equilibrium consideration. It is found that high numerical efficiency and flexibility can be achieved using the body force model when compared to boundary integral formulations through the selection of appropriate displacement influence functions and a ‘parent domain’ in the analysis. Numerical results are presented to illustrate the influence of the embedment ratio, frequency of excitation, foundation geometry and Poisson's ratio on the vertical, horizontal, rocking and coupled impedances of a single embedded foundation. The effect on the impedance due to the presence of an adjacent embedment is investigated for various distances between foundations and embedment ratios.
Seismic risk analysis with predictable models
Authors: Grandori Guagenti E. , Molina C. , Mulas G.
Published: March 2007

Recent studies show that, in some seismogenetic areas, strong earthquakes occur rather predictably. Their pattern of occurrence, however, cannot be interpreted according to a classic model of seismic risk analysis.

It is shown that semi‐Markov models are capable of interpreting predictable behaviour and, in particular, the types suggested by the Slip Predictable Model, the Time Predictable Model and the Characteristic Earthquake Model. A number of general properties are demonstrated, dealing with return periods, waiting times, damage cost, stationary and variable characteristics of seismic risk analysis.

The case of Friuli is then examined and its semi‐Markovian interpretation is discussed. This interpretation is compared with others which also are possible, and the consequences for the computation of hazard and risk terms are evaluated.
Lifeline response to spatially variable ground motions
Authors: Zerva Aspasia , Ang Alfredo H‐S. , Wen Y. K.
Published: March 2007

Lifeline systems have been heavily damaged during past earthquakes; this has often been attributed to the effect of differential ground motion at the supports of these long structures. Based on a stochastic model for the ground excitation the responses of pipelines and bridges of various span lengths subjected to either perfectly or partially correlated random input motions in the axial, lateral (i.e. transverse horizontal) and vertical directions are investigated and the significance of the spatial variation of ground motion is examined.
On low‐frequency errors of uniformly modulated filtered white‐noise models for ground motions
Authors: Safak Erdal , Boore David M.
Published: March 2007

Low‐frequency errors of a commonly used non‐stationary stochastic model (uniformly modulated filtered white‐noise model) for earthquake ground motions are investigated. It is shown both analytically and by numerical simulation that uniformly modulated filter white‐noise‐type models systematically overestimate the spectral response for periods longer than the effective duration of the earthquake, because of the built‐in low‐frequency errors in the model. The errors, which are significant for low‐magnitude short‐duration earthquakes, can be eliminated by using the filtered shot‐noise‐type models (i.e. white noise, modulated by the envelope first, and then filtered).
Comparative performance of friction damped systems and base isolation systems for earthquake retrofit and aseismic design
Authors: Filiatrault A. , Cherry S.
Published: March 2007

The seismic performance of a steel framed structure equipped with (i) friction damping devices and (ii) base isolators is compared. A parametric study based on energy concepts is performed first using time‐history dynamic analysis to determine the optimum properties of the two systems when excited by an earthquake whose energy is distributed over a relatively broad frequency band (1940 El Centro, N‐S). Using these same properties, the responses of the two structural systems are then examined when excited by earthquakes whose power content essentially is concentrated at the low frequency end of the energy spectrum (1977 Romania, Bucharest, N‐S and 1985 Mexico, SCT E‐W). The results of the study show that, while both systems similarly reduce the response of conventional structures to the California earthquake, the friction damped structure exhibits a superior performance under the low frequency earthquakes. Very large shear forces and displacements are observed when the Romania and Mexico earthquakes are applied to the base isolated structure, indicating that the performance of a base isolated structure depends on the characteristics of the site earthquake. By comparison, friction damped structures are shown to behave favourably under the three earthquakes studied; this suggests that friction damping devices offer a more consistent way of protecting structures during earthquakes.
Open‐loop vibration control of elastic structural elements
Authors: Ebrahimi N. D.
Published: March 2007

This paper discusses a general technique for vibration control of simple, continuous mechanical systems. The discussion involves giving the expressions for the response of an illustrative element (fixed‐free bars) to a sinusoidal disturbance and then formulating the problem of open‐loop vibration control of this system as a mathematical programming problem. The final step uses numerical optimization techniques to find the control forces. When these techniques are used, the amplitude of the system's steady state response is minimized. The discussion also shows that while this method effectively controls the vibration, it has a great deal of flexibility in accomplishing its stated purpose.
Pounding of buildings in series during earthquakes
Authors: Anagnostopoulos Stavros A.
Published: March 2007

A simplified model of several adjacent buildings in a block is used to study the pounding of such buildings due to strong earthquakes. Considerable structural damage and even some collapses have sometimes been attributed to this effect. Each structure is modelled as a S.D.O.F. system and pounding is simulated using impact elements. A parametric investigation of this problem shows that the end structures experience almost always substantial increases in their response while for ‘interior’ structures the opposite often happens. This may explain why high percentages of corner buildings have collapsed in some earthquakes.
Analysis of shaking table‐structure interaction effects during seismic simulation tests
Authors: Blondet Marcial , Esparza Carlos
Published: March 2007

An analytical model is developed to evaluate performance characteristics of unidirectional seismic simulators (shaking tables). The validity of the model is verified with experimental measurements of the frequency response of the shaking table at the Catholic University of Peru.

Interaction effects between shaking table and structure are first studied by analysing the response of a two DOF (degree of freedom) oscillator with mechanical properties representative of the actuator‐table‐structure system. A single DOF viscoelastic oscillator representing the structural test specimen is then included in the analytical model of the seismic simulator, and the behaviour of the combined system is evaluated, in the frequency domain, in terms of response stability and accuracy of reproduction of the command signal. Numerical simulations of system response under different load conditions are subsequently performed in order to study the influence of shaking table and test structure characteristics on the interaction phenomenon.

The results obtained explain some of the performance degradation observed in seismic simulation tests involving very heavy structures and provide guidelines for the design of more reliable shaking table systems.
Decoupled dynamic analysis of combined systems by iterative determination of interface accelerations
Authors: Spanos P. D. , Cao T. T. , Jacobson C. A. , Nelson D. A. R. , Hamilton D. A.
Published: March 2007

A dynamic analysis technique is presented that can be used to determine the response of a discrete model of a large linear structural system composed of multiple substructures. The technique circumvents the costly computation of the modal characteristics of the combined system. This is accomplished by relying on a predictor‐corrector scheme to converge iteratively to the interface accelerations of the combined system, while the equations of motions of the individual structures are integrated separately. In this regard, the temporal slopes of the interface accelerations (jerks) are computed at each time point of integration to predict the interface accelerations at the next time point. The proposed technique is exemplified by conducting a space shuttle landing loads analysis; the obtained numerical data demonstrate its reliability and efficiency.
Vibration control of structures under earthquake loading by three‐stage friction‐grip elements
Authors: Roik K. , Dorka U. , Dechent P.
Published: March 2007

The behaviour of a building subjected to a strong‐motion earthquake depends highly on its energy dissipation capacity. By introducing three‐stage friction‐grip elements, the energy dissipation within each storey can be ‘designed’ according to definable stages (e.g. serviceability, medium‐ and strong‐motion earthquake). Tests on simple steel‐concrete‐ and steel‐steel‐friction‐grip connections have proved their very satisfactory behaviour under high dynamic loading, showing no considerable damage when well designed. Examples of horizontal stiffening elements are given to illustrate the construction of three‐stage elements with either steel‐steel‐ or steel‐concrete‐friction‐grip joints.

By computing the response of a seven storey building designed as a steel frame (‘ductile system’ philosophy), concrete core (‘stiff system’‐philosophy) and three‐stage truss and being subjected to the 1940 El Centre earthquake, the superior performance of three‐stage elements and its economic advantage over the other two systems becomes apparent. Although this is just one illustrative example, it is nevertheless an important one, because it resembles the type of building that would respond best to the application of three‐stage building brakes. Finally, the result of an online test on a three‐stage element is given. This realistic earthquake simulation proved the behaviour to be adequately close to the basic philosophy and yielded important design implications for three‐stage elements.
Optimum design of single‐frequency dynamic dampers
Authors: Ebrahimi Nader D.
Published: March 2007

The problem of damping the vibration amplitude of machines and structures has considerable practical importance. This paper discusses the design of optimum vibration absorbers for linear damped systems operating at a certain excitation frequency. The problem is first formulated as a mathematical programming scheme. The systematic design discussed in this paper has significant advantages for those vibratory systems run primarily at a specific frequency.
Elastic‐plastic response spectra for different hysteretic rules
Authors: Minami Tadao , Osawa Yutaka
Published: March 2007

The general features of elastic‐plastic response spectra for several accelerograms that are widely used for the design buildings in Japan were studied in terms of the effects of the different hysteretic models used in the analyses. Lare fluctuations existed in the spectra for both input ground motion and the different models. The models were classified according to their strain energy‐absorbing capacities in three groups, within each of which the relevant nature of elastic‐plastic responses of the structures were similar. Finally, empirical formulae with which to estimate two measures structural damage, the ductility factors and cumulative plastic displacement normalized by the yielding displacement, wer developed for each group of hysteretic models.
Criterion of stability and implementation issues of hybrid frequency‐time‐domain procedure for non‐linear dynamic analysis
Authors: Darbre Georges R. , Wolf John P.
Published: March 2007

A criterion of stability pertaining to the hybrid frequency‐time‐domain procedure is derived. It stems from the initial‐value theorem on one side and from the condition of convergence which applies to the harmonic counterpart of the procedure on the other side. The criterion depends on the dynamic stiffnesses of both the original non‐linear system and the pseudo‐linear system evaluated at the Nyquist frequency. Since at this frequency both stiffnesses are usually controlle by the mass, the criterion of stability is satisfied for most structural systems. The procedure must, however, be applie sequentially to individual time segments. The validity of this criterion is confirmed by a numerical investigation performe for a SDOF system.

The solution of non‐linear dynamic problems requires consideration of implementation issues which are also discusse in the paper. The analysis of a non‐linear soil‐structure‐interaction system in which the soil's stiffness coefficients an directly defined in the frequency domain also demonstrates the accuracy of the hybrid frequency‐time‐domain procedure.
Spatial variation and stochastic modelling of seismic differential ground movement
Authors: Loh Chin‐Hsiung , Yeh Yeong‐Tein
Published: March 2007

Specially designed arrays of strong motion seismographs located near earthquake sources are required for engineering studies of near‐source earthquake properties as well as spatial variation of seismic waves. The SMART‐1 array in Tath provides good records for this type of study. Based on the SMART‐1 array data, the analysis of the principal direction wave propagation and the space‐time correlation of some events recorded by SMART‐1 have been studied. A stoce model for predicting the differential ground movement was also developed. This stochastic model includes the effect of source characteristics, attenuation of wave passage and spatial correlation characteristics. The performance of this more discussed and compared with the ground movement recorded by the SMART‐1 array. From the present study, it is that spatial correlations do exist as seismic waves propagate across the array site. Generally, the loss of coherence is direction of propagation can be explained by energy at the same frequency exhibiting a slightly different velocity with the measurement intervals. It is also concluded that the phase velocity of seismic waves and the corner frequency of the grep displacement spectrum are controlling factors in the prediction of the root mean square of differential grep displacement.
Implementation of effective seismic input for soil‐structure interaction systems
Authors: Cremonini Marco G. , Christiano Paul , Bielak Jacobo
Published: March 2007

A previously introduced method for transmitting effective seismic excitation to a discretized soil‐structure system implemented. The method permits free‐field excitation of a linear soil system to be specified within the regie of computation, arbitrarily close to a zone that includes the (possibly non‐linear) structure and local subgrade and bae, thus eliminating the need to transmit the seismic excitation through artificial boundaries. This approach is demonse through a numerical example comprising a linear, two‐dimensional system. Some comments also are made on the rere efficiencies of various local absorbing boundaries.
Fluid‐structure interaction effects for offshore structures
Authors: Veletsos A. S. , Prasad A. M. , Hahn G.
Published: March 2007

Comprehensive analyses are made of the differences in the responses of simple models of offshore structures computed by the standard and extended versions of Morison's equation for the hydrodynamic forces, and of the effects and relative importance of the numerous parameters involved. The responses also are evaluated by the equivalent linearization technique and Penzien's decoupling technique, and the interrelationship and accuracy of these approaches are elucidated. The results are displayed graphically in the form of response spectra for absolute maximum displacement employing dimensionless parameters that are easy to interpret and use. In addition, the decoupling technique is generalized to include consideration of a current of constant velocity, and a simple modification is proposed which improves the accuracy of this approach. A particularly simple approximation is included for the hydrodynamic modal damping values of multi‐degree‐of‐freedom, stick‐like systems.
Modal superposition method for seismic design of non‐linear multistorey structures
Authors: Villaverde Roberto
Published: March 2007

An approximate procedure is introduced to analyse non‐linear multistorey structures within the framework of the conventional response spectrum method. Its derivation is based on the use of non‐linear response spectra and an approximate decomposition of the equation of motion for multi‐degree‐of‐freedom non‐linear systems. The decomposition is attained by considering the non‐linear terms in this equation of motion as additional external forces and, thus, by interpreting it as the equation of motion of linear systems with the initial properties of the non‐linear ones when subjected to a modified set of inertia forces. For simplicity, the procedure is herein limited to elastoplastic systems of the shear‐beam type. Its accuracy is evaluated by comparing the approximate and step‐by‐step integration solutions of systems with three and ten degrees of freedom when subjected to three different earthquake ground motions.
Response of a randomly inhomogeneous layer overlying a homogeneous half‐space to surface harmonic excitation
Authors: Hryniewicz Z. , Hermans A. J.
Published: March 2007

The paper is concerned with the study of the effect of the randomness of material parameters on mean wave propagation in a semi‐infinite viscoelastic medium. The medium considered in this paper is a configuration of a randomly non‐homogeneous layer overlying a homogeneous half‐space and is loaded harmonically on the top surface. The method used is that of Karal and Keller and is based on the idea of fundamental matrix and Bourret approximation. The integro‐differential equation obtained in this paper is solved by the Laplace transform method. By using boundary and continuity conditions the mean wave solution is obtained. Numerical results show that the correlation functions, which introduce long‐range interactions, can be the source of the wave amplification.
A solution procedure for the earthquake analysis of arch dam‐reservoir systems with compressible water
Authors: O'Connor J. P. F. , Boot J. C.
Published: March 2007

Two processes using the Newmark implicit integration scheme are presented for the analysis of the earthquake response of a three‐dimensional model for arch dam‐reservoir systems including the effect of compressibility of the water. The solid structure and fluid regions are modelled separately, and the forcing functions at the interface are due to the hydrodynamic pressures from the reservoir acting on the upstream face of the dam wall, and the accelerations from the dam wall acting in turn on the reservoir.

For the purposes of an initial investigation, elastic properties are assumed for the material of the dam, whilst in the reservoir radiation damping at the upstream boundary has been included, but bottom absorption has not. The excitation is provided by means of a combisweep which is fashioned so that its continuously varying frequencies pass through the fundamental frequencies of both the arch dam‐reservoir system and the reservoir alone. Consequently the response is highly resonant, thus providing a severe test for the numerical procedures. From the numerical results obtained for an example problem it is concluded that both schemes provide an acceptable solution to the problem posed, and the possibility of enhancement to cater for more complex situations is discussed.
Draft eurocode 8—sample seismic force calculations for discussion purposes
Authors: Hayhurst C. J. , Maguire J. R.
Published: March 2007

Draft Eurocode 8 (Common Unified Rules for Structures in Seismic Regions1) is open for study and comment until the latter part of 1989. This paper presents sample seismic force calculations for an idealized building, to illustrate the differing forces which result from the alternative calculation methods allowed. It is tentatively suggested that part of the Draft be revised as a result of the above.
Calculation of foundation uplift effects using a numerical laplace transform
Authors: Hillmer P. , Schmid G.
Published: March 2007

A Laplace domain technique to calculate non‐linear foundation uplift effects is presented. Analysis in the Laplace domain permits the modelling of the building structure more precisely by using continuous mass models. Different damping models for every single finite element of the sturcture can easily be utilized via the correspondence principle. Moreover, it is possible to use the substructure method, which permits the modelling of the soil and the building structure separately by different methods. Using, e.g. the boundary element method for the soil, the damping mechanism caused by waves travelling away from the foundation (geometric damping effects) is implicitly included. The model can be condensed to the relevant degrees of freedom of the structure. Two illustrative numerical examples demonstrate the applicability of the method presented.
Wave scattering by a canyon of arbitrary shape in a layered half‐space
Authors: Vogt Rudolf F. , Wolf John P. , Bachmann Hugo
Published: March 2007

To calculate the generalized scattered motion in the region of a canyon of arbitrary shape in a horizontally layered half‐space, the indirect‐boundary‐element method in the frequency domain is applied. Fictitious distributed source loads acting on the line which will form the surface of the canyon are used. The corresponding Green's functions, which are determined by a transformation to the wave‐number domain, satisfy the conditions at the interfaces of the adjacent layers including those at the free surface. The discretization with boundary elements can thus be restricted to the line which will form the surface of the canyon. By formulating a weighted residual statement, the sum of the surface tractions composed of those of the free field and of the fictitious loads averaged over each boundary element are set equal to zero.

Based on vast parametric studies addressing inclined body waves and surface waves for the out‐of‐plane and in‐plane cases, the amplification patterns within and adjacent to the canyon are studied and conclusions are stated.
Spline approximations for direct integration of structural dynamics
Authors: Liao Ching‐Lung , Wang Hung‐Chih
Published: March 2007

The application of spline functions in the analysis of structural dynamics is presented in this paper. The nodal points in time discretization for determining the spline curve can be separated into two classes: the p nodal points before the current time (including current time) and the q nodal points after the current time. On the p nodal points, the structural responses were calculated at previous time steps. The q nodal points represent the unknown structural response at future time steps which should meet the requirement of dynamic equilibrium. By a trial and error procedure, at least 16 families of spline curves with different locations of p and q nodal points can be found to meet the requirements of unconditional stability. The accuracy of each family is dependent on the order of the spline and the locations of the nodal points. The 16 families of spline curves supply a wide range of accuracy that can be selected easily. It can be shown that the well‐known Wilson‐method and the Houbolt method are special cases of the present spline approximations.
A simple dynamic substructure method
Authors: Leung A. Y. T.
Published: March 2007

The dynamic substructure method in harmonic vibration is reformulated. A method to accelerate the convergence of D−1 with respect to the number of fixed interface modes is introduced. Comparison is made with the methods of Guyan and Irons, Ritz vector, substructure synthesis and dynamic substructure. A close relation among the methods is examined. The present method can predict more global modes than the number of degrees of freedom retained. It is the most economical in operation counts among the methods for systems having many identical substructures.
Seismic response of structures supported on R‐FBI system
Authors: Mostaghel N. , Khodaverdian M.
Published: March 2007

Aseismic base isolation is increasingly being utilized to protect structures and their contents against earthquakes. The R‐FBI (Resilient‐Friction Base Isolator) bearings provide a new isolation system. The equations of motions of elastic plane structures supported on R‐FBI bearings and a procedure for their solutions are presented. The responses of a five‐storey 1/3‐scaled frame model to both horizontal components and horizontal and vertical components of six different ground motion records for fixed base and isolated base are evaluated. To estimate the prototype response, the ground motion records are time scaled by The effects of initial base displacement and non‐symmetric friction caused by small differential settlements are also considered. It is concluded that R‐FBI reduces the acceleration response considerably without inducing large base displacements or leaving large residual displacements.
Seismic stability of concrete gravity dams
Authors: Léger P. , Katsouli M.
Published: April 2007

Linear finite element analyses are commonly used to simulate the behaviour of gravity dam—foundation systems. However, the foundation is generally unable to develop any significant tensile stresses. Therefore any tension occurring in the vicinity of the dam—foundation interface is largely fictitious. Moreover, the traditional overturning and sliding stability criteria have little meaning in the context of the oscillatory response of dams during earthquakes.

In this study, time domain analyses using non‐linear contact elements located at the dam—foundation interface have been used to determine the dynamic sliding and uplifting response of gravity dam monoliths considering various elastic foundation properties. The magnitudes of the relative interface displacements, of the percentage of base not in contact (PBNC) and of the compressive stresses at the heel or toe of the dam have been used to monitor the seismic stability.

The numerical results have shown that the non‐linear behaviour of the dam—foundation interface reduces the seismic response of the system, indicating the possibility of more rational and economical designs. The PBNC was identified as the critical seismic stability response parameter for all analyses except for very flexible foundation conditions where the maximum values of relative interface displacements need to be considered.
Bracketed and normalized durations of earthquake ground acceleration
Authors: Kawashima Kazuhiko , Aizawa Koh
Published: April 2007

Multiple regression analyses of the duration of earthquake ground acceleration are presented. Two types of duration are considered, i.e. bracketed duration and normalized duration. The bracketed duration ta is defined as the elapsed time between the first and last acceleration excursions greater than a [cm/s2], and the normalized duration Tα is defined as the elapsed time between the first and last acceleration excursions greater than α times (0 < α < 1) the peak acceleration. Employed are 394 components of horizontal strong motion acceleration records obtained at 67 free field sites in Japan. With the use of multiple regression analysis, the dependence of the bracketed and normalized durations on earthquake magnitude and epicentral distance is studied.
Dynamic response of axisymmetric embedded foundations
Authors: Emperador J. M. , Dominguez J.
Published: April 2007

The boundary element method is used to obtain dynamic stiffness functions of rigid cylindrical foundations embedded in a uniform or layered viscoelastic half‐space. Dynamic stiffness functions of hemispherical foundations embedded in a uniform half‐space are also computed. The direct integral equation formulation is used in combination with the complete space point load fundamental solution that is integrated numerically along the azimuthal coordinate. The approach is easy to implement because of the simplicity of the fundamental solution. The numerical results obtained by this method for cylindrical and hemispherical foundations are very close to corresponding published results obtained by different procedures. A parametric study shows the important effects of the Poisson's ratio on the dynamic stiffness functions of cylindrical foundations embedded in a uniform viscoelastic half‐space. The effect of the bedrock compliance on the stiffness functions is also shown in the case of cylindrical foundations embedded in a soil layer that rests on a bedrock.
Additional seismic inelastic deformation caused by structural asymmetry
Authors: Tso W. K. , Ying Hongshan
Published: April 2007

Using a single mass monosymmetric model, this paper examines the additional seismic inelastic deformations and displacement caused by structural asymmetry of the model. Stiffness eccentricity and resistance eccentricity are used as measures of asymmetry in the elastic and inelastic range respectively. Seven ways of specifying strength distribution among resisting elements are considered, including code provisions from Canada, Mexico, New Zealand and the United States. These specifications are related t o the model resistance eccentricity.

It is shown that when torsional shears are included in the strength design of the elements, the structure in general will have small resistance eccentricity, even if it has large stiffness eccentricity in the elastic range. For structures which are designed with allowance for torsional shears, the ductility demands on the elements are similar to those when the structure is symmetrical. However, the edge displacements can be up to three times that if the system is symmetrical. This finding has significant implications in evaluating adequate separation between buildings to avoid the pounding problem during earthquakes.
Discrete models for vertical vibrations of surface and embedded foundations
Authors: De Barros Francisco C. P. , Luco J. Enrique
Published: April 2007

A five‐parameter discrete model that approximates the dynamic force4isplacement relationship for rigid foundations undergoing vertical vibrations on a uniform elastic half‐space is presented. The model involves a combination of two springs, two viscous dampers and a mass. Values of the parameters for circular, square and rectangular foundations placed on the surface or embedded in an elastic half‐space are listed. The parameters are obtained by minimizing the discrepancy between the force4isplacement relation for the model and that obtained by solution of the mixed boundary‐value problem of the rigid foundation on an elastic half‐space. The definition of an appropriate input motion to represent wave excitation is also discussed. The input motion to the discrete model differs from the input motion that should be used in a continuum model.
Response analysis of flexible MDF systems for multiple‐support seismic excitations
Authors: Yamamura Nobumichi , Tanaka Hiroshi
Published: April 2007

Two practical approaches, response spectrum and time‐history methods, are developed to evaluate the response of flexible multi‐degree‐of‐freedom (MDF) systems, notably long‐span bridges, to multiple‐support seismic excitations. For practical convenience, ground motions within a group of adjacent supports on continuous soil or rock are assumed to be uniform and synchronized, while those of different groups are treated as non‐uniform and uncorrelated. The response spectrum analysis is extended to include the cross‐correlation of modal responses, which prove important when closely spaced modal frequencies exist. An example of the significance of multiple‐support excitations is illustrated by application to a suspension bridge. Qualitatively comparable effects can be expected for other bridges of similar type or dimensions.
Solution of viscously damped linear systems using a set of load‐dependent vectors
Authors: Chen Harn C. , Taylor Robert L.
Published: April 2007

This paper considers a solution method for viscously damped linear structural systems which are subjected to transient loading. The equations of motion of such systems are written in a first‐order form. A solution subspace is generated using the damped dynamic matrix and the static deflection from the first‐order form of the equations of motion. Two convenient bases, Lanczos vectors and Ritz vectors, are constructed from this subspace. An approximate solution is then obtained by superposition of the Lanczos vectors or the Ritz vectors. In contrast to the traditional mode superposition method using complex eigenvectors, the Lanczos vectors or the Ritz vectors are less expensive to generate than the complex eigenvectors, yet yield comparable accuracy. In addition, there is no need for a static correction since the static deflection is already contained in our solution subspace. Numerical examples are presented to show the potential of using the Ritz vectors to compute responses of damped dynamic systems.
Seismic damage assessment based on different hysteretic rules
Authors: Loh Chin‐Hsiung , Ho Ri‐Chuan
Published: April 2007

The inelastic response of a single‐degree‐of‐freedom (SDOF) system to different sets of earthquake records was analysed to study the significance of ground motion characteristics on structural damage. Six non‐linear models were used. The ductility ratio and hysteretic energy index were chosen as two important damage indices to measure the structural damage. The dispersion phenomenon exhibited by yield spectra due to input ground motion was reduced by incorporating the ground motion a/v ratio into the two damage indices. Finally, empirical formulae for estimating two measures of structural damage were developed for each hysteretic model.
Random response of a single‐degree‐of‐freedom vibro‐impact system with clearance
Authors: Jing Hung‐Sying , Young Mindhu
Published: April 2007

The closed form solutions of the stationary random response of a single‐degree‐of‐freedom vibro‐impact system with clearance are formulated in this paper. The Hertz contact law from elasticity is used to model the contact phenomena between the mass and constraint during vibration. The excitation is assumed to be a stationary white Gaussian process with zero mean. Through solving the time‐independent Fokker‐Planck equation, the stationary responses are obtained analytically. The effects of contact stiffness and clearance on the response are discussed probabilistically. It is found that, when the clearance is about twice the square root of the mean square response of the corresponding linear system, the contact phenomena are almost negligible.
How to model amplification of strong earthquake motions by local soil and geologic site conditions
Authors: Trifunac Mihailo D.
Published: April 2007

A simple equation is proposed to describe the physical nature of the frequency dependent amplification of strong earthquake shaking by local soil and geologic site conditions. For high frequencies, the amplification effects compete with anelastic attenuation. For long periods, along the period axis, the amplification can be described by a low‐pass filter with roll‐off near the period for which the quarter wavelength of wave motion in soil, or in sediments, coincides with their thickness. In the intermediate period range the amplification depends only on the impedance jump between the ‘soft’ surface materials and ‘hard’ basement, and is independent of the thickness of soil or of sedimentary layers.
Inelastic seismic response of one‐storey, asymmetric‐plan systems: Effects of stiffness and strength distribution
Authors: Goel Rakesh K. , Chopra Anil K.
Published: April 2007

The effects of plan‐wise distribution of stiffness and strength‐as determined by the number, location, orientation and yield deformations of resisting elements‐on the inelastic response of one‐storey systems are evaluated. In particular, various systems are investigated for wide ranges of parameters involved, with the objective of establishing how the response is influenced by: (i) the presence of resisting elements perpendicular to the direction of ground motion; (ii) the number of resisting elements along the direction of ground motion; (iii) the overstrength typical of code‐designed buildings; (iv) the relative values of strength and stiffness eccentricities; and (v) whether the asymmetry of the system is due to eccentricity in stiffness or in mass. The results presented for a simple excitation make it possible to explain the inconsistencies in conclusions from various earlier investigations, and to evaluate their applicability to actual buildings.
Seismic‐response‐controlled structure with active mass driver system. Part 1: Design
Authors: Kobori Takuji , Koshika Norihide , Yamada Kazuhiko , Ikeda Yoshiki
Published: April 2007

An Active Mass Driver (AMD) system is proposed to suppress actively the response of a building to irregular external excitations such as earthquakes and typhoons. This system has been introduced to an actual ten‐storey office building for the first time in the world. The system controls the motions of a structure by means of an external energy supply. It consists of an auxiliary mass installed in a building and an actuator that operates the mass and produces a control force which counters disturbances to the building. The design method of the AMD system, including the location of the installation and the capacity and stability of the system, is proposed. Simplification of the control algorithm is also described.
Identification of equivalent structural schemes for coupled systems
Authors: Benedetti D. , Benzoni G. M.
Published: April 2007

Some arrays of buildings in historical nuclei of Central Italy are currently monitored by steady‐state accelerometers. The aim is to identify the structural scheme of a single building representing the effect on it of the other systems of the array. A method for interpreting the recorded responses is presented. It is based on the a priori assumption of a scheme for the building of interest, thought of as being isolated, and on the identification of two sets of masses and of stillnesses to add in order to account for the array effect. The method is limited to linear behaviour and to planar systems.
Strong‐motion accelerograph array in Santiago, Chile, and preliminary evaluation of site effects
Authors: Midorikawa Saburoh , Riddell Rafael , Cruz Ernesto
Published: April 2007

A strong‐motion accelerograph array in Santiago, Chile has been installed. One of the sites is located on rock and the other six sites are on soil ground with different surface geology, so that local site effects on ground motions can be studied. As a preliminary evaluation of the site effects, the spectral ratios of weak‐motion records at soil sites with respect to the rock site are calculated. The spectral ratios show that the amplification of ground motions with respect to the rock site is approximately 1.25 on dense gravel deposits, 2.5 on stiff pumice ground and 3.5 on soft silt ground.
A unified earthquake‐resistant design method for steel frames using arma models
Authors: Takewaki Izuru , Conte Joel P. , Mahin Stephen A. , Pister Karl S.
Published: April 2007

The objective of this paper is to develop a unified earthquake‐resistant design method for moment‐resisting steel frames, including the design earthquake via a dynamic ARMA model.

Important features of this design method are: (i) to make it possible to incorporate inherent uncertain features of design earthquakes into the design process itself through the dynamic ARMA model, (ii) to provide a simplified design formula for a preliminary design of moment‐resisting steel frames based upon the concept of stiffness‐oriented design and (iii) to facilitate the formulation of a new probabilistic multi‐objective optimal design problem aimed at finding the design with the minimum level of designer's dissatisfaction. In this optimal design problem, constraints and objectives are handled in a unified manner after a feasible design is obtained.

A design example is presented to demonstrate the validity of this unified design method and to examine the convergence of response statistics. Finally, the generality and practicality of this design method are assessed.
Controlling seismic response of eccentric structures by friction dampers
Authors: Pekau O. A. , Guimond R.
Published: April 2007

Previous studies have demonstrated the good performance of friction dampers in symmetric frame structures subjected to earthquake excitation. This paper examines their effectiveness in asymmetric structures where lateral‐torsional coupling characterizes the behaviour. A parametric study is first performed employing an idealized single‐storey structure; this is followed by the example of a three‐dimensional 5‐storey prototype structure equipped with friction dampers. The parametric results show that it is necessary to tune the friction damped braces with respect to both the stiffness of the braces and the slip load of the devices. For properly tuned structures, maximum response for all magnitudes of eccentricity between the centres of stiffness and mass is reduced to levels equal to or less than that of the corresponding symmetric structure. Compared to this prediction, the prototype structure with friction damped bracing exhibits the desired improvement in performance; namely, the devices slip at all storey levels while the frames remain elastic.
Insights on cutoff frequency for foundation on soil layer
Authors: Meek Jethro W. , Wolf John P.
Published: April 2007

In foundation dynamics a most important effect, often overlooked, is that for a soil layer on rock a cutoff frequency exists, below which there is no radiation damping. Valuable insights into the nature of the cutoff frequency may be obtained without solving differential equations. Physically motivated wave‐propagation techniques enable modification of familiar unbounded cone models to represent layered soil. Echoes corresponding to the natural period of the layer appear to account for the cutoff frequency. The cone models have simple solutions in both the time and frequency domains.

An investigation of the simplest system with a cutoff frequency, the shear bar on an elastic foundation, shows that, for radiation to take place, the radius of penetration of waves must extend to infinity. In order to reach infinity, the waves' displacement amplitude must die off in a special way, otherwise conservation of energy would be violated. These considerations reveal a general radiation criterion, namely, that the waves' amplitude must diminish in inverse proportion to the square root of the far‐field boundary surface. Using the radiation criterion, it is possible to derive transmitting boundaries for shear waves which replace the far field.
Modelling of a cable‐stayed bridge for dynamic analysis
Authors: Wilson John C. , Gravelle Wayne
Published: April 2007

The subject of dynamic response of cable‐stayed bridges has received increasing attention in recent years as this type of bridge becomes ever more popular. In most publications on the dynamic behaviour of cable‐stayed bridges, only cursory treatment is given to many of the details of the actual development of a suitable finite element model. This paper provides a detailed description of the development of one class of linear elastic finite element model for the dynamic analysis of a cable‐stayed bridge. The bridge modelled in this study is the Quincy Bayview Bridge in Illinois. The translation of structural data into a form useful for formulation of a three‐dimensional finite element model is presented in some detail, including evaluation of translational and rotational mass and stiffnesses for the deck, modelling of the towers and cables, modelling of the bearings and considerations for accurate geometric representation between the model and the full‐scale structure. In a companion paper, the modal behaviour predicted by the finite element model is compared to measured ambient vibration properties of the full‐scale structure.
Implicit time integration for pseudodynamic tests: Convergence and energy dissipation
Authors: Shing Pui‐Shum B. , Vannan Mani T.
Published: April 2007

The convergence and energy‐dissipation characteristics of an unconditionally stable implicit time integration scheme that has been adopted for pseudodynamic testing are examined in this paper. A convergence criterion is derived for general multiple‐degree‐of‐freedom softening systems. Furthermore, it is shown that undesired loading and unloading cycles can be avoided in numerical iterations by scaling down the incremental corrections. Finally, it is proved that the total energy dissipation introduced by the residual convergence errors and proposed numerical correction is always positive for any softening structures.
A generalization of the timoshenko beam model for coupled vibration analysis of thin‐walled beams
Authors: Capuani D. , Savoia M. , Laudiero F.
Published: April 2007

A generalization of the Timoshenko beam model is presented which accounts for the influence of the shear strains, due to non‐uniform bending and torsion, on the flexural‐torsional vibrations of thin‐walled cores with open or closed cross‐section. The axial displacement field incorporates the torsion secondary warping as well as the warping terms depending on the shear resultants. It is shown that exact solutions for the interior domain problem can be obtained under proper load conditions. Moreover, a discrete model for the free‐vibration analysis is derived by adopting a linear interpolation of the unknown functions and a reduced integration in order to avoid locking phenomena. Various applications are developed, including the case of the coupled vibrations of a shear‐core‐steel‐frame building.
A bulk power system reliability assessment methodology
Authors: Yang Fang , Meliopoulos A. P. Sakis , Cokkinides George J. , Stefopoulos George
Published: April 2007

This paper describes a methodology for the reliability evaluation of bulk power systems. The method encompasses the systematic enumeration of contingencies and the evaluation of their effects on the system over a range of system load levels. Contingencies and electric load levels are described with Markov models. Reliability indices are computed using these models. Both an adequacy approach and a simplified security approach are considered in the effects analysis. The overall framework of the proposed methodology is capable of considering the full security approach but it is not addressed in this paper. In the adequacy approach, an improved system simulation method is used based on the single‐phase quadratized power flow (QPF). Remedial actions (RAs) are also applied for the purpose of alleviating system abnormal operating conditions. The adequacy approach determines whether the system is adequate for supplying the electric load without operating constraint violations. In the simplified security approach, the immediate response of the system is of interest. The simulation approach consists of an inertial re‐dispatch and operating conditions immediately after a contingency before any controls take effect. The objective is to determine whether cascading failures occur. The proposed methodology has been applied to two reliability test systems. Copyright © 2007 John Wiley & Sons, Ltd.