bluuebunny/crossref_metadata_2025 huggingface dataset:
Parallelization and scalability of a spectral element channel flow solver for incompressible Navier–Stokes equations
Authors: Hamman C. W. , Kirby R. M. , Berzins M.
Published: April 2007

Direct numerical simulation (DNS) of turbulent flows is widely recognized to demand fine spatial meshes, small timesteps, and very long runtimes to properly resolve the flow field. To overcome these limitations, most DNS is performed on supercomputing machines. With the rapid development of terascale (and, eventually, petascale) computing on thousands of processors, it has become imperative to consider the development of DNS algorithms and parallelization methods that are capable of fully exploiting these massively parallel machines. A highly parallelizable algorithm for the simulation of turbulent channel flow that allows for efficient scaling on several thousand processors is presented. A model that accurately predicts the performance of the algorithm is developed and compared with experimental data. The results demonstrate that the proposed numerical algorithm is capable of scaling well on petascale computing machines and thus will allow for the development and analysis of high Reynolds number channel flows. Copyright © 2007 John Wiley & Sons, Ltd.
Efficient parallelization of the iterative solution of a coupled fluid–structure interaction problem
Authors: Hughes Martyn D. , Chen Ke
Published: April 2007

In this paper we consider the parallelization of the generation and iterative solution of coupled linear systems modelling the interaction of an acoustic field in a fluid medium with an elastic structure immersed in the fluid. The particular case studied is that of a hollow steel sphere in water. The aim of the work is to speed up the generation and solution of the systems. We describe the methods used, which involve special sparse storage arrangements and a novel application of a sparse approximate inverse preconditioning technique, and present results showing that the methods are very effective in terms of speeding up the generation and iterative solution of the systems. Copyright © 2007 John Wiley & Sons, Ltd.
Measuring the value of electronic word of mouth and its impact in consumer communities
Authors: Dwyer Paul
Published: April 2007

Marketing practitioners have recognized a need to measure customer-generated media in addition to the traditional marketing metrics. Message boards, chat rooms, blogs, and virtual brand communities have become important venues for customer-generated media.These communities can be modeled as two distinct, albeit connected, networks: social and informational. These networks change over time under the influence of online word of mouth. This study introduces adapted PageRank (APR), a new metric for measuring the value a community assigns each word-of-mouth instance and the value the community assigns to the members that create them. That metric is used to empirically support a model explaining how highly-valued information builds the social network. These communities are egalitarian in assigning value to informational content, without regard to the status of its source, and highly-valued content explains 10% of social network growth.
The impact of consumer Internet experience on channel preference and usage intentions across the different stages of the buying process
Authors: Frambach Ruud T. , Roest Henk C.A. , Krishnan Trichy V.
Published: April 2007

We investigate consumer preference for online versus offline purchasing of a complex service (home mortgage), across the three stages of purchasing, namely, pre-purchase, purchase, and post-purchase. Our analysis of data from 300 consumers shows that (1) the offline channel is generally preferred over the online channel across all the stages, and (2) the channel usage intention in a particular stage is moderated by the consumer's Internet experience. Specifically, in both the pre- and post-purchase stages, the usage intention for the online channel is higher when consumers have more favorable Internet experience. In the purchase stage, consumers prefer the offline channel over the online channel, regardless of their Internet experience. Furthermore, we find that the drivers of channel preference are substantially different across the three buying stages due to (in)congruities between channel benefits desired and channel capabilities offered.
Interaction of HLA‐B27 homodimers with KIR3DL1 and KIR3DL2, unlike HLA‐B27 heterotrimers, is independent of the sequence of bound peptide
Authors: Kollnberger Simon , Chan Antoni , Sun Mei‐Yi , Ye Chen Li , Wright Cynthia , di Gleria Kati , McMichael Andrew , Bowness Paul
Published: April 2007

HLA‐B27 can form beta‐2 microglobulin (β2m)‐associated heterotrimers (HLA‐B27) and β2m‐free homodimers (B272). Here, we study the role of complexed peptide in the interaction of these forms of B27 with the killer cell immunoglobulin (Ig)‐like receptors KIR3DL1 and KIR3DL2 and with Ig‐like transcripts LILRB1 and LILRB2. HLA‐B27 tetramers complexed with three of five different naturally processed self peptides and three of seven pathogen‐derived epitopes bound to KIR3DL1‐expressing transfectants and NK cells. Heterotrimeric complexes containing peptides with charged amino acids at position 8 did not bind to KIR3DL1; however, studies with analogue peptides demonstrated that these are not the only peptide residues involved in binding. KIR3DL1 ligation by HLA‐B27 inhibited NK cell IFN‐γ production in a peptide‐dependent fashion. B27 but not HLA‐A2, B7 or B57 heavy chains formed homodimers in the presence of peptide epitopes. B272 bound to KIR3DL1, KIR3DL2 and LILRB2 but not LILRB1. KIR3DL2 ligation by B272 inhibited NK and T cell IFN‐γ production. By contrast with HLA heterotrimers, B272 binding to KIR did not depend on the sequence of the bound peptide. Differences in KIR binding to classical HLA and B272 could be involved in the pathogenesis of spondyloarthritis.
GITR/GITRL: More than an effector T cell co‐stimulatory system
Authors: Nocentini Giuseppe , Ronchetti Simona , Cuzzocrea Salvatore , Riccardi Carlo
Published: April 2007

Glucocorticoid‐induced TNFR‐related protein (GITR) is a member of the TNFR superfamily, expressed in several cells and tissues including T lymphocytes, NK cells and antigen‐presenting cells (APC). GITR activation, upon interaction with its ligand (GITRL), functions as a co‐activating signal. GITRL is mainly expressed on APC and GITR/GITRL interaction is important for the development of immune response. This review summarizes recent results about the GITR/GITRL system, focusing on the interplay between APC, effector and regulatory T cells.
The flaminio obelisk in Rome: Vibrational characteristics as part of preservation efforts
Authors: Bongiovanni G. , Çelebi M. , Clemente P.
Published: April 2007

The purpose of the paper is to study the vibrational characteristics of the Flaminio Obelisk in Rome as part of general studies being performed for preservation purposes. The scope of the paper is limited to dynamic analysis using a finite element model and comparison of the results with those from the measured response to forced vibrations. The state of preservation of the monument is described as well as the sonic method used to evaluate the integrity of the sections. The results of the sonic tests are used to determine reductions in the cross‐sectional properties. A stick model including two rotational frequency independent soil springs at the basement level of the obelisk is developed. A good agreement between the numerical and the experimental results is obtained for the natural frequencies and for the modal shapes. A response spectrum and stress analysis according to the Italian Seismic Code is performed considering and evaluating the degraded characteristics of sections.
Soil‐structure interaction effects on strong motion accelerograms recorded on instrument shelters
Authors: Luco J. E. , Anderson J. G. , Georgevich M.
Published: April 2007

The distortions of earthquake ground motions recorded in small instrument shelters as a result of soil‐structure interaction effects are investigated by means of a theoretical parametric study. A total of 12 foundation geometries varying in basal radius, embedment depth and extension above the ground surface and a number of soil profiles including uniform and layered soil models were considered. The results obtained show significant amplification and deamplification of the free‐field ground motion for sufficiently soft soils (β<200 m/sec) and sufficiently high frequencies (f>20 Hz).
Estimation of structural parameters in time domain: A substructure approach
Authors: Koh Chan Ghee , See Lin Ming , Balendra Thambirajah
Published: April 2007

A substructure approach is used to estimate the stiffness and damping coefficients of structures from measurement of dynamic responses. The structures are decomposed into smaller subsystems for which state and observation equations are formulated and solved by the method of extended Kalman filter with a weighted global iteration algorithm. Substructural identification methods with and without overlapping members are proposed. In both methods, the convergence of the structural parameters to the optimal values is improved significantly with less computation time as compared to a complete structural approach. Numerical simulation studies are performed for three types of structures, namely a shear building, a plane frame building and a plane truss bridge. The effects of measurement noise and response observations required for identification of system parameters are also investigated.
Seismic ground motion simulations from a class of spatial variability models
Authors: Zerva Aspasia
Published: April 2007

An improved version of the spectral representation method (References 12–14) for the generation of simulations of random processes and random fields by means of the Fast Fourier Transform algorithm is developed. The new formulation produces simulations that are ergodic in the mean without any restricting assumptions at the origin of the spectra and leads to a faster convergence rate of the stochastic characteristics of the simulations to those of the random field. As an example of the methodology, simulations in space and time based on a spatial variability model for the seismic ground motions are generated.
Application of FE‐BE‐IBE coupling to dynamic interaction between alluvial soil and rock canyons
Authors: Chuhan Zhang , Pekau O. A. , Feng Jin
Published: April 2007

A method of coupling finite elements (FE), boundary elements (BE) and infinite boundary elements (IBE) in the frequency domain is presented for wave propagation and soil‐structure interaction problems. The procedure has the advantage of being suitable for considering non‐homogeneous materials in the near region and the radiation condition at the far field. At the same time, the displacement field on the traction free boundary of the semi‐plane is simulated by the IBE rather than by additional discretization of the ground surface as is required in the normal BE procedure. Verification examples show that excellent accuracy is achieved compared with the results by Wong18 who used the generalized inverse method. Finally, the proposed procedure is employed to obtain the response of a semi‐elliptical rock canyon‐alluvial deposit under seismic P and SV waves. Amplification behaviour due to the alluvial soil is observed to be significant for the given geometric dimensions of the canyon and the mechanical properties of the media under the excitation of the El Centro and Parkfield earthquakes.
Active control of the seismic response of structures by combined use of base isolation and absorbing boundaries
Authors: Luco J. E. , Mita A. , Wong H. L.
Published: April 2007

The relative advantages of several control strategies to reduce the seismic response of multi‐storey structures are studied. The strategies involve the separate or combined use of passive base isolation mechanisms and active control forces. The base isolation mechanism is modelled as an equivalent linear soft storey with high damping. The active control forces are selected so that an absorbing boundary is obtained at the top of the structure and non‐reflecting or reflecting boundaries are obtained at the base of the building. It is found that the best results are obtained when a passive base isolation system is combined with an active absorbing boundary placed at the top of the building. However, the incremental gains resulting from adding a base isolation system to a structure already controlled by a roof‐top active absorbing boundary are significant only for relatively soft base isolation systems. Also, the incremental gains appear to decrease as the number of storeys of the structure increases.
Site‐dependent models of earthquake ground motion
Authors: O'connor Jennifer M. , Ellingwood Bruce R.
Published: April 2007

Random vibration analyses of structural systems subjected to seismic loading are dependent upon the characterization of earthquake ground motion as a stochastic process. The response of structural systems to earthquakes is dependent strongly on the local geological conditions, which should be incorporated into seismological models of ground motion. In the study presented herein, three previously developed ground‐motion models are adapted to incorporate site‐dependent characteristics. Records obtained from two recording stations in California are used as a basis for the ground‐motion models. Single‐degree‐of‐freedom (SDOF) oscillators are subjected to ensembles of accelerograms generated from these models, and both elastic and inelastic response are considered. Response statistics are compared to those generated by the analysis of structural response to ensembles of recorded motion from the two sites. The important features of the ground motion for effective reproduction of response statistics are identified, and observations are made on the sensitivity of specific response parameters to site‐dependent characteristics of the ground motion.
Verification of two‐dimensional non‐linear analysis of sand‐structure system by examining the results of the shaking‐table test
Authors: Ohtsuki Akira , Hirota Masanori , Ishimura Kikuo , Yokoyama Kazutomo , Fukutake Kiyoshi
Published: April 2007

The verification of a two‐dimensional non‐linear analysis based on a hybrid constitutive model, which consists of the Ramberg‐Osgood model extended to two‐dimensional problems and a dilatancy model, is discussed through a comparison of the shaking‐table test results for a one‐storey structure standing on a dry sandy deposit with those for the same on a saturated sandy deposit. Since the relationships G vs. γ and h vs. γ for shear strains of 10−5−10−3 can be obtained accurately by an inversion analysis of the resonance curve of the sandy deposit the proposed non‐linear method can represent well the observed non‐linear response of the dry or the saturated sandy deposit including the structure. This method, however, should be applied carefully to assess the response of a soil‐structure system when the three‐dimensional interaction affects significantly the response of the model. An equivalent linear analysis using a sway‐rocking model is applied to simulate the non‐linear ground motion including the three‐dimensional interaction, and it is found that the sway‐rocking model can also represent well the non‐linear response of the system.
Reliability‐based design of R/C water tank structures under seismic action
Authors: Möller Oscar , Rubinstein Marcelo
Published: April 2007

Based on a reliability level 2 method, a procedure is proposed to design reinforced concrete structures for elevated tanks subjected to seismic action, with a specified probability of failure in a 50‐year design life.

To evaluate the probability of failure the ultimate limit state is obtained when the top column displacement demanded by the earthquake, a random variable, reaches the allowable displacement, which is here treated as deterministic.

The seismic action is characterized probabilistically by the power spectral density function of the ground acceleration, which is obtained from a design spectrum. The strength and ductility of an annular column section of confined reinforced concrete for cyclic loads are evaluated with design aids.

Design charts are made for a given tank capacity and specified seismic zone that allow one to choose different combinations of strength, stiffness and ductility for the same tolerable probability of failure. A step by step method is suggested for the design of the annular column section, choosing finally the most convenient design. The advantage of this methodology is shown through a numerical example.
Response spectrum method for multi‐support seismic excitations
Authors: Kiureghian Armen Der , Neuenhofer Ansgar
Published: April 2007

A new response spectrum method is developed for seismic analysis of linear multi‐degree‐of‐freedom, multiply supported structures subjected to spatially varying ground motions. Variations of the ground motion due to wave passage, loss of coherency with distance and variation of local soil conditions are included. The method is based on fundamental principles of random vibration theory and properly accounts for the effects of correlation between the support motions as well as between the modes of vibration of the structure.
Analytical expressions for three different modes in harmonic motion of sliding structures
Authors: Iura Masashi , Matsui Kunihito , Kosaka Iku
Published: April 2007

The problem of response of sliding structures subjected to harmonic support motions is considered. The periodic motions, consisting of the three different modes, stick‐stick, stick‐slip and slip‐slip, are a significant part of the responses to harmonic excitations. Assuming the periodicity of the motion, the condition of the initiation of the slip‐slip motion is derived. Then analytical expressions for the occurrence of the periodic motions are obtained without integrating the equations of motion. The accuracy of the analytical expressions is confirmed by comparison with numerical results herein obtained. It is observed that the numerical results are sensitive to the starting and ending times of slip motions.
Damping and response measurement on A small‐scale model of A cable‐stayed bridge
Authors: Garevski Mihail A. , Severn Roy T.
Published: April 2007

A small‐scale model of an existing cable‐stayed bridge has been designed and built. Hammer, sinusoidal and random signal tests have been performed to determine the dynamic characteristics of the model. An attempt has been made to evaluate the real effect of the vibration of stays upon system damping. Initial measurements have been performed for a model where there was no vibration of the stays because of the absence of appropriately scaled additional mass of these stays. In this way the effect of the cables was eliminated in damping measurement. During the second series of measurements appropriate mass has been added to the stays, causing them to take part in the vibration. The comparison of the measured damping of the model for each case makes possible the estimation of the effect of the stays upon the system damping. By using the shaking table, two types of seismic excitation were applied, with corresponding response quantities in the critical sections being measured. Good agreement between the analytical and the experimental results was achieved.
A three‐stage identification approach for hysteretic systems
Authors: Loh Chin‐Hsiung , Chung Sheng‐Tsai
Published: April 2007

This paper deals with the identification of the parameters of a smoothed hysteretic model which was proposed by Bouc and Wen with emphasis on restoring force hysteresis. The problem of estimating the parameters of this system on the basis of input‐output data, possibly noise corrupted, is considered. Through the application of various simulated time histories from the hysteretic model, a three‐stage systematic method of system identification was proposed. Four different methods of identification are arranged and conducted in this three‐stage system identification. The first stage, a sequential regressional analysis is used to identify the equivalent linear system from which elastic or inelastic response can be identified. The identified parameters can be used in the stage when the system is in elastic response. In the second stage, both time domain least‐squares method and Gauss‐Newton method are applied. The convergence of the Gauss‐Newton method can be guaranteed if the identified results from least‐squares method are adopted as the initial values for Gauss‐Newton method. In the third stage, the extended Kalman filtering technique is needed to identify the noise‐corrupt data. Application of this algorithm to a SDOF non‐deteriorating system is verified.
Propagation and amplification of seismic waves in 2‐D valleys excited by obliquely incident P‐ and SV‐waves
Authors: Papageorgiou Apostolos S. , Kim Jaekwan
Published: April 2007

The seismic motion in sediment‐filled valleys due to incident SH‐waves has been studied exhaustively. However, the response of such geologic structures to incident SV‐ and P‐waves has not been studied as thoroughly. The response of a 2‐D model of the valley of Caracas, Venezuela—a NS cross‐section through the Palos Grandes district—to incident plane SV‐ and P‐waves is investigated using the discrete wave number boundary element method. It is observed that the differences in the predictions of the 1‐D and 2‐D models are more pronounced for SV‐waves than for SH‐waves, especially when SV‐waves are incident at (or near) the critical angle ic. The valley responds very strongly to the horizontally propagating P‐wave (SP‐wave) which is induced when SV‐waves, incident at the critical angle, interact with the free surface of the half‐space. However, the SP‐wave, being a wave diffracted at a boundary, is likely to be sensitive to impedance contrasts, to the presence of other interfaces in the medium, and to the topography surrounding the valley. These aspects of the problem need further investigation.
Cone models for a soil layer on a flexible rock half‐space
Authors: Wolf John P. , Meek Jethro W.
Published: April 2007

A modified truncated cone model is used to calculate approximately the dynamic response of a disk on the surface of a soil layer resting on flexible rock. The procedure is analogous to that for a layer on rigid rock, the only modification being that the reflection coefficient —α at the layer–rock interface is no longer equal to −1. The modified value of α can be determined straightforwardly by considering one‐dimensional wave propagation along the cone. The low‐ and high‐frequency limits lead to a frequency‐independent α, which allows the dynamic analysis to be performed directly in the familiar time domain. This cone represents a wave pattern with amplitude decay and also incorporates the reflection at the free surface and the reflection‐refraction at the layer–rock interface. The results for the static stiffness of the disk are highly accurate for a wide range of geometrical and material properties of the layer and the rock. For the dynamic stiffness the agreement with the exact solution is satisfactory.
Performance of composite steel/concrete members under earthquake loading. Part I: Analytical model
Authors: Elnashai A. S. , Elghazouli A. Y.
Published: April 2007

This paper presents an advanced non‐linear model developed for the analysis of composite steel/concrete frame structures subjected to cyclic and dynamic loads. The formulation consists of beam‐column cubic finite elements accounting for geometric non‐linearities and material inelasticity. The non‐linear cyclic concrete model considers confinement effects and the constitutive relationship for steel includes the effect of local buckling and variable amplitude cyclic degradation. The model is calibrated and compared with experimental data from cyclic and pseudo‐dynamic tests conducted by the writers on a new ductile partially‐encased composite beam‐column. The accuracy and efficiency of the developed model are demonstrated through the correlation between the experimental results and analytical simulations. In a companion paper, the model is used to conduct parametric studies leading to important conclusions for ductility‐based earthquake‐resistant design.
Distance scaling of vertical and horizontal response spectra of the Loma Prieta earthquake
Authors: Bozorgnia Yousef , Niazi Mansour
Published: April 2007

Attenuations of the vertical and horizontal response spectra of the 17 October 1989 Loma Prieta, California, earthquake are developed through analyses of the ground motion at 53 sites within a 100 km radius of the source. The analyses are performed on the spectral ordinates for 16 incremental periods ranging from 0.05 to 2.0 sec. The response spectra are modelled empirically for two different site conditions characterized by rock and stiff‐soil geologies. Data analysis is performed by the application of a non‐linear multivariate regression procedure allowing for distance and site factor as independent variables. Variation of the vertical‐to‐horizontal (V/H) spectral ratios with wave frequency and distance shows the same behaviour as observed previously in the widely separated geographic regions of northeastern Taiwan and east‐central Iran. The predicted ratios at sites underlain by stiff soil are generally higher than the commonly used value of 2/3 at high frequencies ( > 5 Hz) in the near‐source region (R < 30 km), but reduce to 1/2 or less at longer periods and farther distances. This behaviour is also observed at rock sites; however, it is somewhat less pronounced.

With a faster attenuation of spectral ordinates at higher frequencies, the shape of the response spectrum is found to change with distance. As expected, the spectral attenuation with distance is generally higher for the vertical spectrum than for the horizontal spectrum. The difference is particularly significant at the higher‐frequency end of spectrum.

Site amplification factors for stiff soil with respect to rock geology varies between 1.17 and 1.72 for horizontal spectrum and 1.01 and 1.81 for vertical spectrum. Spectral amplifications at four sites underlain by soft soil and artificial fill, are also evaluated. This is done by a comparison of the observed spectra with those predicted for rock geology at corresponding distances. As expected, the resulting amplification factors at soft‐soil sites show significant increase relative to those at sites underlain by rock.
Seismic displacements on shear surfaces in cohesive soils
Authors: Tika‐Vassilikos Theodora E. , Sarma Sarada K. , Ambraseys Nicholas N.
Published: April 2007

The paper is concerned with the earthquake‐induced displacements on pre‐existing shear surfaces in cohesive soils. Results from ring shear tests have shown that during fast shearing the strength of such surfaces depends on displacement and rate of shearing. The test results have been used in a numerical analysis to assess the displacement of a rigid block sliding on a plane surface. The results from the analysis show that the earthquake‐induced displacements on pre‐existing shear surfaces are influenced significantly by the soil behaviour under earthquake loading conditions. The results are consistent with the field performance of pre‐existing slides in cohesive soils during earthquakes.
Boundary integral equation method for the diffraction of elastic waves using simplified green's functions
Authors: Chang Wei‐Lung
Published: April 2007

An alternate formulation of the ‘substructure deletion method’ suggested by Dasgupta in 19791 has been successfully implemented. The idea is to utilize simple Green's functions developed for a surface problem to replace the more complicated Green's functions required for embedded problems while still being able to generate an accurate solution. Since the exterior medium is usually represented by a continuum model, the interior medium in the present approach will also be represented by a continuum model rather than a finite element model as suggested originally, thereby eliminating the incompatibility between the solutions of the interior and exterior media. Detailed studies of the method's accuracy and limitations were performed using two‐dimensional examples in wave scattering of canyons and alluvial valleys, problems which are more suitable for this method than the embedded foundation problem. The results obtained indicate that the alternate formulation gives accurate results only when the vertical dimension of the scattering object is not too large; if the aspect ratio (vertical over lateral) exceeds a certain limit, the results will not approach the known results given by boundary integral equation solutions or indirect boundary integral equations no matter what the refinement of the model may be. The greatest advantage of the present method is that the task of calculating Green's functions is reduced significantly; computational time using this new formulation is approximately five times less than for conventional boundary integral equation methods.
Sloshing response of layered liquids in rigid tanks
Authors: Veletsos A. S. , Shivakumar P.
Published: April 2007

The sloshing action of layered liquids in rigid cylindrical and long rectangular tanks is investigated, considering both their free vibrational characteristics and their response to a horizontal component of base shaking. Special attention is given to the maximum surface displacement induced by the base motion. The analysis is formulated for systems with N superimposed layers of different thicknesses and densities, and is illustrated by a numerical example. In addition, comprehensive numerical data are presented for two‐layered and some three‐layered systems which elucidate the underlying response mechanisms and the effects and relative importance of the numerous parameters involved. It is shown that for each horizontal natural mode of vibration, there are N distinct vertical modes, the frequencies of which are lower than the natural frequency of a homogeneous liquid of the same total depth. It is further shown that the maximum surface sloshing displacement of the base‐excited layered system is typically larger than that of the corresponding homogeneous system, and that the results for the long rectangular and cylindrical tanks are quite similar.
A readily available energy source for active vibration control in buildings
Authors: Utku Senol , Utku Bisulay , Wada Ben K.
Published: April 2007

By equipping structures with appropriate actuators, sensors and microprocessors, it is possible to suppress actively the undesirable vibrations of the structures. Due to small energy requirements, the vibration suppression in large space trusses orbiting the Earth by controlling the elongations and contractions of length‐adjustable bars of the truss has been shown to be feasible both theoretically and experimentally. This method of vibration suppression is part of the ‘adaptive structures technology’. It can be used for suppressing the vibrations of a building subjected to earthquake or wind excitations, provided that the much higher energy and power requirements are met. In this work the use of gravitational energy of the mass of the building is proposed for active vibration control.
The use of damage functionals in earthquake engineering: A comparison between different methods
Authors: Cosenza Edoardo , Manfredi Gaetano , Ramasco Roberto
Published: April 2007

The behaviour of the EPP‐SDOF model under seismic actions is analysed herein by different ‘damage functionals’ to define collapse under cyclic loading. In particular, the damage functionals based on the concept of maximum ductility and dissipated plastic energy are first compared. Afterwards the methods of Banon and Veneziano, Park and Ang and the linear cumulative law of plastic fatigue are reviewed and extensively analysed. Comparisons in the case of simple cyclic histories and in terms of acceleration collapse spectra are carried out with reference to significant earthquake records. In particular, it is shown in which cases the damage functionals of Banon and Veneziano, Park and Ang and the linear cumulative law of plastic fatigue, completely defined by the value of a single parameter, degenerate in the limit methods of ductility or dissipated energy and in which cases they provide similar results.
Prediction of the spatial distribution of the modified mercalli intensity using neural networks
Authors: Tung Albert T. Y. , Wong Felix S. , Dong Weimin
Published: April 2007

This paper presents the development of an adaptive, non‐parametric forecast model for the direct prediction of the spatial distribution of the Modified Mercalli Intensity (MMI) corresponding to an earthquake scenario. The model is based on recent advances in neural networks computation, and is constructed through supervised learning using historical earthquake and regional geological data as training sets. A MMI forecast model for moderate earthquakes with magnitudes between 6 and 7 was developed based on data from the Loma Prieta, Coalinga and Morgan Hill earthquakes. For these data sets, the neural networks forecast model is shown to have excellent data synthesis capability; multiple sets of data can be encapsulated by a relatively simple network architecture. Limited comparison of forecasts made by the neural networks model and conventional models demonstrates that improved accuracy can be achieved. Implementation and operational advantages of the neural networks approach such as general input features, minimum preconceived knowledge of the data sets, the ability to learn and to adapt incrementally and the autonomous and automatic synthesis of the structure underlying the data sets, have been illustrated.
Insight on 2D‐ versus 3D‐modelling of surface foundations via strength‐of‐materials solutions for soil dynamics
Authors: Wolf John P. , Meek Jethro W.
Published: April 2007

To simplify the analysis, three‐dimensional soil–structure interaction problems are often modelled by considering a two‐dimensional slice without changing the material properties of the soil. This procedure, although convenient, is of questionable validity because two‐dimensional modelling inherently overestimates the radiation damping for translational and rocking motions. To make matters worse, two‐dimensional modelling always entails an underestimation of the dynamic‐spring coefficient for the translational motions. The damping ratio of the two‐dimensional case, which is proportional to the ratio of the damping coefficient to the spring coefficient, will thus be even larger. Thus, reliance upon a two‐dimensional analysis based on an equivalent slice of a strip foundation may result in a dangerously non‐conservative design.

Valuable insights into the essence of radiation damping and the difference between two‐dimensional and three‐dimensional models may be obtained via approximate strength‐of‐materials solutions based on cone–wedge models and travel‐time considerations. By examining the decay of the waves along the axes of the cone–wedge models, the essence of radiation damping can be grasped. The heuristic concept of more spreading of waves in three dimensions than in two is misleading. Indeed, just the opposite is true: The less the amplitude spreads and diminishes with distance, the greater is the radiation damping.

Because the damping ratio is grossly overestimated, two‐dimensional modelling of a three‐dimensional case cannot be recommended for actual engineering applications. It is more feasible to take the opposite approach and idealize slender soil–structure interaction problems with a radially symmetric model.

As an alternative, when defining the equivalent slice of the two‐dimensional strip foundation, the impedance of the soil can be changed to achieve a much better agreement of the high‐frequency limits of the damping coefficients. In the low‐frequency range this modified two‐dimensional model also overestimates radiation damping, although to a lesser extent.

As a by‐product, the dimensions of the equivalent slice of a two‐dimensional strip foundation are discussed; and equations for the aspect ratios determining the opening angles of the corresponding wedges are derived. Also addressed is the quite separate but related topic of the transition from square to slender rectangular foundations.
The imaginary counterpart of recorded motions
Authors: Makris Nicos
Published: April 2007

In this paper it is shown that any recorded motion has an imaginary counterpart. Starting from the harmonic input motion where the sine function is the imaginary counterpart of the cosine function, it is shown that all time histories exist in pairs. The imaginary counterpart of records is not needed when the response of a system is described by a real‐parameter constitutive model. However, it is shown that when complex‐parameter models are used, the imaginary counterpart of records has equal importance as the real‐valued record and in this case the input motion should be strictly complex valued. The procedure to construct the imaginary counterpart of any piecewise continuous record is developed. A constructed complex‐valued earthquake time history is used as input motion to a system described by a Kelvin model with complex damping constant. The validity of the procedure is demonstrated by comparing the response of the complex‐damping Kelvin model against the results obtained from a mathematically equivalent real‐valued formulation.
On non‐linear dynamic analysis in the frequency domain: Algorithms and applications
Authors: Aprile A. , Benedetti A. , Trombetti T.
Published: April 2007

It is well known that the solution of the forced vibration of a N‐DOF dynamical problem is very cumbersome when conditions which allow the equations to uncouple do not exist. In the literature several techniques were proposed to overcome the problem, but they were mainly focused on a particular problem in turn. So, we deemed it useful to search for a unifying procedure able to deal with different sources of non‐linear behaviour introducing only minor changes in the operation flow.

In this respect, attention is paid to the Alternating Frequency/Time domain method (AFT) which draws its robustness from the speed and switching capabilities of the Fast Fourier Transform; moreover, taking advantage of the pseudo‐force concept, we can arrive at a solution method featuring greater generality and able to solve different non‐linear dynamical problems by means of specialization of the same conceptual framework (G‐AFT or Generalized AFT).

In the first section of the paper the theoretical background is discussed in detail and the proposed algorithms are presented. In the second one, several examples of technical relevance are documented and solved, highlighting the efficiency, convergence and accuracy of the presented algorithm.

For cases such as an 11‐storey building or a block simulated power plant we introduce the soil‐structure interaction effect by means of non‐proportional damping; the responses computed either by direct frequency analysis or by iteration are compared with existing solutions or with time domain solutions determined through the Newmark β method.

An original example prepared by the authors and fully referenced is finally worked out in order to show the capability of the method when Coulomb damping is taken into account; this effect covers a significant practical relevance in the base isolation field.
Identification of modal quantities from two earthquake responses
Authors: Benedetti D. , Gentile C.
Published: April 2007

The work deals with the identification of modal parameters of a structure from earthquake records when the input ground motion is unknown. This may occur, for example, owing to instrumental malfunctions.

The procedure is based on the assumption that at least two responses are available and consists of two main steps. In the first one, modal frequencies are estimated by searching relative minima of a function that involves the ratio of the Fourier amplitudes of the two records, while the second phase is devoted to the identification of other modal quantities (i.e. effective participation factors and modal dampings).

Once the identification process has been completed, an estimate of the unknown base input may be performed by means of the IFFT algorithm. The proposed approach has been checked against both finite element simulations of simple structures and field measurements on real buildings.
Robust control techniques for buildings under earthquake excitation
Authors: Schmitendorf W. E. , Jabbari Faryar , Yang J. N.
Published: April 2007

Robust control techniques are applied to civil engineering structures subjected to earthquake excitation. Full‐state feedback and observer‐based control laws are used to reduce the response of the building due to earthquake ground motion. Effects of actuator dynamics and a method to incorporate these dynamics into the overall design are also presented. The effectiveness of the control method is demonstrated by simulation results.
Seismic response of a cylindrical shell embedded in a layered viscoelastic half‐space. II: Validation and numerical results
Authors: de Barros F. C. P. , Luco J. E.
Published: April 2007

A procedure to calculate the three‐dimensional harmonic response of a infinitely long cylindrical shell of circular cross‐section embedded in a layered viscoelastic half‐space and subjected to harmonic plane waves impinging at an oblique angle with respect to the axis of the shell is validated by extensive comparisons with previous two‐ and three‐dimensional results for the particular case of a shell embedded in a uniform half‐space. New numerical results describing the motion and stresses within a shell embedded in a multilayered half‐space and subjected to obliquely incident P‐, SV‐ and SH‐waves with different horizontal angles of incidence are presented and discussed.
Magnitude–intensity and intensity–attenuation relationships for atlas region and Algerian earthquakes
Authors: Benouar D.
Published: April 2007

This paper presents the results of an investigation of the magnitude–intensity and intensity–attenuation relationships for earthquakes in the Atlas block and Algeria using macroseismic data. This work is based on a selected sample of isoseismal maps from 32 events which were recently revised. Surface‐wave magnitudes, Ms, are recalculated using the Prague formula and range from 4·2 to 7·45. Because the Atlas mountains block is in a collision zone, earthquakes occur in general within a layer 15 km deep. Expressions of general form for the magnitude–intensity and intensity–attenuation correlations are adopted and are, respectively,

and

where R2 = d2 + h2, d the source distance in km, h the focal depth in km, Ms the revised surface‐wave magnitude, Msc the predicted surface‐wave magnitude, Ii the intensity at isoseismal i, I the predicted intensity, σ the standard deviation and P is zero for 50‐percentile values and one for 84‐percentile, and the coefficients A's and B's are determined by regression analysis. The results of this study show that the intensity–attenuation models are adequate to predict quite well the die‐out of intensity with distance in the Atlas zone and coastal Algeria; it is also found that magnitude can be predicted accurately by calibrating isoseismal radii against revised instrumental surface‐wave magnitude. Such magnitude–intensity relationships may be used to evaluate the magnitude of historical earthquakes in the region under survey, with no instrumental data, for which isoseismal radii and intensities are available.
Accidental torsion in buildings due to base rotational excitation
Authors: de la Llera Juan C. , Chopra Anil K.
Published: April 2007

This investigation is concerned with accidental torsion in buildings resulting from rotational excitation (about a vertical axis) of the building foundations as a result of spatially non‐uniform ground motions. Because of this accidental torsion, the displacements and deformations in the structural elements of the building are likely to increase. This increase in response is evaluated using actual base rotational excitations derived from ground motions recorded at the base of 30 buildings during recent California earthquakes. Accidental torsion has the effect of increasing the building displacements, in the mean, by less than 5 per cent for systems that are torsionally stiff or have lateral vibration periods longer than half a second. On the other hand, short period (less than half a second) and torsionally flexible systems may experience significant increases in response due to accidental torsion. Since the dependence between this increase in response and the system parameters is complex, two simplified methods are developed for conveniently estimating this effect of accidental torsion. They are the ‘accidental eccentricity’ and the ‘response spectrum’ method. The computed accidental eccentricities are much smaller than the typical code values, 0.05bb or 0.1b, except for buildings with very long plan dimensions (b ≥ 50 m). Alternatively, by using the response spectrum method the increase in response can be estimated by computing the peak response to each base motion independently and combining the peak values using the SRSS rule.
Dynamic stiffness of foundation on layered soil half‐space using cone frustums
Authors: Wolf John P. , Meek Jethro W.
Published: April 2007

Approximate dynamic‐stiffness coefficients of a disk on the surface of a single layer on a half‐space may be calculated using cone models. This concept is generalized to the case of a horizontally stratified site consisting of many layers on a homogeneous half‐space. After constructing the so‐called ‘backbone cone’ determining the radii of the disks at all interfaces, the dynamic‐stiffness matrices of the layers (modelled as cone frustums) and the dynamic‐stiffness coefficient of the underlying half‐space (modelled as a cone) are assembled to that of the site. The dynamic‐stiffness matrix of a layer is a complex‐valued function of frequency because radiation of energy in the horizontal direction is considered. In this model of the layered half‐space the properties of the cone reproduce themselves (cloning). The advantages of using cone models are also present for the layered half‐space; in particular, no transformation to the wave‐number domain is performed.
An equivalent linear finite element approach for the estimation of pile foundation stiffnesses
Authors: Maragakis E. A. , Douglas B. M. , Abdel‐Ghaffar S. M.
Published: April 2007

A method is presented for the calculation of the displacement‐dependent lateral, vertical and rotational stiffnesses of the central pier of the Meloland Road Overcrossing. This method is based on a finite element model of the foundation and an ‘equivalent linear’ iterative procedure for the calculation of the stiffness versus displacement curves. The results of this procedure are then compared to the results of system identification studies based on the full‐scale test measurements of the structure and to the results of studies performed by other researchers. It was found that this method produced reliable strain‐dependent stiffness values.