bluuebunny/crossref_metadata_2025_split huggingface dataset:
Coupling method of finite and infinite elements for strip foundation wave problems
Authors: Chuhan Zhang , Chongbin Zhao 
Published: March 2007

AbstractStarting from two‐dimensional wave equations and making use of Galerkin weighted residual approximations, discretized formulations for wave problems of a visco‐elastic foundation have been derived. With considerations of geometrical and mechanical characteristics of a semi‐infinite domain, a frequency‐dependent compatible infinite element is also presented. Finally, by coupling the infinite elements with ordinary finite elements the system is used for simulation of propagating waves in a semi‐infinite foundation. This model is not only suitable for simulations of complicated variations of geometrical conditions, but also for describing the unbounded behaviour of arbitrary multiple layers. Examples given indicate the model has excellent computational accuracy and feasibility for analysing the effects on foundation response due to the existence of faults or any other soft layers.
Earthquake‐resistant design according to the most unfavourable seismic direction under combined internal forces
Authors: Çlakiroǧlu Adnan 
Published: March 2007

AbstractIn this study it has been shown that, in the case of linear theory, the combined internal forces corresponding to each seismic direction lie on an ellipsoid having internal forces chosen as the set of axes. A method is proposed to obtain the most unfavourable results easily, in the neighbourhood of the several unfavourable points without actually determining the ellipsoid. The design can be carried out using linear, as well as non‐linear, theory. Two examples are given to illustrate the application of the proposed method.
On causality in dynamic response analysis by time‐dependent boundary element methods
Authors: Antes Heinz , Von Estorff Otto 
Published: March 2007

AbstractThe ramifications of a particular type of causality constraint, namely so‐called shadow‐zones, are explored in the context of time‐dependent boundary element methods. In particular, wave propagation problems in 2‐D elastic soil media with a non‐convex shape are analysed.
Seismic response analysis of structure–equipment systems with non‐classical damping effects
Authors: Singh Mahendra P. , Suarez Luis E. 
Published: March 2007

AbstractA method is presented to obtain the exact complex‐valued eigenproperties of a classically damped structure and equipment system. The non‐classically damped character of the combined system as well as the effect of dynamic interaction between primary structure and equipment are properly included in the calculation of these eigenproperties. It is necessary only to know the classical modal properties of the structure and, of course, the equipment characteristics. The eigenvalues are obtained as the solution of a non‐linear equation which can be easily solved by the Newton–Raphson algorithm. Once the eigenvalues are known, the corresponding eigenvectors are obtained from simple closed‐form expressions. The method can be used equally effectively with light as well as heavy equipment. Numerical results demonstrating the effectiveness of the method are presented. A procedure which utilizes the complex‐valued eigenproperties is developed for calculating the floor response spectra directly from the ground spectra. Numerical results of floor response spectra obtained from this procedure are presented. The floor spectra calculated by this approach include the structure–equipment interaction effect.
Seismic spectra on soil with uncertain properties
Authors: Hong Han Ping , Rosenblueth Emilio 
Published: March 2007

AbstractExpected spectral ordinates and their standard deviations are computed for ground motions produced by SH waves at the surface of a homogeneous soil formation resting on a half‐space of rock. Wave transmission is idealized as linear and one‐dimensional. Uncertainties about soil properties are taken into account using various approximations: a Taylor series expansion of the Fourier spectrum magnification factors with different numbers of terms and different intervals for numerical differentiation; discretization of the joint probability density function of the soil properties so as to match its moments up to those of third order including the crossed moments; a discretization that matches up to some fifth‐order moments; and a fine numerical integration for the marginal density function of the modulus of rigidity, discretizing the rest of the density function. The latter approach gives sufficiently accurate results for practical purposes.Effects of even moderate uncertainty about soil properties on the statistics of spectral ordinates are found to be decisive.
Generalized method for non‐linear seismic response analysis of a three dimensional soil–structure interaction system
Authors: Toki Kenzo , Fu Chang Sheng 
Published: March 2007

AbstractPrevious achievements using the dynamic non‐linear analysis of an interaction system are reviewed briefly, after which a three dimensional (3D) model of the stress redistribution of soil based on the Mohr–Coulomb failure law is presented to evaluate the unbalanced tensor at every iteration in the load transfer method. A 3D, full non‐linear analysis was used to examine the validity and accuracy of results obtained by 2D analysis by combining the model of redistributed stresses proposed here with the joint element model.Based on the numerical solution reported here, we concluded that both the 3D and 2D models of stress redistribution work well and reflect the yielding pattern of soil during excitation, but the former is more realistic. The failure area in the structural zone obtained by 3D analysis is slightly larger but similar to that obtained by 2D analysis. The ratio of maximum strain to yield strain and non‐linear time ratio, βs, for the soil elements in the structural zone are also a little larger. In contrast, the maximum separation values for the joint elements are much smaller and the separation pattern for the x‐side wall interface is the reverse of that found by 2D analysis. These values, however, affect only responses in the short period range and the regions close to the interface. In general, the tendencies shown by 2D analysis for the effects of non‐linear behaviour on structural responses are confirmed for the parameters investigated.
A simplified analysis procedure for base‐isolated structures on flexible foundation
Authors: Constantinou M. C. 
Published: March 2007

AbstractA simplified method of analysis of base‐isolated structures supported on flexible soil is presented, in which the soil–base‐isolated‐structure system is represented by a SDOF oscillator supported on rigid soil. A parametric study illustrates the application and accuracy of the method. The results obtained lead to the conclusion that the simplified procedure that is presented is sufficiently accurate for purposes of preliminary design of base‐isolated structures, and for studies to determine the feasibility of using base‐isolation.
Seismic analysis of multiply supported secondary systems with dynamic interaction effects
Authors: Burdisso Ricardo A. , Singh Mahendra P. 
Published: March 2007

AbstractFor a proper response spectrum analysis of a secondary system with multiple supports, the seismic inputs are required to be defined in terms of the auto and cross floor response spectra. If no feed‐back or interaction effect from the secondary system to its supporting primary structure is suspected, these inputs can be developed by a direct analysis of the supporting structure alone. However, sometimes the effect of the interaction on the secondary system response can be quite significant. Herein, a method is developed to incorporate the feed‐back effect, through proper modification of the interaction‐free floor spectrum inputs. The interaction coefficients are used to effect such modifications in different floor spectral quantities. A procedure for the calculation of the interaction coefficients is proposed. The modified floor spectra when used as inputs to the secondary system do introduce the interaction effect in the secondary system response. A successful application of this method is demonstrated by numerical examples of secondary systems with three different secondary‐to‐primary system mass ratios.
Isolation of soil‐structure interaction effects by full‐scale forced vibration tests
Authors: Luco J. E. , Trifunac M. D. , Wong H. L. 
Published: March 2007

AbstractForced vibration tests designed to isolate the effects of soil‐structure interaction are described and the results obtained for the nine‐storey reinforced concrete Millikan Library Building are analysed. It is shown that it is possible to determine experimentally the fixed‐base natural frequencies and modal damping ratios of the superstructure. These values may be significantly different from the resonant frequencies and damping ratios of the complete structure‐foundation‐soil system. It is also shown that forced vibration tests can be used to obtain estimates of the foundation impedance functions.In the case of the Millikan Library it is found that during forced vibration tests the rigid‐body motion associated with translation and rocking of the base accounts for more than 30 per cent of the total response on the roof and that the deformation of the superstructure at the fundamental frequencies of the system is almost entirely due to the inertial forces generated by translation and rocking of the base.
Modal summation methods for structural dynamic computations
Authors: Leger P. , Wilson E. L. 
Published: March 2007

AbstractThe rate of convergence of the conventional mode superposition method can be significantly improved for systems subjected to relatively low frequency loadings by adding static correction terms to approximate the contribution of higher modes neglected by the use of a truncated eigenbasis. Two computational variants of the classical mode‐acceleration method are developed for that purpose. It is recommended that the pseudo‐static displacement correction vector should be computed from an expansion of the flexibility matrix in terms of the retained eigenvectors for actual computer implementation.
Assessment of various code provisions based on optimum design of steel structures
Authors: Cheng Franklin Y. , Juang D. S. 
Published: March 2007

AbstractThis paper presents some comparative design results of typical structural systems in accordance with various code provisions, such as UBC and ATC‐03 of the U.S. and TJ‐11–78 of China. The solution comparisons are based on an optimization scheme for a given set of constraints and objective functions. Three levels of recursive procedures are employed in the algorithm to search for an optimum weight or construction cost including damages. Numerical examples are provided to compare the design results based on the aforementioned code provisions.
Effect of peak ground acceleration to velocity ratio on ductility demand of inelastic systems
Authors: Zhu T. J. , Heidebrecht A. C. , Tso W. K. 
Published: March 2007

AbstractA statistical analysis is performed to investigate the significance of peak ground acceleration to velocity ratio (a/v) on the displacement ductility demand of simple bilinear hysteretic systems. Three groups of earthquake records representative of low, normal and high<a/v ranges are used as input ground motions. The design yield strength of the inelastic systems is specified from the base shear formula in the 1980 National Building Code of Canada (NBCC 1980) and that in NBCC 1985 respectively. The former case represents the common practice of specifying seismic design base shear based on a peak site acceleration, while in the latter case the base shear is specified based on peak ground velocity and a/v ratio. Mean displacement ductility demands are obtained for the three groups of ground motions; and the corresponding dispersion characteristics are examined. The results show that the ground motion<a/v range has a significant effect on the displacement ductility demand, and it should be accounted for in design strength specification.
Effects of canyon topography and geological conditions on strong ground motion
Authors: Chuhan Zhang , Chongbin Zhao 
Published: March 2007

AbstractThe finite and infinite element coupling system is used to study the effects of canyon topography and geological conditions on strong ground motion. The system is first applied to a semi‐cylindrical shaped canyon using SH wave propagation to verify its accuracy. It is concluded that different topography conditions may have important effects on the ground motions along the canyon. The geological conditions, by which we mean different softening of weathered strata of the canyon surface, will have significantly amplified effects on the free field motions. This fact suggests that a deep weathered rock excavation of arch dam abutments for stability purposes will also benefit earthquake resistance of the dam due to the reduction of ground motions of the sound rock.
Analytical approach to calculation of response spectra from seismological models of ground motion
Authors: Šafak Erdal 
Published: March 2007

AbstractAn analytical approach to calculate response spectra from seismological models of ground motion is presented. Seismological models have three major advantages over empirical models: (1) they help in an understanding of the physics of earthquake mechanisms, (2) they can be used to predict ground motions for future earthquakes and (3) they can be extrapolated to cases where there are no data available. As shown with this study, these models also present a convenient form for the calculation of response spectra, by using the methods of random vibration theory, for a given magnitude and site conditions. The first part of the paper reviews the past models for ground motion description, and introduces the available seismological models. Then, the random vibration equations for the spectral response are presented. The non‐stationarity, spectral bandwidth and the correlation of the peaks are considered in the calculation of the peak response. The accuracy of the model is found to be satisfactory after comparing the calculated spectra with the empirical spectrum of Joyner and Boore,51which was developed by using records from 12 shallow earthquakes in western North America. The last part of the paper presents some numerical examples that show the variation of response spectra and peak factors (i.e. peak response/RMS response) for different magnitudes and distances.
A simple model for strong ground motions and response spectra
Authors: Safak Erdal , Mueller Charles , Boatwright John 
Published: March 2007

AbstractA simple model for the description of strong ground motions is introduced. The model shows that response spectra can be estimated by using only four parameters of the ground motion, the RMS acceleration, effective duration and two corner frequencies that characterize the effective frequency band of the motion. The model is a windowed band‐limited white noise, and is developed by studying the properties of two functions, cumulative squared acceleration in the time domain, and cumulative squared amplitude spectrum in the frequency domain. Applying the methods of random vibration theory, the model leads to a simple analytical expression for the response spectra. The accuracy of the model is checked by using the ground motion recordings from the aftershock sequences of two different earthquakes and simulated accelerograms. The results show that the model gives a satisfactory estimate of the response spectra.
Quick algorithms for computing either displacement, velocity or acceleration of an oscillator
Authors: Beck J. L. , Dowling M. J. 
Published: March 2007

AbstractAccurate and efficient algorithms are derived for computing any desired response quantity of a single‐degree‐of‐freedom linear oscillator subjected to an arbitrary forcing function. These algorithms are based on linear interpolation of the excitation between discrete points sampled uniformly in time. In the special case of the undamped oscillator, the displacement algorithm is equivalent to a previously published algorithm for this situation which was derived using a finite element approach. However, contrary to the claim made by the authors of this latter algorithm, it does not give an exact solution of the equation of undamped motion for an arbitrary forcing function.
Impedances of embedded rigid strip foundations
Authors: Rajapakse R. K. N. D. , Shah A. H. 
Published: March 2007

AbstractThis 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

AbstractRecent 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

AbstractLifeline 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

AbstractLow‐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

AbstractThe 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

AbstractThis 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

AbstractA 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.