bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved method of generation of artificial time‐histories, rich in all frequencies, from floor spectra
Authors: Khan Mohsin R. 
Published: March 2007

AbstractA method to generate artificial time‐histories from given floor response spectra is presented in this paper. The original method proposed by Levy and Wilkinson1 is modified. New iterative equations are developed, based on extensive computational experimentation, to speed up and stabilize the convergence process. The present approach, when applied to spectra with peaks in the high frequency range (40 to 100 Hz) along with seismic peaks, converges very closely to the target spectra within eight iterations regardless of damping values. The original computer program for synthetic time‐history generation was developed on the UNIVAC 1100 series computer. This program was converted to work on the IBM PC. The PC based program ‘MICRO‐SEIM’ saves the response spectra generated at each iteration and the final synthetic time‐history on the PC diskette. The post processing program reads those saved data from the diskette and plots the spectra and time‐history.
Reinforced concrete hysteresis model based on the damage concept
Authors: Wang Ming‐Liang , Shah Surendra P. 
Published: March 2007

AbstractReinforced concrete members subjected to cyclic inelastic deformation may exhibit both stiffness and strength degradation, depending on the maximum amplitude and the number of cycles experienced by the member. Many of the currently available models do not simulate the cycle‐dependent stiffness loss often observed during the experiments. An analytical model based on a damage parameter which is a function of the cumulative cyclic inelastic deformation is proposed. A small‐scale reinforced concrete beam–column joint was constructed and subjected to cyclic loading to calibrate the damage parameter. The model is able to approximate the complete hysteretic response and is simple to implement. The sensitivity of the analytical model was examined by comparing the model with several experimental results.
Analysis of absorption effects on the dynamic response of dam reservoir systems by boundary element methods
Authors: Antes Heinz , Von Estorff Otto 
Published: March 2007

AbstractUsing reciprocal theorems for dynamic and static boundary value problems, boundary integral equations are presented for wave propagation in elastic, isotropic media and compressible, inviscid fluids in the time domain as well as in the frequency domain. For the analysis of fluid–soil and fluid–structure systems, suitable coupling conditions are prescribed along the interfaces. The numerical treatment of the boundary integral equations consists of a point collocation and of a discretization of the boundary, in which constant and linear approximation functions are assumed. Step‐by‐step integration is applied to the time‐dependent equations, where again the states are taken to be linear and constant over each time interval.These boundary element procedures are used to analyse the response of dams due to horizontal and vertical ground motions considering dam–water interaction and absorption of hydrodynamic pressure waves at the reservoir bottom or at the far end into the soil medium. Both the frequency response and the impulse generated transient response are investigated.
Non‐classical damping in dynamic analysis of base‐isolated structures with internal equipment
Authors: Tsai Hsiang‐Chuan , Kelly James M. 
Published: March 2007

AbstractIt has been shown that the use of base isolation not only attenuates the response of a primary structural system but also reduces the response of a secondary system mounted on or within the main structure. The isolation system, superstructure and equipment may be made of different materials with significantly different energy dissipation characteristics such that the damping matrix for the combined system is non‐classical and can only be approximately expressed by modal damping ratios if the classical mode method is used for analysis. The object of this paper is to evaluate the accuracy of this procedure in approximating the responses of base‐isolated structures and internal equipment.The complex mode method can provide exact solutions to problems with non‐classical damping and is used here to find the exact response of the isolation‐superstructure‐equipment system. The entire system is assumed to be linear elastic with viscous damping and the superstructure is assumed to be proportionally damped so that the deformation of the superstructure can be expressed in terms of its classical modes. Recognizing that the ratio of the equipment mass to the structural mass and the ratio of the stiffness of the isolation system to the superstructural stiffness are both small, perturbation methods are used to find the response.This study shows that the response of base‐isolated structures can be determined by the classical mode method to some degree of accuracy, but the higher frequency content is distorted. The equipment response derived by the classical mode method is much smaller than the exact solution so that the complex mode method should be applied to find equipment response.
Restoring forces on vertical circular cylinders forced by earthquakes
Authors: Tanaka Yoshihiro , Hudspeth Robert T. 
Published: March 2007

AbstractAn eigenfunction solution is presented for the dynamic response of vertical circular cylinders to earthquake excitation in a compressible fluid of finite depth. This single eigenseries expansion eliminates the need for a double summation over both the eigenfunctions and the trial functions as required by Rayleigh‐Ritz methods. Revised definitions for the added mass and hydrodynamic radiation damping coefficients per unit length are derived from the hydrodynamic fluid pressures. Based on comparisons between these newly defined coefficients, the compressibility of the fluid is found to be relatively more important at dimensionless frequencies greater than unity (ω > 1.0) when analysing both rigid and flexible cylinders having relatively large diameter to water depth ratios,r0/h > 0.25 (squatty type). This conclusion regarding the relative importance of the fluid compressibility is derived from a comparison between the relative magnitudes and the vertical distributions over depth of both the added mass and radiation damping coefficients per unit length for both rigid and flexible squatty cylinders. From additional comparisons with Rayleigh‐Ritz solutions that require trial functions, the results for totally immersed flexible slender cylinders (r0/h< 0.10) are shown to be equivalent; but the results for totally immersed flexible squatty cylinders (r0/h > 0.25) are not. The reason for this difference appears to be in the truncation of the trial function series in the Rayleigh‐Ritz methods, which excludes the higher mode shapes, and in the definitions of the added mass coefficients. Comparisons with laboratory data for both rigid and flexible cylinders confirm the accuracy of the solutions obtained by the eigenseries in the limited frequency interval above the highest frequency for surface gravity waves (f > 1.0 Hz) and below the first dimensionless cut‐off frequency for acoustic waves (ω< 1.0).
A test problem for structural systems with discontinuities
Authors: Brown J. M. B. , Borthwick W. K. D. 
Published: March 2007

AbstractThe direct integration method for structural systems having force and/or stiffness discontinuities is known to present considerable numerical difficulties. A non‐linear one‐degree‐of‐freedom test problem having these characteristics is developed and its exact oscillation period determined. The effects on amplitude and phase of small perturbations of the switching point, such as are caused by fixed‐step integration, have been studied. Artificial energy changes introduced at discontinuities by fixed‐step explicit and implicit methods are investigated. For a number of commonly used algorithms orders of convergence in fixed‐step integration of the test problem degrade from design value before, toO(h) after, the first discontinuity traversal.O(h) convergence is maintained for any number of discontinuity traversals thereafter, but design order can be recovered by locating the switching point sufficiently precisely.
Response of tension‐leg platforms to vertical seismic excitations
Authors: Liou Gin‐Show , Penzien Joseph , Yeung Ronald W. 
Published: March 2007

AbstractPresented is a systematic approach, for analysing the vertical motion, tendon force and foundation uplift of a tension‐leg platform (TLP) when the subsea soil is excited by vertical seismic waves. The complex problem of multiple interactions among the soil, foundation, fluid and platform can be mathematically modelled using the substructure technique. Having obtained the frequency dependent impedance function for each substructure, the total system is then solved in the frequency domain. A specific TLP is analysed to show the application of the procedures developed and the importance of response to vertical seismic excitation.
Seismic vulnerability and risk evaluation for old urban nuclei
Authors: Benedetti Duilio , Benzoni Gianmario , Parisi Maria A. 
Published: March 2007

AbstractThe evaluation of the seismic damageability of existing buildings is a primary element in the planning for mitigation of earthquake effects. To this purpose, the use of the vulnerability index has been recently proposed and adopted in various surveys in Italy. The index results from grading the status of various structural and non‐structural components exposed to damage in a seismic event. The effectiveness of the vulnerability index as a measure of the health status of buildings is discussed on the basis of regional surveys of vulnerability index versus reported damage, carried out in various Italian areas such as Friuli and the city of Gubbio. Also, investigation of the items most effective in describing damageability among those contributing to the index is performed, in view of formulating a reduced survey procedure. A damage versus vulnerability index database collected in these surveys is presented as well. Finally, a vulnerability index based procedure to evaluate the expected damage in a territory is proposed.
Convergence and stability of step‐by‐step integration for model with negative‐stiffness
Authors: Cheng Minxian 
Published: March 2007

AbstractThe convergence and stability of step‐by‐step integration schemes used in the inelastic dynamic analysis of structures and their corresponding criteria were studied for a restoring force model with negative‐stiffness. Convergence conditions and stability conditions 1, 2 or 3 were established. The numerical stability of the integration under negative‐stiffness belongs to the category of relative stability; consequently, the concepts and the conclusions concerning numerical stability in the case of positive‐stiffness (which belongs to absolute stability) cannot be used.Research into several step‐by‐step integration methods usually employed in inelastic dynamic analysis has shown great differences in numerical stability for models with negative‐stiffness as compared with positive‐stiffness models. The central difference method is convergent and unconditionally stable in the case of negative‐stiffness, though it is only conditionally stable in the case of positive‐stiffness. The Houbolt method satisfies the requirement for convergence; its stability, however, depends not only on the integration step size Δt but also on the stiffness ratio β for the model with negative‐stiffness, unlike the unconditional stability for the model with positive‐stiffness. The Newmark constant acceleration method is convergent and unconditionally stable in the case of negative‐stiffness just like it is in the case of positive‐stiffness.
Evaluation of dynamic eccentricities obtained using a probabilistic approach, response spectrum methods and modern building codes
Authors: Rady M. A. , Hutchinson G. L. 
Published: March 2007

AbstractIn this paper a probabilistic approach has been adopted to study both the effects of uncertainty in earthquake frequency content and the correlation between earthquake frequency content and ground motion intensity on the response of a single‐storey torsionally coupled elastic structure. The earthquake ground motion has been assumed to be a Gaussian, zero mean, stationary random process which is fully characterized by a power spectrum. The ground acceleration power spectrum is idealized as a probabilistic normalized power spectrum computed from actual earthquake records. The advantage of such an idealization is that it enables the effect of the natural frequency as a controlling structural parameter in torsional coupling to be assessed. Comparisons of the dynamic amplifications of eccentricity with those obtained from modern codes of practice and conventional response spectrum analyses have been made.The results of this study have shown that the variation in the frequency content has a significant effect on the response of low frequency structures, while the correlation between the frequency content and the intensity of seismic ground motion is insignificant for the wide range of structures considered.The structure natural frequency has been shown to be an important controlling parameter in the torsionally coupled response of structures subject to seismic loading. The frequency dependence of the dynamic amplification of eccentricity was found not to be reflected in the response spectrum analysis and the torsional provisions of modern building codes.
An exact component mode synthesis approach
Authors: Suarez L. E. , Singh M. P. 
Published: March 2007

AbstractThe paper presents a method for synthesizing the modal properties of substructures to obtain the exact modal properties of a combined structure. Unlike the currently available modal synthesis approaches, the proposed approach does not require the solution of any transformed eigenvalue problem of the combined structure by conventional means. The substructures are assumed to be coupled by connecting elements and the coupling is done sequentially with one element at a time. The eigenvalues at each stage of coupling are obtained by solving a non‐linear characteristic equation. A simple Newton‐Raphson solution scheme is adequate for this purpose. Once the eigenvalues are determined, the eigenvectors can be calculated in closed form. Several examples demonstrating the applicability of the proposed approach are presented.
Rosenblueth's modal combination rule for systems with non‐classical damping
Authors: Villaverde Roberto 
Published: March 2007

AbstractA simple rule is derived to combine, within the framework of a complex mode superposition, the maximum modal responses of systems such as soil‐structure and structure‐equipment systems, for which closely spaced natural frequencies are likely, and for which, because of the large difference in the damping values of their various components, the assumption of an orthogonal damping matrix may lead to significant errors. The rule constitutes the generalization of Rosenblueth's rule for systems with closely spaced natural frequencies and classical modes, and is expressed in terms of their complex mode shapes and natural frequencies. Its derivation is based on the theory of a complex modal analysis for systems with non‐classical modes of vibration and on Rosenblueth's original derivation. As in this original derivation, earthquake ground motions are modelled as a stationary white noise process, but the formulae obtained under this assumption are modified later on to account for the transient nature of actual earthquakes. A numerical example is presented to illustrate the application of the rule, and a comparative study with numerical integration solutions is performed to assess its accuracy. In this comparative study, it predicts the numerical integration solutions with an average error of 0.3 per cent.
Dynamic response of vertically excited liquid storage tanks considering liquid‐soil interaction
Authors: Fischer F. D. , Seeber R. 
Published: March 2007

AbstractThe paper presents a dynamic response analysis of vertically excited liquid storage tanks including both liquid‐tank and liquid‐soil interaction. The system considered is a thin‐walled, elastic cylindrical shell entirely filled with an incompressible and inviscid fluid, resting on a flexible foundation over an elastic halfspace with frequency dependent stiffness and damping parameters. The problem is treated analytically by the generalized‐coordinate approach and then solved numerically using the complex frequency response analysis. For one special tank, natural frequencies and equivalent damping ratios are evaluated and compared with those corresponding to a rigid ground. The maximum dynamic pressure is calculated using the response spectra of the 1976 Friuli earthquake. A parameter study is carried out to show the great influence of variable soil stiffness upon the damping ratio of the shell‐liquid‐soil system.
Hydrodynamic‐stiffness matrix based on boundary elements for time‐domain dam‐reservoir‐soil analysis
Authors: Wepf Dieter H. , Wolf John P. , Bachmann H. 
Published: March 2007

AbstractFor a reservoir with an arbitrary shape of the upstream dam face and of the bottom including an adjacent regular part of constant depth extending to infinity, the hydrodynamic‐stiffness matrix in the frequency domain for a displacement formulation is derived using the boundary‐element method. The fundamental solution takes the boundary condition at the free surface into account. The analytical solution of the semi‐infinite reservoir is used to improve the accuracy. To be able to transform the hydrodynamic‐stiffness matrix from the frequency to the time domain, the singular part consisting of its asymptotic value of ω ∞ is split off. It consists of an imaginary linear term in ω which can be interpreted as a damper with a coefficient per unit area equal to the product of the mass density and the wave velocity. This also applies for a reservoir bottom of arbitrary shape. The remaining regular part of the stiffness matrix is transformed numerically. The corresponding interaction force‐displacement relationship involves convolution integrals. This boundary‐element solution agrees well with analytical results and with those of other numerical procedures based on a time‐stepping method. The method is also applied to an actual earthquake acting on a reservoir with an irregular part with an inclined bottom and a regular part extending to infinity. The results of the analysis in the time domain coincide with those determined in the frequency domain.
Dynamic finite strip analysis of surface foundations
Authors: Chow Y. K. , Swaddiwudhipong S. , Lim S. A. 
Published: March 2007

AbstractThe finite strip method is used to study the dynamic response of surface strip foundations. This method is simple to use and versatile. The two‐dimensional problem is effectively reduced to an equivalent one‐dimensional problem. The choice of trigonometric series for the displacement functions results in the uncoupling of the terms of the series and a significant reduction in the semi‐bandwidth of the complex set of equations, making the method well suited to small computers. Non‐homogeneous soil profiles are treated as a matter of course. The finite strip solutions are shown to be in general agreement with other theoretical methods of analysis.
Transient pressures in hydrotechnical tunnels during earthquakes
Authors: Kojic Slobodan B. , Trifunac Mihailo D. 
Published: March 2007

AbstractTransient pressures generated by earthquake shaking in hydrotechnical tunnels are evaluated by the discrete Fourier transform technique. The effects of the horizontal ground motion accelerating the closed downstream tunnel gate, as well as the upstream dam face, and the influence of the vertical motion of the reservoir floor are considered in this analysis. An example of a typical bottom outlet is analysed by subjecting it to several computed accelerograms. It is shown that high hydrodynamic pressures can be developed, several times larger than the hydrostatic pressure.
The use of optimization to construct critical accelerograms for given structures and sites
Authors: Pirasteh Ali Akbar , Cherry Jeffery L. , Balling Richard J. 
Published: March 2007

AbstractIn this paper a methodology has been presented for constructing the most critical accelerogram from among a be class of candidate accelerograms for a given site and structure. This most critical accelerogram could be used to assess seismic resistance of a structure with a high level of confidence. Specifically, the method superimposes accelerograms recorded at similar sites to create the candidate accelerograms, then uses optimization and approximation techniques find the most critical accelerogram. The most critical accelerogram is defined as the one which maximizes damage is structure, as computed by non‐linear dynamic structural analysis, as well as satisfies constraints on ground parameters to ensure credibility. The damage has been defined as cumulative inelastic energy dissipation or sure of interstorey drifts. The method is applied to ten examples in the paper.
Dynamic analysis of 3‐D flexible embedded foundations by a frequency domain BEM‐FEM
Authors: Gaitanaros Alexandros P. , Karabalis Dimitris L. 
Published: March 2007

AbstractA study on the dynamic response of three‐dimensional flexible foundations of arbitrary shape, embedded in a homogenous, isotropic and linear elastic half‐space is presented. Both massive and massless foundations are considered. The soil‐foundation system is subjected to externally applied forces, and/or to obliquely incident seismic waves. The numerical method employed is a combination of the frequency domain Boundary Element Method, which is used to simulate the elastic soil medium, and the Finite Element Method, on the basis of which the stiffness matrix of the foundation is obtained. The foundation and soil media are combined by enforcing compatibility and equilibrium conditions at their common interface. Both relaxed and completely bonded boundary conditions are considered. The accuracy of the proposed methodology is partially verified through comparison studies with results reported in the literature for rigid embedded foundations.
Engineering implications of the 1985 nahanni earthquakes
Authors: Heidebrecht Arthur C. , Naumoski Nove 
Published: March 2007

AbstractA series of strong ground motions was recorded during a set of earthquakes which occurred in the North Nahanni River area of the Northwest Territories of Canada in late 1985. The strongest of these motions were recorded within 10 km of the epicentre of a magnitude 6.9 event; peak accelerations were well above 1g and peak velocities exceeded 0.4 m/s.This paper describes a study of the engineering characteristics of the Nahanni strong motions, particularly as they affect the response of building structures. The response characteristics are analysed in terms of the response spectra and the unit velocity base shear coefficients for multi‐degree‐of‐freedom elastic frame structures. An analysis of the strong motion durations of the records and several measures of intensity is also included. The characteristics of the Nahanni records are compared with those of typical strong seismic ground motions and an ensemble of epicentral region seismic motions recorded under similar conditions. Comparisons are also made with the equivalent parameters in the 1985 edition of the National Building Code of Canada.It is concluded that the Nahanni records are very strong seismic ground motion records with relatively unusual response characteristics, even when compared with those of other records obtained within the epicentral region. The impact of these characteristics on engineering design is most significant for low period structures in epicentral regions. The specifications of typical design codes do not adequately describe the response to such records for very low periods.