bluuebunny/crossref_metadata_2025_split huggingface dataset:
The masonry arch as a four‐link mechanism under base motion
Authors: Oppenheim Irving J. 
Published: April 2007

AbstractThe dynamic response of an unreinforced masonry arch is examined, modelling the rigid body motions of arch segments under the influence of gravitational and inertial forces. This extends earlier studies of single rocking blocks, stacked blocks, and portal mechanisms of blocks; the masonry arch is analysed as another kinematic form of such a system. In this first effort a part‐circular planar arch ring is studied and excitation is restricted to horizontal ground acceleration of the base. The mechanism kinematics are presented and the governing equation of motion is derived in non‐linear form. The instantaneous form is determined for small rotations about the initial geometry and is used to study the conditions for the onset of mechanism motion. Possible failure conditions are posed and bounding principles are stated. One possible failure condition, direct overturning as a four‐link mechanism, is studied for one simplified base motion. The results show that an arch geometry establishes good resistance to earthquake excitation in that ground acceleration must exceed a rather high threshold before any mechanism motion would develop; however, once that threshold has been passed the arch has relatively modest resistance before failure. Other possible failure conditions are discussed; one emerges from pounding effects between segments at impact, and another develops from sliding of blocks over one another as the internal forces (normal and tangential to the masonry joint) vary with the inertial forces.
Scattering of plane sh waves by a semi‐cylindrical hill
Authors: Yuan Xiaoming , Men Fu‐Lu 
Published: April 2007

AbstractA new analytical method is presented to study the problem of scattering of plane SH waves by a semi‐cylindrical hill in an otherwise homogeneous, isotropic and elastic two‐dimensional half‐space, using the series of wave functions and a new expansion technique. The results obtained show that (1) the hill has quite considerable effects on ground motions for both the points on the hill and its environs, (2) these effects depend mainly on the frequency, the angle of wave incidence and the ratio of radius of hill to one‐half the wave length of incident waves, and (3) prominent and depression topographies having equal form and radius for the same incident waves would cause quite different mechanisms of wave propagation in both response performance and magnitude. The results, doubtless, would be useful for further deepening knowledge of the effects of prominent topography on seismic ground motion and for testing the accuracy of various approximate methods so far available.
Dynamic response analysis in the frequency domain
Authors: Humar J. L. , Xia Hong 
Published: April 2007

AbstractAnalysis in the frequency domain using discrete Fourier transforms is an efficient means of calculating the dynamic response of linear systems. In fact, for systems with frequency dependent parameters and also in those cases where the complex frequency response functions are more easily determined, frequency domain analysis may be the only effective means of determining the dynamic response. The use of discrete transforms along with finite summation requires that the forcing function and the impulse function be converted into periodic forms. This modification may introduce unacceptable errors in the results of analysis, unless appropriate steps are taken to avoid or minimize the effect of aliasing or overlapping. For single‐degree‐of‐freedom systems, procedures that will eliminate the effect of aliasing have already been developed. However, problems related to frequency domain analysis still exist for multi‐degree‐of‐freedom systems with non‐proportional damping, in analysis through substructuring and in those cases where a continuum solution is involved. A new procedure which addresses these problems and is applicable to both single‐ and multi‐degree‐of‐freedom system as well as to analysis through substructuring is presented here.
On engineering equivalent linear analysis of soils in the frequency domain
Authors: Lin Jeen‐Shang 
Published: April 2007

AbstractThis study investigated the performance, in the frequency domain, of an engineering equivalent linear method that is widely used in soil dynamics. A stochastic linear method using an extended differential equation by Wen and Baber was employed as the base line for evaluation. Stationary responses of single‐degree‐of‐freedom non‐linear systems under filtered white noise from both approaches were compared. For both a smooth nearly elasto‐plastic material and soils, the study found that the engineering equivalent linear analysis underestimated rms displacements, but provided good estimates of rms acceleration responses. Furthermore, the frequency response functions of acceleration from both approaches were close at all levels of response.
Instability due to time delay and its compensation in active control of structures
Authors: Agrawal Anil K. , Fujino Yozo , Bhartia Binod K. 
Published: April 2007

AbstractTime delay problem and its compensation in active control of civil engineering structures were studied. It has been shown by stability analysis of a SDOF system with time delayed feedback that the maximum allowable time delay depends not only on the natural period of the structure but also on feedback gains. We have demonstrated by numerical simulation that the performance of the control system degrades significantly when the time delay is close to this value and it even becomes unstable when time delay is greater than or equal to this value. The maximum allowable time delay decreases with decrease in natural period of the structure as well as with increase in active damping. The paper presents a technique for compensation by modelling time delay as transportation lag. This method ensures the stability of the controlled system as well as the desired response reduction.
Wave propagation in layered media by time domain BEM
Authors: Cheung Y. K. , Tham L. G. , Lei Z. X. 
Published: April 2007

AbstractA time domain boundary element in a cylindrical co‐ordinate system is developed for the analysis of wave propagation in a layered half‐space. The field quantities (displacements and tractions) are expressed as products of Fourier series in the circumferential direction and as linear polynomials in the other spatial directions. An integral equation is written for each layer as an independent domain, and these equations are then assembled into a general equation by virtue of compatibility and equilibrium conditions between the interfaces. Examples of three‐dimensional wave propagation in the layered half‐spaces due to various forms of surface and inner‐domain excitations are reported to demonstrate the accuracy and versatility of the method.
Performance of composite steel/concrete members under earthquake loading. Part II: Parametric studies and design considerations
Authors: Elghazouli A. Y. , Elnashai A. S. 
Published: April 2007

AbstractIn this paper, an advanced analytical model proposed and verified in a companion paper (Part I: Analytical model) is used to conduct parametric investigations of ductile partially‐encased composite beam‐columns. Particular attention is given to a new configuration of composite member developed and tested at Imperial College. A detailed account of the analytical results is given, and the most significant observations are highlighted and discussed. Quantitative assessments of plastic moment capacity, rotation and displacement ductility and plastic hinge length are undertaken. The implications of the main findings on the seismic design process are also presented. Finally, a procedure for ductility‐based design according to modern codes of practice is outlined.
Arch responses to correlated multiple excitations
Authors: Hao Hong 
Published: April 2007

AbstractThis paper analyses the in‐plane stochastic responses of incompressible circular arches to spatially correlated multiple excitations. The dynamic, quasi‐static and total structural displacements, moments, shear and axial forces are calculated. The results are compared with those obtained by various simplified excitations. The effects of the ground motion spatial variations on arch responses are examined. The results indicate that the responses may be underestimated or overestimated by neglecting the ground motion spatial variations, depending upon the structure and ground motion properties, the locations where the responses are evaluated, and the response quantity under consideration.
Kinematic soil–structure interaction for long‐span cable‐supported bridges
Authors: Betti R. , Abdel‐Ghaffar A. M. , Niazy A. S. 
Published: April 2007

AbstractA general procedure is presented to study the dynamic soil–structure interaction effects on the response of long‐span suspension and cable‐stayed bridges subjected to spatially varying ground motion at the supporting foundations. The foundation system is represented by multiple embedded cassion foundations and the frequency‐dependent impedance matrix for the multiple foundations system takes into account also the cross‐interaction among adjacent foundations through the soil. To illustrate the potential implementation of the analysis, a numerical example is presented in which the dynamic response of the Vincent–Thomas suspension bridge (Los Angeles, CA) subjected to the 1987 Whittier earthquake is investigated. Although both kinematic and inertial effects are included in the general procedure, only the kinematic effects of the soil–structure interaction are considered in the analysis of the test case. The results show the importance of the kinematic soil–foundation interaction on the structural response. These effects are related to the type, i.e. SH‐, SV‐, P‐ or Rayleigh waves and to the inclination of the seismic wave excitation. Moreover, rocking components of the foundation motion are emphasized by the embedment of the foundation system and greatly alter the structural response.
A post‐processing technique and an a posteriori error estimate for the newmark method in dynamic analysis
Authors: Wiberg N.‐E. , Li X. D. 
Published: April 2007

AbstractIn this paper, we present a post‐processing technique and an a posteriori error estimate for the Newmark method in structural dynamic analysis. By post‐processing the Newmark solutions, we derive a simple formulation for linearly varied third‐order derivatives. By comparing the Newmark solutions with the exact solutions expanded in the Taylor series, we achieve the local post‐processed solutions which are of fifth‐order accuracy for displacements and fourth‐order accuracy for velocities in one step. Based on the post‐processing technique, a posteriori local error estimates for displacements, velocities and, thus, also the total energy norm error estimate are obtained. If the Newmark solutions are corrected at each step, the post‐processed solutions are of third‐order accuracy in the global sense, i.e. one‐order improvement for the original Newmark solutions is achieved. We also discuss a method for estimating the global time integration error. We find that, when the total energy norm is used, the sum of the local error estimates will give a reasonable estimate for the global error. We present numerical studies on a SDOF and a 2‐DOF example in order to demonstrate the performance of the proposed technique.
Seismic response of heavily damped base isolation systems
Authors: Tsai Hsiang‐Chuan , Kelly James M. 
Published: April 2007

AbstractThe development of an efficient energy‐dissipating mechanism that works in conjunction with laminated elastomeric bearings in order to reduce the lateral deformation of the isolation system has always been a goal of base isolation research. Theoretically, this deformation will be reduced to the minimum if damping augmentation of the isolation system can reach a critical value. However, augmenting the isolation damping may cause some unwanted side effects. The purpose of this paper is to study the influence of isolation damping on the seismic response of heavily damped base‐isolated buildings. The base isolation system is assumed to be linearly viscoelastic and is analysed using the complex mode method. Solutions derived by using perturbation techniques for a two‐degree‐of‐freedom system and the computer simulation for a multiple‐degree‐of‐freedom system reveal that augmenting the isolation damping can reduce efficiently the deformation of the isolation system, but at the price of increasing the high‐frequency vibration in the superstructure. When the damping ratio of the isolation system is beyond some level, increasing the isolation damping will enlarge the extreme values of the base and superstructural accelerations. It is also found that approximate solutions derived from the use of classical damping and classical modes of vibration in the seismic analysis of heavily damped base isolation systems can be substantially in error.
Synchronization of human walking observed during lateral vibration of a congested pedestrian bridge
Authors: Fujino Yozo , Pacheco Benito M. , Nakamura Shun‐Ichi , Warnitchai Pennung 
Published: April 2007

AbstractObservation of human‐induced large‐amplitude lateral vibration of an actual pedestrian bridge in an extremely congested condition is reported. Walking motions of pedestrians recorded by a video camera are analysed. It is found that walking among 20 per cent or more of the pedestrians on the bridge was synchronized to the girder lateral vibration. With this synchronization, the total lateral force from the pedestrians to the girder is evidently increased and it acts as a resonant force on the girder lateral vibration.
Design formulas for tuned mass dampers based on A perturbation technique
Authors: Fujino Yozo , Abé Masato 
Published: April 2007

AbstractModal properties of tuned mass damper (TMD)‐structure two‐degree‐of‐freedom (2DOF) linear systems are studied employing a perturbation technique. Using the perturbation solutions, formulas relevant to designing the TMD for various types of loading are obtained; they are expressed as a function of mass ratio, tuning ratio, damping ratio of the TMD and damping ratio of the structure. Equivalent additional dampings of the structure due to the TMD are derived for random and harmonic forces. Matched expressions of equivalent damping, which are valid for detuned, i.e. non‐optimal, conditions are also presented. The stability boundary of TMD‐structure systems subject to linear self‐excited forces is derived in a closed form. Using the perturbation solutions, procedures for optimizing the TMD parameters for various types of loading are explained and the optimal values are derived. The formulas obtained in this study can be used with good accuracy for mass ratios less than 0.02.
Probabilistic site‐dependent non‐linear spectra
Authors: Miranda Eduardo 
Published: April 2007

AbstractThis paper presents a probabilistic approach to the estimation of lateral strengths required to provide an adequate control of inelastic deformations in structures during severe earthquake ground motions. In contrast to a deterministic approach, the approach presented herein accounts explicitly for the variability of the response of non‐linear systems due to the inherent uncertainties in the intensity and characteristics of the input excitation by considering the probability distribution of maximum inelastic strength demands. This study is based on the computation of non‐linear strength demands of single‐degree‐of‐freedom (SDOF) systems experiencing different levels of inelastic deformation when subjected to 124 recorded earthquake ground motions. Using empirical cumulative distribution functions site‐dependent probabilistic non‐linear spectra were computed for six probabilities of exceedance of different levels of inelastic deformation. It is concluded that the lateral strength required to control displacement ductility demands is significantly affected by the maximum tolerable inelastic deformation, the system's period of vibration, the local site conditions and the level of risk in exceeding the maximum tolerable deformations.
Fluid–foundation interaction in the seismic response of gravity dams
Authors: Chandrashaker R. , Humar J. L. 
Published: April 2007

AbstractThe seismic response of a dam is strongly influenced by its interaction with the water reservoir and the foundation. The hydrodynamic forces in the reservoir are in turn affected by radiation of waves towards infinity, wave absorption at the reservoir bottom, and cross‐coupling between the foundation below the dam and the reservoir bottom. The fluid–foundation interaction effect, i.e. the wave absorption along the reservoir bottom, can be accounted for by using either an approximate one‐dimensional (1D) wave propagation model or a rigorous analysis of interaction between the flexible soil along the base and the water. The rigorous approach requires enormous computational effort because of (a) cross‐coupling between the foundation of the dam and the soil below the reservoir and (b) frequency dependence of the boundary condition along the fluid‐foundation interface. The analysis can be simplified by ignoring the cross‐coupling and by using the approximate 1D wave propagation model. The effects of each of these two simplifications on the accuracy and computational efficiency of the procedure used for the seismic response analysis of a dam are examined. Analytical results are presented for the complex frequency‐response functions as well as the time histories of the response of Pine Flat dam to Taft and E1 Centro ground motions.
Dynamics of structures with uplift and sliding
Authors: Wang Xiao‐Feng , Gould Phillip L. 
Published: April 2007

AbstractA structure incorporating the mechanism of sliding, as used in seismic isolation, along with the mechanism of uplift, but at a different elevation, is proposed to study the possible beneficial effects on the response of the structure, as compared to allowing partial base uplift only. A two‐mass model of system uplift and sliding is established. The equations of motion for both the phase of full contact and the phase of base uplift are derived. The criteria governing the transformation of these two phases are given. Both the time history and the response spectrum results show that the structure with both uplift and sliding mechanisms is superior to that with only the uplift mechanism. Not only is the response of the structure lessened, but also the amount of uplift is greatly reduced because of the added sliding mechanism.
Accidental torsion in buildings due to stiffness uncertainty
Authors: de la Llera Juan Carlos , Chopra Anil K. 
Published: April 2007

AbstractDiscrepancies between the computed and actual values of the structural element stiffness imply that a building with nominally symmetric plan is actually asymmetric to some unknown degree and will undergo torsional vibration when subjected to purely translational ground motion. Such accidental torsion leads to increase in structural element deformations which is shown to be essentially insensitive to the uncoupled lateral vibration period of the system but is affected strongly by the ratio of uncoupled lateral and torsional vibration periods. The structural deformations increase, in the mean, by at most 10 and 5 per cent for R/C and steel buildings, respectively, and by much smaller amounts for a wide range of system parameters. The increase in structural deformations due to stiffness uncertainty is shown to be much smaller than implied by the accidental torsional provisions in the Uniform Building Code and most other building codes.
Complex‐parameter kelvin model for elastic foundations
Authors: Makris Nicos 
Published: April 2007

AbstractA new rigorous approach in modelling mechanical behaviour is developed. The dynamic response of a rigid disc resting on an elastic half‐space is approximated by a macroscopic force‐displacement relationship, where not only the coefficients but also the order of time derivatives are complex valued. It is shown that comlex‐parameter constitutive models are not simply an elegant alternative in modelling mechanical behaviour, but are the outcome of rigorous non‐linear regression analysis on complex‐valued functions, like the dynamic stiffness of dissipative systems. Complex‐parameter constitutive models are very attractive since a minimum number of parameters is required to obtain a satisfactory fit of the ‘exact’ response. A two‐parameter generalized Kelvin model reproduces closely the ‘exact’ dynamic stiffness of the disc for all three vertical, horizontal and rocking modes studied herein. Frequency‐ and time‐domain algorithms to solve complex‐order differential equations are developed, validated and used to calculate the foundation–response under earthquake excitation. It is the excellent agreement of results and the economy in number of parameters that make complex‐parameter models so attractive in constitutive modelling.
Uniform reliability safety format for seismic design of reinforced concrete structures
Authors: Economou Spiros N. , Fardis Michael N. 
Published: April 2007

AbstractA safety format is proposed for the flexural design of reinforced concrete members for the combination of seismic and gravity loads, with load and resistance factors which depend on member type, on the value of the target theoretical probability of failure and on the ratio of the load effect due to gravity loads to that due to the nominal value of the seismic action, both obtained by elastic analysis. Safety factors are computed through an advanced Level II reliability procedure, using a limit state inequality between the member rotation ductility supply under monotonic loading and the peak rotation ductility and cyclic energy dissipation demands. Uncertainties considered are: for resistance, the uncertainty of failure under imposed cyclic deformations, and for action, the maximum peak ductility and energy dissipation demands in the structure's lifetime, as obtained through a series of non‐linear dynamic analyses of multistorey buildings in 3D. using as input ensembles of bidirectional acceleration time‐histories which describe probabilistically the extreme bidirectional seismic action in the structure's lifetime. Computed load and resistance factors are practically independent of the load‐effects ratio. The load factor on the seismic action is found to be independent of member type and to increase with the theoretical probability of failure much faster than the elastic spectral value at the structure's fundamental period with probability of exceedance in the structure's lifetime. Simple rules for the dependence of the resistance modification factors on the theoretical failure probability are also derived. As for the computed values of the load factors the moment due to gravity loads is negligible in comparison to the factored seismic moment, a simplified safety checking inequality between the design flexural capacity and a reduced seismic moment is proposed, in which the ratio of the resistance to the load factor plays the role of a force reduction or effective behaviour factor for the member.