bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic behaviour of turbine‐generator‐foundation systems
Authors: Liu Weiming , Novak Milos 
Published: April 2007

AbstractIn this paper a comprehensive investigation on the dynamic characteristics of turbine–generator–foundation systems is performed. All the major components of the system, including turbine–generator casing, shaft, rotors, journal bearings, deck, piers, foundation mat, piles, and soil medium, have been included. Full interaction between the turbine–generator set, the foundation superstructure, and the soil medium, is considered.A hybrid method is used to establish the mathematical model for the turbine–generator‐foundation system. The analysis is conducted in the frequency domain through complex frequency response analysis. The response in the time domain is obtained by Fourier transform. The seismic excitation is represented as the control motion on the ground surface, which is generated as an artificial earthquake.A 300 MW turbine‐generator‐foundation system is analysed under excitations from rotor unbalances and earthquakes. The influence of turbine‐generator casing and soil anisotropy on the response of the system is explored. It is found that the presence of casing and soil anisotropy strongly influences the displacements and internal forces of the system under rotor unbalance excitation. Under seismic excitation, however, although the presence of casing and soil anisotropy does affect the displacements of the system, their effect on the internal forces of the system is minimal.
Multi‐directional transmitting boundaries for steady‐state SH waves
Authors: Liao Z. P. , Yang G. 
Published: April 2007

AbstractThe incident steady‐state SH waves in the neighbourhood of a boundary node point are first expanded in terms of a few plane waves at different incident angles, the motion of the boundary point is then related to those of its adjacent node points to form the multi‐directional transmitting boundary conditions, which reduce reflections from the boundary over the entire range of incident angles. This feature of the boundaries is demonstrated by finite element computations of SH motions of a layer fixed at its base, in which the incident wave may travel parallel to the boundary as the frequency of excitation approaches one of the natural frequencies of the system.
An energy approach to sliding of single‐span simply supported slab‐on‐girder steel highway bridges with damaged bearings
Authors: Dicleli Murat , Bruneau Michel 
Published: April 2007

AbstractThis paper investigates the non‐linear inelastic seismic response of existing single‐span simply supported bridges having bearings which can remain stable and slide after their anchor bolts are ruptured. A simplified equivalent model is developed for the inelastic analysis of these single‐span simply supported bridges. Non‐linear inelastic time‐history analyses are conducted for various acceleration inputs. It is found that narrower bridges with longer spans may have considerable sliding displacements and fall off their supports if adequate seat width is not provided. It is also found that for the same ratio of friction coefficient to peak ground acceleration, the sliding displacement of a structural system is linearly proportional to the amplitude of the peak ground acceleration beyond a certain threshold value. This is also demonstrated analytically from an energy approach point of view. The distribution of the energy content of an earthquake, which is related to its velocity time history, can be an indication of the propensity of an earthquake to cause high sliding displacements. Ground motions with high frequency content or high Ap/Vp ratio may produce smaller sliding displacements than ground motions with relatively lower Ap/Vp ratios.
Shifting natural frequencies of plates through preforming
Authors: Mostaghel N. , Fu K. C. , Yu Qiulin 
Published: April 2007

AbstractThrough an energy formulation and the use of a large deflection theory, it is shown that if a thin plate has a slight initial preform, and if its edges are constrained against in–plane displacements, then all of the natural frequencies of the plate will be shifted upward. For a uniform thin plate, the amount of frequency shift depends on the type of boundary conditions and the ratio of the amplitude of preform to the thickness of the plate. Examples of square and rectangular plates preformed in the shape of their first mode shapes are presented. The method holds the promise of shifting or essentially removing a troublesome vibration mode.
Damping in low‐aspect‐ratio, reinforced concrete shear walls
Authors: Farrar Charles R. , Baker William E. 
Published: April 2007

AbstractExperiments were conducted to measure the damping in low‐aspect‐ratio, reinforced concrete shear walls with the specific intent of obtaining a better understanding of how this parameter changes with increasing stress levels. These experiments and the corresponding results are presented, along with a description of the methods used to estimate damping from measured input and response data and a summary of a numerical study that was undertaken to assess the relative accuracy of these methods. Also presented are the testing methods used in this study, including static cyclic tests, experimental modal analyses, and simulated seismic testing on a shake table. The results are summarized and compared with those obtained by other investigators. In conclusion, an empirical relationship is developed for equivalent viscous damping in low‐aspect‐ratio shear walls as a function of the peak nominal base shear stress the shear wall experiences during a seismic event.
Observation and numerical analysis of soil‐structure interaction of a reinforced concrete tower
Authors: Ganev Todor , Yamazaki Fumio , Katayama Tsuneo 
Published: April 2007

AbstractA vast amount of earthquake response records of an observation tower are used together with microtremor data to investigate various aspects of the dynamic behaviour of the soil‐structure system. It is found that separation of the soil from the structure occurs under large dynamic loads, leading to changes in the predominant frequency of the system. As a result of the decreasing of the soil support at the side walls of the foundation, the stress caused by the structural weight on the bottom soil increases during earthquakes. With regard to its practical applicability, a linear sway‐rocking model is applied for numerical modelling of the soil‐structure system. Alterations in the soil support as a result of soil non‐linearity and separation of the structure from the soil are investigated by comparing recorded and simulated structural response. The influence of each of these factors on the softening of the soil support is distinctly assessed. An empirical relationship between the peak ground velocity and the soil constants for earthquake excitations of different magnitude is presented.
Neural networks for quick earthquake damage estimation
Authors: Molas Gilbert L. , Yamazaki Fumio 
Published: April 2007

AbstractThis paper proposes the use of neural networks to predict damage due to earthquakes from the indices of recorded ground motion. Since the relationship between ground motion indices and resulting damage is difficult to express in mathematical form, neural networks are conveniently applied for this problem. Simulated earthquake ground motions are used to have a well‐distributed data set and the ductility factor from non‐linear analysis of two single‐degree‐of‐freedom structural models is used to represent the damage. A sensitivity analysis procedure is described to identify qualitatively the input parameters that have a greater influence on the damage. The result of the trained neural network is then verified by using several recorded earthquake ground motions. It is found that some instability in the prediction can occur. Instability occurs when input values exceed the range of the training data. The neural network model using PGA and SI as input give the best performance in the recall tests using actual earthquake ground motion, demonstrating the usefulness of neural network models for the quick estimation of damage through earthquake intensity monitoring.
Comparative experimental studies of models of self‐controlled and ordinary frames on the shaking table
Authors: Liang Shuting , Ding Dajun 
Published: April 2007

AbstractThis paper presents a comparative test of models of self‐controlled and ordinary frames on the shaking table. Two tested 1/8‐scale models of 4‐storey and single‐bay RC frames made of cement mortar and reinforced with wires were poured on the same base beam. The dynamic characteristics and earthquake responses in the elastic, cracked and failed stages and the failure modes of these two kinds of frame are studied. It is proved that the seismic behaviour of the self‐controlled frame is better than that of the ordinary frame.
A simplified model for analysis and design of asymmetric‐plan buildings
Authors: De Llera Juan C. La , Chopra Anil K. 
Published: April 2007

AbstractA new simplified model for analysis and design of multistorey buildings is developed. The model is based on a single super‐element per building storey capable of representing the elastic and inelastic properties of the storey. This is done by matching the stiffness matrices and ultimate yield surface of the storey with that of the element; this surface relates storey shear and storey torque. For practical convenience, these surfaces are parametrized in terms of seven important physical parameters controlling the seismic response of asymmetric structures. Several numerical studies showed that the accuracy of the super‐element model is satisfactory for most design purposes; the errors in peak responses are expected to be less than 20 per cent for most practical structures. Among the important advantages of this simplified model is that the time required in formulating, analysing and interpreting the structural model and its response is at least an order of magnitude smaller than for any conventional 3‐D inelastic model. This enables the engineer to try different structural configurations and, thus, produce designs that have the desired seismic behaviour and are cost‐effective. Furthermore, it has been shown through a multistorey building example that the super‐element model is a powerful tool for conceptual design of a building. In spite of its simplicity, the model uses an accurate representation of the storey‐shear and torque surfaces, which enables it to capture the fundamental features controlling the inelastic behaviour of the building.
A model of tuned liquid damper for suppressing pitching motions of structures
Authors: Sun L. M. , Fujino Y. , Koga K. 
Published: April 2007

AbstractA tuned liquid damper (TLD), which consists of rigid tanks partially filled by liquid, is a type of passive control device relying upon liquid sloshing forces or moments to change the dynamical properties and to dissipate vibrational energy of a structure. An analytical non‐linear model is proposed for a TLD using rectangular tanks filled with shallow liquid under pitching vibration, utilizing a shallow water wave theory. The model includes the linear damping of the sloshing liquid, which is an important parameter in the study of a TLD as it affects the efficiency of the TLD. Shaking table experiments were conducted for verification; good agreement between the analytical simulations and the experimental results was observed in a small excitation amplitude range. The simulations of TLD‐structure interaction by using the proposed model show that the TLD can efficiently suppress resonant pitching vibration of a structure. It is also found that the effectiveness of a TLD for suppressing the pitching vibration depends not only on the mass of liquid in the TLD but also on the configuration of the liquid as well as upon the position where the TLD is located. If the configuration of the liquid, i.e. the liquid depth and the TLD tank size, is designed suitably, the TLD can have a large suppressing moment and can be very effective even with a small mass of liquid.
Global lumped‐parameter model with physical representation for unbounded medium
Authors: Paronesso Antonio , Wolf John P. 
Published: April 2007

AbstractA systematic procedure to construct a consistent global lumped‐parameter model consisting of springs, dashpots and possibly masses with frequency‐independent coefficients connecting the degrees of freedom of the nodes of any structure‐medium interface for the unbounded medium is presented. The dynamic‐stiffness matrix is first diagonalized which then permits each term to be modelled independently from the others. Physical insight is thus provided. Alternatively, the (symmetric) static‐stiffness and damping matrices and possibly mass matrix of the unbounded medium can be established directly.
Passive seismic response controlled high‐rise building with high damping device
Authors: Niwa Naoki , Kobori Takuji , Takahashi Motoichi , Hatada Tomohiko , Kurino Haruhiko , Tagami Jun 
Published: April 2007

AbstractThis paper describes a feasibility study on a high‐damping device (HiDAM) installed in a building structure by way of a bracing mechanism.A seismic response analysis with respect to a high‐rise building approximately 100 m high is reported. Proper adjustment of the damping coefficient of the HiDAM (oil damper) provided an over all damping factor of about 10–20 per cent to the building structure, and reductions in the response, deformation and shear forces were verified analytically.This paper reports also the performance confirmation tests conducted on a model device of the HiDAM which satisfied the specifications determined from the analytical results. The test results demonstrate the feasibility of the HiDAM and the possibility of utilizing it in high‐rise buildings.
Time‐delay control of structures
Authors: Chung L. L. , Lin C. C. , Lu K. H. 
Published: April 2007

AbstractTime‐delay causes unsynchronized application of the control forces which may not only degrade the performance of the control system but also even induce instability to the dynamic system. Time‐delay control algorithm is developed in this paper to solve this practical problem. The control system is first formulated in discrete‐time form. In the presence of time‐delay, the motion equation of the discrete‐time control system remains a difference equation which can be transformed into first‐order difference equation by augmenting the state variables. Optimal time‐delay control algorithm is derived based on the augmented system. The time‐delay control forces are simply generated from the time‐delay states multiplied by the constant feedback gain. Numerical simulation is illustrated to verify the feasibility of the proposed control algorithm. Since time‐delay effect is incorporated in the mathematical model for the structural control system throughout the derivation of the proposed algorithm, system performance and dynamic stability are guaranteed.
An unconditionally stable hybrid pseudodynamic algorithm
Authors: Thewalt Christopher R. , Mahin Stephen A. 
Published: April 2007

AbstractThere is a significant motivation to implement an unconditionally stable scheme in the pseudodynamic test method. As more complex experiments with many degrees of freedom are tested, explicit time integration methods limit the size of time step on the basis of the highest natural frequency of the system. This is true even though the response of the structure may be dominated by a few lower frequency modes. The limit on step size is undesirable because it physically increases the duration of a test, but more importantly, because the number of steps to completion increases and error propagation problems increase with the number of steps in a test. In addition, incremental displacements within each step become smaller, introducing the potential for problems associated with stress relaxation. An unconditionally stable algorithm allows the time step to be selected to give accurate response in the modes of interest without regard for higher mode characteristics.
Non‐planar pseudodynamic testing
Authors: Thewalt Christopher R. , Mahin Stephen A. 
Published: April 2007

AbstractThe pseudodynamic test method provides a means of inexpensive seismic performance testing for laboratories that do not have a shaking table. However, most pseudodynamic tests to date have used planar portions of structures subjected to a single lateral component of base excitation, mimicking the type of testing that would occur on a shaking table. There has been little work on the extension of the pseudodynamic test method to three‐dimensional testing of structures under multiple components of base excitation. In this paper a three‐dimensional specimen is tested under a multicomponent fixed base excitation and the response is compared to shaking table tests. The paper presents an overview of the pseudodynamic test method, including non‐planar extensions, and highlights many physical problems that occurred during the testing process. Many of these problems apply to any pseudodynamic test, not just non‐planar tests, but the results show that very accurate non‐planar tests can be achieved with careful error control.
Active control of building seismic response by energy dissipation
Authors: Kannan Sankaran , Uras H. Mehmet , Aktan Haluk M. 
Published: April 2007

AbstractActive energy dissipation is proved to be very effective for abating seismic effects on buildings. The implementation of this concept in seismic design of buildings is studied by response simulations of a single storey building subjected to earthquake motion. Active energy dissipaters can be installed as part of the building lateral load bracing, and they regulate the strength and stiffness of the bracing during the building's response to the seismic events. The energy is dissipated when the bracing load exceeds the axial strength provided by the dissipater, and the bracing telescopes in and out. The design parameters of active energy dissipaters are described using the simulated response of a single storey building to ground pulse and harmonic ground excitation.The feasibility of the energy dissipater is demonstrated by the development and construction of a full‐scale prototype device called an Active Slip Bracing Device (ASBD). The device utilizes Coulomb friction. The active characteristics are implemented by a computer controlled clamping mechanism on the friction interface. The ASBD's control of the strength and stiffness is investigated.
Hydrodynamic effects in rigid tanks containing layered liquids
Authors: Veletsos A. S. , Shivakumar P. 
Published: April 2007

AbstractAs a supplement to a recently reported study, the hydrodynamic wall pressures and the associated tank forces induced by horizontal ground shaking in a rigid, vertical, circular cylindrical tank containing liquid layers of different thicknesses and mass densities are examined, and comprehensive numerical solutions are presented for two‐layered and some three‐layered systems which elucidate the underlying response mechanisms and the effects of the various parameters involved. Both the impulsive and convective actions are studied. Additionally, solutions are presented for multi‐layered systems approximating a liquid with an exponential, continuous variation in density, and the interrelationship of the solutions for the continuous system and its discretized, layered approximation is discussed.
Dynamic soil–structure interaction of coupled shear walls by boundary element method
Authors: Capuani D. , Klein R. , Antes H. , Tralli A. 
Published: April 2007

AbstractFor a class of civil engineering structures, that can be accurately represented by ‘coupled shear walls’ (CSWs), a discrete model for the analysis of the dynamic interaction with the underlying soil is proposed. The CSWs, with one or more rows of openings, rest on a rigid foundation embedded in the elastic or viscoelastic half‐space. A hierarchical finite element model based on an equivalent continuum approach is adopted for the structure. A frequency‐domain boundary element method is used to represent the half‐space. Finally, the set of equations governing the response of the coupled soil‐structure system to harmonic lateral loads acting on the structure is also given. The frequency deviation effect with respect to the fixed‐base structure and the effects of radiation and material damping in the soil are presented for different characteristics of the structure and different soil properties.
Accuracy and improvement of natural frequency prediction using component mode synthesis
Authors: Smith M. J. , Hutton S. G. 
Published: April 2007

AbstractThis paper is concerned with establishing error bounds on natural frequencies of a discrete structural model using the MacNeal–Rubin Component Mode Synthesis (CMS) method. A method is proposed whereby lower bounds to natural frequencies of a finite element model with compatible elements can be obtained after upper bounds have been calculated with the CMS technique. This method uses the idea that the inertial contribution from the neglected high frequency component modes can be expressed as a function of a residual approximation frequency. Increasing the residual approximation frequency raises the effective inertia added to the system, which in turn decreases the system natural frequencies. The technique is formulated for discrete, undamped systems, and is applied to finite element models of a beam and a container ship.It is also shown that for a particular mode of the system, estimates of the residual approximation frequency can be improved using Newton's method. Thus, a frequency determined with CMS can be steadily improved until it converges to the frequency of the model. Numerical results for the finite element models indicate that convergence is fast, even when the initial error is large.
Dynamic analysis of large 3‐D underground structures by the bem
Authors: Stamos A. A. , Beskos D. E. 
Published: April 2007

AbstractAn up to date literature survey on the dynamics of underground structures is presented briefly. The dynamic response of large three‐dimensional underground structures to external or internal dynamic forces or to seismic waves is numerically determined by the frequency domain boundary element method. This method is used to model both the structure and the soil medium, which are assumed to behave as linear elastic or viscoelastic bodies. The full‐space dynamic fundamental solution is employed in the formulation and this requires a free soil surface discretization, confined to a finite portion around the area of interest, in addition to soil—structure interface and free structural surface discretizations. The dynamic disturbances can have a harmonic or a transient time variation. The transient case is treated with the aid of numerical Laplace transforms with respect to time. Various numerical examples involving lined cavities and long lined tunnels buried in the full‐ or the half‐space subjected to harmonic or transient external forces or seismic waves are presented to illustrate the method and demonstrate its advantages.
Propagation of normal modes due to impulsive loading to 3‐D medium on a rigid basement
Authors: Touhei Terumi 
Published: April 2007

AbstractGenerally, waves in layered media include several surface wave modes showing dispersive properties. These properties often complicate the understanding of the propagation characteristics of elastic waves. In this paper, not only a method for decomposing transient elastic waves into normal modes is presented but also investigations are applied to decomposed normal modes. This method is developed by means of DWFE and the modal superposition method. In the formulation process, transfer functions describing the relationship between the amplitude of normal modes and that of force density are defined. It was found that the propagation properties of the normal modes were well explained by the dispersion curves and transfer functions. From investigations of the normal mode propagation, properties of each normal mode can be discussed.