bluuebunny/crossref_metadata_2025_split huggingface dataset:
Boundary element method with exterior collocation in two‐dimensional elastodynamic problems
Authors: Fu T. M. , Xiong J. G. , Cheung Y. K. 
Published: April 2007

AbstractIn the present paper, the boundary element method with exterior collocation was applied to two‐dimensional elastodynamic problems. The stability of the numerical solution was discussed and the collocation rule of source points outside the region being studied was investigated in the frequency domain by means of the computed error in the boundary displacement and the condition number of the coefficient matrix for two typical wave propagation problems. The achieved results are helpful to the practical application of this method to earthquake ground motion analysis.
Modal equations of linear structures with viscoelastic dampers
Authors: Inaudi José A. , Kelly James M. 
Published: April 2007

AbstractSeveral types of energy dissipation devices using viscoelastic materials have been proposed to reduce vibration in structures subjected to wind and earthquake excitations. At constant temperature and small strain levels, the mechanical behaviour of Viscoelastic (VE) materials can be described using linear operators. In general, the stiffness and damping matrices of structures using VE devices are frequency dependent; this implies that the classical second‐order differential equations for the modal co‐ordinates are not a complete model for this type of structures. In this paper, the concept of modal coupling in the frequency domain is addressed, expressions for diagonalizable frequency‐dependent stiffness and damping matrices are given, and an iterative technique for the computation of the response of viscoelastic structures is studied. Necessary and sufficient conditions for convergence of the technique are given and numerical examples are developed to illustrate the application of the method.
An application of damage mechanics for seismic analysis of concrete gravity dams
Authors: Ghrib Faouzi , Tinawi René 
Published: April 2007

AbstractThis paper discusses the local approach of fracture using damage mechanics concepts to evaluate the seismic response of concrete gravity dams. A constitutive model for plain concrete, subjected to tensile stresses, is presented. The mesh‐dependent hardening technique is adopted such that the fracture energy dissipated is not affected by the finite element mesh size. The model is implemented in conjunction with the Hilber, Hughes Taylor alpha algorithm for time marching. Koyna dam is utilized to validate the proposed formulation. The importance of initial damage prior to the advent of an earthquake is also investigated. A 60 m concrete gravity dam is therefore selected and subjected to ground motion typical of eastern North America. Five scenarios of initial damage are presented and the results confirm the importance of accounting for the initial state for the seismic safety evaluation of an existing dam.
Impulse‐momentum and resistance analysis of reinforced concrete structures
Authors: Selna Lawrence G. , Chow Hoong‐Leong 
Published: April 2007

AbstractThe viability of most analytical approaches developed to predict the inelastic response of Reinforced Concrete (RC) structures requires the load‐deformation relationship to have a positive slope. In many realistic cases the slope is not positive. When this happens, most analytical approaches consider the maximum point as the failure point or use unrealistic material laws, e.g., the assumption of a positive slope when it really is negative. Hence, there is a need to develop a new analytical approach which recognizes load‐deflection relationships which have ascending and descending branches. A method based on the impulse momentum principle and the resistance force (IMR) of an RC structure is developed. The resistance force vector {R(t)} is used in place of the stiffness approach. The material non‐linearity of RC systems can be elegantly accounted for in the {R(t)} vector. An examination of numerical properties of the IMR method shows that stability and convergence are dependent on a time step length ratio. Applications of the IMR method which predict the inelastic seismic response of RC structures are performed.
Passive seismic control of cable‐stayed bridges with damped resonant appendages
Authors: Villaverde Roberto , Martin Scott C. 
Published: April 2007

AbstractA study is conducted to investigate the effectiveness of attaching to cable‐stayed bridges resonant appendages with a relatively small mass and a high damping ratio as a means to reduce their response to earthquake excitations. The study is based on a previously developed formulation that shows that the use of these appendages may increase the inherent damping of building structures and, as a result, may reduce their response to seismic disturbances. It includes numerical and experimental tests that are conducted to assess the validity of such a formulation for the case of cable‐stayed bridges and the extent to which such appendages can reduce their seismic response. In the numerical study, an actual cable‐stayed bridge is modelled with finite elements and analysed with and without the proposed appendages under different earthquake ground motions. Appendages with damping ratios of 10, 15, 20 and 30 per cent and masses that, respectively, represent 0.67, 1.5, 2.7 and 6.0 per cent of the total mass of the bridge are considered. In the experimental test, a 3.7 m long cable‐stayed bridge and an appendage consisting of a small mass, a small spring and a small viscous damper are built and the bridge tested, without and with the appendage, on a pair of shaking tables which are set to reproduce ground acceleration records from past earthquakes. The damping ratio of the appendage in this test is 32 per cent and its mass represents about 8 per cent of the total mass of the bridge model. In the numerical test, it is found that the appendages reduce the longitudinal response of the bridge deck up to 88 per cent. Similarly, in the experimental test it is found that the appendage reduces the longitudinal bridge deck response by about 41 per cent. From these studies, it is concluded that the suggested appendages may indeed be effective in reducing the seismic response of cable‐stayed bridges as they are for building structures.
Continuous pulse control of structures with material non‐linearity
Authors: Pantelides Chris P. , Nelson Paul A. 
Published: April 2007

AbstractA control method is presented for reducing the dynamic response of structures in the inelastic material range using a control force from an active bracing system. Recent full‐scale experiments have verified the feasibility of implementing active control systems for control of seismic structures with existing technology. The proposed method of continuous pulse control uses closed‐loop feedback control as a combination of two algorithms. The first is the instantaneous optimal algorithm which was derived assuming linear material behaviour, and the second is pulse control which applies a corrective pulse when a prespecified structural displacement, velocity, or acceleration threshold is exceeded. The three criteria of displacement, velocity, and acceleration lead to three pulse control schemes. Each of the three schemes is used in conjunction with the instantaneous optimal control to yield three continuous pulse algorithms, the displacement continuous pulse, velocity continuous pulse and acceleration continuous pulse. Comparisons between the three continuous pulse algorithms and the pulse control for seismic structures in the inelastic range show that the continuous pulse algorithms use less control energy and reduce the response better than pulse control. A comparison between the velocity continuous pulse and the non‐linear optimal algorithm shows that the velocity continuous pulse uses a larger control force but is more adaptable than the non‐linear optimal algorithm, in the sense that it can reduce the response of a given structure to various probable earthquakes. The non‐linear optimal algorithm is more effective than the velocity continuous pulse for a single specific earthquake but is not as effective for other earthquakes which may occur in the life of the structure.
Dynamic interaction between 3‐D rigid surface foundations and comparison with the ATC‐3 provisions
Authors: Qian J. , Beskos D. E. 
Published: April 2007

AbstractThe dynamic behaviour of a system of three‐dimensional, massless, rigid, surface foundations of arbitrary shape perfectly bonded to the elastic half‐space is numerically studied with the frequency domain boundary element method. This method employs the dynamic Green's function for the surface of the half‐space and this results in a discretization of only the soil‐foundation interfaces. In addition, use of isoparametric quadratic quadrilateral boundary elements increases the accuracy of the method, which is confirmed by comparison with other known numerical solutions. Externally applied loads, harmonically varying with time, are considered. The through the soil coupling effect between the foundations as a function of distance and frequency is assessed through extensive parametric studies involving two and four rigid foundations being isolated or interconnected. It is found that the assertion of ATC‐3 regulations that omission of coupling effects leads to conservative results is not always correct for all frequencies.
Application of microtremor measurements to the estimation of earthquake ground motions in Kushiro city during the Kushiro‐Oki earthquake of 15 january 1993
Authors: Suzuki Takeyasu , Adachi Yoshitaka , Tanaka Minato 
Published: April 2007

AbstractMicrotremor measurements were conducted in Kushiro City, Hokkaido Island of Japan. The thickness of alluvial deposits in the central area of Kushiro City abruptly changes from 0 to 80 m. Predominant ground motion at a microtremor measuring site is represented by the spectral ratio, the ratio of Fourier amplitude spectrum of microtremor in the horizontal direction to that in the vertical direction. The peak frequency of the spectral ratio corresponds well to the predominant frequency estimated from the thickness of alluvial layer at each site. Based on a hypothesis that the spectral ratio can be regarded identical with a half of the amplification factor from diluvial bed rock to the ground surface, the strong ground motion due to the Kushiro‐oki earthquake at each site is estimated. The method of estimation is verified by the comparison of the synthesized accelerogram with the recorded one at West Port of Kushiro. The results satisfactorily explain major damages and vibrations felt in Kushiro City during the earthquake.
CQC and SRSS methods for non‐classically damped structures
Authors: Sinha R. , Igusa T. 
Published: April 2007

AbstractTwo mode combination methods are presented for structures with non‐classical (non‐proportional) damping. They are of the same level of complexity as the well‐known SRSS and CQC methods. They require only a single, real‐valued participation factor for each mode, a single correlation coefficient, and standard relative displacement response spectra. A base‐isolation study shows that the standard SRSS and CQC methods for classically damped structures give under‐conservative response predictions, and that the proposed methods give accurate predictions.
Earthquake analysis of concrete gravity dams including base sliding
Authors: Chávez Juan W. , Fenves Gregory L. 
Published: April 2007

AbstractA numerical method, the hybrid frequency‐time domain (HFTD) procedure, is used to compute the earthquake response of concrete gravity dams, including sliding along the interface between the dam base and the foundation rock. The solution procedure accounts for the non‐linear base sliding behaviour and the frequency‐dependent response of the impounded water and flexible foundation rock. A Coulomb friction model represents the force‐displacement relationship for sliding at the base interface. Using the solution procedure, an analysis of a typical dam (122 m high) shows that base sliding will occur during a moderate earthquake but the sliding displacement will be a tolerable amount when dam‐foundation rock interaction is considered.
Dynamic response of a multi‐layered poroelastic medium
Authors: Rajapakse R. K. N. D. , Senjuntichai T. 
Published: April 2007

AbstractAn exact stiffness matrix method is presented to evaluate the dynamic response of a multi‐layered poroelastic medium due to time‐harmonic loads and fluid sources applied in the interior of the layered medium. The system under consideration consists of N layers of different properties and thickness overlying a homogeneous half‐plane or a rigid base. Fourier integral transform is used with respect to the x‐co‐ordinate and the formulation is presented in the frequency domain. Fourier transforms of average displacements of the solid matrix and pore pressure at layer interfaces are considered as the basic unknowns. Exact stiffness (impedance) matrices describing the relationship between generalized displacement and force vectors of a layer of finite thickness and a half‐plane are derived explicitly in the Fourier‐frequency space by using rigorous analytical solutions for Biot's elastodynamic theory for porous media. The global stiffness matrix and the force vector of a layered system is assembled by considering the continuity of tractions and fluid flow at layer interfaces. The numerical solution of the global equation system for discrete values of Fourier transform parameter together with the application of numerical quadrature to evaluate inverse Fourier transform integrals yield the solutions for poroelastic fields. Numerical results for displacements and stresses of a few layered systems and vertical impedance of a rigid strip bonded to layered poroelastic media are presented. The advantages of the present method when compared to existing approximate stiffness methods and other methods based on the determination of layer arbitrary coefficients are discussed.
Seismic torsional response and design procedures for a class of setback frame buildings
Authors: Duan X. N. , Chandler A. M. 
Published: April 2007

AbstractThis paper presents results of an analytical study of the inelastic earthquake torsional response of a class of setback frame buildings. In the first part of the study, the modal response spectrum analysis procedure is utilized to determine the yielding strengths of structural members in an idealized but representative setback frame building model. Results are then presented for the inelastic dynamic response of this setback building model subjected to an ensemble of six earthquake ground motions. The results indicate that the modal response spectrum analysis procedure is inadequate for preventing excessive response leading to concentration of damage in vulnerable structural members, such as those in the tower near the notch and those in the base (the part of the structure below the tower) near the perimeter at the opposite side of the tower. The second part of the study develops a modified equivalent static force procedure for strength design of such setback frame buildings. Response analyses show that the proposed procedure results in improved and satisfactory inelastic performance of the selected class of setback frame buildings, having a wide range of realistic configurations.
Duration of earthquake fault motion in California
Authors: Trifunac M. D. , Novikova E. I. 
Published: April 2007

AbstractDuration of high frequency (5–25 Hz) radiation of energy from earthquake sources in California is consistent with the estimates of fault length and with dislocation velocity estimates of 2–3 km/sec. This duration can be described by an exponential function of magnitude for 2·5 < M < 7·5. It is related to the times it takes the dislocation to spread over the fault width (1/f2), and the fault length (∼ 1/f1), and to reach its ultimate amplitude (T0).The results in this paper can be used to estimate the range of amplitudes and the duration of long period pulses of strong ground motion near faults, as these long period pulses can be related to the properties of high‐frequency radiation from the source. Such pulses must be considered in the analyses of yielding structures, when the average peak acceleration of the pulse exceeds the yield resistance seismic coefficient of the structure.
Semi‐analytical techniques for the determination of the dynamic response of equipment in structures supported on coulomb friction elements
Authors: Hernried Alan G. , Lei Kai‐Ming 
Published: April 2007

AbstractTechniques for the analysis of equipment in structures supported on a Coulomb friction type support that is subjected to harmonic and earthquake ground motion are presented. The behaviour is governed by two phases—a sliding phase and a non‐sliding phase. Since the behaviour in each of the phases is linear, an analytical expression for equipment response can be obtained in terms of the roots of an appropriate characteristic polynomial. The times of phase transition are determined by an iterative scheme. The methodology is accurate, less computationally intensive, and avoids the difficulties that can be encountered with standard numerical integration techniques for highly non‐linear systems.
Earthquake simulator testing of pounding between adjacent buildings
Authors: Papadrakakis Manolis , Mouzakis Harris P. 
Published: April 2007

AbstractTwo‐storey‐building frames have been designed and built in an effort to investigate the pounding phenomenon of adjacent buildings during earthquakes. Static tests have been first performed to determine the static characteristics and the support conditions of the test structures. Sinusoidal and random acceleration signal tests have been subsequently performed to determine the dynamic characteristics of the test structures. Two series of tests were carried out using the shaking table simulator. In the first case, the dynamic response has been recorded without pounding, while in the second case, the test structures have been placed with zero‐gap separation and pounding was induced. Input energy time histories were correlated and compared with and without pounding. The experimental results were compared with analytical ones based on a formulation of the contact impact problem by the Lagrange multiplier method. Good agreement between the experimental and the analytical results was achieved.
Numerical technique for dynamic analysis of structures with friction devices
Authors: Dimova S. , Meskouris K. , Krätzig W. B. 
Published: April 2007

AbstractIn recent years a number of studies on employing friction elements for the seismic protection of buildings has demonstrated conclusively that such devices can markedly reduce earthquake‐induced vibrations. Any numerical estimate of the effectiveness of such isolation systems implies a correct solution of the pertinent nonlinear equations of motion. In direct integration algorithms, the phase transitions between adherence and sliding, or the sliding phase may be accompanied by marked high‐frequency oscillation of the relative velocity difference.The paper presents a numerical technique for overcoming these problems, thus leading to increased accuracy of the solutions of equations of motions with Coulomb damping. Since only the damping matrix and the loading vector are involved, the procedure is also computationally efficient. In order to validate the proposed numerical technique, an experimental study of a friction system has been carried out. The dynamic response of a four‐storey braced frame with friction devices is presented as an example for the practical application of the proposed numerical technique.
Seismic interaction at separation joints of an instrumented concrete bridge
Authors: Malhotra Praveen K. , Huang Moh J. , Shakal Anthony F. 
Published: April 2007

AbstractA multi‐span, curved, concrete box‐girder bridge has been extensively instrumented by the California Strong Motion Instrumentation Program (CSMIP) in cooperation with the California Department of Transportation (Caltrans). On 28 June 1992, the bridge was shaken by the magnitude 7–5 Landers and magnitude 6–6 Big Bear earthquakes in southern California. The epicentres of these earthquakes were 50 and 29 miles (81 and 46 km) from the bridge, respectively. All 34 strong‐motion sensors installed on the bridge recorded the response to these earthquakes and provided an insightful set of data. A striking aspect of the response is the presence of intermittent sharp spikes in nearly all of the acceleration records from sensors at the deck of the bridge. Among these the highest spike was 0.8g for the Landers and 1.0g for the Big Bear earthquake. The peak ground acceleration at the bridge site was only about 0.1g for both these earthquakes. With the aid of visual examination and simple analysis it is deduced that (1) the spikes were caused by forces generated at separation joints by impacts and stretching of the cable restrainers between adjacent bridge segments; (2) the forces of impacts and cable stretching are directly proportional to the size of the spikes and can be estimated by the use of a simple formula; and (3) the spikes travelled from their source to other locations on the bridge with the velocity of a compression wave propagating through concrete.
Basin effects analysis from a dense strong motion observation network
Authors: Wen Kuo‐Liang , Peng Han‐Yih , Liu Liang‐Fang , Shin Tzay‐Chyn 
Published: April 2007

AbstractThe strong ground motion observation network began to operate in the Taipei Basin area as part of the Taiwan Strong Motion Instrumentation Program (TSMIP). It is operated by the Seismological Observation Centre of the Central Weather Bureau. Forty‐three free‐field accelerometers have been installed in the Taipei Basin, and several earthquakes have been recorded by this network since its installation. Three events with magnitudes of 5–7, 5–4 and 6–2 that triggered more than ten stations are used here to study the characteristics of the basin effects on ground motions both in the time and frequency domains. From this study, it is clear that vibrations of different frequencies have different amplifications in the Taipei Basin. In fact, the frequency responses show the variation can even be up to about 7 times. The horizontal peak ground acceleration (PGA) and spectral ratio contours in the low‐frequency band are closely correlated with the geological structure in the Taipei Basin. The analysis of the response spectra also shows this correlation phenomenon and the relation between the damage from an earthquake and the basin effects.
Strong‐motion instrumentation of dams
Authors: Darbre G. R. 
Published: April 2007

AbstractStrong‐motion instrumentation schemes are developed for dams. Emphasis is put on the observation of the free‐field motions at the dam sites, of the effective motions at the abutments and of the global dam responses from which the dynamic properties of the dams are also obtained. Array configurations that are compatible with these observation goals are developed for arch, gravity and embankment dams. The associated accelerograph and array specifications are also presented.