Vibration of foundations on incompressible soils with no elastic region

Vibration of foundations on incompressible soils with no elastic region

SURFACE STRUCTURES:DYNAMIC lateral dynamic loading and lateral seismic loading of the single pile foundation are given. (from English summary) 956295 ...

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SURFACE STRUCTURES:DYNAMIC lateral dynamic loading and lateral seismic loading of the single pile foundation are given. (from English summary) 956295 Response controlled determination of parameters of base isolation system coupled in biborizontal - torsional motion (in Chinese) Lu Shunyong & Zhao Zhendong, Earthquake Engineering & Engineering Vibration, 14(3), 1994, pp 30-37. The determination of parameters, i.e. the stiffnesses k,,K,,& and the damping constants c+,,Cs of a base isolation foundation coupled in bihorizontal - torsional motion is carried out so that the bihorizontal and torsional absolute accelerations of the foundation induced by special ground motion coincide with limited values. For this purpose, an iterative improving method to determine the parameters of the base isolation foundation are presented. Calculations show that only if the initial iterative values of the parameters are chosen properly can the parameters be determined with any accuracy. How to choose these initial iterative values of the parameters is also explained. (from English summary) 956296

Stability of base isolation bearing (in Chinese) Zhang Xiong & Liu Haowu, Earthquake Engineering & Engineering Vibration, 14(3), 1994, pp 114-l 19. The isolation technique, developed in recent years for earthquake mitigation, is very effective. A simplified model for isolation bearing in which the bearing is treated as an anisotropic and homogeneous pillar is proposed. Based on the model the stability of bearing and the dependence of stability on shape factors are studied. (from English summary) 956297 Theoretical and experimental research of damper control of horizontal seismic responses of moltistorey buildings (in Chinese) Li Zhongxian 8z Xu Shouze, Earthquake Engineering & Engineering Vibration, 14(3), 1994, pp 97-104. In this paper, the damper control is applied to horizontal seismic responses of multistorey buildings, and a theoretical analysis is performed. An efficient passive control measure, the damper tube control system, is proposed, which is of simple construction, convenient for installation on buildings and has wide practical applications. (from English summary) 956298 Experimental study of earthquake response of the soft first storey structure with hydraulic mass control system (in Chinese) Liu Ji & Li Hui, Earthquake Engineering & Engineering Vibration, 14(3), 1994, pp 38-46. Based on the experimental study of earthquake response of soft first-storey structures with a Hydraulic Mass Control System (HMS), the characteristics of HMS are studied and its control mechanism is revealed. (from English summary) 956299 Tuned mass dampers for structures with closely spaced natural frequencies M. Abe & T. Igusa, Earthquake Engineering & Structural Dynamics, 24(2), 1995, pp 247-261. Analytical results are developed for vibration control of structures with one or more tuned mass dampers (TMDs). The input is a harmonic load with a range of possible frequencies. It is shown analytically that for structures with widely spaced natural frequencies, the response can be approximated accurately by the response of the well-known

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single-mode structure/TMD system. For structures with p closely spaced natural frequencies, more general analytical results are developed to describe the coupling between the motions of the p modes of the structure and the multiple TMDs. The TMD placement is shown to be always important, regardless of the spacing of the structure’s natural frequencies. The results are illustrated for both lumped-mass and continuous structures. (from Authors) 956300 Performance of multiple mass dampers under random loading A. Kareem & S. Kline, Journal of Structural Engineering AXE, 121(2), 1995, pp 348-361. The dynamic characteristics and effectiveness of multiple mass dampers (MMDs), a collection of several mass damps with distributed natural frequencies, under random loading are investigated in this paper. The random loads considered here include wind and seismic excitations. It is demonstrated that the MMD configuration is more effective in controlling the motion of the primary system. It offers the advantages of portability and east of installation (because of the reduced size of an individual damper) which makes it attractive not only for new installation, but also for temporary use during construction or for retrofitting existing structures. (Authors) 956301 Modal equations of linear structures wifb viscoelastic dampers J. A. Inaudi & J. M. Kelly, Earthquake Engineering h Structural Dynamics, 24(l), 1995, pp 145-151. Several 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 stiffnass 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 a.re developed to illustrate the application of the method. (Authors) 956302 Effhzient modal analysis for structures with soil-structure interaction Wen-Hwa Wu B H. A. Smith, Earthquake Engineering & Structural Dynamics, 24(2), 1995, pp 283-299. An efficient methodology is presented which uses modal analysis implemented in the frequency domain to obtain the structural response of a system with soil-structure interaction. The interaction effects are represented using a free-field ground motion modification factor, derived for each mode of vibration and used in the determination of structural response. (from Authors) 956303 Vibration of foundations on incompressible soils with no elastic region R. I. Borja 8z Wen-Hwa Wu, Journal of Geotechnical Engineering - ASCE, 120(9), 1994, pp 1570- 1592. The dynamic response of rigid foundations supported on a homogeneously nonlinear elastoplastic half-space is investi-

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gated in the context of nonlinear finite-element. It is shown that reflected P waves have no significant influence on the dynamic response of finite-size foundations; nor do they have any significant effect on the response of strip foundations vibrating in the rocking mode. Furthermore, it is shown that nonlinear effects can have a significant influence on the dynamic response of vibrating foundations over a wider range of excitation frequencies than originally thought. (from Authors) 956304 Dynamic interaction between 3-D rigid surface foundations and comparison with the ATC3 provisions J. Qian & D. E. Beskos, Earthquake Engineering % Structural Dynamics, 24(3), 1995, pp 419-437. The 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 discretixation of only the soil-foundation interfaces. 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. It is found that the assertion of ATG3 regulations that omission of coupling effects leads to conservative results is not always correct for all frequencies. (from Authors) 956305 Dynamic behaviour of turbine-generator-foundation systems Weiming Liu & M. Novak, Earthquake Engineering & Structural Dynamics, 24(3), 1995, pp 339-360. In this paper a comprehensive investigation on the dynamic characteristics of turbine-generator-foundation systems is performed. AU 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 turbinegenerator 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. 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. (Authors) 956306 Implications of design pbilosopbies for seismic response of steel moment frames A. Osman, A. Ghobarah & R. M. Korol, Earthquake Engineering & Structural Dynamics, 24(l), 1995, pp 127-143. During a severe earthquake, steel moment resisting frames are expected to experience significant inelastic deformation in their members and joints. This behaviour is dependent upon several design parameters such as member size, frame overstrength, member deformation capacity and the detailing of components. In this study, the influence of such aspects on the inelastic response of frames is investigated. Inelastic static and dynamic analyses were performed on four frames of differeut designs for a typical six-storey building. Recom-

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mendations for a design procedure are suggested for improving the structural performance of low-rise steel frames subjected to strong earthquake excitation. (from Authors) 956307 Seismic response of nonductile flat-plate buildings Hoong-Leong Chow & L. G. Selna, Journal of Structural Engineering - ASCE, 121(l), 1995, pp 115-123. A method for representing the seismic response of nonductile Bat-plate buildings is developed. The oooductile buildings are represented by elements with interpolated ooolinear zooes that are adapted to fit with the expcrimeotal data. The loaddeflection relation obtained from near-full-scale tests of the is nearly elastic until punching column slab co~ectioos failure occurs in the slab. Thereafter, there is a branch representing descending resistance associated with the punching failure. A flat-plate building represented with these elements evinces the progression of punching failures in the building. It is found that if the cohunns are ductile, a building ofthistypecan remain standing after a moderate seismic event, but the damage is so extensive that the building might not be repairable. (Authors) 956308 Behaviors of RX. ‘+ ’ shape columns under cyclic loading (in Chinese) Cao Wanlio, Wang Guaogyuan, Gu Jiopiog, Wei Wenxiaog & Wu Jiaoyou, Earthquake Engineering & Engineering Vibration, 14(3), 1994, pp 60-67. On the basis of experimental study on 10 ‘+ * shape columns and 3 rectangular columns under cyclic loading, the behavior of these cohunos is analysed, and some data for aseismic design of ‘+ ’ shape columns are presented. (from English summary) 956309 Efficient modeling scheme for transient analysis of inelastic RC structures S. K. Kunoath & A. M. Reinhom, Microcomputers in Civil Engineering, 10(2), 1995, pp 97-l 10. Simple modeling schemes for efEcient and reliable analysis of reinforced concrete structures in the inelastic range are presented. A reinforced concrete structure is discretixed into a series of macroelements: beam columos, shear walls, and general-purpose inelastic springs. Each element macromodel is developed from distributed flexibility concepts in which the effects of spread plasticity are implicitly included Nonlinear material behavior is specified by means of hysteretic forcedeformation models that incorporate stiffness degradation, strength deterioration, and pinching or bond-slip effects. The models are incorporated into a microcomputer program that is capable of analyzing two-dimensional or entire threedimensional wall-frame systems that can be discretixed into a series of iotercoooected parallel frames. Solution modules for nonlinear static, monotonic, quasistatic cyclic, and transient seismic loads are developed. The efficiency and reliability of the modeling are demonstrated in terms of its effectiveness in reproducing experimentally observed behavior. (Authors) 956310 Damping in low-aspect-ratio, reinforced concrete shear walls C. R. Farrar & W. E. Baker, Earthquake Engineering & Structural Dynamics, 24(3), 1995, pp 439-455. Experiments were conducted to deduce how damping 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. Also presented are the testing methods used in this study, including static cyclic tests, experimental modal analyses, and simulated seismic testing