Seismic isolation of buildings with sliding concave foundation (SCF)   总被引：1，自引：0，他引：1  

M. Hamidi  M. H. El Naggar  A. Vafai  G. Ahmadi 《地震工程与结构动力学》2003,32(1):15-29

In this paper, a new base isolation system, namely the sliding concave foundation (SCF), is introduced and the behaviour of the buildings using such a system is theoretically investigated. A building supported on the new system behaves like a compound pendulum during seismic excitation. The pendulum behaviour accompanied by the large radius of foundation curvature shifts the fundamental period of the system to a high value (e.g. more than 8sec), in a frequency range where none of the previously recorded earthquakes had considerable energy. This results in a large decrease in the structural responses. Since small friction forces are essential on the contact surfaces, PTFE sheets can be used as sliding surfaces. Although the pure frictional sliding systems have the same efficiency as the SCF, in reducing the responses of the superstructure, the main advantage of the new system is a significant decrease in sliding displacement. The performance of the SCF subjected to a number of harmonic and non‐harmonic base excitations is studied and its ability to reduce the structural responses is examined. Some numerical examples are solved for a single‐degree‐of‐freedom (SDOF) structure and the responses are compared with the responses of the same SDOF structure on a fixed base or a pure frictional sliding support system. The comparisons confirm the effectiveness of the new system. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

A comparative study of performances of various base isolation systems,part II: Sensitivity analysis     

Lin Su  Goodarz Ahmadi  Iradj G. Tadjbakhsh 《地震工程与结构动力学》1990,19(1):21-33

A series of numerical experiments on the performance of different base isolation systems for a non-uniform shear beam structure is carried out. Several base isolation systems are considered and the peak relative displacements and the maximum absolute accelerations of the base-isolated structure and its base raft under a variety of conditions are evaluated. Several sensitivity analyses for variations in properties of the base isolator and the structure are carried out. A number of different earthquake excitations are also used in the study. The results show that performances of the base isolation systems are not sensitive to small variations in their natural period, damping or friction coefficient. The presence of a frictional element in the isolators reduces their sensitivity to severe variations in frequency content and amplitude of the ground acceleration. In particular, the resilient-friction base isolators with or without sliding upper plate perform reasonably well under a variety of loading conditions. The rubber bearing type, however, leads to the lowest peak transmitted accelerations for moderate intensity earthquakes.  相似文献   

Stiffness identification of two- and three-dimensional frames     

Morteza A. M. Torkamani  Ahmad K. Ahmadi 《地震工程与结构动力学》1988,16(8):1157-1176

Four widely used structural system identification methods are presented. Based on Bayesian estimation theory, two new formulae and their derivations are shown. Time domain responses of two frames when subjected to the ground motion of the El Centro earthquake are computed then transformed to the frequency domain. Frequencies and mode shapes of frames are extracted from Fourier spectra. Using these frequencies and mode shapes, a parametric study is conducted, and the system identification methods are compared and discussed. The importance of a prior analytical model on the rate of convergence of the revised parameters is investigated. Recommendations are given regarding the feasibility of each method for more accurate estimation. A model suitable for parameter identification of three-dimensional frames is presented. This model, with different identification methods, is used to estimate the parameters of a two-storey frame.  相似文献   

A comparative study of performances of various base isolation systems,part I: Shear beam structures     

Lin Su  Goodarz Ahmadi  Iradj G. Tadjbakhsh 《地震工程与结构动力学》1989,18(1):11-32

A comparative study of performances of different base isolators for shear beam type structures is carried out. Several leading base isolation systems, including the laminated rubber bearing with and without lead plug, the resilient-friction base isolator with and without sliding upper plate, and the EDF system are considered. Displacement and acceleration response spectra for a shear beam structure subject to the accelerograms of the N00W component of El Centro 1940 and the N90W component of Mexico City 1985 earthquakes and their magnified forms are evaluated. A series of parametric studies is carried out and advantages and disadvantages of various base isolation systems are identified. Comparisons of the results with the response spectra of a fixed-base structure show that the base isolation systems are, in general, highly effective in reducing the peak acceleration transmitted to the superstructure. Thus, the deflections and stresses generated in a base-isolated structure are significantly lower than those of a fixed-base one. Furthermore, the results of the study also show that the friction-type base isolators are less sensitive to severe variations in frequency content and amplitude of the ground acceleration.  相似文献   

Response of base-isolated buildings to random excitations described by the Clough-Penzien spectral model     

B. C. Lin  I. G. Tadjbakhsh  A. S. Papageorgiou  G. Ahmadi 《地震工程与结构动力学》1989,18(1):49-62

The stationary response of base-isolated buildings subjected to earthquake excitation is studied. The frequency content of earthquake input is described by the Clough-Penzien spectral model. The response parameters of interest are (1) the root-mean-square (RMS) displacement σ_x of the basement relative to the foundation (i.e. shear deformation of the isolation system) and (2) the ratio (σ_a/σ_a0) of the RMS value of the absolute acceleration at the roof of the isolated structure over the corresponding value when the isolation system is locked. The variation of these response parameters with the effective frequency f₀ of the base-isolated structure is investigated. As input, earthquakes with moment magnitudes M = 7-3 and M = 6-0 are considered. The acceleration spectra corresponding to these two earthquake sizes have pronouncedly different frequency content over the frequency range 0–1-1–0 Hz which is of primary importance for base-isolated structures. An important conclusion that comes from these analyses is that confidence in the effectiveness of a base-isolated system should be based primarily on its capacity to absorb/dissipate energy and less on its influence in shifting the fundamental period of the structure out of the range of dominant earthquake energy.  相似文献   

Performance of a high damping rubber bearing base isolation system for a shear beam structure     

Yu Chen  Goodarz Ahmadi 《地震工程与结构动力学》1994,23(7):729-744

Performance of High Damping Laminated Rubber Bearing (HD-LRB) base isolation system in protecting the structure and the structural content is studied. A non-uniform shear beam structural model is considered, and the generalized non-stationary Kanai–Tajimi model for the El Centro 1940 earthquake is used as excitation. The technique of equivalent linearization is utilized and the mean-square response statistics of secondary systems and primary structure are evaluated. Statistically estimated peak responses of the secondary system and the primary structure are evaluated and the results are compared with the response spectra for the actual earthquake accelerogram. Comparison of the stochastic responses for base-isolated structures with the HD-LRB and the linear Laminated Rubber Bearing (LRB) and the fixed-base structure is also carried out. It is shown that the HD-LRB system significantly reduces the mean-square, as well as the peak acceleration and deflection responses without generating large base displacements. Furthermore, the non-linear behaviour of the HD-LRB somewhat improves the performance of the bearing in reducing the peak responses of the secondary system and the primary structure when compared with the linear LRB model.  相似文献   

Petrology and geochemistry of the granitoid complex of Boroujerd, Sanandaj-Sirjan Zone, Western Iran     

A. Ahmadi Khalaji  D. Esmaeily  M.V. Valizadeh  H. Rahimpour-Bonab 《Journal of Asian Earth Sciences》2007,29(5-6):859-877

The Middle Jurassic Boroujerd Granitoid Complex of the Sanandaj-Sirjan Zone (with a U–Pb zircon age of 169–172 Ma) was emplaced in an active continental margin setting. This complex consists of three main units: an elongate NW–SE extending granodioritic unit (SiO₂ = 58–71 wt%), which is widespread throughout the area, a quartz-dioritic unit (SiO₂ = 52–63 wt%), exposed as small stocks within the granodioritic body, and a monzogranitic unit (SiO₂ = 70–75 wt%), widely scattered as separate small outcrops through the southern part of the area. A series of NW trending aplites and pegmatites are present in the granodioritic unit and its aureole.Geochemically this complex is metaluminous to slightly peraluminous, typical of I-type granites. It belongs to high-K calc-alkaline series and displays the geochemical characteristics typical of volcanic arc granites related to an active continental margin (e.g. significant Nb, Ti, P and Sr depletion). Isotopic data (Sr_i = 0.7062–0.7074 and εNd_t = −3.02 to −3.62) are consistent with a crustal protolith. In addition, fractional crystallization may have played an important role in the formation of the whole spectrum of the granitoid types that occur in the Boroujerd area.  相似文献   

On multicomponent gas diffusion and coupling concepts for porous media and free flow: a benchmark study     

Ahmadi  Navid  Heck  Katharina  Rolle  Massimo  Helmig  Rainer  Mosthaf  Klaus 《Computational Geosciences》2021,25(5):1493-1507

Computational Geosciences - Multicomponent gas transport in porous media and at the interface between porous media and free flow occurs in a wide range of technical and environmental systems....  相似文献   

A possible continuum theory for densification and liquefaction of saturated sand     

Goodarz Ahmadi 《Mathematical Geology》1981,13(1):37-52

A previously developed continuum theory of granular media is applied to the problems of densification and liquefaction of saturated sand. An expression for the free energy of saturated sand is developed. The process of densification of sand subjected to cyclic shear stress is studied and several expressions for an increase of the solid volume fraction are obtained and discussed. The problem of the initial liquefaction of saturated sand samples under cyclic shear stress is then considered and several criteria relating the shear stress amplitude, over-burden pressure, time to liquefaction, and physical properties of the sand sample are established. Some semiempirical relations for field applications are also presented.  相似文献   

Mental health preparedness for natural disasters in Iran     

Naghmeh Sadeghi  Mohammad H. Ahmadi 《Natural Hazards》2008,44(2):243-252

Appropriate emergency preparedness and response rely on social, economical, cultural, and political infrastructures, which vary widely according to the level of the development of each country. Mental health damages are among the consequences of absence of such infrastructure, which have not been studied comprehensively till to date. In most countries, planning for natural disasters and earthquakes has been mainly focused on physical and economical impacts; however, lessons learnt from recent earthquakes in Iran and other countries show that psychological impacts need to be considered more seriously. The first responder to an emergency is really the affected community, which consequently should be mentally prepared by appropriate training programs. These should include simple psychosocial interventions developed for people with average level of education in a way to be easily understandable and practicable. After the Bam earthquake, local community volunteers have been selected and trained to provide post-disaster mental health services.  相似文献