Effect Of Earthquake Ground Motions Research Articles

Seismic Impact of LRB-based Base Isolation on Stepped Buildings

Abstract: The base isolation design strategy uncouples the superstructure from the foundation, reducing the effects of earthquake ground motion. The structure is isolated from the ground motion by a flexible base. Installing base isolators in columns, the base shear values. The structural response accelerations are usually less than the ground motion acceleration. In general, base isolation reduces storey shear and acceleration while simultaneously increasing time period, storey displacement, and storey drift, allowing rigid buildings to be more flexible by dispersing energy to the foundation. The basic seismic isolation design provides a shielding technique, allowing the structure to function without harm even after significant earthquakes. The current study explores the seismic effects of a G+6 stepped building with an LRB isolator. An isolator with a lead rubber bearing was used. E-tabs is used to conduct the base isolation study and seismic analysis. The reaction of the structure, including time period, and Lateral shear force, was observed. This paper presents time-history Analysis and performance assessment analyses on a base isolated stepped building.

Effect of Base Isolation using LRB on Stepped Building

Abstract: The base isolation design strategy uncouples the superstructure from the foundation, reducing the effects of earthquake ground motion. The structure is isolated from the ground motion by a flexible base. Installing base isolators in columns. The structural response accelerations are usually less than the ground motion acceleration. In general, base isolation reduces storey shear and acceleration while simultaneously increasing time period, and storey drift, allowing rigid buildings to be more flexible by dispersing energy to the foundation. The basic seismic isolation design provides a shielding technique, allowing the structure to function without harm even after significant earthquakes. The current study explores the seismic effects of a G+6 stepped building with an LRB isolator. An isolator with a lead rubber bearing was used. E-tabs is used to conduct the base isolation study and seismic analysis. The reaction of the structure, lateral shear force, time period, and base shear, was observed. This paper presents time-history analysis and performance assessment analyses on a base isolated stepped building using Bhuj Earthquake ground motion data.

Fragility curves for light damage of clay masonry walls subjected to seismic vibrations

The probability of light damage to unprepared, unreinforced masonry structures exposed to induced seismicity due to gas extraction in the north of the Netherlands is still under investigation. Repeated light seismic excitations caused by frequent, light and nearby earthquakes have been linked to economical losses and societal unrest in particular, with extensive damage claims. Moreover, the damaging potential of the seismic events has been related to the condition of the structure, especially if damage corresponding to settlement causes is already present. A comprehensive testing campaign oriented towards the initiation and progression of light damage of replicated clay brick masonry has been conducted at Delft University of Technology. Based on these tests, calibrated finite element models have been produced. This article uses the calibrated non-linear time-history models to simulate the effect of earthquake ground motion on a variety of initial conditions, wall geometry, material properties, and number, type and intensity of earthquakes. The results are then used to regress a relationship between damage and these parameters. This is subsequently employed to run a MonteCarlo simulation and produce fragility curves where the probability of exceeding specific damage values for various initial damage levels is presented against the seismic hazard. The vulnerability or fragility curves show that visible damage, with cracks wider than 0.1 mm, appears, with a 10% exceedance probability, at 13 mm/s of peak ground velocity; but, if the masonry had already undergone some light, yet imperceptible damage, a PGV of 6 mm/s was sufficient to aggravate it into visible cracks. To attain a 1% probability of exceeding light damage however, for which the masonry would need more invasive repair, it was observed that PGVs larger than 15 mm/s were required. These fragility curves were finally compared to graphs from other authors and found to capture well the variability in the range assigned to light damage.

A New Model for Vertical-to-Horizontal Response Spectral Ratios for Central and Eastern North America

ABSTRACT It is a well-known fact that critical structures are required to be designed for the vertical effects of earthquake ground motions as well as the horizontal effects. We developed a new model for the spectral ratio of vertical-to-horizontal components of earthquakes (V/H ratio) for central and eastern North America (CENA). The proposed V/H ratio model has the advantage of considering the earthquake magnitude, source-to-site distance, and the shear-wave velocity of soil deposits in the upper 30 m of the site for peak ground acceleration and a wide range of spectral periods (0.01–10.0 s). The model evaluation is based on a comprehensive set of regression analysis of the compiled Next Generation Attenuation-East database of the available CENA recordings with M ≥ 3.4 and Rrup<1000 km. The median value of the geometric mean of the orthogonal horizontal motions rotated through all possible nonredundant rotation angles, known as the RotD50, is used along with the vertical component to perform regression using the nonlinear mixed-effect regression. We excluded the earthquakes and recording stations in the Gulf Coast region due to their different ground motion attenuation (Dreiling et al., 2014). To compute V/H ratios for the Gulf Coast region, we refer the readers to the study of Haji-Soltani et al. (2017). Moreover, we excluded the National Earthquake Hazard Reduction Program site class E sites from consideration because of their complex site response characteristics and their potential for nonlinear site effects. The predicted V/H ratios from the proposed model are compared with recently published V/H ratio models. We suggest our model to be used for developing the vertical response spectra for CENA sites.

Effects of Soil Amplification on Ground Motion Response Spectra with High-Frequency Contents at Generic Soil Sites for Nuclear Facilities in Korea

Ground motion response spectra (GMRS) at rock/soil sites in regions where earthquake ground motions have dominant contents at high frequencies of 10 Hz or more are evaluated and the effects of soil amplification on the GMRS are studied. The seismic hazard levels at the soil sites are estimated from soil amplification functions and hazard curves for rock outcrop motions. The soil amplification functions are obtained using modified earthquake ground motions which match the uniform hazard response spectra (UHRS) for rock outcrop motions with various mean annual frequencies of exceedance in order to consider the effects of earthquake ground motions consistently in a site response analysis. UHRS at soil sites are determined from the calculated seismic hazard curves. Subsequently, design factors, which will be applied to UHRS, and the corresponding GMRS are evaluated such that the seismic risk for the structures, systems, and components of nuclear facilities would be equal to a target seismic risk. It can be observed from example applications that the UHRS and GMRS at soil sites have peaks at the natural frequencies of the soil, where the soil responses are amplified. Amplification at soil sites depends on the frequency contents of rock outcrop motions.

An updated consecutive modal pushover (UCMP) procedure for estimating the ductility level earthquake design demands of jacket offshore platforms

According to API- RP-2EQ/ISO 19901-2:2004(E), the static pushover method is allowed to be utilized for the abnormal level earthquake (ALE) design check of jacket type offshore platforms (JTOP) under the effects of earthquake ground motions. Therefore, the pushover method can be employed to check the ductility adequacy of JTOP structures under ALE (the ductility level earthquake in the previous versions of the API). In this paper, two modifications to the consecutive modal pushover (CMP) procedure are proposed in order to take into account the progressive changes in the dynamic characteristics of JTOP structures as well as the effects of higher modes on the seismic demands of JTOPs. The first modified procedure is called the updated consecutive modal procedure (UCMP), in which the load pattern for the second mode is updated at the beginning of the second stage of the CMP procedure based on the inelastic state of the structure at the end of the first stage. The UCMP procedure conceptually introduces a great advantage over the current enhanced pushover procedures as it considers the change of the dynamic characteristics in the applied load pattern, while it maintains the non-adaptive nature of the CMP method. The second modified procedure, that is called the adaptive-alfa consecutive modal pushover (ACMP) procedure, is proposed to define the displacement increments for the two-stage UCMP procedure based on the instantaneous effective modal participating mass ratio (α). The proposed methods are applied to two case study JTOP models, and the predicted seismic demands are compared with those from the benchmark nonlinear time history (NTH) analyses. A suite of earthquake records, selected based on the ductility level response spectrum, is used for the NTH analysis. The results show that notable improvements are achieved by the UCMP method in estimating the seismic demands of the lower braced stories of the jacket, where the effects of higher modes are expected to be more significant. Therefore, it is recommended to utilize the UCMP method when a trade-off between the accuracy of the pushover analysis and its simplicity is of interest. Moreover, the ACMP method produces an excellent prediction of the seismic demands at the lower stories of the jacket, and provides satisfactory estimations at the foundation part. Consequently, this method is proposed as a rigorous one to be utilized in the design phase of the fixed offshore platforms for the ductility level earthquake check.

Quantification of the Influence of Deep Basin Effects on Structural Collapse Using SCEC CyberShake Earthquake Ground Motion Simulations

This paper examines the effects of earthquake ground motions in deep sedimentary basins on structural collapse risk using physics-based earthquake simulations of the Los Angeles basin developed through the Southern California Earthquake Center's CyberShake project. Distinctive waveform characteristics of deep basin seismograms are used to classify the ground motions into several archetype groups, and the damaging influence of the basin effects are evaluated by comparing nonlinear structural responses under spectrum and significant duration equivalent basin and nonbasin ground motions. The deep basin ground motions are observed to have longer period-dependent durations and larger sustained spectral intensities than nonbasin motions for vibration periods longer than about 1.5 s, which can increase structural collapse risk by up to 20% in ground motions with otherwise comparable peak spectral accelerations and significant durations. Two new metrics are proposed to quantify period-dependent duration effects that are not otherwise captured by conventional ground motion intensity measures. The proposed sustained amplitude response spectra and significant duration spectra show promise for characterizing the damaging effects of long duration features of basin ground motions on buildings and other structures.

Seismic Analysis of a Ten-Storey Reinforced Concrete Building in Jazan Area, KSA

Jazan area is located in the most active seismic zone region of the Kingdom of Saudi Arabia where there is a complicated geological structures and tectonics. This project reviews the seismic activities occurred in Jazan area together with reviewing the Saudi Building (Seismic) Code (SBC-301-2007) [1]. A multi-story reinforced concrete building, in Jazan city, was seismically analyzed using the Equivalent Lateral Force Procedure with the aid of STAAD PRO software. The building, which was Ordinary Reinforced Concrete Moment Resisting Frame (ORCMRF), was analyzed in compliance with the provisions of (SBC-301-2007) [1]. The most important parameters governing the analysis of this frame were dead load, live load and seismic loads. Seismic loads were computed as pairs of accelerations versus times. The damping ratio was taken as 0.05 (5% of the critical damping). The ground accelerations versus time periods were calculated using SBC-301-2007 together with parameters necessary to be used as input data for the program to calculate the seismic parameters, i.e., reactions, displacements, base shear, bending moments, shearing forces, drifts. The obtained results show effects of earthquake ground motions on building studied herein are so greater for the higher increases of the values of outputs resulting from seismic loads comparing to that due to static load only. Finally, the results obtained, clearly, show the importance of taking the Saudi seismic code provisions into account when analyzing and designing multi-story buildings in Jazan area.

Effects of earthquake ground motion on tracking characteristics of new Global Navigation Satellite System receivers

AbstractWe use a shake table capable of large (7 G) three‐dimensional accelerations with large payloads to simulate ground motion reconstructed from acceleration data collected during the February 2010 Mw = 8.8 Maule, Chile, earthquake. The tracking performance of five modern geodetic GNSS receiver and antenna combinations was investigated while undergoing simulated seismic shaking at three two levels of amplification. Individual system performance was characterized by the number of tracked GNSS observations. The L1 and L2 GPS signal tracking was significantly impacted for the majority of the receiver models during simulations with maximum accelerations of 4 G, and the tracking performance for all of the tested receiver types was significantly impaired during the 7 G simulations. Results show improved tracking when only the antenna was shaken suggesting that vibration‐induced oscillator phase noise may contribute significantly to tracking degradation during shaking.

Building earthquake resilience in sustainable cities in terms of input energy

Abstract Input energy to building structures during earthquakes is an important index to measure the influence of earthquake ground motions on building structures. Such input energy can be defined after the structural system is specified and the input mechanism is described clearly. The energy input to structures consists mainly of the energy dissipated by hysteretic deformation and that by viscous damping. The excessive dependence on the former mechanism leads to unrepairable and unpreferable states of structures after earthquakes which should be avoided from the viewpoint of sustainability of building structures and cities. In this sense, the measure of energy is appropriate from the viewpoint of total management of buildings in a sustainable city. Then the upper bound of earthquake input energy is derived and discussed under uncertain conditions on input ground motions. It is shown that the earthquake energy input rate is another key parameter for measuring the instantaneous effect of earthquake ground motions on structural responses. A historical review is also made on the development of treatment of earthquake input energy into buildings and on its role into greater building earthquake resilience in sustainable cities.

Centrifuge modelling for evaluation of seismic behaviour of stone masonry structure

Many surviving ancient monuments are freestanding stone masonry structures, which appear to be vulnerable to horizontal dynamic loads such as earthquakes. However, such structures have stood for thousands of years despite numerous historic earthquakes. This study proposes a scaled-down dynamic centrifuge modelling test to study how these masonry structures resist seismic loading. The test is proposed for seismic risk assessments to evaluate risk of damage from a future seismic event. The seismic behaviour of a 3-storey, freestanding stone block structure has been modelled and tested within a centrifuge. Models were made at 3 different scales and dynamic tests were conducted using different centrifugal acceleration fields so that the behaviours could be transformed to an equivalent full-scale prototype and compared. Data from 2 earthquakes and a sweeping signal were used to simulate the effects of earthquake ground motion within the centrifuge. The acceleration and frequency responses at each storey height of the model were recorded in different centrifugal acceleration fields. Similar behaviours appeared when the results of the small-scale models were transformed to a full-size prototype scale. This confirms that the seismic behaviour of stone masonry structures can be predicted using scaled-down models.

Seismic response analysis of a double-deck long-span cable-stayed bridge under multi-support excitations

In this article, the effect of earthquake ground motions, especially spatially varying motion, on the seismic response of a long-span double-deck cable-stayed bridge is investigated. Static and dynamic response analyses, with the focus on internal forces on web members, are carried out on the Shanghai Minpu Bridge which is the longest long-span double-deck cable-stayed highway bridge. Firstly, a program for the generation of multi-ground motions has been developed, based on the multivariate stochastic processes of the weighted amplitude wave superposition method in FORTRAN. Secondly, a refined finite element model composed of beam and shell elements and a simplified model using equivalent beam elements to model girders of the bridge are established in ABAQUS. Geometrical nonlinear static analysis is performed to get initial equilibrium configuration of the bridge for both the above models. Modal analysis is carried out on the initial equilibrium configuration and the natures of mode shapes for the refined model are discussed in detail. The dynamic response analyses under two groups of uniform seismic excitation indicate that the two models result in approximately identical results. Thirdly, the effect of nonlinear viscous dampers, located between the tower and the girder, on movement due to seismic excitation is investigated on the simplified model under uniform excitation. Results show that the dampers magnify the shear force and moment on lower tower columns in the longitudinal direction, but have relatively small effect on the upper tower columns. The shear force and moment of the tower base increase with the damping coefficient in a certain range. Finally, the characteristics of internal force for towers, subsidiary piers, and web members (vertical and oblique web members and side oblique chords) under multipoint excitation are examined. It is concluded that the abrupt changes on the shear envelope curves at the intersection of the tower column and the lower transverse beam are aroused due to the eight nonlinear fluid viscous dampers. The lateral moment of the subsidiary piers increases with the distance from the tower to subsidiary piers. The maximum axial forces of web members of side-span vary acutely, especially those of the vertical and oblique members close to the piers. For side oblique chords, the maximum axial force is uniformly distributed with the exception of members at the piers and the mid-span sections. Therefore, attention should be paid to the fluctuation forces of cables in seismic analysis of long-span cable-stayed bridges, since the uplift of girder ends may cause severe damage to bridges.

Effect of earthquake ground motions on soil liquefaction

During the 2011 off the Pacific Coast of Tohoku Earthquake, which was the largest earthquake in Japanese history, the soil liquefaction phenomenon was observed over a wide area along the Pacific Coast in Tohoku and in Kanto, including the Tokyo Bay area. Extensive damage was caused by the effect of soil liquefaction to residential lands and houses, as well as to infrastructures, such as roads, rivers, ports, and water supply/sewage systems. Since the 2011 off the Pacific Coast of Tohoku Earthquake occurred in a mega-size fault zone, with an area of 500km×200km, the duration of the strong shaking was extremely long compared to that in the data recorded for past earthquakes. Clarifying the effect of the characteristics of the ground motion on the soil liquefaction mechanism is one of the essential studies to be conducted, and effective countermeasures for the damaged structures need to be found.This paper presents the strong motion observation data obtained on the liquefied and the non-liquefied grounds and raises preliminary discussions on the mechanism of soil liquefaction based on this data. The effect of the duration and the number of cyclic loadings on the progress of the soil liquefaction phenomenon is also compared with that found in past strong motion data.

Simulation of Seismic-Wave Propagation through Geometrically Complex Basins: The Dead Sea Basin

Abstract The Dead Sea Transform (DST) is the source for some of the largest earthquakes in the eastern Mediterranean. The seismic hazard presented by the DST threatens the Israeli, Palestinian, and Jordanian populations alike. Several deep and structurally complex sedimentary basins are associated with the DST. These basins are up to 10 km deep and typically bounded by active fault zones. The low seismicity of the DST, the sparse seismic network, and limited coverage of sedimentary basins result in a critical knowledge gap. Therefore, it is necessary to complement the limited instrumental data with synthetic data based on computational modeling, in order to study the effects of earthquake ground motion in these sedimentary basins. In this research we performed a 2D ground‐motion analysis in the Dead Sea Basin (DSB) using a finite‐difference code. Cross sections transecting the DSB were compiled for wave propagation simulations. Results indicate a complex pattern of ground‐motion amplification affected by the geometric features in the basin. To distinguish between the individual contributions of each geometrical feature in the basin, we developed a semiquantitative decomposition approach. This approach enabled us to interpret the DSB results as follows: (1) Ground‐motion amplification as a result of resonance occurs basin‐wide due to a high impedance contrast at the base of the uppermost layer; (2) Steep faults generate a strong edge‐effect that further amplifies ground motions; (3) Sub‐basins cause geometrical focusing that may significantly amplify ground motions; and (4) Salt diapirs diverge seismic energy and cause a decrease in ground‐motion amplitude.

Soil–structure interaction analysis of cable-stayed bridges for spatially varying ground motion components

In this study, it is intended to determine the effects of soil–structure interaction (SSI) and spatially varying ground motion on the dynamic characteristics of cable-stayed bridges. For this purpose, ground motion time histories are simulated for spatially varying ground motions, depending on its components of incoherence, wave-passage and site-response effects. The substructure method, which partitions the total soil–structure system into the structural system and the soil system, is used to treat the soil–structure interaction problem. To emphasize the relative importance of the spatial variability effects of earthquake ground motion, bridge responses are determined for the fixed base bridge model, which neglects the soil–structure interaction (no SSI) and for the bridge model including the soil–structure interaction (SSI). This parametric study concerning the relative importance of the soil–structure interaction and spatially varying ground motion shows that these effects should be considered in the dynamic analyses of cable-stayed bridges.

Simulation of floor response spectra in shake table experiments

Among several different experimental techniques, used to test the response of structures and to verify their seismic performance, the shake table testing allows to reproduce the conditions of true effects of earthquake ground motions in order to challenge complex model structures and systems. However, the reproduction of dynamic signals, due to the dynamics of the shake table and of the specimen, is usually imperfect even though closed-loop control in a shake table system is used to reduce these errors and obtain the best fidelity reproduction. Furthermore, because of the dynamic amplifications in the specimen, the signal recorded at desired locations could be completely different from the expected effect of shake table motion. This paper focuses on the development of practical shake table simulations using additional ‘open loop’ feedforward compensation in form of inverse transfer functions (i.e. the ratio of the output structural response to an input base motion in the frequency domain) in order to obtain an acceptable reproduction of desired acceleration histories at specific locations in the specimen. As the first step, a well-known global feedforward procedure is reformulated for the compensation of the table motion distortions due to the servo-hydraulic system. Subsequently, the same concept is extended to the table-structure system to adjust the shake table input in order to achieve a desired response spectrum at any floor of the specimen. Implementations show how such a method can be used in any experimental facility. Copyright © 2010 John Wiley & Sons, Ltd.

Development of Neural Network Based Hysteretic Models for Steel Beam-Column Connections Through Self-Learning Simulation

Beam-column connections are zones of highly complex actions and deformations interaction that often lead to failure under the effect of earthquake ground motion. Modeling of the beam-column connections is important both in understanding the behavior and in design. In this article, a framework for developing a neural network (NN) based steel beam-column connection model through structural testing is proposed. Neural network based inelastic hysteretic model for beam-column connections is combined with a new component based model under self-learning simulation framework. Self-learning simulation has the unique advantage in that it can use structural response to extract material models. Self-learning simulation is based on auto-progressive algorithm that employs the principles of equilibrium and compatibility, and the self-organizing nature of artificial neural network material models. The component based model is an assemblage of rigid body elements and spring elements which represent smeared constitutive behaviors of components; either nonlinear elastic or nonlinear inelastic behavior of components. The component based model is verified by a 3-D finite element analysis. The proposed methodology is illustrated through a self-learning simulation for a welded steel beam-column connection. In addition to presenting the first application of self-learning simulation to steel beam-column connections, a framework is outlined for applying the proposed methodology to other types of connections.

Identification of modal parameters of non‐classically damped linear structures under multi‐component earthquake loading

AbstractA method for parametric system identification of classically damped linear system in frequency domain is adopted and extended for non‐classically damped linear systems subjected up to six components of earthquake ground motions. This method is able to work in multi‐input/multi‐output (MIMO) case. The response of a two‐degree‐of‐freedom model with non‐classical damping, excited by one‐component earthquake ground motion, is simulated and used to verify the proposed system identification method in the single‐input/multi‐output case. Also, the records of a 10 storey real building during the Northridge earthquake is used to verify the proposed system identification method in the MIMO case. In this case, at first, a single‐input/multi‐output assumption is considered for the system and modal parameters are identified, then other components of earthquake ground motions are added, respectively, and the modal parameters are identified again. This procedure is repeated until all four components of earthquake ground motions which are measured at the base level of the building are included in the identification process. The results of identification of real building show that consideration of non‐classical damping and inclusion of the multi‐components effect of earthquake ground motions can improve the least‐squares match between the finite Fourier transforms of recorded and calculated acceleration responses. Copyright © 2006 John Wiley & Sons, Ltd.

Experimental study of the semi‐active control of building structures using the shaking table

AbstractA magnetorheological (MR) damper has been manufactured and tested and a non‐linear model is discussed. The parameters for the model are identified from an identification set of experimental data; these parameters are then used to reconstruct the force vs. displacement and the force vs. velocity hysteresis cycles of the MR damper for the hysteretic model. Then experiments are conducted on a three‐storey frame model using impact excitation, which identifies dynamic parameters of the model equipped with and without the MR damper. Natural frequencies, damping ratios and mode shapes, as well as structural properties, such as the mass, stiffness and damping matrices, are obtained. A semi‐active control method such as a variable structure controller is studied. Based on the ‘reaching law’ method, a feedback controller is presented. In order to evaluate the efficiency of the control system and the effect of earthquake ground motions, both numerical analysis and shaking table tests of the model, with and without the MR damper, have been carried out under three different ground motions: El Centro 1940, Taft 1952, and Ninghe 1976 (Tangshan Earthquake in Chinese). It is found from both the numerical analysis and the shaking table tests that the maximum accelerations and relative displacements for all floors are significantly reduced with the MR damper. A reasonable agreement between the results obtained from the numerical analysis and those from the shaking table tests is also observed. On the other hand, tests conducted at different earthquake excitations and various excitation levels demonstrate the ability of the MR damper to surpass the performance of a comparable passive system in a variety of situations. Copyright © 2003 John Wiley & Sons, Ltd.

Shake table testing of a base isolated model

The seismic characteristics of a five-storey benchmark model isolated with rubber bearings have been studied using a shake table. Experimental modal analyses using impact excitation, a HP-VXI data acquisition system and LMS CADA-X software were conducted to identify dynamic parameters of the benchmark model with and without rubber bearings. The natural frequencies, damping ratios and mode shapes as well as structural properties, namely, the mass, stiffness and damping matrices, were obtained. In order to evaluate the efficiency of the base isolation system and the effect of earthquake ground motions, both numerical analysis and shake table testing of the model with and without the isolation system were carried out under four different strong ground motions, namely Northridge 1994, Hachinohe 1968, El-Centro 1940, and Kobe 1995 earthquakes. It was found, from both numerical analysis and shake table testing, that the isolation effectiveness offered by the rubber bearings to earthquake inputs is strongly dependent on the type of earthquake motion. The maximum acceleration for all floors was significantly reduced with the addition of a rubber isolation system, regardless of ground motion input. However, the relative displacements of the rubber-isolated model are strongly dependent on the type of earthquake excitation. The seismic responses of the isolated model were improved when subjected to the Northridge 1994, Hachinohe 1968, and Kobe 1995 earthquakes, with best results obtained when Hachinohe earthquake was applied. The maximum accelerations, displacements, inter-storey drifts and base shear force as well as over-turning moment for the base-isolated model were significantly reduced, and the vibration amplitude of the accelerations, and inter-storey drifts decreased much more quickly with time than those without rubber bearings. The present base isolation system was not effective in combating the El-Centro earthquake. A reasonable agreement between results obtained from numerical analysis and those of shake table testing was also observed.