• Earthquakes and Structures
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• v.4 no.3
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• pp.285-297
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• 2013

The effect of soil structure interaction (SSI) on seismic response of a multi-degree-of-freedom structure isolated with a friction pendulum system (FPS) is studied. In the analysis, the soil is considered as an elastic continuum and is modeled using the finite element method. The effect of SSI on response of the structure is evaluated for twenty far-field and twenty near-fault earthquake ground motions. The effect of friction coefficient of sliding material of FPS on SSI is also studied. The results of the study show that the seismic response of the structure increases for majority of the earthquake ground motions due to SSI. The sliding displacement and base shear are underestimated if SSI effects are ignored in the seismic analysis of structures isolated with FPS.

• Smart Structures and Systems
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• v.20 no.1
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• pp.23-33
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• 2017

Variable Curvature Friction Pendulum (VCFP) bearing is one of the alternatives to control excessive induced responses of isolated structures subjected to near-fault ground motions. The curvature of sliding surface in this isolator is varying with displacement and its function is non-spherical. Selecting the most appropriate function for the sliding surface depends on the design objectives and ground motion characteristics. To date, few polynomial functions have been experimentally tested for VCFP however it needs comprehensive parametric study to find out which one provides the most effective behavior. Herein, seismic performance of the isolated structure mounted on VCFP is investigated with two different polynomial functions of the sliding surface (Order 4 and 6). By variation of the constants in these functions through changing design parameters, 120 cases of isolators are evaluated and the most proper function is explored to minimize floor acceleration and/or isolator displacement under different hazard levels. Beside representing the desire sliding surface with adaptive behavior, it was shown that the polynomial function with order 6 has least possible floor acceleration under seven near-field ground motions in different levels.

• Journal of the Earthquake Engineering Society of Korea
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• v.21 no.6
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• pp.265-275
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• 2017

In order to improve the seismic performance of structures, friction pendulum system (FPS) is the most commonly used seismic isolation device in addition to lead rubber bearing (LRB) in high seismicity area. In a nuclear power plant (NPP) with a large self weight, it is necessary to install a large number of seismic isolation devices, and the position of the center of rigidity varies depending on the arrangement of the seismic isolation devices. Due to the increase in the eccentricity, which is the difference between the center of gravity of the nuclear structure and the center of stiffness of the seismic isolators, an excessive seismic response may occur which could not be considered at the design stage. Three different types of eccentricity models (CASE 1, CASE 2, and CASE 3) were used for seismic response evaluation of seismically isolated NPP due to the increase of eccentricity (0%, 5%, 10%, 15%). The analytical model of the seismic isolation system was compared using the equivalent linear model and the bilinear model. From the results of the seismic response of the seismically isolated NPP with increasing eccentricity, it can be observed that the effect of eccentricity on the seismic response for the equivalent linear model is larger than that for the bilinear model.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.331-338
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• 2001

Seismic performances of the base isolated model of Five Story Stone Pagoda were studied through shaking table tests. Friction pendulum system (FPS), Pure-friction system with laminated rubber bearing (LRB) and Ball with rubber bearing were selected fur the comparison of performances. Performances of specially designed isolation systems were tested dynamically using shaking table. The test results of isolated model are compared with those of fixed base model. Compared with fixed base model, the isolated model showed that it could withstand much higer intensity of earthquake motion. The Effective Peak Ground Acceleration (EPGA) value of isolated model when the top component tipped over was above twice of that value in case of fixed base model. According to the additional test results, the lower value of coefficient of friction than that of common frictional base isolation systems is more effective to protect the piled multi-block system of Pagoda against moderate intesity of ground motion.

• Earthquakes and Structures
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• v.7 no.4
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• pp.511-525
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• 2014

The main object of this study is to determine and compare the structural behavior of base isolated long span highway bridge, $G\ddot{u}lburnu$ Highway Bridge, using single concave friction pendulum (SCFP) and triple concave friction pendulum (TCFP). The bridge is seismically isolated in the design phase to increase the main period and reduce the horizontal forces with moments using SCFP bearings. In the content of the paper, firstly three dimensional finite element model (FEM) of the bridge is constituted using project drawings by SAP2000 software. The dynamic characteristics such as natural frequencies and periods, and the structural response such as displacements, axial forces, shear forces and torsional moments are attained from the modal and dynamic analyses. After, FEM of the bridge is updated using TCFP and the analyses are performed. At the end of the study, the dynamic characteristics and internal forces are compared with each other to extract the TCFP effect. To emphasize the base isolation effect, the non-isolated structural analysis results are added to graphics. The predominant frequencies of bridge non-isolated, isolated with SCFP and isolated with TCFP conditions decreased from 0.849Hz to 0.497Hz and 0.338Hz, respectively. The maximum vertical displacements are obtained as 57cm, 54cm and 44cm for non-isolated, isolated with SCFP and isolated with TCFP conditions, respectively. The maximum vertical displacement reduction between isolated with TCFP bearing and isolated with SCFP bearing bridge is %23. Maximum axial forces are obtained as 60619kN, 18728kN and 7382kN, maximum shear forces are obtained as 23408kN, 17913kN and 16249kN and maximum torsional moments are obtained as 24020kNm, 7619kNm and 3840kNm for non-isolated, isolated with SCFP and isolated with TCFP conditions, respectively.

• Structural Engineering and Mechanics
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• v.61 no.5
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• pp.645-655
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• 2017

To determine the seismic applicability of a long-span railway concrete upper-deck arch bridge with concrete-filled steel-tube (CFST) rigid skeleton ribs, some fundamental principles and seismic approaches for long-span bridges are investigated to update the design methods in the current Code for Seismic Design of Railway Engineering of China. Ductile and mixed isolation design are investigated respectively to compare the structural seismic performances. The flexural moment and plastic rotation demands and capacities are quantified to assess the seismic status of the ductile components. A kind of triple friction pendulum (TFP) system and lead-plug rubber bearing are applied simultaneously to regularize the structural seismic demands. The numerical analysis shows that the current ductile layout with continuous rigid frame approaching spans should be strengthened to satisfy the demands of rare earthquakes. However, the mixed isolation design embodies excellent seismic performances for the continuous girder approaching span of this railway arch bridge.

• Journal of the Earthquake Engineering Society of Korea
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• v.2 no.2
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• pp.13-22
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• 1998

This paper summarizes a study on the application of the friction pendulum system in bridge seismic isolation. Shaking table tests have been carried out on a model structure isolated with F.P.S and the obtained structural responses are compared to those of non-isolated. It can be concluded the F.P.S increases the earthquake resistance capacity of the isolated structure. It is also found that the stiffness of bearing, being controlled by the radius of curvature of the spherical sliding interface, is unaffected by the amplitude of the input excitation. Furthermore, the coefficient of sliding friction is velocity dependent so that in weak excitation the sliding velocity is low and, accordingly, the mobilized friction force is less than the one mobilized in strong excitation. Also, the frictional properties of the bearings remain markedly stable after extensive testing, and the permanent displacements are small and not cumulative in successive earthquakes.

• Structural Engineering and Mechanics
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• v.59 no.5
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• pp.803-820
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• 2016

In this study a direct displacement-based design (DDBD) procedure for a continuous deck bridge isolated with triple friction pendulum bearings (TFPB) has been proposed and the seismic demands of the bridge such as isolator's displacement and drift of piers obtained from this procedure evaluated under two-directional near-field ground motions. The structural model used here are continuous, three-span, castin-place concrete box girder bridge with a 30-degree skew which are isolated with 9 different TFPBs. By comparing the results of DDBD method with those of nonlinear time history analysis (NTHA), it can be concluded that the proposed procedure is able to predict seismic demands of similar isolated bridges with acceptable accuracy. Results of NTHA shows that dispersion of peak resultant responses for a group of ground motions increases by increasing their average value of responses. It needs to be noted that the demands parameters calculated by the DDBD procedure are almost overestimated for stiffer soil condition, but there is some underestimation in results of this method for softer soil condition.

• Earthquakes and Structures
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• v.20 no.3
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• pp.295-307
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• 2021

The gap provided between adjacent structures in the metropolitan cities is mostly narrow due to architectural and financial issues. Consequently, structural pounding occurs between adjacent structures during earthquakes. It causes damages, ranging from minor local to more severe ones, especially in the case of seismically isolated buildings, due to their higher displacements. However, due to the increased flexibility of isolated buildings, the problem could become more detrimental to such structures. The effect of the seismic pounding of moat walls on the response of buildings isolated by Triple Friction Pendulum Bearing (TFPB) is investigated in this paper. To this propose, two symmetric three-dimensional models, including single-story and five-story buildings, are modeled in Opensees. Nonlinear Time History Analyses (NTHA) are performed for seismic evaluation. Also, five different sizes with four different sets of friction coefficients are considered for base isolators to cover a whole range of base isolation systems with various geometry configurations and fundamental period. The results are investigated in terms of base shear, buildings' drift, and roof acceleration. Results indicated a profound effect of poundings against moat walls. In situations of potential pounding, in some cases, the influence of impact on seismic responses of multistory buildings was more remarkable.

• Structural Engineering and Mechanics
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• v.51 no.2
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• pp.277-297
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• 2014

Since the isolation bearings undergo large displacements in base-isolated structures, impact with adjacent structures is inevitable. Therefore, in this investigation, the effect of impact on seismic response of isolated structures mounted on double concave friction pendulum (DCFP) bearings subjected to near field ground motions is considered. A non-linear viscoelastic model of collision is used to simulate structural pounding more accurately. 2-, 4- and 8-story base-isolated buildings adjacent to fixed-base structures are modeled and the coupled differential equations of motion related to these isolated systems are solved in the MATLAB environment using the SIMULINK toolbox. The variation of seismic responses such as base shear, displacement in the isolation system and superstructure (top floor) is computed to study the impact condition. Also, the effects of variation of system parameters: isolation period, superstructure period, size of seismic gap between two structures, radius of curvature of the sliding surface and friction coefficient of isolator are contemplated in this study. It is concluded that the normalized base shear, bearing and top floor displacement increase due to impact with adjacent structure. When the distance between two structures decreases, the base shear and displacement increase comparing to no impact condition. Besides, the increase in friction coefficient difference also causes the normalized base shear and displacement in isolation system and superstructure increase in comparison with bi-linear hysteretic behavior of base isolation system. Totally, the comparison of results indicates that the changes in values of friction coefficient have more significant effects on 2-story building than 4- and 8-story buildings.