Double Concave Friction Pendulum Bearings Research Articles

Effect of Friction Dependencies on the Bidirectional Earthquake Response of Double Concave Friction Pendulum Bearings

ABSTRACT The reliability of friction dependencies under real earthquakes has rarely been validated and the effect of the velocity and temperature increase caused by bidirectional excitation on the maximum displacement remains unclear. In this study, friction dependencies were validated using full-scale dynamic tests under earthquake response orbits, and their contribution to the maximum displacement was assessed under strong ground motions. In general, friction dependencies are still applicable to real earthquakes. Moreover, the effect of velocity increase can be ignored, but the effect of temperature increase on displacement is significant, particularly under ground motions with large magnitudes and small distances to faults.

Seismic performance of reinforced concrete buildings with double concave friction pendulum base isolation system: case study of design by Indonesian code

Seismic isolation systems for buildings design are not as popular in the seismically active developing countries as they are in the developed ones. Several factors contribute to this, namely the lack of knowledge on the benefits of the seismic isolation systems, unfamiliarity with the design procedure, and the absence of relevant building codes that provide design guideline using seismic isolation system in such countries. Recently, the Indonesian seismic design code has been updated and has included the design guideline of structures using seismic isolation system. This paper describes a case study of design procedure and performance evaluation of base-isolated reinforced concrete buildings using double-concave friction pendulum (DCFP) isolation bearing following the most recent Indonesian seismic code. Seismic performances of typical 10-story fixed-base and base-isolated buildings under the risk-targeted maximum considered earthquake (MCER) in Jakarta city, the capital of Indonesia, are investigated using nonlinear finite element analysis. The results demonstrate that buildings with DCFP isolation bearings have better seismic performance than the conventional fixed-base building under the MCER. The improvements of seismic performances are observed in the form of reductions of base shear force, top-story acceleration, acceleration amplification ratio, and the interstory drift ratio. Comparisons of seismic performance of base-isolated buildings with different DCFP friction types and arrangement have demonstrated that the building with all low friction DCFP bearing performed the best among all base-isolated building models with DCFP bearings.

Energy-Based Prediction of the Displacement of DCFP Bearings

Isolation systems are currently being widely applied for earthquake resistance. During the design stage for such systems, the displacement response and input energy of the isolation layer are two of the main concerns. The prediction of these values is also of vital importance during the early stages of the structural design. In this study, the simple prediction method of double concave friction pendulum (DCFP) bearings is proposed, which can relate the response displacement of the isolation layer to the ground velocity through energy transfer with sufficient accuracy. Two friction models (the precise and simplified model) and a constant friction coefficient of double concave friction pendulum (DCFP) bearings are comprehensively validated by full-scale sinusoidal dynamic tests under various conditions. In addition, a response analysis, based on previous studies, was conducted using the friction models under selected unidirectional earthquake excitations, and the accuracy of using the simplified model in the response analysis was verified. Based on the response analysis data, this article verifies and optimizes the proposed prediction method by parameterizing the characteristics of earthquakes and combining the energy balance in order to gain a deeper understanding of the design of the isolation systems.

Shake table testing on restoring capability of double concave friction pendulum seismic isolation systems

SummaryAfter an earthquake, non‐negligible residual displacements may affect the serviceability of a base isolated structure, if the isolation system does not possess a good restoring capability. The permanent offset does not affect the performance unless the design is problematic for utilities, also considering possible concerns related to the maintenance of the devices.Starting from experimental and analytical results of previous studies, the restoring capability of Double Concave Friction Pendulum bearings is investigated in this paper. A simplified design suggestion for the estimation of maximum expected residual displacements for currently used friction pendulum systems is then validated. The study is based on controlled‐displacement and seismic input experiments, both performed under unidirectional motion. Several shaking table tests have been carried out on a three‐dimensional isolated specimen structure. The same sequence of seismic inputs was applied considering three different conditions of sliding surfaces corresponding to low, medium and high friction. The accumulation of residual displacements is also investigated by means of nonlinear dynamic analysis. Copyright © 2017 John Wiley & Sons, Ltd.

Shaking table tests of a base isolated structure with Double Concave Friction Pendulum bearings

An extensive experimental testing programme named JETBIS project (Joint Experimental Testing of Base Isolation Systems) was developed within the RELUIS II project (Task 2.3.2) and RELUIS III project (Line 6) involving partners from different Italian universities. This paper describes the seismic tests performed by the research unit of University of Basilicata (UNIBAS) on an isolation system based on Double Concave Friction Pendulum (DCFP) bearings. The DCFP bearing contains two separate concave sliding surfaces and exhibits different hysteretic properties at different stages of displacement response. The main objective of this work is to evaluate the horizontal response of the DCFP isolators by means of controlled-displacement tests and shaking table tests. The experimental model was a 1/3 scaled steel framed structure with one storey and one bay in both directions. Four DCFP bearings with equal properties of the sliding surfaces were considered. In this work, three different sliding surface conditions (with and without lubrication) have been studied. The isolated base model was subjected to 8 natural earthquakes of increasing seismic intensities and considering two mass configurations (with both symmetrical and eccentric masses). The reliability of the design procedure considered for the isolation system was verified also when relevant residual displacements occurred due to previous earthquakes. In this paper, the comparisons between the experimental outcomes and the numerical results of nonlinear time-history analyses using SAP2000 are shown.

The effect of impact with adjacent structure on seismic behavior of base-isolated buildings with DCFP bearings

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.

The effect of impact with adjacent structure on seismic behavior of base-isolated buildings with DCFP bearings

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.

Impact of structures with double concave friction pendulum bearings on adjacent structures

The double concave friction pendulum bearing is a new kind of friction pendulum bearing that consists of two sliding surfaces. To study the seismic responses of three-dimensional base-isolated structures using double concave friction pendulum systems during impact with adjacent structures, after deriving the coupled differential equations of motion, a computer program was developed in order to obtain the time history response of base-isolated structures under earthquake excitations. In the first part of this paper, the seismic response of three-dimensional base-isolated structures using double concave friction pendulum bearings considering tri-linear and bi-linear behaviours without adjacent structures is investigated. The advantages and disadvantages of tri-linear over bi-linear behaviour, considering the principal parameters, are scrutinised. It is demonstrated that using tri-linear double concave friction pendulum bearing behaviour rather than the bi-linear one can decrease the base shear up to 48%. However, tri-linear double concave friction pendulum bearings cause larger displacements of sliding surfaces than bi-linear ones, by up to 57%. The second part of the paper studies the effects of essential parameters such as separation distance, stiffness of impact elements, isolation period and the behaviour of double concave friction pendulum bearings on the seismic response of base-isolated structures using double concave friction pendulum systems during impact with adjacent structures. Numerical simulations demonstrate that base shear force increases significantly and, vice versa, bearing displacement decreases considerably due to impact of the isolated structure with adjacent structures. In addition, the hysteretic curve of the bearing affects the responses of the isolated structure during impact with adjacent structures.

Seismic Response of Elevated Liquid Storage Tanks Using Double Concave Friction Pendulum Bearings with Tri-Linear Behavior

In the current paper, the seismic response of elevated liquid storage tanks using double concave friction pendulum bearings (DCFP) considering bi-linear and tri-linear behaviors have been investigated. After deriving the coupled differential equations of motion, the MATLAB programming language is employed to solve the differential equations in each time step in order to obtain the time history response of isolated tank under near fault ground motions. The advantages and disadvantages of tri-linear behavior over bi-linear one on the response of isolated tanks is scrutinized by studying the effects of main parameters such as isolation period, tank period with fixed base, tank aspect ratio and base mass ratio on the tank response. It is demonstrated that change in bearing behavior form bi-linear to tri-linear dramatically affects the bearing maximum displacement while the peak value of other parameters such as sloshing displacement or tower shear force may experience less variations.

Investigation of effectiveness of double concave friction pendulum bearings

This paper presents the investigation of the stochastic responses of seismically isolated bridges subjected to spatially varying earthquake ground motions including incoherence, wave-passage and site-response effects. The incoherence effect is examined by considering Harichandran and Vanmarcke coherency model. The effect of the wave-passage is dealt with various wave velocities in the response analysis. Homogeneous firm, medium and soft soil conditions are selected for considering the siteresponse effect where the bridge supports are constructed. The ground motion is described by filtered white noise and applied to each support points. For seismic isolation of the bridge, single and double concave friction pendulum bearings are used. Due to presence of friction on the concave surfaces of the isolation systems, the equation of motion of is non-linear. The non-linear equation of motion is solved by using equivalent linearization technique of non-linear stochastic analyses. Solutions obtained from the stochastic analyses of non-isolated and isolated bridges to spatially varying earthquake ground motions compared with each other for the special cases of the ground motion model. It is concluded that friction pendulum systems having single and double concave surfaces have important effects on the stochastic responses of bridges to spatially varying earthquake ground motions.

Seismic behaviour of isolated multi-span continuous bridge to nonstationary random seismic excitation

This paper concentrates on the results of responses of a multi-span continuous bridge isolated with double concave friction pendulum bearings subjected to non-stationary random seismic excitation characterized by the incoherence, the wave-passage, and the site-response effects. The earthquake excitation is modelled as a non-stationary random process as uniformly modulated broad-band excitation. To perform the seismic isolation procedure, the double concave friction pendulum bearings which are sliding devices that utilize two spherical concave surfaces are placed at each of the six support points of the deck. The non-stationary response of the isolated bridge is compared with the corresponding stationary response in order to study the effects of non-stationary characteristics of the earthquake input motion. Solutions obtained from the stationary and non-stationary stochastic analyses for the isolated bridge to spatially varying earthquake ground motions are compared for the special cases of the earthquake ground motion model. The spatially varying earthquake ground motions are described stochastically based on an empirical coherency loss function and a filtered power spectral density function. The site effect is considered by a transfer function derived from one dimensional wave propagation theory. It is observed that the stationary assumption is reasonable for the considered ground motion duration.

Seismic Response of Base-Isolated Structures using DCFP Bearings with Tri-Linear and Bi-Linear Behavviors

Double concave friction pendulum (DCFP) system is the new developed kind of friction pendulum systems that consists of two sliding surfaces. In the current paper, the seismic response of three dimensional base-isolated structures using DCFP systems considering tri-linear and bi-linear behaviors have investigated. Aftter deriving the coupled differential equation of motion, a computer proggram has been developed in order to obtain the time history response of base-isolated structures under earthquake excitations. Advantages and disadvantages of tri-linear behavior over bi-linear one are scrutinized by studying the effect of main parameters such as issolation period, amplitude of the ground motion, and friction coefficient of the surfaces on the peak responsees under seven earthquakes. It is demonstrated that tri-linear DCFP bearings, in comparison with bi-linear bearings, can decrease the base shear up to about 48 percent. However, tri-linear DCFP bearings cause bigger displacements of sliding surfaces than bi-linear ones that reach to 57%.

Example of application of response spectrum analysis for seismically isolated curved bridges including soil-foundation effects

This paper presents seismic behaviour of isolated curved bridges in the earthquake prone regions. For the seismic isolation of bridges, double concave friction pendulum bearings are placed between the deck and the piers, and the abutments as isolation devices. A curved bridge is selected to exhibit the application for seismic isolation. The mentioned bridge is a three-span featuring cast-in-place concrete box girder superstructure supported on reinforced concrete columns found on drilled shafts and on integral abutments founded on steel pipe piles. Additionally, the bridge is located on site underlain by a deep deposit of cohesionless material. The drilled shaft-soil system is modelled by equivalent soil springs method and is included in the finite element model. The soil modelled as a series of springs is connected to the drilled shaft at even intervals. The multi mode method of analysis is typically implemented in a computer program capable of performing response spectrum analysis. The response spectrum specified for the analysis is the 5%-damped spectrum modified for the effects of the higher damping. Each isolator is represented by its effective horizontal stiffness with a linear link element. As seen from the results of the outlined analysis, usage of the isolation devices offers some advantages for the internal forces on the deck for the considered curved bridge as per the non-isolated curved bridge. The response spectrum analysis is substantially required to make a decision of the displacement capacity of the double concave friction pendulum bearings used in the study.

Example of application of response history analysis for seismically isolated curved bridges on drilled shaft with springs representing soil

The main objective of this study is to perform a parametrical study associated with the effects of the earthquake ground motions on the seismic response of isolated curved bridges including soil–structure interaction. For the isolated bridge system, double concave friction pendulum bearings are placed between the deck and the piers, the abutments as isolation devices. A curved bridge is selected to exhibit the application for seismic isolation. The bridge is to be modeled and analyzed in a seismic zone with an acceleration coefficient of 0.7 g. The configuration of the bridge is a three-span, cast-in-place concrete box girder superstructure supported on reinforced concrete columns found on drilled shafts and on integral abutments founded on steel pipe piles. The bridge is located on site underlain by a deep deposit of cohesionless material. The drilled shaft–soil system is modeled by equivalent soil springs method, and is included in the finite element model. The soil is modeled as a series of springs connected to the drilled shaft at even intervals. The reduction of the internal forces on the deck for the isolated curved bridge is observed, if the forces are compared with those obtained for the non-isolated curved bridge.

Earthquake response of isolated cable-stayed bridges under spatially varying ground motions

A comprehensive investigation of the stochastic response of an isolated cable-stayed bridge subjected to spatially varying earthquake ground motion is performed. In this study, the Jindo Bridge built in South Korea is chosen as a numerical example. The bridge deck is assumed to be continuous from one end to the other end. The vertical movement of the stiffening girder is restrained and freedom of rotational movement on the transverse axis is provided for all piers and abutments. The longitudinal restraint is provided at the mainland pier. The A-frame towers are fixed at the base. To implement the base isolation procedure, the double concave friction pendulum bearings are placed at each of the four support points of the deck. Thus, the deck of the cable-stayed bridge is isolated from the towers using the double concave friction pendulum bearings which are sliding devices that utilize two spherical concave surfaces. The spatially varying earthquake ground motion is characterized by the incoherence and wave-passage effects. Mean of maximum response values obtained from the spatially varying earthquake ground motion case are compared for the isolated and non-isolated bridge models. It is pointed out that the base isolation of the considered cable-stayed bridge model subjected to the spatially varying earthquake ground motion significantly underestimates the deck and the tower responses.

Seismic response characteristics of bridges using double concave friction pendulum bearings with tri-linear behavior

The friction pendulum system (FPS) is one of the most effective and frequently used seismic isolation devices. In this paper, a double concave friction pendulum system (DCFP) with tri-linear behavior is studied. The DCFP consists of two sliding surfaces with different friction coefficients and radii of curvature. The effects of DCFP systems with various friction values and restoring properties on a bridge are investigated under various earthquake excitations. Earthquake response analyses are carried out in the time domain on a simple bridge model with a DCFP system having various properties. Investigations are carried out on the reduction of the base-shear force on the bridge pier due to the DCFP. The advantages of a DCFP with tri-linear behavior are explored.

Behaviour of the double concave Friction Pendulum bearing

AbstractThe double concave Friction Pendulum (DCFP) bearing is an adaptation of the well‐known single concave Friction Pendulum bearing. The principal benefit of the DCFP bearing is its capacity to accommodate substantially larger displacements compared to a traditional FP bearing of identical plan dimensions. Moreover, there is the capability to use sliding surfaces with varying radii of curvature and coefficients of friction, offering the designer greater flexibility to optimize performance. This paper describes the principles of operation of the bearing and presents the development of the force–displacement relationship based on considerations of equilibrium. The theoretical force–displacement relationship is then verified through characterization testing of bearings with sliding surfaces having the same and then different radii of curvature and coefficients of friction. Lastly, some practical considerations for analysis and design of DCFP bearings are presented. Copyright © 2006 John Wiley & Sons, Ltd.