Double Concave Friction Pendulum Research Articles

Optimum design parameters for double concave friction pendulum system considering ground motion characteristics and friction heating

Optimum design parameters for double concave friction pendulum system considering ground motion characteristics and friction heating

Seismic evaluation and retrofit of a typical reinforced concrete hospital building in Indonesia with DCFP isolation system

In this paper, a study on seismic evaluation and retrofit of a typical reinforced concrete (RC) hospital building in Indonesia is presented. Seismic evaluation is performed against basic structural performance objectives outlined in the current code for structural seismic evaluation. The target building is a typical 5-story RC building designed by the 1970s Indonesia seismic and building codes, which imposed lower seismic demand and were not as strict as the current codes in the requirements for strength and ductility. The first part of the paper describes a seismic evaluation procedure against specific target performance levels. Nonlinear time history analysis (NLTHA) is conducted and structural performances were evaluated against structural responses (base shear force and inter-story drift ratio) and acceptance of seismic performance level for local (element rotational limit) and global (roof drift ratio) performance criteria under 225, 975, and 2475-year return period earthquake scenarios. Results reveal that seismic performances of some structural elements are unsatisfactory and under the acceptable performance level, especially for 2475-year return period (BSE-2 N/MCER) earthquake scenario. Seismic retrofit is thus recommended and the use of double-concave friction pendulum (DCFP) base-isolation system as a retrofit strategy is explored. The seismic performance of DCFP-retrofitted building is examined by NLTHA, where effectiveness of DCFP base-isolation system in improving seismic performance is confirmed by comparing structural responses, local and global structural performance of the existing building and the DCFP-retrofitted building under 2475-year return period earthquake scenario. Results of NLTHA demonstrate that local structural performance level has improved from Collapse Prevention to Immediate Occupancy level, whereas the global structural performance has improved from Limited Safety level to Operational level.

Assessment and measurement of ground motion risk levels for structures isolated by double concave friction pendulum system

Determining the risk level of ground motions (GM) for structures is crucial for their damage control and resilience enhancement, while the assessment and measurement criteria of GM risk levels for structures isolated by double concave friction pendulum system (DCFPS) remain unclear. Through statistical analysis of the response distribution of DCFPS with various design parameters under 1013 GM records, this study determines an energy dissipation efficacy of 99 %, a floor velocity of 0.35 m/s, a floor velocity of 0.60 m/s, and the displacement capacity of DCFPS as the response criteria for assessing four performance states of efficacy, habitability, functionality, and safety, respectively. In addition, the value of GM intensity in PGA, PGV, PGD, and the equivalent velocity of seismic input energy (VE) for measuring the four GM risk levels corresponding to the four performance states are obtained. Furthermore, a classification of GMs based on earthquake magnitude and fault distance is proposed according to their risk to DCFPS. It is found that the intensity value of each GM risk level varies for different design parameters of DCFPS but fluctuate within a small range, however, great differences exist when using different intensity measures (IM) in classifying GM risk levels. Therefore, based on the correlation between IMs and DCFPS responses, the conservatism of PGA, PGV, PGD and VE in assessing the risk of GMs for DCFPS are evaluated.

A Novel Three-Dimensional Composite Isolation Bearing and Its Application to the Mitigation of Earthquakes and Traffic-Induced Vibrations

Potential damage caused by earthquakes combined with reduced comfort due to traffic has become a big challenge when designing modern buildings, and base-isolation is one of the most effective solutions to such a problem. However, most isolation bearings cannot provide sufficient mitigation for both earthquakes and traffic-induced vibrations simultaneously. To this end, this research proposes a new type of three-dimensional isolation bearing for the mitigation of both earthquake effects and traffic-induced vibrations, which is composited by a thick rubber bearing, an auto-reset flat sliding bearing, and a double concave friction pendulum bearing. In this study, the analytical hysteresis model of the proposed isolation bearing was derived and experimentally validated. In addition, the fatigue performance and vertical compression performance of the proposed isolation bearing was tested and analyzed. Finally, the mitigation effect for traffic-induced vibrations of the proposed isolation bearing was validated through a field test.

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 isolation effect of a new type of friction pendulum bearing in high-speed railway girder bridge

Residual displacement exists in the traditional friction pendulum bearings (FPB) under the action of earthquakes, which makes them fail to self-reset. In view of this, a new type of FPB called double concave friction pendulum with spring (DCFPS) is proposed. Firstly, the restoring force model and hysteresis characteristics of the theoretical DCFPS are derived. Then, the seismic isolation effect of the high-speed railway simply supported girder bridges (HRSB) equipped with the DCFPS is evaluated. Finally, the optimal spring parameters of the DCFPS are determined in terms of the efficiency coefficient and the optimal order method. The results show that the DCFPS has superior self-reset performance, and the hysteresis curve is “S” shaped. The stiffness of the DCFPS gradually increases with the swing displacement, which heightens the overall stiffness of the structure equipped with DCFPS. After HRSB is installed DCFPS, the displacement of the girder and the residual displacement of the DCFPS itself are reduced. The optimal stiffness and the initial tension of spring for the bridges exemplified in the paper are suggested as 3000 kN/m and 9 kN, respectively, through the efficiency coefficient method and the optimal order method. This research proposes a feasible solution for reducing the maximum displacement and residual displacement of bearings under an earthquake.

Experimental Investigation of Wear Effects on the Friction Coefficient of a Curved Surface Slider: Comparison of Small- and Full-Scale Tests

ABSTRACT The current practice to determine friction properties of sliding isolation systems is to perform displacement-controlled dynamic tests where the effects of several loading conditions with different amplitudes, loading velocities, and vertical forces are of concern. The number of cycles in these tests is generally three for most of the loading conditions assumed to be representative of seismic conditions. On the other hand, the isolator may undergo small-amplitude but large-cycles of service motions due to thermal deformations and accidental loads. In that case, the methodology requires to perform cyclic tests on small-scale samples of the slider material (not the isolator) considering very large accumulated sliding distances such as 1000 m for use in buildings, and 10,000 m for use in bridges. However, two unsettled issues are regarded: (i) the suitability of small-scale slider tests to estimate the characteristics of full-scale sliding isolation systems and (ii) the change in seismic performance of a sliding isolation system after it is subjected to a large amount of accumulated sliding distance. In the present study, both a full-scale double concave friction pendulum (DCFP) and small-scale sample composed of the slider of the DCFP are subjected to a total accumulated sliding distance of 1000 m. The corresponding variations in friction properties are comparatively presented, demonstrating that small-scale test results provide reasonable estimates for the friction properties of the tested full-scale DCFP. Moreover, the seismic response of the investigated DCFP remains almost the same regardless of the considered sliding distance.

Comparative seismic performance of a moment frame equipped with Lateral Impact Resilient Double Concave Frictional devices

This study presents a comparative assessment of the seismic performance of a reinforced concrete moment frame equipped with a new isolator. The Lateral Impact Resilient Double Concave Friction Pendulum (LIR-DCFP) bearing has an enhanced inner slider capable of limiting the magnitude of the lateral impact force generated between the inner slider and the restraining rims of the sliding surfaces. Due to the presence of a plane high-friction interface with an internal gap, the novel isolator has an increased energy dissipation capacity that is activated during the lateral impact. Three isolation systems were considered to evaluate the benefits of using LIR-DCFP devices. One conformed by the suggested isolator, and two composed of classic non-articulated Double Concave Friction Pendulum (DCFP) bearings. The isolation devices were modelled employing a numerical formulation based on rigid body dynamics, capable of accounting for the lateral impact behaviour. The superstructure, a reinforced concrete moment resisting frame designed according to the American ASCE/SEI 7-16 standard, was modelled using beam-column elements considering geometric and material nonlinearities. Furthermore, the degrading behaviour of the building was incorporated using a proper degradation model for both the stiffness and the force. Incremental Dynamic Analyses (IDAs) were performed considering the friction coefficient as a random variable to characterize the statistics of the maximum inter-story responses. With the data generated in the IDAs, fragility curves related to the superstructure performance were constructed. Finally, employing the hazard curve, reliability curves were derived. The superstructure equipped with LIR-DCFP bearings presents better seismic performance than the same building equipped with the same size DCFP isolators. The benefits of using the new isolator are not achieved by increasing the lateral capacity of the classic isolation system.

Bridges seismically isolated by DCFP devices: a study on how the main parameters of the problem affect the seismic performance of the system

This paper deals with the evaluation of the main relevant properties of the double concave friction pendulum devices, namely DCFP, able to influence the seismic behaviour of infrastructures such as isolated multi-span continuous deck bridges. With this aim, a numerical model has been proposed to simulate the dynamic behaviour of seismically isolated bridges, and so an eight-degree-of-freedom system adopted in order to model the elastic reinforced concrete pier and the isolators devices. Furthermore, the interaction pier-abutment has been taken into account and the former modelled as a fully fixed restrain. The deck has been assumed rigid in its plane and a non-linear velocity dependent law adopted to model the friction along the two surfaces of the pendulum isolators. The equations of motion have been proposed in a non-dimensional form by means of a preliminar dymensional analysis. Finally, a widely parametric analysis has been conducted and record-to-record variability taken into account by using a set of natural records with different characteristics either in terms of epicentral distance and magnitude. The response of the system in terms of pier and deck displacements, is presented in a probabilistic fashion and as independent from the seismic intensity thanks to the abovementioned dimensional analysis. The main evidence of the study is how the main structural parameters involved in the analysis are able to control and influence the seismic response, such that the outcomes of this research could be used to better design or retrofit multispan coninuous deck bridges isolated with DCFP.

Seismic reliability of structures equipped with LIR‐DCFP bearings in terms of superstructure ductility and isolator displacement

AbstractThis research deals with the seismic reliability of non‐linear base‐isolated structures equipped with Lateral Impact Resilient Double Concave Friction Pendulum (LIR‐DCFP) devices. Specifically, exceeding probabilities within the reference lifetime are assessed with respect to both superstructure ductility and isolator displacement demand. The innovative LIR‐DCFP bearing has an improved inner slider with an internal gap and is capable to reduce adverse effects of the lateral impact between the inner slider and the restraining rims. The dynamic behavior of the superstructure is represented by a simplified one‐degree‐of‐freedom model describing its lateral response. The isolation system is characterized by a model based on rigid body dynamics also including the lateral impact behavior. A wide parametric analysis is developed for several system properties considering the friction coefficients as relevant random variables. Different sets of natural seismic records able to match conditional spectra for a site in Riverside (California) were selected to consider the aleatory uncertainties of the seismic input. Incremental dynamic analyses were performed to determine the statistics of significant engineering demand parameters and compute probabilities exceeding specific limit states to define fragility curves. Finally, employing seismic hazard curves, the seismic reliability of isolated structures was evaluated. For increasing values of the internal gap, structures equipped with LIR‐DCFP devices exhibit better seismic performance with respect to classical DCFP bearings with same size, especially, if the superstructure is designed to behave essentially elastic when the lateral capacity of the isolation level is not reached, or the hardening post‐yield stiffness of the superstructure is relatively high. Reductions up to 20% in the exceeding probabilities within 50 years related to the ductility demand are achievable using the suggested LIR‐DCFP isolator.

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.

Optimal DCFP bearing properties and seismic performance assessment in nondimensional form for isolated bridges

AbstractThe study analyzes the influence of double concave friction pendulum (DCFP) isolator properties on the seismic performance of isolated multispan continuous deck bridges. The behavior of these systems is analyzed by employing an eight‐degree‐of‐freedom model accounting for the pier flexibility in addition to the rigid presence of both abutment and deck, whereas the DCFP isolator behavior is described combining two single FP devices in series. The uncertainty in the seismic input is taken into account by considering a set of nonfrequent natural records with different characteristics. The variation of the statistics of the response parameters relevant to the seismic performance of the isolated bridges is investigated through the proposal of a nondimensionalization of the motion equations, with respect to the seismic intensity, within an extensive parametric study carried out for different isolator and bridge properties. Moreover, two cases related to different ratios between the sliding friction coefficients of the two surfaces of the DCFP devices are analyzed with the aim also to evaluate the corresponding optimal values able to minimize the seismic demand to the pier. In this way, all the presented nondimensional results are useful for the preliminary design or retrofit of multispan continuous deck bridges, isolated with DCFP devices, located in any site and in relation, especially, to the seismic ultimate limit states.

Lateral Impact Resilient double concave Friction Pendulum (LIR-DCFP) bearing: Formulation, parametric study of the slider and three-dimensional numerical example

Seismic isolation has been one of the best alternatives in protecting structures, being frictional isolators one of the most used devices in constructing isolation systems. Under extreme seismic inputs, the impact between the inner slider and the restraining rims of the plates could occur. This internal impact has been indicated as one of the main contributors to the failure of frictional pendulum bearings. This paper presents a new type of frictional device, the Lateral Impact Resilient double concave Friction Pendulum (LIR-DCFP) bearing. This device has an improved inner slider that enhances the dynamic behavior if the lateral capacity of the isolator is overcome. The three-dimensional formulation of the LIR-DCFP bearing is presented and proposed to perform dynamics analyzes. A parametric analysis was performed to evaluate the influence of the geometry of the inner slider. Finally, a comparative three-dimensional analysis between the dynamic response of a structure isolated using LIR-DCFP bearings and double concave Friction Pendulum (DCFP) bearings is presented. Important reductions in the base shear, inter-story drifts, and absolute accelerations are achieved using LIR-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.

Theoretical study of the double concave friction pendulum system under variable vertical loading

The double concave friction pendulum system has been recognized as an efficient device for decreasing the seismic response of a structure during an earthquake excitation. Previous studies have focused mainly on the properties of the double concave friction pendulum system under constant vertical loading, and the width of the hysteretic loop changed by the vertical ground motion is less considered. In view of this, a theoretical study of the double concave friction pendulum system under variable vertical loading is conducted in this article. Meanwhile, the properties of the hysteretic loops of the double concave friction pendulum system with different friction coefficients between the articulated slider with the upper and lower sliding surfaces are investigated. The results show that the hysteretic loops of the double concave friction pendulum system will be affected by the variation of the vertical loading and the difference of the friction coefficients between the articulated slider with the upper and lower sliding surfaces.

Numerical Simulation of Frictional Heating Effects of Sliding Friction Bearings for Isolated Bridges

Sliding friction bearings are effective passive devices to mitigate the seismic responses of structures. Extensive researches have been conducted on sliding bearings. However, most previous studies were based on the assumption that the effects of frictional heating are negligible. A three-dimensional thermal-mechanical-coupled finite element (FE) model of the friction pendulum system (FPS) was developed in this study. Good agreements between the numerical results and the data measured in the previous tests, in terms of the force–displacement curves and temperature time-histories, indicate that the proposed FE model can predict the response of the FPS. Based on the developed FE model, the surface temperature distribution, the effective stiffness and the energy dissipation of the double concave friction pendulum and multiple friction pendulum bearings were investigated and compared. In addition, the thermal states of the sliding bearings in the bridge during earthquake were evaluated. The numerical results indicate that the temperature rise in the sliding bearings leads to the degradation of the effective stiffness and less energy dissipation. The relative displacements of the bearings increase considering the frictional heating effects in the bearings. If the frictional heating of the bearings is ignored, the peak bearing displacements will be underestimated.

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.

Response of the Double Concave Friction Pendulum System under Triaxial Ground Excitations

Modelling techniques of Double Concave Friction Pendulum (DCFP) system are presented. Seismic responses of the three-dimensional single-story building isolated by DCFP with different coefficient of friction and initial time period of top and bottom sliding surfaces are investigated under triaxial ground excitations and compared with unilateral and bilateral ground excitations. The influence of vertical flexibility on horizontal response is investigated. It is observed that the triaxial ground motion has noticeable effect on response of the building relative to unilateral ground motion. The error in peak resultant absolute deck acceleration and the error in peak resultant isolator deformation, occurring by neglecting vertical ground motion component, could be significant.

Investigation on the Effect of Near-Fault Earthquake on Double Concave Friction Pendulum (DCFP) Base Isolated Buildings

Near-fault earthquakes have different properties compared to far-fault earthquakes. Due to the phenomenon of forward directivity in near-fault earthquakes, the component perpendicular on fault has pulses with longer periods and wider range than the parallel component. Seismic isolators as the types of damping systems prevent structure to enter into non-linear range through their deformation. In this study, Single Degree of Freedom Structures (SDOFS), which are connected to FPS and DCFP isolators, was analyzed under time history implementing the records of near-fault and far-fault earthquakes. In addition, base shear, displacements, and acceleration incurred on the foundation of upper structure were examined. The obtained results indicated that in comparison with DCFP isolator, FPS isolator transfers less base shear on its structure in near-fault earthquake, whereas in comparison with FPS isolator, DCFP isolator transfers less displacements on its structure in near-fault earthquake. In addition, it transfers smaller acceleration on its foundation in near-fault and far-fault earthquakes.

Implementation of smart-passive dampers combined with double concave friction pendulum devices to retrofit an existing highway viaduct exploiting the seismic early warning information

The seismic events occurred in recent years have highlighted the extreme vulnerability of a large part of existing Italian highway infrastructure. The principal skeleton of Italian highway network was built during the mid-century, where the knowledge of seismic engineering was still limited. Also, the old age of structures with the need of seismic assessment, is forcing highway stakeholders to give an answer to a strategic query: should thousands of highway bridges be destroyed and re-built with in force regulations, or do they just need a retrofit? The objective of this work is to reply concretely to that issue, investigating the combined use of a dissipative smart-passive control strategy and an innovative isolation system to protect seismically excited structures. It is based on the use of seismic early warning information (SEWI) to optimally calibrate variable dampers for a higher reduction of the structural response. In particular, the adoption of dissipative magnetorheological (MR) dampers calibrated according to the forecasted value of the seismic peak ground acceleration, and a new adaptive control algorithm, are herein proposed. Moreover, to reduce the influence of support devices in the global viaduct behavior, a prototype of double concave friction pendulum (DCFP), with a very low value of friction coefficient, is implemented. The effectiveness and robustness of the DCFPs system with smart-passive MR dampers driven by the SEWI, are demonstrated with reference to an existing Italian highway viaduct for the first time. The results of non-linear time history analysis using seismic registrations of natural events are then compared with a consolidate passive technique characterized by lead rubber bearings (LRB), applied to the same structure. The control technique results were promising for the ease of implementation for structures, effectiveness, even compared with a widespread passive system and robustness, given an estimate of the incoming earthquake by a seismic early warning system.