Triple Concave Friction Pendulum Research Articles

EFFECTIVENESS OF WAVE PASSAGE EFFECT OF SEISMIC ISOLATED AND NONISOLATED BRIDGES UNDER SPATIALLY VARYING GROUND MOTION

In this study, stochastic analyses of isolated and nonisolated highway bridges under spatially varying ground motion are performed. The bridge is isolated with triple concave friction pendulum (TCFP) bearing. The selected bridge is assumed to be constructed on homogeneous soft soil. Incoherency effects are neglected and wave passage effect is taken into account in the stochastic analyses. The bridge model subjected to spatially varying earthquake ground motions in the horizontal direction. The horizontal input is assumed to travel across the bridge from left to right side with finite velocities of 100m/s, 200m/s and 400m/s. The means of the maximum responses of displacement and internal forces of bridge deck are investigated. The results of these stochastic analyses are also compared with the results of infinite velocity. Analysis results show that using TCFP bearing on Highway Bridge reduces means of maximum values of total axial force, shear force and bending moment of bridge deck by 89%, 86% and 96%, respectively. In generally, low speed is more effective than high speed at the means of the maximum responses of internal forces of bridge deck. The finite velocity is the most effective at means of the maximum responses of horizontal displacement of bridge deck.

Reliability of Symmetric and Asymmetric Structures Mounted on TCFP Base Isolators Subjected to Near-Field Earthquakes

AbstractThe reliability of structures isolated with Triple Concave Friction Pendulum (TCFP) bearings subjected to near-field earthquakes is investigated. An extensive study is conducted to reveal t...

Acceleration amplification due to rotational components of near-fault earthquakes in triple concave friction pendulum base-isolated structures

Recent studies show that rotational components of earthquakes can amplify the floor acceleration in a base-isolated structure. As a result, the seismic force of nonstructural components could be significantly increased. In this paper, a simple rectangular deck with various geometrical properties mounted on triple concave friction pendulum (TCFP) bearings is examined. At first a set of three translational components from 25 near-fault ground motion records are considered. Then, three rotational components, i.e., torsional and two rocking motions are computed for each earthquake. The results of nonlinear dynamic analysis in a rectangular structure with an aspect ratio in plan equal to 3, demonstrate that the acceleration approximately intensifies 3.4 times in presence of all six ground motion components compared to three translational ones. Finally, a new formula is proposed to determine the maximum acceleration of base-isolated structure without performing the dynamic analysis due to rotational components of ground motions.

Stochastic responses of isolated bridge with triple concave friction pendulum bearing under spatially varying ground motion

This study aims to investigate the stochastic response of isolated and non-isolated highway bridges subjected to spatially varying earthquake ground motion model. This model includes wave passage, incoherence and site response effects. The wave passage effect is examined by using various wave velocities. The incoherency effect is investigated by considering the Harichandran and Vanmarcke coherency model. The site response effect is considered by selecting homogeneous firm, medium and soft soil types where the bridge supports are constructed. The ground motion is described by power spectral density function and applied to each support point. Triple concave friction pendulum (TCFP) bearing which is more effective than other seismic isolation systems is used for seismic isolation. To implement seismic isolation procedure, TCFP bearing devices are placed at each of the support points of the deck. In the analysis, the bridge selected is a five-span featuring cast-in-place concrete box girder superstructure supported on reinforced concrete columns. Foundation supported highway bridge is regarded as three regions and compared its different situation in the stochastic analysis. The stochastic analyses results show that spatially varying ground motion has important effects on the stochastic response of the isolated and non-isolated bridges as long span structures.

Seismic Fragility Assessment of Asymmetric Structures Supported on TCFP Bearings Subjected to Near-field Earthquakes

Seismic Fragility curves of asymmetric steel structures isolated with Triple Concave Friction Pendulum (TCFP) bearings are studied in this paper. To consider the record-to-record uncertainty an ensemble of 45 sets of near-fault ground motion is selected. The main sources of eccentricity in torsionally coupled base-isolated structures, namely mass eccentricity in the superstructure and stiffness eccentricity in isolators are investigated elaborately. The seismic performance of structures is studied through the damage states (DS) framework introduced by HAZUS-2003 including slight, moderate, extensive, and complete structural damage states. In order to quantify the damage states, two engineering demand parameters i.e. interstory drift and acceleration are implemented. Three-dimensional nonlinear analysis of steel moment-frame superstructures mounted on a reasonable variety of TCFP bearings shows that among different types of eccentricity, mass eccentricity of superstructure affects the fragility characteristics more than the other. Generally, torsion due to mass eccentricity decreases the seismic intensity of different damage states; however, this reduction is more noticeable in slight and moderate ones. The 5% damped spectral acceleration at the isolation system effective period, Sa(Teff) reduces up to 20% in slight DS because 30% mass eccentricity, while this reduction is nearly 2% in the collapse DS. It affirms that TCFP bearing is capable of controlling great responses through strong ground motions. Furthermore, it is demonstrated that mass eccentricity will increase the risk of collapses calculated through the FEMA P-695 method which considers earthquake, modeling, design and test data uncertainties.

Effects of vertical component of near-field ground motions on seismic responses of asymmetric structures supported on TCFP bearings

The effects of vertical component of earthquakes on torsional amplification due to mass eccentricity in seismic responses of base-isolated structures subjected to near-field ground motions are studied in this paper. 3-, 6- and 9-story superstructures and aspect ratios of 1, 2 and 3 have been modeled as steel special moment frames mounted on Triple Concave Friction Pendulum (TCFP) bearings considering different period and damping ratios. Three-dimensional linear superstructures resting on nonlinear isolators are subjected to both 2 and 3 component near-field ground motions. Effects of mass eccentricity and vertical component of 25 near-field earthquakes on the seismic responses including maximum isolator displacement and base shear as well as peak superstructure acceleration are studied. The results indicate that the effect of vertical component on the responses of asymmetric structures, especially on the base shear is significant. Therefore, it can be claimed that in the absence of the vertical component, mass eccentricity has a little effect on the base shear increase. Additionally, the impact of this component on acceleration is remarkable so the roof acceleration of a nine-story structure has been increased 1.67 times, compared to the case that the structure is subjected to only horizontal components of earthquakes.

Rotational components of near-fault earthquakes effects on triple concave friction pendulum base-isolated asymmetric structures

In this paper, attempts are made to demonstrate the effects of the rotational components of near-fault ground motions on asymmetric base-isolated structures. The effects of mass eccentricity in intensifying the impact of rotational components are investigated as well. A reasonable variety of superstructures with different aspect and slenderness ratios is considered. Three-dimensional models of superstructures with linear behavior mounted on nonlinear TCFP isolators with various effective periods and damping are studied elaborately. Base shear, isolator displacement, base torsional angle and roof acceleration are selected as prominent responses of base-isolated structures. Results demonstrate that rotational components play an essential role in raising the structural responses. Furthermore, the effects of mass eccentricity are notable. Structures with an aspect ratio in plan equal to 3, the roof acceleration can increase to 255% in the presence of rotational components and mass eccentricity simultaneously. In similar conditions, the base shear of a 9-story building enhances 135%. Generally, the torsional component of earthquake affects the isolator displacement, base torsional angle and roof acceleration, while the base shear is influenced by the rocking components. It is revealed that the effects of mass eccentricity on the isolator displacement could be ignored.

Seismic responses of asymmetric steel structures isolated with the TCFP subjected to mathematical near-fault pulse models

In this paper, the effects of mass eccentricity of superstructure as well as stiffness eccentricity of isolators on the amplification of seismic responses of base-isolated structures are investigated by using mathematical near-fault pulse models. Superstructures with 3, 6 and 9 stories and aspect ratios equal to 1, 2 and 3 are mounted on a reasonable variety of Triple Concave Friction Pendulum (TCFP) bearings considering different period and damping ratio. Three-dimensional linear superstructure mounted on nonlinear isolators are subjected to simplified pulses including fling step and forward directivity while various pulse period (Tp) and Peak Ground Velocity (PGV) amounts as two crucial parameters of these pulses are scrutinized. Maximum isolator displacement and base shear as well as peak superstructure acceleration and drift are selected as the main engineering demand parameters. The results indicate that the torsional intensification of different demand parameters caused by superstructure mass eccentricity is more significant than isolator stiffness eccentricity. The torsion due to mass eccentricity has intensified the base shear of asymmetric 6-story model 2.55 times comparing to symmetric one. In similar circumstances, the isolator displacement and roof acceleration are increased 49 and 116 percent respectively in the presence of mass eccentricity. Furthermore, it is demonstrated that torsional effects of mass eccentricity can force the drift to reach the allowable limit of ASCE 7 standard in the presence of forward directivity pulses.

Seismic Responses of Isolated Structures with Mass Asymmetry Mounted on TCFP Subjected to Near-Fault Ground Motions

This study is devoted to investigate the effects of mass eccentricity on seismic responses of base-isolated structures subjected to near-field ground motions. Superstructures with 3, 6 and 9 stories with aspect ratios equal to 1, 2 and 3 have been idealized as steel special moment frames resting on a reasonable variety of triple concave friction pendulum bearings considering different period and damping ratios for the isolators. Three-dimensional linear superstructures mounted on nonlinear isolators have been subjected to three components of near-field ground motions. Under 25 near-field ground motions, effects of mass eccentricity on the main parameters of the systems have been studied. These parameters have been selected as the main engineering demands including maximum isolator displacement and base shear as well as peak superstructure acceleration. The results indicate that the mass eccentricities do not have a remarkable effect on isolator displacement. In contrary to displacement, torsional effect of mass eccentricity has raised the base shear up to 1.75 times in a three-story superstructure. Additionally, mass eccentricity can amplify the roof acceleration of a nine-story model approximately 3 times in comparison with a symmetric one. It is also concluded that eccentricity in the direction of the subjected earthquake has the most impact on the base shear, while the isolator displacement and roof acceleration are mostly influenced by the eccentricity perpendicular to the earthquake path.

Torsionally Seismic Behavior of Triple Concave Friction Pendulum Bearing

In this paper, attempts are made to investigate the responses of torsionally coupling base-isolated structure supported on Triple Concave Friction pendulum bearing (TFP) subjected to near field ground motions. Nonlinear dynamic analyses are conducted to study the effects of essential parameters such as superstructure and isolation system eccentricity, and the uncoupled torsional to lateral frequency ratio of superstructure on seismic responses of TFP isolated structures. Further, the responses of base-isolated structure using TFP are compared with the same base-isolated structure using friction pendulum system (FPS) as well as double concave friction pendulum (DCFP). Results indicate that TFP isolated structure significantly outperforms other types of friction bearings. Moreover, increasing effective period causes TFP isolated structures to behave better than the others in reducing torsional responses of structure. It is concluded that effectiveness of TFP isolators in respect to others bearings is negligible on seismic responses of structures through increasing effective damping.

Comparison of seismic behavior of long period SDOF systems mounted on friction isolators under near-field earthquakes

Friction isolators are one of the most important types of bearings used to mitigate damages of earthquakes. The adaptive behavior of these isolators allows them to achieve multiple levels of performances and predictable seismic behavior during different earthquake hazard levels. There are three main types of friction isolators. The first generation with one sliding surface is known as Friction Pendulum System (FPS) isolators. The double concave friction pendulum (DCFP) with two sliding surfaces is an advanced form of FPS, and the third one, with fully adaptive behavior, is named as triple concave friction pendulum (TCFP). The current study has been conducted to investigate and compare seismic responses of these three types of isolators. The structure is idealized as a two-dimensional single degree of freedom (SDOF) resting on isolators. The coupled differential equations of motion are derived and solved using state space formulation. Seismic responses of isolated structures using each one of these isolators are investigated under seven near fault earthquake motions. The peak values of bearing displacement and base shear are studied employing the variation of essential parameters such as superstructure period, effective isolation period and effective damping of isolator. The results demonstrate a more efficient seismic behavior of TCFP isolator comparing to the other types of isolators. This efficiency depends on the selected effective isolation period as well as effective isolation damping. The investigation shows that increasing the effective isolation period or decreasing the effective isolation damping improves the seismic behavior of TCFP compared to the other isolators. The maximum difference in seismic responses, the base shear and the bearing displacement, for the TCFP isolator are calculated 26.8 and 13.4 percent less than the DCFP and FPS in effective isolation damping equal to10%, respectively.

Effects of rotational components of earthquakes on seismic responses of triple concave friction pendulum base-isolated structures

In this research, the effects of rotational components of earthquakes on seismic responses of Triple Concave Friction Pendulum (TCFP) base-isolated structures are investigated elaborately. Although it is common to ignore the influence of rotational components of earthquakes on structural analysis, this investigation demonstrates the significant effects of these components on seismic responses of isolated structures mounted on TCFP bearings. Extensive base-isolated structures models with different superstructure specifications such as slenderness and aspect ratios as well as isolation properties such as effective period and damping are investigated. Essential seismic responses such as base shear, roof acceleration, isolator displacement and base slab rotation are studied while isolated structures subjected to the translational components of earthquakes as well as the rotational and translational components of earthquakes simultaneously. The results demonstrate the sensitivity of seismic responses to the superstructure properties such as the slenderness ratio and plan aspect ratio in presence of rotational components; whereas it does not show such sensitivity to isolation properties. Generally, the roof acceleration and the base shear can be affected by the rotational components, tremendously. For instance the roof acceleration can be raised 220% in a structure when its plan length is three times more than its plan width and the base shear can be increased 33% for a 9-story building in presence of rotational components.

The effects of peak ground velocity of near-field ground motions on the seismic responses of base-isolated structures mounted on friction bearings

This research has been conducted in order to investigate the effects of peak ground velocity (PGV) of near-field earthquakes on base-isolated structures mounted on Single Friction Pendulum (SFP), Double Concave Friction Pendulum (DCFP) and Triple Concave Friction Pendulum (TCFP) bearings. Seismic responses of base-isolated structures subjected to simplified near field pulses including the forward directivity and the fling step pulses are considered in this study. Behaviour of a two dimensional single story structure mounting on SFP, DCFP and TCFP isolators investigated employing a variety range of isolators and the velocity (PGV) of the forward directivity and the fling step pulses as the main variables of the near field earthquakes. The maximum isolator displacement and base shear are selected as main seismic responses. Peak seismic responses of different isolator types are compared to emphasize the efficiency of each one under near field earthquakes. It is demonstrated that rising the PGVs increases the isolator displacement and base shear of structure. The effects of the forward directivity are greater than the fling step pulses. Furthermore, TCFP isolator is more effective to control the near field effects than the other friction pendulum isolators are. This efficiency is more significant in pulses with longer period and greater PGVs.

The effects of peak ground velocity of near-field ground motions on the seismic responses of base-isolated structures mounted on friction bearings

This research has been conducted in order to investigate the effects of peak ground velocity (PGV) of near-field earthquakes on base-isolated structures mounted on Single Friction Pendulum (SFP), Double Concave Friction Pendulum (DCFP) and Triple Concave Friction Pendulum (TCFP) bearings. Seismic responses of base-isolated structures subjected to simplified near field pulses including the forward directivity and the fling step pulses are considered in this study. Behaviour of a two dimensional single story structure mounting on SFP, DCFP and TCFP isolators investigated employing a variety range of isolators and the velocity (PGV) of the forward directivity and the fling step pulses as the main variables of the near field earthquakes. The maximum isolator displacement and base shear are selected as main seismic responses. Peak seismic responses of different isolator types are compared to emphasize the efficiency of each one under near field earthquakes. It is demonstrated that rising the PGVs increases the isolator displacement and base shear of structure. The effects of the forward directivity are greater than the fling step pulses. Furthermore, TCFP isolator is more effective to control the near field effects than the other friction pendulum isolators are. This efficiency is more significant in pulses with longer period and greater PGVs.

Comparison of the dynamic responses of Gülburnu Highway Bridge using single and triple concave friction pendulums

The main object of this study is to determine and compare the structural behavior of base isolated long span highway bridge, <TEX>$G\ddot{u}lburnu$</TEX> 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.

Effect of vertical component of earthquake on seismic responses of triple concave friction pendulum base-isolated structures

The current investigation has been conducted to examine the effect of the vertical component of earthquake on the responses of base-isolated structures mounted on a triple concave friction pendulum (TCFP) bearing. The varying inherent stiffness and damping of this new generation of friction isolators make smart behavior to mitigate damages during different earthquake hazard levels. To investigate, the structure was idealized as a two-dimensional single story (single degree of freedom) resting on a TCFP isolator and the coupled differential equations of motion were derived and solved using state-space formulation. Based on these equations, a computer program was developed to study the influence of the vertical component of earthquake on the seismic responses of a TCFP isolated structure such as bearing displacement and base shear of the isolated structure. The variation of essential parameters such as superstructure period, isolation period and friction coefficient of sliding bearing surfaces was studied when the TCFP isolated structure was subjected to seven near field earthquake motions. This study demonstrates the significant effects of the vertical component of earthquakes on seismic responses of base-isolated structure mounted on TCFP bearings, which is why the maximum error caused by neglecting the vertical component of earthquake in calculating the base shear of the structure is 29.5%.

Site-response effects on RC buildings isolated by triple concave friction pendulum bearings

The main object of this study is to evaluate the seismic response effects on a reinforced concrete building isolated by triple concave friction pendulum (TCFP) bearings. The site-response effects arise from the difference in the local soil conditions at the support points of the buildings. The local soil conditions are, therefore, considered as soft, medium and firm; separately. The results on the responses of the isolated building are compared with those of the non-isolated. The building model used in the time history analysis, which is a two-dimensional and eight-storey reinforced concrete building with and without the seismic isolation bearings and/or the local soil conditions, is composed of two-dimensional moment resisting frames for superstructure and of plane elements featuring plane-stress for substructure. The TCFP bearings for isolating the building are modelled as of a series arrangement of the three single concave friction pendulum (SCFP) bearings. In order to investigate the efficiency of both the seismic isolation bearings and the site-response effects on the buildings, the time history analyses are elaborately conducted. It is noted that the site-response effects are important for the isolated building constructed on soft, medium or firm type local foundation soil. The results of the analysis demonstrate that the site-response has significant effects on the response values of the structure-seismic isolation-foundation soil system.

Modeling of triple concave friction pendulum bearings for seismic isolation of buildings

Seismic isolated building structures are examined in this study. The triple concave friction pendulum (TCFP) is used as a seismic isolation system which is easy to be manufactured and enduring more than traditional seismic isolation systems. In the TCFP, take advantage of weight which pendulum carrying and it's geometry in order to obtain desirable result of seismic isolation systems. These systems offer advantage to buildings which subject to severe earthquake. This is result of damping force of earthquake by means of their internal constructions, which consists of multiple surfaces. As the combinations of surfaces upon which sliding is occurring change, the stiffness and effective friction change accordingly. Additionally, the mentioned the TCFP is modeled as of a series arrangement of the three single concave friction pendulum (SCFP) bearings. A two dimensional- and eight- story of a building with and without isolation system are used in the time history analysis in order to investigate of the effectiveness of the seismic isolation systems on the buildings. Results are compared with each other to emphasize efficiency of the TCFP as a seismic isolation device against the other friction type isolation system like single and double concave surfaces. The values of the acceleration, floor displacement and isolator displacement obtained from the results by using different types of the isolation bearings are compared each other. As a result, the findings show that the TCFP bearings are more effective devices for isolation of the buildings against severe earthquakes.