Hybrid RNC-isolation of StructuresUnder Near-fault Earthquakes

Mohammed Ismail, Francesc Pozo and Jose Rodellar

Abstract— The problem of combining active damping witha purely passive isolation system, with hysteretic damping,to reduce possible pounding effects under near-fault groundmotions is addressed. The used isolation system is a recentlyproposed one that is referred to as roll in cage (RNC) isolator.It has an integrated buffer mechanism to prevent excessivebearing displacements under strong seismic excitations. There-fore, possible pounding under such strong earthquakes willbe within the bounds of RNC isolator to avoid adjacentstructural pounding. Active control is invoked at a certainbearing displacement to reduce it before reaching its designlimit, after which pounding takes place. It was found thatincreasing the RNC isolator’s inherent hysteretic dampingreduces the bearing displacement and consequently alleviatesor even eliminate pounding. Moreover, the integration of activecontrol, at smaller bearing displacements, with the RNC isolatorcan reduce the bearing displacement but adds more rigidity tothe isolation system, which leads to less efficient isolation.

I. INTRODUCTION

Seismic isolation systems are essentially designed topreserve structural safety, prevent occupants injury andproperties damage. The major concept in base isolation is todiminish the fundamental frequency of structural vibrationto a value lower than the dominant energy frequencies ofearthquake ground motions. However, seismically isolatedstructures are expected to experience large displacementsrelative to the ground especially under near-fault (NF)earthquakes. The NF ground motions are characterized byone or more intense long-period velocity and displacementpulses, which lead to a large isolator displacement [12], [18].Such large displacements are accommodated by providinga sufficient seismic gap around the isolated structure. Insome cases, the width of the provided seismic gap islimited due to practical constraints. Therefore, a reasonableconcern is the possibility of pounding of a seismicallyisolated structures with the surrounding adjacent structuresduring severe seismic excitations such as NF ground motion

M. Ismail is an assistant professor, Structural EngineeringDepartment, Zagazig University, 44519-Zagazig, Egypt. Post-doctoralresearcher, Universitat Politecnica de Catalunya–BarcelonaTECH,EUETIB, C/ Comte d’Urgell 187 08036-Barcelona, Spain.mohammed.ismail@upc.edu

F. Pozo is an associate professor and is with CoDAlab, Departament deMatematica Aplicada III, Escola Universitaria d’Enginyeria TecnicaIndustrial de Barcelona, Universitat Politecnica de Catalunya–BarcelonaTECH, Comte d’Urgell, 187, 08036 Barcelona, Spain.francesc.pozo@upc.edu

J. Rodellar is a professor and is with CoDAlab, Departamentde Matematica Aplicada III, ETSECCPB, Universitat Politecnica deCatalunya–BarcelonaTECH, Jordi Girona 1-3, 08034 Barcelona, Spain.jose.rodellar@upc.edu

This work was supported by the Spanish Ministry of Science andInnovation project (DPI2011-28033-C03-01)

earthquakes.

Compared to the extensive research work on pounding ofconventional buildings and bridges, very limited researchstudies have been carried out for pounding of seismicallyisolated buildings [19]. [23] simulated the superstructureof an isolated building as a continuous shear beam inorder to investigate the effects of pounding on structuralresponse. A very high acceleration response was observedduring pounding with the surrounding retaining wall at theisolation level. Similar work was done by [16] and it wasfound that the base shear forces increase with the stiffnessof the isolated structure or the surrounding retaining wall.Pounding of seismically isolated structures consideringdifferent types of isolation systems was analyticallyinvestigated by [17]. They concluded that pounding effectsare more significant if the isolated superstructure is flexibleor the adjacent structures are stiff. Through parametricanalysis, [14], [13] studied the effects of pounding of aseismically isolated building with the surrounding retainingwall, revealing the damaging effects of structural impact onthe effectiveness of seismic isolation. Considering a slidingisolation system with varying friction, [4] investigatedthe earthquake induced upper story pounding responseof two buildings in close proximity. They concludedthat the impact force is very high when the slidingfriction coefficient is constant, while it becomes quite lowwhen the friction coefficient is allowed to vary with velocity.

The combination of passive base isolators and feedbackcontrollers (applying forces to the base) has been proposedin recent years. Some researchers have proposed activefeedback systems, for instance, [5]–[7]. More recently,semi-active controllers have been proposed in the samesetting with the hope of gaining advantage from their easierimplementation (see, for instance, [6], [22]). It is acceptedthat passive, semi-active and active control systems installedin parallel with base isolation bearings have the potentialof reducing responses of base-isolated structures moresignificantly than classical passive dampers [25], [22].

In this paper, the possibility of pounding and its mitigationof seismically isolated buildings is investigated using arecently proposed isolation system, referred to as roll incage (RNC) isolator [9], [11], [10], under NF groundmotion, see Fig. 1. The RNC isolator provides in a single

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Fig. 2. The integrated buffer mechanism of the RNC isolator

unit all the necessary functions of rigid support, horizontalflexibility with enhanced stability and energy dissipationcharacteristics. It has an integrated buffer mechanismto prevent excessive bearing displacements under strongseismic excitations. This means that pounding would takeplace within the RNC isolator itself, after exceeding acertain predetermined design bearing displacement, underearthquakes stronger than the design earthquake, so thatpounding of the isolated structures itself with the adjacentstructures is avoided. Therefore, the very likely damage dueto structural pounding during strong earthquakes could beminimized or even avoided.

The approach of reducing pounding in this research istwofold: first by investigating the ability of the providedRNC isolator damping, by means of metallic hystereticdampers arranged around the rolling body as seen inFig. 1, to limit the bearing displacement to be withinaffordable limits. Therefore, pounding may not take place.The second is by actively controlling, reducing, the isolatedbase displacement just before attaining the design bearingdisplacement, as demonstrated by Fig. 2. This reduces thepossibility of pounding or at least alleviate the severityof shock within the bounds of the RNC isolator and itsundesirable effects on the isolated superstructure.

II. NEAR-FAULT GROUND MOTIONSNF ground motions are characterized by one or more

intense long-period velocity and displacement pulsesthat can lead to a large isolator displacement [12], [18].Therefore, five NF ground motions of different intensitiesand various velocity and displacement pulses are consideredto assess the performance of the RNC isolator dampingand buffer mechanisms. These NF ground motions wereobtained from the near-most station to the fault rupture,with intensities that range from 0.27g to 1.23g to representsmall to severe intensity earthquakes. The peak ground

accelerations (PGA), velocities (PGV) and displacements(PGD) against their corresponding time instants of eachground motion are listed in Table I. On measuring theintensity of NF ground motions, [15] revealed that thepeak ground acceleration is a better representative intensitymeasure than the peak ground velocity. Accordingly, theused NF ground motions are sorted by their PGA in anascending order.

III. MODELING OF ISOLATED STRUCTURE

The RNC-isolated structure in this paper is a symmetric3D building of 5 bays, each of 8.0 m span, with doubleend cantilevers, each of 2.5 m length, in each horizontaldirection. It has 8 floors plus the isolated base floor witha typical story height of 3.0 m. The base isolated structureis modeled as a shear type supported on 36 heavy-loadRNC isolators, one under each column. Each floor has2 lateral displacement degrees of freedom (DOF) besideone rotational DOF around the vertical axis. However, dueto the symmetry of the 3D structure, only one horizontaldisplacement DOF is considered at each floor and isexcited by a single horizontal component of earthquakeground motion in its direction. The superstructure isconsidered to remain within the elastic limit duringthe earthquake excitation and impact phenomenon. Theconstruction material of the isolated structure is normal-weight reinforced concrete with a total material volume of4068.36 m3 and the structure has a total weight of 10170.90tons. The fixed-base structure has a fundamental periodof 0.436 sec and modal frequencies of 2.29, 6.80, 11.06,14.94, 18.29, 21.02, 23.03 and 24.26 Hz for modes fromone to eight, respectively. The structural damping ratio forall modes is fixed to 2.50% of the critical damping, see Fig.4.

The RNC isolator has three main forms as shown inFig. 1. In this study, the heavy loads form shown in Fig.1(c) is used to safely support the heavy column reactions.The designed RNC isolator for this study is 1.45 m high.The outer diameter of the upper and lower bearing steelplates is 2.73 m. It is provided with 8 hysteretic mildsteel dampers of the shape shown in Fig. 1, each has adiameters of 5.0 cm. This RNC isolator design allows fora horizontal design displacement of 53.0 cm, after whichthe integrated buffer stops the motion through impactwithin the lock mechanism shown in Fig. 2. As shownin Fig. 1(c), the heavy load form of the RNC isolator isprovided with a hollow elastomeric cylinder around therolling body to represent the main load carrying capacity,while the rolling body itself works as a secondary supportin this case. The inner and outer diameters of the hollowelastomeric cylinder are 1.73 m and 2.33 m, respectively.This elastomeric part was initially designed to followsome available recommendations of the Uniform BuildingCode [1] and AASHTO [2]. At the end, the designed RNC

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Fig. 1. The available forms of the RNC isolator

TABLE IMAIN CHARACTERISTICS OF THE NF GROUND MOTIONS USED IN THIS STUDY.

Earthquake Station Magn- Distance Peak Accel.a Peak Vel.b Peak Disp.c

No. name Year name itude to fault PGA time PGV time PGD time

1 Kocaeli, Turkey 60° 1999 Yarimca 7.51 4.80 km 0.27 13.84 67.0 13.57 58.2 14.752 Imperial Valley 230° 1979 El Centro Ar. #7 6.53 0.60 km 0.46 5.00 111.4 5.94 45.6 6.853 Kobe, Japan 0° 1995 Takarazuka 6.90 0.30 km 0.69 6.02 69.9 6.58 27.2 6.024 Northridge 18° 1994 Sylmar - Conv. SE 6.69 5.20 km 0.83 3.51 119.8 3.44 35.1 3.025 San Fernando 164° 1971 Pacoima Dam 6.61 1.80 km 1.23 7.76 114.7 3.07 36.1 7.81

a Units: g - secb Units: cm/sec - secc Units: cm - sec

isolator for this study can support up to 4000.0 kN vertically.

IV. INFLUENCE OF RNC ISOLATOR’SHYSTERETIC DAMPING

The RNC isolator is provided with a set of triple-curvaturemetallic yield dampers as shown in Fig. 1, which render thedevice a hysteretic behavior [11], [10]. Such curvatures aredesigned to allow for smooth extension and contraction ofdampers during motion, provide adequate length of dampersto allow unrestrained rolling motion of the rolling body upto the buffer and to reduce or avoid stress concentrationsat bends in order to increase the dampers working life.Three structures were employed in the parametric studyperformed in this section: the one described in Section III;the same structure but one time is 25% lighter in weightand the other time is 25% heavier. This to investigatethe influence of the isolated structural weight on bearingdisplacement and pounding intensity. On the other hand,to investigate the influence of the provided amount ofhysteretic damping by the RNC isolator on the bearing

displacement and consequently on pounding, four designsof the RNC isolator of the form mentioned in Section IIIare considered. These isolator designs provide differentamount of hysteretic damping that, relatively, ranges fromlow to high damping and referred to as RNC-1, RNC-2,RNC-3 and RNC-4, respectively. Then, all the RNC-isolatedstructures were subjected to the five earthquakes of SectionII, one at a time, and the resulting bearing displacementsas well as the pounding forces are displayed in Fig. 3.Each earthquake is referred to by its serial number foundin the first column from left of Table I. All the responsequantities in this section were obtained by simulating theRNC-isolated structures using the structural finite elementsoftware SAP2000 [3]. The RNC isolator was modeledby activating the Plastic-Wen hysteretic element, wherethe buffer mechanism was represented by a nonlinearGap element. The structure floors were modeled as rigidhorizontal diaphragms while the columns were modeledwith zero axial deformation and the structural mass islumped at floor levels.

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Fig. 3. Effect of structural weight and hysteretic damping on bearing displacement and pounding intensity

The bearing displacements of RNC isolators RNC-1and RNC-2 are displayed in Figs. 3(a,b), respectively. Thecorresponding pounding forces are shown in Figs. 3(c,d),respectively. It seems evident that increasing the isolatorhysteretic damping decreases the bearing displacement. Insome cases, pounding is avoided as the bearing displacementbecame lower than the design displacement. In other cases,where the bearing displacement is still higher than thedesign one, increasing damping alleviated the poundingintensity. Fig. 3 also demonstrates that pounding is alwaysmore intense in the case of isolated heavy structures,even if they exhibit closer bearing displacements to thoseof isolated lighter structures. Moreover, the poundingintensity is directly proportional to the amount of extrabase displacement beyond the bearing design displacementand the heavier isolated structures are less responsive toincreasing the isolator hysteretic damping than lighterisolated structures.

NF ground motions are rich in long period frequencies.This can lead to resonance conditions with seismicallyisolated structures of long fundamental periods causingundesirable higher bearing displacements. Such resonanceseems obvious in this study under the first two earthquakes,particularly, using RNC-1 and RNC-2 isolators. Althoughthe Kocaeli and the Imperial Valley earthquakes have thelowest PGA in Table I, the resulting bearing displacementsare the highest, even are higher than those produced by SanFernando earthquake, which has the highest PGA amongthe used earthquakes. This is mainly attributed to the closestructural and loading, dominant, frequencies.

Based on the above results, adding more hysteresis damp-ing to the RNC isolator improves the behavior of the isolatedstructures in terms of reducing the bearing displacementsand the resulting pounding intensity, if there is any. But,practically, this solution should not obstruct the isolatoritself to achieve efficient isolation regarding reducing thepeak absolute structural accelerations. To investigate that,the corresponding peak absolute structural accelerations ofthe case study shown in Fig. 3 were obtained and listed inTable II. The performance measure is taken as the reductionpercentage of acceleration responses. This percentage (%) isexpressed as:

% =(xfixed−base)− (xRNC−isolated)

(xfixed−base)× 100 (1)

where xfixed−base is the peak acceleration of fixed-basestructure and xRNC−isolated is the peak acceleration of RNC-isolated structure. The negative values of % in Table IIindicates the undesired negative effect of pounding on struc-tural accelerations. From this table, the following conclusionscould be drawn:

• Increasing the isolator hysteretic damping slightly re-duces the peak accelerations of the isolated structure.

• Intense pounding of an isolated structure results instructural accelerations higher than those of its fixedbase case. This becomes more obvious in structures withrelatively light weight.

• Increasing the isolator hysteretic damping can remark-ably attenuate the undesirable increase of the structuralaccelerations due to pounding.

• The RNC isolator can achieve high levels of structuralaccelerations reduction, especially under severe groundmotions.

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TABLE IIPEAK ABSOLUTE STRUCTURAL ACCELERATIONS USING DIFFERENT RNC ISOLATORS WITH AND WITHOUT BUFFER MECHANISMS. M/SEC2 UNITS

25% lighter structure

RNC-1 RNC-2 RNC-3 RNC-4

Earthquake Fixed No With No With No With No Withnumber base buffer % buffer % buffer % buffer % buffer % buffer % buffer % buffer %

1 7.35 0.890 88% 15.883 -116% 1.095 85% 1.095 85% 1.487 80% 1.487 80% 1.946 74% 1.946 74%2 9.50 1.129 88% 22.698 -139% 1.534 84% 11.442 -20% 1.790 81% 1.790 81% 2.351 75% 2.351 75%3 19.91 1.028 95% 1.028 95% 1.684 92% 1.684 92% 1.912 90% 1.912 90% 2.334 88% 2.334 88%4 28.77 0.711 98% 5.028 83% 1.282 96% 1.282 96% 1.590 94% 1.590 94% 2.078 93% 2.078 93%5 53.01 1.092 98% 1.092 98% 1.693 97% 1.693 97% 1.808 97% 1.808 97% 2.246 96% 2.246 96%

Normal weight structure

1 11.35 0.616 95% 14.538 -28% 0.988 91% 4.209 63% 1.176 90% 1.176 90% 1.508 87% 1.508 87%2 15.15 0.924 94% 22.809 -51% 1.329 91% 16.814 -11% 1.495 90% 8.783 42% 1.745 88% 1.745 88%3 24.66 1.064 96% 1.064 96% 1.498 94% 1.498 94% 1.521 94% 1.521 94% 1.741 93% 1.741 93%4 21.55 0.654 97% 9.104 58% 0.996 95% 0.996 95% 1.285 94% 1.285 94% 1.664 92% 1.664 92%5 44.26 0.728 98% 0.728 98% 1.265 97% 1.265 97% 1.530 97% 1.530 97% 2.000 95% 2.000 95%

25% heavier structure

1 10.51 0.486 95% 14.652 -39% 0.847 92% 10.994 -5% 1.057 90% 3.067 71% 1.287 88% 1.287 88%2 13.32 0.746 94% 22.773 -71% 1.206 91% 19.280 -45% 1.355 90% 12.683 5% 1.525 89% 7.324 45%3 27.89 0.696 98% 0.696 98% 1.207 96% 1.207 96% 1.288 95% 1.288 95% 1.525 95% 1.525 95%4 19.56 0.566 97% 10.414 47% 0.958 95% 1.769 91% 1.104 94% 1.104 94% 1.375 93% 1.375 93%5 34.22 0.680 98% 0.680 98% 1.154 97% 3.445 90% 1.230 96% 1.230 96% 1.639 95% 1.639 95%

• Where there is no pounding, isolation of light-weightstructures is less efficient under low-intensity earth-quakes compared to heavier structures under the sameearthquakes. This isolation efficiency becomes higherunder stronger earthquakes showing similar behavior tothat of heavier structures under such strong earthquakes.

V. HYBRID RNC-ISOLATION

In this section, the RNC isolator is allowed to behave asa purely passive isolation system, with hysteretic damping,within a particular range of the design bearing displacementas denoted in Fig. 2 by ∆p. Then active control force isapplied over ∆h, after which pounding will take place.The purpose of active control is to reduce the bearingdisplacement to avoid or even reduce pounding intensity,see Fig. 2.

A. Modeling of RNC-isolated structure with active damping

The equations of motion of an N -story linear shear typesuperstructure subjected to earthquake excitation is writtenin the matrix form as:

Msxs + Csxs + Ksxs = −Ms{1}(xb + xg) (2)

where Ms, Ks, and Cs are the N × N mass, stiffnessand damping matrices of the superstructure, respectively;xs = {x1, x2, . . . , xN}T is the relative displacement vectorof the superstructure; xs and xs are the relative velocity andacceleration vectors, respectively; xj(j = 1, 2, . . . , N) isthe lateral displacement of the jth floor relative to the basemass; {1} = {1, 1, 1, . . . , 1}T is the influence coefficientvector; xb is the relative acceleration of the base mass; andxg is the earthquake ground acceleration.

The governing equation of motion of the base mass isgiven by

mbxb + ηFb − c1x1 − k1x1 = −mbxg + u (3)

where mb is the suspended mass of the base raft; c1 and k1

are the damping and stiffness of the first story, respectively;η is the total number of RNC isolators; Fb is the restoringforce transmitted to the suspended base mass by a singleRNC isolator and u is the active control force.

The RNC isolator restoring force is represented by thestandard Bouc-Wen model [24], [8] as:

Fb(t) = αkx(t) + (1− α)Dy kz(t) (4)

z = D−1y (Ax− β|x||z|n−1z − γx|z|n) (5)

where x is the displacement, z is an auxiliary variable,Fb is the isolator restoring force, αkx is the elastic forcecomponent, z denotes the time derivative, n > 1 is aparameter that governs the smoothness of the transitionfrom elastic to plastic response, Dy > 0 is the yield constantdisplacement, k > 0 and 0 < α < 1 represents the post topre-yielding stiffness ratio (kb/ke), while A, β and γ arenon-dimensional parameters that govern the shape and sizeof the hysteresis loop.

B. Controler design

Two active control laws are considered in this study. Thefirst is a simple static discontinuous active bang-bang typecontrol, which was developed using only the measurementof velocity of the suspended base floor of an isolatedstructure as a feedback information [21]. The control forceis expressed as:

u = −ρ sign(xb) (6)

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where ρ is a design parameter and xb is the velocity of thesuspended base floor of the isolated structure.

The second controller is based on using a passive statichyperbolic function depending only on the base floor velocity[20]. This function ensures energy dissipation capability withalways bounded control force. The control law is:

u = −ρ sech

(xb

a

)tanh

(xb

a

)(7)

where ρ > 0 and a > 0 are design parameters.

C. Parametric study

Using the RNC isolator, the expected pounding will takeplace within the isolator components when the displacementof the suspended base floor reaches the end of the bearingdesign displacement with considerable amount of kineticenergy. The undesirable pounding effects are then reflectedfirst on the suspended base floor, as the first structural partconnected to the RNC isolator, then spread through theisolated structure. Active damping is studied in this sectionas a possible mean of reducing the base floor velocityto reduce its kinetic energy and consequently to alleviatepounding intensity. Therefore, the value of controlled basevelocity is considered as a measure of both the poundingintensity and the efficiency of control laws in this section.

The three isolated structures of Section IV were studiedin this section along with only the RNC-1 isolator underearthquake 1. Active control force was applied over thewhole range of the bearing design displacement, that is[1 cm – 53 cm], with an increment of 1 cm. This is tocheck weather there is an optimum distance for applyingthe control force or not before the RNC isolator reachesthe end of its design displacement. The resulting bearingdisplacements are plotted in Fig. 5. This figure shows thatthe active control can reduce the bearing displacementespecially when applied at smaller values of ∆p and theheavier isolated structure is less responsive to active controlforce than lighter ones.

To investigate the influence of combining active controlwith the purely passive RNC isolator to reduces bearingdisplacement on the isolation efficiency, different values ofactive control force, using the first control law (6), wereapplied at three different values of ∆p/∆ of 20%, 50%and 80%. The corresponding response quantities are foundand listed in Table III under earthquake 1 using the threeexample structures. The main conclusion that can be drawnfrom that table is that the hybrid seismic isolation is moreeffective if the active control forces are applied at smallervalues of the ratio ∆p/∆ to avoid pounding. The resultingstructural absolute accelerations are higher than those ofpurely passively isolated structures, which means that hybrid

Fig. 4. Idealized RNC-isolated structural model with control devices

isolation adds more rigidity to the isolated structure. Thisdecreases the structure-ground decoupling and consequentlyleads to less effective isolation. Moreover, the lighter theisolated structure the lower the control force and the moreefficient the hybrid isolation. However, in all cases, thehybrid isolation provides higher structural accelerations thanthe purely passive isolation.

VI. CONCLUSIONS

In this paper, a recently proposed isolation system withhysteretic damping was used to study pounding mitigationunder near-fault earthquakes. This isolation system is re-ferred to as roll in cage (RNC) isolator. It has an integratedbuffer mechanism to prevent excessive bearing displacementsunder strong seismic excitations. Since the pounding dependson the bearing displacement and the isolated base velocity,the influence of increasing the isolator’s hysteretic dampingand applying active damping on the bearing displacementand the base floor velocity, respectively, was studied with theaim of pounding mitigation or even its avoidance. Based onthe performed study, the following conclusions were drawn:

1) Increasing the isolator hysteretic damping decreases thebearing displacement and consequently alleviates thepounding intensity.

2) The heavy-weight isolated structures are less responsiveto increasing the isolator hysteretic damping than thelight-weight ones.

3) Pounding is always more intense in the case of isolatedheavy structures, even if they exhibit closer bearingdisplacements to those of isolated lighter structures.

4) Pounding intensity is directly proportional to the amountof extra base displacement beyond the bearing designdisplacement.

5) Increasing the isolator hysteretic damping slightly re-duces the peak accelerations of the isolated structure.

6) Intense pounding of an isolated structure results instructural accelerations higher than those of its fixedbase case. This becomes more obvious in structures withrelatively light weight.

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Fig. 5. Peak actively controlled bearing displacements under earthquakes1 using control laws 1 and 2

7) Increasing the isolator hysteretic damping can remark-ably attenuate the undesirable increase of the structuralaccelerations due to pounding.

8) The RNC isolator can achieve high levels of structuralaccelerations reduction, especially under severe groundmotions.

9) Where there is no pounding, isolation of light-weightstructures is less efficient under low-intensity earth-quakes compared to heavier structures under the sameearthquakes. This isolation efficiency becomes higherunder stronger earthquakes showing similar behavior tothat of heavier structures under such strong earthquakes.

10) Hybrid isolation can reduce the bearing displacementto avoid pounding, particularly when the active controlforces are applied at smaller values of the ratio ∆p/∆.

11) Lighter isolated structures are more responsive to hybridisolation using less control forces compared to theisolated heavier structures.

12) Hybrid control renders the isolation system more rigid-ity, which leads to less efficient isolation in terms ofhigher structural peak absolute accelerations comparedto purely passive isolation system.

VII. REFERENCES

REFERENCES

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[3] SAP2000 release 15.0 documentation. Computers and Structures, Inc.,1995 University Ave, Berkeley CA 94704, 2011.

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[7] J. Inaudi, F. Lopez-Almansa, J.M. Kelly, and J. Rodellar. Predictivecontrol of base isolated structures. Earthquake Engineering andStructural Dynamics, 21(6):471–482, 1992.

[8] M. Ismail, F. Ikhouane, and J. Rodellar. The hysteresis Bouc-Wenmodel, a survey. Journal of Archives of Computational Methods inEngineering, 16:161–188, 2009.

[9] M. Ismail, J. Rodellar, and F. Ikhouane. A Seismic Isolation System forSupported Objects. Spanish Patent No. P200802043, Spanish Officeof Patents and Marks, 2008.

[10] M. Ismail, J. Rodellar, and F. Ikhouane. A novel isolation bearingfor light- to moderate-weight structures. Journal of Structural Controland Health Monitoring, 2009. DOI: 10.1002/stc.421.

[11] M. Ismail, J. Rodellar, and F. Ikhouane. An innovative isolation devicefor aseismic design. Journal of Engineering Structures, 32:1168–1183,2010.

[12] R.S. Jangid and J.M. Kelly. Base isolation for near-fault motions.Earthquake Engineering and Structural Dynamics, 30:691–707, 2001.

[13] P. Komodromos. Simulation of the earthquake-induced pounding ofseismically isolated buildings. Computers & Structures, 86:618–626,2008.

[14] P. Komodromos, P.C. Polycarpou, L. Papaloizou, and M.C. Phocas.Response of seismically isolated buildings considering poundings.Earthquake Engineering and Structural Dynamics, 36:1605–1622,2007.

[15] N. Makris and C.J. Black. Evaluation of peak ground velocity as agood intensity measure for near-source ground motions. EngineeringMechanics (ASCE), 130(9):1032–1044, 2004.

[16] P.K. Malhotra. Dynamics of seismic impacts in base-isolated buildings.Earthquake Engineering and Structural Dynamics, 26:797–813, 1997.

[17] V.A. Matsagar and R.S. Jangid. Seismic response of base-isolatedstructures during impact with adjacent structures. Engineering Struc-tures, 25:1311–1323, 2003.

[18] D. Murat and B. Srikanth. Equivalent linear analysis of seismic-isolated bridges subjected to near-fault ground motions with forwardrupture directivity effect. Engineering Structures, 29:21–32, 2007.

[19] P.C. Polycarpou and P. Komodromos. Earthquake-induced poundingsof a seismically isolated building with adjacent structures. EngineeringStructures, 32:1937–1951, 2010.

[20] F. Pozo, L. Acho, and J. Rodellar. Hyperbolic control for vibrationmitigation of a base-isolated benchmark structure. Structural Controland Health Monitoring, 16:766–783, 2009.

[21] F. Pozo, P.M. Montserrat, J. Rodellar, and L. Acho. Robust activecontrol of hysteretic base-isolated structures: Application to the bench-mark smart base-isolated building. Structural Control and HealthMonitoring, 15:720–736, 2008.

[22] J.C. Ramallo, E.A. Johnson, and B.F. Spencer. Smart base isolationsystems. Journal of Engineering Mechanics, 128:1088–1100, 2002.

[23] H.C. Tsai. Dynamic analysis of base-isolated shear beams bumpingagainst stops. Earthquake Engineering and Structural Dynamics,26:515–528, 1997.

[24] Y.K. Wen. Method for random vibration of hysteretic systems. Journalof the Engineering Mechanics Division, 102(EM2):246–263, April1976.

[25] J.N. Yang and A.K. Agrawal. Semi-active hybrid control systemsfor nonlinear buildings against near-field earthquakes. EngineeringStructures, 24(3):271–280, 2002.

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ding

Bas

eA

ccel

erat

ion

(iso

late

d)A

ccel

.

forc

efo

rce

disp

.N

obu

ffer

Buf

fer

(fixe

db.

)fo

rce

forc

edi

sp.

No

buff

erB

uffe

r(fi

xed

b.)

forc

efo

rce

disp

.N

obu

ffer

Buf

fer

(fixe

db.

)

220.

917

7.5

0.54

85.

860.

897.

3524

8.7

735.

00.

604

10.5

40.

6211

.35

266.

110

83.0

0.63

811

.89

0.49

10.5

134

2.7

0.0

0.44

93.

450.

897.

3544

9.0

249.

60.

555

8.80

0.62

11.3

548

6.5

625.

20.

593

9.99

0.49

10.5

139

6.4

0.0

0.23

84.

360.

897.

3555

2.2

0.0

0.29

04.

900.

6211

.35

770.

60.

00.

491

4.79

0.49

10.5

141

2.6

0.0

0.31

24.

270.

897.

3559

8.5

0.0

0.25

65.

380.

6211

.35

779.

10.

00.

366

4.58

0.49

10.5

145

9.9

0.0

0.22

14.

860.

897.

3560

1.7

0.0

0.40

74.

580.

6211

.35

774.

40.

00.

230

5.20

0.49

10.5

152

6.9

0.0

0.21

15.

250.

897.

3567

1.3

0.0

0.24

05.

670.

6211

.35

812.

40.

00.

269

5.42

0.49

10.5

158

3.6

0.0

0.20

36.

170.

897.

3573

0.5

0.0

0.22

86.

190.

6211

.35

857.

70.

00.

249

5.94

0.49

10.5

163

0.5

0.0

0.19

67.

300.

897.

3577

7.3

0.0

0.21

76.

460.

6211

.35

909.

70.

00.

236

6.50

0.49

10.5

166

9.2

0.0

0.19

08.

430.

897.

3581

4.3

0.0

0.20

86.

860.

6211

.35

950.

30.

00.

225

7.03

0.49

10.5

170

1.9

0.0

0.18

49.

430.

897.

3584

3.5

0.0

0.20

09.

080.

6211

.35

981.

80.

00.

215

7.33

0.49

10.5

172

9.4

0.0

0.17

910

.33

0.89

7.35

867.

30.

00.

193

9.69

0.62

11.3

510

06.0

0.0

0.20

77.

490.

4910

.51

∆p/∆

=50%

,Ear

thqu

ake

1∆

p/∆

=50%

,Ear

thqu

ake

1∆

p/∆

=50%

,Ear

thqu

ake

1

160.

856

6.3

0.58

710

.91

0.89

7.35

185.

410

58.0

0.63

614

.14

0.62

11.3

520

6.4

1478

.00.

678

16.9

60.

4910

.51

287.

322

3.0

0.55

28.

700.

897.

3532

5.2

602.

00.

5910

.74

0.62

11.3

536

7.3

1023

.00.

632

14.9

40.

4910

.51

424.

40.

00.

477

5.09

0.89

7.35

543.

467

.00.

537

5.59

0.62

11.3

562

9.2

496.

00.

580

9.34

0.49

10.5

155

1.2

0.0

0.44

96.

420.

897.

3564

8.4

0.0

0.48

15.

750.

6211

.35

845.

816

9.3

0.54

79.

170.

4910

.51

635.

90.

00.

424

8.04

0.89

7.35

794.

50.

00.

464

6.30

0.62

11.3

510

67.0

16.9

0.53

28.

350.

4910

.51

710.

10.

00.

407

8.96

0.89

7.35

912.

00.

00.

447

7.87

0.62

11.3

512

19.0

0.0

0.50

99.

550.

4910

.51

774.

40.

00.

391

9.70

0.89

7.35

1010

.00.

00.

433

9.14

0.62

11.3

513

49.0

0.0

0.49

010

.69

0.49

10.5

182

7.4

0.0

0.38

310

.30

0.89

7.35

1090

.00.

00.

421

11.1

90.

6211

.35

1463

.00.

00.

474

11.3

00.

4910

.51

870.

50.

00.

374

10.9

50.

897.

3511

54.0

0.0

0.40

913

.26

0.62

11.3

515

62.0

0.0

0.46

011

.42

0.49

10.5

190

6.0

0.0

0.36

611

.83

0.89

7.35

1205

.00.

00.

399

14.9

20.

6211

.35

1641

.00.

00.

447

11.2

60.

4910

.51

935.

70.

00.

359

13.1

40.

897.

3512

47.0

0.0

0.39

016

.29

0.62

11.3

516

98.0

0.0

0.43

511

.01

0.49

10.5

1

∆p/∆

=80%

,Ear

thqu

ake

1∆

p/∆

=80%

,Ear

thqu

ake

1∆

p/∆

=80%

,Ear

thqu

ake

1

94.3

826.

20.

613

14.5

70.

897.

3511

6.6

1273

.00.

657

14.3

40.

6211

.35

127.

514

91.0

0.67

916

.85

0.49

10.5

117

5.2

692.

10.

599

12.7

20.

897.

3521

8.1

1121

.00.

642

14.0

80.

6211

.35

272.

116

61.0

0.69

616

.76

0.49

10.5

131

5.2

515.

90.

582

12.1

70.

897.

3538

6.4

872.

10.

617

13.5

0.62

11.3

549

0.8

1394

.00.

669

16.5

60.

4910

.51

433.

738

5.6

0.56

912

.35

0.89

7.35

515.

465

8.0

0.59

611

.76

0.62

11.3

564

9.6

1105

.00.

641

16.4

80.

4910

.51

542.

129

5.2

0.56

011

.64

0.89

7.35

629.

551

3.7

0.58

111

.05

0.62

11.3

577

9.2

887.

90.

619

13.3

30.

4910

.51

632.

320

4.5

0.55

110

.76

0.89

7.35

740.

942

1.9

0.57

29.

880.

6211

.35

898.

673

7.2

0.60

412

.31

0.49

10.5

170

0.8

108.

10.

541

10.0

20.

897.

3584

1.6

342.

70.

564

9.05

0.62

11.3

599

4.7

597.

90.

590

11.5

60.

4910

.51

747.

88.

30.

531

7.64

0.89

7.35

929.

726

8.2

0.55

710

.18

0.62

11.3

510

74.0

475.

00.

578

10.5

60.

4910

.51

774.

40

0.52

18.

430.

897.

3510

07.0

198.

10.

5510

.88

0.62

11.3

511

44.0

370.

20.

567

9.73

0.49

10.5

180

1.1

00.

513

9.63

0.89

7.35

1074

.013

3.2

0.54

311

.40.

6211

.35

1204

.027

8.2

0.55

810

.59

0.49

10.5

182

7.8

00.

507

11.0

00.

897.

3511

32.0

72.1

0.53

711

.24

0.62

11.3

512

57.0

197.

30.

550

12.4

20.

4910

.51

6139