Effect Of Combined Isolation System On Low-Rise …Effect Of Combined Isolation System On Low-Rise RC Structure Paper ID IJIFR/ V3/ E2/ 051 Page No. 538-550 Subject Area Civil Engineering

538

Available online through - http://ijifr.com/searchjournal.aspx Accepted After Review On: October 25, 2015

Published On: October 27, 2015

International Journal of Informative & Futuristic Research

ISSN: 2347-1697 Volume 3 Issue 2 October 2015

Abstract

Hospital buildings are of great importance after any natural calamity such as earthquake. The structural and non-structural components should remain operational and safe after earthquake. So to mitigate the effects of earthquake on the structure the base isolation technique is the best alternative as a seismic protective system. The basic idea of base isolation system is to reduce the earthquake induced inertia forces by increasing the fundamental period of the structure. The aim of this study is the use of High Density Rubber Bearing (HDRB) and Friction Pendulum System (FPS) as an isolation device and then to compare various parameters between fixed base condition and base isolated condition by using SAP2000v14 software. In the present paper 6-storey hospital structure is used as a test model. Nonlinear time history analyses were carried out for both fixed base and base isolated structure by considering international El-Centro earthquake ground motion record. In the second part of this study, response of combined isolation system or mixed isolation system has been presented on same structure by considering various combinations. This paper is intended to give an insight on the seismic performance of seismically isolated buildings using a combination of base isolation devices. This paper also intends to answer the questions that, what is the performance expected from the use of more than one device. If the combination of different systems gives a good level of seismic performance, so which is the better combination to achieve the best performance is presented here. Finally, parameters such as storey displacement, storey drift, storey acceleration and base shear are compared and obtained results were presented by graphically.

Effect Of Combined Isolation System

On Low-Rise RC Structure Paper ID IJIFR/ V3/ E2/ 051 Page No. 538-550 Subject Area Civil Engineering

Key Words Base Isolation, HDRB, FPS, Non-linear Analysis, SAP2000V14

1st T. R. Wankhade

Assistant Professor,

Department Of Civil Engineering

Prof. Ram Meghe Institute of Technology & Research

Badnera, Amravati-Maharashtra (India)

2nd

A. R. Wankhade

Assistant Engineer-II,

Water Resources Department

Maharasthra (India)

539

ISSN: 2347-1697 International Journal of Informative & Futuristic Research (IJIFR)

Volume - 3, Issue -2, October 2015 Continuous 26th Edition, Page No.:538-550

T. R. Wankhade, A. R. Wankhade:: Effect Of Combined Isolation System On Low-Rise RC Structure

1. Introduction

Earthquake occurrence is still remaining a mystery and is unpredictable. The traditional method of

providing earthquake resistance to a structure is by increasing its strength as well as energy

absorbing capacity. The basic need is to save the structure from earthquake ground motion and keep

it to minimum hazard level. As the base isolation technique reduces the response of structure hence

there is a need to find out the effect of different types of base isolators on the response of structure.

Work has been done earlier by using one type base isolator on the low rise, mid-rise to high rise

structure but very less work has been done on the combined effect of isolation on same structure.

Hence, there is a need to find out the response of above mentioned structures by taking various

combinations of two different types of base isolators on same structure rather than using only one

type of isolator [1]. Generally, two categories of isolation system used widely. The first category

includes the family of elastomeric bearings, in which we find the high damping rubber bearing

system (HDRB) [2], the lead rubber bearing system (LRBs) and other systems. The second

category includes the family of sliding bearings, in which we found the friction pendulum system

(FPS) [3]. In this paper, we studied the seismic performance of the two rarely used isolation devices

i.e. HDRB and FPS and then the study further continued to investigate the seismic performance of

combined isolation system on symmetric structure for every combination taken and get some

conclusions from the whole study which is presented graphically at every stage.

The main objectives of the present study are:

i. To check the response of High Density Rubber Bearings (HDRB) base isolator on low rise

structure

ii. To check the response of Friction Pendulum System (FPS) base isolator on low rise

structure

iii. To make a comparison of High Density Rubber Bearing and Friction Pendulum System

isolation systems with the fixed base structures[4]

iv. To check the response of the structure by taking the various combinations of High Density

Rubber Bearing (HDRB) and Friction Pendulum System (FPS) based on the location of

columns, on low rise structure

v. To study the parameters such as time period, storey drift, storey acceleration, base shear

and the storey displacement of fixed base and base isolated structures

2. Modeling Of 3D Regular Building

The (G+5) storey RCC modeled structures is considered for analysis. Building has plan dimensions

of 36m x 12m as shown in figure 2.1. Slab is modeled as a rigid diaphragm. Building is symmetric

with respect to stiffness and mass. Nonlinear time history analysis is carried out in SAP2000

software [9] using El-Centro Earthquake record. The plan of buildings is depicted in figure 2.1. The

structural details for the above G+5 structure are tabulated in table 2.1. The elevation of 6-storey

building in both X and Y directions are shown in figure 2.2. The present work was divided into two

parts:

i.) Comparative study of only one type isolation system

ii.) Comparative study of combined isolation systems

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Figure 2.1: Plan Of RCC Building

Figure 2.2: Elevation of 6-storey structure in x-direction and y-direction

Table 2.1: Numerical Data For Modeld Structure

Sr. No. Storey (G+5) Data

1 Plan Dimension 36 m x12 m

2 Height of Storey 3 m

3 Plinth Height 1 m

4 Sizes of Beam 0.23 m × 0.3 m

5 Sizes of Column 0.3 m × 0.45 m

6 Thickness of Slab 0.15 m

7 Thickness of External Wall 0.23m

8 Thickness of Internal Wall 0.15 m

9 Live Load at Floor 3 KN/m2

10 Grade of Concrete M 40

11 Grade of Steel Fe 415

12 Density of Concrete 25 KN/m3

13 Density of Brick Masonry 20 N/m3

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3. Performance Of Various Base Isolation Systems

3.1 Comparative Study of Isolation Systems

To access the performance of low-rise reinforced concrete structure with different

arrangement of base isolators at the base of structure such as Fixed Based, High Density Rubber

Bearings (HDRB) and Friction Pendulum System (FPS) type. For this study, structure is analyzed

with the help of SAP2000v14 software. And results were compared on key parameters like base

shear, storey displacement, storey drift and storey acceleration. For this part of study we used the

HDRBs as the only device (let’s call it BI-HDRBs) and then use only the FPS (let’s call it BI-FPS).

Figure 3.1.1 shows the modeled fixed base structure (FB) and the isolation devices designed for it

using the UBC-97 (UBC, 1997) [10] and IBC2000 requirements.

In this section total 3 analysis was done for 6-storey structure using BI-HDRB & BI-FPS

isolators by El-Centro earthquake ground motion data. All the analysis was done by nonlinear time

history analysis. Type of analysis for all the structures is modal nonlinear time history analysis

considering international El-Centro ground motion data. International ground motion data for

El-centro is the 1940 North South component also known as peknold version having 1559

acceleration data points at 0.02 sec. The PGA value for El-centro earthquake is 0.33g. In this

section comparative results are presented fixed base model what we call it FB, then for BI-HDRB

and at last BI-FPS.

Figure 3.1.1: fixed base 6-storey structure

Time Period:

Table 3.1 shows the comparison of time period for all three cases i.e. fixed base, for HDRB

and for FPS isolation system and it is seen that time period in both X and Y directions increased by

the use of base isolator over the conventional fixed base structure. But, friction pendulum system

lengthens the time period at greater extent compared to High Density Rubber Bearing.

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Table 3.1: time period for 6-storey structure

TIME PERIOD FIXED BASE FPS HDRB

X-Direction 1.37 sec 3.21 sec 2.61 sec

Y-Direction 1.32 sec 3.20 sec 2.61 sec

Base Shear:

From figure 3.1.2 it is seen that the base shear in X-direction is reduced by 92 %

and in Y-direction it is reduced by 70 % for the case of Friction Pendulum System when

compared with fixed base. The base shear in X-direction is reduced by 67 % and in

Y-direction it is reduced by 65 % for the case of High Density Rubber Bearing when

compared with fixed base.

Figure 3.1.2: base shear in x & y direction

Storey Displacement:

From figure 3.1.3 & figure 3.1.4, it is seen that maximum base displacement given by

friction pendulum system isolators compared to the high density rubber bearing type

isolator in both X and Y direction. Figures 3.1.3 & 3.1.4 also show, in both BI-HDRB &

BI-FPS cases the base displacement is much greater when compared to FB case.

Figure 3.1.3: storey displacement in x-direction

X Y

Fixed base 5172 4937

FPS 402 1450

HDRB 1716 1713

Base

Sh

ear

(kN

)

Fixed base

FPS

HDRB

Sto

rey

Lev

el

Storey Displacement (m)

Fixed base

FPS

HDRB

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Figure 3.1.4: storey displacement in y-direction

Storey Drift

From figure 3.1.5 it is seen that storey drift was greatly reduces by friction

pendulum type isolators (BI-FPS) compared with high density rubber bearing (BI-HDRB).

Both types of isolators reduce drift at greater extent compared with fixed base (FB)

structure. Same conclusion was made from figure 3.1.6

Figure 3.1.5: storey drifts in x-direction

Figure 3.1.6: storey drifts in y-direction

0

1

2

3

4

5

6

7

0 0.05 0.1 0.15 0.2 0.25

Fixed base FPS HDRB

0

1

2

3

4

5

6

7

0 0.002 0.004 0.006 0.008 0.01

Fixed base FPS HDRB

0

1

2

3

4

5

6

7

0 0.002 0.004 0.006 0.008 0.01 0.012

Fixed base FPS HDRB

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Storey Acceleration

From figure 3.1.7 it is seen that storey acceleration was greatly reduces by the use of

friction pendulum type isolators compared with high density rubber bearing isolator. Both

types of isolators reduces storey acceleration at greater extent compared with fixed base

structure. Same conclusion was made from figure 3.1.8.

Figure 3.1.7: storey acceleration in x-direction

Figure 3.1.8: storey acceleration in y-direction

3.2 Comparative Study of Combined Isolation Systems

For this study the above 6-story reinforced concrete structures is analyzed for different

combinations using two types of base isolators i.e. High Density Rubber Bearings (HDRB) and

Friction Pendulum System (FPS) on same structure. All the different combinations are shown in

figure 3.2.1. And based on these results comparative study is carried out to compare various

parameters such as base shear, storey displacement, storey drift and storey acceleration for all the

thirteen combinations.

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6

Fixed base FPS HDRB

0

1

2

3

4

5

6

7

0 1 2 3 4 5

Fixed base FPS HDRB

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In this section total 13 analyses was done for 6-storey structure by taking various

combinations (Model-0 to Model-12) as shown in figure 3.2.1. All the analysis was done by

nonlinear time history analysis. Type of analysis for all the structures is modal nonlinear time

history analysis considering international El-Centro. International ground motion data for El-centro

is the 1940 North South component also known as peknold version having 1559 acceleration data

points at 0.02 sec time interval. The PGA value for El-centro earthquake is 0.33g. In this section

comparative results are presented for fixed base model (Model-0), BI-FPS (Model-1), BI-HDRB

(Model-2) and rest of the 10 different combinations (Model-3 to Model-12) as shown in figure 3.2.1

Figure 3.2.1: plans of different combinations of isolators

Base Shear:

From figure 3.2.2 and figure 3.2.3 it is observed that all the 12 models reduces the

base shear at greater extent. For the fixed base case base shear is nearly about 5000 kN

which is reduced by more than 3000 kN for all the 12 combinations. Model-1 reduces the

maximum base shear compared to other combinations.

Figure 3.2.2: base shear in x-direction

model0

model1

model2

model3

model4

model5

model6

model7

model8

model9

model10

model11

model12

X 5172 402 1716 912 1144 977 1220 904 1057 1165 809 977 1117

0

1000

2000

3000

4000

5000

6000

Base

Sh

ear

in X

- d

irec

tio

n

X

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Figure 3.2.3: base shear in y-direction

Storey Displacement:

From figure 3.2.4 it is seen that maximum base and top displacement given by

Model-1 combination. It is also seen that all the combinations i.e. Model 1-12 will gives

higher top and base displacement compared to fixed base structure i.e. Model-0. From

figure 3.2.5 it is seen that Model-5 gives maximum top and base displacement and all the

other models will gives higher value of top and base displacement compared to fixed base

structure.

Figure 3.2.4: storey displacement in x-direction

Figure 3.2.5: storey displacement in y-direction

model0

model1

model2

model3

model4

model5

model6

model7

model8

model9

model10

model11

model12

y 4937 1450 1713 1501 1608 1856 1535 1310 1399 1386 1330 1856 1678

0100020003000400050006000

Base

Sh

ear

in Y

- d

irec

tion

y

0

2

4

6

8

0 0.05 0.1 0.15 0.2 0.25

Model 0 Model 1 Model 2 Model 3 Model 4


Model 10 Model 11 Model 12

0

2

4

6

8

0 0.05 0.1 0.15 0.2 0.25 0.3




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Storey Drift:

From figure 3.2.6 it is seen that all the combinations gives lower values of storey

drift compared to fixed base case (Model-0). But minimum value of storey drift was given

by Model-10. From figure 3.2.7 it is observed that all the combinations gives lower value

of storey drift compared to fixed base case (Model-0). But minimum value of storey drift

was given by Model-1

Figure 3.2.6: storey drifts in x-direction

Figure 3.2.7: storey drifts in y-direction

Storey Acceleration:

From figure 3.2.8 it is seen that all the combinations gives lower values of storey

acceleration compared to fixed base case (Model-0). But minimum value of storey

acceleration was given by Model-1. From figure 3.2.9 it is observed that all the

0

1

2

3

4

5

6

7

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01




0

1

2

3

4

5

6

7

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016




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combinations gives lower value of storey acceleration compared to fixed base case (Model-

0). But minimum value of storey acceleration was given by Model-10.

Figure 3.2.8: storey acceleration in x-direction

Figure 3.2.9: storey acceleration in y-direction

4. Conclusions

In the present work an attempt has been made to show the efficiency of base isolation

system in low-rise reinforced concrete structure over conventional fixed base structure. For this

purpose two different types of base isolation systems such as High Density Rubber Bearing

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6




0

1

2

3

4

5

6

7

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5




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(HDRB) and Friction Pendulum System (FPS) are studied. The performance of base isolated

buildings with different arrangement of base isolation patterns is studied and based on these study

results are compared on the basis of various key parameters like base shear, time period, joint

displacement, storey drift and storey acceleration. Present study also attempts to compare all

assumed combined isolation systems with each other and to find out which combination will gives

the proper response for earthquake. Based on results derived some major conclusion are drawn

which are presented in current paper.

i.) It is concluded that time period of the structure in X directions in case of FPS increased by

about 1.8 seconds and for HDRB it is increased by about 1.3 seconds over conventional fixed

base structure.

ii.) It is concluded that time period of the structure in Y directions in case of FPS increased by

about 1.88 seconds and for HDRB it is increased by about 1.3 seconds over conventional

fixed base structure.

iii.) It is concluded that base shear of the structure reduces by the use of base isolators. But it is

greatly reduced by the use of FPS over HDRB.

iv.) It is also concluded that FPS gives maximum base displacement compared to HDRB.

v.) Storey drift & Storey acceleration are both reduces by both HDRB and FPS over

conventional fixed base structure. But it is greatly reduces by the use of FPS.

vi.) It is also concluded that base shear reduces for all mixed (combined) isolation systems.

vii.) It is observed that mixed isolation system helps to increase base displacement compared to

fixed base structure.

viii.) It is observed that when alternate layers of FPS and HDRB are provided in transverse

direction then reduction in storey drift and storey acceleration was more compared to other

combined isolation systems.

ix.) As compared to all 13 models, model-7, model-8, model-9 & model-10 gives more fine result

for storey displacement, storey drift & storey acceleration. i.e. gives more displacement

compared to others and reduces both drift & acceleration compared to others.

5. References

[1] Moussa, L, “Combined Systems for Seismic Protection of Buildings”, International symposium on

strong vrancea earthquakes and risk mitigation, Bucharest, Romania, Oct. (4-6) 2007, pp. 1-11.

A. R. Akhare and T. R. Wankhade “Seismic Performance of RC Structure Using Different Base Isolators”,

International journal of engineering science and research technology (IJESRT), ISSN: 2277-9655, vol.3

(5), 2014, pp. 724-729.

[2] Takalkar, N. & Paul, D. K, “Seismic Response of Friction Pendulum Isolated Medium Rise Multistory

Buildings”, International Journal of Engineering Science and Technology (IJEST), Vol. 4 No. 06,

June 2012, pp. 1-12.

[3] Torunbalci, N. & Ozpalanlar, G, “Earthquake Response Analysis of Mid-Story Buildings Isolated with

Various Seismic Isolation Techniques” The 14 World conference on earthquake engineering, October

12-17, 2008, pp. 1-8.

[4] Torunbalci, N. & Ozpalanlar, G, “Evaluation of Seismic Response for Low-Rise Base Isolated Building”

The 14 World conference on earthquake engineering, October 12-17, 2008, pp. 1-8.

Gomase, O.P, & Bakre, S.V, “Performance of Non-Linear Elastomeric Base-Isolated Building Structure”,

International journal of civil and structural engineering, ISSN:0976–4399, volume 2, No 1, 2011, pp.

1-12.

[5] Jangid, R.S. & Sharma, A, “Behaviour of Base-Isolated Structures with High Initial Isolator Stiffness”,

World academy of science engineering and technology, 26-2009, pp. 1-6.

[6] Naeim, N. & Kelly, J.M, “Design of Seismic Isolated Structures from Theory of Practice”,Thereference

book, 1999.

[7] CSI Analysis Reference Manual for SAP2000®, ETABS®, and SAFE™.

[8] UBC97, “Uniform Building Code”, Chap. 16, Div. I 1601 1605.2.1 Volume 2.

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Biographies

Prof. T. R. Wankhade is presently working as a assistant professor At Prof.

Ram Meghe Institute Of Technology And Research, Badnera engineering

college at Amravati, Maharastra, India. He compleated his graduation (B.E.

Civil engineering) in year 2012 from the same institute where he is working

as a assistant professor now. Also, he completed his M.Tech. (Structural

Engineering) from Government college of engineering, Amravati (An

autonomous institute) in year 2014. Apart from all he owns a memberships of

ISTE.

Documents

Effect Of Combined Isolation System On Low-Rise …Effect Of Combined Isolation System On Low-Rise RC Structure Paper ID IJIFR/ V3/ E2/ 051 Page No. 538-550 Subject Area Civil Engineering