Seismic Analysis of Building using E-Tabs


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Seismic Analysis of Building using E-Tabs

Nagalakshmi.P, Poojashree. B. S

UG Scholar,

Civil dept. AIeMS, Bidadi

Vidya .B. R

Asst. Professor, Civil dept. AIeMS, Bidadi

Abstract – The concept of isolator in building at base level reduces the possibility of resonance pf the structure and increases the time period of the structure giving rise to better seismic performance of the building.This study is performed for comparing the effectiveness of fixed base and base isolated multistoreyed RC framed building .For this study G+5 building is designed and analysed. The Lead Rubber Bearing (LRB) is designed according to IS1893-2002 and UBC -97 and the same was used for the analysis of base isolated system. The results obtained from analysis is Time Period. Time period for the base isolated structure is higher than that of the fixed base structure. The commercial building is anlysed in Etabs-2015.

KeywordsIsolater,time period,base isolation,Etabs,Lead Rubber bearing.

  1. INTRODUCTION

    Base isolation of structures is one of the most desired means to protect it against earthquake forces. The term base isolation have two word first is base its meaning is a part that supports from underneath or perform as a foundation of a structure, and second is isolation its meaning of the state of being disparate. During earthquake attacks, the traditional building structures in which the base is fixed to the ground, respond with a gradual increase from ground level to the top of the building, like an amplifier.

    This may result in heavy damage or total collapse of structures. To avoid these results, while at the same time satisfying in-service functional requirements, flexibility is introduced at the base of the structure, usually by placing Lead Rubber Bearing isolators between the structure and its foundation. Seismic base isolation is the one of best method among the lateral load resisting systems. The term base isolation uses the word isolation in its meaning of the state of being separated and base as a part that supports from beneath or serves as a foundation for an object or structure. The system namely Lead Rubber Bearing (LRB) selected for this study includes sample of materials such as plate, rubber and central core. It has been selected to establish an innovative simplified design procedure for isolators incorporated in multi-storey building structures. Recent studies have shown that most isolated buildings is important to use multi-layer Laminated Rubber Bearings with steel reinforcement layers. Ease of Use

    Objective

    To analyse a commercial building in Etabs 2015 software to find out and compare the values of Time period in fixred and base isolated building.

  2. MODELLING AND DESIGNING OF BUILDING. Time period of proposed structures is estimated in the

    application software i.e. ETABS. The model of prototype structure of given geometry and sizes of elements is prepared in the ETABS. Analysis provids the time period of the structure[1].

    The ETABS building is idealized as an assemblage of area, line and point objects.[6] Those objects are used to represent wall, floor, column, beam, and brace and link/spring physical members. The basic frame geometry is defined with reference to a simple three-dimensional grid system. Material properties such as concrete, rebar and section properties such as beam, column are defined as frame element and slab element defined as area element. Modal analysis is done.

    Building Configuration.

    SLNO

    PROPERTIES

    BUILDING DATA

    1.

    No of storeys

    G+5

    2.

    Height of the building.

    15.45

    3.

    Beam .

    Dimension

    240*500mm

    Grade of concrete

    M25

    Torsion Constant

    0.01

    4.

    Column

    Dimension

    240*400mm

    Grade of concrete

    M30

    Torsion Constant

    0.01

    5.

    Slab

    Dimension

    140mm

    Grade of concrete

    M25

    6.

    Plinth Beam

    300*450mm

    7.

    Dead Load

    1.5Kn/mt2

    8.

    Live Load

    4Kn/mt2

    9.

    Soil Type

    3

    10.

    Damping

    5%

    11.

    Load Combination

    1. 1.5(DL+LL)

    2. 1.2(DL+LL±Ex)

    3. 1.2(DL+LL±Ey)

    4. 1.5(DL±Ex)

    5. 1.5(DL±Ey)

    7.

    Dead Load

    1.5Kn/mt2

    8.

    Live Load

    4Kn/mt2

    9.

    Soil Type

    3

    10.

    Damping

    5%

    11.

    Load Combination

    1. 1.5(DL+LL)

    2. 1.2(DL+LL±Ex)

    3. 1.2(DL+LL±Ey)

    4. 1.5(DL±Ex)

    5. 1.5(DL±Ey)

    1. Design of building.

      FIG . 1 PLAN OF THE BUILDING.

      Grid Dimensions (mt).: IN X – DIRECTION.

      A

      B

      C

      D

      E

      F

      G

      H

      I

      J

      0

      1.2

      2.7

      3.9

      4.5

      5.8

      6.7

      7.6

      8.8

      12.6

      K

      L

      M

      N

      16.4

      17.49

      18.13

      19

      IN Y – DIRECTION.

      Fig. 2 ELEVATION OF BUILDING.

      Fig. 33-D VIEW OF THE BUILDING.

  3. LEAD RUBBER BEARING.

LRBs are consisting of a standard elastomeric laminated rubber bearing. The rubber compound can be of chloroprene rubber or natural rubber[2]. The shape can be either rectangular or round[3]. For this testing a circle shape is chosen. The LRBs are usually made with low-damping (unfilled) elastomers with shear modules of 0.4 1.2N /mm2 and lead cores with diameters ranging 15% and 33% of the bonded bearing diameter for circle bearings.[2] The minimum of shear modulus 0.4N /mm2 is taken for the testing performed. The elastomer offers the isolation and recanting, while the lead core provides the damping component or the necessary dissipation of energy[5].

SLNO

PROPRTIES

VALUES

1.

Target period

2.5secs

2.

Eff Damping

5%

3.

Design Displacemet(Dd)[5]

0.372mt

4.

Rubber Shear Modulus(G)

1Mpa

5.

Axial load on LRB

1037.71Kn

6.

Eff Stiffness (Keff)

836.06KN/mt

7.

Stiffness Ratio

0.1

8.

Post yield Elastic Stiffness (k1)

7704.1Kn/mt

9.

Post yield Elastic Stiffness (k2)

770.41kn/mt

SLNO

PROPRTIES

VALUES

1.

Target period

2.5secs

2.

Eff Damping

5%

3.

Design Displacemet(Dd)[5]

0.372mt

4.

Rubber Shear Modulus(G)

1Mpa

5.

Axial load on LRB

1037.71Kn

6.

Eff Stiffness (Keff)

836.06KN/mt

7.

Stiffness Ratio

0.1

8.

Post yield Elastic Stiffness (k1)

7704.1Kn/mt

9.

Post yield Elastic Stiffness (k2)

770.41kn/mt

THEORITICALLY CALCULATED VALUES .

1

2

3

4

5

0

5.7

9

11.5

13.5

Dimensions of LRB.

RESULTS

SLNO

PROPERTIES

VALUES

1.

Total plud diameter (dpb)

0.05mt

2.

Single layer rubber thickness

0.01mt

3.

Steel plate thickness

0.003mt

4.

Top and Bottom Plate thickness

25mm

5.

Total height of LRB (H)

0.311mt

6.

Total beraing diameter

0.63mt

7.

No of rubber layers

22

8.

No of steel layers

21

SLNO

PROPERTIES

VALUES

1.

Total plud diameter (dpb)

0.05mt

2.

Single layer rubber thickness

0.01mt

3.

Steel plate thickness

0.003mt

4.

Top and Bottom Plate thickness

25mm

5.

Total height of LRB (H)

0.311mt

6.

Total beraing diameter

0.63mt

7.

No of rubber layers

22

8.

No of steel layers

21

It is observed that tim period of the fixed base structure for different modes is lesser than that of the structure which is base isolated structure .

Mode No

Time period with fixed

Time period with base isolation

1

1.203

1.888

2

1.566

1.703

3

0.491

1.579

4

0.453

0.53

5

0.373

0.455

6

0.284

0.365

7

0.283

0.355

8

0.281

0.283

9

0.279

0.280

10

0.223

0.272

11

0.218

0.271

12

0.206

0.245

25mm

0.33

0.28

0.63mt

7m 7m

7m 7m

0.58mt

Fig. 4 SECTION OF LEAD RUBBER BEARING

REFERENCES

    1. K. Naga Sai Gopal,N. Lingeshwaran ,Analysis and design of G+5 residential building in Etabs,IJCIET,Vol 8,April 2017.

    2. M.Rajesh Reddy, N.Srujana,N .Lingeshwaran ,Effect of base Isolation in multi storeyed reinforced concrete building,IJCIET,Vol 8,March 2017.

    3. Amer Hassan,Ahamed Saeed ,Design of LRB isolaters for sismic resistance,Reaseach gate publications

    4. C.G.Konapure,MS Muddiddi,Determination of Time Period and Elvalution of seismic response of framed Structure,IRJET,Vol 5,April 2018.

    5. Omar Jimenez,Arturo Tena,Dymanic Design procedure for the design of Base Isolated structure,WCEE,2000.

    6. Sudhar K Patel,VB Patel,Effect of number of storeys to natural time period of building, NCRTET

    7. Peerzade,Tejashree Kulkarni,Seismic evaluation of high raised building with and without base isolation,IJSRD,Vol 4,2016.

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