Seismic Performance of Asymmetrical Steel Structure using Lateral Load Resisting Systems

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Seismic Performance of Asymmetrical Steel Structure using Lateral Load Resisting Systems

Mohmmad Younes Fazly1

1Post Graduate Student,

School of Civil Engineering, REVA University, Bengaluru.

Mr.Venkatesh Wadki 2

2Assistant Professor,

School of Civil Engineering, REVA University, Bengaluru.

Abstract The demand for high rise structure in commercial, residential and industrial areas are increasing all over the world. Such types of structure are flexible and constructed as light as possible, which have low value of damping that makes them unsafe to unwanted vibration. These vibrations generate some problem to the serviceability requirement of the structure and also decrease structural integrity with possibility of failure. In this study steel structures are taken for seismic performance evaluation. The steel buildings are modeled with different structural control system such as base isolator, damper and bracing with use of ETABS software. After that to evaluate structural response of building various ground motion data is applied. Equivalent static analysis is carried out for building model with each control system and the result of the seismic response of each control system is compared with other control system. Equivalent static analysis result shows that building with cross bracing shows lesser displacement than building with FVD and building with LRB.

Key Words: Seismic Performance, Conventional Bare Frame, Cross Bracing, Lead Rubber Bearing, Damper, Equivalent Static Analysis

  1. INTRODUCTION

    Generally the reason for elevated structure is to exchange the primary gravity load securely. The common gravity loads are dead, live load. Likewise the structure should withstand the lateral load brought about by earthquake, blasting, and wind depending upon terrain categories. The lateral load decreases stability of structure by creating sway moments and induces high stresses. So in such cases stiffness could easily compare to strength to resist lateral loads.

    There are various ways of providing lateral load resisting system, for example, bracing, base isolation, damper, to improve seismic performance of structures. Base isolations is a passive vibration control system that does not require any outer power sources for its task and uses the movement of the structure to build up the control force. The upside of this method is to keep the structure basically versatile and along these lines guarantees security among enormous earthquake. Viscous damper are hydraulic devices that disseminate the kinetic energy of seismic occasions and pad the effect between the structures. They are flexible and can be intended to permit free movements just as controlled damping of a structure to protect from wind load, thermal motion or seismic event. The improvement of bracing made the construction of high rise structure possible.

    Bracing are strong in compression. At the point when bracings are put in steel outline it acts as diagonal compression strut and transmits compression force to another joint. Variety in the column stiffness can impact the method of failure and lateral stiffness of the bracing

    Fig. 1 A: Typical Floor Plan

    Fig.2: 3D Modeling steel structure with Bare frame ofu10, 15, 20 storey.

    Fig.3: 3D Modeling steel structure with Brace frame ofu10, 15, 20 storey.

    Fig.4: 3D Modeling of steel structure with friction damper of 10, 15, 20 storey.

    Fig.5: 3D Modeling of steel structure with Lead Rubber Bearing of 10, 15, 20 storey.

    Table 1: Data of Structure

    SECTION MODEL

    DIMENSIONS

    Beam

    ISMB 600

    Column

    ISMC 400

    Plan

    10, 15, 20 storey model

    Column Spacing

    4m in both direction

    Floor height

    3 m

    Steel section

    Fe345

    Slab thickness

    100mm M25 grade

    Shear wall thickness

    200 mm

    Bracing (X)

    ISMB 450

    Damper type

    Friction Damper

    Base isolation

    Lead Rubber Bearing

    Live Load

    3.5 KN/ m^ 2

    Superimposed Dead Load

    1.5 KN/ m^ 2

    Live Loads on Roof

    1.5 KN/ m^ 2

    Seismic Zone

    V

    Seismic Factor

    0.36

    Soil Type

    Medium type 2

    Importance Factor

    1.5

    Reduction Factor

    5

    Earthquake Load

    X and Y Direction

    Floor Finish

    1 KN/ m^ 2

    Unit Weight of Steel

    78 KN/ m^ 3

  2. DETAILS OF LEAD RUBBER BEARING (LRB)

    Lead rubber bearing are made up of a standard elastomeric laminated rubber bearing the rubber compound can be natural or chloroprene rubber. The shape can be round or

    rectangular. The calculations for the design of LRB are as per the provisions of UBC-97.

    Table 1: Detail of LRB Base isolator

    Effective Stiffness

    1065 KN/ m

    Horizontal stiffness

    350

    Vertical Stiffness

    180

    Yield Force

    20 KN

    Stiffness Ratio

    0.1

    Damping

    0.05

  3. DETAILS OF FRICTION DAMPER

    In these kinds of damper the energy is consumed by surfaces with frictions between them scouring against one another.

    Table 2: Detail of friction damper

    Link Type

    Plastic (Wen)

    Mass (Kg)

    222.07

    weight (KN)

    2.18

    Effective Stiffness (KN/m)

    152500

    Yield Strength (KN)

    450

    Post Yield Stiffness Ratio

    0.0001

    Yield Exponent

    10

    Effective Damping (KNs/m)

    0

  4. RESULTS AND DISCUSSIONS

Lateral loads resisting systems are used to reduce the seismic effect of the structure which is subjected to the earthquake load. The frames with base isolation, LRB and cross bracing are modeled according to the properties of structure which are explained in the work. The model is subjected to analysis for gravity load i.e. dead load and live load and seismic loads. The seismic behavior of the steel structure is judged by observing the roof displacement.

Roof Displacement:

Displacement is the parameter of maximum importance as it governs the failure pattern of the structure. From this present study, the displacement of the model with cross bracing, base isolation (LRB) and FVD damper and without lateral load resisting systems are is observed. By providing the cross bracing to the structure we observed that the displacement of the structure is reduced.

Table 3: Roof Displacement value for G+10

Maximum displacement (mm)

Sl. No

Storey

Maximum displacement (mm)

Bracing

Damper

Isolator

Conventional Bare Frame

1

Story 1

0.04

0.06

0.09

0.01

2

Story 2

0.52

0.6

0.78

0.8

3

Story 3

1.005

1.122

1.162

1.231

4

Story 4

1.450

1.525

1.650

1.826

5

Story 5

1.805

1.831

1.987

2.296

6

Story 6

1.919

1.986

2.215

2.589

7

Story 7

2.009

2.256

2.425

2.860

8

Story 8

2.097

2.998

3.005

3.126

9

Story 9

2.183

3.105

3.106

3.604

10

Story10

2.264

3.998

4.125

4.652

11

Story11

2.339

4.125

4.998

5.530

12

Story12

2.408

4.650

6.125

6.458

13

Story13

2.469

5.005

7.310

7.425

14

Story14

2.730

5.987

7.998

8.424

15

Story15

3.034

6.526

9.125

9.445

16

Story16

3.346

7.565

9.875

10.476

Sl.No

Storey

Maximum displacement (mm)

Maximum displacement (mm)

Bare Conventional Structure

Bracing

Damper

Isolators

1

Story 1

0.001

0.021

0.040

0.102

2

Story 2

0.310

0.378

0.381

0.65

3

Story3

0.720

0.750

0.765

0.956

4

Story 4

0.985

1.005

1.135

1.325

5

Story 5

1.395

1.405

1.431

1.686

6

Story 6

1.590

1.600

1.610

1.95

7

Story 7

1.850

1.869

1.875

2.105

8

Story 8

1.890

1.950

1.987

2.895

9

Story 9

2.101

2.130

2.142

3.986

10

Story 10

2.325

2.198

2.456

4.986

11

Story 11

2.625

2.690

2.726

5.552

12

Story 12

3.002

3.121

3.150

5.996

13

Story 13

3.182

3.158

3.229

6.005

14

Story 14

3.630

4.103

4.250

6.995

15

Story 15

4.105

4.568

4.762

7.668

16

Story 16

4.596

4.861

5.335

8.865

17

Story 17

5.103

5.785

5.998

9.865

18

Story 18

5.623

5.865

6.210

10.965

19

Story 19

6.15

6.986

7.152

11.950

20

Story 20

6.690

7.001

7.861

13.656

21

Story 21

6.622

7.565

9.856

14.535

Sl.No

Storey

Maximum displacement (mm)

Maximum displacement (mm)

Bare Conventional Structure

Bracing

Damper

Isolators

1

Story 1

0.001

0.021

0.040

0.102

2

Story 2

0.310

0.378

0.381

0.65

3

Story3

0.720

0.750

0.765

0.956

4

Story 4

0.985

1.005

1.135

1.325

5

Story 5

1.395

1.405

1.431

1.686

6

Story 6

1.590

1.600

1.610

1.95

7

Story 7

1.850

1.869

1.875

2.105

8

Story 8

1.890

1.950

1.987

2.895

9

Story 9

2.101

2.130

2.142

3.986

10

Story 10

2.325

2.198

2.456

4.986

11

Story 11

2.625

2.690

2.726

5.552

12

Story 12

3.002

3.121

3.150

5.996

13

Story 13

3.182

3.158

3.229

6.005

14

Story 14

3.630

4.103

4.250

6.995

15

Story 15

4.105

4.568

4.762

7.668

16

Story 16

4.596

4.861

5.335

8.865

17

Story 17

5.103

5.785

5.998

9.865

18

Story 18

5.623

5.865

6.210

10.965

19

Story 19

6.15

6.986

7.152

11.950

20

Story 20

6.690

7.001

7.861

13.656

21

Story 21

6.622

7.565

9.856

14.535

Graph 1: Roof Displacement value for G+10 for bracing, damper, isolator, and conventional bare frame

Table 4: Roof Displacement value for G+15

Graph 2: Roof Displacement value for G+15 for bracing, damper, isolator, and conventional bare frame.

Graph 3: Roof Displacement value for G+20 for bracing, damper, isolator, and conventional bare frame

Table 5: Roof Displacement value for G+20

Sl.No

Storey

Maximum displacement (mm)

Maximum displacement (mm) conventional Bare Frame

Bracing

Damper

Isolator

1

Story 1

0.110

0.06

0.09

0.039

2

Story 2

0.283

0.352

0.588

0.518

3

Story 3

0.793

0.985

1.15

1.094

4

Story 4

0.929

1.430

1.69

1.672

5

Story 5

1.313

1.560

2.102

2.125

6

Story 6

1.422

1.656

2.164

2.186

7

Story 7

1.648

1.856

2.306

2.359

8

Story 8

1.778

1.942

2.453

2.537

9

Story 9

2.050

2.157

2.596

2.714

10

Story 10

2.190

2.236

2.735

2.889

11

Story 11

2.439

2.525

2.847

3.043

From the graph it is shown that maximum roof displacement of building with bracing, damper and isolator are very less compared to normal conventional building.

CONCLUSION

After carrying out results by using ETABS software for buildings with various heights, the parameters like roof displacement for different lateral load resisting systems are compared. Following conclusion is made.

  1. By comparing the results from (Graph 1, 2, 3 ) it is concluded that the roof displacement for steel structure with bracing is less as compared to the other lateral load resisting system.

  2. Lead rubber isolator generally increases the maximum displacement of the structures in high rise building compared to fixed base structures, but in middle rise buildings the difference is negligible.

  3. In low rise, simple base isolation has good performance and there is no need to modify the superstructure characteristics. Indeed, these modifications cannot have positive effect on isolation performance.

  4. In middle rise building we can reach better isolation by assigning additional base mass and increasing the damping of the structure.

  5. In high rise building, stiffening superstructure and increasing the damping will cause an effective base isolation.

  6. Comparison between building with damper and building with braces showed that bracing are more significant to reduce seismic quantities with same direction of placement as brace.

REFERENCES

  1. A K Sinnha et al.; (2017), Assurance of RC frame utilizing friction Damper. International journal of civil engineering & technology, volumes 8 , Feb- 2017, pp. 289-299.

  2. S.M Kalantari, H Naderpour, S.R Hoseini Vaez, investigation of base isolator, types, determination on seismic conduct of structures including story drift and plastic hinge formation., The 14th world conference on earthquake engineering October 1217, 2008, Bejing, China, pp.312.322.

  3. C.P. Providkis, Impact of LRB Isolator and supplemental viscous dampers on seismic isolated structures under near-fault excitation. Engineering structures 30 (2008) 1187-1198.

  4. Franco Braga, Michelangelo Laterza. Field testing of low rise base isolation building, Engineering structures 26 (2004) 1599-1610.

  5. Liyaa Matheew, C prabhaa; Effect of fluid viscous dampers in multistory buildings,International Journal of research in Engineering & technology, Volume 2 , Issues 9 , September 2014.

  6. Nitendra G Mahehan, D B Raijiwala, Seismic Response Control of a Building Installed with Passive Dampers., Internal Journal of Advanced Engineering Technology, vol.2, Issue 3, July-sep 2011.

  7. A Kadid; D. Yahiaouill, Seismic Assessment of Braced RC Frames, precedia Engineering 14 (2011) 2899 – 2905.

  8. Amnart Khampaint, Sutat L elataviwat, jensak Kochanin, Pennung warnitchai, energy Based Seismic Strengthening Design of Non Ductile Reinforced concrete Frames utilizing

    Buckling Restrained Braces., Engineering structure 81 (2014) 110-122.

  9. Pooja Desai, Vikhyat Katti, Bracing as Lateral Load Resisting Structural System, International Research Journal of Engineering & Technology, Volume 4, Issue 5; May 2017.

  10. Charles K. Erdey Earthquake engineering application to design vol.1 No.2, pp.25-26, 2007.

CODES OF PRACTICES:

  1. IS: 456-2000 Plain & Reinforced Concrete code of practice. Bureau of Indian Standard, New Delhi.

  2. IS: 800 2007 General Construction in Steel code of practices. Bureau of Indian Standard, New Delhi.

  3. IS: 1893 (part 1) General provisions on building & Dynamic Analysis of structure, criteria for earthquake Resistance Design. Bureau of Indian Standard, New Delhi.

  4. International building code 2000 Edition by International code council.

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