i

EFFECT ON BASE SHEAR UNDER SEISMIC LOAD FOR

MASONRY INFILLED RC SOFT STORY BUILDINGS

Submitted by

Rumia Tasmim

Submitted to the

DEPARTMENT OF CIVIL ENGINEERING

BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY In partial fulfillment of requirements for the degree of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

2011

ii

DECLARATION

This is hereby declared that the studies contained in this thesis is the result of research

carried out by the author except for the contents where specific references have been

made to the research of others.

The whole thesis is done under the supervision of Professor Dr. Khan Mahmud

Amanat (Department of Civil Engineering, BUET) and no part of this thesis has been

submitted concurrently for any degree or other qualification to any other institution.

Signature of author

(Rumia Tasmim)

iii

ACKNOWLEDGEMENT

My profound gratitude to almighty Allah for his unlimited kindness and blessings for

what this effort has been successfully carried out.

I wish to express my heartiest thanks to Dr. Khan Mahmud Amanat, Professor,

Department of Civil Engineering, BUET for his encouraging supervision al through

the study. His systematic and invaluable guidance with affectionate persuasion have

helped me greatly during the study.

My special gratitude to my parents, sister and my husband, the source of inspiration

for all my efforts and achievements.

iv

ABSTRACT

In present time, Bangladesh is going through extensive urbanization process.

Development in infrastructure is very high. These structures are mainly RC framed

buildings, which provide parking facilities. As the number of automobiles is

increasing exponentially, the need to house them in close proximity creates a

challenging design problem. To do so the whole structural system gets the

characteristics of soft story and thats vulnerable to seismic load.

The structural effect of masonry infill is not considered during the design of such RC

frames having soft story and thus the design becomes really unsafe under lateral

loading. The Equivalent Static Force Method (ESFM) used to calculate the base shear

cant consider the structural effect of masonry infill and the base shear calculated is

underestimated, which doesnt varies with the amount of infill application. RC framed

structures without regards to the structural action of the masonry infill (MI) walls

present in the upper floors. However, in reality, masonry infill (MI) walls in the upper

floors make those floors much stiffer against lateral load (e.g. earthquake) compared

to ground floor rendering these buildings into soft story buildings. Experience of

different nations with the poor and devastating performance of such buildings during

earthquakes always seriously discouraged construction of such a building with a soft

ground floor.

This study will be confined to analyze the effect of random applied structural infill

and observe the variation in base shear value for the uncertain infill location for

different parameters. To sort out the actual behavior of masonry infill as structural

component of RC frame system a numerical study has been carried out using response

spectrum method (RSM). The study was involved to find the base shear modification

due to the application of random infill with soft ground floor and to get safe design

value for such structurally modified building system. For design simplicity and safety,

a modification factor for such soft floor system is sorted. Thus a suitable modification

factor is expected to be suggested for the safe design of MI-RC framed structure

against seismic vulnerability.

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CONTENTS Page No.

DECLARATION ii ACKNOWLEDGMENT iii ABSTRACT iv LIST OF FIGURES vii LIST OF TABLES xii BBREVIATIONS xiii Chapter 1: INTRODUCTION

1.1 GENERAL 1

1.2 OBJECTIVE AND SCOPE OF THE STUDY 1

1.3 ASSUMPTIONS FOR MODELING SIMPLICITY 2

1.4 ORGANIZATION OF THE THESIS 2

Chapter 2: LITERATURE REVIEW

2.1 INTRODUCTION 4

2.2 BEHAVIOR OF MASONRY INFILLED RC FRAME UNDER LATERAL LOAD 5

2.3 COMPUTATIONAL MODELLING AND ANALYSIS OF INFILLED FRAME 9

2.3.1 Equivalent Diagonal Strut Method 10 2.4 EFFECT OF EARTHQUAKE ON BUILDING FRAME WITH SOFT STORY 11

2.5 BUILDING CODES 13

2.5.1 Without Considering Soft Story Phenomenon 13

2.5.2 Considering Soft Story Phenomenon 14 2.6 PAST RESEARCH ON SOFT STORY BUILDING 15

Chapter 3: FINITE ELEMENT MODELING OF INFILL FRAME

3.1 INTRODUCTION 17

3.2 SOFTWARE FOR FINITE ELEMENT ANALYSIS 17

3.3 ASSUMPTIONS FOR MODELING SIMPLIFICATION 17

3.4 CHARACTERIZATION OF STRUCTURAL COMPONENTS IN MODEL 17

3.4.1 BEAM4 (3-D Elastic Beam) for Beam and Column 17

3.4.2 Shell63 (Elastic Shell) for Slab 19

3.4.3 MASS21 (Structural Mass) for load application 20

3.4.4 LINK8 (3-D Spar or Truss) for load application 21

3.4.5 Support Condition 22

3.4.6 Load application 22

vi

3.5 SEISMIC LOAD CALCULATION 22

3.5.1 Static Analysis (Equivalent static Force Method) 23

3.5.2 Response Spectrum Method (RSM) 23

3.6 MODEL CHARACTERISTICS FOR ANALYSIS AND TYPICAL RESULT 31

CHAPTER 4: RESULTS AND DISCUSSION

4.1 INTRODUCTION 36

4.2 VARIATION IN BASE SHEAR FOR RANDOM APPLICATION OF INFILL 36

4.2.1 Range of variation in base shear value 36

4.2.2 Modification factor for different parameters 37

4.2.3 Range of variation in base shear value with span no. and length 37

CHAPTER 5: CONCLUSION AND RECOMMENDATION

5.1 GENERAL 86

5.2 FINDINGS OF THE INVESTIGATION 86

5.3 RECOMMENDATION FOR FUTURE STUDY 87

REFERENCE 88

APPENDIX: ANSYS SCRIPT USED IN THE ANALYSIS 91

vii

LIST OF FIGURES

Figure Caption Page No.

2.1a Multistoried apartment building with open ground floor for parking 4 2.1b Soft story mechanism 5 2.2 Change in lateral load transfer mechanism due to masonry infills 6

(Murty and Jain 2000)

2.3 Interactive behavior of frame and infill 6 2.4 Analogous braced frame 7 2.5 Modes of infill failure 8 2.6 Modes of frame failure 8 2.7 Material modeling of masonry infill as diagonal strut 10 2.8 (a) Masonry infilled frame sub-assemblage in masonry infill panel frame 10 2.8 (b) Masonry infill panel in frame structure 10 2.9 Open ground story building

(a) actual building 11 (b) building being assumed in current design practice 11

2.10 Effects of masonry infills on the first mode shape of a typical frame of a ten story RC building , Displacement profile (a) fully infilled frame 11 (b) open ground floor frame 11

2.11 Some effects of Earthquake on soft story building 12 3.1 BEAM4 Geometry 18 3.2 SHELL63 Geometry 19 3.3 MASS21 Geometry 20 3.4 LINK8 Geometry 21 3.5 Finite Element modeling of total structure 23

3.6 Normalized response spectra for 5% Damping ratio 24

3.7 Different patterns of random infill application (6 storied building) 25

3.8 Different patterns of random infill application (8 storied building) 26

3.9 Different patterns of random infill application (10 storied building) 27

3.10 Different patterns of random infill application (12 storied building) 28

3.7 (a) First mode shape 29 3.7 (b) third mode shape 30

viii

3.7 (c) Sixth mode shape 30 3.7 (d) Seventh mode shape 30 3.7 (e) 10th mode shape 30 3.7 (f) 15th mode shape 30 3.8 (a) Variation in base shear in RSM analysis with % infill on upper floors 32 3.8 (b) Variation in base shear in Static analysis with % infill on upper floors 32 3.9 (a) Deformation due to application of DL for 40%infill on upper floors 33

and no infill on GF

3.9 (b) Deformation due to application of LL for 40%infill on upper floors 33

and no infill on GF

3.9 (c) Deformation due to EQ load in X-direction (Static) for 40%infill 34

on upper floors and no infill on GF

3.9 (d) Deformation due to EQ load in X-direction (RSM) for 40%infill 34

on upper floors and no infill on GF

3.9 (e) Deformation due to EQ load in X-direction (Static) for 40%infill 35

on upper floors and 20% infill on GF

3.9 (f) Deformation due to EQ load in X-direction (RSM) for 40%infill 35

on upper floors and 20% infill on GF

4.1 Variation in base shear value (RSM) of 6 storied building(EQ load in X-dir)for 38 random infill pattern (no infill on Ground floor and 20% infill on upper floors)

4.2 Variation in base shear value (RSM) of 6 storied building(EQ load in X-dir)for 39 random infill pattern (no infill on Ground floor and 40% infill on upper floors)

4.3 Variation in base shear value (RSM) of 6 storied building(EQ load in X-dir)for 39 random infill pattern (no infill on Ground floor and 60% infill on upper floors)

4.4 Variation in base shear value (RSM) of 6 storied building(EQ load in X-dir)for 39 random infill pattern (no infill on Ground floor and 80% infill on upper floors)

4.5 Variation in base shear value (RSM) of 6 storied building(EQ load in X-dir)for 40 random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

4.6 Variation in base shear value (RSM) of 6 storied building(EQ load in X-dir)for 41 random infill pattern (20% infill on Ground floor and 40% infill on upper floors)

4.7 Variation in base shear value (RSM) of 6 storied building(EQ load in X-dir)for 41 random infill pattern (20% infill on Ground floor and 60% infill on upper floors)

4.8 Variation in base shear value (RSM) of 6 storied building(EQ load in X-dir)for 41 random infill pattern (20% infill on Ground floor and 80% infill on upper floors)

4.9 Variation in base shear value (RSM) of 8 storied building(EQ load in X-dir)for 42 random infill pattern (no infill on Ground floor and 20% infill on upper floors)

4.10 Variation in base shear value (RSM) of 8 storied building(EQ load in X-dir)for 43 random infill pattern (no infill on Ground floor and 40% infill on upper floors)

4.11 Variation in base shear value (RSM) of 8 storied building(EQ load in X-dir)for 43 random infill pattern (no infill on Ground floor and 60% infill on upper floors)

4.12 Variation in base shear value (RSM) of 8 storied building(EQ load in X-dir)for 43 random infill pattern (no infill on Ground floor and 80% infill on upper floors)

ix

4.13 Variation in base shear value (RSM) of 8 storied building(EQ load in X-dir)for 44 random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

4.14 Variation in base shear value (RSM) of 8 storied building(EQ load in X-dir)for 45 random infill pattern (20% infill on Ground floor and 40% infill on upper floors)

4.15 Variation in base shear value (RSM) of 8 storied building(EQ load in X-dir)for 45 random infill pattern (20% infill on Ground floor and 60% infill on upper floors)

4.16 Variation in base shear value (RSM) of 8 storied building(EQ load in X-dir)for 45 random infill pattern (20% infill on Ground floor and 80% infill on upper floors)

4.17 Variation in base shear value (RSM) of 10storied building(EQ load in X-dir)for 46 random infill pattern (no infill on Ground floor and 20% infill on upper floors)

4.18 Variation in base shear value (RSM) of 10storied building(EQ load in X-dir)for 47 random infill pattern (no infill on Ground floor and 40% infill on upper floors)

4.19 Variation in base shear value (RSM) of 10storied building(EQ load in X-dir)for 47 random infill pattern (no infill on Ground floor and 60% infill on upper floors)

4.20 Variation in base shear value (RSM) of 10storied building(EQ load in X-dir)for 47 random infill pattern (no infill on Ground floor and 80% infill on upper floors)

4.21 Variation in base shear value (RSM) of 10storied building(EQ load in X-dir)for 48 random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

4.22 Variation in base shear value (RSM) of 10storied building(EQ load in X-dir)for 49 random infill pattern (20% infill on Ground floor and 40% infill on upper floors)

4.23 Variation in base shear value (RSM) of 10storied building(EQ load in X-dir)for 49 random infill pattern (20% infill on Ground floor and 60% infill on upper floors)

4.24 Variation in base shear value (RSM) of 10storied building(EQ load in X-dir)for 49 random infill pattern (20% infill on Ground floor and 80% infill on upper floors)

4.25 Variation in base shear value (RSM) of 12storied building(EQ load in X-dir)for 50 random infill pattern (no infill on Ground floor and 20% infill on upper floors)

4.26 Variation in base shear value (RSM) of 12storied building(EQ load in X-dir)for 51 random infill pattern (no infill on Ground floor and 40% infill on upper floors)

4.27 Variation in base shear value (RSM) of 12storied building(EQ load in X-dir)for 51 random infill pattern (no infill on Ground floor and 60% infill on upper floors)

4.28 Variation in base shear value (RSM) of 12storied building(EQ load in X-dir)for 51 random infill pattern (no infill on Ground floor and 80% infill on upper floors)

4.29 Variation in base shear value (RSM) of 12storied building(EQ load in X-dir)for 52 random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

4.30 Variation in base shear value (RSM) of 12storied building(EQ load in X-dir)for 53 random infill pattern (20% infill on Ground floor and 40% infill on upper floors)

4.31 Variation in base shear value (RSM) of 12storied building(EQ load in X-dir)for 53 random infill pattern (20% infill on Ground floor and 60% infill on upper floors)

4.32 Variation in base shear value (RSM) of 12storied building(EQ load in X-dir)for 53 random infill pattern (20% infill on Ground floor and 80% infill on upper floors)

4.33 Variation in base shear value (RSM) of 6 storied building(EQ load in Z-dir)for 54 random infill pattern (no infill on Ground floor and 20% infill on upper floors)

4.34 Variation in base shear value (RSM) of 6 storied building(EQ load in Z-dir)for 55 random infill pattern (no infill on Ground floor and 40% infill on upper floors)

4.35 Variation in base shear value (RSM) of 6 storied building(EQ load in Z-dir)for 55 random infill pattern (no infill on Ground floor and 60% infill on upper floors)

4.36 Variation in base shear value (RSM) of 6 storied building(EQ load in Z-dir)for 55 random infill pattern (no infill on Ground floor and 80% infill on upper floors)

4.37 Variation in base shear value (RSM) of 6 storied building(EQ load in Z-dir)for 56 random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

4.38 Variation in base shear value (RSM) of 6 storied building(EQ load in Z-dir)for 57 random infill pattern (20% infill on Ground floor and 40% infill on upper floors)

x

4.39 Variation in base shear value (RSM) of 6 storied building(EQ load in Z-dir)for 57 random infill pattern (20% infill on Ground floor and 60% infill on upper floors)

4.40 Variation in base shear value (RSM) of 6 storied building(EQ load in Z-dir)for 57 random infill pattern (20% infill on Ground floor and 80% infill on upper floors)

4.41 Variation in base shear value (RSM) of 8 storied building(EQ load in Z-dir)for 58 random infill pattern (no infill on Ground floor and 20% infill on upper floors)

4.42 Variation in base shear value (RSM) of 8 storied building(EQ load in Z-dir)for 59 random infill pattern (no infill on Ground floor and 40% infill on upper floors)

4.43 Variation in base shear value (RSM) of 8 storied building(EQ load in Z-dir)for 59 random infill pattern (no infill on Ground floor and 60% infill on upper floors)

4.44 Variation in base shear value (RSM) of 8 storied building(EQ load in Z-dir)for 59 random infill pattern (no infill on Ground floor and 80% infill on upper floors)

4.45 Variation in base shear value (RSM) of 8 storied building(EQ load in Z-dir)for 60 random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

4.46 Variation in base shear value (RSM) of 8 storied building(EQ load in Z-dir)for 61 random infill pattern (20% infill on Ground floor and 40% infill on upper floors)

4.47 Variation in base shear value (RSM) of 8 storied building(EQ load in Z-dir)for 61 random infill pattern (20% infill on Ground floor and 60% infill on upper floors)

4.48 Variation in base shear value (RSM) of 8 storied building(EQ load in Z-dir)for 61 random infill pattern (20% infill on Ground floor and 80% infill on upper floors)

4.49 Variation in base shear value (RSM) of 10storied building(EQ load in Z-dir)for 62 random infill pattern (no infill on Ground floor and 20% infill on upper floors)

4.50 Variation in base shear value (RSM) of 10storied building(EQ load in Z-dir)for 63 random infill pattern (no infill on Ground floor and 40% infill on upper floors)

4.51 Variation in base shear value (RSM) of 10storied building(EQ load in Z-dir)for 63 random infill pattern (no infill on Ground floor and 60% infill on upper floors)

4.52 Variation in base shear value (RSM) of 10storied building(EQ load in Z-dir)for 63 random infill pattern (no infill on Ground floor and 80% infill on upper floors)

4.53 Variation in base shear value (RSM) of 10storied building(EQ load in Z-dir)for 64 random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

4.54 Variation in base shear value (RSM) of 10storied building(EQ load in Z-dir)for 65 random infill pattern (20% infill on Ground floor and 40% infill on upper floors)

4.55 Variation in base shear value (RSM) of 10storied building(EQ load in Z-dir)for 65 random infill pattern (20% infill on Ground floor and 60% infill on upper floors)

4.56 Variation in base shear value (RSM) of 10storied building(EQ load in Z-dir)for 65 random infill pattern (20% infill on Ground floor and 80% infill on upper floors)

4.57 Variation in base shear value (RSM) of 12storied building(EQ load in Z-dir)for 66 random infill pattern (no infill on Ground floor and 20% infill on upper floors)

4.58 Variation in base shear value (RSM) of 12storied building(EQ load in Z-dir)for 67 random infill pattern (no infill on Ground floor and 40% infill on upper floors)

4.59 Variation in base shear value (RSM) of 12storied building(EQ load in Z-dir)for 67 random infill pattern (no infill on Ground floor and 60% infill on upper floors)

4.60 Variation in base shear value (RSM) of 12storied building(EQ load in Z-dir)for 67 random infill pattern (no infill on Ground floor and 80% infill on upper floors)

4.61 Variation in base shear value (RSM) of 12storied building(EQ load in Z-dir)for 68 random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

4.62 Variation in base shear value (RSM) of 12storied building(EQ load in Z-dir)for 69 random infill pattern (20% infill on Ground floor and 40% infill on upper floors)

4.63 Variation in base shear value (RSM) of 12storied building(EQ load in Z-dir)for 69 random infill pattern (20% infill on Ground floor and 60% infill on upper floors)

4.64 Variation in base shear value (RSM) of 12storied building(EQ load in Z-dir)for 69 random infill pattern (20% infill on Ground floor and 80% infill on upper floors)

xi

4.65 Base shear comparison(for EQ loading in X-dir) between ESFM and RSM 70 (20% infill on upper floors with no infill on ground floor) 4.66 Base shear comparison(for EQ loading in X-dir) between ESFM and RSM 70 (40% infill on upper floors with no infill on ground floor) 4.67 Base shear comparison(for EQ loading in X-dir) between ESFM and RSM 71 (60% infill on upper floors with no infill on ground floor) 4.68 Base shear comparison(for EQ loading in X-dir) between ESFM and RSM 71 (80% infill on upper floors with no infill on ground floor) 4.69 Base shear comparison(for EQ loading in X-dir) between ESFM and RSM 72 (20% infill on upper floors with 20% infill on ground floor) 4.70 Base shear comparison(for EQ loading in X-dir) between ESFM and RSM 72 (40% infill on upper floors with 20% infill on ground floor) 4.71 Base shear comparison(for EQ loading in X-dir) between ESFM and RSM 73 (60% infill on upper floors with 20% infill on ground floor) 4.72 Base shear comparison(for EQ loading in X-dir) between ESFM and RSM 73 (80% infill on upper floors with 20% infill on ground floor) 4.73 Base shear comparison(for EQ loading in Z-dir) between ESFM and RSM 74 (20% infill on upper floors with no infill on ground floor) 4.74 Base shear comparison(for EQ loading in Z-dir) between ESFM and RSM 74 (40% infill on upper floors with no infill on ground floor) 4.75 Base shear comparison(for EQ loading in Z-dir) between ESFM and RSM 75 (60% infill on upper floors with no infill on ground floor) 4.76 Base shear comparison(for EQ loading in Z-dir) between ESFM and RSM 75 (80% infill on upper floors with no infill on ground floor) 4.77 Base shear comparison(for EQ loading in Z-dir) between ESFM and RSM 76 (20% infill on upper floors with 20% infill on ground floor) 4.78 Base shear comparison(for EQ loading in Z-dir) between ESFM and RSM 76 (40% infill on upper floors with 20% infill on ground floor) 4.79 Base shear comparison(for EQ loading in Z-dir) between ESFM and RSM 77 (60% infill on upper floors with 20% infill on ground floor) 4.80 Base shear comparison(for EQ loading in Z-dir) between ESFM and RSM 77 (80% infill on upper floors with 20% infill on ground floor) 4.81 Modification factor (X-dir) for random application of Infill (in different 80 percentage) with no infill on ground floor 4.82 Modification factor (X-dir) for random application of Infill (in different 81 percentage) with 20 infill on ground floor 4.83 Modification factor (Z-dir) for random application of Infill (in different 81 percentage) with no infill on ground floor 4.84 Modification factor (Z-dir) for random application of Infill (in different 82 percentage) with 20% infill on ground floor 4.85 Modification factor for different number of spans for a 6 storied building 83 with 40% infill on upper stories and no infill on GF (EQ loading in X-dir) 4.86 Modification factor for different number of spans for a 6 storied building 84 with 40% infill on upper stories and no infill on GF (EQ loading in Z-dir)

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LIST OF TABLES

Table Caption Page No.

3.1 Values and dimensions for the parameters and structural components 31

Of an example

4.1 Base shear variation of 6 storied building(EQ loading in X-dir) for random 38 application of Infill (in different percentage) with no infill on ground floor

4.2 Base shear variation of 6 storied building(EQ loading in X-dir) for random 40 application of Infill (in different percentage) with 20% infill on ground floor

4.3 Base shear variation of 8 storied building(EQ loading in X-dir) for random 42 application of Infill (in different percentage) with no infill on ground floor

4.4 Base shear variation of 8 storied building(EQ loading in X-dir) for random 44 application of Infill (in different percentage) with 20% infill on ground floor

4.5 Base shear variation of 10 storied building(EQ loading in X-dir) for random 46 application of Infill (in different percentage) with no infill on ground floor

4.6 Base shear variation of 10 storied building(EQ loading in X-dir) for random 48 application of Infill (in different percentage) with 20% infill on ground floor

4.7 Base shear variation of 12 storied building(EQ loading in X-dir) for random 50 application of Infill (in different percentage) with no infill on ground floor

4.8 Base shear variation of 12 storied building(EQ loading in X-dir) for random 52 application of Infill (in different percentage) with 20% infill on ground floor

4.9 Base shear variation of 6 storied building(EQ loading in Z-dir) for random 54 application of Infill (in different percentage) with no infill on ground floor

4.10 Base shear variation of 6 storied building(EQ loading in Z-dir) for random 56 application of Infill (in different percentage) with 20% infill on ground floor

4.11 Base shear variation of 8 storied building(EQ loading in Z-dir) for random 58 application of Infill (in different percentage) with no infill on ground floor

4.12 Base shear variation of 8 storied building(EQ loading in Z-dir) for random 60 application of Infill (in different percentage) with 20% infill on ground floor

4.13 Base shear variation of 10 storied building(EQ loading in Z-dir) for random 62 application of Infill (in different percentage) with no infill on ground floor

4.14 Base shear variation of 10 storied building(EQ loading in Z-dir) for random 64 application of Infill (in different percentage) with 20% infill on ground floor

415 Base shear variation of 12 storied building(EQ loading in Z-dir) for random 66 application of Infill (in different percentage) with no infill on ground floor

4.16 Base shear variation of 12 storied building(EQ loading in Z-dir) for random 68 application of Infill (in different percentage) with 20% infill on ground floor

4.17 Modification factor for different no. of spans for a 6 storied building with 83

40% infill on upper stories and no infill on GF(for EQ loading in X-dir)

4.18 Modification factor for different no. of spans for a 6 storied building with 84

40% infill on upper stories and no infill on GF(for EQ loading in X-dir)

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ABBREVIATIONS

ESFM - Equivalent Static Force Method.

RSM - Response Spectrum Method.

EQ - Earthquake

BNBC - Bangladesh National Building Code

y - Vertical Compressive stress

xy - Shear stress

E - Youngs Modulus of elasticity

K - Stiffness of the structure

fm - masonry prism strength

Vm - maximum lateral force

um - Displacement corresponding to the lateral force

Ad - Area of equivalent diagonal strut

Ld - Length of equivalent diagonal strut

Mn - nominal moment

As - Steel area

fy - yield strength of steel

fc - strength of concrete

- Density

- Poissons ratio

V - Design base shear

Z - Seismic zone coefficient

I - Coefficient of structural importance

C - Numerical coefficient

R - Response modification factor for structural system

W - Total seismic Dead load

T - time period of natural vibration

S - Seismic zone coefficient

DL - Dead Load

LL - Live load

PW - Partition wall

MI - Masonry Infill

1

CHAPTER 1

INTRODUCTION

1.1 GENERAL Masonry building is a type of building that uses RCC columns and beams as a bearing

system. In this paper masonry walls are modeled by FEM and analyzed linear

statically. Linear properties of materials are considered in the modeling too. The

vulnerability of masonry building bear frame and a soft story building are compared

under seismic load and LL and DL and the combination of loading as per BNBC by

creating 3D models through linear static analysis.

Masonry buildings are common constructions all over the world because of low-cost

and availability of material as well as convenient and simple construction technology.

Due to past Earthquake, there are several financial damages of masonry buildings. For

this reason now-a-days Earthquake has been a major concern for structural engineers.

Primary objectives of infill application are to functioning as partition wall. It also

braces the frame laterally and increases the stiffness of the surrounding frame units.

The horizontal bracing act of infill modifies the vibration behavior of the building

frame. The natural period of building is modified due to the mass contribution on total

weight and due to the increase of inplane rigidity on upper floors. Conventional

analysis techniques dont consider infill as structural component and the structural

behavior of building frame is different under seismic load than predicted. Presence of

masonry infill on upper floors making them stiffer causes rigid body movement under

seismic vibration. Thus the columns at open ground floor not being strong enough get

damaged permanently under horizontal vibration. So the structural effect of masonry

infill is to be recognized and the proper modification on RC frame design procedure

should be adopted.

1.2 OBJECTIVE AND SCOPE OF THE STUDY The objective of the study is to determine the base shear modification under the action of

earthquake load on masonry infilled RC frame having open ground floor. The elementary

goal is to feature on the consideration of combined structural effect of infill with soft ground

2

floor compared to bare frame. The specific objectives of the investigation can be summarized

as follows;

To develop a 3D finite element model of building

a) With infill on upper floors and soft ground floor.

b) With infill on both upper floors and ground floors.

Modeling of infill as diagonal struts and applied in different percentage

randomly on frame system.

To analyze the building system by both Equivalent Static Force Method

(ESFM) and dynamic Response Spectrum Method (RSM) following

Bangladesh National Building Code (BNBC, 1993).

Comparison of base shear values by the two methods for certain structural

variables.

To analyze the variation in base shear for same percentage of randomly

applied infill in different methods.

To obtain some modification factor for base shear respective to the traditional

design value by ESFM.

To study the change in modification factor with change of span number and

length.

There are a number of factors and variables on which the study can be carried but here, the

base shear value for earthquake load on infilled structure will be focused and analyzed.

Buildings with regular and symmetric geometry will be considered only.

1.3 ASSUMPTIONS FOR MODELING SIMPLICITY The investigation is based on the following assumptions;

Material is linearly elastic and isotropic

All dead and live loads are taken as vertical while only earthquake load is

taken as lateral

Infill is modeled as diagonal strut with material properties of brick

Dead load including infill (partition wall) mass contribution is modeled as

mass element with vertical acceleration only

1.4 ORGANIZATION OF THE THESIS The whole thesis is organized into five chapters. Chapter 1 introduces the present

study while Chapter 2 focuses on the review of relevant theories, methods of analysis

3

and behavior of RC frame with infill. Chapter 3 illustrates the methodology of finite

element modeling by suitable program package. Chapter 4 is organized with analysis

and discussion on output results based on various parameters. Chapter 5 is for the

summary of findings from current study and concluding recommendations for future

investigation and extension of this work.

4

CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION Bangladesh is experiencing a rapid pace of urbanization. As a result, a lot of

multistoried buildings are built in order to fulfill the demand. Normal trend is

to provide parking facilities by keeping open story at ground level or basement while

there are brick masonry infill wall panels at the upper floors. This building procedure

makes the upper floors stiffer and a soft story on ground floor.

Fig. 2.1b A Building with soft ground floor

Irregularities of lateral stiffness in vertical direction are occurred due to the

application of random infill on different floor levels with open ground floor.

Buildings are classified as having a "soft story" if that level is less than 70% as stiff as

the floor immediately above it, or less than 80% as stiff as the average stiffness of the

three floors above it. Soft story buildings are vulnerable to collapse in a moderate to

severe phenomenon known as soft story collapse. The inadequately-braced level is

relatively less resistant than surrounding floors to lateral earthquake motion, so a

disproportionate amount of the building's overall side-to-side drift is focused on that

5

floor. Subject to disproportionate lateral stress, and less able to withstand the stress,

the floor becomes a weak point that may suffer structural damage or complete failure,

which in turn results in the collapse of the entire building.

In reality the design is done assuming no infill contribution in most of the cases

because of the absence of adaptable ideal procedures to count the effect of infill on

frame structure.

The significance of strength contribution and modification of masonry infill in RC

frame under lateral load is recognized from few decades and some practical

application of some research outputs is trying to be established under regular

simplified form. Here the application features and limitations of these approaches will

be highlighted and an acceptable conclusion for effect of random infill application

will be attempted to formulate.

2.2 BEHAVIOR OF MASONRY INFILLED RC FRAME UNDER

LATERAL LOAD The masonry infill is used to fulfill some functional requirements of the building

structure like partitioning, providing building envelope, temperature & sound barrier

etc. The structural contribution of masonry infill under seismic load is not considered

correctly due to the lack of analytical knowledge.

Researchers (Klingner and Bertero in 1978, Bertero and Brokkenc in 1983, Mehrabi

et al. in 1996) have concluded that the proper and careful use of infill can

significantly increase the strength and stiffness of structure subjected to seismic

excitations. To ensure the adequate safety of building the selection of infill location

Fig-2.1b Soft story mechanism

6

must be such that the torsional and soft story effect is minimized under architectural

restrictions.

In 3D RC frame system the confined masonry infill walls contribute a vital part on

resisting lateral seismic loads on building. To develop a logical approach of designing

such RC frames the behavior of masonry infill is closely investigated (Moghaddam

and Dowling in 1987, Smith and Coul in 1991, Murty and Jain in 2000). It was also

investigated experimentally that the masonry infill walls have a very high lateral

stiffness and low deformability. So, the application of masonry infill in RC frames

changes the lateral load transfer mechanism from predominant frame action to

predominant truss action as shown in fig-2.2.

(a) Predominant frame action (b) Predominant truss action

Fig. 2.2 Change in lateral load transfer mechanism due to masonry infills (Murty and Jain 2000)

Fig. 2.3 Interactive behavior of frame and infill

7

Under the effect of high in plane rigidity of the masonry wall the relatively flexible

frame is stiffened significantly. The relatively stiff bracing system is contributed

partly by its in plane shear resistance (Fig. 2.3) and by the behavior as diagonal

bracing strut.

Under horizontal loading the frame is deformed with double-curvature bending of the

columns and beams. The translation of the upper part of the column in each story and

the shortening of the loading diagonal of the frame causes the column to learn against

the wall as well as to compress the wall along its diagonal. Its roughly analogous to a

diagonal braced frame (Fig. 2.4).

The potential modes of failure of masonry infilled frame structure are occurred due to

the interaction of infill walls with frame.

The failure modes are given below (Fig. 2.5 and 2.6):

Tension failure of tensioning column due to overturning moments.

Flexure or shear failure of the columns.

Compression failure of the diagonal strut.

Diagonal tension cracking of the panel and

Sliding shear failure of the masonry along horizontal mortar beds.

Fig. 2.4 Analogous braced frame

8

The perpendicular tensile stresses are caused by the divergence of the compressive

stress trajectories on the opposite sides of the leading diagonal as they approach the

mid region of the infill. The shear failure of wall steps down through the joints of

masonry and participated by the horizontal shear stresses in the bed joints. The

diagonal cracking of the wall is through the masonry along a line or line parallel to

the loading diagonal and caused by tensile stresses perpendicular to the loading

diagonal. The perpendicular tensile stresses caused by the divergence of the

compressive stress trajectories on opposite sides of the loading diagonal as they

Fig. 2.5 Modes of infill failure

Fig. 2.6 Modes of frame failure

9

approach the middle region of the infill. The diagonal cracking is initiated and

spreads from the middle of the infill while the tensile stresses are at maximum

tending to stop near the compression corners, where the tension is suppressed.

The nature of the forces in the frame can be understood by referring to the analogous

braced frame shown in (fig. 2.4). The windward column or the column facing the

seismic load first is in tension and the leeward column or the other side of the

building facing seismic load last is in compression. Since the infill bears on the frame

not as exactly a concentrated force at the corners, but over the short lengths of the

beam and column adjacent to each compression corner, the frame members are

subjected also to transverse shear and a small amount of bending. Consequently the

frame members or their connections are liable to fail by axial force or shear and

especially by tension at the base of the windward column.

2.3 COMPUTATIONAL MODELLING AND ANALYSIS OF

INFILLED FRAME Different types of modeling approach were attempted for featuring infill

characteristics in RC frame. Holmes (1961) replaced the infill by an equivalent pin-

jointed diagonal strut. Smith (1962) conducted a series of tests on laterally loaded

square mild steel frame models infilled with micro-concrete. From the model

deformation results he concluded that the wall could be replaced by an equivalent

diagonal strut connecting the loaded corners. As the elastic methods were not able to

fully feature the actual characteristics of infilled frames, attention was paid to the

theories of plasticity. Wood (1958) extended the limit analysis of plasticity with the

assumption of perfect plasticity. Recently a method was developed by Saneinejad

(1995) that allows for interface shear forces and both the elastic and plastic behavior

of material. The stiffness of structural system is determined with variations in

geometrical and mechanical characteristics. The analysis is carried out utilizing the

boundary element method (BEM) for the infill and dividing the frame into finite

elements, so as to transform the mutual interactions of the two subsystems into

stresses distributed along the boundary for the infill and into nodal actions for the

frame. In this study we have worked with the Equivalent Diagonal Strut Method

stated bellow.

10

2.3.1 Equivalent Diagonal Strut Method

The first published research on modeling of infill panel as an equivalent diagonal

strut method was applied by Holmesh (1961). He assumed that the infill wall acts as

diagonal compression strut as shown in (fig-2.7) of the same thickness and elastic

modulus as the infill with a width equal to one-third the diagonal length. He also

concluded that at the infill failure, the lateral deflection of the infilled frame is small

compared to the deflection of the corresponding bare frame.

Saneinejad and Hobbs (1995) developed a method based on the equivalent diagonal

strut approach for the analysis and design of steel or concrete frames with concrete or

masonry infill walls subjected to in-plane forces.

The analytical assumptions are the contribution of the masonry infill panel (fig-2.8 a)

to the response of the infilled frame can be modeled by replacing the panel by a

system of two diagonal masonry compression struts (fig-2.8 b). However, the

combinations of both diagonal struts provide a lateral resisting mechanism for the

opposite lateral directions of loading.

Fig. 2.7 Material modeling of masonry infill as diagonal strut

Fig. 2.8 (a) Masonry infilled frame sub-assemblage in masonry infill panel frame

Fig. 2.8 (b) Masonry infill panel in frame structure

11

2.4 EFFECT OF EARTHQUAKE ON BUILDING FRAME WITH

SOFT STORY Open ground floor or soft story mechanism forms a poor framing system because of

sudden drop in stiffness and strength in ground floor. In practice, stiff masonry infill

walls (fig- 2.11 a) are neglected and only bare frames (fig- 2.11 b) are considered for

design consideration. The mode shapes vary based on the location and quantity of

infill on upper floor levels with soft floor on ground level.

In case of fully infilled frame, lateral displacements are uniformly distributed along

the height as shown in Fig-2.12 (a). But in case of open ground floor , the major

portion of the lateral displacement is accumulated on the ground floor level because

of its flexible behavior due to lack of infill in Fig-2.12 (b). Similarly, in case of

seismic loading the shear force and bending moment are concentrated on soft ground

floor level instead of being distributed uniformly.

(a) (b) Fig. 2.9 Open ground story building (a) actual building (b) building being

assumed in current design practice

Fig. 2.10 Effects of masonry infills on the first mode shape of a typical frame of a ten story RC building , Displacement profile (a) fully infilled frame (b) open ground floor frame

12

Fig. 2.11 some effects of Earthquake on soft story buildings

13

The seismic force distribution and energy dissipation is dependent on the distribution

of stiffness and mass of the structure along its height. The upper stories being very

stiff undergoes less inter-floor lateral drift while the soft ground floor being less stiff

undergoes very high lateral drift and the soft story columns dissipate most of the

seismic energy in the process of plastic hinges. Thus the possibility and risk of

collapse is very high in case of soft story under lateral loads. The feature of soft story

mechanism is not considered in the present method of analysis for earthquake load. In

static method we only consider the first mode of vibration (thats suitable for regular

bare frames) while the behavior of infilled and irregular frames are far more

complicated and uncertain. Thats why the dynamic analysis is helpful to account for

the other modes of vibration and consider the irregularity of stiffness features in

building frame caused by random distribution of infill on upper floors. If we can

consider the true dynamic features of the frame system then the design will be safer

and adequate.

2.5 BUILDING CODES Building codes specify the design and construction requirements ensuring public

safety from structural failure and loss of life and wealth. Because of the differences in

magnitude of earthquake, geological formations, construction types, economical

development and other features the seismic design aspects are different in different

building codes. The national building codes of different countries can be classified in

two broad categories for our discussion. First are those Codes do not consider the

features of Masonry Infill walls while designing RC frames and the others are those

consider the features of Masonry Infill walls while designing RC frames.

2.5.1 Without Considering Soft Story Phenomenon

There are some advantageous features of masonry infill walls like high initial lateral

stiffness, cost effectiveness, ease in construction etc. Proper location and distribution

of infill application can increase the defense tremendously against seismic action.

These codes want to ensure the safety through proper layout and quality control

instead of considering the soft story features directly. In most cases the codes state

that the regular geometry of structures perform better against earthquake loads while

unsymmetrical application of MI walls introduce irregularities in structure. In case of

14

low rise buildings and low risk zone for seismic danger the codes normally

recommend static analysis while for high rise structures dynamic analysis is

recommended for adequate modeling and to obtain actual seismic design force.

Natural period of vibration is an important factor for seismic force design. Normally

the natural period is higher in case of bare frames than masonry infilled RC frames.

Thats why the design force for MI RC frames is higher than bare frames. There are

some suggestions in different codes about the natural period in case of MI-RC frames.

The following empirical formula in Eqn 2.7.1 is given by IS-1893 (2002), NBC-105

(1995), NSR-98 (1998) Egyptian code (1988), Venezuelan code (1988), Algerian

code (1988), ESCP-1 (1983);

Ta = dh09.0 2.7.1

Where, h is the height of building in meter and d is the base dimension of building in

meter at the plinth level along the considered direction of the lateral force.

French code (AFPS-90, 1990) recommends the following Eqn 2.7.2 for masonry

infilled buildings;

T = 0.06hd

hdh

+2 2.7.2

2.5.2 Considering Soft Story Phenomenon

Vertical irregularities are introduced in MI-RC frames due to the reduction or absence

of MI in particular stories compared to other adjacent stories. This matter creates

irregularities in mass, stiffness, strength along the height of the structure. As a result

the design of the beam and column is needed to be modified according to

modification of base shear value under lateral load due to formation of irregularities

for random MI application. There are some building codes where instruction for

design modification for soft story phenomenon is given.

The Indian seismic code (IS-1893 2002) requires members of the soft story (story

stiffness less than 70% of that in the story above or less than 80% of the average

lateral stiffness of the three stories above) to be designed for 2.5 times the seismic

story shears and moments obtained without considering the effects of MI in any story.

The factor of 2.5 is specified for all the buildings with soft stories irrespective of the

extent of irregularities. The other option is to provide symmetric RC shear walls

15

designed for 1.5 times the design story shear force in both directions of the building

as far away from the center of the building as feasible.

2.6 PAST RESEARCH ON SOFT STORY BUILDING

Amanat and Hoque (2006) studied the fundamental periods of vibration of a series of

regular RC framed buildings using 3-D FE modeling and modal eigenvalue analysis

including the effects of infill. The time period determined from eigenvalue analysis

was remarkably close to those predicted by the code formulas. Its also observed that

the randomness of infill application does not cause much variation of the period if the

total amount of infill panel is same. Based on the findings of the study some practical

guidelines were suggested for determining the fundamental period of RC frames

using rational approaches like modal analysis.

Costa Rican code (1986) requires that all structural resisting system must be

continuous from the foundation to the top of the building and stiffness of a story must

not be less than 50% of that of the story below.

Arlekar, Jain and Murty (1997) highlighted the importance of explicitly recognizing

the presence of the open ground story in the analysis of the building. The error

involved in modeling such buildings as complete bare frames, neglecting the presence

of infills in the upper story, is brought out through the study of an example building

with different analytical models.

Fardis and Panagiotakos (1997) studied through numerical analyses the effects of

masonry infills on the global seismic response of reinforced concrete structures.

Response spectra of elastic SDOF frames with nonlinear infills show that, despite

their apparent stiffening effect on the system, infills reduce spectral displacements and

forces mainly through their high damping in the first large post-cracking excursion.

Mezzi (2004) illustrated soft story to be very dangerous from seismic viewpoint as

the lateral response of these buildings is characterized by a large rotation ductility

demand concentrated at the extreme sections of the columns of the ground floors,

while the superstructure behaves like a quasi-rigid body. A solution was proposed for

the preservation of a particular architectonic double soft story configuration.

Huang (2005) studied the structural behaviors of low-to-midrise concrete buildings of

various configurations with emphases on dynamic properties, internal energy, and the

magnitude and distribution of seismic load. Several idealized models were made to

16

represent different structural configurations including pure frame, frames with fully or

partially infilled panels, and frames with a soft story at the bottom level, and

comparisons were made on the fundamental periods, base shear, and strain energy

absorbed by the bottom level between these structures.

M. Helen Santhi, G. M. Samuel Knight (2005) studied two single-bay, three-story

space frames, one with brick masonry infill in the second and third floors representing

a soft-story frame and the other without infill were designed and their 1:3 scale

models were constructed according to non-seismic detailing and the similitude law.

Rodsin (2005) evaluated the potential seismic performance of building with soft story

in an area of low to moderate seismicity regions (such as Australia) by a

displacement-based method involving a push-over analysis.

Nagae (2006) studied six storied reinforced concrete building and focused on seismic

response of the soft ground floor based on the results on dynamic response analysis.

Jahid Hasnain (2009) studied this phenomenon of soft story building. He determined

the effect of randomly distributed infills on seismic base shear for RC buildings with

soft ground floor. In spite of providing an extensive analysis, his study is also limited

due to the following issues:

Random application of infill.

Constant beam and column size.

Application of earthquake load only along X direction.

Application of partition wall load as a constant.

Equal distribution of total number of infill along the span and bay.

In our research we provide an extensive study of the above mentioned issues and

successfully overcome the limitations. The following modifications have been

proposed with randomly applied infill:

Variation of beam and column size with varying span or bay length. A

minimum dimension is also used.

Application of earthquake load along X and Z directions.

Variation of partition wall load along with varying percentage of infill.

Distribution of total number of infill as a ratio of span and bay along the span

and bay.

17

CHAPTER 3

FINITE ELEMENT MODELING OF INFILL FRAME

3.1 INTRODUCTION In this chapter the full structural modeling of 3D MI-RC frame is made including

individual modeling like beam, column, slab, infill, load etc. with proper support

condition. To model the masonry infill, link element is taken as diagonal strut and for

load application, mass element is chosen accordingly. For the analysis both

equivalent static force method (according to BNBC) and RSM is considered. The

comparison of effect of infill between ESFM and RSM is done to assess the real

structural characteristics of soft story.

3.2 SOFTWARE FOR FINITE ELEMENT ANALYSIS A good number of software packages are available for finite element analysis in civil

engineering field. Some of those are designed for specialized structural analysis and

specific behavioral characteristics. Among them ANSYS program package has more

advantageous features for the analysis performed in this research. So, the ANSYS

10.0 package has been selected for its vastness, flexibility and ease in use as finite

element analysis tool.

3.3 ASSUMPTIONS FOR MODELING SIMPLIFICATION We assumed linearly elastic homogeneous material for the RC frame that is always

steel reinforced in reality. According to ACI recommendation, the analysis results for

RC frame are accurate enough for this simplification only if appropriate properties of

concrete are considered. The structural property of masonry infill is modeled as

compressive diagonal strut assuming negligible tensile strength of masonry. This

simplification is fare enough to resist the lateral load by compression only.

3.4 CHARACTERIZATION OF STRUCTURAL COMPONENTS

IN MODEL

3.4.1 BEAM4 (3-D Elastic Beam) for Beam and Column

18

Element Description

BEAM4 is a uniaxial element with tension, compression, torsion, and bending

capabilities. The element has six degrees of freedom at each node: translations in the

nodal x, y, and z directions and rotations about the nodal x, y, and z axes. The

geometry, node locations, and coordinate systems for this element are shown in fig

3.1 The element is defined by two or three nodes, the cross-sectional area, two area

moments of inertia (IZZ and IYY), the torsional moment of inertia (IXX) and the

material properties.

Input Summary

Element Type - BEAM4

Nodes - I, J, K (K orientation node is optional)

Degrees of Freedom - UX, UY, UZ, ROTX, ROTY, ROTZ

Fig. 3.1 BEAM4 Geometry

19

Real Constants - AREA, IZZ, IYY, HEIGHT, WIDTH, IXX

Material Properties - EX, PRXY, DENS

Output Data The solution output associated with the element is in two forms:

Nodal displacements included in the overall nodal solution

Additional element output

3.4.2 Shell63 (Elastic Shell) for Slab

Element Description

SHELL63 has both bending and membrane capabilities. Both in-plane and normal

loads are permitted. The element has six degrees of freedom at each node: translations

in the nodal x, y, and z directions and rotations about the nodal x, y, and z-axes.

Stress stiffening and large deflection capabilities are included. A consistent tangent

stiffness matrix option is available for use in large deflection (finite rotation)

analyses.

Input Summary

Element Type - SHELL63

Nodes - I, J, K, L

Degrees of Freedom - UX, UY, UZ, ROTX, ROTY, ROTZ

Fig. 3.2 SHELL63 Geometry

20

Real Constants - TK(I), TK(J), TK(K), TK(L)

Material Properties - EX, PRXY, DENS

Output Data

The solution output associated with the element is in two forms:

Nodal displacements included in the overall nodal solution

Additional element output

3.4.3 MASS21 (Structural Mass) for load application

Element Description

MASS21 is a point element having up to six degrees of freedom: translations in the

nodal x, y, and z directions and rotations about the nodal x, y, and z axes. A different

mass and rotary inertia may be assigned to each coordinate direction.

Input Summary

Element Type - MASS21

Nodes - I

Degrees of Freedom - UX, UY, UZ, ROTX, ROTY, ROTZ

Real Constants - MASSX, MASSY, MASSZ

Material Properties - DENS

Output Data

Nodal displacements are included in the overall displacement solution. There is no

printed or post element data output for the MASS21 element.

Fig. 3.3 MASS21 Geometry

21

3.4.4 LINK8 (3-D Spar or Truss) for diagonal strut

Element Description

LINK8 is a spar which may be used in a variety of engineering applications. This

element can be used to model trusses, sagging cables, links, springs, etc. The 3-D spar

element is a uniaxial tension-compression element with three degrees of freedom at

each node: translations in the nodal x, y, and z directions. As in a pin-jointed

structure, no bending of the element is considered. Plasticity, creep, swelling, stress

stiffening, and large deflection capabilities are included.

Input Summary

Element Type - LINK8

Nodes - I, J

Degrees of Freedom - UX, UY, UZ

Real Constants - AREA

Material Properties - EX, PRXY, DENS

Output Data

The solution output associated with the element is in two forms:

Nodal displacements included in the overall nodal solution

Additional element output

Fig. 3.4 LINK8 Geometry

22

3.4.5 Support Condition

At foundation level all column ends are considered to act under fixed support

condition with all degrees of freedom of the support being restrained.

3.4.6 Load application

The x-z plane is acting as the horizontal plane in global co-ordinate system. The load

cases considered according to BNBC, 1993.

The considered load can be categorized to vertical and lateral directions.

Vertical load

Dead Load: Weight of permanent structural and nonstructural component of the

structure is considered as dead load. The structural self weight is already taken with

the modeling and the rest nonstructural vertical load is applied as mass for floor finish

(1.43 x 10-3 N/mm2) and partition wall (Infill) on nodes as uniformly distributed load.

Live Load: The temporary load acting on structure as occupancy load is called live

load and considered as uniformly distributed surface load (valuing 2.395 x 10-3

N/mm2) in vertical direction.

Lateral Load

Earthquake Load: The earthquake load acts at lateral direction. Here, this seismic

load is considered for both static and modal analysis according to BNBC, 1993.

3.5 SEISMIC LOAD CALCULATION

Two methods are used to compare the results of seismic load.

Static analysis (Equivalent static Force Method)

Modal analysis

23

3.5.1 Static Analysis (Equivalent static Force Method)

According to BNBC, 1993 empirical equations are given in this method is applied for

calculation of seismic base shear based on vibration period of whole structure. No

consideration for structural nonlinearity and stiffness is made here and the considered

period is for first mode of vibration only.

Design Base Shear, WRZICV = 3.1

Where, Z = Seismic zone co-efficient

I = Structural importance coefficient

W = Total seismic dead load

R = Response modification factor for structural system

C =1.25S/(T)2/3 3.2

S = Sight co-efficient for soil characteristics

T = Fundamental period of vibration

=0.073(hn)3/4 3.3

hn = Height of structure above base (in meter)

3.5.2 Response Spectrum Method (RSM)

In this method of dynamic analysis the multiple modes of response of a structure are

taken into account. Its a plot of the peak or the steady-state response of a series of

frequencies that are forced to oscillate under same base vibration. From the resulting

Fig. 3.5 Finite Element modeling of total structure

24

plot we can asses the pick of the natural frequency for a particular mass of the linear

structure. To get the actual dynamic impact all significant modes should be

considered. The number of mode considered should be at least the number of floors.

A value for damping is needed to input otherwise the response will be infinite. RSM

can also be performed for multiple degree of freedom systems but its accurate only

for a low value for damping. Modal analysis is performed only to identify the mode

shape while the response for the particular mode can be assessed from the response

spectrum. The peak response is then combined to get the resultant response. The

combination of dynamic response must be done under specified established procedure

like SRSS (square root of sum of squares), CQC (Complete Quadratic Combination)

etc.

Random distribution of infill:

The position of infill is very important to the contribution on structural modification.

In current 3D analysis the random infill position is featured for each cases so that we

can find the base shear for different position of infill after each time run.

Fig. 3.6 Normalized response spectra for 5% Damping ratio

25

Fig- 3.7 Different patterns of 20% random infill application (6 storied building)

26

Fig- 3.8 Different patterns of 20% random infill application (8 storied building)

27

Fig- 3.9 Different patterns of 20% random infill application (10 storied building)

28

Fig- 3.10 Different patterns of 20% random infill application (12 storied building)

29

Methods of modal combination:

SRSS meaning Square root of the Sum of the Squares is a very common approach of

modal combination. Its done on the maximum modal values in order to estimate the

values of displacement or forces. Another method is CQC meaning Complete

Quadratic Combination for modal combination. Its a more modern method over

SRSS as it has overcome the limitation of SRSS. This method was first applied by

Wilson, Kiureghian and Bayo, 1981 is applicable to a wider class of structures. Its

based on random vibration theories with wide acceptance to most engineers and has

been incorporated as an option in most modern computer programs for seismic

analysis.

In this study the CQC method of modal combination is used for its useful features for

closely spaced modes of complex 3-D structures.

Different mode shapes:

In case of modal analysis different mode shapes for probable vibration pattern are

encountered. Different mode shapes have different frequencies of vibration. Some of

the modes are closely spaced showing similar pattern of vibration. Here some well

distinguished mode shapes are featured to give some ideas about the different modes

of vibration in dynamic analysis.

(1) Elevation (2) Top view Fig. 3.7 (a) First mode shape

30

Fig. 3.7 (f) 15th mode shape

Fig. 3.7 (c) Sixth mode shape Fig. 3.7 (d) Seventh mode shape

(2) Elevation (2) Top view Fig. 3.7 (b) third mode shape

Fig. 3.7 (e) 10th mode shape

31

3.6 MODEL CHARACTERISTICS FOR ANALYSIS AND TYPICAL RESULT

In the present study the main objective is to study the variation range in seismic effect

in multistoried building for random application of infill with soft story. For the study

6, 8, 10 and 12 story buildings having 4 span 4 bay has been analyzed by ANSYS

package. A reference structure is shown in fig.- 3.5. The dimensions of structural

components were assumed relatively and the material parameters were taken

accordingly for normal concrete.

Table 3.1: Values and dimensions for the parameters and structural components

of an example:

Parameter Value/Dimension Span length 6000 mm Bay width 5000 mm Floor height 3000 mm Slab thickness 150 mm Floor finish 1.43710-3 N/mm2 Live load 2.39510-3 N/mm2 Beam Width 250 Beam Height SPAN/14 Column as per design requirement Gravitational acceleration 9810 mm/sec2 Concrete properties Modulus of elasticity 20000 N/mm2 Poissons ratio 0.13 Density 2.410-9 Ton/mm3 Unit weight 2.3610-5 N/mm3

Infill properties Density 1.9210-9 Ton/mm3

Thickness 130mm

32

Base Shear Comparison

Fig. 3.8(a) Variation in base shear in RSM analysis with % infill on upper floors

Fig. 3.8(b) Variation in base shear in Static analysis with % infill on upper floors

The base shear for 0% infill on both ground floor and upper floors remains the same

incase of both Response Spectrum Method and Equivalent Static Force Method.

33

Deformed shapes for deferent loading pattern:

Fig. 3.9(a) Deformation due to application of DL

For 40%infill on upper floors and no infill on GF

Fig. 3.9 (b) Deformation due to application of LL

For 40%infill on upper floors and no infill on GF

34

Fig. 3.9 (c) Deformation due to EQ load in X-direction (Static)

For 40%infill on upper floors and no infill on GF

Fig. 3.9 (d) Deformation due to EQ load in X-direction (RSM)

For 40%infill on upper floors and no infill on GF

35

Fig. 3.9 (e) Deformation due to EQ load in X-direction (Static)

For 40%infill on upper floors and 20% infill on GF

Fig. 3.9 (f) Deformation due to EQ load in X-direction (RSM)

For 40%infill on upper floors and 20% infill on GF

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CHAPTER 4

RESULTS AND DISCUSSION

4.1 INTRODUCTION

Seismic characteristics of masonry infilled RC frame with soft ground story effect

have been examined and compared with that of a building having infill on ground

story in this study considering variable parameters. The parameters taken based on

practical values and dimensions so that the actual building behavior under natural

seismic load is reflected accordingly. The variation of base shear value under

dynamic analysis for the random application of infill is tried to investigate.

The current study is actually involved with a large number of variables but our

concentration will be limited to the effect of random distribution of infill. Firstly the

random effect of infill on upper floors has been studied for 6,8,10 and 12 storied

building with open ground floor and 20% infill on ground floor. The effect of number

of span on modification factor has been investigated for similar building systems.

4.2 VARIATION IN BASE SHEAR FOR RANDOM APPLICATION OF

INFILL

The findings of the parametric study are discussed according to the results. The study

is done for 6, 8, 10 and 12 storied building having different percentage of infill on

upper floors with soft ground story.

4.2.1 Range of variation in base shear value with infill

The results obtained from the analysis of finite element model of MI-RC frame are

tabulated sequentially and shown graphically.

From the results obtained (table-4.1 to table-4.16 and fig-4.1 to fig-4.80) we find that

for a particular frame the effect of randomly applied infill is not the same on base

shear value. For 20% and 40% infill on upper floors the RSM analysis is done for 15

times. For 60% and 80% infill on upper floors the RSM analysis is done for 10 times.

The variation in result is observed for each parameter. The bar charts show that for

infill percentage less than 50% (20% and 40%) the base shear value has a wider range

of variation while for infill percentage greater than 50% (60% and 80%) the range of

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variation is narrower. This is because for less % of infill the opportunity of variation

in infill location and pattern is far higher while for high % of infill the opportunity of

variation in infill location and pattern is less.

It is observed that for higher % of infill application the standard deviation of base

shear value by RSM is not of large value. So we can use individual value of base

shear for random effect with certain reliability. But in case of infill % less than 50%

we must take an average of close values neglecting the highly deviated ones.

4.2.2 Modification factor for different parameters

To find the modification factor for randomly applied infill at different percentage, the

average values have been used. Here two sets of ground floor condition with different

% of infill on upper floors for 6, 8, 10 and 12 storied buildings have been analyzed.

From the previous results we have some correlations for modification factor for

application of different percentage of infill. The factor increases with increase of

number of floors.

Modification factor = static

RSM

VV

Where, RSMV = Base shear by RSM

STATICV = Base shear by static analysis

4.2.3 Range of variation in base shear value with span no. and length

From the results obtained (table-4.17 and table-4.18 and fig-4.49 and fig-4.80) we

find that for a particular frame the effect of floor number or span length is almost

same for base shear values.

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Table 4.1: Base shear variation of 6 storied building (EQ loading in X-dir) for random application of Infill (in different percentage) with no infill on ground floor

Upper floor infill percentage 20% 40% 60% 80%

Base shear values by RSM for different patterns of infill application (KN)

1475 1664 1835 2002 1253 1541 1820 1999 1470 1654 1830 1994 1438 1615 1834 2000 1470 1635 1825 2001 1477 1664 1832 2002 1491 1663 1826 2002 1487 1619 1835 1997 1433 1593 1832 2001 1449 1623 1825 1999 1439 1655 --- --- 1493 1659 --- --- 1441 1637 --- --- 1473 1637 --- --- 1451 1653 --- ---

Average Base shear by RSM (KN) 1449 1634 1829 2000 Maxima (KN) 1493 1664 1835 2002 Minima (KN) 1253 1541 1820 1994 Standard deviation 57.9 33.3 5.12 2.59 Base shear by ESFM (KN) 1004 1084 1164 1245 Modification Factor 1.44 1.51 1.57 1.61

Fig-4.1: Variation in base shear value (RSM) of 6 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 20% infill on upper floors)

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Fig-4.2: Variation in base shear value (RSM) of 6 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 40% infill on upper floors)

Fig-4.3: Variation in base shear value (RSM) of 6 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 60% infill on upper floors)

Fig-4.4: Variation in base shear value (RSM) of 6 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 80% infill on upper floors)

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Table 4.2: Base shear variation of 6 storied building (EQ loading in X-dir) for

random application of Infill (in different percentage) with 20% infill on ground floor

Upper floor infill percentage 20% 40% 60% 80%

Base shear values by RSM for different patterns of infill application (KN)

1178 1245 1760 1633 1377 1421 1682 1560 1406 1265 1618 1592 1309 1375 1424 1705 1305 1627 1660 1917 1117 1454 1447 1762 1380 1432 1601 1974 1212 1562 1414 1976 1290 1603 1807 1857 1243 1399 1412 1829 1365 1343 --- --- 1200 1295 --- --- 1214 1351 --- --- 1080 1299 --- --- 1343 1544 --- ---

Average Base shear by RSM (KN) 1268 1414 1583 1781 Maxima (KN) 1406 1627 1807 1976 Minima (KN) 1080 1245 1412 1560 Standard deviation 99.8 122.7 149 154 Base shear by ESFM (KN) 1018 1099 1179 1259 Modification Factor 1.24 1.3 1.34 1.41

Fig-4.5: Variation in base shear value (RSM) of 6 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

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Fig-4.6: Variation in base shear value (RSM) of 6 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 40% infill on upper floors)

Fig-4.7: Variation in base shear value (RSM) of 6 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 60% infill on upper floors)

Fig-4.8: Variation in base shear value (RSM) of 6 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 80% infill on upper floors)

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Table 4.3: Base shear variation of 8 storied building (EQ loading in X-dir) for random application of Infill (in different percentage) with no infill on ground floor

Upper floor infill percentage 20% 40% 60% 80%

Base shear values by RSM for different patterns of infill application (KN)

2129 2489 2766 3055 2192 2467 2773 3056 2045 2452 2718 3055 2120 2416 2764 3040 2086 2456 2767 3057 1928 2433 2687 3010 2081 2383 2772 3051 1948 2495 2777 3053 2125 2451 2771 3053 2101 2456 2740 3057 1948 2397 --- --- 2141 2487 --- --- 1969 2496 --- --- 2169 2442 --- --- 2156 2392 --- ---

Average Base shear by RSM (KN) 2076 2447 2754 3049 Maxima (KN) 2192 2496 2777 3057 Minima (KN) 1928 2383 2687 3010 Standard deviation 87.7 37.3 29.6 14.4 Base shear by ESFM (KN) 1204 1305 1406 1507 Modification Factor 1.72 1.87 1.96 2.02

Fig-4.9: Variation in base shear value (RSM) of 8 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 20% infill on upper floors)

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Fig-4.10: Variation in base shear value (RSM) of 8 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 40% infill on upper floors)

Fig-4.11: Variation in base shear value (RSM) of 8 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 60% infill on upper floors)

Fig-4.12: Variation in base shear value (RSM) of 8 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 80% infill on upper floors)

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Table 4.4: Base shear variation of 8 storied building (EQ loading in X-dir) for random application of Infill (in different percentage) with 20% infill on ground floor

Upper floor infill percentage 20% 40% 60% 80%

Base shear values by RSM for different patterns of infill application (KN)

1534 2388 2354 2717 1893 2320 2342 2578 1982 2187 2662 2542 1947 2004 2646 2556 1888 2338 2382 2518 2073 2134 2148 2602 1997 2349 2689 2669 1708 2334 2620 2474 2105 2246 2646 2896 1584 2175 2692 2401 1908 2051 --- --- 1897 2343 --- --- 1735 2174 --- --- 1791 2004 --- --- 1978 2276 --- ---

Average Base shear by RSM (KN) 1868 2222 2518 2595 Maxima (KN) 2105 2388 2692 2896 Minima (KN) 1534 2004 2148 2401 Standard deviation 167 129.6 193.4 138.9 Base shear by ESFM (KN) 1217 1318 1419 1520 Modification Factor 1.53 1.68 1.76 1.71

Fig-4.13: Variation in base shear value (RSM) of 8 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

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Fig-4.14: Variation in base shear value (RSM) of 8 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 40% infill on upper floors)

Fig-4.15: Variation in base shear value (RSM) of 8 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 60% infill on upper floors)

Fig-4.16: Variation in base shear value (RSM) of 8 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 80% infill on upper floors)

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Table 4.5: Base shear variation of 10 storied building (EQ loading in X-dir) for random application of Infill (in different percentage) with no infill on ground floor

Upper floor infill percentage 20% 40% 60% 80%

Base shear values by RSM for different patterns of infill application (KN)

2817 3277 3631 4252 2817 3448 3641 4223 2817 3449 3826 4215 2817 3406 3809 4248 2886 2872 3809 4236 2929 3369 3808 4206 2689 3413 3850 4256 2526 2969 3721 4251 2547 3449 3654 4236 2764 3435 3848 4221 2693 3461 --- --- 2887 3420 --- --- 2647 3102 --- --- 2864 3266 --- --- 2776 3156 --- ---

Average Base shear by RSM (KN) 2765 3299 3760 4234 Maxima (KN) 2929 3461 3850 4256 Minima (KN) 2526 2872 3631 4206 Standard deviation 121.5 190 88 17.4 Base shear by ESFM (KN) 1393 1513 1633 1752 Modification Factor 1.97 2.18 2.3 2.42

Fig-4.17: Variation in base shear value (RSM) of 10 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 20% infill on upper floors)

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Fig-4.18: Variation in base shear value (RSM) of 10 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 40% infill on upper floors)

Fig-4.19: Variation in base shear value (RSM) of 6 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 80% infill on upper floors)

Fig-4.20: Variation in base shear value (RSM) of 6 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 80% infill on upper floors)

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Table 4.6: Base shear variation of 10 storied building (EQ loading in X-dir) for random application of Infill (in different percentage) with 20% infill on ground floor

Upper floor infill percentage 20% 40% 60% 80%

Base shear values by RSM for different patterns of infill application (KN)

2833 3082 3370 4136 2660 2640 3332 3936 2449 2800 3465 3985 2544 3185 3594 3732 2703 3004 3649 4059 2477 2792 3485 4108 2615 2978 3218 3405 2714 2952 3692 4075 2523 2995 3551 3557 2711 3260 3318 4128 2493 2676 --- --- 2694 3208 --- --- 2412 3292 --- --- 2672 3285 --- --- 2462 3291 --- ---

Average Base shear by RSM (KN) 2596 3029 3467 3912 Maxima (KN) 2833 3292 3692 4136 Minima (KN) 2412 2640 3218 3405 Standard deviation 125.6 225.3 156 259 Base shear by ESFM (KN) 1405 1525 1644 1764 Modification Factor 1.85 1.98 2.11 2.22

Fig-4.21: Variation in base shear value (RSM) of 10 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

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Fig-4.22: Variation in base shear value (RSM) of 10 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 40% infill on upper floors)

Fig-4.23: Variation in base shear value (RSM) of 10 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 60% infill on upper floors)

Fig-4.24: Variation in base shear value (RSM) of 10 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 80% infill on upper floors)

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Table 4.7: Base shear variation of 12 storied building (EQ loading in X-dir) for random application of Infill (in different percentage) with no infill on ground floor

Upper floor infill percentage 20% 40% 60% 80%

Base shear values by RSM for different patterns of infill application (KN)

2942 4430 4826 5529 3124 4417 5008 5513 3011 4376 4939 5467 2995 4167 5020 5520 3025 4136 4852 5530 3194 3674 5021 5561 3209 4441 4979 5566 2960 4423 4882 5564 2969 4400 4981 5552 3171 4388 4767 5545 2979 4391 --- --- 3002 4494 --- --- 3262 4251 --- --- 3168 4249 --- --- 3027 4485 --- ---

Average Base shear by RSM (KN) 3069 4315 4928 5535 Maxima (KN) 3262 4494 5021 5566 Minima (KN) 2942 3674 4767 5467 Standard deviation 106.5 208.3 90.2 30.3 Base shear by ESFM (KN) 1576 1714 1851 1989 Modification Factor 1.95 2.52 2.66 2.78

Fig-4.25: Variation in base shear value (RSM) of 12 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 20% infill on upper floors)

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Fig-4.26: Variation in base shear value (RSM) of 12 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 40% infill on upper floors)

Fig-4.27: Variation in base shear value (RSM) of 12 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 60% infill on upper floors)

Fig-4.28: Variation in base shear value (RSM) of 12 storied building (EQ load in X-dir) for random infill pattern (no infill on Ground floor and 80% infill on upper floors)

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Table 4.8: Base shear variation of 12 storied building (EQ loading in X-dir) for

random application of Infill (in different percentage) with 20% infill on ground floor

Upper floor infill percentage 20% 40% 60% 80%

Base shear values by RSM for different patterns of infill application (KN)

3068 4234 4761 5017 2950 4292 4508 5317 2760 4300 4693 5313 3149 4161 4833 5347 3122 4256 4777 5249 3260 4289 4765 5364 3588 4222 4735 5210 3033 4218 4628 5342 3007 3979 4619 4867 3366 3973 4706 4983 2967 4095 --- --- 3529 4062 --- --- 3220 4031 --- --- 3518 4128 --- --- 2797 4109 --- ---

Average Base shear by RSM (KN) 3156 4157 4703 5201 Maxima (KN) 3588 4300 4833 5364 Minima (KN) 2760 3973 4508 4867 Standard deviation 257.1 112 95 179 Base shear by ESFM (KN) 1587 1724 1864 1999 Modification Factor 1.99 2.41 2.52 2.6

Fig-4.29: Variation in base shear value (RSM) of 12 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

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Fig-4.30: Variation in base shear value (RSM) of 12 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 40% infill on upper floors)

Fig-4.31: Variation in base shear value (RSM) of 12 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 60% infill on upper floors)

Fig-4.32: Variation in base shear value (RSM) of 12 storied building (EQ load in X-dir) for random infill pattern (20% infill on Ground floor and 80% infill on upper floors)

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Table 4.9: Base shear variation of 6 storied building (EQ loading in Z-dir) for random application of Infill (in different percentage) with no infill on ground floor

Upper floor infill percentage 20% 40% 60% 80%

Base shear values by RSM for different patterns of infill application (KN)

1388 1564 1723 1878 1250 1508 1699 1879 1388 1564 1712 1875 1402 1564 1723 1880 1338 1542 1660 1880 1295 1454 1693 1879 1270 1556 1703 1880 1351 1526 1714 1877 1249 1542 1710 1876 1376 1527 1670 1880 1234 1562 --- --- 1392 1558 --- --- 1286 1550 --- --- 1397 1568 --- --- 1254 1544 --- ---

Average Base shear by RSM (KN) 1321 1542 1701 1878 Maxima (KN) 1402 1568 1723 1880 Minima (KN) 1234 1454 1660 1875 Standard deviation 63.8 29.8 21.2 1.8 Base shear by ESFM (KN) 1004 1084 1164 1245 Modification Factor 1.32 1.42 1.46 1.51

Fig-4.33: Variation in base shear value (RSM) of 6 storied building (EQ load in Z-dir) for random infill pattern (no infill on Ground floor and 20% infill on upper floors)

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Fig-4.34: Variation in base shear value (RSM) of 6 storied building (EQ load in Z-dir) for random infill pattern (no infill on Ground floor and 40% infill on upper floors)

Fig-4.35: Variation in base shear value (RSM) of 6 storied building (EQ load in Z-dir) for random infill pattern (no infill on Ground floor and 60% infill on upper floors)

Fig-4.36: Variation in base shear value (RSM) of 6 storied building (EQ load in Z-dir) for random infill pattern (no infill on Ground floor and 80% infill on upper floors)

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Table 4.10: Base shear variation of 6 storied building (EQ loading in Z-dir) for random application of Infill (in different percentage) with 20% infill on ground floor

Upper floor infill percentage 20% 40% 60% 80%

Base shear values by RSM for different patterns of infill application (KN)

1166 1300 1538 1541 1262 1283 1509 1529 1190 1337 1492 1672 1148 1316 1402 1643 1152 1429 1482 1734 1241 1341 1381 1843 1211 1295 1530 1763 1242 1299 1434 1692 1142 1422 1642 1599 1090 1381 1447 1610 1163 1415 --- --- 1320 1257 --- --- 1169 1288 --- --- 1121 1307 --- --- 1157 1342 --- ---

Average Base shear by RSM (KN) 1185 1334 1486 1663 Maxima (KN) 1320 1429 1642 1843 Minima (KN) 1090 1257 1381 1529 Standard deviation 60.1 54.3 75.9 99.1 Base shear by ESFM (KN) 1018 1099 1179 1259 Modification Factor 1.1 1.21 1.26 1.32

Fig-4.37: Variation in base shear value (RSM) of 6 storied building (EQ load in Z-dir) for random infill pattern (20% infill on Ground floor and 20% infill on upper floors)

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Fig-4.38: Variation i