seismic effect of masonry infill with open and shear wall ... · seismic effect of masonry infill...

M. H Janardanachar, Prakash .D; International Journal of Advance Research, Ideas and Innovations in Technology.

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ISSN: 2454-132X

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Seismic Effect of Masonry Infill with Open and Shear Wall on

Flat Slab Structures

Janardanachar M. H P.G. Student., Civil Engineering Department

Ghousia College of Engineering Ramanagara, Karnataka

[email protected]

D. Prakash Associate Professor. Civil Engineering Department

Ghousia College of Engineering Ramanagara, Karnataka [email protected]

Abstract: In the design of tall structures it is essential that the structure must be enough stiff to resist the lateral loads caused

by the wind and seismic motion. Lateral loads lead to developing high stresses, produce sway movement or cause vibration.

Therefore, it is a must for the structure to have sufficient strength against vertical loads together with adequate stiffness to

resist lateral forces. Many types of research have been carried which describes the suitability of various lateral load resisting

system against deformation and shear exerted due to the seismic and wind forces. The RC structures with shear wall and MI

frame have been recognized as one of the most efficient structural systems for such a purpose.

A flat slab is a typical type of construction in which a reinforced slab is built monolithically with the supporting columns

and is reinforced in two or more directions, without any provision of beams.

Flat slab structures in areas of low seismicity (Zone I & II) can be designed to resist both vertical and lateral loads as

permitted by code IS 1893(Part1)-2002. However, for areas of high seismicity (Zone III, IV & V) code does not permit flat slab

construction without any lateral load resisting system. In a building having frames (without beam) and with the shear wall, the

frames are designed for at least 25% of the seismic force and 75% is taken by the shear wall. If the effect of lateral load

analysis and other design features are to be studied in flat slabs; punching shear is a matter of concern for any structural

designer.

Keyword: BF = Bare frame building, MI = Masonry infill frame with opening, SSMI = Soft storey and masonry infill with

opening, AMI = Alternate MI storey with opening, BFSW = Bare frame with shear wall at core, MISW = masonry infill with

shear wall at core, SSMISW = Soft storey and masonry infill with opening and shear wall at core, AMISW = Alternate MI

storey with opening and shear wall at core.

I.INTRODUCTION This paper includes detailed step by step procedure of modeling and analysis of the models considered in the present study using

standard ETABS software. The grid system is used to draw a plan of the building. Materials property and section properties are

defined and assigned. Reinforced concrete frame element is modeled as beam element. Slab and shear walls are modeled as area

and wall element. The equivalent diagonal strut is used for modeling of MI in which thickness is assumed to be wall thickness.

Modal analysis, Equivalent static analysis, and response spectra analysis are performed on models. Based on the analysis,

parameters such as natural frequency, mode shapes, base shear, storey drift, displacement, acceleration are obtained.

.

1.1 OBJECTIVE

The main objective of the present study is to generate the 3D model of the conventional building, flat slab with and without drop structures. FE modeling and analysis is carried out using FEM software.

Firstly modal analysis is conducted to know the natural frequency and mode shapes. A response spectrum is generated for all zones as per IS: 1893 (Part 1)-2002 used for equivalent static analysis and

response spectrum analysis.

To study the behaviour of the structures with different slab systems with MI with 20% opening. To study the behaviour of the structures with different slab systems under the provision of the shear wall.

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To compare buildings with different slab systems with respect to their natural frequency, base shear, storey drift, displacement, Response acceleration.

II.METHODOLOGY

The literature survey is carried out to find the effect of the shear wall as lateral load resisting system on conventional & flat slab structures with MI, and FEM modeling of MI as equivalent diagonal strut is studied.

Models are generated using standard ETABS software package. The following three distinct building models are considered.

Conventional Beam column slab system.

Flat plate slab system.

Flat slab with the drop. The above floor systems are modeled with following conditions

Bare frame (BF).

Masonry Infill with 20% opening at the periphery (MI).

Soft storey and infill with 20% opening at the periphery (SSMI).

Alternate Masonry infill floors with 20% opening at the periphery (AMI).

Bare frame with the shear wall at the core (BFSW).

Infill frame with 20% opening at periphery and shear wall at the core (MISW).

Soft story and infill with 20% opening at periphery and shear wall at the core (SSMISW).

Alternate infill with 20% opening at periphery and shear wall at the core (AMISW).

Modal analysis is carried out for all floor systems to determine natural frequency and mode shapes. A response spectrum is generated for all zones as per IS: 1893 (Part 1)-2002. Equivalent static analysis and response spectrum analysis are carried and parameters such as natural frequency, base

shear, story drift, displacements, and acceleration are obtained. Results are compared and conclusions are drawn.

2.1PARAMETERS OF THE STUDY

Parameters considered in the Present investigation are discussed in detail for three-dimensional models in case of 5, 10,

15, 20-storey buildings for 7mx7m panel dimensions. Parameters considered in the study are given below.

a) Types of Slab Systems Considered

The following three distinct building models are considered in present work.

Conventional Beam column slab.

Flat plate slab system.

Flat slab with the drop.

The above floor systems are modeled with following conditions

Bare frame (BF).

Masonry infill frame with 20% opening at the periphery (MI).

Soft story and infill with 20% opening at the periphery (SSMI).

Alternate MI floors with 20% opening at the periphery (AMI).

Bare frame with the shear wall at core (BFSW).

Masonry infill frame with 20% opening at periphery and shear wall at core (MISW).

Soft storey and MI with 20% opening at periphery and shear wall at core (SSMISW).

Alternate MI floors with 20% opening at periphery and shear wall at core (AMISW).

b) Model Geometry

5 Number of Bays considered in horizontal direction X and vertical direction Y and each bay are having a constant panel

dimension of 7m x 7m.

c) Building Heights

The project is carried out for following stories: The height of each storey is 3.5m

i. 5 Storey.

ii. 10 Storey.

iii. 15 Storey.

iv. 20 Storey.

2.2 MATERIAL PROPERTIES

Concrete grade = M30

Density of brick wall = 19 kN/m3

Steel grade = Fe415

Density of RCC = 25 kN/m3

Modulus of Elasticity of concrete = 27386.1 N/mm2

Modulus of Elasticity of masonry infill = 14000 N/mm2

Poissons Ratio of Concrete = 0.17

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2 .3 PROPERTIES OF STRUCTURAL ELEMENTS The dimensions of beams and columns are designed for 10 & 20 storey Conventional Beam-Slab system in Seismic Zone

V for live load intensity of 4kN/m2.

i. Cross-Section of Column Square columns for 5 &10 storey: 700mmx700mm

Square columns for 15 &20 storey: 900mmx900mm

Square columns are selected because they offer equal resistance in X and Y directions, irrespective of the direction of

earthquake forces.

ii. Cross-Section of Beam All beams including plinth beams are of the uniform size of 450mmx600mm for all frames considered.

iii. Shear Wall Thickness For all models 150mm thick Shear Wall considered.

iv. Slab Thickness These values are obtained from design for gravity loads for live load intensity of 4kN/m2 as per IS 456:2000 (Appendix E)

For Conventional RC Beam Slab System: 195mm

For Flat Plate System: 210mm

For Flat Slab System: 190mm with a drop of 50mm

v. Masonry Wall Thickness For all models 230mm thick Masonry Wall considered.

vi. Size Of Drop (For Flat Slab System)

Flab slabs with drops but without column capitals are considered in the present study. Around the column, a drop of

50mm is provided thereby making the slab thickness at the column top location equal to 240mm. The size of the drop is

3.5mx3.5m so that the width of the drop is equal to the column strip.

2.4 LOAD CALCULATIONS All the structural systems are subjected to three types of primary load cases as per the provisions of IS 875-1987 (Part I).

They are:

Dead Load (IS:875(Part I)-1987)

Live Load (IS:875(Part II)-1987)

Seismic Load (IS:1893(Part III)-2002)

i. Dead load

Self-weight of structure:

Self-weight of the structure is calculated by the software based on the section properties and material constants.

ii. Super-imposed dead load on slab:

At roof level:

Floor finishes: 3kN/m2

At intermediate floor levels:

Floor finishes: 1.5kN/m2

Live Load: 4 kN/m2

iii. Wall load on beam:

At plinth level and intermediate floor levels = 2.9 x 0.23 x 25 = 16.67 kN/m

iv. Earthquake Forces Data

Lateral load consists of earth quake load in X and Y direction as per the IS: 1893 (Part 1)-2002.

Earthquake load for the building has been calculated as per IS: 1893-2002:

Zone (Z) = 5

Response Reduction Factor ( RF ) = 5 (for SMRF)

Importance Factor ( I ) = 1.5

Rock and soil site factor (SS) = 2 (Medium soil)

Type of Structures = 1 (RC Structure)

Damping Ratio (DM) = 0.05

v. Percentage of Imposed Load For Seismic Weight

As per Clause 7.3.1 & Table 8 of IS: 1893(Part I)-2002, for uniformly distributed live loads intensities of up to 3kN/m2,

25% of imposed loads have been considered and above 3kN/m2, 50% of the imposed loads have been considered.




vi. Support Condition

The columns are assumed to be fixed at the bottom.

2.5 TYPES OF PRIMARY LOADS

The structural systems are subjected to 3 types of Primary Load Cases as per the provisions of IS: 872-1987 (Part I).

They are:

1. Dead Load Case (Vertical or Gravity Load), denoted as DL

2. Live Load Case (Vertical or Gravity Load), denoted as LL

3. Wall Load Case (Super-imposed dead load), denoted as WAL

4. Seismic Load in X-direction (Static Load), denoted as EQX

5. Seismic Load in Y-direction (Static Load), denoted as EQY

6. Response Spectrum in X-direction (Dynamic Load), denoted as RSX

7. Response Spectrum in Y-direction (Dynamic Load), denoted as RSY

The gravity loads (dead, super-imposed dead and live to load) on the frame have been calculated based on the provisions

of IS: 872-1987 (Part II). The dead load consists of self-weight of structural elements and the superimposed dead load consists of

the masonry wall load acting on the structure. The live load is based on requirements as 4kN/m2. The lateral loads (Seismic loads)

on the frame have been calculated based on the provisions of IS: 1893(Part I)-2000 that deals with Criteria for Earthquake

Resistant Design of Structures. The aim is to carry out the seismic analyses of all the structural systems by Equivalent Static

Force Method & Response Spectrum Method.

The results obtained from the analysis are thoroughly investigated for various slab systems with respect to their Natural

frequency, Maximum displacement, Maximum storey drift, Response acceleration, and the Base Shear; their variations are

compared.

3.0 MODELLING AND ANALYSIS PROCEDURE

3.1 DATA FOR INFILL FRAME WITH OPENING:

For 20-storey:

Column = 900 x 900 mm

Beam = 450 x 600 mm

Infill properties:

Elastic modulus of masonry wall ( Em ) = 1400 N/mm2

Thickness of the infill wall (t) =230 mm

Height of MI wall (h) = 2900 mm

Length of MI wall (L) = 6100 mm

Opening % =20 %

Ic = 5.4675x1010 mm4

Ib = 8.1 x109mm4

= tan-1(h/L) = 25.42 D = 6.75m = = 0.6157

W= 0.175 ( H)-0.4 D = 0.86886m

From Figure 5.3, For Opening % = 20 %

Stiffness Reduction factor = 0.38

Provide strut width of 335mm for all structures

3.2 MODELING PROCEDURE

It includes modelling of 5, 10, 15, & 20 storey building with 5 bays in X and Y direction for panel dimension of 7mx7m.

Step 1: Development of geometry

The Building Plan Grid System and Story Data form are used to specify horizontal grid line spacing, story data. In the

form shown in Figure 3.1 number of grid lines in X and Y direction and their spacing are entered. The number of storey and

height of the storey is specified.




Figure 3.1: Building Plan Grid System and Story Data Definition form.

After specifying inputs of model, geometry of the model appears on screen in the main ETABS window with two view windows

tiled vertically, a Plan View on the left and 3D View on the right, as shown in Figure 3.2

Figure 3.2: Geometry of the model.

Step 2: Defining material property

1. To define M30 grade concrete Click the Define menu > Material Property > Concrete > Add New Material. The form shown in Figure 3.3 is displayed.

And then material properties and name are entered.




Figure 3.3: Material property data of M30 concrete. 2. To define Masonry infill material

Click the Define menu > Material Property > OTHER > Add New Material. The form shown in Figure 3.4 is displayed.

And then material properties and name are entered.

Figure 3.4: Material property data of MI.

Step 3: Defining frame section, slab and shear wall

In define menu select frame section in that select Add Rectangle shown in Figure 3.5. For Slab/ Wall select wall/ Slab/

Deck section in that select Add New Slab/ Wall, from shown in Figure 3.6 is displayed.

Figure 3.5: Defining frame section Figure 3.6: Defining slab and shear wall




Step 4: Meshing of area object & pier labeling, and to assign support condition at the base

For meshing of area object select all area objects to mesh and then click Assign>Shell/Area>Area object Mesh Option,

form shown in Figure 3.7 is displayed select auto mesh objects into the structural elements thus meshing of area objects is done

and it is necessary to label the wall element to get output result in wall areas. Select wall element to be labeled click

assign>Shell/Area>Pier label.

In this present study, the base is assumed as fixed. To assign support condition first selects all the joints in the base and

then go to Assign > Joint/ Point> Restraint, popup box shown in Figure 3.8 is shown in that select fixed support.

Figure 3.7: Meshing of area objects Figure 3.8: Assign support condition

Step 5: Selection of required code for design Click Option>Preferences>Concrete Frame Design, from drop down list of Design Code select Indian, IS 456-2000 and

select OK.

4.0 ANALYSIS

In the seismic analysis, it is required for a structure to withstand minor earthquakes elastically without any structural

damage, and major earthquakes with an acceptable level of damage depending on the importance of the building.

Once geometry of the models is completed loads are assigned to the models and then models are checked and analysis is

carried out. In this present study first, modal analysis is conducted to find the natural frequency. And equivalent static analysis is

done as per IS 1893 (Part 1) 2002 for Zone V with response reduction factor as 5, importance factors as 1.5, for all models. From

results of equivalent static analysis base shear is taken. Response spectra analysis is conducted for Zone V as per IS 1893 (Part 1)

2002 for all models. Based on the base shear result of static analysis scale factor is find out for response spectra analysis.

4.1: Modal analysis

Modal Analysis is the study of the dynamic characteristics of the structures. This analysis characterizes the dynamic

properties of the specific elastic structure by identifying its mode of vibration. The response of the structure is different at each of

the different natural frequencies. These patterns of deformations are called mode shapes. Both the natural frequency (which

depends on the mass and stiffness distributions in the structure) and mode shapes are used while the design of structural system

mainly for vibration applications. An attempt has been made to find the natural frequencies and mode shapes of the structure.

Modes are inherent properties of a structure and are determined by the properties of the material (mass, damping, and

stiffness), and boundary conditions of the structure. Each mode is defined by a natural (modal or resonant) frequency, modal

damping, and a mode shape (i.e. the so-called modal parameters). If either the material properties or the boundary conditions of

structure changes, its modes will change. For instance, if the mass is added to a structure, it will vibrate differently.

Modal analysis is a method or a process or a technique to describe a structure in terms of its natural characteristics as follows (its

dynamic properties),

Natural frequency

Mode participation factors

And Mode shapes

Modal analysis is the most fundamental of all the dynamic analysis types. A modal analysis works out the undamped

natural modes of a system. These modes are given in decreasing order of period and are numbered starting from 1. Modal analysis

is the field of measuring and analyzing the dynamic response of structures and or fluids when excited by an input.

Modal analysis is conducted without applying any external loads i,e free vibration which includes the only self-weight of

the structure. Self-weight is default load case in ETABS. If the diagonal strut is included in the model then additional mass is to be

added for each joint where struts are drawn. Before conducting analysis model has to be checked. Once the model is checked if it

has no warnings and errors, the analysis is conducted. To carry out analysis click on Analysis>Set Analysis Option, the form

shown in Figure 5.22 displayed in that select 3d and check on dynamic analysis and select set dynamic parameters, shown in

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Figure 5.23 is displayed in that entered number of modes as 12 and check on Eigen vector. Once analysis completed results are

obtained. From modal analysis, dynamic parameters such as period, natural frequency, mode shapes are obtained.

Figure 4.1: Setting analysis option form for modal analysis

Figure 4.2: Dynamic parameters setting for modal analysis

Table 4.1: Natural frequency for conventional slab system different cases for first 3 modes

Table 4.2: Natural frequency for Flat Plate slab system different cases for first 3 modes

Modal Natural Frequency (Hz)

STORE

Y

Mode BF MI SSM

I

AMI BFSW MISW SSMIS

W

AMIS

W

5

1 0.867 1.99 1.917 1.539 1.89 3.339 3.031 2.709

2 0.867 2.028 1.918 1.54 3.18 3.56 3.508 3.351

3 0.948 3.153 2.819 2.21 3.18 3.561 3.508 3.352

10

1 0.37 0.963 0.961 0.74 0.914 1.488 1.509 1.349

2 0.37 0.984 0.962 0.74 1.12 1.504 1.509 1.35

3 0.4 1.576 1.503 1.096 1.12 1.766 1.701 1.368

15

1 0.244 0.619 0.634 0.487 0.59 0.874 0.891 0.767

2 0.244 0.633 0.634 0.487 0.606 0.885 0.891 0.768

3 0.282 1.004 1.011 0.738 0.606 1.124 1.128 0.899

20 1 0.172 0.468 0.464 0.355 0.38 0.614 0.628 0.522


STOR

EY

Mode BF MI SSMI AMI BFSW MISW SSMISW AMISW

5

1 1.514 2.194 2.073 1.862 2.149 3.649 3.268 2.804

2 1.685 2.195 2.074 1.862 3.15 3.803 3.746 3.535

3 5.03 3.067 2.733 2.353 3.15 3.803 3.746 3.535

10

1 0.723 1.068 1.047 0.907 1.06 1.549 1.54 1.381

2 0.723 1.073 1.047 0.907 1.235 1.549 1.54 1.381

3 0.808 1.535 1.456 1.171 1.235 1.837 1.731 1.397

15

1 0.497 0.711 0.71 0.616 0.715 1.502 0.93 0.848

2 0.497 0.714 0.711 0.616 0.745 1.506 0.93 0.848

3 0.558 1.014 1.003 0.809 0.745 1.681 1.095 0.924

20

1 0.36 0.52 0.521 0.451 0.51 0.645 0.648 0.589

2 0.36 0.522 0.521 0.451 0.51 0.647 0.648 0.589

3 0.41 0.757 0.753 0.601 0.53 0.827 0.823 0.689




2 0.172 0.468 0.464 0.355 0.38 0.614 0.628 0.522

3 0.199 0.769 0.757 0.546 0.438 0.858 0.893 0.668

Table 4.3: Natural frequency for Flat slab system different cases for first 3modes


STOREY Mode BF MI SSMI AMI BFSW MISW SSMISW AMISW

5

1 1.036 2.118 1.977 1.61 1.95 3.506 3.209 2.746

2 1.036 2.119 1.978 1.611 3.26 3.679 3.683 3.471

3 1.103 3.295 2.876 2.272 3.26 3.701 3.683 3.471

10

1 0.457 1.027 0.991 0.773 0.94 1.502 1.504 1.362

2 0.457 1.027 0.992 0.773 1.16 1.506 1.504 1.39

3 0.479 1.65 1.533 1.124 1.16 1.681 1.608 1.391

15

1 0.301 0.669 0.654 0.501 0.61 0.914 0.911 0.782

2 0.301 0.669 0.654 0.501 0.63 0.914 0.911 0.783

3 0.328 1.101 1.047 0.74 0.63 1.228 1.179 0.927

20

1 0.215 0.49 0.482 0.368 0.404 0.629 0.613 0.536

2 0.215 0.49 0.482 0.368 0.404 0.63 0.613 0.536

3 0.234 0.825 0.794 0.552 0.45 0.921 0.845 0.693

4.2 EQUIVALENT STATIC ANALYSIS

4.2.1 Design seismic base shear

The total design lateral force or design seismic base shear (Vb) along any principal direction shall be find out by the

following expression:

Vb = Ah * W --------- (4.1)

Ah = --------- (4.2)

Where

Ah =Design horizontal acceleration spectrum value.

Z = Zone factor is for the Maximum Considered Earthquake (MCE) and service life of structure in a zone.

I = Importance factor, depending upon the functional use of the structures, characterized by hazardous consequences

of its failure, post- earthquake functional needs, historical value, or economic importance.

R = Response reduction factor, depending on the perceived seismic damage performance of the structure, characterized by

ductile or brittle deformations. However, the ratio (I/R) shall not be greater than 1.00

Sa/g = Average response acceleration coefficient, in case design spectrum is specifically prepared for a structure at a particular

project site; the same may be used for design at the discretion of the project authorities.

4.2.2 Fundamental natural period

The approximate fundamental natural period of vibration ( Ta ), in seconds, of a moment-resisting frame building without

brick infill panels may be estimated by the empirical expression:

Ta = 0.075 h 0.75 for RC frame building --------- (4.3)

Ta = 0.085 h 0.75 for steel frame building. --------- (4.4)

The approximate fundamental natural period of vibration (Ta), in seconds, of all other buildings, including moment-

resisting frame buildings with brick infill panels, may be estimated by the empirical expression:

Ta= 0.09 h/d --------- (4.5)

Where h= Height of building in m.

d= Base dimension of the building at the plinth level, in m, along with the considered direction of the lateral force.

Table 4.4: Fundamental natural period

Storey Height

(m)

Conventional

Structure (sec)

Flat plate

Structure(sec)

Flat slab

Structure(sec)

5 17.5 0.6417 0.266 0.266

10 35 1.0792 0.5324 0.5324

15 52.5 1.4627 0.7986 0.7986

20 70 1.8150 1.0649 1.0649

4.2.3 Distribution of design force




The design base shear (Vb) computed in 4.1 shall be distributed along the height of the building as per the following

expression:

Qi = VB*(Wihi2) / (Wihi2), --------- (4.6)

Where Qi = Design lateral force at floor i,

Wi = Seismic weight of floor i,

hi = Height of floor i measured from the base, and

n = Number of storeys in the building is the number of levels in which the masses are located.

The external load has to be defined before conducting the equivalent static analysis. Load cases are defined as follows.

Earth quake load is defined by clicking Define>Static load cases, the form shown in Figure 5.25 is displayed in that enter

EQX and EQY in load column, select quake from drop down list of type, self-weight multiplier must be zero, and select IS 1893-

2002 from drop down list of auto lateral load. Then select add new load. After that select modify lateral load, pop up is displayed

as shown in Figure 4.3 in that enter zone factor, importance factor, response reduction factor, time period and select soil type.

Figure 4.3: Defining earth quake load for static case

4.2.4 Defining mass source

The mass source is to be defined before conducting analysis, to define mass source click Define>Mass source, the form shown in

Figure 4.4 is displayed, select dead form dropdown list of load its multiplier must be 1 similarly LL and its multiplier is 0.5. Click

Analysis>Set analysis option, the form shown in Figure 4.4is displayed, click on 3d and run the analysis. From analysis results

parameters such as base shear is obtained which are used for calculating the scale factor for response spectrum analysis.

Figure 4.4: Defining mass source and Setting analysis option for static case




Figure 4.5: Table showing base shear values of static case

4.3 RESPONSE SPECTRA ANALYSIS

Response spectra analysis is dynamic method of analysis, so, before conducting response spectra analysis for any model

first static analysis is to be carried out because static analysis process provides an instrument to define the base shear, shear

strength coefficient of the structural forms while the dynamic analysis process helps to define the corresponding seismic response

of the building. Response spectra are used in assessing the response of linear systems with multiple modes of oscillation (multi-

degree of freedom systems), although they are only accurate for the low levels of damping.

To define response spectra analysis, click Define>Response Spectrum Function Figure 4.6 is displayed in that select IS:

1893-2002 from drop down list and Add New Function. Pop up shown in Figure 4.6 is opened, in that enter zone factor, damping

ratio and select soil type. After this response spectrum case is to be defined for that click Define> Response spectrum cases, the

form shown in Figure 4.7 is displayed, in that select Add New Spectrum, popup shown in Figure 4.7 is opened scale factors is

calculated by using formula gI/2R.

The scale factors is calculated by using formula gI/2R = (9.81x1.5)/ (2x5) =1.475

SCALE FACTORS = (gI/2R) x VB / VB.

The scale factor is calculated as the ratio of static base shear (VB) to response spectra base shear (VB) multiplied by scale factor

calculated using gI/2R.

Figure 4.6: Defining Response Spectra Function

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Figure 4.7: Defining Response Spectra Cases

4.4.1: To display the analysis result

Click Display> Show Tables from shown in Figure 4.8 is displayed in this table select the parameter and load case for which

result is too obtained.

Figure 4.8: Display Table

5.0 RESULTS AND DISCUSSIONS

The scope of the study of this paper is discussed in detail for three-dimensional models of Flat plates & Flat slabs

compared to Conventional Beam-Slab system in case of 5, 10, 5 and 20 storey buildings for 7mx7m panel dimensions in Zone V

and live load intensities of 4kN/m2. The analyses carried out are modal analysis, equivalent static and response spectrum analysis.

The results of each building models are tabulated for spectrum case in X-direction (SPEC-X) and Zone V.

The results are obtained in terms of Natural frequency, Base Shear, Maximum displacement, Storey drift, & Response

acceleration are tabulated and results are compared.

Note: The notations used below are as follows

1. BF = Bare frame building.

2. MI = Masonry infill frame with the opening.

3. SSMI = Soft storey and masonry infill with the opening.

4. AMI = Alternate MI storey with the opening.

5. BFSW = Bare frame with the shear wall at the core.

6. MISW = masonry infill with the shear wall at the core.

7. SSMISW = Soft storey and masonry infill with opening and shear wall at the core.

8. AMISW = Alternate MI storey with opening and shear wall at the core.

5.1 Natural frequency (HZ):




Table 5.1 shows the values of Natural frequency for different Floor Systems for the first mode.

Table 5.1: Natural frequency (HZ) for different Floor Systems for the first mode

TYPE STOREY BF MI SSMI AMI BFSW MISW SSMISW AMISW

CO

NV

EN

TIO

NA

L

5 1.514 2.194 2.073 1.862 2.149 3.649 3.268 2.804

10 0.723 1.068 1.047 0.907 1.06 1.549 1.54 1.381

15 0.497 0.711 0.71 0.616 0.715 1.502 0.93 0.848

20 0.36 0.52 0.521 0.451 0.51 0.645 0.648 0.589

FL

AT

PL

AT

E

5 0.867 1.99 1.917 1.539 1.89 3.339 3.031 2.709

10 0.37 0.963 0.961 0.74 0.914 1.488 1.509 1.349

15 0.244 0.619 0.634 0.487 0.59 0.874 0.891 0.767

20 0.172 0.468 0.464 0.355 0.38 0.614 0.628 0.522

FL

AT

SL

AB

5 1.036 2.118 1.977 1.61 1.95 3.506 3.209 2.746

10 0.457 1.027 0.991 0.773 0.94 1.504 1.502 1.362

15 0.301 0.669 0.654 0.501 0.61 0.914 0.911 0.782

20 0.215 0.49 0.482 0.368 0.404 0.629 0.613 0.536

Figure 5.1: Natural frequency (HZ) for Conventional Slab System

Figure 5.2: Natural frequency (HZ) for flat plate Slab System




Figure 5.3: Natural frequency (HZ) for Flat Slab System

Natural frequency (HZ): From graphs shown in Figure 5.1, 5.2 and 5.3 it is clear that MISW is having a higher frequency and

BF is having a lower frequency, this is due to masonry infill effect & the provision of the shear wall increases the stiffness of the

structure. Also, the Frequency decreases as the increase in the height of story for all floor systems. Frequency comparison of

different slab systems shows that frequency of all models with the conventional beam-slab system is more comparable to that of a

flat plate and flat slab systems. The flat slab floor system is having frequency more than flat plate slab systems.

On an average, the Natural frequency of conventional beam-slab system with MISW is 14.76% higher than of Flat plate

slab system with MISW and 12.14% higher that of flat slab systems with MISW.

Similarly, on an average compare to Natural frequency of Flat slab system with MISW, Natural frequency values of Flat

slab system with BF is 68.22% lesser, MI is 30.03% lesser, SSMI is 32.36% lesser, AMI is 47.32% lesser, BFSW is 37.7% lesser,

SSMISW is 2.86% lesser, and AMISW is 15.08% lesser.

Similarly, on an average Natural frequency of Flat slab system with BF is 48.92% lesser than that of BFSW, MI is

30.03% lesser than MISW, SSMI is 30.52% lesser than SSMISW, AMI is 37.97% lesser than AMISW.

5.2 Base shear (kN): Table 5.2 shows the values of Base shear for different Floor Systems such as Conventional slab-beam system, Flat plate Slab

system, and Flat Slab system. It can be seen that Flat slab system shows higher Base shear because of higher self-weight and the

Conventional Beam-Slab system shows lower Base shear. Provision of Shear walls in the above Floor Systems shows increased

Base shear.

It is noted that base shear is more for Floor Systems with MISW cases and less for BF Floor Systems because the self-weight of

MISW structure is more and self-weight of BF is less when compared to all other models. But it is also significant to note that, the

increase is gradual for bare frame building but drastic for other buildings. Provision of Shear walls at core increases the Base shear

since the Seismic weight of the building increases as Base shear is directly proportional to the Seismic weight of the building.

Table 5.2: Base shear (k N) for Different Slab Systems (SPEC-X)


CO

NV

EN

TI

ON

AL

5 6730.2 12284.1 11890.9 11301.2 6940.5 12621.4 12228.3 11638.5

10 8450.6 24380.8 23987.8 22415.8 8727.5 25055.6 24662.4 23090.4

15 9670.35 25005.3 24809.3 23530.3 9965.8 25512.2 25316.2 23990.2

20 10537.7 25091.6 24944.3 23618.3 10834.9 25647.6 25500.3 24173.4

FL

AT

PL

AT

E

5 6863.7 13065.6 12672.4 12082.7 7073.9 13402.9 13009.8 12420.1

10 8238.2 26410.3 26017.2 24444.6 8515 27085 26691.9 25119.3

15 9903.7 29696.6 29499.7 28220.7 10199.2 26917.3 26720.4 25441.4

20 10632 29776.6 29629 28303 10929.3 30332.6 30185 28859

FL

AT

SL

AB

5 8068.9 15809.8 15416.5 14827 8279.1 16147 15753.8 15164.2

10 9673.9 31911.8 31518.5 30929 9923.9 32586.5 32193.2 31603.7

15 11404.2 35081.4 34688.1 34098.6 11680.8 35588.3 35195 34605.5

20 12274.3 35159.5 34766.2 34176.7 12571.6 35666.3 35273 34683.5




Figure 5.4: Base shear (kN) for Conventional Slab System for Zone V

Figure 5.5: Base shear (kN) for Flat Plate Slab System for Zone V

Figure 5.6: Base shear (kN) for Flat Slab System for Zone V

From graphs shown in Figure 5.4, 5.5 and 5.6 it can be seen that, with the increase in the story height, the values of Base

shear force increases. On an average, Base shear of Flat slab system with MISW is 25.33% higher that of Conventional Beam-

Slab system with MISW and 18.3% higher than of Flat Plate Slab systems with MISW.

Similarly, on an average compared to Base shear of Flat slab system with MISW, Base shear values of Flat slab system

with BF is 47.07% lesser, MI is 1.4% lesser, SSMI is 2.58% lesser, AMI is 4.36% lesser, BFSW is 46.36% lesser, SSMISW is

1.18% lesser, and AMISW is 2.96% lesser.

Similarly, on an average Base shear of Flat slab system with BF is 2.44% lesser than that of BFSW, MI is 1.75% lesser

than MISW, SSMI is 1.77% lesser than SSMISW, AMI is 1.82% lesser than AMISW.

5.3 Displacement (m): Table 6.3 shows the Maximum Displacement values for different Floor Systems.

Table 5.3: Displacement (m) for Different Slab Systems (SPEC-X)





CO

NV

EN

TIO

NA

L

5 0.0374 0.0264 0.0285 0.0294 0.0125 0.0063 0.0109 0.0111

10 0.152 0.0737 0.11 0.1125 0.0748 0.0292 0.0626 0.0631

15 0.2289 0.1155 0.1691 0.1694 0.1252 0.0535 0.1048 0.1053

20 0.319 0.1736 0.2388 0.2377 0.194 0.0862 0.1577 0.1584

FL

AT

PL

AT

E

5 0.099 0.0336 0.0356 0.0622 0.0445 0.0076 0.0106 0.0108

10 0.3192 .1399 0.14 .2438 0.0836 0.0543 0.0672 0.0914

15 0.5655 0.2239 0.2315 0.3939 0.153

1

0.106

3 0.116 0.118

20 0.7312 0.3108 0.3135 0.5511 0.328 0.1616 0.1816 0.2314

FL

AT

SL

AB

5 0.0658 0.0291 0.0318 0.0538 0.0128 0.007 0.0097 0.0099

10 0.2216 0.1205 0.1256 0.2117 0.0766 0.0386 0.0611 0.0625

15 0.3862 0.1934 0.199 0.351 0.1504 0.0778 0.1111 0.1426

20 0.5932 0.272 0.2771 0.486 0.2485 0.118 0.1667 0.1837

Figure 5.7: Maximum Displacement (m) for Conventional Slab System for Zone V

Figure 5.8: Maximum Displacement (m) Figure 5.9: Maximum Displacement (m)

for Flat Plate Slab System for Zone V for Flat Slab System for Zone V

From Figure 5.7, 5.8, and 5.9 it can be seen that the displacement values of Flat plates and Flat slabs structures are

always higher than that of structures with the Conventional Beam-Slab system. This is mainly because of the reduction in

stiffness due to the absence of beams framing into the columns. Displacement is less for MISW case of all slab system. BF is

having larger displacement value. Compare to BF, BFSW is having fewer displacement values. Similarly, compare to SSMI &

AMI, slab systems with SSMISW & AMISW are having less displacement value because of infill action and the provision of the

shear wall at core increases the stiffness of the structure.

On an average, the displacement of Flat plates system with MISW is 39.91% higher and Flat slab system is 23.13%

higher than of Conventional Beam-Slab system. Reduced displacement values of the Beam-Slab system is because of increased

stiffness of the system contributed by the beams framing into the columns.

Similarly, on an average compared to displacement of Flat slab system with MISW, displacement values of Flat slab

system with BF is 82.97% higher, MI is 65.05% higher, SSMI is 66.39% higher, AMI is 80.5% higher, BFSW is 48.92% higher,

SSMISW is 30.96% higher, and AMISW is 37.18% higher.




Similarly, on an average displacement of Flat slab system with BF is 66.28% higher than that of BFSW, MI is 65.07%

higher than MISW, SSMI is 51.21% higher than SSMISW, AMI is 68.41% higher than AMISW.

5.4: Storey Drift (mm)

Inter-storey drift or Storey drift is defined as the relative horizontal displacement of one level relative to the other level

above or below it, or between two adjacent floors bounding the story. Table 5.4 shows the Storey Drift values for 5-story Building

with different Floor Systems for Zone V.

TABLE 5.4: STOREY DRIFT (MM) VALUES OF 5-STORY BUILDING FOR DIFFERENT SLAB SYSTEMS

Storey Drift (mm) (Zone V)


CO

NV

EN

TI

ON

AL

5 2.256 1.224 1.27 1.64 1.005 0.632 0.81 1.005

4 2.797 2.05 2.11 2.59 1.11 0.75 1.01 1.11

3 4.483 2.8 2.83 3.37 1.29 0.78 1.1 1.29

2 3.912 3.323 3.39 3.45 1.13 0.75 1.07 1.134

1 3.043 2.23 2.89 2.99 0.865 0.63 0.78 0.865

FL

AT

PL

AT

E

5 1.77 2.11 2.97 9.47 17.23 1.77 2.11 2.97

4 2.61 2.96 5.14 10.4 18.61 2.61 2.96 5.14

3 3.51 3.73 7.21 10.49 18.55 3.51 3.73 7.21

2 4.3 4.1 5.61 8.85 15.77 4.3 4.1 5.61

1 3.43 2.9 3.67 4.02 7.27 3.43 2.9 3.67

FL

AT

SL

AB

5 16.23 1.77 2.11 2.97 1.27 0.66 0.83 0.869

4 18.61 2.61 2.96 5.14 1.42 0.74 0.98 1.025

3 18.55 3.51 3.73 7.21 1.44 0.75 1.05 1.09

2 15.77 4.3 4.1 5.61 1.31 0.68 1.02 1.12

1 7.27 3.43 2.9 3.67 0.835 0.43 0.77 0.816

Figure 5.10: Drift (mm) for 5-Storey Conventional Slab System for Zone V

Figure 5.11: Drift (mm) for 5-Storey Figure 5.12: Drift (mm) for 5-Storey

Flat Plate Slab System for Zone V Flat Slab System for Zone V

Storey Drift (mm): Figure 5.10, 5.11, and 5.12 shows the storey level verses maximum storey drift graphs for 5-story

Building for Different Slab Systems. From graphs, it is clear that the provision of the shear wall at the core into masonry infill

model helps in reducing storey drift. Buildings with Conventional Beam-Slab system have minimum Storey drift, while maximum




Storey drift is obtained for buildings with Flat plate slab system. Drift values of structures having Flat slab lie between structures

having Flat plates and Conventional Beam-Slab system.

Storey drift is less for MISW case of all slab system. BF is having larger drift value. Compare to BF model, BFSW is

having less storey drift values. Similarly compare to SSMI & AMI, SSMISW & AMISW is having less drift value because of the

provision of the core. It can be observed that fully infilled Slab systems show fewer values of Storey drift compare to the bare

frame and partially infilled Slab systems.

Hence, it can be observed that the Slab systems with masonry infill & without Shear walls show high values of Storey

drift compare to Slab systems with masonry infill & Shear walls.

Table 5.5: Storey Drift values of 20-story Building for Conventional Slab Systems



CO

NV

EN

TIO

NA

L S

LA

B S

YS

TE

M

20 7.96 1.88 3.96 5.11 1.78 1.20 2.96 3.47

19 8.82 2.50 4.28 7.86 1.64 1.93 3.17 4.04

18 9.95 3.22 4.64 6.88 2.15 2.03 3.45 4.13

17 11.69 3.89 5.19 9.81 2.66 2.12 3.68 4.59

16 12.99 4.49 5.64 9.26 3.11 2.19 3.88 4.60

15 13.93 5.00 6.10 9.91 3.51 2.24 4.03 4.99

14 15.12 5.41 6.88 12.87 3.83 2.28 4.15 4.89

13 16.09 5.75 7.50 10.94 4.10 2.29 4.24 5.22

12 16.88 6.02 7.91 12.82 4.33 2.29 4.29 5.03

11 17.56 6.26 8.47 12.05 4.53 2.28 4.33 5.30

10 18.20 6.48 8.95 13.53 4.73 2.26 4.35 5.06

9 18.84 6.71 9.36 12.86 4.93 2.23 4.35 5.29

8 19.52 6.95 9.70 13.93 5.14 2.19 4.33 5.00

7 20.24 7.20 10.11 12.61 5.34 2.13 4.28 5.15

6 20.94 7.45 10.50 13.94 5.53 2.04 4.18 4.75

5 21.58 7.66 10.79 12.55 5.64 1.91 4.01 4.74

4 22.00 7.77 10.95 14.72 5.62 1.74 3.74 4.16

3 21.89 7.66 10.57 13.93 5.29 1.50 3.38 3.85

2 20.24 6.96 8.29 12.36 4.34 1.20 2.92 2.99

1 11.87 3.96 4.44 9.03 2.03 0.64 1.70 1.73

Figure 5.13: Drift (mm) for 20-Storey Conventional Slab Building for Zone V

zle 5.6: Storey Drift (mm) values of 20-story Building for Flat Plate Systems



FL

AT

PL

AT

E

SY

ST

EM

20 42.14 3.81 3.81 5.42 24.07 2.61 2.63 4

19 48.49 4.02 4.03 6.02 24.81 3.27 3.29 5.55

18 56.9 4.25 4.25 6.65 25.29 4.13 4.15 5.98

17 66.16 5 5.02 8.72 25.63 4.45 4.45 6.49

16 75.51 5.78 5.81 9.46 25.78 4.62 4.62 6.35




15 84.5 6.45 6.48 11.5 25.73 4.74 4.75 6.78

14 92.9 7 7.03 11.7 25.49 4.83 4.83 6.51

13 100.63 7.45 7.48 13.59 25.08 4.88 4.88 6.85

12 107.7 7.82 7.84 13.35 24.52 4.9 4.9 6.49

11 114.1 8.15 8.16 15.19 23.84 4.89 4.89 6.75

10 119.8 8.45 8.47 14.71 23.06 4.87 4.87 6.33

9 124.62 8.75 8.78 16.62 22.19 4.82 4.82 6.52

8 128.23 9.08 9.1 15.98 21.2 4.75 4.75 6.04

7 130.07 9.41 9.44 17.94 20.04 4.64 4.64 6.12

6 129.36 9.73 9.76 16.99 18.67 4.47 4.47 5.53

5 124.98 9.99 10 18.63 17 4.22 4.23 5.4

4 115.39 10.09 10.05 16.81 14.96 3.87 3.87 4.62

3 98.4 9.85 9.68 16.86 12.47 3.39 3.39 4.16

2 70.9 8.76 8.25 12.15 9.45 2.75 2.78 3.1

1 28.31 4.8 4.05 5.74 4.69 1.5 1.6 1.68

Figure 5.14: Drift (mm) for 20-Storey Flat Plate Building for Zone V

Table 5.7: Storey Drift (mm) values of 20-story Building for Flat Slab Systems



FL

AT

SL

AB

20 19.65 3.43 3.43 4.81 12.3 2.19 2.19 2.93

19 24.03 3.65 3.66 5.52 12.59 2.9 2.9 4.8

18 29.81 3.87 3.87 5.51 12.76 3.72 3.72 5.36

17 36.24 4.07 4.48 8.03 12.88 4.07 4.42 6

16 42.85 5.09 5.14 7.92 12.92 4.23 4.24 5.74

15 49.36 5.65 5.7 10.61 12.87 4.37 4.37 6.32

14 55.61 6.11 6.16 9.72 12.73 4.46 4.46 5.94

13 61.5 6.48 6.53 12.45 12.52 4.52 4.52 6.44

12 66.98 6.79 6.83 10.99 12.23 4.55 4.55 5.97

11 72 7.04 7.08 13.79 11.88 4.56 4.56 6.4

10 76.48 7.27 7.31 11.97 11.47 4.55 4.55 5.87

9 80.35 7.5 7.54 14.97 10.99 4.52 4.53 6.24

8 83.41 7.73 7.79 12.94 10.44 4.47 4.48 5.65

7 85.41 7.98 8.04 16.21 9.8 4.38 4.39 5.92

6 85.92 8.23 8.3 13.9 9.04 4.24 4.24 5.21

5 84.26 8.47 8.54 17.33 8.14 4.01 4.02 5.26

4 79.35 8.67 8.72 14.49 7.05 3.69 3.69 4.38

3 69.44 8.75 8.85 17.34 5.76 3.23 3.23 4.06

2 51.69 8.26 9.15 12.15 4.26 2.63 2.66 2.95

1 21.38 4.82 6.78 7.33 2.2 1.58 1.72 1.79




Figure 5.15: Drift (mm) for 20-Storey Flat Slab Building for Zone V

Table 5.5, 5.6 and 5.7 show the Storey Drift values for 20-storey Building with different Floor Systems such as

conventional slab system, flat plate, and flat slab systems. From graphs 5.13, 5.14 and 5.15 we can say Buildings with

Conventional Beam-Slab system have minimum Storey drift, while maximum Storey drift is obtained for buildings with Flat plate

slab system. It can be observed that fully infilled Slab systems i.e. MI, shows fewer values of Storey drift compare to the bare

frame and partially infilled Slab systems SSMI & AMI.

Hence, it can be observed that the Slab systems with masonry infill & without Shear walls show high values of Storey

drift compare to Slab systems with masonry infill & Shear walls.

Table 5.8: Maximum Storey Drift (mm) for Different Slab Systems for Zone V

Maximum Storey Drift (mm) for Zone V


CO

NV

EN

TI

ON

AL

5 4.48 3.32 3.45 3.59 1.29 0.75 1.1 1.29

10 9.34 4.72 7.16 7.51 3.96 1.5 3.34 3.96

15 9.65 4.96 7.37 7.55 4.52 1.85 3.74 3.79

20 21.89 7.77 10.95 14.72 5.64 2.29 4.35 5.3

FL

AT

PL

AT

E

5 19.95 4.1 4.3 7.21 1.83 0.971 1.05 1.18

10 60.11 9.1 9.41 17.49 8.19 3.19 4.54 4.67

15 81.7 9.53 9.97 17.14 15.71 3.91 4.15 5.56

20 130.05 10.05 10.09 18.63 25.78 4.9 4.989 6.85

FL

AT

SL

AB

5 18.55 3.47 3.85 4.96 1.44 0.789 0.968 1.12

10 54.15 7.7 8.43 15.23 6.21 2.9 3.18 4.16

15 78.01 8.42 8.95 16.8 8.61 3.58 3.9 5.29

20 85.91 8.75 9.05 17.34 12.91 4.5 4.55 6.43




Figure 5.16: Maximum Drift (mm) for Conventional Slab System for Zone V

Figure 5.17: Maximum Drift (mm) Figure 5.18: Maximum Drift (mm)

for Flat Plate Slab System for Zone V for Flat Slab System for Zone V

Figure 5.16, 5.17, and 5.18 shows the storey level verses maximum storey drift graphs for zone V. Unlike displacement

values, storey drift does not increase at higher rates. There is a gradual increase in storey drift as the height of the building H

increases.

From graphs, it is clear that the provision of the shear wall at the core of masonry infill model helps in reducing storey

drift. Storey drift is less for MISW case of all slab system because MI slab systems modeled as equivalent diagonal strut and shear

wall at core increases stiffness and mass on the structure. BF is having larger drift value. Compare to BF, BFC is having less

storey drift values. Similarly compare to SSMI & AMI, SSMISW & AMISW is having less drift value because of the provision of

the core.

From above-mentioned graphs, Buildings with Conventional Beam-Slab system have minimum Storey drift, while

maximum Storey drift is obtained for buildings with Flat plate slab system. Drift values of structures having Flat slab lies

between structures having Flat plates and Conventional Beam-Slab system.

On an average, the Maximum Storey drift of Flat plates system with MISW is 45.42% higher and Flat slab system is

37.66% higher that of Conventional Beam-Slab system. Reduced drift values of the Beam-Slab system is because of increased

stiffness of the system contributed by the beams framing into the columns.

Similarly, on an average compare to Storey drift of Flat slab system with MISW, displacement values of Flat slab system

with BF is 95.14% higher, MI is 61.41% higher, SSMI is 63.84% higher, AMI is 79.44% higher, BFSW is 55.51% higher,

SSMISW is 9.15% higher, and AMISW is 30.54% higher.

Similarly, on an average Storey drift of Flat slab system with BF is 88.67% higher than that of BFSW, MI is 61.41%

higher than MISW, SSMI is 60.82% higher than SSMISW, and AMI is 70.38% higher than AMISW.




5.5: Response Acceleration (m/sec2)

Table 5.9 shows the Response Acceleration (m/sec2) values for Different Slab Systems with masonry infill and with & without a

shear wall.

Table 5.9: Response Acceleration (m/sec2) for Different Slab Systems for Zone V


CO

NV

E

NT

ION

AL

5 1.374 1.628 1.599 1.536 1.383 1.658 1.647 1.6317

10 1.162 1.542 1.545 1.548 1.221 1.6524 1.642 1.628

15 0.814 1.022 1.016 0.944 0.91 1.068 1.058 1.056

20 0.64 0.749 0.758 0.755 0.706 0.818 0.797 0.792

FL

AT

PL

AT

E

5 1.301 1.576 1.571 1.523 1.322 1.6326 1.614 1.59

10 0.674 1.541 1.526 1.502 0.777 1.638 1.627 1.577

15 0.487 1.035 1.034 1.002 0.583 1.064 1.048 1.032

20 0.354 0.741 0.739 0.718 0.4771 0.797 0.787 0.777

FL

AT

SL

AB

5 1.327 1.627 1.595 1.536 1.364 1.6506 1.632 1.607

10 0.725 1.539 1.51 1.511 0.778 1.64 1.629 1.591

15 0.547 0.998 1.003 0.929 0.613 1.064 1.052 1.046

20 0.429 0.743 0.74 0.727 0.516 0.803 0.792 0.788

Figure 5.19: Response Acceleration (m/sec2) for Conventional Slab for Zone V

Figure 5.20: Response Acceleration (m/sec2 ) Figure 5.21: Response Acceleration (m/sec2)

for Flat Plate Slab System for Flat Slab System for Zone V

Response Acceleration (m/sec2): From Figure 5.19, 5.20, and 5.21 it is noted that Response Acceleration decreases with increase

in the height of the building. Buildings with Conventional Beam-Slab system have higher Response Acceleration while lower

Response Acceleration is obtained for buildings with a Flat plate and Flat slab. From the graph it is clear that MISW is having

higher Response Acceleration than BF, BFSW, and all other models, this is due to the infill effect and provision of shear wall

increase stiffness as well as Acceleration of the structure.




On an average, the Response Acceleration of Flat slab system with MISW is 0.85% lesser and Flat plate system is 1.33%

lesser that of Conventional Beam-Slab system. Similarly, on an average compare to Response Acceleration of Flat slab system

with MISW, Response Acceleration values of Flat slab system with BF is 42.64% lesser, MI is 5.31% lesser , SSMI is 6.21%

lesser, AMI is 9.24% lesser, BFSW is 37.01% lesser, SSMISW is 1.07% lesser, and AMISW is 2.29% lesser.

Similarly, on an average the Response Acceleration of Flat slab system with BF is 9.28% lesser than that of BFSW, MI is

5.31% lesser than MISW, SSMI is 5.19% lesser than SSMISW, AMI is 7.1% lesser than AMISW.

CONCLUSION

In this study, an attempt has been made to compare the seismic behaviour of Multi-storied Flat plate and Flat slab structures

with Conventional Beam-Slab structure for varying building heights in Seismic Zone V. In addition to this, an effect of masonry

infill (fully infilled & partially infilled) with 20% opening for all the above slab systems with & without shear walls at core is

considered.

The variation with respect to above parameters for all building models in terms of their natural frequency, maximum

displacements, maximum storey drifts, base shears, and response acceleration are presented and discussed in detail.

Based on the results we obtained from the present study, the following conclusions are made:

Modeling of slab systems with masonry infill as equivalent diagonal strut add stiffness and strength to the structure. Natural Frequency decreases with the increase in height of the building for all slab systems. Natural Frequency for models

with flat plate and flat slab systems is less compared to that of the conventional beam-slab system. The flat slab system is

having a frequency higher than that of flat plate systems.

Natural frequency increases when an increase in stiffness so natural frequency is more for the slab systems with masonry infill and shear wall, compare to masonry infilled slab systems without a shear wall.

For structures with different slab systems considered, maximum Base shear is obtained for Flat slab building with masonry infill & shear wall shear wall and minimum Base shear is obtained for the Conventional Beam-Slab system. Provision of

Shear walls increases the Base shear due to increase in the Seismic weight of the structure.

The displacement of Masonry infilled slab systems is higher than that of slab systems with Masonry infill & shear wall. Displacement of structures with a Flat plate and Flat slab systems are always higher than that of structures with the

Conventional Beam-Slab system. The displacement of all models with Flat slab system is lower than that of Flat plate slab

system.

Buildings with Conventional Beam-Slab system have minimum Storey drift, while maximum Storey drift is obtained for buildings with Flat plate slab system. All models with Flat slab system show minimum Storey drift compare to Flat plates

slab system.

Displacement & Storey drift is very large in the case of the bare frame as compared to that of fully Infilled (MI) and partially infilled (SSMI & AMI) slab systems.

Fully Infilled and partially infilled slab systems with Shear walls i.e (MISW, SSMISW & AMISW) show reduced Displacement & Storey drift than infilled slab systems without a shear wall (MI, SSMI & AMI). Due to the effect of infill

and provision of Shear walls, Displacement & Storey drift are drastically reduced.

The Response Acceleration decreases with the increase of height of the structure. Acceleration of Conventional Beam-Slab system is higher compared to Flat Slab system. Response Acceleration of Flat slab system with masonry infill and shear

wall at the core is more than Flat slab system with masonry infill.

Response Acceleration is very less in the case of the bare frame as compared to that of fully Infilled (MI) and partially infilled (SSMI & AMI) slab system.

Higher Response Acceleration is obtained for fully & partially infilled slab systems with Shear walls i.e (MISW, SSMISW & AMISW) compare to infilled slab systems without a shear wall (MI, SSMI & AMI).

REFERENCES 1. Altug Erberik M, Amr S Elnashai, Fragility Analysis of Flat-Slab Structures, Engineering Structures 26 (2004) 937

948.

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