an evaluation based study on bare rcc framed...

Volume 04, Issue 04, Apr 2020 ISSN 2581 – 4575

AN EVALUATION BASED STUDY ON BARE RCC FRAMED

STRUCTURE SUBJECTED TO LATERAL SEISMIC LOADS BY

CONSIDERING STIFFNESS OF SLAB KANAKATLA RAJKUMAR

1, Mrs. R. SUMATHI

2

1 Student, Malla Reddy Engineering College (Autonomous), Maisammaguda, Medchal(M),

Malkajgiri(D), 500100 2Assistant Professor, Malla Reddy Engineering College (Autonomous), Maisammaguda,

Medchal(M), Malkajgiri(D), 500100

ABSTRACT

Till recent times to predict the exact capacity of the R.C structure with considering stiffness

of slab, need to depend on non-linear static analysis .To Model the Complex behavior of

reinforced concrete analytically in its non-linear zone is difficult. This has led Engineers in

the past to rely heavily on empirical formulas which were derived from numerous

experiments for the design of reinforced concrete structures for structural design and

assessment of reinforced concrete structures including force redistribution. This analysis of

the non-linear response of R.C Structures to be carried out in routine fashion, it helps in the

investigation of behavior and the cracks pattern of R.C structure with considering stiffness

of slab skeleton framing system. Building composed of only reinforced concrete columns,

beams and slabs have been adopted in analysis for many framed buildings. Generally,

flexural stiffness of slabs is ignored and the floor load is transferred as uniformly

distributed load on to the supporting beams in the conventional analysis of bare frame

structures. However, in reality, the floor slabs may have some influence on the lateral

response of the structures. Consequently, if the flexural stiffness of slabs in a frame system

structure is totally ignored, the lateral stiffness of the framing may be underestimated. So,

to study on the behavior of R.C structure with considering stiffness of slab is very essential.

The research was already done on linear analysis.Therefore the objective of the present

investigation is to study the nonlinear behavior of the G+5 R.C building by considering the

effect of increased stiffness due to slab elements in R.C space frames, subjected to seismic

loading, on the parameter like displacement etc., for zone II, III, IV and V. By comparing

the two models of frame such has skeleton framed structure (SFS), skeleton framed

Structure with considering stiffness of slab (SFWS), the effect of increased stiffness on the

above parameters is studied and also the increased capacity of framed system is also

studied. From the present study it is concluded that non-linear analysis of R.C structures

with considering stiffness of slab (SFWS) to seismic load can resist for more deformation

and base shear than Skelton framing system (SFS).

Keywords: Non-linear analysis, skeleton framed structure (SFS), skeleton framed Structure

with considering stiffness of slab (SFWS), Displacements, pushover capacity curves.


INTRODUCTION

The Buildings, which appeared to be

strong enough, may crumble like hours of

cards during earthquake and deficiencies

may be exposed. Experience gain from

the recent earthquake of Bhuj,

demonstrates that the most of buildings

collapsed were found deficient to meet

out the requirements of the present day

codes. In last decade, four devastating

earthquakes of world have been occurred

in India, and low to mold intensities

earthquake of world frequently. Due to

wrong construction practices and

ignorance for earthquake resistant design

of buildings in our country, most of the

existing buildings are vulnerable to future

earthquakes. In the simplest case, seismic

design can be viewed as a row-step

process. The first, and usually most

important one, is the conception of an

effective structural system that needs to

be configured with due regards to all

important seismic performance

objectives, ranging from serviceability

consideration to life safety and collapse

prevention. This step comprises the art of

seismic engineering, since no rigid rules

can, or should, be imposed on the

engineer’s creativity to devise a system

that not only fulfills seismic performance

objectives, but also pays tribute to

functional and economic constraints

imposed by the owner, the architect, and

other professionals involved in the design

and construction of a building. By

default, this process of creation is based

on judgment, experience, and

understanding of seismic behavior, rather

than rigorous mathematical formulations.

Rules of thumb for strength and stiffness

targets, based on the fundamental

knowledge of ground motion and elastic

and inelastic dynamic response

characteristics, should involve a

demand/capacity evaluation at all

important performance level, which

requires identification of important

capacity evaluation at all important

performance level, which requires

identification of important capacity

parameters and prescription of acceptable

values of these parameters, as well as the

prediction of the demands imposed by

ground motions. Suitable capacity

parameters and their acceptable values, as

well as suitable methods for demands

prediction will depend on the

performance level to be evaluated. In

light of these facts, it is imperative to

seismically evaluate the existing building

with the Present day Knowledge to avoid

the major destruction in the future

earthquakes. The Buildings found to be

seismically deficient should be retrofitted

or strengthened.

ObjectiveofthePresentStudy:

The objective of the presentwork is to

study the nonlinear static behavior of

the structure with and without

considering stiffness of slab,

subjected to seismic loading.

Comparing the two models of frame

such has Skeleton framed structure

(SFS) and Skeleton framed Structure

with considering stiffness of slab

(SFWS) at different seismic zones,

the effect of increased stiffness on the

above parameters studied & increased


capacity of framed systems were also

studied.

ScopeofthePresentStudy:

For the purpose of Comparison,

building type, floor system, floor area,

bay size and column height are kept

constant throughout the study.

Ordinary moment resisting frames

(OMRF) with response reduction

factor of 3 and importance factor 1

(general building) is considered

throughout the study.

The study is made for 6 storied

structures with plan dimensions of 15

m X 15 m, in all the seismic zones of

India (Zones II to Zone V)

LiteratureReview

Santhosh. D Pushover analysis is non-

linear static analysis in which Provide

‘capacity curve’ of the structure, it is a

plot of total base force vs. roof

displacement. The analysis is carried out

up to failure; it helps determination of

collapse load and ductility capacity of the

structure. The pushover analysis is a

method to observe the successive damage

state of the building.Pushover analysis is

a non-linear static analysis used to

determine the force-displacement

relationship, or capacity curve, for a

structural element. To evaluate the

performance of RC frame structure, a

non-linear static pushover analysis has

been conducted by using ETABS 9.7.1.

To achieve this objective, three RC bare

frame structures with 5, 1, 15 stories

respectively were analyzed. And also

compared the base force and

displacement of RC bare frame structure

with 5, 1, 15 stories.

A. K. Chopra extracted an improved

Direct Displacement-Based Design

Procedure for Performance-Based seismic

design of structures. Direct displacement-

based design requires a simplified

procedure to estimate the seismic

deformation of an inelastic SDF system,

representing the first (elastic) mode of

vibration of the structure. This step is

usually accomplished by analysis of an

“equivalent” linear system using elastic

design spectra. In their work, an equally

simple procedure is developed that is

based on the well-known concepts of

inelastic design spectra. This procedure

provides: (1) accurate values of

displacement and ductility demands, and

(2) a structural design that satisfies the

design criteria for allowable plastic

rotation. In contrast, the existing

procedure using elastic design spectra for

equivalent linear systems is shown to

underestimate significantly the

displacement and ductility demands.

In this work, it is demonstrated

that the deformation and ductility factor

that are estimated in designing the

structure by this procedure are much

smaller than the deformation and ductility

demands determined by nonlinear

analysis of the system using inelastic

design spectra. Furthermore, it has been

shown that the plastic rotation demand on

structures designed by this procedure may

exceed the acceptable value of the plastic

rotation.

Krawinkler and Seneviratnaconducted

a detailed study that discusses the

advantages, disadvantages and the

applicability of pushover analysis by


considering various aspects of the

procedure. The basic concepts and main

assumptions on which the pushover

analysis is based, target displacement

estimation of MDOF structure through

equivalent SDOF domain and the applied

modification factors, importance of lateral

load pattern on pushover predictions, the

conditions under which pushover

predictions are adequate or not and the

information obtained from pushover

analysis were identified. The accuracy of

pushover predictions were evaluated on a

4-story steel perimeter frame damaged in

1994 Northridge earthquake. The frame

was subjected to nine ground motion

records. Local and global seismic

demands were calculated from pushover

analysis results at the target displacement

associated with the individual records.

The comparison of pushover and

nonlinear dynamic analysis results

showed that pushover analysis provides

good predictions of seismic demands for

low-rise structures having uniform

distribution of inelastic behavior over the

height. It was also recommended to

implement pushover analysis with caution

and judgment considering its many

limitations since the method is

approximate in nature and it contains

many unresolved issues that need to be

investigated.

Ceroni et al., formulated that ductility of

R.C. elements has been widely studied

either experimentally and theoretical

since its evaluation is basic to carry out a

reliable non-linear analysis of structures;

post-elastic deformability is a resource for

redistributing stresses in a structure to

increase the ultimate load but, above all,

to absorb and dissipate energy during

major earthquakes. However, the problem

remains open and models still need an

improvement in two directions. On one

side, mechanical models can be

implemented to take into account

constructive details, shear-flexure

interaction, size effects as well as non-

linear constitutive relationship of

materials and steel-concrete bond. On the

other side, simplified approaches have to

be assessed in order to allow an easy but

reliable ductility evaluation without using

any sophisticated analytical model,

generally not very designers friendly. In

this paper a wide parametric analysis with

a refined model is carried out in order to

build on a reliable formulation for the

plastic hinge length of R.C. columns

subjected to axial and flexural load. The

model used to analyze the non-linear

behavior of the element and to estimate

the plastic rotation is a point by point

model, including an explicit formulation

of the bond slip relationship and capable

to take into account the effect of the

distributed and concentrated non-

linearity, as the spread of plasticity along

the member and the fixed end rotation. Its

efficiency has been already successfully

applied to experimental comparison.

Habibullah and Pyle, Yielding and post-

yielding behavior can be modeled using

discrete user-defined hinges. Currently

ETABS allows hinges can only be

introduced into frame elements; the PHP

properties can be assigned to a frame

element at any location along it. The

authors have been developed a dual


parameters method to define the PHP

properties of RC frame structure for the

pushover analysis

Ho and Wang, The purpose of this paper

is to extend the application of this method

to the RC structures containing RC shear

wall. In order to use the functions

provided by the ETABS code, the RC

shear wall is treated as a wide, flat

column. Modeling a RC wall as a wide

and flat column (frame elements) not only

can consider the steel reinforcements in

RC elements exactly, but also can assign

the PHP of RC walls according to its

plastic behavior. In ETABS, the default

properties are available for hinges in the

following degrees of freedom:

1. Axial (P)

2. Major shear (V2)

3. Major moment (M3)

4. Coupled P-M2-M3 (PMM)

He concluded that a dual parameters

method is introduced to define the plastic

hinge properties (PHP) of RC wall in the

pushover analysis of RC structure. The

effectiveness of this simple method is

verified by the agreement of the

prediction curves with some additional

test data. This newly proposed method is

quite simple and is easy for engineers to

link with commercial structural analysis

code to conduct the performance design

of structure under seismic loading.

Dileep . M et al.,explained the practical

difficulties associated with the non-linear

direct numerical integration of the

equations of motion leads to the use of

non-linear static pushover analysis of

structures. Pushover analysis is getting

popular due to its simplicity. High

frequency modes and non-linear effects

may play an important role in stiff and

irregular structures. The contribution of

higher modes in pushover analysis is not

fully developed. The behavior of high

frequency model responses in non-linear

seismic analysis of structures is not

known. In this paper an attempt is made

to study the behavior of high frequency

model responses in non-linear seismic

analysis of structures.

Non-linear static pushover

analysis used as an approximation to non-

linear time history analysis is becoming a

standard tool among the engineers,

researches and professionals worldwide.

High frequency modes may contribute

significantly in the seismic analysis of

irregular and stiff structures. In order to

take the contribution of higher modes

structural engineers may include high

frequency modes in the non-linear static

pushover analysis. The behavior of high

frequency modes in non-linear static

pushover analysis of irregular structures

is studied. At high frequencies, the

responses of non-linear dynamic analysis

converge to the non-linear static pushover

analysis. Therefore non-linear response of

high frequency modes can be evaluated

using a non-linear static push over

analysis with an implemental force

pattern given by their modal mass

contribution times zero period

acceleration. The higher modes with rigid

content as a major contributing factor

exhibit a better accuracy in non-linear

pushover analysis of structures when

compared to the damped periodic modes.


Mayuri D. Bhagwat, Dr.P.S.PatilIn the

present work dynamic analysis of G+12

multistoried practiced RCC building

considering for Koyna and Bhuj

earthquake is carried out by time history

analysis and response spectrum analysis

and seismic responses of such building

are comparatively studied and modeled

with the help of ETABS software. Two

time histories (i.e. Koyna and Bhuj) have

been used to develop different acceptable

criteria (base shear, storey displacement,

storey drifts). Conclusions drawn are.

1. From the graphs it is observed that the

values of base shear for Bhuj earthquake

is 49.11% more than the Koyna

earthquake. Response spectrum method

gives 50% more results than time history

analysis.

2. As a result of comparison between time

history method and response spectrum

method it has been observed that the

values obtained by response spectrum

analysis of base shear and top story

displacement for Koyna earthquake

39.70% & 31.18% and for Bhuj

earthquake 40.53% & 31.99% are higher

than time history analysis.

3. From the tabulated values it is

observed that the values of the Storey

drifts for all the stories are found to be

within the permissible limits.

4. From the results it is recommended that

time history analysis should be performed

as it predicts the structural response more

accurately than the response spectrum

analysis.

K. Venkataraostudied the seismic

behavior of conventional RC framed

building, flat slab with drop and without

drop building in all seismic zones of

India. Different parameters like lateral

drift, base shear, time period and axial

force are compared. It was concluded that

lateral displacement of conventional RC

frame is less as compared to flat slab

without drop building.

Kusuma B The paper aims at evaluating

the seismic actions by considering various

codal provisions, which are particularly

provided for the analysis of RC building

with unsymmetrical configuration and

with different types of irregularities. The

analysis is carried out on a model of

G+49 stories of RC framed structure with

unsymmetrical floor plan located in Zone

IV, soil type III, using finite element

based ETABS (V 13.1) software. The

various structural response parameters

such as, storey displacement, storey drift,

base shear and storey stiffness are

determined by considering different

irregularities such as mass irregularity,

vertical geometric irregularity, re-entrant

corner, diaphragm discontinuity and

stiffness irregularity in the model and the

structural parameters stated above are

compared for the models having different

irregularities. Seismic analysis is carried

out using response spectrum method for

both symmetrical and unsymmetrical

building. The data required for the input

is collected from IS code 1893 (Part

I):2002. Then the analytical work is

carried out as per the procedure

formulated and the results are obtained.

The major part of the study includes the

comparison of values of set of response

parameters such as, mode period, storey

lateral displacement, storey drift, base


shear and the storey stiffness. It is

concluded that RC moment resisting

frame and with masonry walls, perform

better under the action of seismic load,

compared to irregular structure, the lateral

displacement is increased in case of

vertical irregular structure and the

stiffness of the structure is reduced in

vertical irregular.

DileshwarRana, Prof. JunedRaheem

studied seismic analysis of regular &

vertical geometric irregular RCC framed

building. They concluded that 4 bay

frames is appropriate for lower building

height and for higher stories, 8 bay

frames is suitable. Seismic performance

improves with number of bays.

Arvindreddy, R.J.FernandesIn this

paper an analytical study is made to find

response of different regular and irregular

structures located in severe zone V.

Analysis has been made by

takingreinforced concrete regular and

irregular 15 storey buildings and is

analyzed by static and dynamic methods.

Six models are modeled. One is of regular

structure and remaining are irregular

structural models. Linear Equivalent

Static analysis is performed for regular

buildings up to 90m height in zone I and

II, Dynamic Analysis is performed for

regular and irregular buildings in zone IV

and V. Behavior of structures is found by

comparing responses in the form of storey

displacement for regular and irregular

structures. They concluded that structure

built-in with stiffness irregularity will be

on non-conservative side and as seen

from time history analysis, as storey

increases behavior of stiffness irregularity

and diaphragm irregularity becomes

reverse.

M V Naresh, K J Brahma ChariIn this

paper seismic reaction of a private G+10

RC outline building is breaking down by

the direct examination methodologies of

Equivalent Static Lateral Force and

Response Spectrum techniques utilizing

ETABS Ultimate software according to

the Seems to be 1893-2002-Part-1. These

analyses are carried out by considering

different seismic zones. A substitute

response like lateral force, story drift,

displacements, base shear are plotted to

think about the consequences of the static

and dynamic investigation. It is

concluded that for high rise buildings

static analysis is not enough its necessary

to provide dynamic analysis, base shear

approval is more in the zone 5 and that in

the delicate soil in normal setup, the

maximum displacement is increased from

first storey to last storey and

unpredictable shapes are seriously

influenced amid quakes particularly in

high seismic zones.

Prof. P. S. Lande discussed about flat

slab structure is most vulnerable to the

seismic excitation therefore the careful

analysis of flat slab is important. In this

paper the seismic analysis on flat slab is

performed and compared it with the

conventional RC building. To improve

the performance of flat slab system shear

wall and beam at periphery is applied and

the seismic response of the same is

determined and compared it with the flat

slab building.


Model Geometry:

The structure analyzed is a six-storied,

three bays along X-direction and three

bays along Y-direction moment-resisting

frame of reinforced concrete with

properties as specified above. The

concrete floors are modeled as rigid. The

details of the model are given as:

Number of stories = 6

Number of bays along X-direction = 3

Number of bays along Y-direction = 3

Storey height = 3 m

Bay width along X-direction = 5 m

Bay width along Y-direction = 5 m

PlanofBuilding:

Fig1Planofbuilding

ElevationofBuilding:

Fig2Elevationofbuilding

3d-ViewofBuilding:

Fig 3 3DViewofbuilding

FLOWCHARTOFMETHODOLOGY


ResultsandDiscussions

Studiedthenonlinearstaticbehaviorofthestr

ucturewithandwithoutconsideringstiffness

ofslabsubjectedtoseismicloading.Bycomp

aringthetwomodelsofframesuchhasSkelet

onframedstructure(SFS)andSkeletonfram

edStructurewithconsideringstiffnessofslab

(SFWS)atdifferentseismiczones,theeffect

ofincreasedstiffnessontheaboveparameter

s&increasedcapacityofframedsystemswer

estudied.

Case I. The R.C Framed Structure

without considering Stiffness of slab

(SFS)

Figure5: Deformed shape of the

structure


CaseII.TheR.CFramedStructurewithco

nsideringStiffnessofslab

Figure10: Deformed shape of the

structure


Comparison of Pushover Curves:

Pushover or nonlinear static analysis is

carried out for all the cases considering in

the thesis and finally pushover curves are

obtained. Pushover curves are obtained

with displacement on x-axis and base

reaction on y-axis Depending on the

pushover curves comparisons are carried

out between.

The comparison of R.C Framed

Structure without and with

considering stiffness of slab(SFS

&SFWS) to seismic zones-II, III, IV,

V.


Structure without considering

stiffness of slab(SFS) to seismic zone-

II and with considering stiffness of

slab(SFWS) for seismic zones-III

The comparison of R.C.C Framed



III and with considering stiffness of

slab(SFWS) for seismic zones-IV




IV and with considering stiffness of

slab(SFWS) for seismic zones-V.

Comparison -1: The R.C Framed

Structure with and without considering

Stiffness of slab (SFWS & SFS) for

seismic zone-II:

R.C Framed structure with considering

Stiffness of slab (SFWS) can take the

base force of 2.072x10 3

kN and

Displacement of 164.7x10 -3

m.

R.C Framed structure without considering

Stiffness of slab (SFS) can take the base

force of 2.057x10 3kN and Displacement

of 154.6x10 -3

m.

Comparison-2: The R.C Framed


Stiffness Of slab (SFWS & SFS) for

seismic zone-III:




KN and

displacement of 164.9x10 -3

m.

R.C Framed structure without considering


force of 2.057x10 3 KN and displacement

of 153.7x10 -3

m.


Comparison - 3: The R.C Framed


Stiffness Of slab (SFWS & SFS) for

seismic zone-IV:

R.C. Framed structure with considering



kN and


m.

R.C. Framed structure without

considering Stiffness of slab (SFS) can

take the base force of 1.473x10 3kN and


m.

Comparison -4: The R.C Framed


Stiffness Of slab (SFWS & SFS) to

seismic zone-V:




kN and


m.

R.C Framed structure wit out considering


force of 1.472x10 3kN and Displacement

of 155.4x10 -3

m.

Conclusions:

The performance R.C frame with &

without considering stiffness of slab (SFS

& SFWS) was investigated using the

pushover analysis. Following were the

major conclusions drawn from the Study.

Zone – II:

a) Comparing with SFS and SFWS, The

SFS Base Shear is 7.2% less than

SFWS.

b) Comparing with SFS and SFWS, The

SFS Displacement is 6.53% less than

SFWS.

Zone – III:



SFS Base Shear is 1% less than

SFWS.



SFWS.

Zone – IV:



SFWS.



SFWS.

Zone – V:



SFWS.


SFS Displacement is 11% less than

SFWS.

1. In the comparison of performance

based study on R.C. framed structure

with and without considering

Stiffness of slab (SFWS & SFS) to

seismic load at different zones-II, III,

IV, V, the capacity curve based on

with considering stiffness of slab

(SFWS) can with stand for more

deformation and base shear than

without considering stiffness of slab

(SFS).

2. From the pilot study, non-linear

analysis of R.C structures with

considering stiffness of slab (SFWS)

to seismic load can resist for more

deformation than Skelton framing

system (SFS).

Scope for Further Study:

1. The similar study can be carried out

for structures with irregularities

2. In this present work, studied the effect

of stiffness of slab elements along

with frames. Can also study the

effects of infill walls.

REFERRENCES

1. Applied Technology Council, ATC-4,

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an evaluation based study on bare rcc framed...

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