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International Journal of Research and Innovation (IJRI)
DESIGN AND ANALYSIS OF MULTI STORIED STRUCTURES USING STATIC NON
LINEAR ANALYSIS
P.Swetha1, K. Mythili2, G.Venkat Ratnam3
1 Research Scholar, Department Of Civil Engineering, Aurora's
Scientific Technological & Research Academy, Hyderabad, India2
Associate Professor, Department Of Civil Engineering, Aurora's
Scientific Technological & Research Academy, Hyderabad, India3
Associate Professor,Department Of Civil Engineering, Aurora's
Scientific Technological & Research Academy, Hyderabad,
India
*Corresponding Author: P.swetha, Research Scholar, Department of
CIVIL Engineering, Aurora's Scientific Technological & Research
Academy, Hyderabad, India Published: october 28, 2014Review Type:
peer reviewedVolume: I, Issue :IICitation:P.Swetha,(2014)DESIGN AND
ANALYSIS OF MULTI STORIED STRUCTURES USING STATIC NON LIN-EAR
ANALYSIS
INTRODUCTIONGENERAL
Earthquakes in general occur due to intense tec-tonic activity
of earth . In recent times there is a marked increase in the
frequency of occurrence of earthquakes all over the world .the
intensity and lo-cation of the earthquake is unpredictable even as
on date . structures designed to withstand gravity loads alone
cannot be expected to resist the dam-ages caused due to seismic
effects . structures de-signed for gravity loads are normally well
below the elastic limiting stage and lie within the service loads .
it is neither practical nor economically viable to de-sign
structures to remain within elastic limits dur-ing earthquakes .
the design approach adopted in
the Indian code IS 1893(Part1): 2002 Criteria for Earthquake
Resistant Design of Structures is to en-sure that structures
possess at least a minimum strength to withstand minor earthquakes
which oc-cur frequently , without damage ; resist moderate
earthquakes without significant structural damage through some
non-structural damage may occur ; and aims that structures
withstand major earth-quakes without collapse .
India has experienced many large earthquakes in the last two
decades resulting in heavy loss of life and property . In fact ,
more than 50% area in the country is considered vulnerable to
earthquake dis-asters .Hence there is an urgent need for seismic
evaluation and retrofitting of deficient buildings. The
retrofitting is more so desirable as most of the majestic
structures are designed to resist gravity loads alone .
A systematic procedure is to be followed while as-sessing the
vulnerability of existing buildings . De-tailed survey of the
buildings under the interest is to be undertaken. The basic
information collected in the survey should include review of the
build-ing configuration , soil profile and the period of
construction . This is done with the help of quick checks and
evaluation statements .
Abstract
The main objective of the research work presented in this thesis
is to provide a systematic procedure to as-sess the behavior of a
structure symmetrical and unsymmetrical
In plan during the seismic excitation using nonlinear static
analysis (pushover) have been performed on the same structure. The
literature pertaining to pushover analysis is reviewed. The
pushover analysis adopted in the present study is on similar lines
with the procedure presented by Ashraf Habibullah and Stephen Pyle
using ETABS V 9.7 structural analysis software. The effect of
earthquake force in a idealized G+4 story building under maximum
earthquake zone, with the help of pushover analysis has been
investigated and the results were compared in terms of base shear,
displacement, spectral acceleration, spectral displace-ment and
effective damping and effective time period .to strengthen the
symmetric and un symmetric RCC framed buildings` steel braces are
included by using retrofitting method.
The present structure is studied using the evaluation procedures
provided in ATC-40 and FEMA-356 docu-ments and IS 1893:2002.
From the above studies it has been observed that nonlinear
pushover analysis provides a good estimate of in elastic
deformation demands and also reveals weakness that may remain
hidden in an elastic analysis.
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1401-1402
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International Journal of Research and Innovation (IJRI)
However , a detailed evaluation is necessary in or-der to
identify the deficiencies associated with the structural components
with regard to the expected behavior of the building. The code
compliance of the building can be ascertained only when the
available member capacities are compared with the respec-tive
demands due to the earthquake .the demand in structural members are
determined for the seis-mic forces estimated as per IS 1893-2002
through linear static analysis . The member capacities are
determined using the procedures prescribed in IS 456-2000 .The
deficient members are identified and the Demand to Capacity
Ratio(DCR) exceeds unity indicating the need for retrofitting in
order to estab-lish compliance with prevailing codes.
NEED FOR THE INVESTIGATION
Low to medium height reinforced concrete frame buildings with
masonry infill are common in ur-ban India . All these buildings in
general designed to resist gravity loads and hence cant be expected
to resist the latest seismic provisions . Earthquake causes shaking
of the ground in unspecified direc-tions . The horizontal shaking
along X and Y direc-tions remain a matter of concern . Structures
de-signed for gravity loads , in general may not be able to safely
sustain the effects of horizontal shaking due to earthquakes .
Hence it is necessary to en-sure the strength of the structure
against horizontal earthquake effects
OBJECTIVES OF THE STUDY
The primary objective of this work is to study the seismic
response of RC framed building. The ef-fect of earthquake force on
building in a symmetric and un symmetric building under maximum
earth quake zone ,with the help of push over analysis has been
investigated.
In the present study the main objective is the investigate the
impact of steel bracings in improving the seismic capacity of RC
buildings.The main objective of undertaking the present study are
as follows :
1)To analyze a RC framed building both symmetric and un
symmetric using pushover analysis proce-dure , with ETABS v 9.7 for
ascertaining the seis-mic load carrying .
2)To compute the seismic response of building in terms of base
shear , spectral acceleration, spectral displacement and roof
displacements.
3)To study the effect of the steel bracings as a meth-od of
retrofitting .
4)The increasing in base shear .
5)The reduction in amplitude of maximum displace-ments.
The study is propose to made with ETABS package on a symmetric
and non-symmetric RCC buildings of five story height , the
introduction of steel brac-ings may be consider as one method of
retrofitting.
In the conventional retrofitting technologies adopt-ed to
strength the RCC buildings to begin with the pushover analysis is
carried out on RCC buildings there after depending on the
deficiencies, the retro-fitting technologies are adopted in the
present study the capacity of the building is increased by the use
of steel braces provided to connect the columns and beams at the
beam columns junction below the roof. a study is made to access the
additional shear capacity of the building as well as the additional
stiffness for both buildings with both symmetric and un symmetric
plans
SUMMARY
In this chapter, the importance of earthquake and the post
disaster effects of it and some light has been thrown on the
earthquake design philosophy to be adopted in the construction and
the various impor-tant seismic codes of India. The scope and
objective is also been discussed. Based on the objective of the
present study, research papers were collected and studied
thoroughly. The review of research papers is discussed in the next
chapter named as literature review.
TERMINOLOGY
The following are the definitions which are most commonly used
in pushover analysis
Performance Point
It is the point where the capacity spectrum inter-sects the
appropriate demand spectrum (capacity equals demand ). To have
desired performance , every structure has to be designed for this
level of forces
Representing capacity spectrum , demand spec-trum , performance
point
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International Journal of Research and Innovation (IJRI)
Building Performance Levels
Building performance is a combination of the per-formance of
both structures and non-structural components . Different buildings
performance level, used to described the performance of building in
pushover analysis are described below
Operational Level (OL):
Building meeting this performances level are ex-pected to
sustain no permanent drift and the struc-ture substantially retains
original strengths and stiffness .major cracking of facades,
partition and ceilings as well as structural elements are seen .
All the system important to normal operation are func-tional .
Non-structural components are expected to sustain negligible damage
.
Immediate Occupancy Level (IO) :
Building meeting this performances level are ex-pected to
sustain no permanent drift and the struc-ture substantially retains
original strengths and stiffness . Minor cracking of facades ,
partition and ceilings as well as structure elements are seen .
El-evators can be restarted . Fire protection is operable . Non-
structural components such as equipments and contents stays
generally secure , But may not be operative due to mechanical
failure or lack of utilities.
Life Safety Level (LS):
This level is indicated when some residual strength and
stiffness is left in all stories .Gravity load bear-ing elements
function, no out-of-plane failure of walls or tripping of parapets
occurs . There may some permanent drift , damage to partitions and
the building may be beyond economical repair . Among the
non-structural components falling haz-ards mitigated but many
architectural , mechanical and electrical system get damaged
Collapse Prevention Level (CP): Building meeting this
performance level are ex-cepted to have little residual stiffness
and strength ,but load bearing columns and walls function . The
building is expected to sustain large permanent drifts , some exit
blocked , infill and un-braced parapet failure .Extensive damage to
occur to non-structural component . At this level of performance ,
the building remains near collapse state
Building Performance Levels
A typical force deformation curve
GENERAL
The existing buildings can become seismically de-ficient since
seismic design code requirements are commonly upgraded and
advancement in engineer-ing knowledge . Future , Indian buildings
built over past two decades are seismically deficient because of
lack of awareness regarding seismic behavior of structure , The
widespread damage especially to RC buildings during earthquakes
exposed the con-struction practices being adopted around the world
, and generated a great demand for seismic evalu-ation and
retrofitting of existing building stocks Thus , it leads to the
necessary of non-linear static pushover analysis .
The static pushover analysis is becoming a popu-lar tool for
seismic performance evaluation of ex-isting and new structures .
The expectation is that the push over analysis will provide
adequate system and its components
The purpose of the study is to summarize the ba-sic concepts on
which the pushover analysis can be based , assess the accuracy of
the pushover predic-tions, identify conditions under which the
pushover will provide adequate information and perhaps more
importantly , identify causes in which the pushover predictions
will be inadequate or even misleading
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International Journal of Research and Innovation (IJRI)
PRESENT STUDY
INTRODUCTION
In the present study a rectangular building of G+4 stored
symmetrical building and unsymmetrical building with same height
are considered, push over analysis of the buildings is taken up
with and without steel bracings using the package ETABS.
Description And Plan For Symmetrical Building
In the present work, a G+4 storied reinforced con-crete frame
building situated in maximum earth quack Zone V, is taken for the
purpose of study. The plan area of building is 1200x900mm with
300mm as height of each typical story. It consists of 4 bays in
X-direction and 4 bays in Y-direction. The total height of the
building is 1500mm. The building is considered as a Special Moment
resisting frame. The plan of building is shown in while the
isometric view of the buildings Structure with brace and with-out
braces
symmetrical building plan and section in ETABS V 9.7
As the structure is regular and relatively simple the
identification of the differences in results can be known in easy
and can be discuss in depth.The Structure without braces and
Structure with braces are having same frame properties i.e., same
beam and column properties the only thing that dif-fer is that the
Structure is acquainted with braces on the top of the slab
connected to beams and col-umns.
Description And Plan For Unsymmetrical Build-ing
In this present work a G+4 stored rein forced con-crete frame
building situated in maximum earth quake Zone V, is taken for the
purpose of study . The plan area of building is 1600x1800 mm with
300mm as height of each typical storey. It consists of 5 bays in
X-direction and 7 bays in Y-direction. The total height of the
building is 1500mm. The building is considered as un symmetrical in
plan as a Special Moment resisting frame. The plan of building is
shown in while the isometric view of the buildings Structure with
brace and with out braces
UN symmetrical building plan and section in ETABS V9.7
STRUCTURAL SYSTEMS OF THE BUILDING
storey G+4Slab thickness 125mmBeam dimensions 230 mm x 450
mmColumn dimensions 230mm x 450 mmExterior wall 230 mmInterior wall
150 mm
Structural dimensions of building
General Data Collection
The building is a G+4 storey building located in zone V. Tables
5.2, Table 5.3, Table 5.4 present a summary of the building
parameters .The details of the building are given below.
Variable Type ReferenceType of soil Medium soil IS 1893:2002Type
of founda-tion
Isolated footing ----
Seismic zone V IS 1893:2002
Geo technical and Geo logical data
Introduction To Load Patterns
Nonlinear static analysis, or pushover analysis, could be
performed directly by a computer program which can model nonlinear
behaviour of lateral load resisting members of a structure.
However, the com-putational scheme and the assumptions involved in
modelling nonlinear member behaviour could be dif-ferent that there
may be variations in the pushover results obtained from different
software. Therefore, the underlying principles of any software
utilized for pushover analysis should be well understood to
in-terpret the results of pushover analysis.
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International Journal of Research and Innovation (IJRI)
Pushover Analysis Using Etabs V9.7:
The following steps are included in the pushover analysis. Steps
1 to 4 are to create the computer model, step 5 runs the analysis,
and steps 6 to 10 review the pushover analysis results.
Geometry of symmetric structure
Reinforcement area in the beams and columns ana-lysed by linear
response spectrum
Create the basic computer model (without the pushover data) as
shown in fig 5.6 . The graphical interface of ETABS v9.7makes this
quick and easy task. Assigned sectional properties & applies
all the gravity loads (i.e. Dead load and Live load) on the
structure respectively.
In order to know the reinforcement area in the Beam and Columns
the Response Spectra linear Analysis was done for the zone II with
Soil Type-2 and the Building was designed as per IS 456
Define properties and acceptance criteria for the pushover
hinges. The program includes several built-in default hinge
properties that are based on average values from ATC-40(3) for
concrete members and average values from FEMA-356(2) for concrete
members. In this analysis, M3 hinges have been de-fined at both the
column ends and M3 hinges have been defined at both the ends of all
the beams.
Locate the pushover hinges on the model by se-lecting all the
frame members and assigning them one or more hinge properties and
hinge locations as shown in Fig. 5.9
Frame Hinge Properties Data
Define hinges
Define the pushover load cases, Fig. 5.10, Fig. 5.11 and Fig.
5.12. In ETABS v9.7 more than one pusho-ver load case can be run in
the same analysis. Also a pushover load case can start from the
final condi-tions of another pushover load case that was
previ-ously run in the same analysis. Typically the first pushover
load case was used to apply gravity load and then subsequent
lateral pushover load cases were specified to start from the final
conditions of the gravity pushover. Pushover load cases can be
force controlled, that is, pushed to a certain defined force level,
or they can be displacement controlled, that is, pushed to a
specified displacement. Typical-ly a gravity load pushover is force
controlled and lat-eral pushovers are displacement controlled. In
this case a Gravity load combination of 1.5DL+1.5LL has been used.
This combination has been defined as GRAV. The lateral loads, have
been applied by giv-ing the displacement to the model to be
analysed to a case called PUSH.
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International Journal of Research and Innovation (IJRI)
Static load case
Run analysis windows for the practical building
Pushover curve for the symmetric structure steel bracings
Pushover curve for the symmetric structure with steel
bracings
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International Journal of Research and Innovation (IJRI)
Pushover curve for the un symmetric structure with steel
bracings
Capacity spectrum for symmetrical structure
Capacity spectrum for un symmetrical structure
Capacity spectrum for symmetrical structure with steel
bracings
Capacity spectrum for un symmetrical structure with steel
bracings
The pushover displaced shape and sequence of hinge information
on a step-by-step basis was ob-tained and is shown in the Fig. 6.1
to 6.4 for the Structure without steel bracings and in the Fig. 6.5
to 6.8 for the Structure with steel bracings. Output for the
pushover analysis can be printed in a tabu-lar form for the entire
model or for selected elements of the model. The types of output
available in this form include joint displacements at each step of
the pushover, frame member forces at each step of the pushover, and
hinge force, displacement and state at each step of the
pushover.
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International Journal of Research and Innovation (IJRI)
SUMMARY
This chapter completely takes care of the case study of a
Structure under consideration and the various building data surveys
done to gather the informa-tion for modeling of the structure,
after carrying out the pushover analysis , the pushover curves for
both the buildings with and without steel brac-ings are obtained,
based on the performance points obtained the significant
contribution by the use of steel bracings is noted and found a
great achieve-ment to the field of retrofitting And also
illustrates the step by step procedure followed for the static
non-linear analysis.
DISCUSSION ON RESULTS
GENERAL
The structures has been modelled and the Pushover analysis of
the structures has been carried out ac-cordingly with the ETABS
v9.7
DISCUSSION ON RESULTS OF PUSHOVER ANAL-YSIS FOR THE SYMMETRICAL
STRUCTURE WITHOUT STEEL BRACINGS AND WITH STEEL BRACINGS
Observations under Pushover Curve
The Structures has been given in a Pushover curve for the
Structures was graphically generated for both the symmetric and un
symmetric Building i.e. Structure without steel bracings and
Structure With steel bracings as shown in the Fig. 5.14 and Fig.
5.16 respectively, It has been observe from the Fig. 5.14 and Fig.
5.15 that the base shear was mono-lithically increasing with the
Displacement. And for the Drift the Maximum Base Shear was observed
to be 796.22 kN and 1560.99 kN respectively. Table 6.1 and Table
6.2 show the step by step details for the change in base shear, and
the number of elements falling in different performance levels like
immediate occupancy, life safety and col-lapse prevention as the
roof Displacement changes.
It has been clearly observed from the Table 6.1 for the
symmetric Structure without steel bracings that the hinges were in
the elastic region (i.e. A to B) up to a displacement of 19.31mm
and further increase in the displacement leads to formation of 56
hinge with this the structure enters into non-linear stage (i.e. B
to IO). The structure remains in this Immediate Occupancy
performance level till the displacement reached 44.3 mm with the
Base shear of 642.7kN at this stage it was observed that there were
around 70 element hinges in this Perfor-mance Level and further
increase in the displace-ment increases the number of hinge
formation in other Performance Levels. the structure enter the
performance level of Life Safety With the formation of 10 hinges at
the displacement of about 73.66 mm and the building remained in
this Life safety Per-formance Level for the entire Drift. It was
observed
that the number of element hinges in the life safety Performance
Level started with the formation of two Hinges with the
Displacement of 106.18 mm and re-mained in the life safety
Performance Level for the entire drift with 400 element hinges in
it having the Displacement and Base shear as 77.622 mm and 796.22
kN respectively.
pushover table for symmetrical structure without steel
bracings
It has been clearly observed from the Table 6.2 that the for the
symmetric Structure with Steel bracings it started with the
Immediate Occupancy stage (i.e. B to IO) with the formation of 20
element hinges in this Performance Level.The structure remains in
this Immediate Occupancy performance level till the displacement
reached 26.377 mm with the Base shear of 707.054 kN at this stage
it was ob-served that there were around 280 element hinges in this
Performance Level and further increase in the displacement makes
the structure enters other Performance Levels. the structure enter
the per-formance level of Life Safety With the formation of 108
hinges at the displacement of about 80.512 mm and the building
remained in this Life safety Performance Level for the entire
Drift. It was ob-served that the number of element hinges in the
life safety Performance Level started with the formation of 2
Hinges with the Displacement of 111.372 mm and remained in the life
safety Performance Level for the entire drift with 40 element
hinges in it hav-ing the Displacement and Base shear as 53.316 mm
and 2496.04 kN respectively.
Pushover Curve table for the symmetric structure with steel
bracings
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International Journal of Research and Innovation (IJRI)
Observations under Capacity spectrum curve
The Fig. 5.18 and Fig. 5.20 shows the capacity spectrum curve
for a drift, obtained the intersection of pushover curve with
response spectrum curve. Firstly both these curves are converted in
terms of spectral acceleration and spectral displacement i.e. in
the ADRS format, and then they are superim-posed to give the
performance point of the structure. The green colour curve seen in
the Fig. 5.18 and Fig. 5.20 is the pushover curve for the symmetric
Structure without steel bracings and the symmetric Structure with
steel bracings respectively and the curve in yellow color is the
response spectrum curve in terms of spectral acceleration and
spectral dis-placement. At the performance point for the symmetric
Struc-ture without steel bracings the base shear is 796.22 KN at a
displacement of 77.622 mm, we can observe that the hinges are still
in the state of Immediate Occupancy Performance level. Hence, the
struc-ture is still safe at this performance point for design based
earthquake for the Zone V. Table 6.3 shows the demand, capacity
details in terms of single de-mand spectrum ADRS (variable Damping)
and ca-pacity spectrum at various steps during the pusho-ver
analysis for Drift. The effective time period at the performance
point is 0.978 sec and the effective Damping was 0.185 which can be
seen between the steps 2nd and 3rd (refer Fig. 5.18 and Table
6.3).
Capacity Spectrum Curve table for the symmetric Structure
without steel bracings
At the performance point for the symmetric Struc-ture with steel
bracings the base shear is 1560.99 kN at a displacement of
70.237mm, which was ob-tained between steps 1st and 2nd (refer
Table 6.4), we can observe that the hinges are still in the state
of Immediate Occupancy Performance level. Hence, the structure is
still safe at this performance point for design based earthquake
for the Zone V. Table 6.4 shows the demand, capacity details in
terms of single demand spectrum ADRS (variable Damping) and
capacity spectrum at various steps during the pushover analysis for
Drift. The effective time period at the performance point is 0.639
and the effective Damping was0.077. which can be seen between the
steps 2nd and 3rd (refer Fig. 5.20 and Table 6.4).
DISCUSSION ON RESULTS OF PUSHOVER ANAL-YSIS . FOR THE UN
SYMMETRIC STRUCTURE WITHOUT STEEL BRACINGS AND THE UN SYM-METRIC
STRUCTURE WITH STEEL BRACINGS
Observations under Pushover curve
The Modelled un symmetrical Structures has been given a initial
Drift . The Pushover curve for the un symmetrical Structures was
graphically generated for both the Building i.e. un symmetrical
Structure without steel bracings and Structure With steel bracings
as shown in the Fig. 5.15 and Fig5.17 respectively. It has been
observe from the Fig5.15 and Fig. 5.17 that the base shear was
monolithi-cally increasing with the Displacement. And for the
.Drift the Maximum Base Shear was observed to be 1561.499 kN
and2496.045 kN respectively.Table 6.5 and Table 6.6 show the step
by step de-tails for the change in base shear, and the number of
elements falling in different performance levels like immediate
occupancy, life safety and collapse prevention as the roof
Displacement changes. When the un symmetrical Structure without
steel bracings was given a Drift the further Deformation
Performance of the Building was graphically repre-sented in the
Fig. 5.15. It has been clearly observed from the Table 6.5 that
from the Step 7th the build-ing enter in the Collapse Prevention
Performance Level (i.e. from LS to CP) with the formation of 114
element hinges in it with the Base shear and Dis-placement as
710.770 kN and 19.50mm respec-tively and further increase in the
Displacement at about 44.04mm the building entered in the Resid-ual
Strength zone with the Base Shear as 1288.160 kN and there are 31
element hinges in this Resid-ual strength zone. It has been
observed that the Base shear has increased down from 1288.16kN to
1515.75KN in the Total Failure Zone and the no of element hinges in
this zone are 13 with Displace-ment of about 99.34mm this was
observed. The Building was Totally Elapsed at the Displacement of
about 99.34mm so there is no need for assessing the . Drift of the
building.
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International Journal of Research and Innovation (IJRI)
Pushover curve table for un symmetrical structure without steel
bracings
When the un symmetrical Structure with steel bracings was given
a Drift the further Deformation Performance of the Building was
graphically repre-sented in the Fig. 5.17. It has been clearly
observed from the Table 6.6 that the building enter in the Collapse
Prevention Performance Level (i.e. from LS to CP) with the
formation of 31 element hinges in it with the Base shear and
Displacement as 1288.162 kN and 44.04mm respectively and further
increase in the Displacement at about 71.77mm the build-ing entered
in the Residual Strength zone with the Base Shear as 1542.697 kN
and there are 27 ele-ment hinges in this Residual strength zone .At
.the building has entered the Total Failure Zone with Base shear,
Displacement and number of element hinges as 16207.036kN, 99.34mm
and 4 respec-tively. It has been observed that the Base shear has
increased from 1561.499kN to 2496.045kN .and no of element hinges
in this zone are with Displace-ment of about 77.919mm. The Building
was Total-ly Elapsed at the Displacement is decreased from 77.919
to 53.316.
Pushover Curve table for the un symmetrical Struc-ture with
steel bracings
Observations under Capacity spectrum curve
The Fig. 5.19 and Fig. 5.21 shows the capacity spec-trum curve,
obtained the intersection of pushover curve with response spectrum
curve.At the performance point for the un symmetric Structure
without steel bracings the base shear is 1245.475 kN at a
displacement of 26 mm, which was obtained between steps 1st and 2nd
(refer Ta-ble 6.7), we can observe that the hinges are still in the
state of Immediate Occupancy Performance level. Hence, the
structure is still safe at this per-formance point for design based
earthquake for the Zone V Table 6.7 shows the demand, capacity
details in terms of single demand spectrum ADRS (variable Damping)
and capacity spectrum at vari-ous steps during the pushover
analysis. The effec-
tive time period at the performance point is 1.030sec and the
effective Damping was 0.201 which can be seen between the steps 1st
and 2nd (refer Fig 5.19 and Table 6.7).
Capacity Spectrum Curve table for the un symmet-ric Structure
without steel bracings.
At the performance point for the un symmetric Struc-ture with
steel bracings the base shear is 2496.045 kN at a displacement of
53.316 mm, which was ob-tained between steps 1st and 2nd (refer
Table 6.8), we can observe that the hinges are still in the state
of Immediate Occupancy Performance level. Hence, the structure is
still safe at this performance point for design based earthquake
for the Zone V. Table 6.8 shows the demand, capacity details in
terms of single demand spectrum ADRS (variable Damping) and
capacity spectrum at various steps during the pushover analysis.
The effective time period at the performance point is 0.599 and the
effective Damp-ing was 0.077 which can be seen between the steps
2th and 3th (refer Fig. 5.21 Table 6.8).
Capacity Spectrum Curve table for the un symmet-ric Structure
with steel bracings
HINGE PATTERNS FOR SYMMETRIC STRUCTURE WITHOUT STEEL BRACINGS
AND UN SYMMETRIC STRUCTURE WITH STEEL BRACINGS
Fig. 6.1 to 6.4represent the sequence of formation of hinges
from the initial stage i.e. from the elastic stage to the total
collapse stage for the symmetric Structure without Steel bracings
and the symmetric Structure with steel bracings respectively. These
are color coded and are represented by respective color at
different pushover steps. These hinges are essen-tial to closely
study the behavior of the structure.
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International Journal of Research and Innovation (IJRI)
hing pattern for symmetrical without steel bracings
hing pattern for symmetrical with steel bracings
hing pattern for un symmetrical without steel brac-ings
hingpattern for un symmetrical with steel bracings
Performance of different structures under the zones V
The Capacity Spectrum Curves for The symmetric Structure without
Steel bracings under maximum Earthquake Zones V. The performance
point of the building in terms of Base shear, Roof Displacement,
Spectral Acceleration, Spectral Displacement, ef-fective Time
Period, and Effective Damping of the structure.The symmetric
Structure without Steel bracings and The Structure With Steel
bracings were first analysis by the Non Linear Static analysis and
were Designed accordingly to the Indian IS 456-2000. Pushover
Analysis on these building was performed accordingly under the
different Zones. The Perfor-mance point of the Structures was
tabulated in the Table 6.9 and Table 6.10 accordingly to the change
in the Earthquake Zones
SummaryThis chapter copes with the numerical study and
presentation of results of pushover analysis method for the current
buildings under study and the re-sults are tabulated and are
represented in the form of graphs. The results were studied and
based on the study, the conclusions were drawn. The con-clusions
for the present study are given in the next chapter.
CONCLUSIONS
After having perform the pushover analysis on two different
buildings with and without steel bracings following conclusions are
drawn
In symmetrical building based an the per-formance point obtained
from pushover curve (fig no page no )and the same building with
steel bracings (fig no page no) the value of base share is found
in-creased by % and the amplitude and displacement found by reduced
% In un symmetrical building based on the performance point
obtained from pushover curve (fig no page no )and the same building
with steel bracings (fig no page no) the value of base share is
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International Journal of Research and Innovation (IJRI)
found increased by % and the amplitude and dis-placement found
by reduced %
Based on the above study it is felt that introduc-tion of steel
bracings is one proven method of struc-tural retro fitting
SCOPE FOR FURTHER STUDY
In the present study, the pushover analysis has been carried out
for the G+4 storey buildings. This study can further be extended
for tall buildings.
In the present study, the conceptual design i.e., the sizes of
beams and columns are kept common. Work can be done to optimize the
sizes of various frame elements using pushover analysis.
Further studies can be done to compare the accu-racy of
non-linear pushover analysis and non-linear time history analysis
taking the displacement as a common parameter.
Laboratory tests on the structures should be car-ried out to
backup the numerical results so that these results can be more
informative and valuable.
More studies are required to carried out before generalized
conclusions can be drawn
A retrofitting of frames with weak storey and un symmetrical
elevations are also needed to be stud-ied.
SUMMARY
This chapter, details the discussions drawn based on the present
work and the scope for the further study and Investigation based on
the present study was discussed.
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AUTHOR
P.SWETHAResearch Scholar, Department of CIVIL Engineering,
Aurora's Scientific Technological & Research Academy,
Hyderabad, India
MRS. K. MYTHILIAssociate Professor, Department of CIVIL
Engineering, Aurora's Scientific Technological & Research
Academy, Hyderabad, India
MR. G.VENKAT RATNAM
Associate Professor, Department of CIVIL Engineering, Aurora's
Scientific Technological & Research Academy, Hyderabad,
India
Abstract