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8521 This work is published under Attribution-NonCommercial-ShareAlike 4.0 International License
International Journal of Informative & Futuristic Research ISSN: 2347-1697
Volume 4 Issue 12 August 2017 www.ijifr.com
Abstract
Braced frame structures provide high stiffness and moderate ductility. By employing the braced frame system, the damage is more uniformly distributed over the height. However structures taller than 8-storey are prone to lateral drift amplification due to the higher mode effects. In this study, in order to control the lateral drift, it is proposed to add a set of outrigger trusses at various storey level and to locate the optimum location. Accordingly, in this study G+40 storey steel building is varied with double diagonal bracing and chevron bracing along with varying positioning of outrigger location, in a high risk seismic zone IV and soil type II. Response spectrum analyses conducted in ETABS software are considered in this study to analyze the behavior of the steel frame building with double diagonal bracings and chevron bracings with combination of outriggers at different storey levels in the G+40 storey building.
Dynamic Analysis of Outrigger Braced
Systems in High Rise Steel Building
Paper ID IJIFR/V4/ E12/ 007 Page No. 8521- 8537 Research Area Civil
Engineering
Key Words Bracings, Outrigger, Steel Structure, Tall Building, Earthquake Load,
ETABS
1st Sathyamurthy K.
P G Student,
Department of civil engineering,
Vijaya Vittala Institute of Technology,
Visvesvaraya Technological University ,
Karnataka, India
2nd Kavitha A. S.
Professor,
Department of civil engineering,
Vijaya Vittala Institute of Technology,
Visvesvaraya Technological University ,
Karnataka, India
8522
ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
I. INTRODUCTION
People from rural areas are migrating to cities due to the Industrial Revolution, the
availability of jobs and facilities. Therefore metro cities are very densely populated.
Availability of land has decreased and the price of the land has increased. To solve this
problem the use of multistorey building is needed. However, such provisions only
increase the weight and live load of the structure along with earthquake forces. With an
increase in the amount of stress, strain, deformation and displacement in the structure
there is ultimately increases in the cost of construction due to the increased sectional
elements. Obviously, bare frames are to be more flexible and have great section
requirement to withstand the forces induced. The same can be minimized by making the
structure more rigid, but it appears to be not feasible and also uneconomical. The lateral
stability in the overall frame-work can be improved by using bracing systems. The
bracing members of such braced frame act as truss system to resist lateral forces and are
subjected primarily to axial stress in the elastic range. The efficiency of the braced frame
structure can be further more increased by introducing braced frames with outrigger
system.
To increase the strength and stiffness of steel frames and composite frames the use of
Steel bracing is comparatively effective. It reduces the forces caused by earthquake and
also makes the structure very good in absorbing energy. The structures will safely resist
forces and deformations due to severe ground motions which are good in energy
dissipation.
There are two types of Steel Bracing System such as,
a) Concentric bracing system.
b) Eccentric bracing system
Mentioned below are the bracing schemes for concentrically braced frames,
1. Double diagonal Bracing / X bracing
2. Chevron bracing /Inverted V bracing
3. V-bracing
4. K- bracing
5. Single diagonal bracing
The idea of use of outrigger is nowadays often utilized in tall structures. In this idea,
"outrigger” frames (sometimes, girders) are extended from the core to columns that resist
lateral load at the exterior section of the building. The center or core of the building may
comprise of either shear walls or trusses. It leads to an extremely efficient use of the
structural materials by improving the axial strength and stiffness of exterior columns to
resist part of the overturning moment produced by lateral forces. The bracing system
comprising of core with outriggers is most effective for tall structures in development of
strengths against wind and earthquake loads. In this way, the flexible nature of tall
structures can be reduced and also the structure will have controlled displacement and
inter-storey drift. The incorporation of the outrigger to the concrete core can be
8523
ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
additionally upgraded by optimizing strengths into the outriggers. Based on the
connection to the outer columns, the system is of two types:
a) Conventional outrigger concept
b) Virtual outrigger concept
II. LITERATURE REVIEW
The study of structural performance of tall buildings during the past earthquakes
and wind loading gives the clear picture that these are the causes of irregularities in the
structure due to asymmetric distribution of mass, stiffness and strength, is the main
source of severe damage to the structures. In most of the studies the researches include
the study of use of lateral load resisting systems like bracings, outrigger and combination
of both bracings and outrigger in the building frames. A number of literatures associated
have been studied in detail and the highlights of each are reported below.
Kiran Kamath et al. [1] in this study three-dimensional 40 storey RCC building
with total height of 140m using ETABS. A variation of Hs/H proportion from 0.975 to
0.4 having relative stiffness between 0.25 and 2 was modeled and analyzed for static and
dynamic condition for a six different arrangements of outriggers. The static analysis is
carried out according to the lateral wind load IS-875-Part 3 (1987) and the equivalent
static analysis for seismic according to IS 1893-2002. Displacement is diminished by
37% by giving the outriggers at the top and it is lessened up to 61% by giving the
outriggers at midheight. There is 34% in decreased displacement at the top because of
seismic loads when the outrigger is installed at the top and it is diminished by 64% when
outriggers are set at the midheight (Hs/H). By the introduction of outriggers on each level
the shear force is negligible and also the peak acceleration is reduced upto 30%. Kiran
Kamath et al. [2] in this study three-dimensional structure having 40 stories, each storey
height is of 3.5 m and 140 m is the total height of the building . Results of lateral
displacements, storey drifts, shear forces and bending moments in the core wall are
obtained through ETABS analysis. When the displacement criteria are considered,
31.74% a reduction in the lateral displacement was observed at the top for the structure
with outrigger for a relative height of 1.5 as compared to the structure in the absence of
outrigger. Considering bending moment criteria, the bending moment is reduced by
32.60% when the outrigger structure is compared to a model without a model without
outrigger with a relative height of 6.67. Patil S.S et al. [3] the behavior of the moment
resist V-bracings(complete, partial bay tense and partial level tense and outrigger frame)
5 Bay 12-storey structures are modeled and numerically analyzed, in this study. In the
ninth level V braced completely which claim 7.70% and 7.87% saving in the material
cost respectively has been tried. The net saving in the cost of the structure is 14.31%. In
case of outriggers considering 12th levels and 7th levels braced at a time with the central
bay braced as before it is found that the net saving in the cost of the structure is 13.70%
and 13.23% respectively. It is concluded that Frames with combination of bay wise and
level wise bracing at a time (outrigger) give more economy as compared to bare frame
but give less economy as compared to the separate cases of bay wise and level wise
8524
ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
braced frames. Maximum saving is found to be 14.31% as compared to bare frame.
Dhanaraj M. Patil and Keshav K. Sangle [4] in this study the seismic behaviour of the
outrigger braced system in high rise 2-D steel buildings has been studied with different
locations of the outrigger. Assessment of the structural performance of outrigger braced
high rise 2-D steel buildings of 20, 25, 30 and 35 storeys, with different locations of the
outrigger and Evaluation of seismic performance of different outrigger braced systems
under application of different invariant lateral load patterns in nonlinear static pushover
analysis. A nonlinear static pushover analysis is carried on example outrigger braced high
rise buildings using SAP2000v16 software. Example outrigger high rise buildings are
designed using IS1893 (Part-I):2002, IS875-1987 and IS800:2007. It concludes that
adding outrigger at 0.3H to 0.6H height of building increases stiffness thereby can resist
higher forces during seismic excitation. So optimum locations of the outrigger is 0.3H to
0.6H. Providing multi-outrigger is found to be very effective with one outrigger at the top
and another at the suggested height of buildings. Jagadish J. S and Tejas D. Doshi [5] a G
+15 storey steel frame building is used with different bracing systems such as Single-
Diagonal, X bracing, Double X bracing, K bracing, V bracing is used and analyzed using
STAAD.Pro, in this study. Seismic parameters such as displacement, base shear, axial
force, weight and storey drift of the structure are considered. It explains that According to
displacement criteria, braced frames are good at reducing displacement, and in the case of
K bracings and V bracings, the displacement is higher than without bracings due to
irregularity in the shape of the structure. A S Jagadheeswari and C Freeda Christy [6] In
this study a three-dimensional 40 storey building with 3 bays along x direction and 3 bays
along y direction with the typical storey height is 3.5m and total height of 140m is
considered. The structure consists of central core comprises shear wall with horizontal
girders or cantilever type trusses called outriggers made up of steel bracing, connecting to
the outer columns of building. The size of outrigger is 0.45m x 3.5m. For belt truss and
outrigger bracing ISLB250 structural steel is considered. The shape of outrigger bracing
and belt truss is X-shaped .A total of 9 different arrangements of outriggers by varying
Hs/H ratio has been modeled and analyzed using SAP2000 software. It is concluded that
the 20th and 26th storey (H2/H1=1.3) of the building is considered as the optimum
location of the building because overall the maximum displacement is effectively reduced
in this location. Shivacharan K et al. [7] In this study The Analysis of the tall building is
carried out to find the optimum position of outrigger system and belt truss by using
lateral loads. The three dimensional model is considered and designed for the gravity load
and placing of first and second position of the outrigger. Considering the design of Wind
load is calculated by using IS 875 (Part 3) and Design of Earthquake load is calculated by
using code IS 1893(part-1): 2000 in order to achieve reduction in drift, Deflection and
story shear. The analysis is done by considering tall vertical irregularity of 30th storey of
7 X 7 bay for 1 to 10th storey and 7X6 bay 11th to 20th storey and 7X5 Bay 21st to 30th
storey. It concludes that the by placing outrigger and belt-truss system in tall buildings
increases rigidity and also increases the load bearing capacity and makes the building
8525
ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
efficient from lateral load. The maximum drift at the top of the structure when only core
employed is about 206.9 mm and is reduced by appropriately selecting the outrigger
system by placing them at 0,67 height is 130,4 mm. by placing second outrigger at 0.67h
results in the reduction of 16.64% and 13% for drift and deflection. The optimum
position is the midheight of the building for placing the second outrigger. Krunal Z.
Mistry et al.[8] In this study 40−storey 3D models of outrigger and belt truss systems are analyzed and compared to wind and earthquakes forces to find the lateral displacement
reduction associated with the outrigger and belt truss system. The ETABS software is
used and analyzed for a 150m tall steel concrete building frame, and arrangements of ten
different outriggers are considered. A 40-storey office building of plan area 42m x 42m
with columns spaced 6m from center to center is considered with a height of each storey
being 3m and keeping all floors as typical floors. It concludes that There is maximum
displacement reduction when 1st outrigger is placed at 20th floor i.e. at mid height and
maximum displacement reduction when 2nd outrigger is placed at 10th floor i.e. at 1/4th
height. There is also maximum reduction in drift index when 3rd outrigger is placed at
30th storey i.e. at 3/4th height of the building. P.M.B. Raj Kiran Nanduri et al.[9] In this
study, the use of outrigger and belt truss set at various location subjected to wind or
earthquake force. The position of outrigger and belt truss for decreasing lateral
displacement, moments and building drift can be achieved. The earthquake load was
obtained using IS 1893 (Part-1): 2002 and the wind load was calculated using IS 875
(Part-3). Analysis is carried out using ETABS software.The building models was
analysed for 30 stories with storey a height 3m . The bay-width along 2 horizontal
directions and the number of base are kept constant for all the model.In this study the
building considered here is a 90m tall reinforced concrete structure. A 30 storey office
building with a plan area of 38.5m × 38.5m with columns spaced at 5.5m from center to
center is the model used for analysis. The storey height is 3m and all the floors are
considered as typical Floors. It states that the utilization of outrigger and belt truss
framework in tall structures improves the rigidity and makes the structure safe under
lateral loading. By using second outrigger with cap truss gives the reduction in
displacement of 18.55% and 23.01% with and without belt truss. The ideal area of second
outrigger is midheight of the building. It can be infer that the optimum position of the
outrigger is 0.5 times the building height. Shruti B. Sukhdeve [10] A G+40 reinforced
concrete building was analysed using ETABS software. Building was analysed under
wind and earthquake loads as per the recommendation of IS: 875 (Part 3) 1987 and IS
1893 (Part 1) 2002 respectively. The building was analysed for Delhi city considering its
respective seismic zone basic wind speed. To improve the performance of building in
lateral load outrigger was provided. The analysis was carried out for building with
outrigger in the form of 300mm thick concrete wall provided at each floor from bottom to
top respectively. After running analysis the maximum deflection of building were
calculated and first position of outrigger were fixed at location where maximum
deflection reduction occurs as compare to building without outrigger. Then to find second
8526
ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
position of outrigger first outrigger were fixed at its position and second outrigger were
provided at each floor from bottom to top respectively and maximum deflection reduction
were calculated. Same procedures were followed for third position of outrigger where
first and second outrigger positions were fixed and third outrigger were provided at each
floor from bottom to top respectively. Comparative graphs have been plotted for building
with and without outrigger. It concludes that the maximum deflection at top of structure
reduces up to 272.77mm by providing third outrigger at 1/3rd height of structure i.e.
54.98 % deflection reduction occurs for third position of outrigger. The Axial force goes
on decreasing as infill wall with different openings like corner and centre are provided.
With the application of lateral loads, tall buildings with outriggers shows higher stiffness
making the structure efficient. Outrigger system is not only efficient in controlling the
overall lateral displacement but also very capable of reducing the inter-storey drifts in tall
structures.
III. PROBLEM DEFINITION
The building in this project is a G+40 storey building and has been analyzed and
modelled using ETABS software by applying loads as per IS code requirements i.e.
Gravity loads, Imposed loads, lateral loads as per IS 456, IS 875, IS 1893. Analysis is
carried out for 40 storey bare steel frame structure, steel frame structure with X bracing
and Chevron bracing and also along with outriggers in addition to bracings at various
locations in the building. Static and dynamic linear analysis along with modal analysis is
carried out to obtain natural time period, storey displacement, storey drift, storey shear
and base shear.
The methodology consists of,
1. To carryout extensive literature review, to establish the objective of the study.
2. ETABS Software is used for the modeling and analysis of bare steel frame structure
for 40 storeys and steel frame structure with X bracing and Chevron bracing along
with outriggers.
3. Analyze the models using response spectrum analysis as per IS 1893-2002.
Comparing the parameters such as natural time period, storey displacement, storey
drift, storey shear and base shear.
4. Conclusions are made based on the performance of each structural system under
study.
IV. OBJECTIVES
To carry out the dynamic analysis on bare steel frame structure (equivalent static
analysis and response spectrum analysis).
To carry out the dynamic analysis on steel frames structure with chevron bracings.
To carry out the dynamic analysis on steel frames structure with double diagonal (X)
bracings.
8527
ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
To carry out the dynamic analysis on steel frames structure with chevron bracings
along with outriggers at 13th, 26th and 40th storey level.
To carry out the dynamic analysis on steel frames structure with double diagonal
bracings along with outriggers at 13th, 26th and 40th storey level.
To carry out the dynamic analysis on steel frames structure with chevron bracings
along with outriggers at 10th, 20th and 30th storey level.
To carry out the dynamic analysis on steel frames structure with double diagonal
bracings along with outriggers at 10th, 20th and 30th storey level.
To study the seismic behaviour of all the models based on seismic parameters such as
time period, base shear, storey displacement, storey shear and storey drift.
To compare the results obtained from all the analysis carried out and hence quantify
the effectiveness of outrigger in braced steel structure.
To establish the better type of bracing amongst X and Chevron bracing that can be
adopted along with outriggers.
To observe the effect of variation of outrigger positions in the models and to compare
the results established by various researchers.
To check and establish the effectiveness of outriggers in the absence of a core frame
or core shear wall.
To fix the optimum positioning of outriggers.
V. MODELING AND ANALYSIS
The building in this project is a G+40 storey steel building and has been analyzed and
modelled using ETABS software by applying loads as per IS code requirements i.e.
Gravity loads, Imposed loads, lateral loads as per IS 456, IS 875, IS 1893. Analysis
will be carried out for the following seven models,
1. Bare steel frames structure
2. Steel framed structure with chevron bracings
3. Steel framed structure with X bracings
4. Steel framed structure with chevron bracings and outriggers at 13th, 26th and 40th
storey level.
5. Steel framed structure with X bracings and outriggers at 13th, 26th and 40th
storey level.
6. Steel framed structure with chevron bracings and outriggers at 13th, 26th and 40th
storey level.
7. Steel framed structure with X bracings and outriggers at 13th, 26th and 40th
storey level.
Static and dynamic linear analysis will be carried out to obtain natural time period,
storey displacement, storey drift, storey shear and base shear for all the seven models.
8528
ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
Table 1: Building Modelling and Loading Data
1 Base Units kN-m
2 Type of Structure Steel Moment resisting frame with outrigger
braced
3 Grid Data Plan regular - Rectangle geometric shape
Grid Spacing Two bays of 6m and one 4m central bay
Total Dimension 16m x 16m Base dimension
Storey Height Uniform – 3 meters
No. of Stories 40
4 Material Properties Standard Values input in N-mm
Grade of Structural Steel FE 350
Grade of Concrete Deck M30
Poissons ratio 0.2
5 Frame Section Properties Standard Values input in N-mm
Column Built-up column
Beams ISMB
Wall/Slab Section properties Standard Values input in N-mm
Deck 200 mm
6 Static Loads kN/m2
Self-weight Considered
Super dead load (SDL) 2
Live load (Reducible) 4
Wall load (kN/m) Glazing load considered
7 Seismic Data Values as per IS 1893
Response Reduction
Factor (R)
4
Importance Factor (I) 1
Zone(z) 0.24 (IV)
Soil type II
8 Type of Analysis
Dynamic Analysis Response spectrum
Figure 1: Plan view of model
8529
ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
Model 1: Bare steel frames structure
Figure-2: 3D-view of model
Model 2: Steel framed structure with chevron bracings
Figure-4: Elevation view
Figure-3: Plain view
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ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
Model 3: Steel framed structure with X bracings
Figure-5: Plan view of model Figure-6: Elevation View
Model 4: Steel framed structure with chevron bracings and outriggers at 13th, 26th
and 40th storey level.
Figure-7: Plan view of model Figure-8: Elevation View
8531
ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
Model 5: Steel framed structure with X bracings and outriggers at 13th, 26th and
40th storey level.
Figure-9: Plan view of model Figure-10: Elevation View
Model 6: Steel framed structure with Chevron bracings and outriggers at 10th, 20th
and 30th storey level.
Figure-11: Plan view of model Figure-12: Elevation View
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ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
0
5
10
15
20
25
30
35
40
45
0 50 100 150 200 250 300
ST
OR
EY
NU
MB
ER
DISPLACEMENT (mm)
STOREY DISPLACEMENT
Bare Steel Frame Chevron bracing
X bracings Chevron bracing with outrigger (13-26-40)
X bracing with outrigger (13-26-40) Chevron bracing with outrigger (10-20-30)
Model 6: Steel framed structure with X bracings and outriggers at 10th, 20th and
30th storey level.
Figure-13: Plan view of model Figure-14: Elevation View
VI. RESULTS AND DISCUSSIONS
The results obtained from analysis are observed and graphs are plotted and compared
and discussed for all the seven models. The variation of seismic parameters like natural
period, story displacement, story drift, storey shear and base shear has been studied. By
comparing the results obtained the optimum location of outriggers is determined.
6.1 DISPLACEMENT:
Figure 15 : Variation of displacement
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ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
The graph shows the variation of displacement of dynamic response spectrum
analysis in X direction between bare Steel framed structure, Chevron bracing Steel
framed structure, X bracing Steel framed structure, Chevron bracing with outiggers at
13th, 26th and 40th storey level, X bracing with outiggers at 13th, 26th and 40th storey
level, Chevron bracing with outiggers at 10th, 20th and 30th storey level and X bracing
with outiggers at 10th, 20th and 30th storey level. It can be inferred that X bracing with
outiggers at 10th, 20th and 30th storey level gives the least displacement of 154.54 mm
and bare Steel framed structure gives the maximum displacement 281.68 mm.
6.2 STOREY DRIFT:
Figure 16: Variation of Storey drift
The graph shows the variation of storey drift of dynamic response spectrum analysis
in X direction between bare Steel framed structure, Chevron bracing Steel framed
structure, X bracing Steel framed structure, Chevron bracing with outiggers at 13th, 26th
and 40th storey level, X bracing with outiggers at 13th, 26th and 40th storey level,
Chevron bracing with outiggers at 10th, 20th and 30th storey level and X bracing with
outiggers at 10th, 20th and 30th storey level. It can be inferred that X bracing with
outiggers at 10th, 20th and 30th storey level gives the least storey drift and bare Steel
framed structure gives the maximum storey drift.
0
5
10
15
20
25
30
35
40
45
0 0.001 0.002 0.003 0.004
ST
OR
EY
NU
MB
ER
DRIFT
STOREY DRIFT
Bare Steel FrameChevron bracingX bracingsChevron bracing with outrigger (13-26-40)X bracing with outrigger (13-26-40)
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ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
012345678
Bare Steel
Frame
Chevron
bracing
X bracings Chevron
bracing with
outrigger
(13-26-40)
X bracing
with
outrigger
(13-26-40)
Chevron
bracing with
outrigger
(10-20-30)
X bracing
with
outrigger
(10-20-30)
Tim
e p
er
iod
mode
TIME PERIOD (s) Mode 1 Mode 2 Mode 3
6.3 TIME PERIOD:
Figure 17: Variation of time period
The graph shows the variation of time period in seconds between bare Steel
framed structure, Chevron bracing Steel framed structure, X bracing Steel framed
structure, Chevron bracing with outiggers at 13th, 26th and 40th storey level, X bracing
with outiggers at 13th, 26th and 40th storey level, Chevron bracing with outiggers at
10th, 20th and 30th storey level and X bracing with outiggers at 10th, 20th and 30th
storey level. It is inferred that X bracing with outiggers at 10th, 20th and 30th storey level
gives the least modes of time period and bare Steel framed structure gives the maximum
modes of time period.
5.4 BASE SHEAR :
Figure 18: variation of base shear
11801185119011951200120512101215
Bare Steel
Frame
Chevron
bracing
X bracings Chevron
bracing with
outrigger
(13-26-40)
X bracing
with
outrigger
(13-26-40)
Chevron
bracing with
outrigger
(10-20-30)
X bracing
with
outrigger
(10-20-30)
bA
SE
SH
EA
R
Base shear
RSX RSY
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ISSN: 2347-1697
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Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
The graph shows the variation of base shear between bare Steel framed structure, Chevron
bracing Steel framed structure, X bracing Steel framed structure, Chevron bracing with outiggers
at 13th, 26th and 40th storey level, X bracing with outiggers at 13th, 26th and 40th storey level,
Chevron bracing with outiggers at 10th, 20th and 30th storey level and X bracing with outiggers
at 10th, 20th and 30th storey level. The X bracing with outriggers gives maximum base shear and
the bare steel frame gives the least base shear.
VII. CONCLUSIONS AND SCOPE OF FURUTHER STUDY CONCLUSIONS
Based on the study conducted on various models of G+40 steel framed structure the
following conclusions can be drawn:
The use of chevron bracings reduces top storey displacement upto 25.62% when
compared to bare steel frame structure, whereas the use of X-bracings reduces 24.3%.
The use of chevron bracings increases the base shear by 0.25% and X bracings shows an
increase by 0.85%, when compared with bare steel frame structure.
It is observed that steel frame model with chevron bracings reduces drift upto 37.5%
when compared to bare steel frame structure, whereas the model with X bracings reduces
drift upto 37.8%.
From the above three conclusions it can be inferred that chevron bracings can be more
effective in high rise structures in controlling displacements and drifts without increasing
much of the base shear.
The use of outriggers at three different stories in addition to bracings is found to be very
effective in reducing the storey displacements.
It is found that use of steel frame structure with X bracings along with outrigger at 13th
,
26th
and 40th
storey level have reduced displacement upto 40.99% when compared to bare
steel frame structure, whereas X bracings along with outrigger at 10th
, 20th
and 30th
storey
level have reduced displacement upto 45.33%.
The top storey displacement could be reduced by 5.1% with a combination of X bracing
and outriggers at 10th
, 20th and 30th
storey when compared to outriggers at 13th
, 26th
and
40th
storey level.
It is also found that use of steel frame structure with X bracings along with outrigger at
13th
, 26th
and 40th
storey level have reduced drift upto 49.1% when compared to bare steel
frame structure, whereas X bracings along with outrigger at 10th
, 20th
and 30th
storey level
have reduced drift upto 54%.
The maximum storey drift reduced upto 11.1% in case of X bracing and outriggers at at
10th
,20th
and 30th
storey when compared to outriggers at 13th
, 26th
and 40th
storey level.
The base shear has increased by 1.5% in case of X bracing with outriggers at 10th
,20th
and
30th
storey and also with outriggers at 13th
, 26th
and 40th
storey level.
From the above conclusions it can be inferred that with a combination of X bracings,
outriggers at 10th
, 20th
and 30th
storey performs better than outriggers at 13th
, 26th
and 40th
storey.
8536
ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
It is found that use of steel frame structure with Chevron bracings along with outrigger at
13th
, 26th
and 40th
storey level have reduced displacement upto 38.7% when compared to
bare steel frame structure, whereas Chevron bracings along with outrigger at 10th
, 20th
and 30th
storey level have reduced displacement upto 44.3%.
The top storey displacement could be reduced by 6.4% with a combination of Chevron
bracing and outriggers at 10th
,20th
and 30th
storey when compared to outriggers at 13th
,
26th
and 40th
storey level.
It is also found that use of steel frame structure with Chevron bracings along with
outrigger at 13th
, 26th
and 40th
storey level have reduced drift upto 47.2% when compared
to bare steel frame structure, whereas Chevron bracings along with outrigger at 10th
, 20th
and 30th
storey level have reduced drift upto 52%.
The maximum storey drift reduced upto 8.3% in case of Chevron bracing and outriggers
at 10th
,20th
and 30th
storey when compared to outriggers at 13th
, 26th
and 40th
storey level.
The base shear has increased by 1.5% in case of Chevron bracing with outriggers at
10th
,20th
and 30th
storey and also with outriggers at 13th
, 26th
and 40th
storey level.
From the above conclusions it can be inferred that with a combination of Chevron
bracings, outriggers at 10th
, 20th
and 30th
storey performs better than outriggers at 13th
,
26th
and 40th
storey.
This study concludes that placing three outriggers at 10th
, 20th
and 30th
storey level is not
only proficient in controlling the overall lateral displacement but also very capable of
reducing the inter-storey drifts in tall building and hence for a G+40 steel structure
10th
,20th
and 30th
storey level can be considered as optimum position.
Hence it is also concluded that the use of bracings and outrigger system in high-rise
buildings increase the stiffness and makes the structural form efficient under lateral load.
Scope for further study
1. This study is based on the linear dynamic analysis therefore the results can be compared
with non-linear dynamic analysis of the building.
2. The dynamic analysis is carried out for G+40 storey building and the same dynamic
analysis can be out for G+50 storey and G+60 storey tall buildings.
3. The models may be compared by changing the type of soil and other zones to provide
better information about the response of the system.
4. Composite steel-concrete structure with concrete outrigger can be considered for this
study.
5. The K bracing and V bracings can be used and their effectiveness can be compared with
X bracings and Chevron bracings.
VIII. REFERENCES
[1] A S Jagadheeswari and C Freeda Christy, (2016) “Optimum Position of Multi Outrigger
Belt Truss in Tall Buildings Subjected to Earthquake and Wind Load”. Volume 09, No. 03,
P.P.373-377.
[2] Shruti B. Sukhdeve, (2016) “Optimum Position of Outrigger in G+40 RC Building” IJSTE
- International Journal of Science Technology & Engineering, Volume 2, Issue 10.
8537
ISSN: 2347-1697
International Journal of Informative & Futuristic Research (IJIFR)
Volume - 4, Issue -12, August 2017
Continuous 48th Edition, Page No. : 8521- 8537
Sathyamurthy K., Kavitha A.S. :: Dynamic Analysis of Outrigger Braced Systems in High Rise Steel Building
[3] Krunal Z. Mistry, Proff. Dhruti J. Dhyani, (2015) “Optimum Outrigger Location In
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Engineering and Research Development ,Volume 2, Issue 5.
[4] Shivacharan K, Chandrakala S, Narayana G, Karthik N M, “(2015)Analysis Of Outrigger
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[5] Dhanaraj M. Patil and Keshav K. Sangle, (2015) “Seismic Behaviour of Different Bracing
Systems in High Rise 2-D Steel Buildings”, Structures, 3, PP 282-305.
[6] Kiran Kamath, Avinash A.R., Sandesh Upadhyaya K, (2014) “A Study on the Performance
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[7] Karthik.N.M, N.Jayaramappa, (2014) “optimum position of Outrigger system for High
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[8] Jagadish J. S and Tejas D. Doshi, (2013)” A Study On Bracing Systems On High Rise Steel
Structures” Vol. 2 Issue 7.
[9] Patil S.S., Aland S.S., Kore P.N, (2013)” Seismic Response of Concentrically Barced
Reinforced Concrete Frames” Volume 4, Issue 7.
[10] P.M.B. Raj Kiran Nanduri1, B.Suresh, MD. Ihtesham Hussain, (2013) “Optimum Position
of Outrigger System for High-Rise Reinforced Concrete Buildings Under Wind And
Earthquake Loadings”, American Journal of Engineering Research (AJER) e-ISSN: 2320-
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[11] Kiran Kamath, N. Divya and Asha U. Rao, (2012) “A Study on Static and Dynamic
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[12] Indian Standard Code of Practice for Design Loads (other than earthquake) For Buildings
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Indian Standards, New Delhi, India.
[13] Indian Standard Criteria for Earthquake Resistant Design of Structures, IS: 1893 (Part 1)
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Standards, New Delhi, India.
TO CITE THIS PAPER
Sathyamurthy, K., Kavitha, A.S. (2017) :: “Dynamic Analysis of Outrigger Braced
Systems in High Rise Steel Building” International Journal of Informative & Futuristic
Research (ISSN: 2347-1697), Vol. (4) No. (12), August 2017, pp. 8521-8537, Paper ID:
IJIFR/V4/E12/007. Available online through- http://www.ijifr.com/searchjournal.aspx