IRJET- Effect of Bracing and Unbracing in Steel Stuctures by using ETabs

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 06 Issue: 05 | May 2019 www.irjet.net p-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 1488
EFFECT OF BRACING AND UNBRACING IN STEEL STUCTURES BY USING
ETABS
Ketan Chaudhary
M.TECH (RADHA GOVIND GROUP OF INSTITUTIONS MEERUT UTTAR PRADESH 25001)
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Abstract - The strengthening and stiffening of the system
are most common dynamic performance improvement
methods used for buildings to resist lateral forces. Bracing
system is one of the effective structural system which plays a
vital role in the structural behavior during earthquake.
In the present study, modeling of the steel frame is done under
the analysis mentioned above using E-TABS software is and
the results so obtained for different bracing systems(X-
bracing, Diagonal bracing) are compared. Conclusions are
drawn based on the tables and graphs obtained. It’s found out
that steel frame with X-bracing is most suitable configuration
as it shows Maximum stiffness and lower drift in compare to
frame with diagonal or V-bracing.
Key Words: Bracing System, displacement, drifts, shear
force, Bending moments, E TABS 2015. etc.
1. INTRODUCTION
In the beginning, people needed shelter to protect
themselves from sun, rain and wind. They used to construct
single dwelling houses with one or two storey’s using mud
blocks, timbers, stones etc... Gradually, the desire for better
shelter increased which lead to the new invention and
development in the field of civil engineering and nowadays
cutting edge trend is towards more tall and slender
buildings. In this way, the impacts of lateral loads on tall
buildings are gaining importanceconsequentialityand every
structural engineer is challenged with the quandaries of
providing satisfactory strength and stability. Thus it is
important to give satisfactorysolidnessandsoundnessinthe
structure with a specific end goal todiscoverimperviousness
to horizontal loads instigated by the wind or seismic powers
in tall structures. One simple solution is adopting steel
braces in the RC frames. The blend of reinforced concrete
frame with steel bracing enhances the behavior and
performance of the structure and results in improvement of
stiffness and strength of the structure.
The outline of tall structures includes a theoretical plan,
surmised investigation, preparatory outline and
streamlining, to securely convey gravity and horizontal
burdens. The plan criteria are quality, serviceability,
strength and human solace. Quakes have turned into a
regular occasion everywhere throughout the world. It is
exceptionally hard to anticipate the force, area, and time of
event of tremor. Structures sufficiently intended for normal
burdens like dead, live, wind and so on may not essentially
protected against quake stacking. It is neither down to earth
nor monetarily reasonable to configuration structures to
stay inside flexible farthest point amid quake.
The outline approach embraced in the Indian Code IS
1893(Part I): 2002 'Criteria for EarthquakeResistantDesign
of Structures' to guarantee that structures have no less than
a base quality to withstand minor seismic tremorhappening
much of the time, without harm oppose direct quakes
without noteworthy auxiliary harm however, some non-
basic harm may happen andpointsthatstructures withstand
significant seismic tremor without fall. Structures need
appropriate tremor safe elements to securely oppose vast
parallel strengths that are forced on them amid incessant
quakes. Common structuresforhousesaregenerallyworked
to securely convey their own particular weights.
1.1 Bracing Systems
Bracing is an effective and economical method of resisting
horizontal forces in a framed structure. Braced frame
systems are utilized both in RC as well as in steel buildings.
Normally, the structure comprises of column and beams
whose basic purpose is to transfer gravity load. When
bracings are fixed to it, the total set of members forms a
vertical cantilever truss like structuretoresistthehorizontal
forces.
Bracing members are utilized in the building as a horizontal
load resisting system to improve the stiffness of the frame
for seismic forces. Braces can be connected withfixed-ended
or pin ended connection. In thecaseofpin endedconnection,
it will be subjected to axial forces and it normally fails under
compressive load by global buckling. Once the buckling
occurs, its strength gets reduced in the succeeding cycles.
But there will not be many changes in maximum tensile
strength in subsequent cycles. The main advantage of using
braces is that they dissipate the energy without damaging
the building and also it can be replacedwithoutanydifficulty
when it gets damaged.
1.2 TYPES OF BRACING
● Horizontal bracing: Bracing in every floor level gives a
load path to transfer the horizontal forces to the planes of
vertical bracing. The floor systems that are provided may
themselves act as braces to provide resistance.

● Vertical bracing: Bracinginvertical planes(betweenlines
of the column) provides load paths for transferring
horizontal forces to ground level and provide a stiff
resistance against overall sway.
This thesis work mainly deals with vertical bracing systems
and therefore emphasis is given more to the vertical bracing
system.
2. LITERATURE REVIEWS
Karthick S (2016) [1]: Explains the analysis of RC building
for seismic analysis using different type of structural
systems. Shear walls and bracing systems are the most
appropriate structural forms in the recent decades. A shear
wall is a wall that is designed to resist shear i.e. the lateral
force that causes bulk damage to the structures during
earthquakes. Bracingisalsoa highlyefficientandeconomical
method of resisting horizontal forces in a frame structures.
P. V. Srivardhan et al (2016) [2]: A typical 20 and 30
storeyed buildings are considered with four distinct plan
shapes such as square, rectangle, plus and a T shape within
an area of 40m x 40m having a span of 4m. Each building is
analysed for Wind and Earthquake loads using the load
combinations provided in IS code book. Three bracingtypes,
a concrete shear wall system, steel X-bracing system and a
combination of both shear wall and X-bracing for lower and
upper half of the structure are used A deflection for
rectangular building is lesser than square building along
shorter base dimension and is higher alonglonger baseside.
Raghavendra et al (2016) [3]: The present study made an
attempt to understand the effect of earthquake on building
frames resting on sloping ground with shear walls and
bracings under severe zone. The computation models of
ordinary moment resistingframewasdevelopedinSAP2000
as 3D space frame to carry the seismic analysisasperIS1893
Part (I) -2002. This study may help to understand the effect of
buildings on sloping ground under seismic forces to suggest the
efficient lateral force resisting configuration based on parametric
study.
2.1 METHODOLOGY
In the present study, G+10 storey buildings are analyzed
with and without braces. The plan consists of 5 bays of 5m
center to center each in both X & Y directions and height of
each storey being 3m. The plan of the building remainssame
for all the floors. The study is carried out for different types
of bracing systems with different configurations using
Response Spectrum method of analysis in ETABS 2015.
Different types of models considered for analysis
1. Building without bracings
2. Building with X-Bracing
3. Building with V-Bracing
4. Building with Inverted V-Bracing
5. Building with Diagonal Bracing
6. Building with K-Bracing
Table -1: Description of the model
Plan dimension 25m x 25m
No of grids 5 along both X & Y direction
Width of each bay 5.0 m
Height of each storey 3.0 m
Material Properties Concrete
● Columns: M-30
● Beams: M-25
● Slabs: M-25
Steel
● Main bars: Fe-500
● Confinementbars:Fe-415
Section Properties Column section
● 0.50m x 0.50m
Beam section
● 0.23m x 0.550m
Slab thickness
● 150 mm
Braces section(Isection)
● ISMB 600
Loads
● Live load: 3kN/m2
● Floor finishes: 1.5kN/m2
Table -2: Load combinations
Load
Combination
Dead Load Live Load Earthquake
Load
TDL + TLL 1.5 1.5 -
TDL + WL 1.5 or 0.9* - 1.5
TDL + TLL +
WL
1.2 1.2 1.2
TDL + EQ 1.5 or 0.9* - 1.5
TDL + TLL +
EQ
1.2 1.2 1.2

Fig. 1: Plan of the building.
Fig. 2: G+10 RC framed building with X-bracings for
different configurations.
RESULTS AND DISCUSSION
The displacement of the structure is reduced after
application of braces compared to the bare frame. The
maximum reduction in storey displacementisobservedinX-
braced frame i.e. 85.40% for Configuration 3 and minimum
reduction is for K-braces i.e. 47.28 for Configuration 2.
Fig. 3: Lateral displacements (mm) forG+10storeybuilding.
Fig. 4: Base shear (kN) of bracing system for different
Configurations.
The Base shear for the bare frame is 4992.441kN in X and Y-
direction respectively. It is found that base shear increases
after application of bracings. The increase in base shear is
more for X-braces compared to other bracing systems, as
base shear mainly depends on the weight of the structure.
The time period for a bare frame is 1.745sec. The maximum
reduction is 60.92% in X braces for configuration 3. After
incorporation of braces, there is a reduction of the time
period of the structure. This reduction is due to the fact that
there is an increase in stiffness of the structure after
application of braces. Therefore, bracesinfluencetheoverall
performance the structure.
Fig. 5: Time Period (Sec) values for different bracing system

Figure 6 : Comparison of storey drift in different heights.
Figure 7: Story Drift of unbraced, X braced, V braced and
eccentric braced structures.
3. CONCLUSIONS
● After introducing bracing to bare frame lateral
displacement is found to reduce.
● Maximum reduction in lateral displacement is observedin
inverted V braced frame and X braced frames.
● Inverted V-braces and X-braces shows better resistance to
storey displacement. Hence, it can be recommended.
● Increase in base shear is observed after application of
bracing. The minimum increaseinthe baseshearisobserved
in the frame with X-bracing for all the configurations.
● The time period of the structure decreases with
incorporation of braces as the stiffnessofthebuildingwill be
increased.
REFERENCES :
1. Pravin S. Kamble et.al, Lateral load analysis of a building
with & without knee bracing, journal of Engineering
Research and Application, ISSN: 2248-9622, Vol. 6, Issue 5,
(Part – 4) May 2016, pp. 13-22.
2. Sachindra Kumar Chadhar, Dr. Abhay Sharma, Analysis of
Seismic Behavior of RC Building Frame with Steel Bracing
System UsingVariousConfigurations,International Research
Journal of Engineering and Technology (IRJET), ISSN: 2395-
0056, Vol. 02, Issue 5, Aug 2015, pp 479- 483.
3. Abhijeet Baikerikar and Kanchan Kanagal, Seismic
Analysis of Reinforced Concrete Frame with Steel Bracing,
International journal of Engineering Research and
Technology (IJERT), ISSN: 2278-0181, Vol. 3, Issue 9, Sep
2014, pp 1236- 1239.
4. M. D. Kevadkar and P.B.Kodag, Lateral Load Analysis of
RCC Building, International journal of Modern Engineering
Research (IJMER), ISSN: 2249-6645,Vol.3,Issue3,May-June
2013, pp 1428-1434.
5. Hendramawat A Safarizkia, et.all, Evaluation of the Use of
Steel Bracing to Improve Seismic PerformanceofReinforced
Concrete Building, Proc. 2nd International Conference on
Rehabilitation and Maintenance in Civil Engineering,
ELSEVIER, 2013, pp 2899-2905.
6. A.Massumi and M. Absalan, Interaction between Bracing
System and Moment Resisting Frame in Braced RC Frames,
Archives of Civil and Mechanical Engineering,ELSEVIER,Jan
2013, pp 260-268.
7. A. Kadid and D. Yahiaoui, SeismicAssessmentofBraced RC
Frame, Proc. 12th Asia-Pacific Conference on Structural
Engineering and Construction, ELSEVIER, 2011, pp 2899-
2905.
8. Cengizhan Durucan and Murat Dicleli, Analytical Study on
Seismic Retrofitting of Reinforced Concrete Buildings Using
Steel Braces with Shear Link,
EngineeringStructures,ELSEVIER,May2010,pp2995-3010.
9. M. A. Youssef, et.al, Seismic Performance of RC Frames
with Concentric Internal Steel Bracing, Engineering
Structures, ELSEVIER, 2007, pp 1561-1568.

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