Seismic performance evaluation of rc building connected with and without x braced friction dampers

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 04 Issue: 09 | September-2015, Available @ http://www.ijret.org 45
SEISMIC PERFORMANCE EVALUATION OF RC BUILDING
CONNECTED WITH AND WITHOUT X-BRACED FRICTION
DAMPERS
H Eramma1,
Pulakeshi H L2
1
Associate Professor , University BDT College of Engineering, Davangere 577004KARNATAKA INDIA
h.eramma@gmail.com
2
PG Student CADS, University BDT College of Engineering, Davangere 577004KARNATAKA INDIA
puli.civil@gmail.com.
Abstract
The dissertation work is concerned with the comparison of the seismic evaluation of RC buildings connected with and without friction
dampers, the method carried out in terms of equivalent static, response spectrum and pushover analysis according to IS
1893:2002(part1) code.G+5, G+10 and G+15 storey buildings respectively are considered for the analysis. In this analysis for friction
damper buildings, the dampers are connected at corners of all the buildings. The comparison of equivalent static method and response
spectrum method by using finite element software package ETABS version 9.7.4 is used to perform the modeling and analysis of G+5,
G+10 and G+15 storey buildings by considering the seismic zone IV as per IS 1893:2002(part 1) code. For analysis various IS codes
have been referred. For Gravity load combination IS 456:2000 and for 0.9, 1.2 and 1.5 seismic load combinations as per IS 1893:2002
(part 1) code is referred. In this study building model analysis carried out namely gravity, equivalent static and response spectrum in
longitudinal direction & transverse direction discussed and comparisons of codal values of the software analysis values. Results of these
analyses are discussed in terms of the time period, storey displacement, storey drift and base shear. From these results it is concluded
that time period, storey displacement and storey drift will be more in regular buildings compare with the friction damper buildings,
whereas the base shear will be less in regular buildings compare with the friction damper buildings.
Keywords – Friction dampers; Fundamental natural time period, Base shear, Lateral displacement and Storey drift.
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1. INTRODUCTION
In recent years, an effort is being made to develop and
improve the structural control devices to reduce seismic
impact in buildings and bridges. Full scale implement of
active control systems is difficult as it is expensive and less
reliable. Passive supplemental damping systems such as
base isolation viscoelastic dampers and tuned mass dampers
are widely used in structures to reduce the dynamic
response. Semi-active damping systems i.e. variable-orifice
fluid dampers, controllable friction devices, variable-
stiffness devices, smart tuned mass dampers and tuned
liquid dampers, are more effective in mitigating dynamic
response than active and passive damping system. During an
earthquake, seismic energy is input into the structure which
results in increased vibrational response. Mechanical
devices e.g. dampers are provided throughout the height of
structure to increase the damping hence reduce the response
either by absorbing or dissipating energy. Friction dampers
dissipate specifically kinetic energy through sliding of plate
/surfaces. It can be equivalent to 30% critical damping ratio.
Structural damage is categorized as local and global. Global
damage detection techniques are based on variation in
dynamics of structures such as stiffness, mass, damping and
vibration modes. Structural damage results in a reduction in
structure stiffness and in the modal parameters of building
structures. Approximately 5% change in natural frequency is
considered essential for damage detection. To improve
seismic response friction dampers is provided as X-brace.
Energy dissipation capacity depends upon its damping
coefficient & non-linearity is defined by the damping
exponent. Results show that using friction dampers to
building can effectively reduce the building responses by
selecting optimum damping coefficient i.e. when the
building is connected to the friction dampers, can control
both displacements and accelerations of the building.
Further damper at appropriate locations can significantly
reduce the earthquake response. The reduction in responses
when MDOF building connected with 50%, 40%, 30% of
the dampers at appropriate locations is almost as much as
when they are connected at all floors.
2. METHODOLOGIES FOR SEISMIC
EVALUATION
This research involves the various analysis techniques to
determine the lateral forces ranging from purely linear to
non-linear inelastic analysis. In India the Standardized
method of analysis is followed by using a code – IS1893
(Part 1):2002 – “Criteria for Earthquake resistant design of
structures”. The seismic performance of building connected
with and without friction dampers is carried out by Gravity
analysis, Equivalent static analysis, Response spectrum
analysis and Push-over analysis respectively.

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Table: 1 Load combinations as per IS: 1893-2002 and IS: 875(Part3)-1987
Load Combination Load Factors
Gravity analysis 1.5 (DL+LL)
Equivalent static analysis
1.2 (DL+ LL  EQX)
1.2 (DL+ LL  EQY)
1.5(DLEQX)
1.5 (DL EQY)
0.9(DLEQX)
0.9 (DL EQY)
Response spectrum analysis
1.2 (DL+ LL  RSX)
1.2 (DL+ LL  RSY)
1.5(DLRSX)
1.5 (DL RSY)
0.9(DLRSX)
0.9 (DL RSY)
3. ILLUSTRATIVE MODAL FRAME
The below table 1 shows the details of building considered
for this dissertation work. Link properties of friction
dampers are self-mass (0.225 KN sec/m2
), effective stiffness
(0.2 to 1.2 times the initial stiffness of frame structures) and
damping co-efficient. Initial stiffness of modeled frame
structures is determined from non-linear static analysis
(Pushover Curve) and damping co-efficient is
determined from Eq.(i). Damping co-efficient is a function
of structure mass, stiffness and damping ratio. In this
dissertation work the damping ratio is taken as 5% of critical
value and mass of frame structure is computed by using total
gravity dead loads.
Damp coeff. = ξ x 2 𝑆𝑡𝑖𝑓𝑓𝑛𝑒𝑠𝑠 𝐾𝑖 ∗ 𝑀𝑎𝑠𝑠 ………… (i)
Table 2: Detail data of building studied
Sl. No. DESIGN DATA FOR ALL THE BUILDINGS
1 Details of building
i) Structure OMRF
ii) Number of storey G+5, G+10 & G+15
iii) Type of building Irregular and Unsymmetrical in plan
iv)
Storey height
Ground storey 4.00 m
v) Upper storey 3.50 m
vi) Type of building use Commercial
vii) Seismic zone IV
2 Material Properties
i) Grade of concrete M25 & M30
ii) Grade of Steel Fe 415
iii) Density of reinforced concrete 25 kN/m3
iv) Density of Steel 78.50 kN/m3
v) Young’s modulus of M25 concrete, Ec 25000000.00 kN/m2
vi) Young’s modulus of M30 concrete, Ec 27386127.87 kN/m2
vii) Young’s modulus steel, Es 200000000 kN/m2
viii) Poisson's ratio for Concrete 0.175
ix) Poisson's ratio for Steel 0.300
3 Member properties
a Slab
i) Grade M25
ii) Thickness 0.150 m
b Beam
i) Grade M25
ii) Size ( for all storey ) 0.23 X 0.45 m
c Column
i) Grade M30
ii) Size ( for G+05 storey ) 0.30 X 0.30 m
iii) Size ( for G+10 storey ) 0.45 X 0.45 m

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iv) Size ( for G+15 storey ) 0.60 X 0.60 m
4 Type of Loads & their intensities
i) Floor finish 1.75 kN/m2
ii) Roof finish (DPC) 2 kN/m2
iii) Live load on floors 3.5 kN/m2
iv) Live load on roof 1.75 kN/m2
5 Seismic properties
i) Zone factor ( Z ) 0.24
ii) Importance factor ( I ) 1
iii) Response reduction factor ( R ) 5
iv) Soil type II
v) Damping ratio 0.005
6 Link ( Friction damper ) properties
i) Mass ( for all storey ) 0.225 kN
ii) Weight ( for all storey ) 2.25 kN
iii) Rotational Ineria (for 1,2 & 3) 0
iv) Effective stiffness, Ke
a
For G+05
storey
along X direction 109198.28 kN/m
along Y direction 102476.73 kN/m
b
For G+10
storey
c
For G+15
storey
v) Effective damping, Ke
a
For G+05
storey
along X direction 3570.50 kN-s/m
along Y direction 3458.87 kN-s/m
b
For G+10
storey
c
For G+15
storey
4. RESULTS AND DISCUSSIONS
The results obtained in terms of natural time period, base
shear, lateral displacement and storey drift for different
building models considered for different types of analysis
carried out namely gravity load analysis, equivalent static
analysis, and response spectrum analysis are presented. An
effort has made to study the behavior of irregular RC bare
frame buildings in comparison with RC buildings having
friction dampers.
A. Natural Time Period
The fundamental natural periods obtained for the seismic
designed building models is plotted in fig. 1. From the plot it
is very clear that, stiffness of the building is directly
proportional to its natural frequency and hence inversely
proportional to the natural period. That is, if the stiffness of
building is increased the natural period goes on decreasing.
And as the natural frequency of the taller buildings is low
due to the less stiffness, the natural period goes on
increasing for sixteen storeyed buildings.
The comparison of natural period presented in the table or
plot shows that, the code IS 1893 (part-I) 2002 uses
empirical formula to calculate natural period which is
directly depends on the height of the building. Whereas the
analytical procedure calculates the natural period on the
basis of mass and stiffness of the building (Eigen value and
Eigen vectors).With this code doesn’t consider the irregular
effects on the natural period of vibration of the building.
Fig. 1: Natural time period (seconds) profile for all Storey
buildings for codal and analytical load combination as per IS
1893 (Part 1) -2000.

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B. Base Shear
Table 2: Base shear and scaling factors for all models for
1.2(DL+LL+EQL) combination
Model-I: Without Friction Dampers Building and
Model-II: With Friction Dampers Building
The base shear is a function of mass, stiffness, height, and
the natural period of the building structure. But the
Equivalent static method considers only the mass and
natural period of the building. Moreover the basic
assumption in the equivalent static method is that only first
mode of vibration of building governs the dynamics.In
dynamic response spectrum, all the modes of the building
are considered, and first mode governs in the shorter
buildings and as the storey increases for tall buildings, the
flexibility increases and higher modes come into picture.
Hence base shears obtained from the equivalent static
method are larger than the dynamic response spectrum
method. From above tables 2 shows the results for gravity
and seismic analysis of 1.2(DL+LL+EQL) combination for
G+5, G+10 and G+15 storey for model I and II for static
base shear is more for same models response base shear is
less compared to static base shear.
C. Lateral displacement
Table 3: Lateral displacements (mm) of G+5 storey building in longitudinal direction for seismic combination 1.2(DL+LL+EQX)
and 1.2(DL+LL+RSX).
Storey
Equivalent static method
Reduction of
displacement
in %
Response spectrum method
Reduction of
displacement
in %
Displacement (mm) Displacement (mm)
Model I Model II Model I Model II
6 86.70 13.10 84.89 82.40 10.00 87.86
5 80.40 10.40 87.06 77.50 8.00 89.68
4 68.80 7.70 88.81 68.30 5.90 91.36
3 53.30 5.10 90.43 55.00 3.80 93.09
2 35.40 2.70 92.37 38.30 2.00 94.78
1 16.70 1.00 94.01 18.80 0.70 96.28
0 0.00 0.00 0.00 0.00 0.00 0.00
Fig. 2: Lateral displacements (mm) profile for G+5 storey in longitudinal direction by seismic 1.2 EQX and RSX.

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From the tables and figs. it is observed that lateral
displacement for model I and II when compared model I has
displaced more than model II and they vary have a roof
displacement for equivalent static and response spectrum
method in longitudinal direction for 1.2 combination i.e.
model II got 87.86% reduction in G+5 model, 82.49%
reduction in G+10 model and 81.26% in G+10 model as
compare to model I.
D. Storey Drift
According to IS 1893(Part 1):2002 clause 7.11.1 Storey
drifts limitations are explained that the Storey drifts in any
storey due to the minimum specified design lateral force,
with partial load factor of 1.0 shall not exceed 0.004 times
the storey height. For 4.00 m storey height the storey drift
has got 16.00 mm and for 3.5 m storey height has got 14.00
mm.
Table 4: Storey drifts (mm) of G+5 storey building in longitudinal direction for seismic combination 1.2(DL+LL+EQX) and
1.2(DL+LL+RSX).
Storey
Equivalent static method Reduction of
Storey drift
in %
Response spectrum method Reduction of
Storey drift
in %
Storey drift (mm) Storey drift (mm)
Model I Model II Model I Model II
6 1.81 1.01 44.20 1.80 0.98 45.56
5 3.30 1.03 68.79 3.18 1.01 68.24
4 4.44 0.99 77.70 4.22 0.98 76.78
3 5.11 0.87 82.97 4.98 0.87 82.53
2 5.34 0.65 87.83 5.60 0.65 88.39
1 4.17 0.29 93.05 4.71 0.28 94.06
0 0.00 0.00 0.00 0.00 0.00 0.00

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Fig.5: Storey drifts (mm) profile for G+5 storey in longitudinal direction by seismic 1.2 EQX and RSX.
Fig.6:Storey drifts (mm) profile for G+10 storey in longitudinal direction by seismic 1.2 EQX and RSX.
Fig. 7: Storey drifts (mm) profile for G+15 storey in longitudinal direction by seismic 1.2 EQX and RSX.

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From the table and fig. it is observed that storey drift for
model I and II when compared model I has drift more than
model II and they vary have a roof displacement for
equivalent static and response spectrum method in
longitudinal direction for 1.2 combination i.e. model II got
maximum drift 94.02% reduction in G+5 model, 91.38%
reduction in G+10 model and 89.69% in G+10 model as
compare to model I.
5. CONCLUSION
In the present study G+5, G+10 and G+15 Storey frames are
studied with X-braced friction dampers. Based on this study
following conclusions can be drawn.
 Considering all type of combinations the best
combination for which performance point has to be taken
for the analysis so, 1.2 combination is the best
combination.
 The analytical natural periods do not agree with the
natural periods obtained from the empirical expressions
of the code for irregular buildings, therefore to design
such buildings dynamic analysis should be carried out.
 The fundamental natural period of the structure (Model
II) decrease due to the presence of friction damper in the
buildings.
 Base shear increases with the increase of mass and
stiffness of friction dampers in buildings and it decreases
for the buildings without friction dampers.
 Compared to the building connected with friction
dampers the storey displacement is increases with
increase in stiffness of the buildings.
 The top storey lateral displacement of Model II get
reduced about 88% for G+5 model, 82% for G+10
Model and 81% for G+15 Model respectively when
compare to Model I.
 The storey drift will decrease as the flexibility decreases
in building, due to dampers connected to the buildings.
 The storey drift of Model II get reduced about 94% for
G+5 model, 91% for G+10 Model and 89% for G+15
Model respectively when compare to Model I.
 The friction devices limit the amount of energy that is
input into the structure.
 The amplitude of displacements, natural time periods,
storey drifts and accelerations is considerably reduced.
 The result shows that, the buildings with friction
dampers are more vulnerable compared to
 buildings without friction dampers.
 The building can be tuned for optimum response
without resorting to expensive devices.
REFERENCES
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[3]. Dong-Dong, GE, Hong-Ping ZHU. And Dan-Sheng,
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[11]. Xu, Y.L, He, Q and Ko, J.M (1999). “ Dynamically
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[12]. Yang, Xu, W.L and Lu, X.L(2003). “Experimental
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