International Journal of Advanced Engineering Research and Studies E-ISSN2249–8974
Research Article
STUDY OF RESPONSE OF OPEN GROUND STOREY
BUILDING WITH SEISMIC DAMPER UNDER HARMONIC
EXCITATIONS
Vipul H. Vyas1 and C. S. Sanghvi2
Address for Correspondence
1
Applied Mechanics Department, L. D. College of Engineering, Ahmedabad
2
Asso. Prof. Applied Mechanics Department, L. D. College of Engineering, Ahmedabad
ABSTRACT:
Open first storey is a typical feature in the modern multistorey constructions in urban India. Such features are highly
undesirable in buildings built in seismically active areas; this has been verified from strong shaking during the past
earthquakes. Structural control is basically the modification of the properties of a structure, the modification of the
structures properties include changes in the damping and stiffness of the structures Study of dynamic response of building
is carried out on three storied soft storey building model & three stories soft storey building model with seismic damper.
The experimental set ups which would enable the study of basic issues related to acceleration, velocity, displacement,
damping, natural frequency, mode shape, natural period, etc. Model made up with steel bars and plate. Upon completion of
the model, static stiffness tests and free vibration tests are perform to determine the actual properties of the model such as
stiffness, damping ratio, and natural frequencies of vibration. Comparison of the system properties identified
experimentally with those predicted by the theory or simulated numerically. Shake table is used for excitations and
corresponding response of the physical model is measured in terms of natural frequency, acceleration, phase angle.
KEYWORDS: Dynamic response of building, Experimental Testing, soft storey,Seismic damper
INTRODUCTION
Vibrations in structures which are induced by natural
disasters such as earthquake and hurricanes may lead
to greater dynamic responses of the structures. Study
of the response of structure is very important. Effort
has been made to study the behavior of a soft story
building model without & with seismic damper
subjected to harmonic base motions.
This experiment also enables the understanding of
occurrence of resonance phenomenon in multi-degree
of freedom (MDOF) systems. The frame of model is
rectangular in plan as well as in elevation. Soft storey
model consists of three storeys with shear wall at first
and second storey.
OBJECTIVE OF STUDY
1. To find out stiffness of building model
experimentally.
2. To find out dynamic properties of the model
like damping, natural frequency with free
vibration test.
3. To find out dynamic properties of model like
acceleration, natural frequency, time period,
phase angle, mode shapes, with shake table
testing.
4. Comparison of dynamic responses of model
from shake table test with SAP 2000 software.
GEOMETRIC DEFINATION
The plan & elevation of model and 3D model are
shown in figure 1, 2 & 3. Three storey bare frame
model of building is regular in plan as well as in
elevation and soft storey model with shear wall. The
soft storey model of model is rectangular in plan as
well as in elevation.
Model is made up with steel bars and plates. Material
used to construct model along with its dimensions are
given below.
Materials:
1. 18” x 18” of 2mm mild steel base plate.
2. 18” x 18” of 3 mm mild steel top plate.
3. 6 mm diameter rod (Mild steel).
4. 12”x0.2’’ of 3mm mild steel plate(shear
wall)
IJAERS/Vol. I/ Issue III/April-June, 2012/05-08
Figure 1 Plan view of model
Figure 2 Elevation of model
Figure 3 Bare frame and soft storey building
model
INSTRUMENT USED IN EXPERIMENTS
Instrument used in the experiment is given below
1. Shake table
2. Accelerometer
3. Sixteen
channel
vibration
analyzer
instrument
4. Impact Hammer
5. Laptop
6. Shake table speed controller
7. Stiffness calculation assembly
International Journal of Advanced Engineering Research and Studies E-ISSN2249–8974
EXPERIMENTAL SETUP:
Following test were carried out during experimental
work.
1. Determination of Property of Model.
2. Determination of Stiffness of the model
3. Free Vibration Test.
4. Impact hammer Test.
5. Shake Table Test.
Determination of Property of Model:
The modulus of elasticity of material used in model is
very useful to determine the natural frequency of
structure for manual calculation as well as input for
software. Sample of material used in model is tested
in the universal testing machine and a graph of stress
versus strain graph is plotted to find out the modules
of elasticity
Modules of elastic of model=20500 N/mm2
Stiffness Experiment:
This experiment was designed to measure the interstory stiffness of the three dimensional model which
will be tested on Shake Table.
Equipments:
3D Model, steel platform, fix frame, nut and bolt,
Steel bracket, dial gauge with magnetic base, load
Cell, weights
Procedure:
(1) Construct steel platform. (2) Screw one bracket in
the frame just above each floor level (Figure 4). (3)
Place the 3D model on the steel platform, close
enough to the frame, to clamp each floor to the
bracket. (4) Clamp 3D model to the steel platform
with nut bolt. (5) Attach the dial gauge with magnetic
base. (6) Connect the model with steel wire (7) Place
weight to generate initial tension in steel wire. (8)
Adjust dial gauge to zero position. (9) Gradually
increase the load and measure gauge reading. (10)
Determine K1 (the stiffness between the base and
Floor 1). (11) After determine K1, fixed first floor
with vertical wall with bracket and place gauge at top
floor and repeat step at (6) to (9). (12) Determine K2
(the stiffness between the first floor and second
floor).
Figure 4 Stiffness experiment
Figure 5 Schematics setup
Free vibration test:
This experiment is designed to determine the
damping ratio of the 3D model. The damping ratio is
important input in the SAP 2000 model.
IJAERS/Vol. I/ Issue III/April-June, 2012/05-08
The damping ratio characterizes the rate of decay of
motion of the system. It is not possible to analytically
determine the damping coefficient c or damping
ratio ξ for a structure, there is considerable interest
in evaluation of damping from experiments. The
results of the preceding section provide a basis for
evaluating amount of damping from free vibration
experiments. The natural period of vibration T of the
structure can also be determined from these
experiments.
Equipments:
3D Model, Accelerometer, Sixteen channel vibration
analyzer instrument, Laptop
Procedure:
(1) Fix model on shake table. (2) Place accelerometer
in direction of pull. (3) Attach accelerometer to
instrument. (4) Disturb the structure from its
equilibrium position through some displacement u (0)
and release the structure. (5) Record the free
vibration of the structure to obtain the acceleration
vs. time plot as shown in Fig.13. (6) Measure the
time required to complete one cycle of vibration to
obtain the vibration period T. (7) Measure u&
& i ,
u& &
and i + j , (8) Damping ratio can be determined from
the following equation [Chopra, 2000]:
ξ =
u&& i
1
ln
j * 2π
u&& i +
j
Where j denotes the number of cycles during which
successive peaks üi, üi+1… üi +j are used in the
calculation as shown in Figure.
Also record acceleration vs. frequency in FFT graph
and finally compute natural frequency of model.
Figure 6 Damping ratio determined by
logarithmic decrement
Shake table test:
The vibration properties of a structure are determined
by varying the frequency of the shake table through
appropriate range. The amplitude of the steady state
acceleration of the structure at each forcing frequency
is measured. Frequency-response curves, in the form
of acceleration amplitude vs. forcing frequency, may
be plotted directly from the measured data. The
natural frequency of vibration, acceleration and time
period can be determined from any one of the
frequency-response curves
Equipments:
3-D Model, shake table, accelerometer, sixteen
channel vibration analyzer, laptop.
Procedure:
(1) Securely attach the 3-D model to shake table. (2)
Place accelerometer on 3-D model. (3) Start NVgate
software and run it (4) Arrange the experimental
setup as shown in figure 3. Note that the
accelerometer needs to be placed on slab in such a
way that acceleration along x-direction can be
measured. (5) Connect accelerometer to vibration
analyzer instrument. (6) Run the base motion (7)
Identify the frequencies at which the structure
International Journal of Advanced Engineering Research and Studies E-ISSN2249–8974
undergoes resonance by observing the variation of
response amplitudes with change in frequency of
shake table. (8) At resonance conditions, note the
amplitude of acceleration at slab level. (9) Plot the
response amplitudes along x-axis versus time. (10)
Find out natural frequency, acceleration and natural
period of structure (11) Also find natural frequency
and acceleration in other direction by placing model
in y-axis and repeat step from (1)
RESULTS OF EXPERIMENTS:
FREE VIBRATION TEST RESULTS
BARE FRAME MODEL
Free vibration test:
ξ = (1 / 2 * 3 . 14 * m ) ln Vn Vn + m
(
Figure 9 Time vs. acceleration graph
)
m=Number of cycle required for calculation
Vn=Peak value of graph in m/s^2
Table: 1 Free vibration test results for Bare frame
Figure 10 Natural frequency vs. acceleration
graph
FREE VIBRATION TEST RESULTS
SOFT STOREY MODEL
ξ = (1 / 2 * 3 . 14 * m ) ln Vn Vn + m
(
)
m=Number of cycle required for calculation
Vn=Peak value of graph in m/s^2
SOFT STOREY MODEL WITHOUT SEISMIC DAMPER
fz = frequency.
Ac1 = Acceleration of first floor.
Ac2 = Acceleration of second floor.
Ac3 = Acceleration of third floor.
D1 = Displacement of first floor.
D2 = Displacement of second floor.
D3 = Displacement of third floor.
Table :3 Free vibration test results for soft storey
Figure 7 Time vs. acceleration graph
Figure 11 Time vs. acceleration graph
Figure 8 Natural frequency vs. acceleration graph
IMPACT HAMMER TEST RESULTS
ξ = (1 / 2 * 3 . 14 * m ) ln Vn Vn + m
(
)
m=Number of cycle required for calculation
Vn=Peak value of graph in m/s^2
Table :2 Impact hammer test results for Bare
frame
Figure 12 Natural frequency vs. acceleration
graph
IMPACT HAMMER TEST RESULTS
SOFT STOREY MODEL
ξ = (1 / 2 * 3 . 14 * m ) ln Vn Vn + m
(
m=Number of cycle required for calculation
IJAERS/Vol. I/ Issue III/April-June, 2012/05-08
)
International Journal of Advanced Engineering Research and Studies E-ISSN2249–8974
Vn=Peak value of graph in m/s^2
Table : 4 Impact hammer test results for soft
storey
•
Table:09 (Acceleration at various floor levels)
•
Figure 13 Time vs. acceleration graph
SOFT STOREY MODEL WITH SEISMIC DAMPER
fz = frequency.
Ac1 = Acceleration of first floor.
Ac2 = Acceleration of second floor.
Ac3 = Acceleration of third floor.
D1 = Displacement of first floor.
D2 = Displacement of second floor.
D3 = Displacement of third floor
Table:05 frequency through experiment (soft
storey with system
It can be concluded that the soft storey building
swing back and fort like inverted pendulum
during earthquake shaking and column in the
open ground storey are severely stressed due
excessive deformation. Soft storey model with
seismic damper is reducing the response as
compared to soft storey model. Seismic damper
is very efficient to resist structural vibrations.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
Figure 14 Natural frequency vs. acceleration
graph
Table:06 Acceleration through experiment : f z
= 2.625 Hz
Figure 15 frequency vs. acceleration graph
CONCLUSION
• Result of impact hammer & free vibration test
are very close to each other.
• Relative displacement of Soft storey model with
seismic damper is decreased as compared to Soft
storey model
Table:07( displacement)
First floor
Second floor
Third floor
Soft storey Without
seismic damper
D1(mm)
8.829
10.07
10.79
Soft storey model
With seismic damper
D1(mm)
6.678
7.394
7.826
Table: 08(Drift)
Between First Floor &
Second Floor
Between Second &
third Floor
Soft storey
modelWithout seismic
damper
Drift
Soft storey model
With seismic
damper
Drift
1.24
0.71
0.72
0.432
IJAERS/Vol. I/ Issue III/April-June, 2012/05-08
Chopara A. K. “Dynamic of structure “
Shake table demonstration of dynamic response of Base
isolation of buildings by UCIST.
Demonstration of lateral tensional coupling in building
structure by UCIST.
Small scale shake table experiments of simple three
storey building by UCIST.
Earthquake Engineering Education through Laboratory
Experiment by iis Bangalore.
Annam pravin kiran.”Shake table study with shear link
with brace frame”
Dynamic signal analyzers - Oros vibration and noise
analyzer reference manual
PCB Piezotronics, accelerometer uniaxial, triaxial,
impact hammereference manuals.