CD07-007
DAMPER CONCRETE FOR SEISMIC WAVES
H. Khoshroo1, F.Sinaeian2
Apply Research Office of NAJA
2
Building and Housing Research Centre (BHRC). I.R.Iran
1
ABSTRACT
When an earthquake happens, different kinds of compression and shear waves are
produced. Structures in direction of compression waves P (sense's weight of
structure) have good enforcement and main loss of structures is in sense of shear
(sense of propagation S waves). By reducing amplitude of seismic waves, we can
reduce damages to the building. Nowadays, one of the most important difficulties
in front of engineering structure is finding ways for reducing side movement of
structure and vibrations caused by the device measuring earthquakes in buildings
especially high structures for adding to their factor of safety. Seismic waves are
among mechanic waves and for propagation need material environment and their
reduction has opposite environment's density. So, reducing density of propagation
environment is one of ways for reducing amplitude of waves. On the other side,
liquids do not have a stiffness shear and cannot effect and propagation S waves. So,
in this plan, we have tried using this specifications and installing sphere full of
fluid in the sample environment of ordinary concrete, make new concrete and
evaluate its behavior so that has considerable reduce against shear waves.
For considering the made sample behavior and comparing it with ordinary concrete,
cubic samples with sizes 10x20x20 and 10x20x60cm are made and were put under
impulse loads. Comparing test results, it was observed that amplitude of registered
wave on the concrete sample with fluid compare to sample of ordinary concrete has
reduced on average %50. So, by using this damping concrete, we can reduce the
seismic energy and acceleration effected to the structure and considering amount of
this reduction, the structure weight is also reduced. Reduction of structure weight
caused reduction of secondary seismic force.
Keywords: damper, shear wave, fluid
1. INTRODUCTION
Buildings are always subject to great dynamic loads which are caused by different
environment factors, and the seismic load caused by earthquake is one of them. So,
today one of the most important problems in front of structure engineers is finding
ways for reducing side movement of structure and produced vibrations in buildings
especially high structures for increasing the structure's factor of safety, ease and
tranquility of inhabitants. Nowadays, in some buildings of advanced countries such
as Japan and USA, passive dampers are used and they have different kind so
bracing rod damper and pillar damper. You can see some pictures of the most
1054 / Damper Concrete for Seismic Waves
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useful ones in picture No. 1. Also, other kinds of dampers such as Viscous Damper
(VEDs) and the one which can be adjusted for its weight (TMDs)… exist and by
changing ductility of structure (R), it causes reduction of vibrations in the time unit
or earthquake's rock. Using dampers is the base of reducing the seismic energy
after entrance to structure. So, in this method, all changes are mechanic and do not
have effect on nature of entrance waves. And, the seismic acceleration is exactly
effected to the structure and is subject to dampers which constitute part of
structure, are a mortised.
Although reducing R has effect in ductility, but another effective parameter is the
structure weight which is independent of R. using the present dampers, for every
structure, considering its weight, damping should be calculated separately. But, in
this plan, we tried considering the nature of seismic waves, as much as effective
acceleration on the structure is reduced, we can say definitely that we will have as
much as force reduction for structure that has made a lighter structure design and
this again will lead to reducing final shear force.
B
A
Figure 1. Kinds of mechanical damp ions a) pillar. b) Bracing Rod
Figure 2. The style of production and diffusion of body waves
2. SEISMIC WAVES
When an earthquake happens, different types of body waves are produced which
are mainly mechanic and are propagation only in material environments. These
waves are produced in the center of earthquake and are distributed in all directions.
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They are two main groups: compression waves (P) and shear waves (S). In picture
No. 2, way of production and propagation of these waves is observed. The first
group which is primary, compression and length waves cause compression and
connection of materials which pass through them. Second group is secondary;
shear or width waves cause vibration of environment particles in vertical line on
distributing waves and perform shear waves on the distribution environment.
Velocity of waves is subject to material and hardness of composed materials in the
distributed environment and the steady fluid which does not have stiffness shear
can not effected and distribute shear waves.
3. DAMPER CONCRETE
This concrete considering specifications of the propagation environment of shear
waves and in order to amortize more these waves is made. Since sense of
propagation compression waves is in line with the structure gravity and structures
for effect this force in sense vertical are very rigidity designs, so that compression
waves of the earthquake often are not serious damage. But, shear waves while
happening of earthquake cause the most damages. But, if we can make shear waves
before entrance to damped structure, we can reduce favorably the caused damages
by earthquake. In this case, a lighter structure will have stability against
earthquake. This in return causes reduction of the force to structure. If this cycle
continues, we can achieve the below diagram is obtained. Some sentences of it are
economical from engineering viewpoint. It means that we can do this several times
and this cycle is effective depending on the structure weight.
Fn=aqn-1
Fn: Reduced earthquake force
A: Primary seismic force
Q: Amount of reduced seismic force in percent
N: No. of sentences
In making the sample concrete, sphere full of water have low shear resistance are
available easily and are used as vertically sheets. Picture No. 3 shows a sample of
these spheres. Shear waves of earthquake while passing these spheres because of
their fluid are reduced. Amount of this reduction is subject to specifications and the
amount of fluid inside the concrete and also the way of putting spheres in the
concrete.
4. PERFORMING TESTS
Considering hypotheses and theories presented in the preface, we expect that waves
and especially shear waves by passing this concrete are reduced. In this concrete,
quite equal spheres by passage of time do not exit these spheres so that fluids are
preserved for longer period in the environment. For primary considerations,
effectiveness of the innovative concrete, at first a sample 20 x 20 x 10 cm is made
and necessary considerations are made.
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Figure 3. Arrangement of the beads full of fluid
Since the primary sample was cubic, one side of the cubic is chosen and a
pounding device for impact shown in picture No. 4 is used for making waves.
Figure 4. The pounding is used in experiments.
Since our aim is comparing reduction of wave's amplitude in the made concrete
sample and also waves amplitude in addition to distribution environment is the size
is impact, the pounding device system is so made that it has equal conditions in all
impact. Besides, by repeating the test and taking average, we tried to reduce the
fault of these tests. Also, another parameter which is determining is time's impact.
Impact should be in a way which is equal in time. So, in every test, equal impact
with equal time intervals are used and in processes of data equal time window are
considered. In these considerations on cubic samples, we observed that these
spheres as expected by theory can cause amortization of shear waves and amplitude
of vibrations is reduced. These changes are observed in picture No. 5-A and 5-B.
Since the primary sample was small, a second sample with sizes 60 x 20 x 10 were
made, and results of the test were repeated.
A)
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B)
Figure 5. Vibrations domain A) In sample of typical concrete B) In sample of damping
concrete
During tests, two samples were used so that a suitable comparison is made in
produced waves. I mean one sample of ordinary concrete and a sample of damping
concrete in which fluid sphere existed. Difference of these samples is the spheres.
And from other viewpoints such as: mixing design, amount of cement, type,
grading of gravel and sand est. are considered the same. Before performing tests, it
was necessary to get insured of producing shear waves by the pounding system. So,
the test was done according to the picture No. 6. In this test, two horizontal single
element sensors in two vertical lines were installed. And, from the side, we impact
the samples. We expected that considering direction of the impact, the produced
waves are shear; also the arrived polarity is changed. Results of this test shown in
picture No. 7 confirm this hypothesis
B
A
Figure 6. Using form uni-vector geophone for assessment of Shear wave production
A) Sensors placement B) the way of doing impact
Figure 7. Polarity changing of wave with changing of impact direction is confirmation
of producing shear wave in experiment
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Continuing the tests, as observed in picture No. 8, hits are produced from side and
instead of using geophone, horizontal device of systems measuring acceleration are
very sensitive. 20 impacts are equally impact on the sample. The reason for using
20 impacts is getting average and reducing fault of impact size.
Figure 8. Testing in different environment.
In processing registered data, seismosignal is used and for omitting it, first it
should pass though a filter in frequency limit of 1 to 25 Hertz. Considering
acceleration response spectrum in damping %5, %10, and % 20 evaluation of data
pseudo acceleration are received. Previous amount of them for both samples of
concrete are measuring and reducing amplitude waves is got. And, by getting this
ratio, we can say that the sample of produced concrete how much has role in
reducing the amplitude and as result energy of seismic waves. Table No. 1 shows
this ration in 10 samples tested for ordinary concrete and damping concrete.
Table 1: Obtained acceleration of data in typical and damping concrete and their ratios
Awc (g)
Acc (g)
Test
Awc/Acc
Max acceleration in
Max acceleration in
number
ratio
damping concrete
typical concrete
1
0.9
2.6
0.35
2
1.3
2.4
0.54
3
0.55
2.3
0.24
4
0.55
2.3
0.24
5
1.25
2.8
0.45
6
1.15
2.3
0.50
7
0.95
2.6
0.37
8
1.25
2.4
0.52
9
1.2
1.8
0.67
10
1.05
1.8
0.58
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A)
B)
Figure 9. Acceleration domain, speed and changes of recorded movement resulting
form impacts, respectively A) before and B) after filter
Figure 10 is the response spectrum of amplitude figure of shear wave acceleration in
the ordinary and damper concrete in 1.5 second compared together. In one test,
amount of acceleration in damped concrete is less than ordinary concrete. And, in the
figure of picture No. 11 the reduction ration of acceleration for 10 tests is shown.
Figure 10. The comparison of acceleration response spectrums for section wave in damper
and normal concrete- blue for normal concrete and balk & white for damper concrete
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Figure 11. Shows the proportions ratio of acceleration decrease for 10 tests
As observed in pictures 10 and 11, using this damper concrete, we can seismic
energy can be affected to structure. And, considering this amount of structure
reduction is reduced. Also, reduction of structure weight causes secondary
reduction of seismic force. This concrete reduces the wave acceleration directly
and causes reduction of seismic force and reduces the structure weight indirectly.
Later on, we intend to consider other parameters such as: dimensions, fluid
volume, kind of fluid, arrangement of sphere and entrance of unit energy to the
sample so that we achieve a reduction factor.
5. CONCLUSIONS
Since effect of spheres in small dimensions is considerable, we hope that by
considering more, we can reduce seismic waves and consequently earthquake
danger considerably. And, by reducing human losses, consumption of building
materials, structure weight and seismic force are reduced. This is a useful method
for reducing the seismic waves' intensity before entrance to structures.
ACKNOWLEDGEMENT
At the end, we would like to express our gratitude to Building and Housing
Research Center BHRC presidency for providing the test facilities and engineer
Mirzaei, management of center of controlling strong motion network of (BHRC)
for his kind supports.