Experimental Study on Two Full Scale Iranian Viscous...

3rd

International Conference on Steel & Structure

11-12 December 2018

Olympic Hotel, Tehran, Iran

Experimental Study on Two Full Scale Iranian Viscous Dampers

Seyed Amin Mousavi1, Reza Esfandiyari

2 Seyed Mehdi Zahrai

3

1 PhD, Behsazan Larzeh Davam Co., The Science and Technology Park of University of

Tehran. E-mail: [email protected]

2 Graduate student, Behsazan Larzeh Davam Co., The Science and Technology Park of

University of Tehran

3 PhD, Professor, Behsazan Larzeh Davam Co., The Science and Technology Park of University

of Tehran and School of Civil Engineering, College of Engineering, University of Tehran,

Tehran, Iran

Abstract This study is devoted to investigate behavior of two 200 kN and 250 kN full-scale viscous

dampers with a novel design manufactured by an Iranian company, Behsazan Larzeh Davam.

Details of the damper differ with the currently available commercial viscous dampers such that it

includes a cylinder with extremely smoothed inner face fully filled with a viscous fluid, a piston,

a shaft and a flexible high pressure hose as an external orifice for viscous fluid passing through.

Both dampers have been tested under seismic excitations and harmonic loads with different

frequencies and amplitudes and both of them have shown very stable cyclic behaviors under all

imposed dynamic loads. 8 months after the tests, the 250 kN damper was again tested using

similar protocols to investigate its long-term behavior. Obtained results from the second phase

test indicated no degradation in the behavior of the damper even after 8 months with no

maintenance. Using both simplified link elements and sophisticated Computational Fluid

Dynamics (CFD), behavior of the dampers are numerically evaluated and compared to the

experimental results. Obtained results indicated that even the most advanced technologies in the

field of earthquake resisting design can be successfully manufactured by domestic companies.

Keywords: viscous damper, passive control, energy dissipating device, damper, experimental study,

structural dynamics

Introduction Different passive energy dissipating devices have been experimentally and numerically investigated by

different researchers during the last three decades and it is now well known that all of the above

mentioned dampers are effective in mitigating seismic-induced vibrations. Comprehensive review of

performance of different dampers can be found in Soong and Dargush (1997) and Constantinou et al.

(1998). This paper focuses on viscous dampers which can significantly add viscous damping of the

structures without altering its lateral stiffness. The pure velocity-dependent nature of the viscous damper

is a unique characteristic which cannot be found in other supplemental energy dissipating devices. This

feature makes the viscous damper a versatile option from architectural point of view. For example, there

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is no need to place the damper on all stories and also there is no need to place them symmetric in plan as

viscous dampers virtually have no stiffness and they have no effect on the center of stiffness. Another

advantage of viscous dampers over other energy dissipating devices is the fact that viscous dampers

always reduce all structural responses including story displacements, inter-story drifts, story shears, story

accelerations, etc. However, other dampers, especially displacement-dependent ones, can potentially

increase some of the structural responses such as story shear and story accelerations (Apostolakis and

Dargush, 2010). This is because of the fact that viscous dampers have virtually no stiffness and the

damper force would be out-of-phase with the internal force of the structural elements. Many experimental

and numerical studies have been carried out on structures with viscous dampers (Reinhorn et al. 1995,

Seleemah and Constantinou 1997,Takewaki 1997, Zhou et al. 2012, Mousavi and Ghorbani-Tanha 2012,

Palermo et al. 2018) and many seismic codes (ASCE 7 2016, ASCE 41 2017) have acknowledged viscous

dampers to be used in both new designs and rehabilitation projects.

Figure 1.Details of a patented viscous damper manufactured by Behsazan Larzeh Davam Co.

Figure 1 illustrates a patented viscous damper manufactured by Behsazan Larzeh Davam Co. As

depicted in the figure, viscous dampers consist of a cylinder filled with viscous oil and divided into two

chambers by a piston and a shaft set to reciprocate along the axis of the damper. During a seismic event,

the oil would be forced to pass through a small diameter orifice (in this case the hose) with high pressure

and extremely high velocity. This mechanism would efficiently dissipate the input energy. Therefore,

viscous dampers operate based on principles of fluid dynamics such that the input energy would be

dissipated into heat and the temperature of the oil inside the damper can reach to up to 200 Celsius

degrees (Black and Makris, 2006). As a result, the internal components of the damper should be designed

to sustain extremely high temperature and pressure and still result in stable cyclic behaviors. This is a

multidisciplinary task and calls for significant expertise and only limited number of countries are able to

fully design and manufacture this technology.

Recently, an Iranian company, Behsazan Larzeh Davam, has started to design and manufacture large

capacity viscous dampers with linear and nonlinear force-velocity behaviors. The company has launched

an extensive experimental program to investigate dynamic behavior of its products and this study is

devoted to represent a part of the obtained results.

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Considered damper specimens Experimental results of two full-scale viscous dampers, ND100 and D125, would be presented. Figure

2 shows the considered specimens and Table 1 presents the main characteristics of the dampers.

Figure 2. Full-scale ND100 and D125 viscous dampers

Table 1. Characteristics of the specimens

Name Damping

Coefficient

Velocity

exponent Capacity Stroke weight

ND100 4 kN.(s/mm)0.75

0.75 200 kN ∓80 mm 70 kg

D125 2.6 kN.s/mm 1 250 kN ∓100mm 90 kg

Set-up and loading protocols Both ND100 and D125 dampers were tested in the 1

st phase of the experimental program. 8 months

after the 1st phase, the 2

nd phase of the program was launched to again test D125 damper. Comparing

D125’s behavior during the 1st and the 2

nd phases, long-term behavior of the damper can be investigated.

Adopted set-ups in the 1st and the 2

nd phases of the experimental program are depicted in Figure 3.

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Figure 3. Adopted set-up for the (a) 1st phase and (b) 2nd phase tests

Dynamic loading protocols were selected per ASCE 7 (2016) with higher number of cycles. So the

imposed loadings were more stringent than those proposed by ASCE 7. Moreover, per ASCE 7, the

damper should be tested in only one frequency (0.67 f1, f1= fundamental frequency of the structure).

However, both dampers were subjected to 6 different frequencies ranging from 0.20 Hz to 1 Hz. In

addition to harmonic loading, the dampers were also subjected to many seismic time histories. At the end

of the 2nd

phase, an extremely conservative loading protocol including 40 continuous cycles were imposed

on the D125 damper to investigate its performance under high duration loads such as wind and wave

loads (in offshore structures). Although ASCE 7 proposed 2000 cycles for wind loads, it permits to use

alternate protocols as well. The induced 40-cycle protocol includes large amplitudes and forces such that

the cumulative dissipated energy in this protocol is estimated to be equivalent to that would be dissipated

during large duration small amplitude wind loadings.

First phase experimental results Due to space limitation, obtained results from only three frequencies of 0.25 Hz, 0.50 Hz, and 1.00 Hz

are presented in this paper. Cyclic behaviors of ND100 and D125 dampers under different frequencies

and amplitudes are illustrated in Figures 4 and 5, respectively. Obtained results indicate that both ND100

and D125 dampers revealed stable cyclic behaviors in all frequencies and amplitudes and they would

easily satisfy acceptance criteria of ASCE 7.

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Figure 4. Cyclic behavior of ND100 in frequencies of (a) 0.25 Hz, (b) 0.50 Hz, (c) 1.00 Hz and (d) force-velocity behavior of

ND100.

Figure 5. Cyclic behavior of D125 in frequencies of (a) 0.25 Hz, (b) 0.50 Hz, (c) 1.00 Hz and (d) force-velocity behavior of

D125.

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Second phase experimental results As mentioned earlier, D125 specimen is again tested 8 months after the 1

st phase tests. Figure 6

compares some of the obtained results from the 2nd

phase tests with those measured in the 1st phase. It can

be observed that the damper has shown very satisfactory long-term performance as results from the 2nd

phase tests are very similar to those obtained in the 1st phase. The minor difference between the results is

mainly due to variation of the experimental set-up and the used actuator.

Figure 6. Cyclic behavior of D125 damper in the 1st and 2nd phase tests (8 months time gap). (a) frequency = 0.25 Hz and (b)

frequency=0.50 Hz.

Figure 7. Cyclic behavior of D125 damper under the extreme loading protocol of 40 cycles with amplitudes of 30 mm and

maximum forces close to the design capacity of the damper.

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Performance of D125 damper in 40 cycles with frequency of 0.67 Hz and amplitude of 30 mm is

depicted in Figure 7. It is obvious that the damper revealed quite stable force output with no degradation.

Numerical simulation Both simplified and sophisticated numerical simulations have been carried out. Due to page number

limitations, only results of the D125 damper are presented in this section. Figure 8 illustrates simplified

link model of the damper in SAP2000 (2017) and the CFD model of the damper in Abaqus (2016).

Simulated damper behaviors from the numerical models are compared to those from the experimental

results in Figure 9. Note that the simplified model is verified using seismic excitations obtained from

inter-story drift of a 12-story steel MRF with D125 viscous dampers subjected to the Victoria earthquake.

The 12-story building would be discussed in the subsequent section. The CFD model is verified by

imposing different piston velocity on the model and comparing the corresponding damper force to that

obtained from the tests.

Numerical models have shown promising results and it can be concluded that these techniques can be

effectively used to simulation behavior of the damper itself and behavior of the structure equipped with

viscous dampers.

Figure 8. Cyclic behavior of D125 damper in the 1st and 2nd phase tests (8 months time gap). (a) frequency = 0.25 Hz and (b)

frequency=0.50 Hz.

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Figure 9.Verification of the numerical models. (a) Simplified model of the D125 damper in SAP2000 subjected to displacements

obtained from a 12-story building under the Victoria earthquake along North-South and East-West directions. (b) CFD model of

the D125 damper in Abaqus subjected to different piston velocities.

Numerical assessment This section represents seismic behavior of a 12-story steel building with and without viscous

dampers. In order to make a fair comparison, the building without damper has a dual system of SCBF and

SMRF and the building with damper has only one lateral load resisting system of SMRF with viscous

dampers as shown in Figure 10. The inherent damping ratio of the building is 5% and in the case with

viscous dampers, the damper characteristics and placements are designed such that the damping ratio of

the building would be increased from 5% to 17.5% in the case A and 30% in the case B. The building is

designed per ASCE 7 (2016) and AISC 341 (2010). Some of the characteristics of the designed building

in different cases are presented in Table 2.

Table 2. The main characteristics of the design building

Building Damping

ratio

Period along X

(s)

Period along Y

(s)

Steel weight

Without damper 5% 1.82 s 1.45 s 325 ton

With damper-Case A 17.5% 4.45 s 3.42 s 290 ton

With damper- Case B 30% 4.45 s 3.42 s 290 ton

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Figure 10.Considered 12-story steel building with and without viscous dampers.

Using 7 scaled ground motion pairs, with return period of 475 years (10%-50 years), nonlinear time-

history analyses are carried out on the building. Averaged obtained results are summarized in Figure 11

and Table 3. It turned out that the building with conventional braces can experience less inter-story drift

compared to building with dampers in some cases. However, this was achieved at the expense of very

large story accelerations and shears and significant inelastic demands on the braces. As presented in Table

3, the building without damper failed to satisfy LS criteria stipulated in ASCE 41 (2013). Note that

viscous damper can easily reduce story acceleration by up to three times. This is an important

characteristic of viscous dampers when it comes to design of acceleration-sensitive non-structural

elements such as partitions, claddings, façade, and so on.

Table 3. Averages of maximum responses

Building

Maximum

Inter-story

drift

X-direction

Maximum

Inter-story

drift

Y-direction

Maximum

story

acceleration

X-direction

Maximum

story

acceleration

Y-direction

Maximum

base shear

Average of

both directions

Performance

Without

damper 1.80% 1.4% 0.60g 0.64g 5350 kN CP

With

damper-

Case A 1.65% 1.95% 0.28g 0.23g 2400 kN LS

With

damper-

Case B 1.35% 1.70% 0.30g 0.21g 2450 kN LS

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Figure 11.Averaged response of the building in terms of (a) inter-story drift and (b) story acceleration.

Conclusions Behsazan Larzeh Davam Co. as an Iranian company has started to design and manufacture a new

viscous damper with an external orifice. To investigate dynamic behavior of the manufactured devices,

extensive experimental campaign has been launched by the company. This paper represents parts of the

obtained results from dynamic testing of two full-scale dampers, ND100 and D125. Both dampers

revealed very stable cyclic behaviors under different frequencies and amplitudes. Using a double-phase

experimental program with a time gap of 8 months between them, it is shown that the manufactured

dampers have a reliable long-term behavior. The dampers were also subjected to 40 cycles of large

amplitude/high frequency protocols and it turned out that they are reliable devices under long duration

excitations.

Both simplified link element models and sophisticated CFD models were able to simulate behavior of the

tested dampers with reasonable accuracy. Finally a numerical assessment was carried out on a 12-story

residential building with and without viscous dampers. Obtained results indicated that, as expected,

viscous damper is an efficient technology in order to alleviate seismic-induced demands.

Acknowledgements All of dynamic tests on ND100 and D125 dampers have been carried out in the Structural Laboratory at

International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran. The cooperation

of IIEES, specially Prof. Ziyaeifar, Eng. Jabbarzadeh, Eng. Mortezaei and Eng. Javali, is highly

appreciated.

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Apostolakis, G. and Dargush, G.F., 2010, Optimal seismic design of moment-resisting steel frames with hysteretic

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ASCE 41, 2017, Seismic evaluation and retrofit of existing buildings,American Society of Civil Engineers, Reston,

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