16th World Conference on Earthquake Engineering, 16WCEE 2017
Santiago Chile, January 9th to 13th 2017
Paper N° 1157 (Abstract ID)
Registration Code: S-Y1464095086

Development of distributed hybrid experimental system of coupling
1G-40G fields for soil-foundation-structure interaction
Y. Sasaki(1), Y. Takahashi(2)(1) Kozo Keikaku Engineering, yoshiyuki-sasaki@kke.co.jp(2)

Kyoto University, takahashi.yoshikazu.4v@kyoto-u.ac.jp

Abstract
In this research, distributed hybrid experimental system of coupling 1G-40G fields is developed to consider soil-foundationnonlinear structure interaction. Static loading test on nonlinear structure on 1G field and pile foundation on 40G field areconnected by computer, then this computer conducts seismic response analysis by applying results of static loading tests.
From comparison with this experiment, another hybrid experiment and numerical analysis, it revealed that developed hybrid
experimental system works well and it can be evaluate soil-foundation-nonlinear structure interaction.
Keywords: hybrid experiment, shake table test, soil-foundation-structure interaction, centrifuge

16th World Conference on Earthquake Engineering, 16WCEE 2017
Santiago Chile, January 9th to 13th 2017

1. Introduction
Soil-foundation-structure interaction (SFSI) has great influence on the response of structural system during
earthquake. Because of this fact, many experimental or analytical researches are attempted to evaluate SFSI.
For example, Nishimura[1] conducted shake table test for soil-pile foundation-RC column system on 1G field todiscuss the relationship between nonlinearity of RC column and SFSI during earthquake. As a result, the factthat influence of kinematic interaction can be stronger than that of inertia interaction when RC column shows
nonlinear behavior was revealed. Boulanger[2] conducted shake table test by using centrifuge. Comparing
experimental result with reproduce analysis of experiment, interaction springs between pile and soil aredeveloped. Penzien[3] modeled soil-foundation-structure system as concentrated mass system to makeformularization of equation of motion easier. Then calculation speeds become faster than previous numericalmodel.
Large scale shake table test can evaluate precise seismic response of structural system because real scalespecimen is used. On the other hand, experimental scale is so huge that experiments can’t be conducted
repeatedly. Centrifuge test can make smaller the structural system. Then the scale of experiment becomes
smaller and many times of experiments is able to be conducted. While nonlinear behavior of soil can beevaluated quite precisely, that of superstructure is very hard to reproduce. Numerical analysis is another methodof evaluating SFSI. In numerical analysis, real scale model is considered easily. However, if constitutive laws orparameters used in numerical model are invalid, results of analysis become meaningless. Hence constitutive laws
or parameters should be selected considerably carefully.
To deal with these problems, Takahashi[4] developed experimental system, called “hybrid experiment withcentrifuge”. The objective of this research was showing the validity of experimental system, so superstructure
was assumed as linear elastic. Shake table test was also conducted in centrifuge to compare with hybrid
experiment. From these results, it was clarified that developed experimental method can evaluate vibration
phenomena of structural systems.
In this paper, another new hybrid experimental system named “distributed hybrid experiment with centrifuge” isdeveloped and discussed. This experimental system is developed to evaluate the nonlinearity of superstructure.
In experiment, RC column is assumed as superstructure. Experiment is conducted with connecting RC column
on 1G field and pile foundation by computer and the validity of this experimental system is discussed.

2. Hybrid experiment and distributed experiment
2.1 Hybrid experimentHybrid experiment is the method of evaluating seismic response of the structural system with combining model
test and numerical analysis. Fig.1 shows concept of hybrid experiment. Structural system is divided into a few
subsystems. Model test is conducted on elements which show complex nonlinear behavior because theseelements are generally very difficult to describe by numerical model. Other parts of structural system aremodeled in client computer. Then, load-deformation relationship of each time step can be gain from model test.
This nonlinear characteristic is used in seismic response analysis in client. Hybrid experiment can evaluate
seismic response of structural system having complex nonlinear elements without constructing monolithic large
scale model.

Fig. 1 – Concept of hybrid experiment2

16th World Conference on Earthquake Engineering, 16WCEE 2017
Santiago Chile, January 9th to 13th 2017

2.2 Distributed experimentDistributed experiment is defined as experimental system of determining behavior of structural system with
conducting experiments on some geographically separated places, and experimental data is communicated byusing network. In distributed experiment, the structural system is divided into smaller structural system. Only
data communication system is needed on each experimental site to communicate sites each other, experiments oneach substructure system can be conducted depending on its capacity.
By using distributed experimental system, behavior of structural system can be evaluated with experiments on
smaller subsystems. Moreover, if the model scales are different subsystems each other, distributed experimentmust be used. Takahashi et. al. [5] conducted distributed experiment with connecting Japan and America toevaluate seismic response of L-shaped RC column.

2.3 Similitude rule
Similitude rule has a great effect on model test. Similitude rule of shake table test on 1G field, hybrid experimentand experiment in centrifuge is confirmed and applicability of similitude rule to “hybrid experiment withcentrifuge” is discussed by Takahashi[4].
Equation of motion on 1G field is described as follows.

Mp

d 2xp
dt 2p

Cp

dx p
dt p

 R p  M p

d 2 u gp
dt 2p

(1)

In equation, subscript p means prototype, m means model. M , C , R mean mass, damping and reaction
force each. x means response displacement of structural system and u g means displacement of input motion.
Prototype scale and model scale is characterized as follows by using coefficient  .

x p   l xm ,u gp   l u gm

t p   ttm ,M p mM m

R p   r Rm ,C p   cCm

 l ,  m ,  r ,  c mean similitude ratio of length, mass, force and damping. From () and (), () is gained.
d 2 u gmm l m l 
d 2 xm   l   c 
dx m






  2 M m dt 2    C m dt   r Rm    2 M m dt 2
t
m


t
m
t
m





(2)

(3)

This equation is equivalent to () if all of coefficients are the same in (). Thus,m l  l c 

 

(4)
  2      r
t

t

 
If the scale factor is defined as 1 n ,  l becomes n . Assuming that model and prototype are consisted of the2same material,  m becomes n 3 . To satisfy geometric similarity, the surface ratio is n 2 and  r  n incondition that stress ratio is same as prototype and model scale.
() is not satisfied in shake table test because acceleration ratio  l  t2 is fixed as 1. Owing to this fact, anothermass is put on structural model to make  m  n 2 to satisfy similitude rule. By the way, Strain rate of material is2ignored at hybrid experiment or centrifuge experiment, load R is the same as static load. Thus,  r  n can besatisfied. From (), relationship showed below is derived.

 t2 

 m l n2r

Acceleration ratio is described as follows.

 t  nl 1
 t2 n(5)(6)

In centrifugal field, similitude rule is satisfied due to centrifugal force acting on experimental model. In hybrid
experiment, only displacement x and reaction force R are communicated between computer and experimental

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16th World Conference on Earthquake Engineering, 16WCEE 2017
Santiago Chile, January 9th to 13th 2017setup, mass M and time t are only given to computer. Satisfying similitude rule, stress of model and prototype
are fit by actuators.
Table.1 shows calculated similitude ratios. From this discussion, the same similitude ratio can be used between
hybrid experiment and centrifuge experiment.
Table 1 – Similitude ratio
Similitude ratio (prototype/model)
centrifuge

Hybrid experiment1G shake table test

Length

N

N

N

Mass

N3

N3

N3

Stress111

Acceleration

N

N

1

Time

N

N

N0.5

Frequency

1/N

1/N

N-0.5

3. Distributed Hybrid Experiment witn Coupling 1G-40G Fields
3.1 Concept of distributed hybrid experimentFig.2 shows developed hybrid experimental system in this paper, named “distributed hybrid experiment withcentrifuge”. In this system, soil-foundation-structure system is modeled as 2 DOF system in client computer.
Characteristics of these two springs at each time are determined from static loading tests on superstructure andpile foundation. Using results of static loading tests, seismic response analysis is conducted.
In seismic response analysis, the follow equation is solved.

M s
 0


0   xs   C s
 
M f  x f   C s

 C s   x s   Rs 
M s        ugC s  C f   x f  R f M f 

(7)

R s and R f mean restoring force of superstructure and pile foundation determined from static loading tests.
Static loading test on superstructure is conducted in Katsura Campus, Kyoto University on 1G field and used
specimen is prototype scale. The experimental result is passed from Katsura Campus to client computer at Uji
Campus, Kyoto University by using Internet. Static loading test on pile foundation is conducted in centrifuge at
Uji Campus and used specimen is small model. When experimental data is communicated between client andexperiment system of pile foundation, control displacement and acquired force of pile foundation should be
converted according to similitude rule because equation of motion is solved by using real scale parameters.
Fig.3 shows the flowchart of loading test on pile foundation. Displacement xf(t) is given to specimen andrestoring force R ' f(t) is measured. Then R ' f(t) is converted as real scale value Rf(t). Using this Rf(t), clientcomputer calculates the next step displacement xf(t+1). xf(t+1) is converted as model scale value and given to
pile foundation, then restoring force R ' f(t+1) is acquired. The nonlinearity of soil in experiment can be taken
into account in term of R ' f(t+1) by iterating this operation. Moreover, using centrifuge, the smaller pilefoundation can be used compared to prototype scale.
In this hybrid experimental system, OpenFresco[6, 7] and OpenSees[8, 9] are used. OpenFresco is the hybrid
simulation framework and OpenSees conducts numerical analysis.

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Fig. 2 – Distributed hybrid experiment with centrifuge

Fig. 3 – Flowchart of static loading on pile foundation during hybrid experiment

3.2 Target Model
Fig.4 shows soil-foundation-structure system considered in this paper. To evaluate the nonlinearity ofsuperstructure, RC column is applied. This RC column is assumed that its height is 1600mm, section is 320mm
square and weight of mass is 10.1 t.
Footing is assumed that its height is 2000mm, section is 2000mm square and its weight is 80.64t. Piles are
assumed that its length is 7200mm, section is 200mm×400mm, ground depth is 6400mm and piles keep elastic
during vibration.
Input motion is shown in Fig.5. This wave was observed at Hyogo-ken Nanbu Earthquake.

Fig. 4 – Targetted soil-foundation-structure system5

16th World Conference on Earthquake Engineering, 16WCEE 2017
Santiago Chile, January 9th to 13th 2017

Fig. 5 – Input acceleration

3.3 Structural model of RC column and experimental setup
The detail of RC column used in this experiment is shown in Fig.6. The height of RC column is 1800mm. This
column is consisted of RC part and jigs for loading.
The height of RC part is 1370mm, its section is 320mm square. 16-D10 main reinforcement is inserted and D4
tie foops are put at 40mm pitch. Intermediate foops are put at the center of section. Height of jigs are 430mm andthese are fixed at the top of RC part. This RC column is fixed on the ground by using footing shown in left of
Fig.6.
Nominal strength of concrete is 24N/mm2, slump value is 12cm, the maximum size of coarse aggregates is
15mm. Result of compressive strength test is 30.49 N/mm2.
Right of Fig.6 shows experimental setup for RC column. Load is applied by actuator at jigs, so loading point
become 1600mm from the bottom of RC column. Swivel head is used for preventing that moment is generated
during loading test. Weight of superstructure is applied by axial force installed by prestressing steel bars.
Applied axial force on each steel bars are 50kN, thus RC column has 10.1t mass at the top of column.

Fig. 6 – Detail of RC column and static loading system

3.4 Structural model of pile-soil system and experimental setup
Pile models used in this experiment has 5mm×10mm section, 200mm length and are made of phosphor bronze.
Weight of pile is 0.00801kg in model scale. In prototype scale, each pile has 5.13t weight. To fix piles andfooting, the net length of piles become 180mm in pile foundation. Pile tips are also fixed at base.
Fig.7 shows footing and piles. Height of footing is 30mm, section is 50mm×72mm and weight is 0.7655kg.
The size of soil tank used in experiment is 450mm×150mm×300mm and its boundary is fixed. Soil foundation ismade of dried silica sand. The depth of soil foundation is 160mm.
Fig.7 also shows the detail of loading test on pile foundation. To apply displacement from actuator to footing,another block is put on the footing. Displacement of footing is measured by laser displacement transducer. Strain
gauges are put on each pile to measure strain of pile.
Static loading test is conducted in centrifuge at Uji campus. Centrifugal acceleration is kept 40G duringexperiment.
In this experiment, loading direction for pile foundation is restricted only horizontal. Moreover, because mass offooting is set on numerical model in client computer, mass of footing model used in centrifuge has no influenceon experimental result.

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16th World Conference on Earthquake Engineering, 16WCEE 2017
Santiago Chile, January 9th to 13th 2017

Fig. 7 – Detail of pile foundation and Static loading system

3.5 Preliminary experiment
Developed experimental system needs to conduct distributed experiment. Thus, “hybrid experiment withcentrifuge” is conducted as preliminary experiment to verify the validity of distributed experimental system.
Fig.8 shows preliminary experimental system. The same soil foundation-pile system and experimental
equipment are used between preliminary experiment and developed hybrid experiment. On the other hand, RC
column is described as fiber element in client computer. Thus, preliminary experiment is conducted on locally.

Fig. 8 – Preliminary experimental system

5.6 Preliminary analysis
Developed experimental system needs to connect 1G field and 40G field. Thus, to verify its validity, a numericalanalysis is conducted as preliminary analysis.
Fig.9 shows numerical analysis model. Material parameters are used in analysis model. Pile is described bybeam element, soil movement is ignored and interaction spring[2] is applied between pile and soil. In realvibration problem, soil movement should be considered. However, soil movement isn’t considered in developed
hybrid experimental system in this paper. Thus, soil movement isn’t considered in preliminary analysis forfitting conditions between experiment and analysis. This analysis model is constructed by 1G prototype scale.

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16th World Conference on Earthquake Engineering, 16WCEE 2017
Santiago Chile, January 9th to 13th 2017

Fig. 9 – Preliminary analysis model

4. Results of distributed hybrid experiment and discussion
Fig.10 shows displacement time series of developed hybrid experiment and preliminary analysis. Displacementof RC column is defined as relative displacement between top of column and footing, and that of footing isdefined as relative displacement between footing and base. Fig.11 shows load-deformation curves of RC column
and footing. Load of RC column is derived from inertia force of RC column and that of footing is derived fromsum of inertia force of RC column and footing. Except for negative response and stiffness of RC column,
responses of RC column and footing show good agreement.
Considering that all elements of preliminary analysis model are constructed on 1G prototype scale and 1G field
and 40G field are connected in developed hybrid experiment, the system of connecting 1G field and 40G fieldworks well.
Fig.12 shows displacement time series of developed hybrid experiment and preliminary experiment, Fig.13
shows load-deformation curves of RC column and footing and Fig.14 and Fig.15 show moment distribution ofpile of two experiments. Similar to consideration of preliminary experiment, except for negative response andstiffness of RC column, responses of RC column and footing show good agreement. Moreover, moment
distribution of pile has also no difference between two experiments. From these results, distributed experimental
system is working well. Hence, it can be said that combining distributed experimental system and the system ofconnecting 1G field and 40G field is possible.
Buckling of main reinforcement is considered as a main reason of difference of RC column displacement andstiffness among distributed hybrid experiment, preliminary analysis and preliminary experiment. In general,buckling causes reduction of stiffness of RC column and it has great influence on the ultimate behavior of RC
column. However, it is quite difficult to describe buckling phenomenon by analytically because of its complexity.
In developed hybrid experiment, the complex nonlinear behavior of RC column can be considered by conducting
model test.
Analysis time step of developed hybrid experiment is 3.65  10 3 , this is equal to that of input motion. As aresult, 20 seconds vibration phenomenon is reproduced by spending about 6 hours, which is very close to the test
duration of preliminary experiment. Thus, experiment speed of developed hybrid experiment is equivalent toprevious hybrid experiment with centrifuge.

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Fig. 10 – Displacement time series of distributed hybrid experiment and preliminary analysis

Fig. 11 – Load-deformation curve of distributed hybrid experiment and preliminary analysis

Fig. 12 – Displacement time series of distributed hybrid experiment and preliminary experimentFig. 13 – Load-deformation curve of distributed hybrid experiment and preliminary analysis

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Fig. 14 – Moment distribution of pile (developed experimental system)10

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Santiago Chile, January 9th to 13th 2017

Fig. 15 – Moment distribution of pile (preliminary experiment)

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16th World Conference on Earthquake Engineering, 16WCEE 2017
Santiago Chile, January 9th to 13th 2017

5. Conclusion
In this paper, new hybrid experimental system named “distributed hybrid experiment with centrifuge” isdeveloped. This experimental system has the system of connecting 1G field and 40G field. Experiment isconducted by setting RC column at Katsura campus and small pile foundation model at Uji campus. Duringexperiment, the Internet is used for data communication.
Compared to preliminary experiment and analysis, it revealed that distributed experimental system and system ofconnecting 1G field and 40G field work well and combining these two experimental system is possible.
Furthermore, this experimental system can evaluate buckling or rapture of steel reinforcement, which is very
difficult to describe by numerical analysis, and continue experiment stably in spite of complex nonlinear
behavior.
Only sway movement is assumed in this consideration. However, the influence of rocking can’t be ignored inreal structure. Hence, it is needed to clarify whether this experimental system is applicable when foundation
form is changed and rocking motion is large.
Soil deformation is also an important factor on evaluating response of structural system. To consider its effect,
the loading system of applying soil deformation in hybrid experiment should be developed.

6. References[1] Nishimura, S., Takahashi, Y., Murono, Y., Nishimura, T., and Ejiri, J. : Shake table test of nonlinear structure – pilefoundation – soil system, Proc.of 15 th World Conference on Earthquake Engineering, No.4289, 2012.
[2] Boulanger, Ross W., Curras, Christina J., Kutter, Bruce L., Wilson, Daniel W., and Abghari, Abbas. : Seismic soil-pilestructure interaction experiments and analysis, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 125,
No.9, pp. 750-759, 1999.
[3] Joseph Penzien., R. A. P., Charles F. scheffey : Seismic analysis of bridges on long piles, Journal of eht Engineering
Mechanics, Vol. 90, No. EM3, pp. 223-254, 1964.
[4][5] Takahashi, Y., S. M., Iemura, H., and Fenves, G. : International distributed hybrid simulation of 2-span continuous
bridge, The 14th World Conference on Earthquake Engineering October 12-17, Beijing, China, 2008.
[6] OpenFresco : http://openfresco.berkeley.edu/[7] Yoshikazu Takahashi and Gregory L. Fenves, : Software framework for distributed experimental computational
simulation of structural systems, Earthquake Engineering and Structural Dynamics, Vol. 35, pp. 367-291, 2006.
[8] OpenSees : http://opensees.berkeley.edu/[9] Gregory L. Fenves, Frank McKenna, Michael H. Scott, and Yoshikazu Takahashi : An object-oriented softwareenvironment for collaborative network simulation, In Proceedings of 13 th World Conference on Earthquake
Engineering, p. No.1492, 2004.

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