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International Journal of Civil Engineering and Technology (IJCIET)

Volume 9, Issue 8, August 2018, pp. 205–216, Article ID: IJCIET_09_08_022

Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=9&IType=8

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

© IAEME Publication Scopus Indexed

DYNAMIC RESPONSE OF BUILDINGS ON

DIFFERENT TYPES OF FOUNDATIONS

THROUGH SHAKE TABLE TESTS

CONSIDERING SSI EFFECT

Madan Kumar

Research Scholar, Department of Civil Engineering,

National Institute of Technology Patna, India

S.S. Mishra

Professor, Department of Civil Engineering,

National Institute of Technology Patna, India

ABSTRACT

From recent earthquakes fixed-base assumption of buildings could be misleading.

Also, neglecting the influence of Soil-Structure-Interaction (SSI) could lead to unsafe

design particularly for structures founded on soft soils. To understand the

performance of a multistoreyed building along with SSI phenomena comprehensively,

a series of shake table tests were performed on multistoreyed building frame models of

different heights supported on a soil container. In this paper the study focuses on the

response determination by shake table testing of a building frame model subjected to

a real earthquake excitation, El-Centro under following conditions: 1) three building

frame model of different heights to examine the effect of height of buildings, 2) all the

three building frame models supported on fixed base condition, 3) for the effect of SSI

with respect to fixed base condition all the three building frame models were

supported on a soil container, 4) all the three building frame models supported on

three different types of foundation namely isolated, mat and pile foundations

supported on soil and 5) all the three building frame models supported on different

pile depths to understand the effect of response due to different depths of pile. The

investigations showed that the pile foundation offers less lateral displacements of the

frame models as compared to other types of foundations. However, the fixed base

offers least lateral response as compared to all other foundations.

Key words: Shake Table Test, Multistoreyed Building, Earthquake Response, Deep

Pile, SSI.

Cite this Article: Madan Kumar and S.S. Mishra, Dynamic Response of Buildings on

Different Types of Foundations through Shake Table Tests Considering SSI Effect.

International Journal of Civil Engineering and Technology, 9(8), 2018, pp. 205-216.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=9&IType=8

Madan Kumar and S.S. Mishra


1. INTRODUCTION

In recent years several earthquakes have come which caused damage of building structures.

The importance of soil-structure interaction (SSI) for both static and dynamic loads have been

an interesting area of research among structural engineers. It elongates the period of the

structure and increases the damping of the structural system. There is no general agreement

among researchers on the effects of SSI on the overall performance of a structure, especially

on soft soils. Gazetas [1] carried out analysis on flexible piles with low frequency loading and

concluded that kinematic interaction is also important. Understanding the effect of depth of

pile on response of structures during earthquake in becomes important cases where the effect

of SSI on structures situated on massive foundations, such as silos, offshore caissons and

bridge piers, and slender tall structures, such as chimneys and towers and structures supported

on very soft soils. During Mexico City earthquake (1985) [2–6] and Christchurch earthquake

(New Zealand, 2011) [5, 7] it has been seen that the local soil properties affect the earthquake

response of structures.

These earthquakes confirmed that the ground motions got significantly amplified at the

base of the structure. In 2002, Han [8] studied the effect of the seismic soil-pile-structure

interaction (SSPSI) and observed that, because of translation and rotation of the foundation,

SSPSI may increase the overall displacement of the superstructure as compared to the fixed

base condition. The increase in the lateral deformation of the building can change the

performance level of the structure. The seismic excitation experienced by structures [9] is a

function of the earthquake characteristics, travel path effects, local site effects, and soil-

structure interaction effects. the flexibility of the foundation and the difference between

foundation and free-field motions affect the structure [3, 10]. Prishati [11] using beam-on-

nonlinear-Winkler-foundation (BNWF) approach and concluded that when the foundation

nonlinearity is accounted in case of a high intensity earthquake event, force and displacement

demands are reduced significantly. Thanuja [12] used FEM to analyse the pile foundations

under seismic loads considering both kinematic and inertial effects. Rainer (1975) [13]

presented a simplified method of analysis for the determination of dynamic properties of

single-story structures founded on flexible foundations and observed that the natural

frequency of the fundamental mode of a structure-foundation system is primarily dependent

on the stiffness ratio of structure to ground and the aspect ratio of height to width of

foundation. Saha et.al [6] investigate the seismic response of soil-pile raft-structure system

considering SSI effect. In their study they modelled the structure as a one storey system

consisting of a mass in the form of a rigid floor slab supported by four columns. The piles are

modelled as springs and dampers. They observed that the SSI affect the period of the

structure. In Hosseinzadeh (2004) [14] studied the SSI effects in dynamic response of single

and adjacent building structures experimentally using a ground model specimen which was

made of relatively soft soil and 5, 10, 15, and 20 stories steel building models. They

concluded that in comparison to inertial interaction the effect of kinematic interaction is

negligible. Chau et al. [4] conducted a shaking table test which was subjected to both

sinusoidal wave of various magnitudes and El Centro earthquake in a soil–pile–structure

system. They found that different pounding phenomenon was observed between soil and pile

which was due to the development of a gap separation between soil and pile. They observed

that the acceleration response of the pile cap increased by three times larger than that of the

structural response.

For observing the effect of SSI on a structural system a series of shake table test has been

conducted. For this, study has been accounted into different cases as: 1) three building frame

model of different heights to examine the effect of height of buildings, 2) all the three

Dynamic Response of Buildings on Different Types of Foundations through Shake Table Tests Considering

SSI Effect


building frame models supported on fixed base condition, 3) for the effect of SSI with respect

to fixed base condition all the three building frame models were supported on a soil container,

4) all the three building frame models supported on three different types of foundation namely

isolated, mat and pile foundations supported on soil and 5) all the three building frame models

supported on different pile depths to understand the effect of response due to different depths

of pile.

Many high-rise buildings supported on pile foundations are constructed in soft soil in

seismically active areas. The SSI interaction are divided into two parts: Inertial interaction

and kinematic interaction [9].

The dynamic equation of the motion [15] for the structure can be written as:

[ ]{ } [ ]{ } [ ]{ } [ ]{ }gM u C u K u M u (1)

where, M , C and K are the mass, damping, and stiffness matrices of the structure,

respectively. u , u and u are the relative nodal accelerations, velocities and

displacements of the structure with respect to ground, respectively. gu is the ground

acceleration.

2. DESCRIPTION OF TEST MODEL

The consistency of model tests relies on whether the model represents the real behavior of the

actual building. Due to limitation of the shake table, similitude law has been considered

keeping in mind the behavior of prototype model. The method established the similar

relationship between model and prototype is called dimensional analysis method. Similitude

formulas and similitude factors of all physical quantities are deduced from Buckingham π

theorem. The size of the SSI models was scaled from full-scale buildings and foundations.

During modelling the distortion due to dead load and live load was ignored. Parameters of

dynamic loads such as acceleration, frequency, amplitude are controlled to meet the limiting

values of shaking table.

Figure 1 Plan and elevation of frame models



Three types of conventional moment resisting frame model are used as prototype

superstructure of four, six and eight storey. The slender frame building models are assumed to

be a residential building and it has plan dimension of 3m X 3m and the height of 12 m, 18m

and 24m from the ground level, respectively. The plan and elevation of the test models are

shown in Fig 1. Each frame model consists of one span with a total width of 3m. For the

prototype frame model mild steel plates have been used as floor slabs and ISA 25 X 25 X 3

mm is used for preparation of beams and columns of the frame. The characteristics of the

prototype frame buildings are obtained from the preliminary design of the buildings as per

Indian standard codes. Thus, the prototype system can be regarded as some typical small

high-rise building systems. The scale considered for dimension of the superstructure and for

pile is λ=1/10 and λ=1/30, respectively. The model similitudes of physical parameters are

defined in terms of the geometric scaling factor λ and are summarized in Table 1.

Table 1 Prototype Model Scaling Factors

Physical quantity Scale factor

Length λ

Mass Density 1

Acceleration 1

Time λ1/2

Force λ3

Stiffness λ2

Frequency λ-1/2

Stress λ

Strain 1

3. PROPERTIES OF SOIL AND SIMULATION OF SOIL BOUNDARY

CONDITION

The soil was a critical part to deal the modeling procedure. Soil parameters were derived from

laboratory tests to get a broad view of the geotechnical properties. The specific gravity, dry

density and plasticity index of soil considered for the tests are 2.69, 16.8 kN/m3

and 8.9%

respectively. While considering SSI, the simulation of soil boundary condition plays a key

role. The soil theoretically has no boundary [16]. In shake table test, the soil cannot be placed

in an infinite dimension box. Due to variation of system vibration and wave reflection on the

boundary, error will occur in test results. Ignoring these effects laminar soil container was

designed to simulate the boundary [10, 16, 17].

The soil container used in the experiments is shown in Fig.2. The dimension of flexible

soil container properly stiffened is 650mm×650mm×650mm. It is composed of steel plate of

thickness 3mm. To minimise the boundary effects the inner sides of soil container were filled

with foam of thickness 2mm. The base plate was made of steel plate. To avoid over-

deformation during lifting container was stiffened with small steel beams. To avoid the

slipping of container the base of the soil container was fixed with shake table platform by

using steel fasteners and bolts.

4. FREE VIBRATION TEST

Initially, the free vibration test was performed to determine the natural frequency of the frame

models. For free vibration test the structural model was directly fixed on shake table and a

pull was applied by using non-extensible rope. The rope was suddenly cut and the resulting

acceleration of the model was recorded by fixing accelerometer at the storey levels. The


SSI Effect


damping of the building frame models is calculated by the Equation 2 [15]. The values of

frequency and damping are given in Table 2.

1ln

2

i

i j

u

j u

(2)

where j = number of cycles, iu = acceleration at thi peak, i ju = acceleration at ( )thi j

peak.

Table 2 Natural frequency and damping of models

Type of structure Frequency (Hz) Damping (%)

Four storey 14 5.00

Six storey 12 3.95

Eight storey 9 2.67

5. INPUT MOTIONS

In this study the acceleration time histories and response values of the El-Centro (California,

1940) earthquake of N-S component was used. The N-S component of acceleration time-

history of the El-Centro earthquake is shown in Fig. 3. Acceleration records containing higher

frequency components require a finer spatial mesh and consequently a more expensive

computation. These earthquake excitations are filtered with 50Hz low-pass filter to remove

high frequency components. In order to consider the influence of different seismic wave input

to structural system, seismic wave excitations are considered acting horizontally. The

frequency of El-Centro N-S earthquake input earthquake is 2.92 Hz.

The shake table has six degrees of freedom. The shake table platform size is 1.5m X 1.5m

which is capable of carrying a maximum payload of one ton. The shake table is operated by

digital control system. The digital control unit allows simulation of various types of dynamic

displacement time-histories pre-stored earthquake records. The shake table can be efficiently

run up to 50Hz, it has a maximum 200mm displacement limit in horizontal directions.

Because of the frequency limit of the generated input motion the input motions for the shake

table tests are filtered with a 50 Hz low-pass filter to filter out the frequency component above

50 Hz.

Figure 2: El-Centro N-S earthquake motion

6. SHAKE TABLE TEST ON THE SOIL-STRUCTURE MODEL

In this paper the study focuses on the response determination by shake table testing of a

building frame model subjected to real earthquake excitation El-Centro under following

conditions: 1) three building frame model of different heights to examine the effect of height



of buildings, 2) all the three building frame models supported on fixed base condition, 3) for

the effect of SSI with respect to fixed base condition all the three building frame models were

supported on a soil container, 4) all the three building frame models supported on three

different types of foundation namely isolated, mat and pile foundations supported on soil and

5) all the three building frame models supported on different pile depths to understand the

effect of response due to different depths of pile.

During experiments, for fixed base condition, the frame models had been mounted

directly on shake table platform and fixed by the steel plate at pre-located connections using

sixteen 10-Φ bolts.

This section summarizes the main outcomes measured from the experimental study. The

dynamic response of the building frames was recorded by using accelerometers. The recorded

accelerations have been used to obtain the displacement of the structure by using

Seismosignal software [18].

Case-1: When structural model was considered as fixed base condition.

Figure 4: Top floor responses of six storey frame model due to El-Centro for fixed base condition

Figure 5: Top floor responses of four storey frame model due to El-Centro for fixed base condition


SSI Effect


6.1. For Soil-Foundation-Structure System

For soil-foundation-structure system, firstly soil container was placed on the shake table

platform and fixed it by using fasteners and bolts. The container was filled with soil in five

layers and compacted each layer by means of overburden loads. The foundation systems were

placed on soil. After installing all of the components of the system, including the soil

container, soil, piles, and building frame models, the same arrangement of accelerometers as

in fixed base condition was used in the model structures to make it comparable with the fixed-

base models. The shake table tests were performed by applying previously recorded

earthquake data as mentioned earlier. In each condition, the responses of the structural models

were recorded. The experimental models are shown in Fig. 6.

Figure 6: Experimental setup of frame models: (a) four, (b) six and (c) eight storey frame model on

soil container and shake table.

Case-2: In this case isolated footing was taken. Figs 7-9 shows the top floor responses of the

eight, six and four storey frame models to El-Centro N-S earthquake.

Figure 7: Top floor responses of eight storey frame due to El-Centro for isolated footing

Figure 8: Top floor responses of six storey frame due to El-Centro for isolated footing



Figure 9: Top floor responses of four storey frame due to El-Centro for isolated footing

Case-3: In this case mat footing was taken. Figs. 10-12 shows the top floor responses of the

eight, six and four storey frame models to El-Centro N-S earthquake.

Figure 11: Top floor responses of six storey due to El-Centro for mat footing

Figure 12: Top floor responses of four storey due to El-Centro for mat footing

Case-4: When pile foundation (Pile 1) was taken. Figs. 13-15 shows the top floor responses

of the eight, six and four storey frame models to El-Centro N-S earthquake.


SSI Effect


Figure 13: Top floor responses of eight storey due to El-Centro for pile 1

Figure 14: Top floor responses of six storey due to El-Centro for Pile 1

Figure 15: Top floor responses of four storey due to El-Centro for Pile 1

Case 5: When pile foundation (Pile 2) was taken. Figs. 16-24 shows the top floor responses of

the eight, six and four storey frame models to El-Centro N-S earthquake

Figure 16: Top floor responses of eight storey due to El-Centro for Pile 2



Figure 17: Top floor responses of six storey due to El-Centro for Pile 2

Figure 18: Top floor responses of four storey due to El-Centro for Pile 2

Fig. 19 shows the comparative top floor displacements of all types of foundation system

for the eight storey frame model.

The responses of the model under different condition of forced vibration showed a

significant decrease in acceleration at the top of the structural model. The peak storey

acceleration and displacement responses of the models are shown in Fig 3-5 for fixed base

condition of models in El-Centro earthquake excitation. The acceleration and displacement

responses when models situated on isolated, mat foundation are shown in Fig. 7-9 and 10-12

respectively. For pile foundation the acceleration and displacement responses are shown in

Fig. 13-15 for pile 1 and 16-18 for pile 2.


SSI Effect


7. SUMMARY AND CONCLUSION

In this paper, three steel frame structural models of four, six and eight storeyed buildings

models were designed and fabricated for experimental study. Different cases were considered-

1) fixed base condition, 2) isolated, 3) mat and 4) pile foundations supported on soil and 5)

different pile depths. Based on the experimental study performed in this paper the following

conclusions have been obtained:

Pile foundation offers less lateral displacements of the frame models as compared to other

types of foundations.

Fixed base offers least lateral response as compared to all other foundations.

Damping of smaller height building is more as comparable to taller building.

The natural frequency of taller building is low as comparable to smaller height building.

The displacement responses of building frame models are increasing with increase in height.

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